Evaluation of Thiosulfate as a Substitute of Hydrogen Sulfide in Sour Corrosion Fatigue Studies

Corrosion fatigue is a significant threat to offshore oil and gas pipelines. Waves, tidal motion, and operational vibrations control periodic stresses, which are usually superimposed on static tension stresses arising from the internal pressure of the pipe, or from residual stresses near welds. Hydrogen sulfide (H2S) increases corrosion fatigue crack growth rate (FCGR) and can be present in production fluids transported by carbon steel risers and flowlines used in offshore oil and gas production. Therefore, the evaluation of materials for this application requires the use of gaseous H2S to mimic service environments. Corrosion tests with gaseous H2S require expensive facilities with special safety features, because H2S is a toxic and flammable gas. The possibility of replacing H2S with thiosulfate (S2O3), a non-toxic anion, for studying sulfide stress cracking and stress corrosion cracking of stainless and carbon steels in H2S solutions was first proposed by Tsujikawa et al. [1,2]. In this project, Tsujikawa work was reviewed and extended to sour corrosion fatigue of carbon steels.