Influence of local post-weld heat treatment and its thermal analysis on thick wall carbon steel pipe

Abstract

Local post-heating was a common process during the field fabrication and repair of engineering components. Post Weld Heat Treatment (PWHT) attempts to relax residual stress when service requirement dictates the need for PWHT. The additional objectives such as hardness reduction stress relaxation aimed to be below a specific threshold level. Many factors have influenced on PWHT procedures, such as the size of the pipe, heating width, insulation conditions, heating rates, soaking temperature and holding time, material composition, etc. However, up to now, the influences of these factors on PWHT were not clearly understood and different criteria for sizing the parameters. It can be found in different codes. PWHT was to attempt and duplicate the outcome of furnace heating (i.e heating the whole weldment) within a localized region, referred to the soak band surrounding the weld. The width of heating coil from 500 to 600 mm significantly reduced the temperature gradient in between OD and ID of the carbon steel pipe. The increase in thermal energy moderately enhanced the temperature gradient on the carbon steel pipe.