Synergistic effect of hydrogen embrittlement and corrosion on the pressure dependence of X80 steel in hydrogen-blended natural gas

The synergistic effect of hydrogen embrittlement and corrosion threatens the stable operation of pipelines. This study systematically investigates the synergistic degradation mechanisms of hydrogen embrittlement and corrosion in X80 pipeline steel under 40 % hydrogen-blended natural gas environments at different transportation pressures (6–8 MPa), simulating the operational conditions of China West-East Gas Pipeline II. Key findings include: When the pressure increases from 6 MPa to 8 MPa, the peak hydrogen permeation current density rises by 24.9 % from 31.99 to 39.97 μA/cm² at increased pressure; the charge transfer resistance decreases by 19.7 % to 400.41 Ω·cm². High pressure promotes the formation of a uniform corrosion product film, reducing localized pitting but accelerating general corrosion. Ultimate tensile strength decreases by 16.2 % to 646 MPa at 8 MPa, with elongation dropping to 18.2 %, close to the API 5 L threshold of 18 %. Reduction in area declines from 53.7 % to 39.9 %, accompanied by a fracture mode transition from ductile dimples to brittle quasi-cleavage. Based on the experimental results, it is recommended that the operating pressure of hydrogen-blended natural gas pipelines under conditions consistent with the experimental conditions be controlled below 6 MPa.