Heat treatment after welding ( PWHT )

It is a process in which the welded material is reheated to a temperature lower than the lower critical transition temperature, and then kept at this temperature for a specified period of time to maintain its mechanical and metallic properties

The need for post-weld heat treatment is mostly due to the residual stresses and subtle structural changes that occur after the welding is completed. These microscopic changes can increase the material’s stiffness and reduce toughness and ductility. The use of post-weld heat treatment helps reduce any increased hardness levels and improve toughness and ductility to acceptable levels according to the design