Post Weld Heat Treatment (PWHT) is the heating process carried out after welding is complete.
In some cases, an intermediate bake-out / de-gas will be performed if not going directly into the stress relieving phase. This involves a soak at around 300°C to remove any hydrogen from the weldment and heat-affected zone (HAZ).
Generally, PWHT is associated with the stress-relieving process. This is where the metal is heated in a controlled manner to a temperature below its lower critical limit. It is held for a specified duration and then controlled cooling is required. The requirement for PWHT is mainly due to the residual stresses and microstructural changes that occur after the welding process.
The code / standard will determine the requirements for the application of the thermocouples and heating band requirements.
RCR Heat Treatment has a range of furnaces in our Welshpool and Sunshine workshops to perform stress relieving on large fabrications. We can also mobilise to your site to perform localised PWHT and set up PWHT on major structures.