What is PWHT and when is it typically applied?

What is PWHT and when is it typically applied?

• A. Post-weld heat treatment; applied to relieve residual stresses and improve toughness for certain steels and thicker sections.
• B. Pre-weld heat treatment; applied before welding.
• C. Post-weld humidity test; checks moisture content.
• D. Process of applying coating to weld.

Answer: (C)

Post-weld heat treatment is a heat-treating step done after welding to relieve residual stresses that develop during the welding process and to improve toughness, especially in certain steels and thicker sections. By heating the welded area (and the surrounding heat-affected zone) to a controlled temperature, holding for a specified time, and then cooling slowly, the internal stresses relax and the microstructure can be tempered to reduce hardness and brittleness. This helps prevent cracking and improves ductility and fracture resistance, meeting mechanical requirements and code specifications for demanding welds. This is typically applied for high-strength or alloy steels, thick-walled welds, and joints where welding-induced stresses or brittle behavior are a concern. Other options described—heating before welding, testing moisture content after welding, or applying a coating—are different processes and do not achieve the same stress-relief and toughness benefits provided by PWHT.

Post-weld heat treatment is a heat-treating step done after welding to relieve residual stresses that develop during the welding process and to improve toughness, especially in certain steels and thicker sections. By heating the welded area (and the surrounding heat-affected zone) to a controlled temperature, holding for a specified time, and then cooling slowly, the internal stresses relax and the microstructure can be tempered to reduce hardness and brittleness. This helps prevent cracking and improves ductility and fracture resistance, meeting mechanical requirements and code specifications for demanding welds.

This is typically applied for high-strength or alloy steels, thick-walled welds, and joints where welding-induced stresses or brittle behavior are a concern. Other options described—heating before welding, testing moisture content after welding, or applying a coating—are different processes and do not achieve the same stress-relief and toughness benefits provided by PWHT.