What is post-weld heat treatment and when is it required?

• A. Controlled heating after welding to relieve stresses or alter microstructure; required for some high-strength steels and thick sections per WPS
• B. Rapid cooling immediately after welding to set the weld
• C. Cleaning with solvent after welding
• D. Painting the weld

Answer: (A)

Post-weld heat treatment is a controlled heating after welding to relieve residual stresses and to adjust the weld and heat-affected zone’s microstructure and mechanical properties. This process helps reduce distortion, lower residual stresses that can lead to cracking, and improve toughness and ductility in the weld area. It’s typically required for certain materials and thick sections as specified by the Welding Procedure Specification or governing codes, especially for high-strength steels where maintaining mechanical performance is critical.

The other actions described around welding—rapid cooling after welding, cleaning with solvent, or painting the weld—are not PWHT. Rapid cooling is a cooling method that can harden or embrittle metal, cleaning is surface preparation, and painting is a protective coating; none of these qualify as post-weld heat treatment.