5 thoughts on “ What is Post Weld Heat Treatment (PWHT)? ”
by Admin
Posted on 12-09-2023 05:14 PM
Intertek offers post weld heat treatment (pwht) to improve weld microstructure and reduce residual stresses developed during welding. Intertek specialises in performing pwht for the steel and metal fabrication industries including the construction of pressure vessels, pressure piping, storage tanks, buildings, bridges, offshore platforms, power plants, oil and gas refineries, and petrochemical plants.
Welding is an essential part of operating and maintaining assets in the petroleum (upstream, midstream, downstream) and chemical processing industries.
While it has many useful applications, the welding process can inadvertently weaken equipment by imparting residual stresses into a material, leading to reduced material properties. In order to ensure the material strength of a part is retained after welding, a process known as post weld heat treatment (pwht) is regularly performed. Pwht can be used to reduce residual stresses, as a method of hardness control, or even to enhance material strength. If pwht is performed incorrectly, or neglected altogether, residual stresses can combine with load stresses to exceed a material’s design limitations.
Grade 410 steels can be welded using all conventional welding techniques, but the materials should pre-heated at 150 to 260 °c followed by post-weld annealing treatment, to mitigate cracking. Grade 410 welding rods are recommended for tempering and post-hardening. In the "as welded" conditions, grade 309 filler rods can be used to achieve a ductile joint. According to as 1554. 6 standards, grade 309 electrodes or rods are preferred for welding 410 steels.
Post weld heat treatment (pwht), or also called stress relief (sr) is a method for reducing- relieving, and redistributing the residual stresses in the material that have been introduced by welding. Post weld heat treatment is a controlled heat treatment method in that welded components (welded material) are reheated in a furnace or localized heating arrangement to a temperature that is lower than it’s critical transformation temperature (known as ac1). This is followed by keeping the part at this pre-determined temperature for certain time duration known as holding time. This is followed by slow & controlled cooling in the furnace to allow uniform-controlled expansion & contraction.