Investigation of the fatigue crack growth behavior of X65 welded joints in high pressure natural gas/hydrogen mixed environment.

In this study, the fatigue crack growth behavior of X65 welded joints in a natural gas mixed hydrogen environment with a total pressure of 10 MPa and hydrogen volume fractions of 0%, 5%, 10%, 15%, and 20% was examined. The addition of hydrogen increased the fatigue crack growth rate (FCGR) of X65 welded joints by more than 10 times that of nitrogen. With an increase in the hydrogen volume fraction, the fatigue crack acceleration rate gradually increased, and was proportional to the square root of the hydrogen partial pressure. The fatigue crack propagation performance and hydrogen embrittlement sensitivity of the heat affected zone (HAZ) were the worst, which is related to the distribution of lath bainite (LB) with a high dislocation density and hard, brittle martensite/austenite (M/A) constituents in the HAZ. The mechanism of hydrogen-promoting fatigue crack propagation is that hydrogen promotes dislocation movement and enhances plasticity in the base metal (BM) and weld metal (WM) specimens, whereas it inhibits dislocation mobility and reduces plasticity in the HAZ specimens. Thus, the findings of this study can be expected to support the application of hydrogen transportation in natural gas pipelines. • The effect of hydrogen mixing ratios on FCGR of X65 welded joints was evaluated. • The HAZ exhibited the highest hydrogen embrittlement susceptibility. • The hydrogen embrittlement mechanism of X65 welded joints was analyzed. [ABSTRACT FROM AUTHOR]