Crack initiation due to low cycle fatigue in X60 pipeline steel tested in high pressure gaseous hydrogen using hollow and conventional specimens

• A X60 pipeline steel was low cycle fatigue tested in ambient air and 5 MPa hydrogen gas. • The results in air using conventional and hollow specimens were comparable. • The results in hydrogen using conventional and hollow specimens showed a longer lifetime of the hollow specimen be a factor of about 2 to 4. • The longer lifetime is presumably due to a delayed crack initiation in a fine-grained surface layer induced by deep-hole drilling. • The presence of a borehole had no significant influence on the elastic-plastic deformation of the specimen. The present work compares strain controlled low cycle fatigue results using hollow (HS) and conventional specimens (CS) for a X60 pipeline steel in ambient air and 5 MPa hydrogen gas, R ε = -1, f = 0.1 Hz. When tested in air, the LCF lifetimes of CS and HS are comparable. When tested in 5 MPa gaseous hydrogen, the lifetimes of HS are higher by a factor of 2 to 4 presumably due to a delayed crack initiation in the fine-grained surface layer induced by the deep-hole drilling technique used for manufacturing. For the HS tested in ambient air, fatigue cracks initiate randomly at the outer and inner gauge surface. For the HS tested in hydrogen gas, fatigue cracks always initiated at the inner bore gauge surface. A finite element analysis of the elastic–plastic response of CS and HS at typical LCF strain amplitudes revealed no significant difference between the specimen types.