The corrosion of steel by aqueous solutions of hydrogen sulfide

Steel corrosion has been investigated through polarization studies in aque-ous H2S systems of acid pH using a rotating disk electrode cell. H2S does not change the Tafel slopes of the anodic and cathodic processes. The anodic curves are shifted toward more negative potentials mainly due to the de-crease of the reversible potential of iron, while the exchange current density appears to remain unchanged. The cathodic process maintains the reversible potential and the exchange current density of the H2S free system, but the H+ diffusion control gradually disappears. A corrosion current density depen-dence on the H2S concentration is found which matches that obtained from published weight-loss experiments. The product of corrosion, mackinawite is essentially nonadherent and in certain circumstances enhances the cor-rosion rate. A new method for the compensation of ohmic overpotential in polarization measurements is described. The corrosion of steel by aqueous H2S is a significan