Evaluating hydrogen embrittlement susceptibility in pipeline steel welds

Abstract The objective of this study was to investigate the applicability of the delayed hydrogen cracking test (DHCT), standardized as AMPP TM21453, for evaluating hydrogen embrittlement (HE) susceptibility in pipeline steel welds. A comparative analysis of the HE mechanisms induced by the DHCT and the slow strain rate test (SSRT) was performed by quantifying the mechanical energy of crack nucleation and propagation in failures induced by these tests. The DHCT applies a static tensile load below the material yield strength (YS) in an electrochemically generated atomic hydrogen environment. Test results of X65 PSL2 steel welds demonstrated that the DHCT generates low-energy HE failures, associated with brittle QC and IG mechanisms, and can differentiate the effects of microstructure and weld profile-induced stress concentration on HE susceptibility. SSRT, performed in atomic hydrogen, induced brittle failures at plastic strains below 2%, showing potential application for evaluating HE susceptibility in pipeline welds for strain-based design service. Analysis of published results from SSRT in high-pressure gaseous hydrogen revealed that the related failure mechanism absorbs mechanical energy of up to three orders of magnitude higher than the DHCT. This was attributed to the large magnitude of plastic strain generated at loading above the material UTS, which is necessary for absorbing a sufficient amount of hydrogen to initiate HE failures.