Corrosion Behavior of Nickel Base Alloy G3 in High H₂S and CO₂ Containing Environment

Corrosion behaviors of the nickel base alloy G3 in the environment containing high contents of H2S and CO2 were investigated by simulated high temperature and high pressure corrosion test, dynamic potential scanning technique and X-ray photoelectron spectroscopy (XPS). The results show that the nickel base alloy G3 corroded distinctly in simulated natural gas field produced-water under the conditions of 90℃, total pressure of 32 MPa, H2S partial pressure of 3.4 MPa and CO2 partial pressure of 3.3 MPa. Corrosion scale formed on the alloy surface was made up with flake-like grains. Adding CO2 enhanced the pitting corrosion susceptibility of the alloy in the simulated natural gas field produced-water containing 50% H2S, however, pitting corrosion was suppressed when CO2 content further increased. In 50%H2S and 50%CO2 containing environment, chloride increased the pitting corrosion susceptibility, and high concentration of chloride harmed the self-repair of the passive film. The passive film was consisted of Cr2S3, Cr2O3, FeS, Fe2O3, Ni(OH)2 and MoO3 in above corrosive environment. The passive film formed on the alloy was damaged and corrosion becames more badly when the alloy was used under the condition of higher temperature and partial pressures of H2S and CO2, and higher concentration of chloride.