The basic principles associated with the SHB based technique are first demonstrated on a simple straight pipe girth weld configuration. The method involves the use of a secondary heat band (SHB) that strategically positioned at some distance away from primary PWHT heat band (HB) in terms of vessel characteristic length parameter √Rt, where R is vessel radius and t wall thickness. This paper introduces a novel method for effectively mitigating high thermal stresses caused during local postweld heat treatment (PWHT) of welds in pressure vessels on which traditional heating method such as bull's eye heating arrangement has been proven difficult in meeting Code requirements for avoiding "harmful" temperature gradients. The paper addresses both circumferential and spot PWHTs and demonstrates that the guidelines provided in WRC 452 can also be used as a starting point for determining the band widths for spot PWHT. WRC Bulletin 452 provides guidelines for local PWHT to satisfy this requirement.This paper provides examples of local PWHT (if not heated as a whole vessel in a furnace) based upon utilizing a soak band and calculated heated band and gradient band widths based upon WRC 452 recommendations. This document considers various issues associated with the local heating of welds in pressure vessels and addresses the application of controlled heat in the weld metal, heat affected zone (HAZ) and a limited volume of base metal around the weld.ASME Boiler and Pressure Vessel Code Section VIII Division 1, paragraphs UW-40, (a) 3 and 8 require that post weld heat treatment (PWHT) be carried out in a manner such that the thermal gradients are not harmful. The Welding Research Council (WRC) Bulletin 452 titled “Recommended Practices for Local Heating of Welds In Pressure Vessels”(1) was first published in June 2000.
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