Study on the synergistic failure of hydrogen embrittlement and corrosion in high-pressure hydrogen-blended natural gas pipelines

Blended hydrogen into natural gas pipelines enables efficient long-distance hydrogen transport. However, the synergistic effects of hydrogen embrittlement and corrosion in high-pressure environments remain unclear. Therefore, hydrogen blending ratios and transport pressure are limited for safety in engineering applications. To address this challenge, this study aimed to improve the safety and efficiency of hydrogen transportation. A highpressure in-situ permeation hydrogenation and electrochemical corrosion system was developed. Experiments were conducted in an 8 MPa hydrogen-blended natural gas environment. The research focused on X80 pipeline steel under two simultaneous degradation mechanisms: Hydrogen diffusion-induced embrittlement and impurity-induced corrosion. Surface characteristics and mechanical properties of the steel were systematically analyzed. The results show that under high-pressure hydrogen-blended natural gas, the fractures of the sample present a combination of ductile dimples and quasi-cleavage fractures, and the corrosion products are mainly FeCO3 and FeS. With the increase of hydrogen blending ratios, the number and size of dimples on the fracture surface of the sample decreased. At the same time, the corrosion resistance of the surface increases, while the loss of mechanical properties becomes more obvious. Elongation (14.3 %) fails to meet API 5L X80 requirement (18 %). Although strength values comply, safety margins become insufficient. Finally, the synergistic mechanism model of hydrogen embrittlement and corrosion was established by discussing the hydrogen diffusion and the corrosion behavior in hydrogen-blended natural gas.