Effect of in service weld repair on the performance of CrMo steel steam pipelines

Abstract

This article presents a literature overview and discusses a practical case involving the effect of in service weld repair on the performance - behavior under creep conditions and remanent life - of low alloy CrMo steel steam pipelines with longstanding use. According to the specialized literature, several authors argue that the in service weld repair of low alloy CrMo steel steam pipes can be done successfully, while others disagree, reporting a reduction of up to 30% or more in the remanent life. According to the case analyzed here, which involves the weld repair of a 1¼Cr½Mo ferrite-pearlite steel steam pipe operating for 20 years at 480 °C, in service weld repair leads to the intragranular precipitation of Fe2MoC-type carbides and decreases the solute concentration of the ferrite in the base metal adjacent to the welded joint, thereby considerably reducing the pipeline's remanent life, since the estimated rupture time for the service-aged material is 3.6 times that estimated for the weld-repaired joint.