Combining Thermodynamics and Kinetics to Investigate the Corrosion of 3Cr Steel and HP-13Cr Stainless Steel in Extreme Oil-Gas Environments

ABSTRACT The corrosion behavior of 3Cr steel and HP-13Cr stainless steel (SS) under high temperature and CO2 or H2S pressure environments was investigated by immersion tests and multiple characterizations of corrosion films, and analyzed by combining the Pourbaix diagram and kinetic calculations. At 180 °C/3.8 MPa CO2, both 3Cr steel and HP-13Cr SS exhibited double-layered corrosion films, comprising a crystalline FeCO3 outer layer and an inner Cr2O3 and Cr(OH)3 layer. Furthermore, at 180 °C/3.8 MPa H2S, the corrosion films of both steels consist of an outer crystalline pyrrhotite and pyrite layer and an inner Cr2O3 and Cr(OH)3 layer. The corrosion resistance of 3Cr in H2S is inferior to that of HP-13Cr SS due to the influence of stress corrosion cracking but is close to that of HP-13Cr SS in CO2. Therefore, 3Cr steel could be considered a cost-effective alternative to HP-13Cr SS in CO2 environments.