Preheating & PWHT Requirement

Preheating : The process of preheating involves heating the area around the weld joint or the entire part to a specified temperature before welding. This reduces the cooling rate of the weld and drives out moisture, which in turn helps prevent hydrogen buildup and the potential for cracking.

PWHT: Post heating is utilized to decrease the potential for hydrogen-induced cracking (HIC). HIC typically occurs when the weldment has a sensitive microstructure, a high level of stress, and/or a sufficient level of hydrogen. In ferritic steels, hydrogen embrittlement occurs at temperatures close to ambient temperature.