The influence of trapped hydrogen on the passivity of iron oxides

The influence of cathodic charging on the passivity of iron oxides was investigated on X65 and X70 pipeline steels. The microstructure of X65 and X70 dictates the amount of hydrogen that could be trapped and subsequently desorbed during both potentiodynamic polarization scans and corrosion potential measurements. X65 was found to be more susceptible to hydrogen trapping and subsequent enhanced anodic dissolution due to a microstructure comprising pearlite and ferrite, compared to X70, which is almost a single-phase ferrite. • Trapped hydrogen accelerates corrosion by degrading surface oxides. • Reversible trapped hydrogen is dominantly located at ferrite/pearlite grain boundaries. • Microstructure of steel will influence susceptibility to breakdown of the passive film.