Extreme heat caused by welding can also reduce the flexibility of a material but an appropriate PWHT will keep it strong while maintaining durability.
While a PWHT may be necessary in many cases, it’s important to remember that a post weld treatment may also cause irreparable damage if administered incorrectly.
There is a certain amount of confusion surrounding post weld treatments but it is critical for the safety of your consumer and the reputation of your business that you always make the right choice regarding PWHT. Doing so will avoid weakening materials unnecessarily, waste, and potential danger.
Post Weld Heat Treatment is also known as Stress relieving, and after materials have been welded, if they cool too quickly, brittle fracture and corrosion can occur caused by the stress of the extreme heat.
The PWHT/Stress relief process is performed by heating to a temperature as detailed in the welding code for the appropriate material, and holding at that temperature long enough to achieve the desired reduction in residual stresses. The steel is then cooled at a sufficiently slow rate to avoid formation of excessive thermal stresses.
Stress relieving as the name suggests, is heat treatment designed to reduce the residual stresses produced by weld shrinkage. It relies upon the fact that, as the temperature of the metal is raised, the yield strength decreases, allowing the residual stresses to be redistributed by creep of the weld and parent metal. Cooling from the stress relief temperature is controlled in order that no harmful thermal gradients can occur.