Corrosion Behavior of Highly Alloyed Materials in H2S-CO2-Cl- Environments

Abstract Corrosion behaviors of several highly alloyed materials were studied in aqueous H2S-CO2-Cl- environments at elevated temperatures. Both corrosion loss and susceptibility to stress corrosion cracking (SCC) increased with increasing the test temperature and the partial pressure of H2S. CO2 had no significant influence on the corrosion behaviors. Of the materials tested, ferritic and duplex stainless steels suffered both severe weight loss corrosion and SCC in H2S containing environments, while nickel base alloys were much corrosion resistant. Anodic polarization measurements in elevated temperature solutions proved that the presence of H2S increased the passive current density and shifted the pitting potential more negative, which means that localized corrosion is more liable to occur in H2S environments than in ones containing no H2S. Surface film analysis also revealed that the layer formed on low nickel alloys exposed in H2S environment was primarily composed of Cr-oxide. On the other hand, the nickel base alloys which exhibited excellent corrosion resistance were covered predominantly with Ni-Cr-Mo sulfide layer. This data suggests that sulfide formation on the surface plays an important role to sustain the corrosion resistance in H2S containing environments.