When is PWHT required?

• A. For any piping above 1 meter in length
• B. Only for welds with defects
• C. When material is stainless steel
• D. When thickness exceeds code limit

Answer: (D)

Post-weld heat treatment is used to relieve the residual stresses and soften the heat-affected zone created by welding, improving ductility and reducing the risk of cracking. The need for PWHT is driven by section thickness: thicker welds cool more slowly and develop higher residual stresses and harder microstructures near the weld, which can raise the risk of brittle failure. The code specifies a thickness limit above which PWHT becomes mandatory; if the weld exceeds that limit, PWHT must be performed to meet the required properties and integrity for the service. Thinning the focus to thickness mirrors how the code enforces heat treatment: it isn’t a blanket requirement for pipe length, for the presence of defects, or simply for certain materials like stainless steel—those factors may influence the decision in some cases, but the primary trigger in the code is crossing the prescribed thickness threshold.