What is Post Weld Heat Treatment (PWHT)? PWHT is a controlled process in which a welded material is reheated to a temperature below the lower critical transformation temperature and held at that temperature for a period of time. The need for PWHT is mainly due to the residual stresses and microstructural changes that occur after welding. At Delta Heat Services, we specialize in heat treatments and are happy to explain the entire process.
Post Weld Heat Treatment
Welding creates a high temperature between the weld metal and the base material. When the welded material has cooled, residual stress is formed. Particularly for thicker materials, these stresses can reach unacceptable levels and exceed design stresses. By applying Post Weld Heat Treatment, the stresses are reduced to an acceptable level.
Post Weld Heat Treatment ensures that in addition to residual stresses, microstructural changes also occur as a result of the high temperatures caused by the welding process. These changes increase the hardness of the material.
What about the heating and cooling rate?
The heating rate when PWHT is performed is usually based on the thickness of the part and is specified by the applicable codes. If the heating rate is not done properly, either by heating too fast or unevenly, temperature gradients in the part can become harmful to the part. As a result, stress cracks can occur and previously uncreated residual stresses can form when the part is cooled to ambient temperature.
As with the heating rate, the cooling rate must be controlled to avoid adverse temperature gradients that can cause cracks or introduce new stresses during cooling. In addition, rapid cooling rates can increase hardness, which can increase susceptibility to a brittle fracture.
About Delta Heat Services
As a qualified and experienced specialist in heat treatment, Delta Heat Services offers a broad range of services. Our advanced knowledge and technology, combined with a flexible and customer-oriented approach, allow Delta Heat Services to provide versatile solutions for every heat treatment enquiry. We provide high quality heat treatment services on-site on projects worldwide and at our own facilities. We are specialized in preheat, annealing, post weld heat treatment (PWHT), bake outs, dry outs and shrink fittings. Do you want to know more about Post Weld Heat Treatment? Contact us or request a quote without obligation directly.