Fatigue and fracture of high-hardenability steels for thick-walled hydrogen pressure vessels

Stationary pressure vessels for the storage of large volumes of gaseous hydrogen at high pressure (>70 MPa) are typically manufactured from Cr-Mo steels. These steels display hydrogen-enhanced fatigue crack growth, but pressure vessels can be manufactured using defect-tolerant design methodologies. However, storage volumes are limited by the wall thickness that can be reliably manufactured for quench and tempered Cr-Mo steels, typically not more than 25-35 mm. High-hardenability steels can be manufactured with thicker walls, which enables larger diameter pressure vessels and larger storage volumes. The goal of this study is to assess the fracture and fatigue response of high hardenability, Ni-Cr-Mo pressure vessel steels for use in high-pressure hydrogen service at pressure in excess of 1000 bar. Standardized fatigue crack growth tests were performed in gaseous hydrogen at frequency of 1Hz and for R-ratios in the range of 0.1 to 0.7. Elastic-plastic fracture toughness measurements were also performed. The measured fatigue and fracture behavior is placed into the context of previous studies on fatigue and fracture of Cr-Mo steels for gaseous hydrogen.