A multiscale study on the synergistic failure mechanism of H2S corrosion and hydrogen embrittlement of X80 pipeline steel

The corrosion and hydrogen embrittlement behavior of X80 Pipeline steel in an H 2 S-containing acidic environment (pH = 3.0, 0.02–20 mmol L −1 ) was systematically investigated, and electrochemical hydrogen permeation tests, slow strain rate tensile tests, and density functional theory calculations were employed. Additionally, an atomic-scale analysis was performed on the adsorption and dissociation characteristics of H 2 S/H 2 on FeS corrosion scale. The results indicated that FeS structure evolved significantly with H 2 S concentration, its thickness increased with H 2 S concentration, only it was dense and continuous formed at higher H 2 S concentration (20 mmol L −1 ). The steady-state hydrogen flux ( J ∞ ) of X80 steel coated with FeS reduced by approximately 80% compared with that of bare steel, and a 31.5% decrease in the effective diffusion coefficient ( D eff ) was observed. When the edge hydrogen concentration exceeded a critical value, a distinct transition in fracture morphology was observed, which corresponded to an approximately 27% decrease in reduction of area after 14 d of hydrogen charging. Both the dissociation of H 2 S and H 2 on FeS surface provided hydrogen atoms, while the dissociation energy barrier of H 2 was as low as 0.37 eV, and a high energy barrier of 1.24 eV need be overcome when hydrogen diffused to the outermost atomic layer of FeS. This was highly consistent with the observed changes in macroscopic hydrogen permeation behavior, and a cross-scale failure mechanism from the atomic scale to macroscopic fracture was hence elucidated. • A quantitative “film-densification-extended diffusion-reduced flux” model is established for hydrogen permeation. • A unified multiscale framework bridges atomic surface reactions to macroscopic mechanical degradation. • The spatiotemporal competition between hydrogen-induced damage mechanisms is revealed.