Reaction Paths of Thiosulfate during Corrosion of Carbon Steel in Acidified Brines

Corrosion tests with gaseous H 2 S require special facilities with safety features, because H 2 S is a toxic and flammable gas. The possibility of replacing H 2 S with thiosulfate (S 2 O 3 2− ), a non-toxic anion, for studying stress corrosion cracking of stainless and carbon steels in H 2 S solutions was first proposed by Tsujikawa in 1993. H 2 S production was detected in presence of carbon steel corroding in acidified thiosulfate-containing solutions. In this paper, the kinetics of H 2 S evolution are used to estimate the range of partial pressure of H 2 S that can be simulated with thiosulfate solutions. It was determined that acid brines containing 10 −4 M and 10 −3 M S 2 O 3 2− could be used for replacing continuous bubbling of dilute H 2 S/N 2 mixtures in tests of degradation of carbon steels, with H 2 S partial pressures ranging between 0.03 and 0.56 kPa. The kinetics of H 2 S production were compared with the amount of sulfur in side reactions, like formation of iron sulfide films and elemental sulfur.