Passivation of X80 pipeline steel in a carbonate/bicarbonate solution and the effect of oxide film on hydrogen atom permeation into the steel

In this work, passivation of X80 pipeline steel was established at various passive potentials in a carbonate/bicarbonate solution. The passive films were characterized by topographical, compositional, and structural analysis techniques and electrochemical measurements. The effect of the passive film on hydrogen (H) atom permeation was investigated by electrochemical H permeation testing and scanning Kelvin probe force microscopy. The passive films primarily comprise Fe2O3/Fe3O4 and FeOOH. In the stable passive region, notably at 0.25 V (saturated calomel electrode, SCE), the formed passive film exhibits the highest film resistance, and the smallest double-layer capacitance and donor density. In contrast, oxide films formed at −0.1 V(SCE) and 0.55 V(SCE), which close to the active-passive transition and the transpassive regions, respectively, differ in their characteristics. The oxide films formed at −0.1 V(SCE) and 0.25 V(SCE) exhibit resistance against H atom permeation, and a superior performance is observed in the film formed at 0.25 V(SCE). The oxide film formed at 0.55 V(SCE) exhibits increased H atom permeation, which is attributed to the degraded structure of the film. Thus, the presence of compact oxide film (scale) on steel surface can effectively inhibit H atom permeation into the steel.