Recently,some client feel query and ask “is there any PWHT requirement?” for some prefabrication.What’s post weld heat treatment (PWHT)?

Broadly speaking, post weld heat treatment is the heat treatment of the welded area or welded component after the workpiece is welded, including stress relief annealing, full annealing, solid solution, normalizing, normalizing and tempering, tempering, and low temperature stress relief. In the narrow sense, it refers to stress relief annealing, the purpose is to improve the performance of the weld zone and eliminate harmful effects such as welding residual stress.

Pipeline prefabrication

Post weld heat treatment generally uses a single high temperature tempering or normalizing plus high temperature tempering. For gas welding joints, normalizing and high temperature tempering are used. This is because the grain size of weld and heat affected zone of gas welding is coarse and need to be refined, so normalizing treatment is adopted. However, a single normalizing cannot eliminate the residual stress, so high temperature tempering is needed to eliminate the stress. The single medium temperature tempering is only suitable for the assembly and welding of large ordinary low carbon steel vessels assembled in the construction site. Its purpose is to partially eliminate the residual stress and dehydrogenation. In most cases, single high temperature tempering is used. The heating and cooling of heat treatment shall not be too fast, and the inner and outer walls shall be uniform.

Now you should understand what PWHT is.Whether all material need PWHT and PWHT  process, we will discuss them in detail in the future.As professional supplier of prefabrication pipeline,weldment or cladding, Hebei HaiHao Group accept all kinds welding works.Welcome your inquiry.Email:sales@haihaogroup.com