[1] It is often referred to as being any heat treatment performed after welding; however, within the oil, gas, petrochemical and nuclear industries, it has a specific meaning.
[1] In addition to residual stresses, microstructural changes occur due to the high temperatures induced by the welding process.
[1] A final consideration in deciding the need for PWHT is based on the components' intended service, such as one with a susceptibility to stress corrosion cracking.
[6] Great care should be taken as to not heat the component above the lower transformation temperature, as detrimental metallurgical effects and impaired mechanical properties can result.
Holding above the original tempering temperature can reduce the strength of the material to below ASME required minimums.
Computer software is typically used in conjunction with the thermocouples to monitor the fore-mentioned variables and provide documentation that the PWHT was performed properly.