What is post-weld heat treatment (PWHT)?

• A. A cosmetic coating applied after welding.
• B. A process performed during welding to improve fusion.
• C. Controlled heating and cooling after welding to relieve residual stresses and improve properties.
• D. A procedure for verifying welder performance.

Answer: (C)

Post-weld heat treatment is a controlled heating and cooling process applied after welding to relieve residual stresses and improve the properties of the weld and surrounding metal. The idea is to heat the weld area to a specific temperature and hold it there for a set time, then cool it in a controlled way. This helps reduce tensile stresses locked in by welding, lowers hardness in the heat-affected zone, and can improve ductility, toughness, and fatigue resistance. It’s especially important for thicker sections or critical steel welds where uncontrolled cooling could lead to cracking or distortion.

This isn’t a cosmetic coating applied after welding, nor is it something done during the welding itself to improve fusion, and it isn’t a test or verification of welder performance. Those are separate concepts; PWHT is specifically about controlled post-weld heating and cooling to enhance the welded joint’s stability and performance.