This website is designed as a training tool for welding, materials, standards, weld imperfections, calculations and process visualisations. Select a module from the left-hand menu and work with it actively—many elements respond to clicks, option changes or slider movements.
Recommendation: first expand one of the main categories on the left, select a specific module, and then experiment with the settings. The content is intended primarily for advanced welding personnel, welding technologists, students and production teams.
| Formula | Meaning |
|---|---|
| CEV = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15 | Classical carbon equivalent for unalloyed and low-alloy steels |
| CET = C + (Mn+Mo)/10 + (Cr+Cu)/20 + Ni/40 | Frequently used when estimating preheat requirements |
| PCM = C + Si/30 + (Mn+Cu+Cr)/20 + Ni/60 + Mo/15 + V/10 + 5B | More sensitive for low-carbon microalloyed steels |
A process is not an isolated entry in a WPS. It is a system comprising the energy source, heat and material transfer, weld-pool protection, mechanisation, personnel competence and process-control architecture. The objective is a process that repeatedly produces the required joint under real fit-up and production variation.
Before comparing productivity and cost, define the critical product property and the failure mode that is not acceptable.
Flame, arc, resistance, beam or mechanical energy generate different thermal cycles, HAZ conditions and distortion.
Consumable or non-consumable electrode, pressure joining or brazing determines dilution and joint geometry.
Gas, slag, vacuum, flux or mechanical expulsion of oxides controls cleanliness and metallurgy.
Quality must remain stable with real gaps, positions, surfaces, operators, wear and input variation.
| Decision factor | Processes often favoured | Principal limitation | What must be controlled in the WPS / manufacturing plan |
|---|---|---|---|
| High productivity on structural steels | 135/138 GMAW, 136 FCAW, 121 SAW | Sensitivity to position, access, shielding and wire-feeding stability | Process and transfer mode, gas/flux, current, voltage, travel speed, CTWD, heat input, cleaning and degree of mechanisation. |
| Maximum root and thin-section control | 141 GTAW, or process 15 plasma welding | Lower deposition rate and high sensitivity to cleanliness and operator skill | Root preparation, face and root shielding, electrode/wire diameter, polarity, gas flow and permitted thermal cycle. |
| Site work, repair and restricted access | 111 MMA, 114 self-shielded FCAW, 311 gas welding where appropriate | Manual variability, electrode handling, fumes and lower productivity | Electrode classification, storage/rebaking, polarity, bead technique, preheat and interpass temperature. |
| Long heavy welds in PA/PB | 121 SAW, tandem or multi-wire variants | High heat input, restricted positions and lack-of-fusion risk with poor preparation | Wire/flux system, flux recovery, number of wires, angles, stick-out, joint preparation and heat-input control. |
| Thin sheet and automated series production | 21 spot, 22 seam, 23 projection resistance welding; laser | Sensitivity to surface, force, electrodes, assembly tolerance and heat extraction | Current/time/force, pulse sequence, electrode geometry, wear limits, inspection frequency and process monitoring. |
| Low distortion or very high speed | 52 laser, 51 electron beam, laser-arc hybrid | Narrow process window, accurate fit-up, investment cost and special safety controls | Focus, power, speed, focal position, shielding, gap, seam tracking and acceptance criteria. |
| Joining without melting the parent material | 91 brazing, 94 soldering, adhesive or hybrid joining | Strength and temperature capability depend on clearance, wetting and service conditions | Flux/atmosphere, clearance, thermal cycle, cleanliness, material compatibility and inspection method. |
| Area | Why it changes | Typical evidence |
|---|---|---|
| Metallurgy | Different heat input, cooling rate, hydrogen, dilution and metal-transfer behaviour. | CCT/SH-CCT data, hardness, macro/micro, Charpy and weld-metal chemistry. |
| Qualification range | A process change may be an essential variable or outside the existing WPQR. | Applicable part of EN ISO 15614, WPQR and WPS. |
| Personnel | A different process, mechanisation level or joint can require different qualification. | EN ISO 9606, EN ISO 14732, employer authorisation and training records. |
| Inspection | Different imperfection mechanisms and geometry require different NDT sensitivity. | ITP, EN ISO 17635 and the relevant VT/PT/MT/UT/RT standard. |
| Economics | Deposition rate, operating factor, preparation, repair and consumables all change. | Standard time, OEE, filler/gas consumption, repair rate and inspection cost. |
The approved process package should contain the WPS, qualification records, inspection plan, machine set-up, consumable-part limits, work instruction, competence records and reaction plan.
Why is GMAW not inherently “better” than GTAW? A complete answer compares joint function, material, thickness, position, productivity, thermal cycle, typical imperfections, qualification and process robustness.
ISO 6520-1 classifies imperfections. ISO 5817 a ISO 10042 set acceptance limits by quality level. The drawing, product standard or contract then determines whether a particular imperfection is acceptable.
B = most stringentC = intermediateD = less stringent| ISO 6520-1 group | Examples | Typical examination | General acceptance |
|---|---|---|---|
| 100 – cracks | longitudinal, transverse, crater, hot, cold, liquation and lamellar cracks | VT, PT/MT, UT/RT depending on location and thickness | Generally unacceptable at all quality levels B/C/D. A crack is a sharp notch and a critical fracture initiator. |
| 200 – cavities | pores, uniformly distributed porosity, clustered porosity, cavity, crater pipe | VT for surface-breaking pores; RT/UT for internal porosity | Acceptance depends on size, number, aggregate area and quality level B/C/D. |
| 300—solid inclusions | slag, oxide, metallic inclusion, tungsten inclusion in TIG welding | RT/UT; VT/PT also for surface-breaking indications | Level B is very stringent; C/D may permit small isolated indications within the limits of the standard. |
| 400—lack of fusion and penetration | lack of fusion, incomplete penetration, incomplete root penetration | UT/RT; VT from the root side | Often unacceptable for dynamically loaded joints and quality level B; for C/D only where permitted by the standard and dimensional limits. |
| 500—shape and dimensional imperfections | undercut, overlap, excessive reinforcement, root concavity, burn-through, crater | VT, weld gauges, profilometer | Assessed by dimensions such as depth, height, width, length and material thickness. |
| 600—miscellaneous imperfections | spatter, arc strikes, grinding marks, indentations and surface tearing | VT, supplemented by PT/MT where required | Often acceptable after removal or where function is unaffected; arc strikes are particularly hazardous on hardenable steels. |
The CGHAZ lies adjacent to the fusion boundary and has coarse grains. The FGHAZ has finer grains. The ICHAZ is heated between the critical temperatures, while the SCHAZ is the subcritically affected region.
Standards are not a list to memorise. For an IWE, it is essential to know which standard covers the quality system, which covers welding procedure qualification, which covers welder qualification, which covers weld imperfections and which covers testing and examination. This module is designed as a practical map from customer requirements through to release of the welded product. Standards are identified by their European designation—EN ISO or EN—where applicable.
Scope: Establishes quality requirements for welding processes in both workshop and site fabrication.
Intended users: Manufacturers and suppliers of welded products for automotive, machinery, pressure equipment and structural steelwork.
Scope: Tasks and responsibilities of welding coordination personnel.
Intended users: IWE/IWT/IWS personnel, production management, quality personnel and auditors.
Scope: Framework for the specification and qualification of welding procedures.
Intended users: Welding technologists, IWE/IWT personnel, production teams and customer auditors.
Scope: Specifies the information to be included in a welding procedure specification.
Intended users: Welding technologist, supervisor, welder and inspector.
Scope: How a pWPS is qualified using a procedure test weld.
Intended users: Welding technologists, laboratories, certification bodies and customers.
Scope: Welder qualification testing for fusion welding.
Intended users: Welders, human resources, production and quality personnel.
Scope: Qualification of operators and setters for mechanised and automatic welding.
Intended users: Robotic stations, production lines, resistance welding and automated cells.
Scope: Uniform process reference numbers.
Intended users: WPSs, drawings, certificates and audits.
Scope: Designation of welding positions.
Intended users: Welders, welding technologists and test centres.
Scope: weld symbols, supplementary symbols and rules for presentation on drawings.
Intended users: design engineers, welding engineers, fabrication personnel and inspectors.
Scope: bevel forms and joint preparation for different processes.
Intended users: design, production preparation, cutting and machining workplaces, and welders.
Scope: general tolerances for linear and angular dimensions, shape and position of welded structures.
Intended users: design, fabrication, dimensional inspection and customer inspection.
Scope: acceptance limits for weld imperfections.
Intended users: inspectors, NDT personnel, welding engineers and customers.
Scope: names, groups and numerical designations of geometric weld imperfections.
Intended users: visual inspectors, NDT personnel, fabrication, quality and claims handling.
| Group | Name | Typical imperfections | How to remember it |
|---|---|---|---|
| 1xx | Cracks | longitudinal, transverse, crater and branching cracks | The most critical group. A crack is a sharp imperfection with a high stress concentration. |
| 2xx | Cavities | pores, gas cavities, crater cavities and shrinkage cavities | Volume is missing from the weld: gas or shrinkage has left a pore or cavity. |
| 3xx | Solid inclusions | slag, oxides, metallic inclusions and tungsten inclusions in TIG welding | Foreign solid material remained trapped in the weld. |
| 4xx | Incomplete penetration and lack of fusion | lack of fusion, incomplete penetration and incomplete root penetration | The metal did not bond where it was required to bond. |
| 5xx | Shape and dimensional imperfections | undercut, overlap, excessive reinforcement, root concavity and incorrect weld transition | The weld geometry is incorrect even though metallurgical bonding may have occurred. |
| 6xx | Miscellaneous imperfections | spatter, surface damage, grinding marks, and start/stop imperfections depending on the specific case | Imperfections that do not fit cleanly into groups 1 to 5. |
Scope: selection and coordination of non-destructive testing of welds.
Intended users: quality personnel, NDT coordinators, IWE personnel and customers.
Scope: visual testing and examination of fusion welds.
Intended users: supervisors, inspectors, welders and quality control personnel.
Scope: surface and near-surface imperfections in ferromagnetic materials.
Intended users: steel structures, pressure equipment and maintenance.
Scope: imperfections open to the surface, detected using a penetrant.
Intended users: stainless steel, aluminium, non-ferrous metals and smooth surfaces.
Scope: internal volumetric imperfections using X-rays or gamma radiation.
Intended users: pressure equipment, pipelines and weldments requiring internal examination.
Scope: internal imperfections using ultrasound.
Intended users: thicker materials, pressure equipment and steel structures.
Scope: qualification and certification of personnel performing NDT.
Intended users: VT/PT/MT/RT/UT personnel, NDT companies and customers.
Scope: classification of gases and gas mixtures for welding and allied processes.
Intended users: MIG/MAG/TIG welding engineers, purchasing and fabrication personnel.
What they cover: classification of wires and electrodes.
Intended users: welding engineering, stores, purchasing and welders.
What they cover: mechanical and macroscopic tests of welded joints.
Intended users: laboratories, WPQR qualification, quality and process development.
Scope: execution and conformity assessment of load-bearing metallic structures.
Intended users: manufacturers of structural steelwork, erection contractors, auditors and CE-marking personnel.
Scope: acceptance levels for imperfections in arc-welded aluminium and its alloys.
Intended users: aluminium structures, transport applications, frames, tanks and manufacturing audits.
EN ISO Use the European designation EN ISO where an ISO standard has been adopted by CEN. On drawings, WPSs, certificates and audit records, always verify the exact edition, publication year and amendments such as A1 or A2.
The lattice is not decorative theory. It determines the number of slip systems, dislocation mobility, diffusion of interstitial atoms, transformation stresses and therefore the behaviour of weld metal and the HAZ.
joint properties = chemical composition + lattice + defects + grain structure + thermal cyclePlastic slip is not initiated by nominal tensile stress alone, but by the resolved shear component on a specific slip plane and in a specific slip direction. Texture, grain orientation and the dendritic structure of weld metal therefore change local plasticity.
A smaller grain size generally increases yield strength because grain boundaries impede dislocations. A coarse-grained HAZ has the opposite problem: lower toughness and greater susceptibility to brittle fracture.
Hydrogen is a highly mobile interstitial element. It is particularly dangerous in the combined presence of martensite, tensile stress and traps at grain boundaries or inclusions.
Plastic deformation occurs by dislocation motion. Strengthening impedes that motion through solid-solution strengthening, precipitates, grain boundaries or transformation-produced martensite.
Slip plane is the most densely packed crystallographic plane along which dislocations move most readily. Slip direction is the most densely packed direction within that plane.
Twinning is a mode of plastic deformation in which part of a crystal is mirror-reoriented about a twinning plane. It does not occur by continuous movement over a long distance as in conventional slip, but by coordinated displacement of atomic planes.
A metal requires several independent slip systems so that differently oriented grains can accommodate a change in shape. If too few are available, deformation localises and cracking occurs more readily.
| Mechanism | How it works | When it is significant | Consequence for welding and materials |
|---|---|---|---|
| Slip | Movement of dislocations along a slip plane in a slip direction. | The principal mechanism of plastic deformation in most metals. | It governs ductility, local strain caused by weld shrinkage and the ability of the HAZ to relax stresses. |
| Twinning | Mirror reorientation of part of a crystal about a twinning plane. | HCP metals, low temperature, high strain rate and some austenitic steels. | It can increase plasticity where slip is insufficient, while also creating boundaries that influence crack propagation. |
| Dislocation strengthening | Dislocations accumulate and obstruct one another’s movement. | Cold forming, local deformation, repairs and straightening of components. | Higher strength and lower elongation; the welding thermal cycle may partly remove or alter the strengthening. |
| Barriers to slip | Grain boundaries, precipitates, interstitials, martensite and inclusions impede dislocation motion. | High-strength steels, microalloyed steels and precipitation-strengthened aluminium and nickel alloys. | Heat input, interpass temperature and any required PWHT must be controlled to prevent loss of toughness. |
| Lattice / phenomenon | Materials significance | Consequence for welding |
|---|---|---|
| BCC ferrite | greater temperature sensitivity and a possible ductile-to-brittle transition | control of preheat, t₈/₅, HAZ hardness and impact testing |
| FCC austenite | many active slip systems and high toughness | good resistance to brittle fracture; beware of hot cracking and segregation |
| HCP | limited slip and pronounced anisotropy | sensitivity in titanium, magnesium and their alloys; stringent cleanliness and gas shielding are required |
| Slip planes | the most densely packed planes with the lowest resistance to dislocation motion | local plasticity during weld shrinkage and the ability to relax stresses without cracking |
| Twinning | mirror reorientation of part of the crystal; important where slip is restricted | significant in HCP metals, at low temperatures and in some austenitic steels; influences texture and toughness |
| Martensite | diffusionless transformation, high hardness and high transformation stress | risk of hydrogen cracking; preheat and/or PWHT may be required depending on the material |
| Precipitates | strengthening, but also possible loss of toughness after an unsuitable thermal cycle | control of interpass temperature, PWHT and degradation of creep-resistant steels |
This is a didactic model that illustrates trends. Actual assessment of pressure parts, boilers and piping requires material creep data, code-based calculations, operating history and weld inspection.
Creep becomes technically significant at approximately 0.3–0.4 Tm. The same temperature of 550 °C therefore represents a completely different condition for aluminium, ferritic steel and a nickel alloy.
In Cr-Mo and 9–12% Cr steels, the decisive region is often not the weld metal but the softened fine-grained/intercritical HAZ. Creep strain concentrates there and intergranular damage develops.
Material, heat input, interpass temperature, preheat, PWHT, filler material, HAZ hardness, NDT and the periodic inspection plan. A creep assessment is incomplete without service time and temperature.
| Application | Typical risk | Engineering measure |
|---|---|---|
| Boilers, superheaters and steam piping | long-term service at elevated temperature | material creep data, life assessment, replication, NDT and trending |
| Cr-Mo steels 16Mo3, 13CrMo4-5 | microstructural degradation and HAZ softening | correct PWHT, hardness verification and heat-input control |
| P91 / P92 | Type IV damage in the HAZ and high sensitivity to PWHT | precise WPS, interpass-temperature control, preheat, a defined PWHT window and a qualified repair procedure |
| Austenitic stainless steels | creep, precipitation, sigma phase and sensitisation | appropriate alloy selection and control of time within the critical temperature range |
| Nickel alloys | high-temperature stress, oxidation and creep-fatigue interaction | material data, process cleanliness, and control of stress and surface condition |
First examine morphology: polygonal grains, lamellae, needles/laths, carbide networks, and graphite flakes or nodules. Then relate the microstructure to properties: hardness, toughness, brittleness and cracking risk in the HAZ.
1. Ferrite (α)What I see: Light polygonal ferrite grains with subtly darker grain boundaries.
Properties: A soft and ductile BCC phase with low hardness and high toughness.
2. Austenite (γ)What I see: Equiaxed grains with visible boundaries and occasional annealing twins.
Properties: An FCC phase stable at higher temperatures; non-magnetic and highly ductile.
3. Cementite (Fe₃C)What I see: Hard carbide particles or a carbide network at grain boundaries.
Properties: A very hard and brittle phase that increases hardness and reduces toughness.
4. PearliteWhat I see: A lamellar mixture of ferrite and cementite in colonies with different lamellar orientations.
Properties: Intermediate hardness and strength, readily recognisable after etching.
5. Coarse pearliteWhat I see: Coarser ferrite and cementite lamellae with wider spacing.
Properties: Softer and more machinable than fine pearlite, but with lower strength.
6. Fine pearliteWhat I see: Very fine, closely spaced ferrite and cementite lamellae.
Properties: Higher hardness and strength than coarse pearlite, with lower toughness.
7. SpheroiditeWhat I see: Spheroidal carbides dispersed in a ferritic matrix.
Properties: A soft, ductile and highly machinable structure.
8. MartensiteWhat I see: A needle-like or lath structure formed by rapid cooling.
Properties: Very hard and strong, but brittle and susceptible to cracking.
9. Tempered martensiteWhat I see: Martensite after tempering, containing fine dispersed carbides.
Properties: Lower hardness than fresh martensite and improved toughness.
10. Upper bainiteWhat I see: A feathery or sheaf-like structure with carbides between ferrite laths.
Properties: Forms at a higher bainitic transformation temperature; strong, but less tough than lower bainite.
11. Lower bainiteWhat I see: Fine ferrite needles or laths with fine carbides within the laths.
Properties: Higher strength and often better toughness than upper bainite.
12. LedeburiteWhat I see: A eutectic mixture with pronounced carbide regions.
Properties: A very hard and brittle microstructure typical of high carbon content.
13. Transformed ledeburiteWhat I see: Ledeburite after further transformation, often containing pearlite and cementite.
Properties: Hard and brittle; the final condition depends on cooling rate.
14. White cast ironWhat I see: A continuous cementite network without free graphite.
Properties: Very hard, very brittle, abrasion-resistant and difficult to machine.
15. Grey cast ironWhat I see: Flake graphite in a ferritic or pearlitic matrix.
Properties: Good damping capacity and machinability, but lower strength and greater brittleness.
16. Ductile cast ironWhat I see: Spheroidal graphite in a ferritic/pearlitic matrix.
Properties: Higher strength and toughness than grey cast iron.
17. Compacted graphite ironWhat I see: Worm-like compacted graphite, intermediate between flake and spheroidal forms.
Properties: A compromise between strength, thermal conductivity and damping capacity.
18. Widmanstätten structureWhat I see: Plate-like or acicular ferrite features growing from prior austenite grains.
Properties: A coarse, oriented structure with reduced toughness.
19. Acicular ferriteWhat I see: Fine interlocking ferrite needles in the weld metal.
Properties: High toughness resulting from the random orientation of fine needles.
20. Delta ferrite (δ)What I see: A light BCC ferritic phase in an austenitic or stainless-steel matrix.
Properties: A small amount improves resistance to hot cracking; an excessive amount reduces ductility.
21. Duplex structure (ferrite + austenite)What I see: A two-phase mixture of light ferrite and darker austenite.
Properties: Combines strength, toughness and good resistance to localised corrosion.
Mechanical tests verify whether the welded joint as a whole achieves the required properties of the base material, weld metal and heat-affected zone. For a WPQR this is not a “laboratory formality”, but evidence that the proposed welding procedure produces a joint with acceptable strength, toughness, ductility, hardness and internal quality.
| Test | What it verifies | Typical standard | Meaning for the welding engineer |
|---|---|---|---|
| Transverse tensile test | Strength of the complete joint across the weld. | EN ISO 4136 | If the specimen fractures outside the weld, this often confirms adequate joint strength; the fracture location is as important as the Rm value. |
| Bend test | Ductility and internal imperfections on the tension face of the bend. | EN ISO 5173 | Highly sensitive to incomplete penetration, lack of fusion, cracks and insufficient ductility. |
| Charpy V-notch impact test | Toughness of weld metal and the HAZ at a defined temperature. | EN ISO 9016, EN ISO 148-1 | Critical for low-temperature service, pressure equipment and structures exposed to brittle-fracture risk. |
| Hardness | Hardness of the weld, HAZ and base material. | EN ISO 9015-1, EN ISO 9015-2 | Reveals excessive cooling rates, a hard HAZ and the risk of hydrogen cracking. |
| Macroscopic examination | Geometry, fusion, penetration, layers, imperfections and HAZ shape. | EN ISO 17639 | The fastest clear evidence of whether the process settings actually produced the required cross-section. |
| Fillet-weld fracture test | Internal root-region imperfections and effective throat thickness. | EN ISO 9017 | A practical test for fillet welds, particularly in series production and qualification. |
The scope of testing depends on joint type, material, thickness, process, product standard and customer requirements. Under EN ISO 15614, tests are selected according to the required qualification range, not convenience.
The sampling location must represent the critical regions of the joint. Butt welds require assessment of both weld metal and HAZ; fillet welds require assessment of the root, effective throat and fusion.
Evaluation must state the fracture location, fracture appearance, notch position, hardness traverse and macrostructure. A numerical result without context can be misleading.
Hooke’s law applies only up to the limit of proportionality Ru. In this linear region, the slope of the curve is Young’s modulus E and stress is calculated as σ = E · ε. Above Ru, the relationship may begin to deviate from a straight line; above Re/Rp0.2, plastic and therefore permanent deformation occurs.
Up to Ru, the curve is a straight line and σ = E · ε applies. Deformation is reversible and the slope is Young’s modulus E. Beyond Ru, the relationship need no longer remain ideally proportional.
Ru marks the end of linear proportionality, whereas Re/Rp0.2 is the boundary beyond which plastic deformation occurs. For materials without a distinct yield point, proof strength Rp0.2 is used.
In the plastic region, stress may continue to increase up to Rm, the maximum engineering stress reached in the tensile test.
After Rm is reached, deformation localises in a neck and engineering stress decreases until the specimen fractures.
| Position | Visualisation | Meaning of the position | Typically suitable processes | What to monitor during welding |
|---|---|---|---|---|
| PA1G / 1F | Flat positionthe weld pool lies on the upper side of the joint. | MIG/MAGTIGMMAFCAWSAW |
the most stable weld pool, high productivity and suitable for teaching basic torch manipulation. | |
| PB2F | Horizontal-vertical positionmost commonly a fillet weld on a T-joint or corner joint. | MIG/MAGFCAWMMATIG |
uniform fillet legs, fusion to both members and the risk of undercut at the lower edge. | |
| PC2G | Horizontal positionthe weld axis is horizontal and the weld is deposited on a vertical surface. | MIG/MAGFCAWMMATIG |
the pool tends to sag downward; a shorter arc, smaller pool and correct torch angle help maintain control. | |
| PD4F | Horizontal-overhead positionthe fillet weld is deposited from the underside of the joint. | MMAFCAWMIG/MAGTIG |
small pool, multiple passes, welder protection, and control of sagging, porosity and spatter. | |
| PE4G | Overhead positionthe butt weld is deposited from the underside. | MMAFCAWMIG/MAGTIG |
short arc, lower current, root control and a smaller bead to prevent pool sagging. | |
| PF3G up | Vertical-up positionwelding progresses from bottom to top. | pulsed MIG/MAGFCAWMMATIG |
good sidewall fusion and penetration, slower travel and more frequent use of multi-pass technique. | |
| PG3G down | Vertical-down positionwelding progresses from top to bottom. | MIG/MAG short arcFCAWcellulosic MMA |
faster progression, but a higher risk of insufficient penetration and lack of fusion in thicker components. | |
| PH5G up | Pipe position, vertical-upthe pipe is fixed and the circumferential weld is made with upward progression. | TIG root passMMAFCAWMIG/MAG |
the position changes around the circumference; the welder moves through lower, vertical and upper sectors. | |
| PJ5G down | Pipe position, vertical-downthe pipe is fixed and the circumferential weld is made with downward progression. | cellulosic MMAFCAWMIG/MAG short arc |
requires precise root control, correct travel speed and a suitable process/filler material according to the WPS. | |
| H-L0456G up | Fixed pipe at 45°, upwardcombined position with upward progression. | TIG root passMMAFCAWMIG/MAG |
a demanding qualification position; pool position, torch angle and the direction of gravity relative to the pool all change during welding. | |
| J-L0456G down | Fixed pipe at 45°, downwardcombined position with downward progression. | cellulosic MMAFCAWMIG/MAG short arc |
do not transfer it automatically to every material and thickness; welding direction is an essential variable. |
G 42 4 M21 3Si1, 19 12 3 L, ER5356, E 42 5 B 42 H5, T 46 4 P M21 1 H5 or S2Mo + flux are examples of classifications. The final selection must be compatible with the WPQR, base material, service temperature and customer requirements.| Test | Description and purpose | Standard / relationship |
|---|---|---|
| Transverse tensile test | The specimen contains the complete welded joint. It verifies minimum strength and fracture location. It is used for qualification of butt welds and to demonstrate that the joint is not the weakest link. | EN ISO 4136, ISO 15614 |
| Longitudinal weld-metal tensile test | Tests the properties of deposited weld metal. It is used where weld-metal properties must be separated from those of the base material. | EN ISO 5178 |
| Bend test | The specimen is bent around a former. Insufficient ductility, cracks, incomplete penetration, lack of fusion and larger internal imperfections are revealed on the tension face. | EN ISO 5173 |
| Charpy V-notch impact test | Measures absorbed energy during notched fracture at a defined temperature. The notch is positioned in the weld metal or HAZ as required. | EN ISO 9016, EN ISO 148-1 |
| Hardness test | Maps hardness across the weld, HAZ and base material. Important for steels susceptible to a hard HAZ and hydrogen cracking. | EN ISO 9015-1, EN ISO 9015-2 |
| Macro- and micro-examination | The prepared section reveals fusion, penetration, layers, HAZ, imperfections and, where required, microstructure. Micro-examination assesses phases, grain structure, cracks and precipitation phenomena. | EN ISO 17639 |
| Fracture test | The specimen is intentionally fractured to reveal internal imperfections in fillet or butt welds. It is simple but highly illustrative. | EN ISO 9017 |
A destructive test is meaningful only when specimen location, orientation, preparation, test temperature, acceptance criterion and traceability to the specific WPS/WPQR or production component are defined.
NDT complements metallurgy, WPS/WPQR qualification and ISO 5817. It does not merely state that “the weld looks good”; it helps determine whether the joint is acceptable for the required quality level, structural application and failure risk.
In practice, the method is selected not only by imperfection name, but also by material, thickness, joint geometry, accessibility, standard requirements and quality level B/C/D.
Principle: inspection of the weld surface, geometry and visible imperfections with the unaided eye or visual aids.
Principle: penetrant enters a surface-breaking imperfection and, after development, produces an indication.
Principle: a magnetic field and particles reveal flux leakage at a discontinuity.
Principle: an ultrasonic beam reflects from interfaces and imperfections within the material.
Principle: X-rays or gamma radiation create an image from differences in absorption.
PAUT: electronically steered beam set for improved weld mapping. TOFD: uses diffraction from imperfection tips and is highly effective for sizing imperfection height.
| Imperfection group | Most suitable methods | Evaluation note |
|---|---|---|
| Surface imperfections | VT, PT, MT | Dimensions, length and position are compared with the required quality level. |
| Internal volumetric imperfections | RT, UT | RT gives an intuitive image of pores; UT response depends on reflectivity and imperfection orientation. |
| Internal planar imperfections | UT, PAUT, TOFD | Planar imperfections are particularly dangerous when loading is normal to the imperfection plane. |
| Geometric imperfections | VT, gauges and macro-examination during qualification | Typically reinforcement height, undercut, fillet-weld size or misalignment. |
A full-penetration butt weld is often assessed as base material. A fillet weld is calculated using the effective throat a. For combined normal and shear stress, the von Mises equivalent stress is used.
ISO 6520 names and classifies the imperfection. ISO 5817 determines whether it is still permissible for the specified quality level. Cracks and incomplete penetration are highly critical in practice.
| Level | Meaning | Typical application |
|---|---|---|
| B | most stringent | demanding welds and fatigue-loaded structures |
| C | medium | general engineering structures |
| D | moderate | less demanding welds |
A welder qualification is valid only within its qualified range: process, weld type, material, thickness, diameter, position, filler material and joint details. A more demanding test often qualifies easier positions, but not the reverse.
The pWPS/WPS specifies permitted ranges and technological conditions. The WPQR separately records the actual materials, batches, measured parameters, temperatures, tests and qualified range. In a multi-process procedure each process has its own consumable, gas, polarity, mode and pass groups.
The generator does not invent broadened standard ranges. It creates a conservative qualification matrix from the tested data, and every essential variable must be confirmed by a competent person against the contracted edition, test results and product standard.
EN 1090 addresses steel and aluminium load-bearing structures, factory production control and CE marking. EXC1 is the lowest and EXC4 the highest execution class.
| Class | Simplified meaning |
|---|---|
| EXC1 | simple structures with low consequences |
| EXC2 | general steel structures; often the default level |
| EXC3 | demanding structures, bridges, fatigue and high requirements |
| EXC4 | exceptional consequences of failure and special structures |
A small proportion of δ-ferrite in austenitic weld metal reduces hot-cracking susceptibility. Excessive ferrite, however, may impair properties and corrosion resistance in some applications.
Corrosion is not merely cosmetic rusting. Welded structures often combine a local chemical environment, different microstructures in weld metal and the HAZ, residual stresses, and geometric details such as crevices, washers or lap joints.
The images are used as consistent teaching visualisations. The text beneath each image explains the mechanism, typical risks and basic prevention. A real failure analysis must always confirm the material, environment, stress, surface condition and manufacturing history.
Uniform corrosion — Uniform material loss across the entire exposed surface. Typical of general atmospheric corrosion or environments without pronounced local passivation.
Galvanic corrosion — Occurs when two dissimilar metals are electrically connected in an electrolyte. The less noble metal acts as the anode and corrodes more rapidly.
Crevice corrosion — Localised corrosion in narrow crevices, beneath gaskets, washers or deposits, and in lap joints. The chemistry within the crevice changes and oxygen concentration decreases.
Pitting corrosion — A highly localised form of attack that creates deep pits. Even when visible damage is small, local thickness loss may be severe.
Intergranular corrosion — Corrosion progresses preferentially along grain boundaries. It may result from sensitisation of stainless steels, when chromium carbides form at grain boundaries and the adjacent regions become chromium-depleted.
Selective leaching / dealloying — Preferential dissolution of one alloy constituent. A typical example is dezincification of brass, in which zinc dissolves preferentially and leaves a porous copper-rich structure.
Erosion corrosion — A combination of corrosion and mechanical removal of the protective film by a flowing medium. Typical in pipes, elbows, valves and pumps.
Cavitation corrosion — Damage caused by formation and implosion of vapour bubbles during rapid pressure changes. Implosions disrupt the surface and accelerate corrosion.
Stress corrosion cracking – SCC — Crack formation caused by the simultaneous action of tensile stress and a specific corrosive environment. Cracks may be intergranular or transgranular.
Corrosion fatigue — Growth of fatigue cracks in a corrosive environment under cyclic loading. The environment shortens life compared with fatigue in air.
Hydrogen damage — Hydrogen entering the metal may cause embrittlement, cracking, blistering or delayed failure. In welding it is particularly important for high-strength and hardenable steels.
Microbiologically influenced corrosion – MIC — Corrosion influenced by microorganisms or biofilm. Microorganisms alter local chemical conditions at the metal surface and promote localised attack.
Heat treatment changes the steel microstructure through controlled heating, holding and cooling. In practice it is used to set hardness, strength, toughness, dimensional stability and the level of residual stress.
Welding creates a heat-affected zone in which some heat-treatment phenomena occur locally. Preheat, interpass temperature, cooling rate and any post-weld heat treatment are therefore important.
A simplified teaching map: exact temperatures always depend on chemical composition, thickness, the applicable standard and the required structure. The essential logic is whether treatment occurs below A₁, around A₁ or above A₃/Acm.
Reduces hardness and improves machinability. The aim is to refine or spheroidise carbides, particularly in carbon and tool steels.
Typical result:lower hardness, improved formability and machinabilityHeating above the critical temperatures, holding and cooling in air. Used to refine grain size and homogenise the structure after forming or casting.
Typical result:finer grain and more uniform strength and toughnessPerformed below A₁. It does not fundamentally change the phases, but reduces internal stresses after welding, machining or forming.
Typical result:lower risk of distortion and crackingHeating into the austenitic region followed by rapid cooling. With suitable carbon content, high-hardness martensite forms.
Typical result:high hardness, but greater stresses and brittlenessFollows hardening. Controlled heating below A₁ reduces martensite brittleness and establishes a balance between hardness and toughness.
Typical result:lower brittleness and higher toughnessA combination of hardening and high-temperature tempering. Used for structural steels where both strength and toughness are required.
Typical result:a strong and tough tempered-martensitic structurePost-weld heat treatment is used particularly for thicker components, pressure equipment and alloy steels. Its purpose is to reduce stresses and stabilise welded-joint properties.
Typical result:lower residual stresses and a more stable welded jointRapid cooling promotes hard structures; slow cooling promotes ferritic-pearlitic transformations. In welding this is reflected in HAZ hardness and hydrogen-cracking susceptibility.
Typical result:a key influence on martensite, bainite or pearliteTo soften the material: anneal. To refine the grain: normalise. To achieve high hardness: quenching. To reduce brittleness after hardening: temper. To address stresses after welding: use stress-relief annealing or PWHT according to the material, thickness and applicable requirements.
ISO 4063 is a language for unambiguous process identification. It does not state whether a weld is acceptable and does not replace the WPS. It states the physical principle by which the joint was made: by arc, resistance, gas, pressure, beam, plastics joining, cutting, brazing or soldering.
Do not use only a colloquial name such as “CO₂ welding”, “spot welding”, “laser”, “TIG” or a machine name in documentation. Use the standard process number and add the decisive data: filler material, shielding medium, level of mechanisation, polarity, flux, preheat, interpass temperature, torch path, program or cycle.
| Number | Process | What distinguishes it in practice | Typical application | Documentation caution |
|---|---|---|---|---|
| 111 | MMA / manual metal arc welding with a covered electrode | Electrode covering type, drying, polarity, electrode diameter and position. | Erection, repair, structures, piping and difficult-to-access locations. | State the electrode classification and storage/drying conditions. |
| 112 | Gravity arc welding with a covered electrode | Mechanised electrode feeding by gravity. | Special or legacy production procedures. | Do not confuse it with conventional process 111. |
| 114 | Self-shielded tubular-cored arc welding | No external shielding gas; protection is provided by the wire core. | Field work, erection and structures where gas shielding is problematic. | It is not process 136, because 136 uses an active shielding gas. |
| 121122124125126 | SAW / submerged arc welding: solid wire, strip, metal powder, tubular-cored wire or cored strip | Flux, electrode type, number of wires, high heat input and welding position. | Long butt and fillet welds, pressure vessels, bridges and thick sections. | Do not state only “SAW” — processes 121, 122, 124, 125 and 126 are distinct for WPQR and WPS purposes. |
| 131132133 | MIG in inert gas: solid wire, flux-cored wire or metal-cored wire | Inert gas, wire type, metal transfer and, where applicable, pulsing. | Aluminium, copper, nickel and oxidation-sensitive materials; automation. | If the gas is active or the mixture contains an active component, the process may belong to the MAG group. |
| 135136138 | MAG in active gas: solid wire, flux-cored wire or metal-cored wire | Active gas or mixture, wire type, metal transfer, contact-tip-to-work distance and robot program. | Non-alloy and low-alloy steels, automotive production, structures and series fabrication. | 135 ≠ 136 ≠ 138. All belong to the MIG/MAG family, but they are not the same process. |
| 141142143145146147 | TIG/TAG — non-consumable tungsten electrode with inert or active/reducing gas | Solid or tubular filler material, no filler material, gas type and root shielding. | Root passes, stainless steel, aluminium, titanium, thin sheet and high weld cleanliness. | 141 with filler material ≠ 142 without filler material. For titanium, also specify supplementary shielding. |
| 15151152153154155 | Plasma arc welding and plasma variants | Constricted arc, powder or wire, transferred or non-transferred arc. | Precision welds, overlays, thin sheet, microplasma and automation. | Distinguish it from TIG: the non-consumable electrode is similar, but the arc principle is different. |
| 185 | Magnetically impelled arc welding | A rotating arc controlled by a magnetic field. | Tubular components, circumferential joints and series fabrication. | A special process requiring separate assessment of qualification. |
| Number | Process | Control variables | Typical application | Documentation caution |
|---|---|---|---|---|
| 21211212 | Resistance spot welding, indirect and direct spot welding | Current, time, electrode force, tip diameter, cooling, coating condition and number of spots. | Automotive sheet, sheet-metal assemblies and projection-welded nuts located by fixtures. | Inspection must include electrode wear, expulsion, nugget diameter and peel testing. |
| 22221222223224225226 | Resistance seam welding: lap seam, mash seam, prep-lap, wire seam, foil butt seam and strip seam | Current pulses, continuous or intermittent seam, wheel speed, force and cooling. | Tanks, vessels, tubes and leak-tight sheet-metal joints. | Seam welding is not merely “spot welding in a row”: electrode mechanics and leak-tightness inspection also change. |
| 23231232 | Resistance projection welding, indirect and direct | Projection geometry, force, current, time, electrode parallelism and projection collapse. | Weld nuts, studs, screws, clips and multi-spot joints. | For nuts, verify orientation, centring, the thread after welding, and push-out/torque strength. |
| 24241242 | Resistance flash welding with or without preheating | Flashing, upsetting, burn-off length, preheat and axial alignment. | Rails, rings, bars, chains and frame members. | Do not confuse it with simple resistance butt welding. |
| 25262729 | Resistance butt, resistance stud, high-frequency resistance and other resistance processes | Contact area, current path, pressure, frequency and feed speed. | Pipes, profiles, bars, studs and series components. | For HF resistance welding, state frequency, speed and the method of applying force. |
| Number | Process | What to distinguish | Typical application | Note |
|---|---|---|---|---|
| 31311312313 | Oxy-fuel gas welding: acetylene, propane or hydrogen | Gas type, flame type, filler material, thermal effect and flashback arrestors. | Repairs, thinner sheet, copper and special applications, and teaching of thermal-process principles. | Gas welding differs from flame cutting process 81 and from brazing processes 91/92. |
| Number | Process | Principle | Typical application | What to record in addition to the number |
|---|---|---|---|---|
| 41411412413414 | Ultrasonic welding and its spot, seam and torsional variants | High-frequency mechanical vibration plus pressure. | Foils, conductors, plastics, thin sheet and battery tabs. | Amplitude, energy, pressure, time and sonotrode geometry. |
| 42421422423424425426 | Friction welding: direct-drive, inertia, stud, linear, radial and orbital | Frictional heat plus forging/upsetting. | Shafts, valves, bars, dissimilar metals and series components. | Rotational speed/frequency, pressure, friction time, shortening and flash. |
| 43431432433434435 | FSW — friction stir welding and spot-FSW variants | A rotating tool plastically stirs the material without melting it. | Aluminium alloys, railway vehicles, aerospace, battery enclosures and long seams. | Tool geometry, rotational speed, force, travel speed, and advancing/retreating side. |
| 44441442 | Impact / impulse welding: explosive and magnetic-pulse welding | High mechanical energy and a pressure wave. | Bimetals, aluminium–steel and copper–aluminium transition pieces, and clad plate. | Safety procedure, overlap geometry, impact velocity and interface inspection. |
| 45451474848149 | Diffusion, HIP, gas-pressure, cold-pressure and hot-pressure welding | Diffusion and plastic deformation without a conventional weld pool. | Titanium, nickel, ceramic-to-metal joints with an interlayer, layered materials and special joints. | Temperature, pressure, time, atmosphere/vacuum, surface cleanliness and interlayer. |
| Number | Process | Characteristic | Typical application | Caution |
|---|---|---|---|---|
| 51511512513 | Electron-beam welding in vacuum, atmosphere or shielding gas | A highly concentrated energy source producing a deep, narrow weld. | Aerospace parts, high-precision components, thicker sections and low distortion. | State vacuum/atmosphere, accelerating voltage, focus and welding speed. |
| 52521522523 | Laser welding: solid-state, gas or diode laser | Concentrated beam, high speed, small HAZ and possible keyhole mode. | Automotive, batteries, thin sheet, robotics and precision welds. | “Laser” alone is insufficient: specify the source, optics, power, focus, shielding and gap preparation. |
| Number | Process | Principle | Typical application | Note |
|---|---|---|---|---|
| 61611 | Implant resistance welding / electrofusion welding | Heating by an embedded resistance element. | Plastic pipes, fittings and PE systems. | State plastic material, temperature, time, pressure and cooling. |
| 6263631 | Radio-frequency and solvent welding of plastics | Dielectric heating or chemical softening of the surface. | Films, packaging, PVC and special plastic joints. | For solvent welding, address occupational safety, compatibility and evaporation time. |
| 64641642643644645646647 | Hot-gas welding, manual/machine, with or without filler rod, and extrusion welding | Hot gas softens the faying surfaces and/or the plastic filler material. | Tanks, piping, plastic repairs and chemical equipment. | Gas temperature, flow rate, force and filler-material type. |
| 6565165266661662663664 | Heat sealing and heated-tool welding: impulse, hot bar, hot plate, hot wedge, socket and saddle | Contact heating + pressure + cooling. | Films, packaging, membranes, pipes and fittings. | Variants may have supplementary letters, for example heated-wedge welding assisted by hot gas. |
| 6767169691692 | Flashless, microwave and forming/pin plastic processes | Special methods using local heating or shape-locking insertion. | Automotive plastics, electronics and precision plastic components. | Plastics require different qualifications and tests from metals. |
| Number | Process | Characteristic | Typical application | Caution |
|---|---|---|---|---|
| 71 | Aluminothermic / thermit welding | An exothermic reaction produces molten metal. | Rails, heavy repairs and special joints. | Strongly dependent on mould preparation, preheat and cavity control. |
| 72721722 | Electroslag welding with strip or wire electrode | Heat is generated in molten slag; large thicknesses are welded in the vertical position. | Thick plate, heavy structures and castings. | Extremely high heat input and a specific HAZ structure. |
| 73 | Electrogas welding | Vertical welding with forced weld-pool containment. | Large vertical welds, tanks and ships. | It is not conventional MAG welding and must be qualified separately. |
| 74741742743 | Induction welding: butt, seam and high-frequency induction | Heating by electromagnetic induction plus pressure. | Pipes, profiles and continuous fabrication. | State frequency, power, speed and the method used to form the joint. |
| 7575378783784785786 | Radiant-energy / infrared welding and arc stud welding | Local heating by radiation or arc plus stud pressure. | Studs, fasteners, shear connectors, and special plastic and metallic applications. | For studs, state the ignition method, ceramic ferrule/shielding gas and the stud standard. |
| Number | Process | What matters | Typical application | Risks for subsequent welding |
|---|---|---|---|---|
| 81 | Flame cutting / oxy-fuel cutting | Steel reacts with oxygen; edge quality depends on preheating, speed and oxygen purity. | Joint preparation, plate cutting and erection. | Hard or oxidised edge, drag lines, cracks and the need for grinding on demanding joints. |
| 82821822 | Arc cutting, including air-carbon arc and oxygen-arc cutting | Melting by an arc and removal of the material by a gas jet. | Gouging, repairs, removal of imperfections and root preparation. | Carbon contamination, grooves, overheating and the need for final cleaning. |
| 83831832833834 | Plasma cutting with oxidising gas, non-oxidising gas, air plasma or high-precision plasma | Constricted plasma arc, gas, current, speed and cut quality. | Stainless steel, aluminium, carbon steels and series cutting. | Nitrided/oxidised edge, bevel and heat-affected layer. |
| 84868787187288 | Laser cutting, flame gouging, arc gouging and plasma gouging | Difference between a cut and a groove, surface quality and residual layer. | Precision blanks, weld repairs, back-gouging and bevel preparation. | After gouging, inspect for cracks, carbon residues and cleanliness before welding. |
| Number | Process | Principle | Typical application | Caution |
|---|---|---|---|---|
| 9192 | Brazing with local or overall heating | Filler metal above approximately 450 °C; the base material does not melt, and wetting and capillary action govern. | Copper, brass, stainless steel, carbides, heat exchangers and tools. | State filler metal, flux/atmosphere, capillary clearance, cleanliness and temperature. |
| 9495 | Soldering with local or overall heating | Filler metal with a lower melting temperature, typically for electronics and thin joints. | Electronics, thin sheet and service joints. | It is not welding; its strength and temperature resistance have a different character. |
| 97 | Braze welding | A technique resembling fusion welding but without intentional melting of the base material. | Repairs, cast iron, thin coated sheet and MIG brazing with CuSi. | Distinguish it from capillary brazing and fusion welding. |
The process number is only the first identifier. Only together with filler material, gas, parameters, position, thickness and material group does it form a usable welding specification.
If two processes act simultaneously in one welding zone, designate them by a combination of numbers. Practical examples include laser + plasma or laser + MAG. The WPS must then state the parameters for each energy source separately.
131 MIG uses an inert gas. 135 MAG uses an active gas or active mixture. The same machine does not mean the same process.
136 is MAG welding with a flux-cored wire. 138 is MAG welding with a metal-cored wire. They differ in metallurgy, slag, fume generation and qualification.
141 uses solid filler material. 142 is autogenous TIG without filler material. This is a fundamental distinction for root passes.
21 is resistance spot welding. 23 is projection welding. For nuts and studs it is not sufficient to write “spot welding”.
1. Identify the physical principle of the process. 2. Select the main ISO 4063 reference number. 3. Add the precise subprocess where one exists. 4. Verify that the WPS, WPQR, welder/operator certificate and production record use the same number. 5. For special or variant processes, add a written description, parameters and reference to the specific edition of the standard.
In brazing and soldering, the base material does not melt. The joint is formed by melting the filler metal, wetting the surface and filling the clearance between components by capillary action. Strength is governed not only by filler-metal strength, but especially by surface cleanliness, capillary clearance, overlap, interfacial diffusion, heating method and flux residues. From an IWE perspective, this is a separate joining technology, not “weaker welding”.
The filler metal should melt from contact with the heated component, not solely from the flame. If the wire melts in the flame while the components remain cold or oxidised, the filler beads up and does not flow through the joint.
The filler metal has a liquidus below approximately 450 °C. Typical tin-based solders according to ISO 9453 include SnCu, SnAgCu, SnBi and SnSb; legacy SnPb alloys are subject to legal restrictions. Applications include electrical engineering, sheet-metal enclosures, precision mechanics and low-temperature sealing joints.
The filler metal has a liquidus above approximately 450 °C, while the base material does not melt. Filler metals according to ISO 17672 include silver-, CuP-, copper-, CuZn-, AlSi- and nickel-based alloys. Applications include piping, heat exchangers, tools, stainless steel, copper, brass and carbides.
Usually performed in a furnace, controlled atmosphere or vacuum. Typical applications include stainless-steel and nickel assemblies, turbine parts, honeycomb structures, heat exchangers and precision series components. Advantages include clean joints and repeatable heating of the complete assembly.
The filler metal has a lower melting temperature than the base material and the base material does not melt, but the joint is formed as a bead without a dominant capillary lap. A practical example is MIG brazing of galvanised sheet.
| Filler-metal group | Typical temperature range | Typical materials and applications | Note for the welding engineer |
|---|---|---|---|
| Tin-based soft solders | approximately 140–250 °C depending on alloy | Copper, brass, tinned surfaces, electronics and precision mechanics. | Low temperature resistance; flux residues, cleanliness and Pb/Cd legislation are critical. |
| AlSi aluminium brazing alloys | approximately 570–610 °C | Aluminium heat exchangers, radiators, HVAC and automotive components. | Al₂O₃ is highly stable; special flux, brazing sheet/cladding or a controlled atmosphere is normally used. |
| Silver-based brazing alloys | approximately 600–800 °C | Steels, stainless steel, copper, brass, carbides, and precise or highly loaded joints. | Good fluidity and strength; consider cost, cadmium restrictions and galvanic combinations. |
| Copper-phosphorus CuP / CuAgP | approximately 650–820 °C | Copper and certain copper alloys, piping and HVAC. | May be self-fluxing on clean copper; unsuitable for steels and nickel alloys because brittle phosphides may form. |
| CuZn brass and bronze brazing alloys | approximately 850–950 °C | Steels, cast irons, repairs and braze welding. | Higher temperature and zinc evaporation; ventilation, flux and overheating control are important. |
| Pure copper Cu | approximately 1080 °C | Steels and stainless steels in furnaces, heat exchangers and precision assemblies. | The high temperature may alter base-material properties; a suitable atmosphere reduces oxides. |
| Nickel-based brazing alloys | approximately 950–1200 °C | Stainless steels, nickel alloys, heat-loaded components and vacuum brazing. | High temperature and corrosion resistance; control brittle phases involving B, Si or P and time at temperature. |
Best flow generally occurs with a small, uniform clearance, often in the tenths-of-a-millimetre range. The exact value depends on filler metal, temperature, component size, surface finish and differential thermal expansion. For larger components, the cold clearance may differ from the clearance at brazing temperature.
Good wetting means that the filler spreads over the surface and forms a low contact angle. Poor wetting produces globules. Typical causes are oxides, grease, insufficient component temperature, overheated flux, unsuitable atmosphere or an incompatible filler/base-material combination.
| Joining method | Heat source | Suitable applications | Process risk |
|---|---|---|---|
| Soldering iron / tip | Contact heating by a tip | Electronics, conductors and small tin-soldered joints. | Cold joint, overheating of the component and flux residues. |
| Flame brazing / soldering | Torch, acetylene/oxygen, propane/oxygen or natural gas | Piping, copper and steel components, repairs and erection. | Non-uniform heating, oxidation and overheating of thin parts. |
| Induction brazing | Eddy-current heating by electromagnetic induction | Series ring joints, carbide tools and precision heating. | Incorrect inductor position, local overheating and dissimilar materials. |
| Furnace brazing | Uniform heating of the complete assembly | Heat exchangers, stainless-steel assemblies and high-volume production. | Assembly distortion, diffusion, and sensitivity to cleanliness and fixtures. |
| Vacuum brazing | Vacuum furnace | Stainless steel, nickel alloys and clean flux-free joints. | Evaporation of elements, high cost and the need for exceptional cleanliness. |
| Brazing and soldering in a controlled atmosphere | N₂, H₂, Ar or forming gas according to material | Aluminium heat exchangers, stainless steel and series components. | Incorrect dew point, oxides or inadequate cleaning before the process. |
| Resistance brazing / soldering | Heat generated by electrical resistance | Contacts, local joints and smaller assemblies. | Unstable contact, local overheating and force variability. |
| Dip and wave soldering | Bath of molten solder | Electronics, tin coating and small components. | Bath contamination, bridging and thermal shock. |
| Laser brazing / soldering | Concentrated laser beam | Precision components, galvanised sheet and automotive applications. | Sensitivity to gap, reflectivity and precise beam guidance. |
Flux dissolves or disrupts oxides and protects the surface during heating. It must be active within the correct temperature range. Flux residues may be corrosive and therefore often require removal after processing.
A protective or reducing atmosphere limits oxidation and enables flux-free brazing or soldering. Dew point, gas purity, flow rate, furnace tightness and material compatibility are decisive.
Wire, rod, strip, foil, ring, washer, powder, paste, preform or filler metal clad onto the base material. For series production, a metered preform is usually the most stable option.
| Joint type | Suitability | What to monitor | Typical imperfection |
|---|---|---|---|
| Lap joint | The most typical and suitable configuration for shear loading. | Overlap, uniform clearance, and discharge of flux and gases. | Insufficient overlap or a dry area without filler metal. |
| Tube in socket | Highly suitable for capillary flow and leak-tightness. | Insertion depth, annular clearance and internal cleanliness. | Leakage, pores or flux trapped in the joint. |
| Sleeve / bush joint | Suitable for shafts, bushes and annular joints. | Alignment, thermal expansion during heating and filler-metal quantity. | Non-uniform flow or excessive run-out of filler metal. |
| T-joint and corner joint | Usable when sufficient flow and joint area are provided. | Fillet, root, edge cleanliness and heat access. | Insufficient root filling. |
| Butt joint | Usually unsuitable as a stand-alone load-bearing joint. | Small area, tensile loading and clearance tolerance. | Low strength and sensitivity to misalignment. |
| Material | Suitable filler metals | Main concern | Note |
|---|---|---|---|
| Non-alloy and low-alloy steel | Ag, CuZn, Cu or Ni as required | Oxides, overheating and corrosion caused by flux residues. | For structural components, verify heat effects and required strength. |
| Stainless steel | Ag, Ni or furnace-brazed Cu according to corrosion requirements | Cr₂O₃ passive film and post-process corrosion resistance. | Vacuum or a controlled atmosphere is often suitable. |
| Copper | Sn, Ag, CuP, CuAgP | High thermal conductivity removes heat rapidly. | CuP on copper may not require flux, depending on surface condition and process. |
| Brass / bronze | Sn, Ag or CuP selected carefully according to alloy | Zinc evaporation, dezincification and oxides. | Do not overheat; consider the corrosive environment. |
| Aluminium | AlSi brazing alloys and special soft solders | Stable Al₂O₃ oxide and a narrow processing-temperature window. | Requires a special flux, a clad layer or a controlled atmosphere. |
| Cemented carbides | Silver brazing alloys, sometimes layered preforms | Differential thermal expansion and carbide brittleness. | Often addressed by slow heating/cooling and a ductile interlayer. |
| Titanium and reactive metals | Special Ag-, Ti- or Ni-based, or active brazing alloys | Extremely sensitive to oxides, nitrogen and hydrogen. | Vacuum or a high-purity atmosphere is practically essential. |
For critical components, assess visual condition, continuity of filling, penetration/run-through, porosity, leak-tightness, capillary filling, strength and metallographic sections. For heat exchangers and piping, a leak test is often more important than the appearance of the fillet itself.
| Standard | Application | How to use it in practice |
|---|---|---|
| ISO 4063:2023 | Nomenclature of welding, brazing, soldering and cutting processes. | Process number in documentation, drawings, procedures and qualifications. |
| ISO 857-2:2005 | Terminology for soldering and brazing. | Correct designation of the process, concepts and related terms. |
| ISO 9453:2020 | Soft solders, chemical compositions and product forms. | Selection and designation of tin-based solders. |
| ISO 9454-1:2016 / ISO 9454-2:2020 | Fluxes for soldering. | Classification, designation, packaging and flux performance requirements. |
| ISO 17672:2024 | Filler metals for brazing. | Filler-metal classes by chemical composition, for example Ag, Al, CuP, Cu and Ni. |
| ISO 13585:2021 | Qualification testing of brazers and brazing operators. | Personnel, qualification range, testing and records. |
| ISO 18279:2023 | Imperfections in brazed joints. | Classification of imperfections, quality levels and recommended limits where these are not specified by a product standard. |
1. Define the joint function: strength, leak-tightness, conductivity, corrosion resistance and service temperature. 2. Select a geometry with adequate overlap and capillary clearance. 3. Select a compatible filler metal and either a suitable flux or atmosphere. 4. Design the heating method so that the components are heated while only the filler metal melts. 5. Define cleaning before and after the process. 6. Define inspection: VT, leak testing, macro examination or mechanical testing according to component risk.
Basis for the range of welding-procedure qualification. For special steels, the group and subgroup are decisive, not only the steel designation.
Verify the material group, thickness, diameter, process, position, filler material, heat input, preheat, interpass temperature and PWHT.
For special steels, it is not enough that a person ‘can weld steel’. The qualification range must cover the process, material group, welding position, thickness and weld type.
Pressure equipment, piping, power-generation, LNG or chemical-industry applications may require Charpy testing, hardness, corrosion testing, ferrite measurement, CTOD or a precisely controlled PWHT cycle.
| Steel group | Typical standards framework | What the welding engineer must verify | Typical tests / limits |
|---|---|---|---|
| Fine-grained and high-strength steels | EN ISO 15608 groups for non-alloy and fine-grained steels; product standards in the EN 10025 and EN 10210/10219 series, as applicable to the product. | CEV/CET/PCM, hydrogen-assisted cracking, preheat, interpass temperature, heat-input control, and HAZ softening or hardening. | VT/MT/UT, macro examination, tensile, bend, Charpy and hardness testing as required by the project. |
| Creep-resistant CrMo steels | EN ISO 15608 groups for CrMo steels; commonly product standards EN 10216/10217, EN 10028 or power-generation specifications. | Preheat, low-hydrogen practice, precise interpass control, PWHT, hardness after PWHT and a compatible filler material. | Hardness, NDT, macro examination, tensile/bend testing and, where applicable, creep or long-term-service requirements. |
| Cryogenic steels and 9% Ni steel | EN ISO 15608; product standards for pressure and low-temperature applications, for example EN 10028 according to product type. | Toughness at service temperature, low-hydrogen practice, heat-input control, a suitable nickel-alloyed filler material and avoidance of brittle microstructures. | Charpy testing at low temperature, CTOD where contractually required, NDT, macro examination, tensile and bend testing. |
| Austenitic stainless steels | EN ISO 15608 group 8; filler materials to EN ISO 14343; product standards in the EN 10088 series. | Cleanliness, root shielding, interpass temperature, hot-cracking risk, FN where required, pickling/passivation. | PT, VT, ferrite measurement where specified, corrosion testing according to the environment, and PMI where applicable. |
| Duplex stainless steels | EN ISO 15608 group 10; filler materials to EN ISO 14343; EN 10088 / project specifications. | Heat-input window, low interpass temperature, ferrite/austenite balance, and risk of sigma phase and nitrides. | Microstructure, ferrite, hardness, corrosion testing, PT/VT and, where applicable, Charpy testing. |
| Wear-resistant steels | EN ISO 15608 grouping according to chemical composition and strength; the material manufacturer often specifies mandatory welding parameters. | Preheat and hydrogen control are particularly important, as are HAZ softening, avoidance of excessive heat input and avoidance of unsuitable PWHT. | Hardness, VT/MT, crack inspection and macro examination as specified by the procedure qualification. |
For special steels, clearly state the material standard and designation, material group according to EN ISO 15608, WPS/WPQR, welder-qualification range, required quality level, NDT plan, preheat/interpass requirements, PWHT, hardness and toughness requirements, and any corrosion or microstructural tests.
This module distinguishes two frequently confused groups: steels resistant to oxidation at high temperature and steels intended for long-term loading under creep conditions. For welding, the material standard, EN ISO 15608 group, creep/oxidation behaviour, preheat, PWHT and compatible filler material are decisive.
The priority is chemical resistance of the surface at high temperature: oxidation, scaling, sulfidation and carburisation. Typical grades contain higher chromium, often silicon/aluminium, and nickel in austenitic types.
The priority is strength under long-term loading at elevated temperature: creep, relaxation and precipitate stability. Typical materials include Cr-Mo, Cr-Mo-V and 9–12 % Cr steels, as well as some nickel- or cobalt-base alloys.
| Standard / field | Scope | Typical materials or products | Welding-technology note |
|---|---|---|---|
| EN 10095 | Heat-resistant steels and nickel alloys. | Ferritic and austenitic steels with high Cr/Ni contents for furnaces, burners, heat exchangers and thermal shields. | Check scaling resistance, interpass temperature, hot-cracking susceptibility and surface cleanliness. |
| EN 10302 | Creep-resistant steels, nickel alloys and cobalt alloys. | Materials for high-temperature fasteners, turbines, pressure equipment and power-generation components. | Creep strength, microstructural stability and often precise post-weld heat treatment are important. |
| EN 10028-2 | Flat products of non-alloy and alloy steels for pressure purposes at elevated temperatures. | For example P265GH, 16Mo3, 13CrMo4-5 and 10CrMo9-10. | Typical concerns are preheat, hydrogen, HAZ hardness, PWHT and the effect of the product standard/PED requirements. |
| EN 10216-2 / EN 10217 | Seamless and welded steel tubes for pressure purposes at elevated temperature. | Boiler tubes, steam piping, heat exchangers and piping systems. | For repairs and site welding, verify material group, thickness, PWHT, NDT and the WPQR qualification range. |
| EN 10269 | Steels and nickel alloys for fasteners used at high and/or low temperatures. | Bolts, studs and nuts for pressure and power-generation applications. | For overlay welding or repairs, consider strength class, heat treatment and stress relaxation at elevated temperature. |
| EN ISO 15608 | Grouping of base materials for welding. | CrMo steels are mainly in group 5; high-alloy and stainless steels are in groups 7, 8 or 10 according to type. | This is fundamental to the WPQR and qualification range; a trade name is insufficient. |
| EN ISO 15614-1 | Welding procedure qualification (WPQR). | Procedure test for steels and nickel alloys. | The material group, thickness, process, filler material, heat input, preheat, interpass temperature and PWHT are controlled. |
The basis of heat resistance. It forms a protective Cr₂O₃ layer, improves oxidation resistance and, in CrMo steels, also contributes to creep strength.
Promotes formation of a highly stable Al₂O₃ layer. Excellent for oxidation resistance, but it may impair processability and weldability.
Improves scaling and oxidation resistance, particularly in combination with chromium. At higher contents it may increase brittleness.
Stabilises austenite and improves toughness and resistance in high-temperature corrosive environments.
Increases high-temperature strength and creep resistance. In CrMo steels it is one of the principal alloying elements for power-generation service.
Like molybdenum, it provides solid-solution strengthening and improves creep strength, particularly in modern 9–12 % Cr steels.
They form fine carbides/nitrides that impede dislocation motion and stabilise creep strength.
Nitrogen promotes nitrides and strength in austenitic steels; small additions of boron stabilise grain boundaries and improve creep properties.
| Group | Examples | Principal advantage | Welding risk |
|---|---|---|---|
| Non-alloy / low-alloy pressure steels | P265GH, 16Mo3 | Good processability and use at elevated temperature. | Hydrogen, preheat according to thickness and CEV, and HAZ control. |
| Creep-resistant CrMo steels | 13CrMo4-5, 10CrMo9-10 | Creep strength for steam piping, boilers and power-generation equipment. | Require low-hydrogen practice, preheat, controlled interpass temperature and often PWHT. |
| 9–12 % Cr martensitic steels | P91/P92 types | High creep strength at elevated temperatures. | Highly sensitive to incorrect PWHT, excessive hardness, overheating and local HAZ softening. |
| Ferritic heat-resistant steels | high chromium, often with silicon/aluminium | Oxidation and scaling resistance. | Grain coarsening, brittleness and limited toughness. |
| Austenitic heat-resistant steels | Cr-Ni grades according to EN 10095 | Oxidation resistance, toughness and high-temperature corrosion resistance. | Hot cracking, distortion, and sensitivity to interpass temperature and filler-material selection. |
Preheat, interpass temperature, maximum/minimum heat input, filler-material type, drying of electrodes/fluxes, root shielding, PWHT cycle and permitted scope of repairs.
For CrMo and martensitic creep-resistant steels, it reduces hardness and stress and stabilises the microstructure. Incorrect temperature or holding time may impair creep properties.
Confusing heat resistance with creep resistance. A steel may resist oxidation very well but still lack sufficient creep strength under load.
This module remains focused on technical interpretation: nominal stress, structural stress and local notch stress at the toe, root or an undercut. In a welded structure, the decisive question is whether the geometry forces the load path through an abrupt change of direction or a small effective area.
| Location | Characteristic assessed | Consequence |
|---|---|---|
| Weld toe | transition radius, undercut and weld reinforcement | local stress increase and initiation of a fatigue crack |
| Weld root | incomplete penetration, root notch and joint stiffness | risk of a root crack and hidden crack propagation |
| Weld termination | crater, abrupt termination and stiffness change | stress concentration outside the nominal cross-section |
Stress calculated from the selected load-bearing cross-section. It is used for conventional sizing but does not account for the local weld-toe geometry or imperfections.
Increased stress caused by the geometrical change in the structural detail. It does not yet include the micro-local notch at the weld toe or root.
Maximum local stress at the toe, root, undercut or sharp transition. It is particularly decisive for fatigue.
Enter σx, σy and τxy. The result shows the principal stresses and maximum shear stress.
For a rapid understanding of the influence of weld size a and weld length. The effective throat area is A = a · l.
The interactive diagram explains the individual parts of a weld symbol: arrow, reference line, elementary symbol, dimensions, supplementary information and positioning rules according to EN ISO 2553.
Move the pointer over blue points A–G in the diagram. The panel explains what each part of the symbol means and what the welding engineer should verify.
Preliminary Welding Procedure Specification
Preliminary specification of parameters. It is used to produce the test piece for the welding procedure test.
Welding Procedure Qualification Record
Welding procedure qualification record. It contains the parameters actually used, the qualification range and the test results.
Welding Procedure Specification
Production instruction for the welder. It must be based on a valid WPQR and remain within its range of qualification.
| Document | Typical content | Purpose | Standards basis |
|---|---|---|---|
| pWPS | Process, joint type, material group, thickness, filler material, gas/flux, position, current, voltage, travel speed and heat treatment. | Draft before testing. It is not yet qualified for production welding. | EN ISO 15607, EN ISO 15609-1 |
| WPQR | Actual test-weld parameters, VT/NDT reports, mechanical tests, macro examination, hardness and range of qualification. | Evidence that the procedure has been verified by testing and definition of its range of applicability. | EN ISO 15614-1 or the relevant part of EN ISO 15614 |
| WPS | Clear production parameters for the specific weld: current/voltage ranges, runs, sequence, preheat, interpass temperature, filler material and shielding gas. | Controls production. The welder follows it and inspection verifies conformity. | EN ISO 15609-1, based on the WPQR |
Weld cost is not merely the cost of wire and gas. The largest share is often the time of the operator or robot, component preparation, handling, cleaning, inspection, repairs and downtime. A technically sound weld design is therefore also an economic decision.
Welding itself occupies only part of the shift. In manual welding, handling, cleaning, component changeover, inspection and workplace accessibility are decisive.
Fillet-weld volume increases approximately with the square of the size. Increasing from a5 to a6 does not mean +20 %, but approximately +44 % volume.
MMA, MAG, flux-cored wire, SAW and robotic welding have different deposition rates and operating factors.
A repair includes marking, removal by grinding/gouging, rewelding, repeat inspection and documentation. Prevention is usually less expensive than repair.
| Item | Effect | Typical action |
|---|---|---|
| Oversized weld | More weld metal, longer time and greater distortion. | Size the weld according to joint function and the applicable standard, not habit. |
| Low operating factor | High labour cost per metre of weld. | Improve fixtures, handling, sequence and component availability. |
| Unstable component preparation | Root variability, larger gaps and more repairs. | Tolerances, fixtures and pre-welding inspection. |
| Unsuitable process | Excessively slow welding or disproportionate NDT/repair rate. | Compare processes using actual cycle time, quality and extent of inspection. |
The best saving is not achieved by accelerating a poor weld, but by changing the design, reducing weld volume, stabilising component preparation, reducing repairs and selecting a process with an appropriate deposition rate and quality capability.
| Hazard | Technical significance in welding | Typical measures | Related standards / regulations | |
|---|---|---|---|---|
| Electric current | Electric shock caused by damaged conductors, unsuitable earthing, wet conditions or work in a confined space. | Inspect power sources, cables and holders; use dry PPE; control open-circuit voltage; carry out statutory electrical inspections. | EN IEC 60974-1, EN IEC 60974-10, EN 60204-1, EN 61140 | |
| Optical radiation | UV/IR and visible arc radiation: injury to the cornea, retina and skin, including reflections from surrounding surfaces. | Welding helmet with suitable filter, screens and prohibition of viewing the arc without protection. | EN ISO 16321-1, EN ISO 16321-2, EN ISO 11611, EN 169 | |
| Fumes and aerosols | Metal oxides, ozone, NOx, fluorides, manganese, nickel and Cr(VI); risk depends on the process, material and coating. | Local extraction at source, forced ventilation, exposure measurement and suitable respiratory protection. | EN ISO 15011-1 to EN ISO 15011-4, EN ISO 10882-1, EN ISO 10882-2, EN 12941, EN 14387 | |
| Fire and explosion | Sparks, spatter, heated components, residual flammable substances in vessels, combustible dust and gases. | Fire watch, removal of combustibles, inspection of cavities and vessels, and suitable extinguishing equipment. | EN ISO 11611, EN ISO 11612, EN 13501 and site fire-safety rules | |
| Hot surfaces and spatter | Burns from the weld, slag, spatter, preheating and heat treatment. | Gloves, protective clothing for welding, marking of hot components and handling with tongs. | EN ISO 11611, EN 12477, EN 407, EN ISO 20345 | |
| Gases and gas cylinders | Risk of leakage, asphyxiation by inert gas, flashback, cylinder fall or valve damage. | Secure cylinders; inspect hoses, pressure regulators and flashback arrestors; store gases separately as required. | EN ISO 14114, EN ISO 5175-1, EN ISO 3821, EN 1089-3 | |
| Noise | Plasma cutting, gouging, grinding, straightening and impact work may exceed exposure limits. | Noise measurement, engineering noise reduction, hearing protection and exposure limitation. | EN ISO 9612, EN 458, EN ISO 11690-1 | |
| Robots and mechanisation | Unexpected movement, trapping, maintenance inside a cell, and failure of interlocking or safety logic. | Fencing, door interlocks, safe setting modes, LOTO and validation of safety functions. | EN ISO 10218-1, EN ISO 10218-2, EN ISO 13849-1, EN ISO 12100 |
For occupational safety, hexavalent chromium in respirable fume and dust must be monitored. It must not be confused with alloying chromium contained in the base material.
| Cr source | Processes requiring particular attention | Safer option where technologically permissible |
|---|---|---|
| Austenitic, duplex, ferritic and martensitic stainless steels | MMA/SMAW, FCAW, gouging and plasma cutting; fumes from Cr-Ni materials. | TIG/GTAW or laser welding with low fume generation; solid-wire MIG/MAG instead of covered/flux-cored consumables; local extraction. |
| Ni-Cr alloys and heat-resistant materials | Welding and grinding of Inconel/Hastelloy-type alloys, furnace repairs and hot-section work. | Enclosed or locally extracted workplace; minimise grinding; automate outside the breathing zone. |
| Hardfacings and wear-resistant layers containing chromium carbides | Overlay welding and repairs of crushers, screws, plates and tools. | Alternative hardfacings without high chromium where wear requirements are still met; lower-fume process; extraction directly at the arc. |
| Old paints, pigments, chromate conversion coatings and chromium-plated components | Welding through the coating or thermally damaging it. | Remove the coating by a controlled method before welding; use Cr(VI)-free paints and trivalent Cr(III) passivation instead of Cr(VI) chromates. |
| Category | Typical gases | Risk if confused |
|---|---|---|
| Oxidising | O₂, N₂O and O₂ mixtures | Supports combustion and can react violently with oil or grease. |
| Flammable | H₂, acetylene and propane | Explosion, flashback, incorrect regulator or hose. |
| Inert / asphyxiating | Ar, He, N₂, CO₂ | Displacement of oxygen in a space, causing odourless asphyxiation. |
| Toxic / corrosive | NH₃, Cl₂, CO and HCl | Acute toxicity or chemical burns; separate storage and special procedures. |
| Gas / mixture | Older identification | Newer shoulder identification | Note |
|---|---|---|---|
| Oxygen | blue | white | oxidising gas; the label is decisive |
| Hydrogen | red | red | flammable gas |
| Acetylene | white | maroon | separate rules apply to acetylene cylinders |
| Argon | brown | dark green | inert shielding gas |
| Nitrogen | green | black | asphyxiating inert gas |
| Carbon dioxide | black | grey | asphyxiating gas and active gas for MAG welding |
| Compressed air | silver / grey | bright green | not a shielding gas for welding |
| Forming gas | red | red / grey depending on mixture | often N₂/H₂; hydrogen increases flammability |
A surface layer is not designed solely according to hardness. It must address the actual damage mechanism: wear resistance, friction reduction, corrosion resistance, a diffusion barrier, a thermal barrier or a combination of these requirements.
| Group | Typical purpose |
|---|---|
| Clad layers | Corrosion-resistant or heat-resistant layer on load-bearing plate. |
| Linings | Protection of a structure against corrosion, heat or wear. |
| Overlay welds | Restoration or creation of a functional layer against wear, corrosion or heat. |
| Metallic coatings | Barrier, cathodic protection, and improvement of appearance or function. |
| Paints and enamels | Atmospheric and chemical protection, sometimes with a weldability requirement. |
Non-diffusion: paints, enamels and linings. Diffusion: carburising, nitriding, carbonitriding and aluminising. Fusion-applied: overlay welding and cladding. Thermophysical: PVD. Thermochemical: CVD.
For welded structures, also assess the layer’s behaviour under heat: porosity, weld-metal contamination, HAZ alteration, distortion and formation of brittle interphases.
Fracture mechanics determines whether an existing imperfection remains stable or develops into rapid fracture. In welded structures, the root, weld toe, HAZ, residual tensile stresses and geometrical notch are critical.
σ = E · εK ≈ Yσ√πaK ≥ KICThe model below is educational: it indicates the direction of risk but is not a substitute for calculation according to the applicable standard or assessment by an authorised competent person.
At the entered values, the crack is below the critical fracture toughness. Pay particular attention to fatigue and the weld-to-base-material transition quality.
Notch + residual tensile stress + cyclic loading. A typical fatigue-crack initiation site.
A risk with incomplete penetration, hydrogen, severe restraint and a hard HAZ.
Associated with segregation, shrinkage, unsuitable filler material or hot cracking.
Often associated with high tensile stress, low toughness of weld metal or HAZ.
| Parameter | Practical meaning | How to improve it in welds |
|---|---|---|
| KIC / CTOD / Charpy | The ability of a material to resist crack propagation at a given temperature. | Suitable material, fine-grained steel, correct heat input, preheat and PWHT as required. |
| Crack size a | Even a small imperfection may be critical if it is sharp, tensile-loaded and at low temperature. | NDT, repair of unacceptable indications, a fully penetrated root and undercut control. |
| Geometrical factor Y | A notch, sharp transition and imperfection location increase local stress. | Smooth transition, weld-toe grinding, correct radius and avoidance of abrupt stiffness changes. |
| Temperature | As temperature falls, toughness decreases and the risk of brittle fracture increases. | Material with guaranteed impact energy at service temperature; WPS qualification for the relevant range. |
The power-source characteristic describes how welding current changes when arc voltage changes. In manual arc processes it determines whether the arc remains stable or begins to fluctuate, spatter and reignite poorly.
Isothermal transformation of austenite at constant temperature. The original interactive module remains available.
Continuous-cooling transformation. The original interactive module remains available.
Relationship between cooling rate, the welding thermal cycle and microstructures in the HAZ.
Tensile testing, impact toughness, hardness and fundamental mechanical properties.
Macro examination, fracture, bend and weld tensile tests, and other tests used to assess joints.
The arc has negative dynamic behaviour and changes with length, temperature, ionisation, metal transfer, short circuits, wire feed, polarity and resistance of the entire secondary circuit. IWE/IWT personnel must therefore understand not only the current value, but also how the source generates, rectifies, smooths, measures and regulates current.
This module breaks the source down as a technical system: input stage, transformation, rectification, power switches, DC link, secondary rectifier, inductor, current measurement, feedback, protections and their manifestation in current/voltage graphs.
The objective is not to repair the source at service-technician level. It is to distinguish whether a quality problem originates in the WPS, torch, return connection, wire feeding, source dynamics, inductance/pulse settings or an unsuitable source type for the process.
Static characteristic describes how voltage and current change during slow shifts of the operating point. Dynamic characteristic describes how quickly the source responds during ignition, droplet formation, short circuit, droplet detachment or pulsed welding.
The same average current may be produced by smooth DC, heavily rippled rectified current, a pulsed waveform or severe short-circuit dynamics. The weld pool, spatter, penetration, arc sound and contact-tip loading will differ.
Select the source type. The diagram shows a typical energy path from the mains supply to the arc and explains what occurs in each block.
| Block / component | Electrical function | Effect on the welding process | Typical failure symptoms |
|---|---|---|---|
| Mains input, fuses and contactor | Supplies energy and disconnects the source in the event of a fault or shutdown. | Input-supply stability affects the power reserve of the source. | circuit-breaker trips, random resets and power loss with long supply cables |
| EMI/RFI filter | Suppresses interference travelling both to the mains and from the mains into the source. | Reduces electromagnetic interference, which is important for robotics, sensors and communications. | interference with PLCs, encoders or cameras, unstable sensors and HF-ignition problems |
| Input rectifier | Converts mains AC into pulsating DC. A three-phase source typically uses a B6 bridge. | Determines DC-link ripple and mains loading; three-phase rectification is smoother than single-phase. | overheating diodes, uneven output, excessive ripple and blown fuses |
| DC link — capacitors C | Stores energy and smooths voltage for the power switches. | Helps the source respond to short current peaks without voltage collapse. | increased ripple, humming, weak ignition performance and swollen capacitors |
| IGBT/MOSFET converter | Rapidly switches DC into high-frequency AC controlled by PWM. | Enables precise pulses, fast regulation and a small transformer. It governs arc dynamics. | hard arc, interruptions and overcurrent/overtemperature alarms |
| Transformer | Changes the voltage level and galvanically isolates the mains from the output. | A conventional source uses a heavy 50 Hz transformer; an inverter uses a small high-frequency transformer. | overheating, hum, voltage drop and damaged insulation |
| Secondary rectifier | Rectifies secondary AC to the DC output used for MMA/TIG/MIG/MAG. | Diodes provide uncontrolled DC, thyristors enable phase control, and fast diodes are required in inverters. | asymmetric arc, high ripple and overheating heat sinks |
| Inductor L | Stores energy in a magnetic field and opposes rapid current change. | Reduces short-circuit spatter, smooths current and changes the ‘softness/hardness’ of the arc. | without damping, explosive short circuits; with excessive damping, a sluggish arc and poor droplet detachment |
| Output capacitors / RC snubbers | Filter high-frequency peaks and protect switches and diodes. | Less electrical noise, steadier measurement and smaller overvoltage peaks. | interference, overvoltage faults and unstable starting |
| Shunt or Hall-effect sensor | Measures actual output current for feedback. | Without accurate measurement, the controller cannot maintain the required current or pulse waveform. | incorrect amperage on the display, unstable pulse and deviation from the WPS |
| Control board | Compares the setting with feedback and controls PWM/thyristors, starting, pulse functions and protections. | Defines hot start, arc force, crater fill, burn-back, pulse and synergic programs. | random parameter changes, fault messages and inability to ignite consistently |
| Wire feeder, motor and encoder | Feeds the electrode at a constant or controlled speed. | In MIG/MAG, current is strongly linked to wire-feed speed. Feed fluctuation causes current and arc fluctuation. | wire stubbing, contact-tip burn-back, fluctuating current and wire sticking |
| Torch, contact tip and work clamp | Conduct current to the process and close the secondary circuit. | Contact at the tip and work clamp directly changes voltage drop, heating and arc stability. | hot contact tip, local arcing, irregular arc and a false ‘power-source’ problem |
| Cooling and temperature sensors | Remove losses from semiconductors, transformer, inductor and torch. | When the temperature limit is exceeded, the source reduces output or shuts down. Duty cycle is not merely an administrative value. | thermal fault, output reduction after a period of operation, and burnt contact tips or cables |
The rectifier converts alternating voltage into pulsating direct voltage. The number of phases and control method determine ripple. The graph shows how pulsation changes: a single-phase bridge has deep troughs, a three-phase B6 bridge has lower ripple, a thyristor delays conduction and an inverter produces controlled high-frequency pulses.
| Circuit configuration | What the circuit contains | What the waveform shows |
|---|---|---|
| single-phase bridge | four diodes, full-wave rectification | 100 Hz pulsation on a 50 Hz supply, with deeper troughs between peaks |
| 3f B6 | six diodes or six thyristors | 300 Hz ripple on a 50 Hz supply, with lower ripple amplitude |
| Thyristor | controlled firing angle α | lower average voltage, steeper edges, poorer power factor and greater interference |
| Inverter | rectification + DC link + IGBT PWM | high-frequency pulses and fast current/voltage regulation |
The inductor is a series inductance in the output. Its fundamental relationship is uL = L · di/dt The higher L is, the more slowly current changes. In short-circuit MIG/MAG transfer, it controls the current-rise rate during the short circuit and the energy released when the droplet detaches.
value: 0,80 mH value: 22 VThe operating point is the intersection of the power-source characteristic and the arc characteristic. With a CC source, a change in arc length produces a large voltage change but a smaller current change. With a CV source, a change in arc length produces a significant current change, creating self-regulation in MIG/MAG.
| Process | Typical characteristic | Electrically critical settings | What IWE/IWT personnel monitor in production |
|---|---|---|---|
| MMA / 111 | CC, often with hot-start and arc-force functions. | current, polarity, open-circuit voltage and arc-force dynamics. | electrode sticking, porosity caused by a poor arc, excessive spatter and insufficient penetration. |
| TIG / 141 | CC; DC− for steels, AC for Al/Mg because of the oxide layer. | HF/lift start, slope up/down, pulse, AC balance/frequency. | tungsten-tip stability, aluminium cleaning, contamination and weld-pool width. |
| MIG/MAG / 131/135 | CV or controlled pulsed mode; current results from wire-feed speed. | voltage, wire-feed speed, inductance/dynamics, burn-back and synergic program. | spatter, short-circuit regularity, bead shape and current transfer through the contact tip. |
| FCAW / 136/138 | CV; according to wire and polarity. | polarity, dynamics, electrode extension and arc voltage. | slag, penetration, undercut, spatter and sensitivity to stick-out. |
| SAW / 121 | CV or CC according to the system, high currents and often multiple wires. | current, voltage, polarity, AC/DC combinations and phase shifts. | penetration, dilution, bead shape, heat input and residual stress. |
| Resistance welding | low voltage, extremely high current and time-controlled pulses. | current, time, electrode force, contact resistance and cooling. | nugget diameter, expulsion, electrode wear and variability of transition resistance. |
A WPS should contain more than ‘A/V’. For critical applications, also specify polarity, metal-transfer mode, pulse program, dynamics/inductance, stick-out range, work-clamp location, parameter-measurement method and permissible heat-input range.
For equipment, the typical standards framework is the EN IEC 60974series covering welding power sources, EMC, torches, wire feeders, cooling units, electrode holders and return clamps. In production, equipment, cables and accessories must be suitable for the process, current and duty cycle.
The welding arc is a low-voltage, high-current electrical discharge in an ionised gas. For the welding engineer, it matters not as an isolated physical phenomenon but as the link between the power source, electrode, shielding medium, metal transfer, shape of the weld pool a joint quality.
The same set current can produce a completely different result if arc length, polarity, source dynamics, electrode extension, shielding gas or the magnetic field around the weld changes. The arc must therefore be assessed as a system: power source – torch – electrode – gas/flux – base material – joint geometry – movement.
The model is indicative. It demonstrates trends: arc length increases voltage, gas changes conductivity and heat concentration, and polarity changes the energy loading of the electrode and workpiece.
For engineering purposes, total arc voltage can be divided into cathode drop, anode drop and plasma-column voltage.
Uarc ≈ Uc + Ua + Eplasma · LarcChanging arc length changes more than the voltage value. It also changes heat-flow distribution, footprint width, weld-pool stability, spatter and sensitivity to arc blow.
The cathode supplies electron emission. The anode receives electrons and converts impact energy into heat. Polarity therefore affects electrode heating, melting rate, oxide cleaning and penetration.
In MIG/MAG, a CV source works with the self-regulating effect of wire extension: shortening the arc lowers voltage, increases current and accelerates wire melting. In TIG/MMA, a CC characteristic is more important so that an arc-length change does not cause an excessive current change.
| Mechanism | What changes in the arc | Consequence in the welded joint | Typical technical response |
|---|---|---|---|
| Arc length | Higher voltage, greater plasma volume and lower heat concentration. | Wider bead, more spatter, poorer root control and greater sensitivity to porosity. | Adjust voltage, CTWD/electrode extension, travel speed and, where appropriate, source dynamics. |
| Current density | Plasma constriction, higher electromagnetic pressure and pinch effect. | Greater penetration and melting rate, with risk of undercut or burn-through. | Check electrode/wire diameter, pulse, position and speed. |
| Shielding gas | Different ionisation, thermal conductivity, and molecular dissociation/recombination. | Changes to penetration profile, stability, spatter, oxidation and porosity. | Select Ar/He/CO₂/mixtures according to material, process and required weld profile. |
| Polarity | Change in the location of cathodic emission and anode heating. | Changes electrode melting, cleaning action, penetration and electrode life. | Verify compatibility with the process, electrode, material and WPS qualification. |
| Magnetic field | Lorentz force deflects the plasma column away from the axis. | Unstable root, irregular bead, side-wall deposition and local lack of penetration. | Change the return connection, direction of travel or sequence; use AC/pulse; shorten the arc; demagnetise the component. |
The arc has its own volt-ampere characteristic and the source has an output characteristic. Their intersection determines the actual current and voltage. In manual processes, a change in arc length must not immediately become a large current jump; in MIG/MAG, self-regulation at constant voltage is deliberately used.
operating point = intersection of source and arc U-I characteristicsIn short-circuit transfer, the current-rise rate, droplet detachment and reionisation of the gap are decisive. A source that is too hard creates spatter; one that is too soft causes wire sticking or root instability.
A ‘stiff’ arc holds its axis better, has greater energy concentration and directs pressure into the pool more effectively. Excessive arc pressure may, however, displace metal and cause undercut, root sagging or an unstable keyhole.
| Process | Dominant control issue | What to monitor in the WPS / production |
|---|---|---|
| TIG/WIG | Stability of the cathode spot on tungsten, arc length, DCEN/DCEP/AC thermal balance and electrode contamination. | Tungsten type and diameter, polarity, gas, current, pulse, arc length, root shielding and edge cleanliness. |
| MIG/MAG | Relationship between arc, wire feeding, CTWD and metal transfer. Voltage indirectly represents arc length. | WFS/current, voltage, CTWD, gas, inductance/dynamics, pulse parameters, spatter and bead shape. |
| MMA | Manually varying arc length, covering composition, slag stability, hot start and arc force. | Covering type, polarity, current range, electrode drying, manipulation technique and interpass temperature. |
| SAW | The arc burns in a cavity beneath the flux; visual monitoring of the arc is limited. | Current, voltage, travel speed, stick-out, flux composition, flux-bed height and penetration profile. |
For welding coordination, stating only ‘current and voltage’ is insufficient. The arc is the result of an entire set of essential and supplementary variables. During procedure qualification, assess whether a parameter change alters the thermal cycle, melting rate, chemical interaction of the pool or metal-transfer mechanism.
| Variable | Why it is critical | Review question for IWE/IWT personnel |
|---|---|---|
| Current / WFS | Determines melting rate and current density; with wire electrodes, current is a consequence of wire feeding and CTWD. | Does the actual current match the qualified range, or has electrode extension changed? |
| Voltage | A technological indicator of arc length and stability, not merely an electrical quantity. | Is voltage assessed together with arc length, transfer mode and welding position? |
| Welding speed | Changes heat input, bead dimensions and the time the HAZ remains in critical temperature ranges. | Is heat input still within the WPQR range and compatible with the metallurgical limits of the material? |
| Polarity and power source | Alter energy balance, stability, melting rate and, with AC, cleaning action. | Has a source/polarity change been concealed as an ‘equivalent setting’? |
| Gas / flux | Changes ionisation, thermal conductivity, oxidation/reduction and metallurgical activity of the arc. | Is the changed gas mixture genuinely permitted for the material, transfer mode and qualification? |
The flame melts the component edges and filler rod. The heat source is less concentrated than an electric arc, producing a wider HAZ and greater distortion risk.
Variable oxygen/fuel-gas ratio. The diagram shows the inner cone, reducing zone, oxidising outer envelope, approximate maximum temperature and risks to the weld.
For repairs, erection, smaller thicknesses, local heating, simple piping and where equipment mobility matters.
A flame has a lower energy concentration than an arc. Incorrect manipulation readily increases HAZ width, distortion and surface oxidation.
Oxygen and fuel gases require correct hoses, non-return valves, flashback arrestors, clean pressure regulators, and no oil or grease on oxygen-service components.
TIG/WIG is arc welding with a non-consumable tungsten electrode in an inert gas. Heat is generated by a precise electric arc between electrode and workpiece; filler material may be added separately as a rod or the joint may be welded autogenously.
| Mode | Application | Effect on the process |
|---|---|---|
| DCEN / DC− | steels, stainless steel, copper, titanium and most alloys except Al/Mg | most heat enters the workpiece, the electrode overheats less, and the arc is deep and stable. |
| DCEP / DC+ | special oxide cleaning at very limited current | more heat enters the tungsten and the electrode is heavily loaded; rarely used. |
| AC | aluminium and magnesium | the penetration phase and oxide-cleaning action alternate; AC balance affects cleaning and electrode life. |
MIG/MAG is arc welding with a consumable electrode in the form of continuously fed wire in a shielding gas. The arc burns between the wire end and the base material; the wire melts simultaneously and provides filler metal.
MIG uses an inert gas, mainly Ar or He. MAG uses an active gas or mixture, typically Ar/CO₂, Ar/O₂ or CO₂.
The calculator is for training. Values demonstrate relationships between current, voltage, speed, stick-out and weld shape; final settings must be based on the WPS, weld testing and the specific equipment.
This is a training model. It changes metal-transfer mode according to current, voltage, gas, wire and stick-out. It is not the precise synergic curve of a particular power source.
The wire periodically contacts the weld pool; the droplet detaches during the short circuit and the arc reignites.
Large droplets, often larger than the wire diameter, pass irregularly through the arc; spatter is usually higher.
Many small droplets pass through the arc without short circuiting; typical at higher current with an argon-rich gas.
Controlled pulsed mode: ideally one droplet per current pulse at a lower average heat input.
A transition phenomenon at very high currents with argon-rich gas; droplets may follow a rotating or spiral path due to electromagnetic forces.
With solid wire, weld metal is determined mainly by the wire, gas and base material. With tubular cored wire, the process also includes the core filling: fluxing agents, arc stabilisers, deoxidisers, alloying elements, metal powder and substances that form slag or a shielding atmosphere. This changes current density, deposition rate, penetration profile, weld-pool viscosity, hydrogen regime, fume generation and inter-run cleaning.
| Number | Process | Technological significance |
|---|---|---|
| 114 | Self-shielded welding with tubular cored wire | Shielding gas is not supplied externally. Protection is generated by decomposition of the core. Typical applications are site work, outdoors, piping, repairs and heavy structures. |
| 132 | MIG with flux-cored wire | Inert gas. Less common for steels than MAG 136, but included in the standard. |
| 136 | MAG with flux-cored wire | The most typical European ‘FCAW-G’ for steels. Active gas M21 or C1, slag, high output and good positional capability. |
| 138 | MAG with metal-cored wire | Metal-powder core, minimal slag and a good option for long runs, automation, robotics and reduced inter-run grinding. |
| Standard | Filler-material application | What the classification typically contains | Note for IWE/IWT personnel |
|---|---|---|---|
| EN ISO 17632 | Non-alloy and fine-grained steels | strength class, toughness, chemical alloying, core/usability type, shielding gas, positions and diffusible hydrogen | The principal standard for most structural FCAW wires used in typical S355/S460-strength applications. |
| EN ISO 18276 | High-strength steels | higher weld-metal strength, impact energy, gas, positions, hydrogen and chemical composition | For high-strength steels, hydrogen, preheat, interpass temperature and HAZ softening/hardening are decisive. |
| EN ISO 17633 | Stainless and heat-resistant steels | weld-metal chemical composition, core type, gas, position and mechanical properties | Do not consider strength alone. Monitor Cr/Ni equivalent, ferrite, mixing, corrosion resistance and post-treatment. |
| EN ISO 17634 | Heat-resistant and creep-resistant steels | chemical composition and properties after heat treatment | Typically CrMo steels and pressure/power equipment. Without controlled preheat/PWHT, the wire classification has limited value. |
| EN ISO 544 | Delivery conditions for welding consumables | product type, dimensions, tolerances, marking and delivery requirements | Important for incoming inspection, storage, batch identification and auditability. |
| Typ | Behaviour | When to select it |
|---|---|---|
| R / P rutile | Easy handling, attractive bead and good slag detachability. Type P has fast-freezing slag and is more suitable for positional welding. | Structures, ships, bridges and PB/PF work where productivity and stable geometry are required. |
| B basic | Lower-hydrogen regime and higher toughness, but more demanding arc manipulation and more sensitive parameters. | Thick, high-strength, dynamically loaded and low-temperature applications. |
| M metal-cored | Metal-powder core, little slag, high deposition rate, good filling and less cleaning. | Robotics, mechanisation, long weld lengths, PA/PB/PC and series production. |
| Self-shielded | Shielding is generated by the core. More fume and slag, often specific polarity and longer CTWD. | Outdoor and site repairs where gas shielding of the pool is impractical. |
| Wire | Current | Voltage | CTWD | Gas | Note |
|---|---|---|---|---|---|
| 1,2 mm flux-cored 136 | 160–280 A | 23–32 V | 15–25 mm | M21 or C1 | Versatile diameter for structures and positional work according to P/R type. |
| 1,4–1,6 mm flux-cored 136 | 220–380 A | 26–36 V | 18–30 mm | M21 or C1 | Higher productivity, thicker components and PA/PB/PC; positions according to the data sheet. |
| 1,2 mm metal-cored 138 | 180–320 A | 24–34 V | 15–25 mm | M21 | Very suitable for robotics and long runs; minimal slag. |
| 1,6 mm self-shielded 114 | 140–280 A | 18–27 V | 20–40 mm | without gas | Exact polarity and stick-out according to the manufacturer. Do not generalise. |
| Imperfection | Typical FCAW cause | Correction |
|---|---|---|
| Slag inclusions | incorrect angle, excessively narrow bevel, slag overtaking the pool, or inadequate inter-run cleaning | change the travel angle, improve access, reduce speed, clean every run and adjust run sequence |
| Porosity / wormholes | draught, inadequate shielding gas, moisture, surface contamination, an excessively long arc or unsuitable CTWD | check gas, nozzle, flow rate and leaks; clean the material and verify wire storage |
| Lack of fusion | low heat input, excessive speed, incorrect layering or an excessively large single run | adjust I/V, change technique, divide fill layers and verify preparation geometry |
| Undercut | high voltage, high speed, incorrect angle and an overheated pool edge | reduce voltage or speed, maintain a shorter arc and adjust weaving/dwell at the edges |
| Excessive convexity | low voltage, cold pool, too much metal in one run or excessively low travel speed | increase voltage within the WPS, increase speed, divide layers and adjust torch angle |
| Hydrogen-assisted cracking | moisture, unsuitable wire, absent preheat, high HAZ hardness or excessively low interpass temperature | low-hydrogen consumable, H5/H10 control, preheat, interpass control, drying/storage and delayed NDT |
| Process | Advantage | Limitation | Typical selection |
|---|---|---|---|
| 135 MAG with solid wire | lower-cost wire, minimal slag and straightforward robotics | lower deposition rate and poorer pool support in position | series production, thinner components, robotics and short cycles |
| 136 MAG flux-cored | higher deposition rate, better positional capability and improved bead profile | slag, fumes, cleaning and higher wire cost | heavy structures, shipbuilding, bridges, thick components and PF/PB |
| 138 MAG metal-cored | high productivity, little slag and suitable for robotics | less slag support in position and sensitivity to gas and parameters | long fillet welds, automation, PA/PB/PC and a higher-output alternative to process 135 |
The welding arc burns between a covered electrode and the base material. The metallic core melts and provides filler material; the covering produces gas shielding, slag and, depending on type, metallurgical alloying of the weld metal. Slag is removed mechanically after welding.
The most common selection for basic electrodes and structural welding. The arc is stable, penetration is good and hydrogen control is improved when electrodes are correctly redried.
Used for some rutile, cellulosic or special electrodes according to the manufacturer. It generally gives shallower penetration and more heat in the electrode.
Suitable only for electrodes marked for AC use. Basic electrodes require sufficient source open-circuit voltage and correct drying.
Always verify polarity for the electrode covering. The same covering type may have a different permissible polarity or current range depending on the manufacturer.
| Electrode type | Typical designation / covering | Polarity | Current by diameter | Suitable materials and applications | Note for the welding engineer |
|---|---|---|---|---|---|
| Rutile | E 42 0 RR / R · EN ISO 2560-A: E 42… RR/R | ACDC−DC+ | Ø2,5: 60–90 A Ø3,2: 90–130 A Ø4,0: 130–180 A | Non-alloy and low-alloy steels, ordinary workshop and site welds, short runs and easy ignition. | Good handling and attractive surface, but not the first choice for high toughness and thick dynamically loaded structures. |
| Basic low-hydrogen | E 42/46/50 B · for example AWS E7018 | DC+AC according to type | Ø2,5: 70–100 A Ø3,2: 100–140 A Ø4,0: 140–190 A | Load-bearing structures, pressure parts, fine-grained steels and welds requiring toughness and low diffusible hydrogen. | Storage and redrying according to manufacturer instructions are essential. Use a short arc. The covering is moisture-sensitive. |
| Cellulosic | C · for example E6010 / E6011 | DC+AC for E6011 | Ø2,5: 60–90 A Ø3,2: 80–130 A Ø4,0: 120–180 A | Pipelines, root runs and downhill welding where a forceful arc and good penetration are required. | Higher hydrogen and a specific technique. It is not a suitable substitute for a basic electrode in ordinary load-bearing structures without assessment. |
| Acid / oxidising | A / O types, now less common | ACDC− | Ø2,5: 60–90 A Ø3,2: 90–130 A Ø4,0: 130–180 A | Non-alloy steels with lower requirements, fill welds and good slag fluidity. | Limited use under modern qualification requirements. Verify availability and standard designation. |
| Austenitic stainless-steel | E 19 9 / E 19 12 3 · AWS E308L, E316L | DC+AC according to type | Ø2,5: 50–80 A Ø3,2: 75–110 A Ø4,0: 100–150 A | 304/304L and 316/316L stainless steels, food industry, chemical industry and corrosive service. | Match the consumable to the base material, control low carbon grade, dilution risk, and pickling/passivation requirements. |
| Stainless electrode for dissimilar joints | E 23 12 L / E 309L | DC+AC according to type | Ø2,5: 55–85 A Ø3,2: 80–120 A Ø4,0: 110–160 A | Stainless-to-carbon-steel joints, buttering, repairs and transitions between dissimilar materials. | Used as a buffer; monitor weld-metal dilution and required ferrite content. |
| Creep-resistant CrMo | E CrMo1 / E CrMo2 · 13CrMo4-5, 10CrMo9-10 | DC+ | Ø2,5: 70–100 A Ø3,2: 100–140 A Ø4,0: 140–190 A | District-heating piping, pressure equipment and low-alloy creep-resistant steels. | Requires preheat, interpass-temperature control and often PWHT according to the material and specification. |
| Hardfacing | Fe-Cr-C, Mn and carbide overlays | DC+AC according to type | Ø3,2: 90–130 A Ø4,0: 130–180 A Ø5,0: 180–240 A | Abrasive, impact or combined wear: buckets, crushers, guide surfaces and tools. | Not intended for joining welds. Monitor number of layers, overlay cracks, substrate and any transition layer. |
| Nickel electrode for cast iron | Ni / NiFe electrodes | DC+AC according to type | Ø2,5: 50–80 A Ø3,2: 70–110 A Ø4,0: 90–140 A | Repairs of grey and ductile cast iron, using cold or hot welding according to component size and requirements. | Short runs, peening and slow cooling. The objective is to minimise stress and hard white iron in the HAZ. |
| Aluminium | AlSi5, AlSi12 electrodes | DC+ | Ø2,5: 60–90 A Ø3,2: 90–130 A Ø4,0: 120–170 A | Repairs of aluminium alloys and castings, and less critical joints where TIG/MIG is unavailable. | Requires an exceptionally clean surface, oxide removal and rapid work. TIG AC or MIG is preferable for high-quality aluminium joints. |
| Base material | Typical selection | Mode |
|---|---|---|
| S235–S355 non-alloy steels | Rutile for simple work, basic for load-bearing welds | AC/DC for rutile, DC+ for basic |
| Fine-grained and higher-strength steels | Basic low-hydrogen electrode with the required strength and toughness | DC+, rigorous drying |
| Stainless steel 304/316 | E308L / E316L according to chemical composition | DC+, low heat input |
| Stainless steel + carbon steel | E309L or suitable transition layer | DC+, dilution control |
| CrMo steels | CrMo electrode matching the base material | DC+, preheat and PWHT according to specification |
| Cast iron | Ni or NiFe electrode | Short runs and controlled cooling |
Increases diffusible hydrogen and the risk of cold cracking, especially in thick and high-strength steels.
Spatter, porosity and a wide unstable bead. Keep a very short arc with basic electrodes.
May cause poor penetration, electrode overheating, an unstable arc or poor slag detachability.
Low current = sticking and lack of fusion. High current = undercut, spatter, burn-through and reduced toughness.
In submerged-arc welding, the arc burns in a closed cavity beneath granular flux. The arc is not visible externally, so process quality is controlled not by the welder’s eyes but by current/voltage stability, flux height, stick-out, travel speed, wire position, edge-preparation geometry, wire–flux chemical interaction and subsequent macro/NDT verification. For IWE/IWT personnel, it is critical to understand that weld-metal properties are determined not by the wire alone but by the specific combination of electrode + flux + parameter + thermal cycle.
| Process | Standard process name | Technical meaning | Note for WPS/WPQR |
|---|---|---|---|
| 121 | SAW with solid wire electrode | The most common variant for long butt and fillet welds. Single-wire, tandem or multiple heads are specified in the procedure. | Stating only ‘SAW’ is insufficient. Specify wire diameter, flux, polarity, current, voltage, speed, stick-out and layering. |
| 122 | SAW with strip electrode | Typically used for overlaying large areas, cladding, corrosion-resistant layers or hardfacing. | Dilution, strip width, number of layers and overlay chemical composition are critical. |
| 124 | SAW with added metal powder | Increases deposition rate or changes weld-metal chemical composition. | The powder is part of the WPS. Without its specification, final composition and properties cannot be guaranteed. |
| 125 | SAW with tubular cored electrode | Tubular wire for higher output or more precise control of chemical composition. | The tubular-wire + flux combination must be qualified as a system. |
| 126 | SAW with flux-cored strip electrode | Special overlays, alloyed layers, wide beads and controlled overlay composition. | For overlays, monitor dilution by the base material, transition layers and required chemical analysis. |
SAW can produce an attractive bead and still contain a poor internal weld. The covered arc may conceal wire misalignment, unsuitable root preparation, excessive heat input, centreline cracking or side-wall lack of fusion.
Wire supplies most of the weld metal and its chemical composition is the basis of the final properties. For non-alloy and fine-grained steels, types such as S1, S2, S2Si and S2Mo are used according to required strength, toughness and service temperature. High-strength steels, CrMo steels, stainless steels and overlays are selected according to other material standards.
Flux is not merely ‘sand covering the arc’. It stabilises the arc, forms slag, affects bead shape, desulfurisation/deoxidation, hydrogen, weld-metal oxygen and Mn/Si transfer, and therefore toughness. The same wire with a different flux can produce different mechanical properties.
| Application | Standard / rationale | What the welding engineer must know |
|---|---|---|
| Non-alloy and fine-grained steels | EN ISO 14171 | Classifies solid wires, tubular electrodes and electrode–flux combinations for SAW. One wire may receive a different classification with different fluxes. |
| Fluxes | EN ISO 14174 | Classification of fluxes for SAW and electroslag welding/overlaying. Covers flux type, metallurgical behaviour, suitable current, hydrogen and application. |
| High-strength steels | EN ISO 26304 | For steels above approximately 500 MPa yield strength or 570 MPa tensile strength. Strength, toughness, PWHT condition, hydrogen and compatibility with the flux are decisive. |
| Creep-resistant steels | EN ISO 24598 | For low-alloy steels operating at elevated temperature. Chemical analysis, PWHT, diffusible hydrogen and long-term properties are critical. |
| Stainless and heat-resistant steels | EN ISO 14343 + EN ISO 14174 | Wire or strip according to chemical type, with flux classified separately. For overlays, monitor dilution, ferrite number, corrosion resistance and inter-run cleaning. |
| Supply condition | EN ISO 544 | Dimensions, tolerances, marking and technical delivery conditions for consumables and fluxes. |
Raw materials are melted, crushed and sieved. They offer good homogeneity and lower hygroscopicity, but more limited alloying capability. They are often stable for high-volume applications.
A powder mixture is bonded and baked. It enables basic and alloying systems and better adjustment of metallurgy and toughness, but requires more careful storage and drying.
An active flux may change Mn/Si and properties significantly when voltage, layering or dilution changes. A more neutral flux is preferable where stable chemical composition is required in multi-run welding.
| Parameter | When it increases | Typical effect | Hazard |
|---|---|---|---|
| Current | higher deposition rate and deeper penetration | greater penetration, higher output and more heat into the root | burn-through, excessive dilution, coarse-grained HAZ and distortion |
| Voltage | longer arc and wider bead | greater width, smoother transition and changed flux consumption | undercut, unstable slag and changed Mn/Si transfer with active flux |
| Welding speed | lower heat input per millimetre | narrower bead and less volume per unit length | side-wall lack of fusion, humping and poor degassing |
| Stick-out | greater resistive preheating of the wire | higher deposition rate at the same current | unstable arc, current change and poor penetration profile |
| Flux height | stronger insulation and a larger flux reserve | better arc shielding within the correct range | gas imperfections with damp flux, poor visibility of the track and excessive consumption |
| Wire position in the bevel | offset from the joint centreline | asymmetric melting of the side walls | lack of fusion on one wall, overlap and an asymmetric bead |
| Variant | Current | Voltage | Note |
|---|---|---|---|
| 2.0–2.4 mm wire | approx. 250–550 A | 24–34 V | smaller thicknesses and root or fill runs according to the fixture |
| 3.2 mm wire | approx. 400–800 A | 28–38 V | typical multi-run structural welds |
| 4.0 mm wire | approx. 550–1000 A | 30–42 V | high output, thick components and stable position |
| 5.0 mm and above | approx. 750–1200+ A | 32–44 V | large cross-sections, powerful sources and emphasis on distortion and HAZ |
| Strip electrode | approx. 500–1500 A | 24–36 V | overlaying, low dilution and a wide bead |
| Imperfection | Typical cause | Technological response |
|---|---|---|
| Root or side-wall lack of fusion | poor wire centring, low current, high speed, narrow bevel or unsuitable backing | macro section, correction of wire position, bevel, current, speed and root technique |
| Slag inclusions | incorrect wall angle, sharp inter-run profiles, inadequate slag removal or excessively low energy | adjust layer profile, cleaning, run order and parameters |
| Porosity | damp flux, contamination, rust, oil, incorrect flux height or poor degassing | flux drying/storage, edge cleanliness, reclaimed-flux filtration and moisture testing according to the quality system |
| Centreline crack | unsuitable width/depth ratio, high dilution, sulfur/phosphorus, high restraint or unsuitable layering | adjust bead geometry, reduce penetration or dilution, change flux/wire, sequence and preheat |
| Undercut | high voltage, poor wire position, high speed or poor head guidance | reduce voltage/speed and adjust guidance and wire position |
| Excessive bead / reinforcement | low speed, excessive deposition rate, unsuitable bevel or number of layers | adjust speed, feed, number of runs and target cross-section |
Resistance welding creates a joint through electrical current, resistance at the interface, time and electrode force. The basic relationship for heat generation is Q = I² · R · t.
This module integrates the original blocks Spot welding, Projection welding and the process explanation from the introduction for spot / projection / seam welding.
| ISO 4063 | Process | Typical application |
|---|---|---|
| 21 | Resistance spot welding | sheet, body-in-white and high-volume spot joints |
| 22 | Resistance seam welding | leak-tight seams, tanks, heat exchangers and vessels |
| 23 | Resistance projection welding | nuts, bolts, studs, projections and multiple welds in one cycle |
Current may be switched on only after stable force has been established. Hold time after current switch-off allows the nugget to solidify under electrode force.
Zinc and other coatings reduce contact resistance and accelerate electrode wear. In practice, higher current, longer time and more rigorous tip dressing are often required.
| Material | Indicative electrode-tip pressure | Training note |
|---|---|---|
| Uncoated low-carbon steels | 70 – 100 N/mm² | baseline setting and good weldability |
| Coated low-carbon steels | 100 – 160 N/mm² | coating changes resistance and increases electrode wear |
| Low-alloy steels | 100 – 160 N/mm² | monitor hardness and nugget stability |
| Aluminium alloys | 70 – 160 N/mm² | high current, short time and clean surface |
| Stainless steel | 140 – 250 N/mm² | higher pressure for stable contact |
| Nickel-alloyed steels | 200 – 400 N/mm² | higher thermal and mechanical resistance |
Electrodes clamp the sheets and a short high-current pulse forms a weld nugget between them.
Small nugget, expulsion, stuck joint or electrode wear. Inspection: peel/chisel test, nugget measurement and monitoring of current and force.
| Tip diameter | Current density at 10 kA | Current for the same density as Ø5 mm | Meaning |
|---|---|---|---|
| Ø5 mm | 510 A/mm² | 10,0 kA | reference condition |
| Ø6 mm | 353 A/mm² | 14,5 kA | wear already reduces current density significantly |
| Ø7 mm | 260 A/mm² | 19,6 kA | without tip dressing, the nugget may be inadequate |
In spot welding, distinguish electrode geometry from electrode material. Cap geometry determines contact area, current density and indentation. Material determines electrical conductivity, heat dissipation, resistance to softening, coating pickup and service life between tip dressings.
| Standards designation / group | Typical composition or example | Suitable application | Technology note |
|---|---|---|---|
| ISO 5182 – A 1/… | high-conductivity copper or low-alloy copper, for example Cu or CuAg | conductive components, adapters and less thermally loaded parts | excellent conductivity but lower wear and softening resistance |
| ISO 5182 – A 2/… | heat-treated copper alloys, typically CuCr, CuZr, CuCrZr | the most common electrode caps for steel and galvanised sheet | a good conductivity/hardness compromise; a typical baseline choice for automotive spot welding |
| ISO 5182 – A 3/… | higher-strength copper alloys with lower conductivity, for example CuNiSi or Be-containing alloys according to supplier | higher mechanical loading, harder materials and special electrodes | For Be-containing alloys, control extraction and PPE during grinding; do not use as a direct CuCrZr substitute without testing. |
| ISO 5182 – A 4/… | special copper alloys with specific properties | applications defined by the electrode manufacturer or line technology | materials in this group are not necessarily interchangeable |
| ISO 5182 – B 10 / B 11 | sintered Cu-W, for example W75Cu | inserts, projection welding and highly localised thermal loading | higher contact resistance; poorer thermal conductivity than conventional CuCrZr caps |
| ISO 5182 — B 12 to B 15 | Cu-WC, Mo, W or W-Ag according to type | special contact inserts and difficult highly conductive materials | Do not apply generally to series steel spot welding; testing and supplier recommendations govern. |
| ISO 5182 – C 20/… | dispersion-strengthened copper, typically Cu-Al₂O₃ / DSC | longer tip life, higher softening resistance and coated sheet | Attractive for process stability, but cooling, dressing and spot qualification must match. |
‘Copper electrode’ or ‘standard electrode’ is an incorrect specification. State material + geometry + tip condition. The same current with another material or a larger worn face produces a different current density, nugget and indentation.
Current and force are concentrated in the projection. The projection collapses, localises the weld and forms the joint.
Unfused projection, expulsion, displaced nut or damaged thread. Inspection: torque test, push-off test, thread gauge and visual seating inspection.
In projection welding, projection consistency and height, component flatness, nut position and fixture stiffness are decisive. Excessive force may damage projections prematurely; insufficient force increases expulsion and contact-instability risk.
| Nut | Sheet thickness | Electrode force | Time | Current | Minimum torque |
|---|---|---|---|---|---|
| M4 | 1,0 – 2,0 mm | 2,9 – 3,1 kN | 5 cycles | 7,5 – 8,0 kA | 6 Nm |
| M5 | 1,0 – 2,0 mm | 3,6 – 3,8 kN | 5 cycles | 9,0 – 9,5 kA | 12 Nm |
| M6 | 1,0 – 2,0 mm | 4,2 – 4,5 kN | 6 cycles | 10,5 – 11,0 kA | 20 Nm |
| M8 | 1,0 – 2,0 mm | 4,9 – 5,1 kN | 9–10 cycles | 17,0 – 18,0 kA | 50 Nm |
| M10 | 2,0 mm | 6,0 kN | 10 cycles | 21,0 kA | 100 Nm |
| M12 | 2,0 mm | 7,1 kN | 12 cycles | 24,0 kA | 180 Nm |
| Stud | Sheet thickness | Electrode force | Time | Current | Minimum torque |
|---|---|---|---|---|---|
| M5 | 1,0 – 2,0 mm | 2,7 kN | 12 cycles | 8,0 kA | 6 Nm |
| M6 | 1,5 – 2,5 mm | 3,5 kN | 15 cycles | 8,5 kA | 10 Nm |
| M8 | 1,5 – 2,5 mm | 3,5 kN | 15 cycles | 9,5 kA | 23 Nm |
Wheel electrodes rotate, clamp the sheets and create a continuous or intermittent row of overlapping spots.
Leakage from insufficient overlap, burn-through from excessive energy, seam waviness or wheel wear. Inspection: leak test, VT, seam section and current/speed monitoring.
A row of overlapping spots can create a tighter joint than isolated spots. Insufficient overlap produces a discontinuous joint; excessive energy increases burn-through and distortion risk.
Wheel electrodes simultaneously transfer current, force and movement. Settings must coordinate speed, pulse frequency, current-on time, wheel force and cooling.
Plasma is a constricted electric arc, laser is a photon beam and an electron beam is a stream of accelerated electrons. All can create a narrow weld with a small heat-affected zone, but process stability depends on different factors: nozzle geometry and gases in PAW; resonator type, wavelength, emission mode, optics and absorption in laser welding; and electron gun, accelerating voltage, vacuum, beam current and magnetic cleanliness in EBW.
PAW is more often treated as an arc process using U·I·η/v. For laser and EBW, it is more practical to consider beam power, spot diameter, focus and speed. In both cases, the result depends on absorption, beam position relative to the joint and surface condition.
| Group | Process | Practical meaning | Typical application | Essential WPS requirements |
|---|---|---|---|---|
| 15151152153154155 | Plasma arc welding plasma arc welding, PAW | Constricted arc through a nozzle. Variants include plasma-MIG, powder plasma and transferred/non-transferred or partially transferred arc. | Microplasma, precision thin components, keyhole PAW, overlays and mechanised joints. | Current, voltage, pilot arc, plasma gas, shielding gas, nozzle diameter, electrode setback, torch stand-off and melt-in/keyhole mode. |
| 51511512513 | Electron-beam welding electron beam welding, EBW | A beam of accelerated electrons; most commonly a high-vacuum process with extremely deep and narrow penetration. | Aerospace components, turbines, transmission parts, precise thicker sections, reactive metals and low distortion. | Vacuum, accelerating voltage, beam current, focus, working distance, beam oscillation, speed, cleaning and demagnetisation of the component. |
| 52521522523 | Laser welding laser beam welding, LBW | Optical beam from a solid-state, gas or diode source. It can operate in conduction or keyhole mode. | Automotive, batteries, precision assemblies, thin sheet, stainless steel, aluminium alloys and robotic lines. | Source type, power, CW/pulse, spot/focus, focus position, speed, shielding gas, beam angle, gap, fixture and monitoring. |
| Process | Equipment configuration | Energy source / emission mode | Indicative welding power range | What is technically qualified |
|---|---|---|---|---|
| PAW | CC welding source, plasma torch with tungsten electrode, water-cooled constricting nozzle, pilot arc, gas console, cooler and mechanisation/robot. | Welding arc. Energy is controlled not by ‘beam emission’ but by current, voltage, plasma gas, nozzle and torch geometry. | microplasma: approximately 0.1–15 A melt-in PAW: approximately 15–200 A keyhole PAW: approximately 60–350 A depending on material and thickness. | Torch, nozzle, electrode setback, pilot arc, gases, flow rates, current mode, stand-off and melt-in/keyhole mode. |
| Laser / LBW | Laser source, cooling, optical path or process fibre, collimating/focusing head, protective glass, cross-jet, shielding gas, scanner/wobble or robotic axis. | Photons. Emission may be continuous CW, pulsed, QCW or power-modulated. Wavelength, beam quality and energy distribution in the spot also matter. | fine/pulsed welding: tens to hundreds of watts average industrial fibre/disc LBW: approximately 1–20 kW, and more for special applications diode/conduction: approximately 0.5–15 kW. | Laser type, wavelength, emission mode, time-dependent power, spot diameter, focus, BPP/M², angle, wobble/scanner, optics, shielding and monitoring. |
| EBW | Vacuum chamber or local-vacuum system, electron gun, high-voltage supply, cathode, anode, focusing and deflection coils, pumps, manipulator and X-ray shielding. | Electrons emitted from a cathode, accelerated by voltage and focused by magnetic/electrostatic fields. In practice, accelerating voltage, beam current, focus, oscillation and vacuum are controlled. | fine EBW: approximately 1–6 kW production EBW: approximately 6–60 kW heavy sections: approximately 60–150 kW depending on machine and application. | Vacuum mode, accelerating voltage, beam current, focus, working distance, deflection/oscillation, pumping time, component cleanliness and demagnetisation. |
| PAW equipment type | Construction / principle | Typical application | Technologically sensitive variables |
|---|---|---|---|
| Microplasma | Low current, stable pilot arc and a very small, well-defined arc. The torch is designed for precise small weld pools. | Thin sheet, diaphragms, instrument components, stainless and nickel alloys, and precise circumferential welds. | Pilot-arc stability, gas purity, arc length, positional accuracy and very small speed variations. |
| Melt-in PAW | The plasma melts material without an open keyhole through the full thickness. It behaves like a highly concentrated TIG arc. | Medium-thin components, root runs and precision mechanised welds. | Current, voltage, plasma gas, shielding gas, nozzle, torch stand-off and filler wire. |
| Keyhole PAW | The plasma jet creates an open keyhole around which the weld pool closes, enabling deeper penetration with a narrow weld. | Automated butt joints, stainless steel and selected steels, with fewer layers. | Root gap, speed, plasma-gas pressure, torch centring, root support and keyhole stability. |
| PTA / powder plasma | The plasma arc melts the base material and metal powder. This is often an overlay process rather than a conventional butt weld. | Hardfacing, valve seats, wear-resistant layers and repairs. | Powder feed, dilution, layer height, heat input, preheat and shielding gas. |
| Plasma-MIG / hybrid plasma heads | Combination of plasma with a wire electrode or supplementary arc. The objective is stability, speed or higher deposition rate. | Special mechanised applications, overlays and productive joints. | Relative arc positions, source synchronisation, metal transfer, gas, nozzles and deposition rate. |
| Laser type | Wavelength / beam delivery | Emission mode | Typical welding powers | Technology note |
|---|---|---|---|---|
| Yb:fibre laser | Approximately 1.03–1.08 µm. The beam is delivered through a process fibre to the head or robot. | CW, modulated CW, pulsed or QCW depending on the source. | 1–20 kW is a normal industrial range; higher powers are used for special applications. | The most widely used industrial type. Excellent efficiency and robotic integration. For Cu/Al, address reflection and absorption stability. |
| Disc laser | Approximately 1.03 µm. Fibre delivery and high beam quality. | CW or modulated power. | Typically 2–16 kW, higher depending on manufacturer and configuration. | Very good beam quality at higher power; suitable for deep, high-speed LBW. |
| Diode laser | Approximately 0.8–1.0 µm; generally a larger spot and lower beam quality than fibre/disc systems. | CW or modulated CW. | 0.5–15 kW depending on the head and diode-module combination. | Suitable for conduction welding, brazing, cladding and a wider pool. Less suitable for extremely deep keyhole welding. |
| CO₂ laser | 10.6 µm. The beam is delivered by mirrors, not conventional silica fibre. | CW or pulsed modes. | 2–20 kW and more in older/special lines. | Historically important for deep welding and cutting. Requires a mirror-based optical path and precise maintenance. |
| Nd:YAG / lamp- or diode-pumped | 1.064 µm. Older systems were often fibre-delivered. | Pulsed, QCW or CW depending on source. | Hundreds of watts to several kilowatts. | Still used in fine welding, mould repair, sensors and precision components. |
| Green / blue laser | Green approximately 515–532 nm; blue approximately 445–460 nm. | CW or pulsed depending on source. | Hundreds of watts to several kilowatts, an expanding industrial class. | Better absorption in copper and some highly reflective materials. Important for batteries, e-mobility and copper joints. |
| Mode / optics | Meaning | Effect on the weld | What to record in the WPS / settings |
|---|---|---|---|
| CW – continuous wave | The laser emits nearly continuous power. | Stable long welds and suitable for high-speed automation. Risk of overheating at low speed. | Power, power ramp-up/down, speed, focus, spot and shielding gas. |
| Pulsed mode | Energy is delivered in pulses. Pulse energy, peak power, pulse duration and frequency are important. | Suitable for spot and fine welds, sensitive components and minimising heat. May create an overlapping sequence of spot welds. | Pulse energy [J], pulse duration [ms/µs], frequency, pulse overlap and pulse shape. |
| QCW – quasi continuous wave | Short intervals of high power separated by pauses; between CW and pulsed welding. | High peak power with lower average thermal loading. | Peak power, duty cycle, pulse duration, average power and component cooling. |
| Modulated power | Power changes during the weld according to a program, ramp, path segment or feedback. | More stable start/end, smaller crater and controlled penetration through thickness changes. | Power curve versus time/path, ramp-up/ramp-down and feedback signal. |
| Wobble / scanner oscillation | The beam is deliberately oscillated in a circle, ellipse, line or pattern. | Increases gap tolerance and weld-pool mixing and improves stability for Al/Cu; may reduce pores but increases thermal influence. | Wobble shape, amplitude, frequency, orientation and synchronisation with travel speed. |
| Single-mode / multi-mode | Different beam quality and energy distribution. Single-mode gives a very small spot; multi-mode gives a larger, more robust spot. | Single-mode: high power density and deep keyhole. Multi-mode: wider, more stable pool and greater tolerance. | Fibre type, core diameter, BPP/M², spot diameter and energy distribution. |
| Ring beam / top-hat / multi-spot | Energy is not a Gaussian spot but a ring, area or multiple spots. | Improved control of spatter, porosity and pool width in Cu/Al and battery joints. | Beam profile, core/ring power ratio, spot diameters and optical head. |
| Typ EBW | Vacuum / chamber | Electron gun and power | Application | Risks and limitations |
|---|---|---|---|---|
| High-vacuum EBW · ISO 4063 511 | The component is inside a chamber; low pressure reduces electron scattering and oxidation. | Thermionic cathode, anode, focusing and deflection coils. Typically 30–200 kV and currents from mA to hundreds of mA depending on power. | The most precise deep welds, reactive metals, turbines, transmission components and hermetic joints. | Pumping time, chamber size, component outgassing, cleanliness, magnetism and X-ray shielding. |
| Medium / reduced vacuum | Higher pressure than high vacuum; faster cycle but greater beam scattering. | Similar gun, but the process is a stronger compromise between productivity and beam quality. | Production requiring a shorter chamber cycle and components less sensitive to absolute cleanliness. | Wider beam, lower depth/precision and stricter verification of stability. |
| Non-vacuum / atmospheric EBW · ISO 4063 512/513 | The beam passes through differential pumping or shielding gas into the atmosphere. | Higher power compensates for electron scattering outside the chamber. | Special applications where a chamber is impractical. | High scattering, shorter working distance, radiation protection and lower precision than process 511. |
| Chamber machine with manipulator | The entire component moves inside the chamber on a table, rotary fixture or multi-axis manipulator. | Power ranges from small precision machines to systems above 100 kW. | Rotating rings, gears, turbines, thick sections and high repeatability. | Vacuum-compatible fixture design, thermal expansion, beam access and cleaning before pumping. |
| Local vacuum / mobile heads | A small local chamber surrounds the weld instead of a large chamber. | Suitable where the whole component cannot be placed in a chamber. | Long or large components and special repair applications. | Sealing of the local chamber, vacuum stability, joint geometry and access. |
| Process | Equipment and power source | Beam / torch | Joint and fixture | Inspection and records |
|---|---|---|---|---|
| PAW | source, polarity, current mode, pilot arc and torch cooling | plasma gas, shielding gas, nozzle diameter, electrode setback, torch stand-off and filler material | gap, root backing, position, keyhole/melt-in mode and torch centring | current, voltage, gas flows, nozzle/electrode condition and root macro section |
| Laser | laser type, power, CW/pulsed mode, wavelength, optics and fibre delivery | spot diameter, focus/defocus, beam angle, wobble/oscillation, shielding gas and cross-jet | gap, beam offset, restraint, path accuracy, surface reflectivity and cleaning | power and speed records, camera/pyrometer monitoring, macro examination and CT/RT for porosity according to risk |
| EBW | accelerating voltage, beam current, power, vacuum chamber and pumping cycle | focus, working distance, deflection/oscillation, beam alignment and beam preheating | cleanliness, demagnetisation, chamber assembly, outgassing, thermal expansion and root condition | vacuum, voltage/current/focus, beam-deviation record, RT/CT, macro examination and penetration-depth measurement |
| Imperfection | PAW | Laser | EBW | Technological response |
|---|---|---|---|---|
| Porosity | moisture, incorrect gases and unstable keyhole | keyhole collapse, contamination and poor vapour evacuation | component outgassing, contamination and unsuitable vacuum cycle | cleaning, stabilising speed and focus, adjusting gases/vacuum and monitoring the keyhole |
| Lack of fusion / insufficient penetration | low current, damaged nozzle or excessive speed | defocus, low power, reflective surface or beam offset | incorrect focus/current, beam deflection or excessive working distance | macro examination, beam-axis inspection, focus correction and speed reduction |
| Undercut / sagging | excessive energy or poor root condition | unstable keyhole, high speed or incorrect focus position | excessive depth in a narrow pool and root spike | adjust energy, focus, gap, fixture and root support |
| Cracks | material + rapid thermal cycle | hot cracking in Al/Ni/stainless steel and high gradients | rapid cooling, brittle phases and high stresses | change filler material, preheat, weld shape, thermal cycle and chemical composition |
In MIG/MAG, TIG, MMA or SAW, the welding engineer first considers the arc and weld pool. In this group, the logic changes: some processes form a solid-state joint by pressure and plastic deformation; others use a chemical reaction, induced current, a slag pool, an electromagnetic impulse or a very short discharge.
Not the process name but the joining mechanism: melting, diffusion, plastic deformation, discharge, induction heating or chemical reaction.
There may be no conventional bead or filler material, and the critical variable may be force, amplitude, lift height, burn-off, discharge energy or vacuum.
Series production, rotating components, aluminium profiles, battery terminals, studs, thick vertical joints, rails, tubes and transition joints.
Hidden bond imperfections, oxide layers, an incorrect cycle, high heat input, uncontrolled force, a worn tool or a poorly prepared surface.
| ISO 4063 | Process | Typical equipment | Critical variables | Typical application and risk |
|---|---|---|---|---|
| 41 411–414 | Ultrasonic welding | Generator, transducer/converter, booster, sonotrode, anvil or fixture; typically 20–40 kHz depending on power and application. | Amplitude, frequency, squeeze force, energy/time, collapse distance, sonotrode shape and surface cleanliness. | Battery foils, conductors, thin sheet and plastics. Risks: tool indentation, inadequate bonding, foil cracking and insulation overheating. |
| 42 421–426 | Friction welding | Rotary direct-drive or inertia machines, linear/orbital machines and friction stud-welding units. | Rotational speed, inertia energy, friction pressure, time, burn-off, braking, forge pressure and alignment. | Shafts, valves, tubes and bimetal transitions. Risks: misalignment, cold bond, oxide plane and excessive flash. |
| 43 431–435 | Friction stir welding / spot-FSW variants | Gantry/CNC/robotic machine with a rigid spindle, tool with shoulder and pin, and force or position control. | Rotational speed, travel, axial force, tool angle, plunge depth, dwell, pin geometry and tool wear. | Aluminium profiles, panels, transport structures and battery trays. Risks: tunnel defect, kissing bond, inadequate mixing and thinning. |
| 44 441–442 | Impact welding: explosive or magnetic pulse | Explosive arrangement with flyer plate or magnetic-pulse system with capacitor bank and coil. | Impact velocity, collision angle, stand-off, discharge energy, coil geometry, surface and safety constraints. | Cladding, Al-Cu transitions and tubular joints. Risks: local melting, cracks, non-uniform wavy interface and process safety. |
| 45 451 | Diffusion and HIP welding | Vacuum furnace, hot press or HIP autoclave controlling temperature, pressure, time and atmosphere. | Temperature, pressure, time, vacuum/atmosphere, roughness, cleanliness, interlayer and faying-surface accuracy. | Aerospace parts, sandwich structures and transition materials. Risks: oxides, pores, insufficient diffusion and component distortion. |
| 71 | Aluminothermic / thermit welding | Moulds, preheat, crucible, thermit charge and pouring system; typically mobile rail equipment. | Gap, alignment, mould, preheat, charge, tapping time, riser removal and controlled cooling. | Rails and repairs of large sections. Risks: shrinkage cavities, slag inclusions, incorrect hardness and dimensional error. |
| Electroslag / electrogas welding Vertical machine with water-cooled shoes, wire/strip feed, slag pool or shielding gas, and controlled vertical travel. | Current, voltage, slag depth, wire position, shoe cooling, travel speed, heat input and run sequence. | Very thick vertical joints and heavy fabrication. Risks: coarse-grained HAZ, low toughness, distortion and lack of side-wall fusion. | Travel speed, current, voltage, number of wires, gap width, shoes, slag flow and cooling. | High-frequency / induction welding |
| 74 HF generator, induction coil or contacts, impeder, forming rolls and squeeze rolls. | Frequency, power, line speed, V-angle, impeder position, squeeze force, edge cleanliness and alignment. | Pipes, profiles and longitudinal seams. Risks: cold weld, oxide entrapment, hook cracks and local overheating. | Infrared / radiant-energy welding | IR emitter, lamp or heated radiant panel with pressure fixture and temperature control. |
| 78 Emitter power, distance, time, surface absorption, pressure and cooling. | Plastics, films and specialised components. Risks: uneven heating, degradation and inadequate bond area. | Arc stud welding | Power source, stud gun, ceramic ferrule or shielding gas, lift system and fixture/earthing. | Current, time, lift, plunge, stud diameter, polarity, ferrule/gas, surface condition and return-current path. |
| 185 | Studs, shear connectors, anchors and threaded elements. Risks: lack of fusion, porosity, arc blow, misalignment and insufficient collar. | Capacitor-discharge stud welding | Capacitor bank, stud gun, ignition tip or gap method and fixture. | Capacitance/voltage, discharge energy, spring force, protrusion and surface condition. |
Clamping heads for tubular parts, coil/magnetic system, current source and upsetting unit.
Productive vertical welding of thick sections. The welding engineer must address HAZ toughness, grain size, normalising or the requirements of the product standard. It is not a universal substitute for SAW.
Short high-energy cycle. Quality does not depend on the ‘skill of the welder’, but on the settings of the power source, gun, fixture, surface, ferrule or coil and on contact repeatability.
In thermit welding, heat comes from the charge reaction. The WPS must address alignment, preheat, mould, molten-metal handling and subsequent finishing. Rail welding is typical.
Energy concentrates at strip edges through skin and proximity effects. Frequency, impeder, V-angle, squeeze and edge cleanliness are decisive.
For special processes, a WPS copied from arc welding is insufficient. Qualify the specific mechanism, equipment, tool, fixture and inspection plan.
Select the parameters on the left. The model does not calculate qualification but demonstrates selection logic.
For special processes, everything cannot be reduced to linear energy as with an arc. Nevertheless, the welding engineer must understand the controlled cycle energy.
Direct-drive uses motor-controlled rotational speed during the friction phase. Inertia uses a flywheel with defined energy. In both cases, transition from friction to forge pressure is critical. Monitor shortening, flash, alignment and macrostructure.
Pin and shoulder determine material flow. A small geometry change, wear or incorrect plunge depth may create a kissing bond that visual inspection cannot reveal.
The same set power can produce a different joint when sonotrode, booster, squeeze force, surface or number of foil layers changes. For batteries, monitor temperature, particles and conductor damage.
Typical modes are drawn arc with ferrule/gas, short-cycle and capacitor discharge. The WPS must include current, time, lift, plunge, stud diameter, surface, ferrule or gas, and tensile/bend inspection according to the application.
They are special vertical processes with high heat input. High productivity must be balanced against toughness, grain size and product-standard requirements.
Seam quality depends on the entire line: edge trimming, forming, V-angle, coil, impeder, squeeze rolls, cooling and inline NDT. Changing line speed changes the thermal cycle.
| Application | What to record | Why it is critical |
|---|---|---|
| Process designation | ISO 4063 number, variant name and, for a hybrid process, the process combination. | Without an exact number, WPQR, drawing, WPS and product standard cannot be compared unambiguously. |
| Equipment | Machine type, energy source, power range, force/position control method, and gun, sonotrode, coil, tool or mould type. | For these processes, the equipment is often an essential variable. The same material may not be weldable on another machine. |
| Cycle | Times, forces, pressures, lifts, plunges, rotational speeds, travel speeds, discharge energy, amplitude, burn-off, dwell, preheat and cooling. | The result is determined by the complete cycle, not one nominal parameter. |
| Tool and fixture | Tool geometry, material, wear, permitted tolerances, clamping method, alignment and pressure surfaces. | A worn sonotrode, pin, ferrule, coil or fixture can alter the bonding mechanism without an obvious external change. |
| Surface | Cleaning, oxides, lubricants, coatings, roughness, interlayer, gap, overlap and alignment. | Many solid-state processes are extremely sensitive to oxide layers and contamination. |
| Inspection | VT, dimensional inspection, macro/micro examination, hardness, stud bend/tensile, peel/chisel, UT, RT, pressure test and inline monitoring. | Some bonding imperfections are not visible. The inspection plan must be based on process physics. |
Basis for process designation in drawings, WPSs, WPQRs, databases and training. In hybrid processes, numbers are combined with a ‘+’ sign.
Series for friction stir welding of aluminium: vocabulary, joint design, operator qualification, procedure qualification and quality requirements.
Specific standard for arc stud welding of metallic materials. Studs have their own testing and qualification logic.
For processes outside conventional arc welding, the WPS must capture equipment-specific process variables. Do not copy a MAG form without modification.
A special process must be controlled through a qualified procedure, competent personnel, equipment maintenance, records and traceability.
Pressure equipment, rails, automotive, batteries or construction products may restrict the process or require additional testing.
Review question for welding coordination: When someone proposes a ‘special process’, do not ask only about strength. Ask: what is the joint-formation mechanism, what is the main cycle energy, which variable is essential, how are force and position controlled, how is a hidden bond imperfection detected, is the process permitted by the product standard, and does the WPQR actually cover the equipment, tool and parameter range used?
JOINT moves physical robot axes J1–J6. WORLD uses the fixed robot frame axes. UFRAME uses a user frame attached to the fixture/component — axes are fixed relative to the component but may be translated and rotated relative to WORLD. TOOL uses the local axes of the current TCP. W/P/R follow FANUC convention: W=X, P=Y, R=Z — therefore WORLD, UFRAME and TOOL behave differently when a component is tilted or clamped at an angle.
The robot does not seek a straight TCP path. A specific motor moves, so the TCP describes an arc or complex path. J4–J6 mainly change torch orientation.
+X, +Y and +Z always point in the same cell directions. W/P/R rotations follow FANUC logic: W about X, P about Y and R about Z in the fixed WORLD frame; the TCP remains in position.
UFRAME is the user coordinate system of the workholding. +Xᵤ, +Yᵤ and +Zᵤ follow the rotated component frame, not WORLD and not the torch. In the trainer, UFRAME is deliberately translated and rotated so the difference is visible.
+Zᴛ may point diagonally when the torch is tilted. Wᴛ rotates about local Xᴛ, Pᴛ about Yᴛ and Rᴛ about Zᴛ; TOOL rotations occur in the local TCP frame.
This section builds on the coordinate-system trainer. It focuses on what a welding engineer must address in robotics: motion type, point blending, fixtures, process qualification, cell safety and weld quality.
The robot has three programmed points forming the letter L. With FINE it reaches the middle point exactly, stops momentarily and only then continues. With CNT it rounds the corner: the higher the CNT value, the greater the deviation from the middle point and the smoother the passage.
Exact points, weld end, touch point, calibration, measurement, a point requiring an exact position, or a point where the robot must not round the corner.
Approach, departure, smooth transfer movements and locations where deviation is permitted. During welding, monitor speed uniformity, the crater and bead geometry.
JOINT/J/PTP interpolates the robot joints. It is fast and suitable for transfer movements, but the TCP path between points need not be straight. LINEAR/L interpolates the TCP along a straight line in space, so it is used for the welding path, entry into the weld and movements close to fixtures.
Suitable for rapid transfer between safe positions. Do not use it as a substitute for a straight welding path when the exact TCP path matters.
Suitable for weld segments, precise torch guidance and movements close to the component. Singularities and orientation reachability must be monitored.
The added section is based on the slides 1, 2 and on the supplied images for 1F / 2F welding positions. It focuses on the gap between plates, TCP aiming, torch position, work angle and travel angle.
Slides 1 and 2 — TCP aiming at the start and end of the weld according to gap size.
Visualisation based on the two supplied images: work angle, travel angle and TCP position 1–1.5 wire diameters away from the joint corner.
1F: work angle approximately 60°, travel angle 0–15°. The text on reducing spatter is translated from the slide.
2F: work angle approximately 65°, travel angle 0–15°. The display is retained only for the work angle and TCP position.
| Application | Suitable for a robot | High-risk / unsuitable | What to verify before the project |
|---|---|---|---|
| Production volume | stable series, repeatable cycle time | one-off production with frequent changes | number of components, variants, program and fixture changeover time |
| Weld geometry | accessible torch, clearly defined joint line | obstructions, deep corners, unclear root | reach, collisions, torch length, torch angle, positioner |
| Component tolerances | low variation in edge position | manual adjustment, large gap | variation measurement, trial series, need for seam tracking |
| Fixture quality | positive stops, rapid clamping, cleaning | clearances, distortion, complex manual clamping | repeatability, cleaning access, thermal expansion |
| Process | stable WPS and material batch | frequent repairs, material changes, contamination | WPQR/WPS, gas, wire, CTWD, preheat, interpass temperature |
| Safety | a safeguarded space can be defined for the cell | unclear personnel access, manual intervention during the cycle | risk assessment, fencing, scanners, interlocks, emergency stop |
Plastic welding is primarily applicable to thermoplastics, which soften or melt when heated and solidify again on cooling. Thermosets, thermoset-matrix composites and highly cross-linked materials are not normally fusion welded; they are joined by adhesive bonding, mechanical fastening or special processes.
Joint quality depends on material compatibility, cleanliness, moisture, surface oxidation, pressure during joining, heating time, tool temperature, stable cooling and prevention of polymer degradation.
PE, PP, PVC-U/PVC-C, PVDF, ABS, PA, PC, PMMA and other thermoplastics can be fusion joined when they are compatible and the surface is uncontaminated.
Amorphous plastics soften around the glass-transition temperature; semi-crystalline plastics have a more distinct melting temperature. Their process windows, cooling behaviour and shrinkage differ.
Excessive temperature causes oxidation, bubbles, browning, fumes, joint weakening and internal stresses. For PVC, overheating and release of decomposition products are critical.
PA, PC, PMMA and some engineering plastics may be moisture-sensitive. During welding, moisture appears as foaming, pores and unstable joint strength.
| Method | Principle | Typical application | Key parameters | Typical imperfections |
|---|---|---|---|---|
| Heated-tool butt welding | The component faces are aligned, heated against a hot plate, the plate is removed and the components are pressed together. | PE/PP pipes, sheets, tanks and thicker thermoplastics. | Plate temperature, bead-up pressure, heating time, changeover time, joining pressure and cooling. | Cold joint, excessive bead, contaminated plate, excessive mismatch or exceeded changeover time. |
| Heated-tool socket / saddle welding | A heating tool heats the outer and inner surfaces; the components are then inserted and allowed to cool. | Smaller pipes, fittings and workshop assemblies. | Insertion depth, heating time, coaxial alignment, tool temperature and cooling without movement. | Angled insertion, material scraping, insufficient heating or movement during cooling. |
| Electrofusion fittings | A resistance wire in the fitting heats the joint zone after connection to a control unit. | PE gas and water pipelines, repairs and locations with restricted access. | Scraping of the oxidised layer, cleanliness, insertion, clamping, voltage/time according to the barcode and cooling. | Unscraped surface, pipe ovality, movement during cooling, moisture or incorrectly read data. |
| Hot gas | Hot air or nitrogen softens the base material and filler rod. | Sheets, tanks, ventilation ducts, PVC/PP/PE repairs and manual welds. | Gas temperature, flow rate, travel speed, pressure on the rod, torch angle and nozzle shape. | Cold areas, burn-through, pores, poor mixing or inadequate V-groove preparation. |
| Extrusion welding | An extruder plasticises the filler material and deposits it into a preheated groove. | Thicker sheets, tanks, geomembranes and large PP/PE structures. | Extrudate temperature, preheat, welding-shoe pressure, output, speed and joint preparation. | Lack of bonding at side walls, porosity, overheated extrudate or incorrect rod/pellet material. |
| Hot-wedge / hot-air welding for films | Continuous heating and roller pressure join two films or membranes. | Geomembranes, films, roofing membranes and thermoplastic-coated technical textiles. | Temperature, speed, roller pressure, overlap cleanliness and a trial weld before production. | Leaking channel, overheated edges, wrinkles or contamination in the overlap. |
| Ultrasonic welding | High-frequency mechanical oscillations generate local heat at an energy director. | Small series-produced components, housings, filters and automotive plastic parts. | Amplitude, force, energy/time, sonotrode geometry, energy director and component support. | Cracks, cold joint, surface marking, inadequate support or a missing energy director. |
| Vibration / friction / spin welding | Relative movement of components under pressure generates frictional heat. | Automotive components, vessels, piping parts and circular parts for spin welding. | Frequency, amplitude, pressure, time, stop position and interface geometry. | Excessive flash, particles in the joint, component distortion or insufficient melting. |
| Laser transmission welding | The upper component transmits the laser; the lower component absorbs the energy and melts the interface. | Precision components, medical devices, electronics, automotive sensors and housings. | Optical transmission/absorption, clamping, pressure, power, beam path and gap. | Insufficient absorption, local burning, gap between components or contamination. |
| Adhesive and solvent bonding | This is not fusion welding; the joint forms by adhesion or partial dissolution of the surface. | PVC piping, PMMA, ABS, housings, composites and components unsuitable for fusion welding. | Surface energy, surface preparation, open time, curing, temperature and humidity. | Low adhesion, residual solvent, chemical incompatibility or joint ageing. |
For piping and safety-relevant joints, a welder's signature is not enough. The material, diameter/thickness, machine, plate temperature, pressure phases, times, ambient temperature, welder, WPS/procedure number and visual-inspection result must be traceable.
For electrofusion fittings, the control-unit record, barcode, cooling time, surface preparation and restraint against movement are essential.
| Material | Typical joining method | Technical notes |
|---|---|---|
| PE-HD / PE100 | Heated-tool butt welding, electrofusion fittings, extrusion welding and hot-wedge welding for films. | Sensitive to scraping of the oxidised layer, cleanliness, cooling time and alignment. Common in gas and water systems. |
| PP | Hot-gas, extrusion and heated-tool welding; ultrasonic welding for smaller components. | Good chemical resistance, higher processing temperature than PE; beware of oxidation and UV ageing. |
| PVC-U / PVC-C | Hot-gas welding, extrusion welding and solvent bonding for piping. | Narrow process window; overheating causes degradation. Extraction and the correct filler material are required. |
| PVDF | Hot-gas, heated-tool and extrusion welding; high cleanliness for the chemical industry. | Requires a clean surface and precise temperature; often used in chemically demanding applications. |
| ABS | Ultrasonic, vibration, laser or adhesive/solvent bonding depending on the application. | Suitable for series-produced components; energy-director design and component support are decisive. |
| PA | Ultrasonic, vibration, laser and friction welding. | Moisture-sensitive; drying and stabilisation of conditions may be required before welding. |
| PC / PMMA | Ultrasonic, laser or adhesive bonding; take care with internal stresses. | Risk of stress cracking, optical requirements, sensitivity to chemicals and overheating. |
| Imperfection | Visible indication | Probable cause | Prevention |
|---|---|---|---|
| Cold joint | Weak or irregular bead, low strength, smooth separation surface. | Low temperature, short heating time, long changeover time or low pressure. | Verify tool temperature, times, pressure and component movement during cooling. |
| Overheating / degradation | Browning, burnt surface, bubbles, odour or brittle joint. | Excessive temperature, slow travel or incorrectly set hot-gas torch/extruder. | Temperature calibration, trial weld, extraction and correct speed. |
| Pores and foaming | Bubbles in the bead or extrusion weld. | Moisture, contamination, overheating or incorrect filler material. | Drying, cleanliness and verification of the material and extrudate temperature. |
| Unacceptable alignment | Face mismatch or non-uniform bead. | Poor clamping, pipe ovality, residual restraint or movement during cooling. | Restraint, alignment, ovality measurement and no handling during cooling. |
| Contaminated interface | Local lack of bonding, delamination or leakage. | Dust, grease, PE oxide layer, hand contact or moisture. | Scraping, cleaning, protection of prepared surfaces and immediate welding after preparation. |
| Application | Standard / document | Practical application |
|---|---|---|
| Qualification of plastics welders | EN 13067:2020 | Testing of a welder's knowledge and skill for thermoplastic welded assemblies in new fabrication and repair. |
| Butt welding of PE pipes | ISO 21307:2017 + Amd. 1:2020 | Procedures for butt fusion of PE piping systems, including low-pressure and high-pressure variants according to the application. |
| Equipment for PE fusion joining | ISO 12176-1 / ISO 12176-2 | Requirements for butt-fusion machines and control units for electrofusion fittings. |
| Testing of PE joints | ISO 13953, ISO 13954 or ISO 13955 according to joint type | Tensile, peel or decohesion tests for assessing the quality of the fused interface. |
| Product requirements for piping | ISO 4427, ISO 4437 and applicable national regulations | Water, gas and pressure applications have their own requirements for material, installation, testing and documentation. |
| Technical practice | DVS 2207 series and internal WPSs/procedures | Practical procedures frequently used in Europe for welding thermoplastics; verify the current edition and its relationship to the customer specification. |
Material identification, compatibility, certificate, surface condition, drying, ambient temperature, machine calibration, welder qualification and trial weld.
Temperature, pressure/force, times, speed, clamping, protection from wind and moisture, no contact with the molten zone and parameter recording.
Cooling without movement, visual inspection of the bead, dimensional inspection, leak/strength testing, marking and traceability.
Ceramics have high hardness and excellent temperature and chemical resistance, but low fracture toughness and virtually no plastic reserve. Composites offer high specific strength, but are anisotropic and sensitive to delamination, moisture, the matrix glass-transition temperature and surface quality. The joint must therefore be designed as a system: material — interlayer — geometry — thermal cycle — inspection — service environment.
Al₂O₃, ZrO₂, SiC, Si₃N₄, AlN, glasses and glass-ceramics. They provide excellent hardness, wear resistance and thermal stability, but fail in a brittle manner and are sensitive to local tensile stress.
SiC/SiC, C/SiC, oxide/oxide. They have better damage tolerance than monolithic ceramics, but the fibre/matrix interface is a functional part of the material.
CFRP, GFRP and aramid composites with a thermoset or thermoplastic matrix. Strength is directional, so the joint must respect fibre orientation.
Al/SiC, TiC or oxide-reinforced metals. They behave partly like metals, but the reinforcement changes melting behaviour, reactions and tool wear.
Under local tensile loading or thermal shock, stress cannot be relieved by plastic deformation. A microcrack may propagate immediately, especially near a notch, edge or excessively stiff interlayer.
Ceramic, metal, braze alloy, adhesive and composite have different coefficients of thermal expansion. Residual stress develops during cooling even without external loading.
Instead of point load transfer, use a larger bonded area, shear loading, radii, interlayers, graded stiffness and hybrid solutions.
| Technology | Suitable for | Parameters to control | Typical risk |
|---|---|---|---|
| Adhesive bonding | CFRP/GFRP, ceramic–metal at lower temperature, large joining areas | surface, roughness, activation, adhesive thickness, curing cycle, moisture | peel loading, kissing bond, degradation above Tg, ageing and moisture |
| Mechanical fastening | composites, sandwich structures, detachable joints | drilling, washers, clamping pressure, tolerances, hole sealing | drilling-induced delamination, bearing damage, stress concentration, galvanic corrosion |
| Hybrid joint | bonded + riveted/bolted joint, safety-critical structures | assembly sequence, load sharing, tightening after curing | false sense of redundancy – the fastener may locally tear the laminate |
| Active brazing | ceramic–metal, ceramic–ceramic, vacuum and high-temperature components | active element Ti/Zr/Hf, vacuum/inert atmosphere, wetting, reaction layer | excessively thick brittle reaction layer, CTE-mismatch cracking, pores |
| Metallisation + brazing | Al₂O₃ with Kovar, feedthroughs, vacuum and electrical insulators | Mo–Mn or other metallisation, Ni interlayer, cleanliness, furnace cycle | leakage, metallisation delamination, residual edge stress |
| Diffusion bonding / HIP / SPS / TLP | ceramics, CMC, MMC, specialised metal–ceramic applications | temperature, pressure, time, roughness, interlayer, diffusion and reaction phases | incomplete contact, brittle intermetallic phases, deformation of thin components |
| Welding of thermoplastic composites | CF/PEEK, GF/PP, thermoplastic laminates | energy, time, pressure, temperature, consolidation, cooling under pressure | insufficient matrix fusion, polymer degradation, porosity, fibre displacement |
| Co-curing / co-bonding | composite parts manufactured in a mould or autoclave | prepreg preparation, tack layer, pressure/vacuum, thermal cycle | voids, peel-ply contamination, insufficient cure, dimensional instability |
| Application | Information to include in the procedure | Why it is critical |
|---|---|---|
| Surface | grinding, blasting, peel ply, degreasing, plasma/corona treatment, time between preparation and joining | surface energy and contamination often matter more than the inherent strength of the adhesive or braze alloy |
| Interlayer | adhesive/braze/film type, thickness, storage, expiry, orientation, active element | an excessively stiff or thick layer increases residual stresses or creep |
| Thermal cycle | ramp-up, dwell, atmosphere, pressure, cooling, maximum temperature relative to Tg or oxidation | rapid cooling and differential thermal expansion can create a crack without any visible surface indication |
| Clamping | clamping pressure, vacuum, part position, gap tolerance, stops, compensation for fixture compliance | non-uniform clamping pressure creates voids, adhesive squeeze-out or local ceramic-to-metal contact |
| Traceability | material batch, adhesive/braze batch, open time, moisture, operator, furnace/autoclave, cycle profile | for non-metals, traceability is often the only evidence that the joint was not degraded before inspection |
Most often caused by an excessive thermal gradient, unsuitable interlayer, abrupt stiffness transition or overly rapid cooling.
Occurs during drilling, local clamping, impact loading or peel stress in the joint.
The surfaces are in contact and the joint may appear continuous, but the chemical or mechanical bond is weak. Conventional visual inspection may not reveal it.
Typical causes are oxide, an incorrect atmosphere, low temperature, insufficient Ti/Zr activity or an unsuitable ceramic surface.
In adhesive bonding, these are associated with dispensing, entrapped air, moisture and clamping pressure; in brazing, with the atmosphere and outgassing.
CFRP in contact with aluminium can form a galvanic couple; control requires electrical isolation, sealing and surface protection.
| Method | Application | Limitation |
|---|---|---|
| Visual and dimensional inspection | squeeze-out, joint edge, position, edge voids, laminate damage, ceramic cracks | cannot detect kissing bonds or internal delamination |
| Ultrasonic testing / PAUT / C-scan | delamination, area disbonding, voids in the laminate and bonded joint | depends on probe coupling, geometry and the material’s acoustic attenuation |
| Thermography / lock-in thermography | planar defects in composites, disbonding, dry areas | sensitivity decreases with depth and with thick or highly conductive layers |
| RT / CT | pores, metallic inserts, geometry, internal voids, some ceramic cracks | expensive; poor contrast where layers have similar density |
| Leak test | vacuum feedthroughs, ceramic–metal joints, tanks, piping, battery and chemical applications | leak tightness does not automatically demonstrate adequate mechanical margin |
| Destructive coupon tests | lap-shear, peel, interlaminar shear, ceramic-joint shear, thermal cycle followed by testing | a coupon result is not directly the design strength of the finished component |
| Application | Examples of standards / documents | Use in this module |
|---|---|---|
| Adhesive-bonded joints | ISO 4587, EN 1465, ISO 11339, ISO 10365 | lap-shear and T-peel tests and designation of adhesive-joint failure modes |
| Ceramic tiles and adhesives | ISO 13007 series | classification of adhesives, properties and testing for construction ceramic applications |
| Advanced ceramic joints | ASTM C1469 | room-temperature shear strength of advanced-ceramic joints |
| Ceramic-matrix composites | ISO/TC 206, ISO 19634, ISO 19635 and related test methods | terminology, notation and testing of fine/technical ceramics and ceramic composites |
| Composite structures | ASTM D1002, ASTM D3165, ASTM D5868, ASTM D5379, customer specifications | application-specific testing of bonded, sandwich and shear properties of composites |
| Brazing and filler metals | EN ISO 17672, AWS A5.8 / A5.8M, internal BPS/BPQR | selection of braze alloy, flux or vacuum cycle; active brazing also requires customer-specific requirements to be added |
For cryogenic service, yield strength is not the governing property. Resistance to brittle fracture at design temperature, HAZ stability, correct weld metal, low hydrogen and complete traceability are decisive. The process window must be qualified at the required test temperature.
Has toughness of parent material, HAZ and weld metal been demonstrated for the design temperature, thickness and stress state?
Low plastic deformation and rapid crack propagation mean prevention must combine design, material and fabrication controls.
Coarse grain, local hard structures or inappropriate tempering can give lower toughness than the parent material.
It must provide the required toughness and compatible strength, thermal expansion and service-environment performance.
Heat input, interpass, hydrogen, cleaning, magnetism and sequence are controlled from the pWPS stage.
| Group | Typical service | Metallurgical advantage | Welding risk |
|---|---|---|---|
| Fine-grain C-Mn steels | Mild to moderately low temperatures within the guaranteed toughness range | Fine grain and controlled rolling lower the transition temperature. | Coarse-grained HAZ, hydrogen cracking and Charpy loss from excessive heat input. |
| Approximately 1.5–5 % Ni steels | Lower-temperature pressure vessels and piping | Nickel improves toughness and lowers the brittle-transition temperature. | Incorrect filler, dilution or thermal cycle can reduce toughness. |
| 9 % Ni steels | LNG and very low temperatures | Properly heat-treated martensitic base microstructure with high low-temperature toughness. | Mismatch with Ni-alloy weld metal, magnetic arc blow and stringent cleanliness requirements. |
| Austenitic stainless steels | Cryogenic piping, inner vessels and components | No ferritic-martensitic ductile-to-brittle transition and high cryogenic toughness. | Hot cracking, distortion, contamination and incorrect ferrite/chemistry in weld metal. |
| Control | Purpose | IWE note |
|---|---|---|
| Charpy V | Demonstrates absorbed energy and fracture appearance at the specified temperature. | Specimen location and notch orientation are as important as the numerical result. |
| CTOD / fracture mechanics | For critical thickness and high consequence, assesses resistance to crack extension. | Required only where specified by design, contract or product standard. |
| Hardness and macro | Reveals local hard zones, lack of fusion, geometry and HAZ condition. | Limits must be material- and specification-specific, not a universal number. |
| UT/RT plus surface NDT | Volumetric and surface imperfections can act as sharp notches. | Sensitivity and acceptance follow thickness, geometry and consequence of failure. |
| PMI and traceability | Confirms alloy identity of parent and filler materials. | PMI does not replace certification or full chemical analysis, but is an effective mix-up barrier. |
For 9 % Ni and similarly critical systems, production cannot be released with current and voltage ranges alone. The package should also control magnetism, bead technique, maximum interpass, filler handling and exact test-specimen location.
Explain why a weld that passes tensile testing can fail at −100 °C. The answer should connect transition temperature, notch, HAZ, thickness, dynamic loading, Charpy/CTOD and filler-metal type.
Cast-iron weldability is governed by carbon morphology, matrix, thickness, ageing and service contamination. The critical mechanisms are hard brittle structures at the fusion boundary and the inability of the casting to absorb shrinkage stress. A successful repair therefore starts with diagnosis, not electrode selection.
Is repair technically and safely permissible, is the cast-iron type known, and has the cause of the original damage been removed?
Rapid cooling can bind carbon as cementite and create an extremely hard, brittle and unmachinable zone.
Carbon dissolved in austenite can transform to a hard HAZ during cooling and initiate cracking.
A steep thermal gradient in a rigid casting produces stress that a low-ductility material cannot relax plastically.
Oil, graphite, corrosion products and service fluids in pores cause porosity, unstable arc and poor bonding.
| Cast-iron type | Carbon form | Welding behaviour | Preferred strategy |
|---|---|---|---|
| Grey cast iron | Flake graphite | Low ductility and strong notch effect; rapid cooling promotes white iron and martensite. | Either controlled hot welding with slow cooling, or a cold-repair sequence with short beads and Ni filler. |
| Ductile iron | Spheroidal graphite | Higher ductility, but the HAZ can lose its favourable matrix and develop a hard transition zone. | Minimise dilution and thermal gradient; qualify thermal cycle and machinability. |
| Malleable iron | Temper carbon | Properties depend on the original heat treatment, which local welding can impair. | Assess repair individually, commonly using Ni weld metal and low heat input. |
| White / highly alloyed cast iron | Carbides and cementitic matrix | Very hard and brittle; conventional fusion welding is high risk. | Mechanical repair, brazing, an insert or a specialist procedure after testing is often preferable. |
| Approach | Characteristics | Benefit | Risk / condition |
|---|---|---|---|
| Hot welding | Uniform high preheat of the whole component, temperature maintenance, low gradients and very slow cooling. | Lower residual stress and less tendency to form a hard white-iron layer. | Difficult handling, safety, distortion and controlled heating of a large casting. |
| Cold repair | Minimum local heat input, very short beads, skip sequence, peening where qualified, and complete cooling between increments. | Suitable for large components that cannot be fully preheated. | Higher local stress; success depends on discipline, crack-end treatment and low dilution. |
| Braze welding / brazing | Parent material is melted minimally or not at all; bonding is by wetting with filler metal. | Lower risk of hard HAZ and cracking. | Lower temperature and often lower structural capacity; requires suitable geometry and cleanliness. |
| Mechanical repair plus sealing | Stitching, locks, inserts or bolted elements without a fusion cycle. | Useful for sensitive or irreplaceable castings. | Must be structurally and leak-tightness designed; not automatically equivalent to the original component. |
In a cold repair, each bead and its heat input must be sufficiently limited to prevent neighbouring areas accumulating an uncontrolled thermal cycle. Exact bead length and temperature must be established for the specific component.
Compare hot and cold welding of grey cast iron. Explain white iron, martensitic HAZ, dilution, Ni/Ni-Fe fillers, short beads, slow cooling and crack inspection.
Aluminium does not merely require “more current”. High thermal conductivity, low melting temperature, a refractory oxide film, high hydrogen solubility in liquid metal and the thermal-cycle sensitivity of heat-treatable alloys create a demanding process window.
Are the exact alloy and temper known, and is the design based on weld and HAZ properties rather than only the catalogue strength of the parent material?
It must be removed in a controlled manner to prevent poor fusion, inclusions and unstable geometry.
Moisture, organic contamination, wire and shielding conditions are the principal gas sources.
Strain-hardened and precipitation-hardened alloys locally lose their strengthening mechanism.
Composition, dilution, solidification, joint geometry, restraint and filler selection govern the risk.
| Series / strengthening principle | Typical welding behaviour | Main risk | Technology note |
|---|---|---|---|
| 1xxx — commercially pure Al | Very good corrosion resistance and weldability, with high thermal conductivity. | Porosity, distortion and low strength. | Rigorous oxide removal, stable shielding and sufficient power-source capability. |
| 3xxx and 5xxx — strain hardened | Part of the work-hardening is lost in weld and HAZ; 5xxx alloys combine useful strength and corrosion resistance. | HAZ softening; Mg-rich alloys may be sensitive to unsuitable prolonged temperature exposure. | Structural calculations must use welded-zone properties, not parent-material temper alone. |
| 6xxx — precipitation-hardened Al-Mg-Si | Very common extrusions; weldable but with marked HAZ softening from dissolution/coarsening of precipitates. | Strength reduction near welds, hot cracking in unsuitable combinations and distortion. | Choice between 4xxx and 5xxx filler depends on strength, cracking, anodising and service. |
| 2xxx and 7xxx — high-strength heat-treatable | Many grades have limited fusion weldability or require a special route. | Hot cracking, porosity, property loss and corrosion sensitivity. | Verify the exact alloy; FSW, mechanical joining or a specially qualified process may be preferable. |
| Cast aluminium alloys | Weldability strongly depends on Si, casting porosity and heat-treatment condition. | Gas and contamination released from the casting, cracking and machinability variation. | Repair requires cleaning, component-specific preheat and representative qualification. |
| Criterion | 4xxx Al-Si | 5xxx Al-Mg | Note |
|---|---|---|---|
| Hot-cracking resistance | Often very good because of silicon and fluidity. | Good in suitable combinations, but depends on Mg and dilution. | Use manufacturer compatibility data and EN ISO 18273, not merely matching the alloy series. |
| Weld-metal strength | Usually lower than Mg-based filler metals. | Often higher for 5xxx/6xxx applications. | The design requirement and actual as-welded properties govern. |
| Colour after anodising | Can differ markedly from the parent material. | Usually gives a closer colour match. | Appearance may be a customer essential requirement. |
| Elevated-temperature service | Some Al-Si combinations are more suitable. | Mg-rich weld metals can have restrictions under prolonged elevated temperature. | Verify service temperature and the specific filler classification. |
A stainless-steel brush dedicated to aluminium is used only after solvent or chemical degreasing. Brushing a greasy surface drives contamination into the soft metal and increases porosity risk.
Explain why a 6082-T6 weld can look visually acceptable yet fail the design resistance. Address HAZ softening, precipitates, 4xxx/5xxx filler choice, porosity, EN ISO 10042 and EN 1999.
These materials do not form one technology group. Copper removes heat rapidly, nickel demands strict control of cleanliness and solidification, and titanium reacts aggressively with the atmosphere when hot. Their common requirement is exact alloy identification and a qualified process regime.
Is the alloy unambiguously identified, and is the dominant failure mechanism known: inadequate heat, hot cracking, contamination or corrosion incompatibility?
Power and preheat must overcome rapid heat extraction without excessive overheating and distortion.
Trace contamination, unsuitable filler and a large pool promote segregation and hot cracking.
Shielding must protect not just the arc but the root and cooling weld until a safe temperature.
Connections to steel or another alloy require dilution, galvanic and thermal-expansion assessment.
| Material | Dominant property | Typical processes | Critical controls |
|---|---|---|---|
| Copper and Cu alloys | Extremely high heat extraction; some alloys contain volatile or embrittling elements. | GTAW, GMAW, plasma, brazing; high power and preheat for heavier sections. | Cleanliness, power, preheat, interpass, shielding, alloy chemistry and porosity/cracking risk. |
| Nickel and Ni alloys | High corrosion/temperature resistance, but a viscous pool and sensitivity to contamination and hot cracking. | GTAW, GMAW, MMA and SAW depending on alloy and product. | Very low S/P/Pb/Zn contamination, correct filler, heat-input control, broad cleaning and complete slag removal. |
| Titanium and Ti alloys | Extreme affinity for oxygen, nitrogen and hydrogen at elevated temperature. | GTAW/plasma with inert shielding, laser/EB; chambers or trailing shields. | Surface colour, root and trailing shielding, gas purity/dew point, dedicated tools and zero ferrous contamination. |
| Alloy family | Weldability note | Typical risk |
|---|---|---|
| Deoxidised copper | Requires high power and often preheat, especially in heavy section. | Cold pool, incomplete fusion, porosity and severe heat extraction. |
| Cu-Zn brasses | Zinc evaporates and oxidises; fusion welding is difficult. | Porosity, ZnO fumes, zinc loss and cracking; brazing is often preferred. |
| Cu-Sn bronzes | Many are weldable, but behaviour depends on Sn and casting quality. | Segregation, porosity and hot cracking. |
| Cu-Al bronzes | Good strength and corrosion resistance; aluminium oxide requires cleanliness and suitable technique. | Oxide inclusions, unsuitable microstructure and corrosion sensitivity after a poor thermal cycle. |
| Cu-Ni | Generally good weldability with suitable filler and cleanliness. | Fe/S contamination, porosity, poor shielding and galvanic considerations. |
| Post-weld surface condition | Interpretation | Action |
|---|---|---|
| Metallic silver to very light tint | Good inert protection within the qualified process. | Continue to WPS and maintain cleanliness. |
| Straw / light blue tint | Increased oxidation; acceptability depends on specification and qualification. | Check flow, trailing shield, root, post-flow and temperature at loss of protection. |
| Dark blue, grey, white or powdery surface | Severe O/N/H contamination and probably an embrittled layer. | Stop production, remove affected metal by an approved route and revalidate shielding. |
For titanium, protection does not end when the arc is extinguished. Post-flow, trailing shield and root purge must remain effective until the weld and wire end are below the temperature at which unacceptable contamination occurs.
Compare the purpose of preheating copper with the purpose of a trailing shield for titanium. Copper is primarily a heat-flow problem; titanium is a chemical-reactivity problem involving hot metal and O, N and H.
A dissimilar joint is a material system in its own right. Weld metal is mixed from three sources, the two interfaces develop different microstructures, and differential expansion, diffusion and corrosion can dominate over static strength during service.
Has stability of the mixed zone and both interfaces been demonstrated for the full thermal, corrosive and mechanical life?
Weld chemistry is controlled by filler and dilution from both parent materials.
Each side may need different preheat, maximum interpass and thermal history.
Expansion mismatch, galvanic potential and diffusion appear during operation.
Buttering, an interlayer or a bimetal component often gives a safer interface than direct fusion welding.
| Mechanism | Effect | Example risk | Control |
|---|---|---|---|
| Dilution | Mixing of both parent materials and filler changes local chemistry. | Martensite in carbon-steel/stainless joints; unsuitable ferrite or brittle intermetallic phases. | Mixing-line assessment, buffer layer, correct filler, penetration limitation and representative WPQR. |
| Differential thermal expansion | Heating and cooling generate cyclic shear and normal stress. | Austenitic stainless attached to ferritic steel in thermal cycling. | More flexible geometry, transition piece, Ni-base filler and controlled thermal cycle. |
| Carbon migration | At long-term high temperature, carbon diffuses across the interface. | Decarburised soft zone on the ferritic side and carbide-rich zone in the weld. | Ni interlayer, appropriate PWHT, service-temperature limitation and metallurgical assessment. |
| Galvanic coupling | Potential difference accelerates corrosion of the less noble material. | Stainless directly joined to carbon steel in a conductive electrolyte. | Electrical isolation, coating, drainage, area-ratio control, material selection and service protection. |
| Brittle intermetallic phases | Some material pairs have very limited mutual solubility. | Al–steel, Ti–steel or Cu–Al under excessive fusion mixing. | Brazing, pressure/friction processes, explosion-clad transitions, interlayers or very low dilution. |
| Combination | Common strategy | Critical issue |
|---|---|---|
| Carbon steel ↔ austenitic stainless | 309L/309Mo or Ni-base filler depending on temperature, corrosion and PWHT; buttering in some cases. | Martensitic region on ferritic side, weld ferrite, corrosion and PWHT compatibility. |
| CrMo steel ↔ austenitic stainless | Ni-base filler or qualified transition layer; often buttering + PWHT + final weld as separate stages. | Carbon migration, creep, expansion mismatch and thermal history. |
| Stainless ↔ duplex | Over-alloyed duplex or Ni filler depending on service. | Duplex phase balance, dilution, interpass and corrosion resistance. |
| Copper ↔ steel | Ni or Cu-Ni interlayer, brazing or a specialist process. | Large conductivity difference, copper penetration into steel and hot cracking. |
| Aluminium ↔ steel | Mechanical joining, brazing, CMT/laser with very low mixing, or a bimetal transition. | Growth of Fe-Al intermetallic layer; layer thickness governs brittleness. |
| Titanium ↔ steel | Bimetal transition, diffusion/friction/explosion joining or a suitable interlayer. | Brittle Fe-Ti phases; direct fusion welding is generally unsuitable. |
The first buttering layer is often qualified and inspected separately because it has the highest dilution and the most critical microstructure. The final layer does not necessarily represent the original interface condition.
Design a P91-to-austenitic-stainless joint. Address Ni-base filler/buttering, PWHT sequence, carbon migration, creep, expansion mismatch, hardness and repair qualification.
A formula is valid only for the mechanical model from which it was derived. In weldments, nominal stress, structural stress, local notch, plasticity and residual stress must be distinguished. The IWE must know where simple statics ends and detailed assessment begins.
Does the selected mechanical model represent the actual force flow, stiffness, geometry and failure mechanism to be prevented?
The same force creates different stress depending on area, geometry and eccentricity.
Forces divide according to relative member and joint stiffness, not merely weld length.
Above yield, plastic deformation develops and a simple Hookean model no longer suffices.
Static yielding, fatigue, brittle fracture, buckling and creep require different criteria.
| Quantity | Relation | Meaning | Typical interpretation error |
|---|---|---|---|
| Normal stress | σ = F / A | Average tension/compression stress on the effective area. | Using gross area while ignoring holes, notches, root condition or actual effective weld throat. |
| Shear stress | τ = V / A | Average shear; welds are often assessed on the effective throat plane. | Assuming uniform distribution in an eccentric or short weld group. |
| Strain | ε = ΔL / L₀ | Relative change in length; linked to stress through E in the elastic range. | Confusing strain with displacement and ignoring local plasticity. |
| Bending stress | σ = M·y / I | Linear elastic stress distribution through depth. | Applying it to a detail with significant plasticity, notch or local buckling without further assessment. |
| Torsion | τ = T·r / J | Shear stress in circular sections; open thin-walled profiles behave more complexly. | Applying the solid-round formula to a non-circular or open section. |
| Von Mises | σᵥ = √(σ² + 3τ²) | Equivalent stress for a simplified combination of normal and shear stress. | Using it as a universal criterion for brittle fracture, fatigue or lamellar tearing. |
| Phenomenon | Mechanism | Design consequence |
|---|---|---|
| Eccentricity | Load does not pass through the centroid of the weld group. | A secondary moment and non-uniform stress along the welds are generated. |
| Stiffness discontinuity | A doubler, stiffener or thicker member changes force flow. | Local bending and stress concentration at the termination. |
| Geometrical imperfection | Misalignment, angular distortion, undercut or a sharp root. | Higher local stress and faster fatigue or fracture initiation. |
| Residual stress | Weld shrinkage creates tensile stress without external load. | Mean stress and superposition require specific treatment in fatigue and fracture. |
| Multiaxial constraint | A rigid detail prevents transverse contraction. | Plastic reserve is reduced and notch/crack sensitivity increases. |
Before calculating, draw the load path through the member, weld root, throat and toe. If the force path is ambiguous, entering numbers into a formula will not create a valid model.
Explain the difference between nominal, structural and local notch stress, and why their corresponding S–N curves or acceptance criteria must not be mixed.
A good joint type carries load directly, permits stable welding and inspection, and minimises notch severity, weld volume, distortion and corrosion traps. Adding a symbol without understanding force flow leads to over-designed or unsafe details.
Is the load path through the joint unambiguous, and do root, toe, parent material and HAZ provide the required resistance and inspectability?
The best detail transfers load without unnecessary eccentricity and local bending.
They are natural notches; significance depends on load direction, penetration and fatigue.
Torch space, cleaning, position and NDT are design inputs, not downstream production problems.
Crevices, pockets and inaccessible roots can govern life even when static resistance is adequate.
| Joint | Load path and advantages | Risks | Design recommendation |
|---|---|---|---|
| Butt joint | With full penetration, load can pass nearly axially and a smooth profile is possible. | Preparation, root control, misalignment, weld volume and penetration verification. | Prefer for fatigue- and pressure-critical joints where access and inspection are feasible. |
| T-joint with fillet welds | Simple manufacture and shear transfer through a weld group. | Eccentricity, root notch, lamellar tearing and stiffener termination. | Design actual effective length, access, soft termination and rolling-direction considerations. |
| Lap joint | Simple assembly and tolerance of less accurate edges. | Eccentric load path, crevice corrosion, fatigue at ends and fluid retention. | Avoid for critical fatigue/corrosion unless specially detailed and sealed. |
| Corner joint | Useful for boxes, vessels and frames; may be open or full-penetration. | Difficult root inspection, burn-through, distortion and inaccessible inner face. | Specify required penetration and inspection, not merely a fillet-weld symbol. |
| Cruciform joint | Compact transfer of forces from several directions. | High restraint, triaxiality, lamellar tearing and weld accumulation. | Use smooth transitions, Z-quality where needed and a low-restraint sequence. |
| Edge/flange joint | Useful for sheet metal and edge closure. | Limited capacity, crevice corrosion and gap sensitivity. | Use only for a defined function; do not assume equivalence to a structural full-penetration butt joint. |
| Plug/slot weld | Transfers shear through an overlap and can replace spots in thicker parts. | Incomplete filling, cracking, high restraint and difficult inspection. | Define hole, preparation, layer sequence, filling and acceptance. |
| Concept | Load transfer | Inspection | Note |
|---|---|---|---|
| Full penetration | Effective section can equal member thickness. | Root, misalignment and volumetric NDT as applicable. | It must be achievable by process; a symbol alone does not create penetration. |
| Partial penetration | Load is carried by a defined effective depth. | Macro/WPQR and production control of fusion depth. | The designer must state effective depth or required size, not an ambiguous “deep weld”. |
| Fillet weld | Transfer through effective throat and length, often under combined stress. | Throat a, length, profile, root and terminations. | Oversized welds increase heat input, distortion and cost without proportional benefit. |
| Contact/non-structural weld | The weld provides sealing, location or manufacturing function. | Functional test according to purpose. | The drawing must make clear that it is not a load-carrying joint. |
If a weld can only be reached using an extreme torch angle, excessive stick-out or without seeing the pool, the problem is the joint design, not merely welder skill.
Compare a full-penetration butt joint with a double-fillet T-joint under fatigue loading. Discuss force flow, root notch, NDT, weld volume, distortion and detail category.
Joint preparation is the interface between design and welding technology. It controls arc access, root stability, filler volume, number of runs, distortion, NDT feasibility and sensitivity to assembly tolerance.
Is the selected preparation robust over the full production range of root gap, root face, offset and welding position?
Angle, gap and root face determine whether energy reaches the root.
Every unnecessary square millimetre multiplies into length, filler, time and distortion.
The process must tolerate real part and fixture variation without repeated unplanned repair.
Geometry should permit VT/NDT, root removal and repair where required.
| Part | Scope | Application | Important limitation |
|---|---|---|---|
| EN ISO 9692-1 | MMA, gas-shielded arc, gas, TIG and beam welding of steels. | Joint preparations for butt and fillet joints, mainly full penetration. | It is not automatically a WPS; dimensions must suit process, position and qualification. |
| EN ISO 9692-2 | Submerged-arc welding of steels. | Preparations suited to SAW and its characteristic penetration. | Process variants, number of wires and position may require a different detail. |
| EN ISO 9692-3 | MIG and TIG welding of aluminium and its alloys. | Geometries reflect oxide, high fluidity and aluminium process behaviour. | Must be coordinated with EN ISO 15614-2 and real gap tolerance. |
| EN ISO 9692-4 | Clad steels. | Preparation of load-bearing substrate, transition layers and cladding. | Sequence and dilution are critical; separate technological stages are often qualified. |
| Parameter | If too small | If too large | What determines it |
|---|---|---|---|
| Groove angle | Poor access, incomplete penetration, slag trapped between sidewall and bead. | Excess weld volume, time, distortion and filler use. | Process, position, electrode/wire diameter, arc manipulation and required penetration. |
| Root gap | Incomplete penetration and poor root fusion. | Burn-through, excessive penetration, unstable root and excess fill volume. | Process, backing, position, automation and fixture capability. |
| Root face | Burn-through and unstable root. | Insufficient penetration and cold root. | Current density, process, thickness and single-/double-sided welding. |
| U/J radius | A sharp transition restricts access and increases local fill volume. | Expensive machining and larger volume. | Thickness, machining capability, automation and position. |
| Misalignment | — | Increases local bending, root notch severity and weld volume. | Part tolerances, fixture, tacks, distortion and EN ISO 13920. |
For automated welding, a narrow and controlled gap range is often preferable to a “universal” broad WPS window. Wide tolerance without adaptive control increases root variation and repair demand.
What happens in a single-V joint if root face increases while root gap decreases? Explain penetration, energy demand, root-bead technique and incomplete-penetration risk.
The standard provides general tolerances for weldments using four classes for linear/angular dimensions and four classes for shape/position. Class selection follows function, not a desire for “maximum precision”, and applies only where the drawing does not state an individual requirement.
Are the selected classes functionally justified, achievable by the fabrication process and unambiguously measurable in a defined product condition?
The actual limit is read from the table for the class and dimensional range.
Assembly- or safety-critical features need individual tolerances.
Datums, temperature, set-up, instrument and uncertainty affect the verdict.
A fixture should create the correct released and cooled condition, not merely freeze the part during welding.
| Tolerance group | Classes | Coverage | Selection |
|---|---|---|---|
| Linear and angular dimensions | A, B, C, D | Linear dimensions and angular deviations of welded structures. | A is generally tighter and D looser; the actual limit depends on the dimensional range in the standard table. |
| Shape and position | E, F, G, H | Straightness, flatness, parallelism and related geometrical deviations. | E is generally tighter and H looser; select from function and process capability. |
| Individual tolerance | Value on drawing | A critical dimension or geometry with a special requirement. | The individual tolerance overrides the general class for that feature. |
| Product standard / contract | Specific requirement | May define tighter or different tolerances and measurement method. | Coordinate with EN ISO 13920 and state clearly on drawing or specification. |
| Conflict | Why it occurs | Correct response |
|---|---|---|
| A very tight class is specified for the entire weldment | The class is copied without analysing function and cost. | Individually tolerance critical dimensions and use a realistic general class elsewhere. |
| Measurement immediately after welding differs from cold measurement | Thermal expansion, fixture release and residual stress. | Specify condition, temperature, timing and whether measured restrained or free. |
| Part tolerances accumulate in assembly | Cutting, forming, fit-up and shrinkage stack together. | Tolerance analysis, in-process measurement points and controlled compensation. |
| Straightening damages properties | Uncontrolled flame or local plastic strain. | Approved straightening procedure with temperature limits, measurement and reinspection. |
| Inspection uses an unsuitable datum | The product is not set up as in functional service. | Measurement plan with datums, fixture, instrument and measurement uncertainty. |
On a long welded frame, diagonals alone are insufficient. Define the datum plane, point elevations, local flatness, twist and functional interfaces; two different geometries can have identical diagonals.
Explain the distinction between classes A–D and E–H, and why “to ISO 13920” without selected classes and functional tolerances is incomplete.
Static weld verification must connect the analytical model with the geometry, process and inspection actually delivered. The welding coordinator does not replace the structural designer, but must verify that the design assumptions are manufacturable and demonstrable.
Does the analytical model reflect the real force path, effective section and quality that production can repeatedly achieve?
Separate axial force, shear, bending and torsion, including eccentricity.
Use effective throat and length—not only the visible bead size.
Check connected plates, notches, local flexibility and through-thickness direction.
WPS, WPQR, quality level and NDT must support the design assumption.
| Model element | Engineering meaning | Frequent error |
|---|---|---|
| Effective throat a | The minimum design throat through which stresses are transferred. For a fillet weld it must not be confused with leg length z. | Calculating from nominal leg size without considering actual throat, penetration and profile. |
| Effective length leff | The part capable of carrying load after allowing for starts, stops, craters and non-uniform force transfer. | Counting the full geometric length including ineffective ends. |
| Weld group | A system of line elements with throat area, centroid and area/polar properties. | Checking each weld in isolation although eccentricity acts on the entire group. |
| Butt weld | A demonstrated complete-penetration weld may be modelled as continuity of parent material where the governing design code permits. | Assuming complete penetration without drawing, WPS, qualification and inspection requirements. |
| Configuration | Dominant effect | IWE/IWT verification |
|---|---|---|
| Longitudinal fillet welds | Predominantly throat shear; load distribution near ends can be non-uniform. | Effective length, force introduction into the plate, end returns and deformation of the connected element. |
| Transverse fillet welds | Combined normal and shear components in the throat. | Throat orientation, toe notch, local stiffness and possible parent-metal failure. |
| Eccentric bracket | Direct force plus moment; the most remote weld-group segment is usually critical. | Actual line of action, plate flexibility and whether the joint behaves as assumed. |
| Circumferential pipe weld | Tension/compression, shear, bending or torsion depending on the action combination. | Full circumference, interruptions, root, ovality, inaccessible areas and NDT. |
| Intermittent weld | Segmented load transfer with higher local concentration and corrosion exposure. | Whether it is permitted, minimum length/pitch, sealing requirements and fatigue exposure. |
| Execution | Appropriate use | Required evidence |
|---|---|---|
| Complete penetration | High static resistance, leak tightness, continuous force flow or inspectable root quality. | Unambiguous symbol/detail, qualified WPS/WPQR, defined root technique and NDT. |
| Partial penetration | The design deliberately uses a defined effective penetration depth and the code permits that model. | Effective penetration must be specified, qualified and verifiable—not merely assumed by production. |
| Fillet weld | Economical connection for many static details where force flow can be arranged appropriately. | Throat/leg size, length, continuity, ends, profile and quality criteria. |
Draw the force-flow arrows through the joint before selecting weld type, location and size. A weld placed away from the force path introduces a moment that is often missed in the initial concept.
Explain the difference between fillet-weld leg length z, effective throat a and effective length. How would you assess an eccentrically loaded weld group, and which manufacturing assumptions must be demonstrated by WPS/NDT?
A welded detail must carry load while permitting stable preparation, torch positioning, welding sequence, inspection and protection throughout its life. A design that ignores production transfers uncontrolled risk to the welder and examiner.
Can the critical property be produced by the selected process and verified by inspection without workshop improvisation?
Minimise eccentricity and abrupt stiffness changes.
Provide angle, stand-off, cleaning, root and manipulation space.
Use the smallest safe and process-stable weld that fulfils the function.
Design NDT and dimensional verification together with the joint.
| Layer | Design question | Manufacturing consequence |
|---|---|---|
| Force flow | Does the force pass directly through the joint, or does eccentricity create secondary bending? | Place welds near the natural load path; avoid unassessed one-sided connections. |
| Stiffness | Does section or stiffness change abruptly? | Use smooth transitions, appropriate stiffener terminations and avoid hard spots. |
| Access | Can the torch/electrode reach the root with the required angle and stand-off? | Define assembly sequence, clearances, welding position and interpass cleaning access. |
| Distortion | Are weld volume and location balanced about the neutral axis? | Minimise volume, balance welds, plan sequence and specify achievable tolerances. |
| Inspection and service | Can the critical area be examined, repaired and protected against corrosion? | Provide probe access, suitable surfaces, drainage and future inspection access. |
| Detail | Risk | Professional solution |
|---|---|---|
| Stiffener terminating on a flange | High notch stress at the end, particularly under cyclic loading. | Shaped termination, separation from the critical zone, smooth transition or a classified fatigue detail. |
| Lap joint | Crevice corrosion, eccentricity and an uncontrolled internal gap. | Assess sealing/perimeter weld, drainage and coating; consider whether a butt joint is better. |
| Doubler plate | Abrupt stiffness change, multiple notches and closed cavities. | Rounded corners, defined terminations, inspection beneath the plate and an explicit load path. |
| Tubular node | Complex local stress, restricted access and variable root gap. | CNC profiling, assembly template, qualification of a representative detail and geometry-appropriate UT/PAUT. |
| Cruciform/T-joint in thick plate | Through-thickness tension and lamellar tearing. | Z-quality material, detail change, buttering, inclusion/sulphur control and hydrogen management. |
| Closed section | Inaccessible root, pressure during galvanizing, condensation and inaccessible coating. | Vent/drain holes, defined closure and coordinated surface-protection sequence. |
| Poor requirement | Why it is harmful | Better question |
|---|---|---|
| “Weld all around everywhere” | Adds volume, distortion and time, and can create sealed cavities. | Is the purpose strength, leak tightness, corrosion sealing or only local load transfer? |
| Oversized fillet weld | Adds heat without proportional resistance and may shift failure into the plate. | What effective throat is required and what is the smallest stable production size? |
| Inaccessible complete penetration | Demands a quality that cannot be made or examined. | Which root technique and assembly sequence permit qualified execution? |
| Sharp doubler corners | Create stress concentration and difficult bead progression. | Which radius and termination fit the force path and fatigue classification? |
Place a “virtual torch” and a “virtual probe” in the 3D model and travel the full weld, including start, stop and root. A collision found in production will always cost more.
Develop a T-joint between thick plates loaded through the flange thickness. Which issues must be addressed for force flow, lamellar tearing, preparation, welding sequence, distortion and NDT?
The welding process may be similar, while the evidence of conformity is fundamentally different in each sector. A professional welding coordinator must distinguish legislation, design code, product standard, welding-quality system and project specification.
Is the hierarchy of legal, design, manufacturing and customer requirements clear for the actual product, including responsible parties?
Identify product, category/class and consequence of failure first.
Separate design, execution, qualification, NDT and conformity assessment.
The ITP must capture customer/third-party intervention and hold points.
Records are technical evidence, not an administrative add-on after production.
| Application | Typical framework | What fundamentally changes welding control |
|---|---|---|
| Steel and aluminium structural products | EN 1090-2 / EN 1090-3, Eurocodes, EN ISO 3834 | Execution class, geometrical tolerances, product-specific CE/DoP duties, weld identification and production records. |
| Unfired pressure vessels | PED 2014/68/EU, EN 13445 or another accepted code | Equipment category, notified-body involvement, permanent joining, material appraisal and pressure testing. |
| Industrial piping | PED, EN 13480 and/or sector code | Piping class, line class, isometrics, weld map, cleanliness, internal root control and pressure testing. |
| Bridges | EN 1993-2, EN 1090-2 and project specification | Fatigue, execution classes, classified details, deck geometry, extensive NDT and repair tracking. |
| Cranes and dynamic machinery | EN 13001 / EN 1993-1-9 plus product standards | Load spectrum, FAT details, critical nodes, toe/root quality and in-service examination. |
| Rail, offshore, power and nuclear products | Sector standards, contract codes and surveillance | Additional qualifications, special materials, third-party surveillance, cleanliness, full traceability and strict change control. |
| Topic | Incorrect approach | Correct approach |
|---|---|---|
| Design code vs execution standard | Assume the Eurocode or calculation code contains all manufacturing requirements. | Build a matrix covering design – product – execution – quality – NDT – legislation. |
| EN ISO 3834 | Treat it as product certification or a replacement for the product standard. | Use it as the fusion-welding quality system required by product/contract rules. |
| EN ISO 5817 quality level | Apply one level to the whole product without functional or NDT context. | Set acceptance from product standard, detail, loading and the specific examination method. |
| WPS qualification | Use a WPQR from another sector without checking range and additional requirements. | Verify process, material group, thickness/diameter, position, heat treatment, impact properties and sector additions. |
| Production change | Approve it verbally in the workshop. | Assess technical/regulatory impact, revise documents and obtain required approval before implementation. |
| Level | Examples | Control question |
|---|---|---|
| Legal/contractual | Directive or regulation, purchase order, customer specification. | Who is responsible for conformity assessment and which requirements are mandatory? |
| Design | Calculation code, actions, material, detail category and drawings. | Are manufacturing assumptions transferred unambiguously into drawings/specifications? |
| Production | WPS, work instruction, tack/sequence plan, PWHT and ITP. | Does the shop floor have the correct approved revision? |
| Records | Material certificates, weld log, NDT, calibration, NCR and repairs. | Can the manufacturer prove who made what, with which equipment/procedure and result? |
| Final | Dossier, declaration, marking, instructions and pressure/functional test. | Is the package complete, consistent and approved before dispatch? |
Create a one-page compliance map at project start: product → legislation → design code → execution standard → ISO 3834 → qualifications → ITP → dossier. Every gap in the map eventually becomes an NCR or delay.
Compare welding control for a pressure vessel under PED/EN 13445 with a steel bridge under EN 1090-2/EN 1993-2. Which elements remain common and which requirements fundamentally differ?
Aluminium combines low density with high thermal conductivity and expansion, a stable oxide and strong dependence on alloy and temper. Professional design must use the properties of the weld and HAZ, not only those of the parent material.
Are design properties, filler, WPS, cleanliness and tolerances based on the exact alloy and temper?
Welding can locally remove precipitation or strain hardening.
Oxide, water and hydrocarbons directly affect fusion and porosity.
High expansion requires minimum weld volume and a planned sequence.
Metal contact, coating, crevices and drainage begin at detail design.
| Property | Structural consequence | Welding consequence |
|---|---|---|
| Low elastic modulus (~one third of steel) | Greater deflection, local buckling and sensitivity of slender parts. | Fixtures must control geometry without excessive force; elastic spring-back may appear after release. |
| High thermal expansion | Greater shrinkage, angular distortion and dimensional movement during welding. | Minimise weld volume, use symmetry, planned sequence and accurate fit-up. |
| High thermal conductivity | Rapid heat removal and changing conditions from cold start to a heat-soaked assembly. | Stable starts, suitable power, controlled travel speed and interpass-temperature management. |
| Al₂O₃ oxide | The oxide melts at a much higher temperature than the base metal. | Mechanical/chemical cleaning shortly before welding, Al-only tools and correct gas shielding. |
| Heat-affected softening | In precipitation-hardened or strain-hardened alloys the HAZ may govern resistance. | Design must use reduced properties appropriate to alloy, temper and distance from the weld. |
| Hydrogen sensitivity | Hydrogen is much more soluble in liquid than solid aluminium, promoting porosity. | Dry gas, clean filler and surfaces, and exclusion of condensation, oil and moisture. |
| Decision | What to verify | Risk of a wrong choice |
|---|---|---|
| Alloy group | EN AW designation, chemistry, weldability and hot-cracking sensitivity. | Cracking, insufficient strength, corrosion or invalid qualification. |
| Temper | O/H/T condition, extrusion/rolling direction and expected softened zone. | Using parent-metal strength where welding has removed the temper effect. |
| Filler | Compatibility, strength, ductility, hot cracking, anodised colour and service temperature. | A weld that is feasible but fails structural, corrosion or appearance requirements. |
| Thickness and profile | Thin extrusions, massive nodes, unequal heat capacity and fit-up tolerance. | Burn-through in the thin wall, cold fusion on the thick member or excessive distortion. |
| Dissimilar-metal contact | Galvanic potential, electrolyte, cathode/anode area ratio and insulating barrier. | Rapid galvanic attack of aluminium beside steel, stainless steel or copper. |
| Phenomenon | Typical cause | Control |
|---|---|---|
| Porosity | Moisture, oxide/hydrocarbon contamination, dirty wire, gas leakage or turbulence. | Clean and dry surfaces, correct flow/nozzle, hose checks, filler storage and removal of condensation. |
| Hot cracking | Adverse alloy/filler combination, high restraint, poor pool shape or crater control. | Alloy–filler assessment, suitable geometry, crater filling, reduced restraint and qualification. |
| Oxide films/lack of fusion | Inadequate cleaning, poor torch angle, low energy or unsuitable manipulation. | Cleaning shortly before welding, appropriate arc characteristics, access and a stable process. |
| Distortion | Large weld volume, one-sided welding, poor sequence and high expansion. | Preset, balanced welding, back-step/skip sequence, segmentation, fixtures and controlled release. |
| Surface damage | Steel tools, ferrous contamination, arc strike or rough handling. | Dedicated tools, managed protective film, clean supports and controlled repair. |
For every aluminium joint write down four items: alloy – temper – filler – HAZ design property. If one is missing, the technical decision is incomplete.
Why can weldable EN AW-6082-T6 have substantially reduced local strength after welding? Explain HAZ behaviour, heat input, filler selection, distortion and EN 1090-3 production requirements.
ISO 14731 defines quality-related tasks and responsibilities in welding coordination. In practice, it is the job description for the person or team ensuring that welding is performed in accordance with customer requirements, drawings, standards, WPS/WPQR documentation and the quality system.
Key principle: the coordinator must be competent for the tasks formally assigned by the manufacturer. A qualification title alone is insufficient; authority, responsibility, product knowledge, material knowledge and process experience must match the assigned scope.
The standard helps the manufacturer determine which welding activities are quality-critical and who is responsible for them.
The manufacturer must allocate specific tasks to named persons and ensure that they have appropriate competence.
ISO 3834 requires welding quality to be controlled. ISO 14731 provides the practical framework identifying who coordinates these activities.
It is not merely a list of IWE/IWT/IWS titles. A qualification is important evidence, but competence also depends on experience, the product, the process and the assigned tasks.
Contract, drawing, product standard, quality level, extent of testing, material and record requirements.
WPS/WPQR, welder qualifications, welding consumables, shielding gas, equipment, fixtures and the ITP.
Compliance with the WPS, preheat, interpass temperature, parameters, CTWD, layer sequence and control of changes.
VT, NDT, testing, evaluation against acceptance criteria, management of nonconformities, repairs and re-inspection.
Complete record package: materials, WPS, qualifications, NDT, repairs, calibration and traceability.
Suitable for a coordinator managing a defined range of products, materials and processes. The person must understand WPS/WPQR applicability, quality criteria, deviation risks and the rules for production release.
Typical decisions: approval of a specific WPS for a component, resolution of a routine nonconformity, verification of welder validity and NDT requirements.
| Application | What welding coordination personnel must ensure | Typical evidence / record | Common practical mistake |
|---|---|---|---|
| Contract and drawing | Review technical requirements, quality level, standards, NDT extent and special requirements. | Contract-review record, technical review, approved ITP. | Production begins before the required quality level and test extent are clearly defined. |
| Material | Verify certificates, material group, thickness, heat-treatment condition and traceability. | 3.1 certificate, goods-receipt record, heat number, traceability map. | Incorrect material or missing link between the component and the heat number. |
| WPS/WPQR | Verify that the WPS is supported by an applicable WPQR and covers the actual production range. | WPS, WPQR, qualification range, list of approved WPS documents. | The WPS is formally available but does not cover the thickness, position, material group or process. |
| Welders / operators | Control qualification validity and conformity with the process, material, position and joint type. | EN ISO 9606 / EN ISO 14732 certificate and records of six-month continuity confirmation. | The welder holds a valid certificate, but the specific work is outside its qualification range. |
| Welding consumables | Ensure the correct type and classification, controlled storage and drying, moisture protection and traceability. | Wire/electrode certificate, stock record, redrying record. | The electrodes or wire are correct by trade name, but storage is uncontrolled. |
| NDT and testing | Define the method, extent, personnel qualification, evaluation criteria and response to indications. | NDT plan, VT/PT/MT/UT/RT reports, EN ISO 9712 qualification. | NDT is performed, but the acceptance standard used for evaluation is unclear. |
| Nonconformities and repairs | Decide whether to stop, repair, re-inspect and document the cause. | NCR, repair WPS, photographic evidence, repeat NDT, CAPA. | A repair is made informally without procedure approval or re-inspection. |
| Subcontracting | Verify that outsourced welding, NDT, PWHT and testing are controlled to the same level as internal processes. | Subcontractor approval, purchase order containing requirements, reports and certificates. | The subcontractor receives the drawing but not the WPS, NDT scope or record requirements. |
The correct answer is not merely a name. The auditor expects evidence of a system:
In a larger company, coordination may be performed by several people. The important point is that no responsibility falls between roles.
Situation: The wire specified by the WPS is exhausted during production and stores offers a ‘very similar’ wire from another manufacturer. The operator wants to continue to avoid stopping the line.
Correct reasoning under ISO 14731: this is not merely logistics. Welding coordination personnel must assess the filler-metal classification, certificate, compliance with the WPS/WPQR, customer requirements, any need for change approval, and the method of recording it in traceability documentation.
The checklist is a training aid. It helps verify that the ISO 14731 module is not completed merely as a formality, but is usable in production.
The Inspection and Test Plan links product requirements to manufacturing stages, responsibilities, intervention points and records. A sound ITP verifies a critical characteristic while it is still visible and correctable.
Does every significant risk have a specific check, acceptance criterion, competent owner, correct timing and required record?
Inspect before the feature is hidden, covered by another pass or dispatched.
State a specific document, revision and limit—not a vague “OK”.
Agree hold/witness points and notification periods before production.
Every mandatory row must produce an identifiable record or sign-off.
| Mandatory field | Content | Why it matters |
|---|---|---|
| Operation / stage | Material receipt, preparation, assembly, welding, PWHT, NDT, dimensions, testing, coating and dispatch. | Creates chronology and prevents inspection only after a feature is hidden or irreversible. |
| Characteristic | What is checked: material, identity, dimension, temperature, parameter, quality or leak tightness. | Without a specific characteristic there is no evidence that the correct risk was controlled. |
| Acceptance criterion | Drawing, WPS, standard, specification and a concrete limit/level. | “According to the standard” is often ambiguous; the applicable revision and criterion are needed. |
| Method and extent | VT, MT/PT, UT/RT, gauge, 100 %, sampling, frequency and location. | Defines whether the inspection can detect the relevant nonconformity. |
| Responsibility | Production, QC, IWE/IWT, NDT, customer or third party. | Separates performance, verification, approval and independent surveillance. |
| Intervention point | H, W, R, S or an internal checkpoint. | Prevents progress without required release or opportunity to attend. |
| Record | Form, report, certificate, weld log, NDT report or release note. | Without defined evidence the activity cannot later be demonstrated. |
| Code | Meaning | Rule for continuation |
|---|---|---|
| H – Hold point | Mandatory stop until formal release by the nominated party. | Continue only after documented approval or a previously defined waiver. |
| W – Witness point | A party has the right to attend and must receive agreed notice. | After correct notification, work may proceed without attendance where contract rules allow, with a record. |
| R – Review point | Document/result review without mandatory physical attendance. | The item must be available, revision-controlled and approved by the nominated competence. |
| S – Surveillance | Ongoing or random observation of the process. | Not an automatic stop, but findings can trigger NCR or a hold. |
| Stage | Inspection | Criterion | Point | Record |
|---|---|---|---|---|
| Before welding | Material identity and joint number | Drawing/BOM, 3.1 MTC, traceability procedure | H or W by risk | Material receipt report + weld map |
| Fit-up | Bevel, gap, mismatch, cleanliness and tacks | WPS, EN ISO 9692, drawing and internal limit | W/S | Fit-up report or weld traveller |
| Process | Preheat/interpass and essential parameters | WPS plus verified/calibrated equipment | S | Weld log / automatic record |
| Post-weld | VT and geometry | EN ISO 17637 plus applicable acceptance criteria | W/R | VT/dimensional report |
| NDT | Method, extent, technique and evaluation | EN ISO 17635, method standard and product specification | H/W | NDT report + indication map |
| Release | Record completeness and NCR closure | Dossier index and approved ITP | H | Final release note |
For every critical characteristic ask: “When is the last reliable moment to see or measure it?” Place the relevant ITP point immediately before that moment.
Explain the difference between a hold and witness point. Develop a basic ITP sequence for a complete-penetration butt weld requiring preheat, UT and PWHT, including the records to be generated.
Traceability demonstrates material origin and the complete manufacturing history of a specific joint. It must work both forward and backward: from a certificate to all affected parts, and from the finished product to the certificate, WPS, personnel, consumable, NDT and repairs.
Can an auditor start with one product mark and reach the heat, consumable batch, WPS, welder, NDT and every repair without assumptions?
Parts, joints, welds and records must not be interchangeable.
Identity moves before cutting, blasting or concealment.
Evidence is created during the activity, not rebuilt for an audit.
Unknown or incomplete material is quarantined, not released to production.
| Object | Minimum identity | Linked evidence |
|---|---|---|
| Parent material | Standard/specification, grade, dimension, heat/lot, certificate and receipt status. | EN 10204 MTC, receipt report, material map and marking transfer after cutting. |
| Welding consumable | Classification, manufacturer/trade name where relevant, diameter, batch/lot and storage condition. | Certificate, receipt, store/oven, issue record, quiver and weld log. |
| Weld | Unique weld/joint ID, drawing location, WPS, date and inspection status. | Weld map/isometric, traveller, VT/NDT report, NCR and repair log. |
| Personnel | Welder/operator, valid qualification and applicable range on the welding date. | Welder ID in the log, certificate, continuity and employer authorisation. |
| Equipment | Power source, oven, thermometer, gauge or NDT instrument identity and verification status. | Calibration/verification record under the defined control system. |
| Process history | Preheat/interpass, parameters, PWHT, repair, change and release. | Weld-data log, PWHT chart, change record, NCR/disposition and final release. |
| Document | Nature of data | Typical note |
|---|---|---|
| 2.1 – Declaration of compliance | Manufacturer statement that the product meets the order, without test results. | Usually insufficient for pressure or critical structural parts when specific properties must be evidenced. |
| 2.2 – Test report | Compliance statement plus results from non-specific inspection. | Results need not originate from the delivered heat/lot. |
| 3.1 – Inspection certificate | Specific inspection results for the supplied product, validated by the manufacturer’s authorised representative independent of production. | Common basis for controlled fabrication; the order must define grade, tests and supplementary values. |
| 3.2 – Inspection certificate | Specific inspection validated by the manufacturer and purchaser’s representative or designated inspection body. | Used where contract, code or the required level of independent validation demands it. |
| Risk | Typical manifestation | Barrier |
|---|---|---|
| Marking lost after cutting/blasting | The part cannot be linked to a heat or identity is recreated by assumption. | Transfer before operation, material map, durable tag/low-stress stamp and quarantine for unknown items. |
| Mix-up of similar grades | Stainless/duplex/CrMo or high-strength steel cannot be distinguished visually. | Segregated storage, colour code only as a secondary aid, risk-based PMI and barcode/RFID. |
| Incomplete weld log | Consumable batch, welder, WPS revision or repair is missing. | Mandatory fields, digital validation and no final release while records are open. |
| Qualification invalid on production date | A certificate exists but its range or continuity is not valid. | Automatic validation against date, process, material, thickness, position and joint type. |
| Records created after production | History is reconstructed without objective evidence. | Record at source and time of activity, with electronic timestamp and approval workflow. |
Select a random weld on the finished product and perform a “one-weld audit.” Within ten minutes the complete chain should be available: material – WPS – personnel – consumable – process – NDT – repair – release.
Compare EN 10204 documents 2.2, 3.1 and 3.2. Propose a heat-number transfer system when one plate is cut into multiple parts and define the action for an unidentified part found in production.
Reliable NDT requires certified personnel, an approved procedure, suitable technique, verified equipment and correct acceptance criteria. A Level 2 card alone is not universal authority for every method, product and decision.
Does the certificate cover the method, sector and level required for the task, and has the employer issued valid authorisation for its procedure and equipment?
Check method, sector, level, validity date and restrictions.
Performance, interpretation, evaluation and approval are different competences.
The employer is responsible for job authorisation and system knowledge.
Personnel must apply an approved procedure and correct product criteria.
| Element | Meaning | Employer/manufacturer verification |
|---|---|---|
| Method | VT, PT, MT, UT, RT, ET, LT, TT, AE or another method within the scheme. | Does the certificate cover the method actually specified by the ITP and procedure? |
| Sector | Product or industrial sector stated on the certificate. | Does the scope cover welds, castings, forgings, tubes or the relevant industry? |
| Level | Level 1, 2 or 3 defines the extent of competence and responsibility. | May the person only test to an instruction, also evaluate, or manage the method/system? |
| Validity | Dates, continuity conditions, visual acuity, renewal and recertification. | Was it valid on the test date, without significant interruption, suspension or withdrawal? |
| Operating authorisation | Written employer authorisation to perform defined tasks in its system. | Knowledge of the specific equipment, procedure, safety, product and local criteria. |
| Level | Typical authorised activities within certification scope | Limits |
|---|---|---|
| Level 1 | Set up equipment, perform testing to written instruction, record and classify results against stated criteria, and report. | Does not select technique or criteria and does not independently interpret beyond the instruction; works under the system’s Level 2/3 supervision. |
| Level 2 | Select technique within the method, translate standards into NDT instructions, set up/verify equipment, perform and supervise testing, interpret and evaluate results. | Must work within certified method/sector and the approved procedure/product criteria. |
| Level 3 | Assume responsibility for NDT operations, procedures and personnel; interpret codes, determine methods/techniques, approve procedures and lead technical decisions. | Level 3 certification does not replace knowledge of the specific product, contract or employer authorisation. |
| Document | Purpose | Approval and use |
|---|---|---|
| NDT procedure | Defines principle, technique, extent, equipment, calibration, surface, sensitivity, evaluation and reporting for an application. | Normally prepared/approved by competent Level 3 or another person permitted by the code and quality system. |
| NDT instruction | Converts procedure/standard into explicit steps that Level 1 can execute without further technical decisions. | Prepared by Level 2 or 3 within competence; includes clear setup, scanning and reporting requirements. |
| Technique sheet / scan plan | Specific probe, angle, sensitivity, coverage, exposure or sequence configuration. | Linked to joint ID, geometry, thickness, material and current procedure revision. |
| NDT report | Objective record of identity, personnel, equipment, conditions, extent, findings and evaluation. | Signed/verified at the authorised level and distinguishes indication, classification and acceptance/rejection. |
When approving NDT, do not check only a name and “Level 2.” Ask six questions: which method, which sector, which task, which procedure, which acceptance criterion and which employer authorisation?
Distinguish Level 1, 2 and 3 competence. Why is EN ISO 9712 certification insufficient without operating authorisation, and why cannot acceptance criteria be taken from this standard alone?
The weld metal and HAZ expand during heating and contract during cooling. The surrounding cooler material restrains this movement. This produces two distinct phenomena: visible distortion component and invisible residual stresses in the material. For IWE/IWT personnel, the key issue is not only ‘how can it be straightened?’, but how distortion can be prevented through design, the WPS, fixtures and welding sequence.
Distortion is often lower with strong restraint, but residual stress may be higher. Free welding allows the component to move; rigid restraint holds the shape, but stress remains in the structure. The decision must therefore consider component function, tolerances, cracking risk and the possibility of subsequent stress relief.
As the weld cools, it contracts transverse to the joint. This typically pulls the plates together, reduces the gap or shifts an assembly dimension.
The weld contracts along its length. Long weld runs may produce bowing, a banana-shaped beam or local buckling of thin sheet.
Caused by asymmetric heating through the thickness. It is typical of fillet welds, V-grooves and single-sided welds without balancing.
Thin sheet with a high length-to-thickness ratio readily buckles under local heating. Excessive heat input and long continuous welds often aggravate it.
The model is not a design standard. It is a decision-training aid showing the direction of influence of heat input, weld length, component thickness, asymmetry, restraint and welding sequence.
| Method | When it helps | Risk / IWE note |
|---|---|---|
| Correct welding sequence | For long structures, frames, ribs, stiffeners and beams. | The lowest-cost measure. It must be specified in the manufacturing procedure to ensure repeatability. |
| Pre-bending / presetting | For repeatable angular distortion or deflection after welding. | It must not conceal an unstable process. First verify repeatability on a trial component. |
| Fixtures and tack welding | For series production and components with tight tolerances. | Reduces dimensional deviation but may increase residual stress. Always inspect dimensions after release. |
| Controlled local straightening | After welding, when the component is outside tolerance. | Thermal straightening must have a temperature limit and a defined procedure. Uncontrolled overheating can change material properties. |
| PWHT / stress-relief heat treatment | For thick-walled components, pressure equipment, certain alloy steels and situations involving brittle-fracture risk. | It must be specified according to material, thickness, product standard and WPS/WPQR. A recorded thermal cycle is required. |
| Mechanical surface treatment | For fatigue-loaded details: improving the weld toe and reducing the notch effect. | It is not a substitute for correct weld quality. Use only where the method is permitted and qualified. |
| Application | What must be controlled | Typical reference |
|---|---|---|
| Tolerances for welded constructions | Linear dimensions, angles, form and position of welded constructions. | ISO 13920 – the tolerance class must be clear from the drawing or order. |
| Manufacturing quality | Competence, WPS/WPQR, process control, records, repairs and changes. | ISO 3834 + ISO 14731 – who decides, what is measured and what is retained. |
| Recommendations for welding | Welding sequence, preparation, temperature control, process selection and limitation of adverse effects. | ISO/TR 17671 – technological recommendations for fusion welding of metallic materials. |
| Heat treatment | PWHT, local heat treatment, equipment, measurement, records and responsibility. | ISO 17663 – quality requirements for heat treatment in connection with welding. |
| Inspection after straightening/repairs | Dimensions, VT/NDT according to risk, and repeat inspection of critical areas. | ITP, product standard, ISO 17635 for NDT selection and ISO 5817/ISO 10042 for weld quality level. |
Important: a standard does not remove distortion. It defines the requirement, responsibility and record. Dimensional stability is achieved only through the combination of design, WPS, welding sequence, fixture, measurement and a corrective procedure.
A fixture is not merely a steel frame with clamps. It is process equipment controlling datums, root gap, access, welding sequence, distortion, ergonomics and repeatability. It must stabilise production without unnecessarily over-constraining the assembly.
Does the fixture locate the part from functional datums while permitting controlled thermal movement, process access and safe release?
Datums and locators create geometry; clamps only seat the part.
Every redundant contact can convert tolerance into internal stress.
A dimension in the fixture may not represent the free final weldment.
Locators, bushes, clamps and sensors are controlled process elements.
| Function | Technical objective | Risk of poor design |
|---|---|---|
| Location | Create unambiguous datums and repeatable part position. | Over-constraint, assembly variation, incorrect datum chain and inaccessible measurement. |
| Clamping | Maintain contact and gaps against assembly and welding forces. | Excess restraint, marking, local deformation or high residual stress. |
| Support | Prevent sagging under self-weight and welding reactions. | The fixture “makes” the dimension, which elastically moves after release. |
| Heat control | Stabilise thin parts, support the root or distribute thermal loading. | Unplanned heat sink, lack of fusion, condensation or copper pickup. |
| Access and position | Provide correct angle, stand-off, welding position, cleaning, NDT and safe handling. | Torch/robot collision, inaccessible root, poor ergonomics and uninspectable weld. |
| Step | Constraint | Weldment note |
|---|---|---|
| 3 points – primary plane | Remove three degrees of freedom and create a stable base. | Distribute points, keep them clean and avoid zones with major thermal movement. |
| 2 points – secondary plane | Remove two further degrees of freedom. | One contact may need to accommodate thermal expansion where full locking would create high reaction. |
| 1 point – tertiary plane | Removes the final translational degree of freedom. | Must not become redundant against the incoming part tolerance. |
| Clamping forces | Seat the part against locators; they should not define geometry by themselves. | Direct force into locators and use only what is needed for stability—not to reshape a bad part. |
| Floating/compensating elements | Permit tolerance and thermal movement along a selected direction. | Important for long weldments, aluminium, stainless steel and robotic welding. |
| Failure | Manifestation | Control |
|---|---|---|
| Spatter on locators | Progressive datum shift and increasing dimensional variation. | Covers, suitable material/coating, scheduled cleaning and go/no-go verification. |
| Worn pin/bush | Clearance, part rotation, variable gap and robot-path shift. | Replaceable hardened bush, wear limit, MSA and recorded replacement interval. |
| Unmonitored pneumatic pressure | Random under-clamping or deformation from excessive force. | Pressure/position sensing, regulation, interlock and reaction plan. |
| Wrong release sequence | Weldment springs, twists or jams. | Minimum cooling time, defined clamp sequence and safe support during release. |
| Fixture used as gauge without verification | Part fits but the functional dimension is outside tolerance. | Independent checking fixture or calibrated measurement and scheduled geometry verification. |
| Undocumented shim | Setup depends on shift experience and is not reproducible. | Controlled shims with ID/thickness, setup revision and approved change. |
On the fixture drawing distinguish locators, clamps and supports. When a clamp also “sets” a dimension, question whether it hides over-constraint or forcibly corrects an out-of-tolerance part.
Explain 3–2–1 location for a long aluminium weldment. Which degree of freedom would you leave for thermal expansion, how would you control spring-back and how would you qualify the fixture?
A weld repair is a new controlled welding operation in a location that has already experienced a thermal cycle and often contains high residual stress. It must restore function without introducing a greater metallurgical, fatigue or geometric risk.
Before intervention, are technical disposition, complete removal scope, qualified repair procedure, examination and authority approved?
Repair without analysis often reproduces the same defect.
Suitable examination must confirm the original indication is gone before welding.
Every repair adds a thermal cycle, shrinkage and possible property change.
Original finding, disposition, repair and final result remain auditable.
| Option | Meaning | Decision authority |
|---|---|---|
| Accept as-is | The nonconformity remains physically unchanged because engineering assessment demonstrates function or an approved deviation. | Authorised design/technical authority and customer/third party where contractually required—not production alone. |
| Rework | Reprocessing by an approved production route so that the result fully meets the original requirement. | Production/QC under the approved procedure and delegated competence. |
| Repair | An intervention under a specific plan that restores acceptable function but may add a thermal cycle or change to the detail. | IWE/IWT and relevant technical authority; customer/inspection body where required. |
| Use-as-concession | Formal permission for a particular deviation on an identified product. | The party authorised to change acceptance requirements; fully identified and recorded. |
| Reject/scrap | The product or part is not used when repair is technically unsafe, unqualified or disproportionate. | Defined disposition authority in the NCR process. |
| Method | Advantage | Critical control |
|---|---|---|
| Grinding/milling | Precise, visually controllable removal with low thermal effect. | Avoid sharp grooves, unauthorised section loss and contamination; control final radius. |
| Air carbon-arc gouging | Rapid removal of large steel volume. | Remove carburised/heat-affected layer by grinding; control sparks, fumes, access and excavation shape. |
| Plasma gouging | Productive for suitable materials and equipment. | Control thermal effect, oxidation, contamination, minimum remaining thickness and subsequent dressing. |
| Machining | Repeatable geometry for series or high-precision repair. | Secure location, no encroachment into prohibited zones, cleanliness and confirmation that the indication is removed. |
| Local cut-out/replacement | Removes the entire problematic detail or section. | Reassess force flow, additional welds, tolerances, thermal history and qualification of the inserted part. |
| Risk | Mechanism | Control |
|---|---|---|
| Accumulated thermal cycles | HAZ growth, tempering/precipitation, grain growth or hardness change. | Repair-count limit, location history, metallurgical review and extra tests beyond the qualified envelope. |
| Hydrogen cracking | New hydrogen source, high stress after excavation and rapid cooling. | Dry consumables, preheat/interpass, post-heat where specified and delayed MT/UT. |
| Residual defect at excavation bottom | The repair weld covers the original crack or lack of penetration. | Suitable excavation, cleaning and MT/PT before welding; confirm complete removal of volumetric indications. |
| Restricted access | Torch angle/CTWD cannot be maintained and new lack of fusion is created. | Widen excavation or remove the obstruction; do not permit a blind repair. |
| Cause concealed | The same defect appears in further welds. | Contain similar joints, review parameter data, apply 5 Why/8D and verify action effectiveness. |
Start every repair with a photograph, map and excavation boundary; finish with a photograph, NDT report and updated weld map. Between them, personnel, WPS, consumable, parameters and temperatures must remain traceable.
Develop a repair for a longitudinal root crack in a thick high-strength-steel weld. How would you establish extent, confirm removal, control hydrogen and thermal cycles, and specify repeat NDT?
Engineering temperature control is not a single number written in a WPS. It combines the metallurgical objective, heating method, heated-zone width, through-thickness equalisation, measurement location and timing, maintenance during interruptions and controlled completion of the cycle.
This model illustrates interacting variables. It does not replace an applicable calculation method, material specification, product code or qualified WPS.
| Term | Engineering meaning | Frequent error |
|---|---|---|
| Preheat temperature | Minimum temperature in a defined region immediately before arc ignition. | Measuring only the spot directly heated by a torch. |
| Preheat maintenance temperature | Minimum maintained during interruptions or throughout a defined operation. | Checking preheat only once at the start of a shift. |
| Interpass temperature | Temperature immediately before depositing the next run; it may have a minimum and maximum. | Measuring the glowing bead without a defined location or waiting time. |
| Postheat | Controlled hold after welding, for example to support hydrogen diffusion or slow cooling. | Calling every postheating operation PWHT. |
| PWHT | Qualified thermal cycle with specified ramps, hold, zones, measurement and record. | Treating it only as “stress relief”. |
| Method | Physical principle | Strength | Critical controls |
|---|---|---|---|
| Manual flame | Convection and radiation from combustion products and flame. | Mobile and inexpensive for site work. | Multiple heating points, burner motion and distance, combustion condition, local overheating, wind and measurement on the opposite face. |
| Multi-flame / ring burner | Distributed flame around a circumference. | More uniform heating of pipes and circular components. | Burner symmetry, shielding, output balance and through-wall equalisation time. |
| Electrical resistance pads | Joule heating in resistance elements followed by conduction into the component. | Controllable, zoned and suitable for preheat or PWHT. | Pad contact, power density, failed elements, insulation, leads and independent control zones. |
| Induction | Eddy-current losses and, in ferromagnetic material, hysteresis losses. | Fast, clean and readily automated. | Coil geometry and coupling, frequency, skin effect, shielding, Curie-region behaviour and depth distribution. |
| Furnace | Controlled convection and radiation around the full component. | Uniform whole-component cycle and good repeatability. | Support, circulation, furnace uniformity survey, recording, handling and delay between furnace and welding. |
| Radiant panels | Absorption of infrared radiation by the surface. | Non-contact area heating. | Emissivity, shadowed areas, stand-off distance and unequal surface absorption. |
A value set on the power-source panel is not automatically the value at the arc. Engineering measurement must define voltage pick-up points, current sensing, time window, sampling rate, pulse processing and synchronisation with actual travel speed.
| Quantity | Correct approach | Failure mode |
|---|---|---|
| Arc voltage | Sense as close as practicable to the electrical process and document both pick-up points. | Source-terminal voltage includes or omits cable, torch, contact and return-path drops. |
| Welding current | Use a calibrated shunt, Hall sensor or current transformer suitable for the waveform. | Insufficient bandwidth or sensor saturation during peaks. |
| Travel speed | Use actual path length over actual time; include robot ramps, weaving and stops. | Using programmed speed through run-in, crater fill or off-path arc time. |
| Arc time | Define a trigger and one common time base for electrical and motion data. | Asynchronous loggers or including preflow/postflow in welding time. |
| Power | Evaluate instantaneous u(t)·i(t), then integrate or average over the defined interval. | Multiplying separate averages for pulsed or short-circuit transfer. |
Important: use “arc energy”, “heat input” and factor k exactly as defined by the current governing standard, product code and WPS/WPQR. A calculated value is not the same as calorimetrically absorbed energy.
Flow indicated at a regulator does not prove what leaves the nozzle or remains at the root. Gas control includes composition, flow, pressure, leakage, turbulence, draught, residual oxygen, dew point and atmosphere-exchange time.
The model assumes a perfectly mixed volume. Real systems contain dead zones, stratification, leakage and strong dependence on inlet and outlet positions.
| Quantity | Principle | Key influences | Correct application |
|---|---|---|---|
| Volumetric flow at regulator | Rotameter: float position in a tapered tube. | Gas density, pressure, temperature, verticality, pulsation and calibration gas. | Read the correct float reference and apply the proper scale or correction for the gas mixture. |
| Flow at nozzle | Slip-on flowmeter or calibrated collection adapter. | Seal, diffuser, spatter, nozzle diameter and valve condition. | Measure close to the actual outlet and compare with the source/regulator setting. |
| Mass flow | Thermal or Coriolis sensor. | Gas configuration, range, valve dynamics and zero drift. | Suitable for automation, recording and alarms when configured for the actual gas. |
| Residual oxygen | Zirconia, electrochemical or paramagnetic sensor. | ppm/% range, moisture, sample line, response time, temperature and calibration. | Sample at the critical root location, not automatically at the purge-hose outlet. |
| Dew point / moisture | Chilled mirror, capacitive or electrolytic sensor. | Condensation, pressure, contamination and long stabilisation at very low moisture. | Define pressure or atmospheric dew point and the exact sampling location. |
| Mixture composition | Thermal conductivity, paramagnetic analysis or GC, depending on accuracy. | Cross-sensitivity, calibration gases, sampling and mixture homogeneity. | Verify suspected cylinder mix-ups, mixer faults and critical applications. |
Oxidation, porosity, nitrogen pickup, unstable arc and an unacceptable root can result from leakage or restriction even when the setting appears correct.
Turbulence may entrain air. A higher rotameter reading therefore does not necessarily mean better shielding.
Gas type, pressure, flow, preflow/postflow, nozzle geometry, stick-out, hose integrity, draught and root oxygen must be assessed together. A compliant cylinder certificate does not prove the atmosphere at the weld.
Temperature during welding varies in space and time. A valid result requires a defined location, timing, sensor type, thermal contact, emissivity, response time, calibration status and uncertainty of the complete measurement chain.
| Method | Physical principle | Best use | Engineering limitation |
|---|---|---|---|
| Temperature crayon, paint or pellet | Threshold melting or colour change. | Fast, robust confirmation that a threshold was reached. | Does not provide the complete cycle; surface state, layer thickness, heating rate and interpretation matter. |
| Contact surface probe | Heat conduction into the sensor. | Routine preheat and interpass checks. | Contact pressure, paste, scale, curvature, gradient and stabilisation time. |
| Thermocouple | Seebeck voltage generated by two dissimilar conductors. | Continuous multi-point recording over a wide temperature range. | Type, reference junction, extension cable, polarity, attachment method, drift and response. |
| Pt100 / Pt1000 | Change in platinum resistance with temperature. | Stable, accurate measurement in a suitable range. | 2/3/4-wire connection, self-heating, contact and generally slower response. |
| IR pyrometer | Spectral thermal radiation converted to temperature. | Fast non-contact measurement of moving or inaccessible hot parts. | Emissivity, reflection, spot size, wavelength, smoke, glass and viewing geometry. |
| Thermal camera | Two-dimensional field of infrared radiation. | Locating non-uniform heating, cold areas and documenting spatial distribution. | Same radiation errors as a pyrometer plus spatial resolution and selected range. |
The result includes sensor, attachment, cable, cold-junction compensation, transmitter, logger, resolution, drift, response time and surface gradient. A calibration certificate for one component does not prove the assembled system.
| Task | Preferred method | Required validation |
|---|---|---|
| Quick confirmation of minimum preheat | Temperature crayon or calibrated contact probe, depending on access and surface. | Correct threshold, location, waiting time and continuous contact. |
| Routine interpass control | Contact probe or pyrometer with qualified emissivity and geometry. | Correlation against a reference method on the actual surface. |
| Local PWHT | Multi-channel thermocouples, controller and independent recorder. | Mapping, calibration, alarms and gradient control. |
| Finding non-uniform preheat | Thermal camera supplemented by contact reference points. | Emissivity, reflections and confirmation of absolute temperature. |
| Process development / t₈/₅ | Fast thermocouple or suitable high-speed pyrometry with logger. | Sensor time constant, sampling and precise HAZ location. |
PWHT is a qualified manufacturing operation. It requires a defined metallurgical objective, material window, heating and cooling rates, holding time, zone widths, thermocouple number and positions, control logic, insulation, support and an auditable record.
Heat sinks such as flanges, valves, supports or thickness transitions require zoning and additional measurement points.
| Area | Required engineering definition |
|---|---|
| Metallurgical objective | Temper martensite, reduce hardness, relax residual stress, promote hydrogen diffusion or another explicitly justified objective. |
| Approved scope | Material group, delivery condition, thickness, weld metal, prior cycles and service condition. |
| Cycle | Initial temperature, heating rate, hold temperature and tolerance, hold time, maximum temperature spread, cooling rate and free-cooling point. |
| Heating equipment | Furnace, resistance or induction; output, zones, controls, backup and insulation. |
| Thermocouples | Control and monitoring locations, attachment, protection, polarity, numbering and expected hot/cold points. |
| Acceptance | Temperature-time chart, deviations, power failures, signatures, disposition and joint-ID traceability. |
A low-hydrogen consumable remains low hydrogen only through controlled purchasing, storage, drying, issue, exposure time, return and traceability. One incorrect oven or open package can invalidate the metallurgical concept of the WPS.
| Consumable | Principal hydrogen sources | Required control |
|---|---|---|
| Basic covered electrodes | Coating moisture, unsuitable drying, excessive time outside the oven and damaged packaging. | Approved drying/redrying, holding oven, heated quiver, exposure limit and prohibition of uncontrolled repeated cycles. |
| Flux-cored wires | Moisture in the fill, condensation, damage and long storage of an opened spool. | Dry storage, acclimatisation before opening, closed feeders and rules for partly used packages. |
| SAW flux | Moisture absorption, contaminated recycled flux, fines and mixed batches. | Manufacturer-defined drying, heated hopper, controlled recycling, sieving/magnetic separation and batch traceability. |
| Solid wire | Surface oil, rust, copper-coating damage, feeder lubricant and condensation. | Clean storage, FIFO, acclimatisation, spool covers and wire-path inspection. |
| TIG rods | Hand contact, oil, dust, moisture and open containers at the workplace. | Closed labelled tubes, surface cleaning and material segregation. |
A cold spool or electrode moved into a warm humid area may become wet without direct water contact. Open packaging only after adequate acclimatisation.
Temperature and time belong to the manufacturer and approved procedure. Overheating can damage coating chemistry, alloy recovery or operating characteristics.
An auditable regime links batch, oven, programme, issue time, welder, WPS and result. For critical production the regime can be verified by testing in accordance with ISO 3690.
| Equipment | Function | What to verify |
|---|---|---|
| Drying / redrying oven | Defined high-temperature cycle for an approved product. | Temperature uniformity, programme, overshoot, timing after setpoint, capacity and record. |
| Holding oven | Keeps already prepared electrodes dry. | Actual operating temperature, doors, overloading, compartment identification and batch mixing. |
| Portable heated quiver | Protects consumables at the workplace. | Power, temperature, lid closure, unpowered time and individual identification. |
| Flux hopper | Keeps flux dry and feeds the process. | Temperature, recirculation, dust, contamination and new/recycled-flux ratio. |
| Dry store / climatic cabinet | Stabilises conditions before opening. | Temperature, RH or dew point, alarms, mapping and response to outage. |