| Abstract Scope |
Extensive research efforts have been focused on quantifying the effect of hydrogen embrittlement (HE) on the mechanical properties of steels used in pipelines and hydrogen storage and production systems. Most of these testing efforts include room or high temperature testing in high pressure gaseous hydrogen environment, using conventional and slow strain rate testing (SSRT), fatigue and fracture toughness testing. However, the applicability of the results from such tests for the service conditions in gaseous hydrogen transporting pipelines is limited. SSRT demonstrates the effects of HE on mechanical properties at loading above the material ultimate tensile strength (UTS). Therefore, SSRT results cannot characterize pipeline service conditions below the yield strength (YS) in stress-based design or up to 5% strain in strain-based design. Fracture toughness testing quantifies the resistance to propagation of existing cracks but cannot characterize the susceptibility to HE crack nucleation.
This paper presents the results of evaluating HE susceptibility in pipeline steel welds using the delayed hydrogen cracking test (DHCT), which was recently standardized as AMPP TM21453-2023. The DHCT applies a constant tensile load below or slightly above the material YS on flat gauge section weld specimens subjected to simultaneous electrolytic charging with hydrogen. The HE susceptibility is quantified by the time to failure at particular load level and by the mechanical energy needed for crack nucleation and growth to critical size. The DHCT replicates service conditions in stress- and strain-based design pipelines where atomic hydrogen can be generated on weld surfaces by local corrosion reactions at presence of moisture in the transported gas.
The paper draws a parallel between the HE phenomena introduced by the above listed tests, in terms of hydrogen adsorption, dissociation, absorption, and diffusion, and their effects on the crack nucleation and propagation mechanisms. |