Performance of Welded High-Strength Low-Alloy Steels in Sour Environments

Sulfide stress cracking (SSC) susceptibility of gas metal arc welded API 5L X70 and X80 line pipe steel was tested using standard and modified NACE TM0177 (Method A) testing. Two applied stresses and three concentrations of dissolved hydrogen sulfide (H₂S) were used. The effect of peak weld hardness was examined by using three weld conditions. Several welds meeting the HRC 22 requirement failed by SSC. Welds containing hardness exceeding 248 HV were resistant to SSC at low H₂S concentrations. The centerline segregation region (CSR) observed in the X70 pipe steel played an important role in the SSC and hydrogen-induced cracking (HIC) susceptibility of the welds. The X80 material was more susceptible at lower hardness values due to localized softening during welding, and subsequent plastic deformation upon loading. An extrapolation to in-service weldments indicated that the NACE MR0175 requirements may be conservative for high-strength low-alloy steel welds not in direct contact with the sour environment.