Influence of Hardness on Fatigue Life of Vintage X42 Pipeline Steel in Gaseous Hydrogen (C2026-00136)

Quinten Yurek, Joseph Ronevich, Chris San Marchi

Compatibility of existing natural gas pipelines with conveyance of hydrogen is of interest to the pipeline industry as a potential strategy to enhance energy security. Vintage pipelines (pre-1970) are of particular concern due to the known presence of microstructural hard spots associated with processing and welding. Gaseous hydrogen exposure is known to accelerate fatigue crack growth rates and lower fracture toughness in pipeline steels, and research has correlated higher hardness and strength to lower fracture toughness. Yet, there is a paucity of fracture data for incumbent material in gaseous hydrogen. Moreover, the relationship between hardness and fatigue crack initiation in pipeline steels is not well understood. The current work explores the influence of hydrogen on fatigue and fracture of ‘hard’ defects in pipeline steels using both existing hard spots from in-service pipelines, as well as artificially created hard material. Fracture tests were performed on vintage X52 steel using compact tension (CT) specimens in gaseous hydrogen at 210 bar. Additionally, artificial hard spots were created from a vintage X42 steel via austenization and direct water quenching. This material was evaluated using circumferentially notched tension (CNT) specimens to study the combined influence of hardness and gaseous hydrogen exposure in vintage pipeline infrastructure.