Corrosion Behavior of Carbon Steel in Acidified, Thiosulfate-Containing Brines

The corrosion rate of carbon steel in acidified, thiosulfate-containing brines increased with thiosulfate content. Thiosulfate also increased the rate of cathodic and anodic reactions, as measured in polarization curves obtained shortly after immersion of the electrode. Current from iron dissolution was balanced by hydrogen evolution and reduction of thiosulfate to produce hydrogen sulfide. Hydrogen sulfide production represented a large fraction of the open-circuit corrosion current. Carbon steel specimens exposed to thiosulfate-containing solutions developed a film on their surface, composed of iron sulfide and cementite. The film was a good conductor of electrons and non-passivating. The rate of cathodic reactions measured for the film-covered electrode was faster than in the absence of the film, suggesting it is a good catalyst for reduction reactions. The ability of acidified, thiosulfate-containing brines to simulate hydrogen sulfide solutions was critically analyzed.