Influence of Hydrogen on Low Temperature Fracture Toughness Behavior of Pipeline Steel X70 in Nordic Operation Conditions

Low (freezing) temperatures that prevail in the Arctic and Nordic regions affect the hydrogen safety assessments. Recently, a Nordic research project was launched with the goal of understanding the combined influence of low temperatures and hydrogen on the fracture toughness of pipeline steels. The objective of this work is to investigate the effect of hydrogen and loss of constraint on fast fracture (> 1 MPa√m/s) and subcritical crack growth behavior of a X70 pipeline steel at subzero temperatures and room temperature. The fast fracture characterization was performed using pre-charged single edge tension (SE(T)) specimens with a/W = 0.2 and single edge bend (SE(B)) specimens with a/W = 0.5. Subcritical crack growth behavior was characterized under gaseous hydrogen at room temperature using disk-shaped compact tension (DC(T)) specimens. The hydrogen charging of the SE(T) and SE(B) specimens was done using electrochemical charging. The testing in hydrogen gas was performed in a double bellow based pneumatically powered Hybello with a miniature autoclave. This work presents the preliminary results from the project and assesses the results with respect to B31.12 and API 934 part 4. The project will enable evaluation of the transferability of fracture toughness in hydrogen conditions and evaluation of critical crack size for X70 hydrogen pipelines at low temperatures.