Impact of oxygen contamination on the electrochemical impedance spectroscopy of iron corrosion in H2S solutions

Oxygen pollution in hydrogen sulfide (H2S) saturated test solutions can compromise the results of standardized tests, which guide materials selection in safety-critical components. To examine the temporal evolution of such contamination, we have used the electrochemical methods of impedance spectroscopy and hydrogen permeation to study the corrosion of iron exposed to oxygen-polluted H2S-saturated solutions. EIS analyses were performed with a previously developed model, which explicitly accounts for the contribution of a conductive and porous iron sulfide overlayer. A good correlation is found between corrosion estimates from EIS and weight loss, measured to be higher than the O-2-free case. Hydrogen permeation studies across the iron membrane were conducted to qualitatively evaluate the impact of dissolved 02 on hydrogen entry. We observe that O-2 contamination was found to significantly reduce hydrogen charging into the metal.