Controlled process of reheating materials
post weld
heat treatment
(pwht) is a controlled process in which a material that has been welded is reheated to a temperature below its lower critical transformation temperature, and then it is held at that temperature for a specified amount of time.
It is often referred to as being any heat treatment performed after welding; however, within the oil, gas, petrochemical and nuclear industries, it has a specific meaning. Industry codes, such as the asme pressure vessel and piping codes, often require mandatory performance of pwht on certain materials to ensure a safe design with optimal mechanical and metallurgical properties.
To ensure that the material strength of the property is not affected after welding, a process known as post weld heat treatment (pwht) is continuously employed. Pwht is one of the methods used by welders to reduce residual stresses to combat hardness or enhance material strength. If pwht is not adequately performed or is overlooked altogether, the residual stresses plus the load stresses can join together to cause a brittle fracture. Therefore, it is required to take great care in choosing the right temperature needed for weld-able steel to stop the following problems from occurring, especially when there is an added adjustment of parameters to properties:.
Application [ edit ]
Induction heating uses an electromagnetic field to create a disturbance in the molecules of the metal that creates heat, the frequency of the electromagnetic field can be quicker than traditional electric resistance heating, the system is quicker to set up and is a good tool for some heat treatment applications.
Not all metals are equal, some do not take well to the induction frequencies, it is always good to check before proceeding with this method
often used for bolt heating and stretching, induction rods can help expedite the opening of turbine casings, presses and heat exchanger systems. These systems often provide quicker heating, faster set up and teardown, and can be a safer option due to cool coils in the vicinity of welders and other personnel.
By samudrapom dam aug 10 2022 this article discusses the post weld heat treatment (pwht) process and its effectiveness in reducing the residual stresses and improving the mechanical properties of weldments. Image credit: funtay/shutterstock. Com.
This article originally appeared in connector magazine, fall 2020 edition.