Effect of water content on the corrosion behavior of X65 pipeline steel in supercritical CO2-H2O-O2-H2S-SO2 environment as relevant to CCS application

Highlights: • The water content limit is 1500 ppmv in CO₂-O₂-H₂S-SO₂ streams at 10 MPa and 50 °C. • The water content in CO₂ streams notably affects the corrosion film characteristics. • The impurity interactions promote the precipitation of water phase from CO₂ streams. • The water chemistry characteristics depend on impurities and impurity interactions. • Effect of water content in CO₂ streams on corrosion mechanism of steel is discussed. - Abstract: The water content limit of 1500 ppmv is obtained in supercritical CO₂ streams containing 200 ppmv O₂, 200 ppmv SO₂ and 200 ppmv H₂S at 10 MPa and 50 °C. Concurrently, the thermodynamic calculation suggests that impurities change the corrosion process through promoting the water precipitation and changing the water chemistry characteristics. When the water content is below 1500 ppmv, the corrosion effect of impurity interactions dominates the corrosion process of X65 steel. Whereas upon increasing the water content over 1500 ppmv, the corrosion effects from impurity interactions and individual impurity jointly control the corrosion process of X65 steel.