Distortion and residual stresses

Topic overview

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.

What the module covers

• Welding always creates a temperature gradient. The question is whether the manufacturer controls it.
• 1. Transverse shrinkage
• 2. Longitudinal shrinkage
• 3. Angular distortion
• 4. Buckling and waviness
• Interactive indicative model: what increases distortion and what increases residual stress
• Prevention through design
• Control in production