Heat Treatment is the controlled heating and cooling of metals to alter their physical and mechanical properties, without changing the product shape.

PWHT is the one of Heat treatment done after the welding/ machining to improve the mechanical property and material structure. In steel fabrication PWHT is commonly known as stress relieving.

• WHY THE NEED FOR PWHT?

Residual Stress
The development of residual stresses approaching or even exceeding the yield stress is possible when welding thick sections. Petrochemical, Chemical, Oil and Gas, etc. the existence of residual stress of this magnitude is completely unacceptable the stress developed due to thermal expansion of pipework can take on a far greater significance than residual stress due to welding.

• Other benefits...
• Improving the diffusion of hydrogen out of weld metal.
• Softening the heat affected zone and thus improving toughness (although not weld metal toughness).
• Improving dimensional stability during machining.