Post weld heat treatment services are vital for maintaining the strength and quality of welded components, structures and vessels. This process reduces the stress that occurs during welding, making the structure more resistant to failure due to dynamic loading conditions. In addition, post weld heat treatment can increase a structure’s resistance to corrosion by lowering its susceptibility to stress corrosion cracking.
What are the 5 basic heat treatment?
PWHT is a controlled heating and cooling process in which the workpiece is heated to a temperature below its lower critical transformation zone (LCT) and held there for a period of time. A variety of techniques can be used to carry out the process, including electrical resistance heating elements and induction heating.
While the advantages of PWHT are clear, the process is not without its risks. If the heat treatment is not properly performed, it can result in excessive stresses or distortions of the structure being treated. These defects can have significant and costly consequences.
Another risk of improperly performed PWHT is the occurrence of hydrogen in the weld zone. This can cause stress cracking in the welds and can also corrode the weld metal. Post weld heat treatment can be used to remove hydrogen from the weld area by applying a heat treatment known as hydrogen bakeout or post-heat, which is usually followed by a low-stress anneal to minimize the thermal stresses in the steel after welding.
For precipitation hardened alloys, proper post weld heat treatment is essential to maintain their strengths and ductility after welding. This process is important because the hardening of these alloys depends on precipitates that block dislocations in the crystalline structure, thus increasing their strength and hardness. When the precipitates are exposed to the high temperatures associated with welding, they may be changed in size and become less effective.