Comparison of corrosion behaviour of low-alloy pipeline steel exposed to H2S/CO2-saturated brine and vapour-saturated H2S/CO2 environments

This work used immersion experiments to elucidate the corrosion behaviour of low-alloy pipeline steel in vapour-saturated H2S/CO2 environment and H2S/CO2-saturated brine environment, typical corrosion environments of carbon capture and storage (CCS) sites. The corrosion behaviour was studied in terms of corrosion kinetics, corrosion products, surface morphology, cross-sectional morphology and elemental distribution. The experimental results demonstrated that the corrosion rate of vapour-saturated H2S/CO2 environment was lower than the corrosion rate of H2S/CO2-saturated brine environment. The difference in the corrosion environments is the underlying reason for the formation of different corrosion products. Compared to the H2S/CO2-saturated brine environment, the vapour-saturated H2S/CO2 environment was beneficial for the formation of fine crystals on a nano-scale because of the difference in the kinetics of crystal formation in corrosion environments. The corrosion products of vapour-saturated H2S/CO2 environment were formed as a cluster, while in the H2S/CO2-saturated brine environment, the corrosion products were precipitated uniformly, which was ascribed to the difference in the corrosion electrolyte structure. Chromium and molybdenum accumulated in the inner layer of corrosion products in the two corrosion environments. The corrosion process of low-alloy pipeline steel exposed to the H2S/CO2 environment is discussed.