Inhibition of hydrogen embrittlement induced by CH₄ in pipeline transportation of hydrogen-natural gas mixtures

The adsorption and dissociation of H₂ on the surface of pipe steel is the prerequisite for the permeation and diffusion of hydrogen atoms in steel matrix. The existence of H₂ in natural gas pipeline increases the risk of hydrogen embrittlement. Based on the molecular dynamics simulation and first-principles calculation method, the H₂ adsorption on the surface of pipeline steel is studied. Also the competitive adsorption law of CH₄ and H₂ at different hydrogen ratios is analyzed. The influence of CH₄ on H₂ dissociation behavior near the pipeline steel surface is probed comprehensively. Major results are listed below: (1) for pure gas components, both CH₄ and H₂ exhibit near surface adsorption characteristics; (2) for CH₄/H₂ mixtures, CH₄ has preferential adsorption characteristics, which significantly reduces the adsorption concentration of H₂ on pipeline steel surface; (3) The adsorption behavior of CH₄ and H₂ on the surface of pipeline steel are distinguished. The existence of CH₄ cannot completely prevent the adsorption of H₂ on the surface, but can effectively reduce the H₂ adsorption possibility. Hydrogen partial pressure cannot accurately and quantitatively reflect the distribution of hydrogen concentration on the surface. In addition, the competitive adsorption of gas components should be considered when conducting relevant research. Simultaneously, the existence of CH₄ could reduce the possibility of Hydrogen Embrittlement (HE) to some extent. The research is beneficial for understanding the mechanism of HE in hydrogen-doped natural gas pipelines.