Stress Relieving (PWHT )

During the welding process, the two metal pieces being joined are subject to extreme temperatures and can cause the crystalline structure of the metal to pass through various metallurgical phases. As a result, hardening and embrittlement of the metal can occur to varying degrees usually dependent on carbon content). Heat treatment is designed to reduce the hardness in the heat affected zone of the metals and also increase ductility in these sections. Various pressure vessel codes contain the specifics regarding the procedures for post-weld heat treatment.