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

Corrosion tests with gaseous H2S require special facilities with safety features, because H2S is a toxic and flammable gas. The possibility of replacing H2S with thiosulfate (S2O32-), a non-toxic anion, for studying stress corrosion cracking of stainless and carbon steels in H2S solutions was first proposed by Tsujikawa in 1993. H2S production was detected in presence of carbon steel corroding in acidified thiosulfate-containing solutions. In this paper, the kinetics of H2S evolution are used to estimate the range of partial pressure of H2S that can be simulated with thiosulfate solutions. It was determined that acid brines containing 10(-4) M and 10(-3) M S2O32- could be used for replacing continuous bubbling of dilute H2S/N-2 mixtures in tests of degradation of carbon steels, with H2S partial pressures ranging between 0.03 and 0.56 kPa. The kinetics of H2S production were compared with the amount of sulfur in side reactions, like formation of iron sulfide films and elemental sulfur. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.085204jes] All rights reserved.