The word Pwht is an abbreviation of Post weld heat treatment, which is defined as a type of heat treatment (heat treatment) after the welding operation and is known as stress relief in Persian language, which is often used to improve the characteristics of the area It is used under the influence of welding. In other words, stress relief, or Pwht, is a controlled process that includes annealing the metal below its critical deformation temperature. This operation is performed following a welding process, which is why it is also called post-warm operation. The material is then kept at a specific temperature for a certain period of time to reduce residual stresses and increase strength. Also, this process reduces the excessive hardness of the weld metal that leads to brittle failure and ultimately reduces the risk of cracking due to microstructural changes. In fact, it can be said that Pwht operation is a heating and cooling control cycle of parts and materials that is used in the petrochemical industry, steel industry, and oil and gas industry.
In this regard, the benefits of Pwht are categorized as follows:
1- Improving the metallurgical structure in terms of graining
2- Reducing the risk of brittle failure to An effect of increasing the softness of the metal
3- Improving the impactability of the material
4- Relaxing the thermal stresses in the metal material due to the redistribution of the remaining stresses
5- Preventing the temperature gradient and creating stress in the metal to The reason for the slow and controlled heating and cooling rate
6- The removal of hydrogen dissolved in the weld metal, which leads to the prevention of the formation of gas pores and hydrogen cracks.
7- Easy machining
8- Dimensional stability of the piece