What is PWHT

Blog on Post Weld Heat Treatment (PWHT)What is PWHT? Post-Weld Heat Treatment (PWHT) is a controlled heat treatment process applied to welded materials to reduce residual stresses and improve the mechanical properties of the weld and adjoining area. It is a heat treatment process heated to a lower critical transformation temperature, and then held at that temperature for a specified time before being cooled at a controlled temperature. This heat treatment involves a specific heating cycle, i.e. rate of heating, rate of cooling, holding temperature & time as per applicable code. PWHT is sometimes referred to as stress relief heat treatment.Why is PWHT Important? During welding, metal expands and contracts due to rapid heating and cooling and induces residual stresses, which affect below mechanical properties. • Hardness and brittleness in the Heat-Affected Zone (HAZ) • Distortion and cracking • Reduced toughness and ductility • Unacceptable microstructures During the welding, pre-heating is also necessary to avoid the above effects. PWHT aims to relieve residual stresses induced during welding, which can cause distortion, cracking and reduced strength of material. PWHT can improve the weld’s toughness, ductility, and resistance to cracking.