Mechanism of corrosion product films on hydrogen permeation and corrosion behavior of X80 steel under electrochemical hydrogen charging conditions

This study systematically investigates the time-dependent evolution of corrosion product layers on X80 steel during 120 days of seawater immersion and their effects on hydrogen transport and electrochemical corrosion behavior. The results show that the corrosion products mainly consist of Fe 3 O 4 , Fe 2 O 3 , and FeOOH, with the Fe 3 O 4 content progressively increasing and the Fe 2 O 3 content decreasing with prolonged immersion. A critical transition occurs between 60 and 75 days, during which the corrosion product film is proposed to develop a bilayer-like configuration, accompanied by an increase in the Fe 3 O 4 fraction to 43.64% and a subsequent reduction in both hydrogen permeation and anodic dissolution. Furthermore, a semi-empirical relationship, D = D 0 ·exp(-k·f), is established to correlate the Fe 3 O 4 fraction (f) with the hydrogen diffusion coefficient (D). Based on these observations, a three-stage evolution framework is proposed: (I) film formation and loosening (0–45 days), (II) compositional transition and enhanced hydrogen transport (45–75 days), and (III) film densification and inhibitory effects (75–120 days). Overall, this study provides a time-dependent and parameterizable description of the evolution of corrosion product layers and their coupled effects on hydrogen transport and electrochemical corrosion, extending the understanding of corrosion-film evolution beyond the qualitative trends reported in previous short-term studies.