Post Weld Heat Treatment (PWHT) is another term for relieving the stress from a material and allowing it to return to its original state. The stress relief process involves diminishing and redistributing the small folds and cracks (called stresses) in the metal that are created during the welding process.
Post Weld Heat Treatment is an essential practice in order to repair the macro structure of the welded material. The primary benefits of this process include the removal of hydrogen (which can cause cracking), increased ductile strength, and increased resistance to corrosion. The process of post weld heat treating includes relaxing and soaking the materials. While there is no universal rule for the temperature and length of time for these processes, the most commonly used formula prescribes a 1 hour soaking period at peak temperature per 1 inch (25mm) of thickness for each joint.
The stress relieving process can be performed in many different types of heat treating furnaces. The type of furnace required for post weld heat treatment can be a gas or electric furnace, the temperature ranges can vary greatly, and can be equipped with or without fans. Each of these options depends on the type of the material being heat treated, the desired outcome, and the specific process that is being performed.
The Post Welding Heat Treating process is a vital procedure for certain metals in order to maintain specific thicknesses or grades of quality. In some cases, heat treating can be detrimental to the welded metal if the procedure is not performed correctly, causing mechanism failure and corrosion. Steel is a metal that is often mishandled more than others and must be cared for properly. The tempering or aging process can cause the mechanical properties of the steel to deteriorate. Quenched and tempered steels, for instance, must be post weld heat treated at a lower temperature than the original tempering occurred at in order to preserve the natural strength and micro-structure qualities.
If you have more questions about the Post Weld Heat Treating process or PWHT Furnaces, contact us at Baker Furnace. Our on-staff industry experts are always available to assist you.