Post Weld Heat Treatment is an essential part of both the Operation and Maintenance of assets in the fabrication, Oil & Gas and Power Industry. The welding process can unintentionally weaken equipment by imparting residual stresses into a material which can lead to reduced material properties. This said, Post Weld Heat Treatment (PWHT) is a method used for reducing and redistributing said residual stresses in materials ensuring that the material strength is retained after the welding course. It is also used as a method of hardness control or even to enhance material strength.
In some standards PWHT is compulsory for certain grades or thicknesses, otherwise it is dependent on the material type and the service requirements. Other factors that impact the need for this Inspection are the welding parameter’s, the likely mechanism failure, its alloying system or whether it’s been subject to Heat Treatment previously. Generally, the higher the carbon content and/or the higher the alloy content in materials, the more likely it is to need PWHT after welding activities.