Influence of pipe steel and welded joint microstructure on failure resistance with testing in hydrogen

The article deals with assessment of hydrogen embrittlement resistance of pipeline steel of strength class K60 (X70 Grade) with different types of microstructure, as well as welded joints. Results of threshold stress tests (according to the ASTM E1681 standard) and slow strain rate tension tests (SSRT) of pipe metal in hydrogen and hydrogen-nitrogen mixtures at a pressure of 10 MPa are presented. Steel structure and Vickers hardness distribution along a subcritical crack front are investigated for specimens after crack resistance tests. Structural features of pipe base metal and welded joint metal (weld metal and heat-affected zone), which may affect pipe steel hydrogen embrittlement and values obtained for crack growth during crack resistance tests are considered.