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Post-Weld Heat Treatment (PWHT)
A controlled heating and slow-cooling process applied to welded assemblies to relieve residual stresses, improve toughness, and restore material properties after welding. PWHT is required by pressure vessel codes and specified for high-strength steel applications.
Post-weld heat treatment slowly reheats the entire assembly to a precise temperature, typically 600-650°C for most structural steels, and holds it there for several hours before cooling at a controlled rate, allowing residual stresses to dissipate. PWHT improves notch toughness and ductility, particularly in high-strength steels where the heat-affected zone becomes brittle and prone to lamellar tearing or hydrogen-assisted cracking.
Pressure vessel construction codes such as ASME mandate PWHT for most materials and thicknesses because the residual stress relief and property restoration are essential to service reliability in cyclic and thermal shock environments. Complex weldments requiring PWHT demand furnace space, temperature monitoring equipment, and extended production lead times, making it essential to evaluate PWHT requirements early in the design phase so that manufacturing logistics and cost can be properly estimated.
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