Transcription of Key Concepts in Welding Engineering - Foundation
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Key Concepts in Welding Engineering - Foundation
Welding Innovation Vol. XV, No. 2, 1998 What is PWHT?Postweld heat treatment (PWHT),defined as any heat treatment afterwelding, is often used to improve theproperties of a weldment. In concept ,PWHT can encompass many differentpotential treatments; however, in steelfabrication, the two most common pro-cedures used are post heatingandstress is it Required?The need for PWHT is driven by codeand application requirements, as wellas the service environment. In gener-al, when PWHT is required, the goal isto increase the resistance to brittlefracture and relaxing residual desired results from PWHT mayinclude hardness reduction, and mate-rial strength HeatingPost heating is used to minimize thepotential for hydrogen induced crack-ing (HIC). For HIC to occur, the follow-ing variables must be present (seeFigure 1): a sensitive microstructure,a sufficient level of hydrogen, or a highlevel of stress ( , as a result ofhighly constrained connections).
Welding Innovation Vol. XV, No. 2, 1998 residual stresses. Carbon steels are typically held at 1,100 to 1,250°F (600 to 675°C) for 1 hour per inch (25 mm)
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