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Abstract

Hydrogen is being considered for low-carbon energy transport, but assessing pipeline readiness requires testing infrastructure and mechanical characterization under gaseous hydrogen. This dissertation addresses both needs by (i) designing and commissioning a modular gas management system with two complementary in-situ setups, a hollow-specimen setup and an autoclave-based testing setup, and (ii) characterizing hydrogen embrittlement in three pipeline steels: a vintage CSA Z245.1 Grade 290 and two modern API 5L X60 steels from different mills. Slow strain rate tensile results show that Grade 290 loses ductility rapidly with increasing hydrogen pressure, whereas the X60 steels retain significantly higher ductility. The hydrogen embrittlement index for X60I indicates a moderate reduction, while X60J shows only slightly higher susceptibility depending on sampling position. Through-thickness variations in X60J, particularly at the inner and middle wall, where segregation and banding are most pronounced, increased secondary cracking was observed. Under cyclic loading, Stage II behaviour observed in air is relatively insensitive to microstructural differences, but hydrogen accelerates crack growth at lower stress intensity ranges. Fatigue crack growth rate results identify X60J as the preferred modern steel for hydrogen service because its banded bainitic ferrite colonies deflect advancing cracks and slow propagation, extending fatigue life compared to X60I. In contrast, Grade 290 transitions earlier toward unstable crack growth, confirming its lower fracture toughness and less suitability for hydrogen repurposing. The developed infrastructure enables safe, repeatable, and service-relevant in-situ testing under gaseous hydrogen, forming a framework for consistent evaluation of hydrogen-assisted degradation. The results demonstrate that microstructural characteristics, rather than the nominal grade, govern hydrogen performance. Modern X60 steels can be viable candidates for hydrogen transport, but each pipeline's heat and wall position must be independently verified to confirm readiness. Overall, this research establishes the first academic capability in Canada for gaseous hydrogen embrittlement testing and bridges a major technological gap in evaluating pipeline materials for hydrogen service. It provides a foundation for future national research supporting pipeline repurposing, qualification protocols, and Canada’s broader transition toward a hydrogen-based energy infrastructure.