Residual Stress Influence on Soft-Zone Cracking in Electric Resistance Welded Line Pipe Steels under Sour Service Conditions

Abstract Soft-zone cracking (SZC) is a form of hydrogen-induced cracking that occurs in the softened heat-affected zone (HAZ) of welds, commonly expressed in low-carbon line pipe steels produced through thermo-mechanically controlled processing (TMCP). When exposed to aqueous H2S (sour service) conditions, constrained deformation of the softened HAZ, in combination with hydrogen degradation and applied loading, leads to localized stress concentrations that promote cracking. The role of residual stresses (RSs) in SZC remains unclear, as specimen preparation for standard sulfide stress cracking (SSC) testing may redistribute stresses and affect test outcome. This study evaluates the influence of RS redistribution on SSC performance. A 52 ksi (359 MPa) yield strength ERW line pipe was evaluated using 4-point bend SSC testing, with SZC consistently observed in the HAZ-pipe body transition region. Hole drilling RS measurements were performed on an untested pipe ring, followed by additional measurements on test coupons cut from the pipe. Finite element analysis (FEA) was performed based on hole-drilling data to assess stress evolution in tested coupons to understand the role of RSs in SZC initiation. This work provides a novel approach to improve SSC test interpretation by accounting for residual stress effects, creating a reliable assessment of sour service performance in welded line pipe steels.