The effect of in-service degradation of X52 gas pipe steel on fracture toughness of hydrogenated specimens evaluated by the J-integral method

The development of hydrogen energy implies various aspects, one of which is hydrogen transportation through pipelines. Repurposing the existing gas pipeline network is considered reasonable. However, the pipe metal is subjected to degradation due to its long-term operation, which results in sensitivity to hydrogen-assisted cracking and embrittlement. Since fracture toughness is an essential indicator of brittle fracture resistance, estimating the hydrogen effect on this parameter is crucial. The pipe steel 17H1S (API 5L X52 grade), is investigated in the as-received state and after 38 years of operation at a gas main pipeline. It is established that the fracture toughness of pipe steel 17H1S, evaluated by the J -integral method, is lower for operated steel. Hydrogen embrittlement is revealed by testing the specimens in air immediately after their electrolytic hydrogen charging. Fracture mechanics indicators are significantly more sensitive to the hydrogen impact on steel than plasticity under moderate hydrogen charging ( i cat = 0.05 mА/сm 2 ) conditions. This effect diminishes under intensive hydrogenation ( i cat = 1.0 mА/сm 2 ). The critical J -integral value is significantly decreased with the displacement rate reducing by two orders of magnitude for steel in both as-received and operated states. The displacement rate affects the crack growth resistance of electrochemically hydrogenated steel specimens. The fractographic signs of hydrogen influence after ex-situ hydrogen charging are cleavage areas, delaminations, secondary cracking, and cementite elimination within pearlitic grains, which are more pronounced in the operated steel than in the as-received one.