NDT – Phils., Inspection Services Corporation
INDUSTRIAL INSPECTION
Post Weld Heat Treatment
(PWHT)
Post Weld Heat Treatment (PWHT) is a critical process applied to welded materials, particularly in industries like petrochemical, nuclear, and construction, to enhance the properties of the weld and the heat-affected zone (HAZ). The primary goals of PWHT are to reduce residual stresses, improve the mechanical properties of the weld, and ensure the integrity and performance of the welded structure.
Objectives of PWHT
1. Reduction of Residual Stresses: Welding induces thermal stresses due to the rapid heating and cooling cycles. PWHT helps to relieve these stresses, reducing the risk of distortion and cracking.
2. Improvement of Mechanical Properties: Enhances the toughness, ductility, and hardness of the welded joint.
3. Reduction of Hardness: Decreases the hardness in the HAZ, minimizing the risk of brittle fracture.
4. Tempering Martensite: In certain steels, PWHT helps to temper martensite formed during welding, improving toughness.
5. Hydrogen Diffusion: Aids in the diffusion of hydrogen from the weld metal, reducing the risk of hydrogen-induced cracking.