Investigation on mechanized pulsed GMAW process for sour-service pipeline welding

Abstract

Abstract This study investigates the applicability of mechanized Pulsed Gas Metal Arc Welding (m-PGMAW) for the girth welding of API 5L X65 subsea pipelines intended for sour service. Welds were fabricated using ER70S-6 filler wire and augmented process parameters, yielding defect-free joints with a controlled heat-affected zone (HAZ). Hardness mapping confirmed a maximum of 210 HV10, well below the industry standard threshold (250 HV10) for sulfide stress cracking resistance. Tensile testing demonstrated strength matching between weld and base metal, with improved properties at sub-zero temperature (−11 °C). Fatigue crack growth rate (FCGR) tests revealed significantly accelerated crack propagation in a sour environment compared to air, attributed to hydrogen embrittlement. The findings provide critical experimental data for Engineering Critical Assessments (ECA), ensuring conservative flaw acceptance criteria and long-term structural integrity of subsea S-lay pipelines operating in aggressive sour environments, and it validates the robustness of the developed m-PGMAW procedure.