CO₂/H₂S Corrosion Behavior of Carbon Steel in Oil-Water Heterogeneous Media

Polarization curves and electrochemical impedance tests were used to study the corrosion behavior of N80 steel under different CO₂ and H₂S partial pressure ratios in a mixed solution of 3% NaCl saline and condensate oil at 50 ℃. The morphology and composition of corrosion products on the surface of N80 steel were analyzed using SEM, XPS, etc. The results showed that in a saturated CO₂ solution, the corrosion of carbon steel electrodes weakened with the increase of H₂S content. When θ＜20, with the increase of θ, the corrosion current density gradually decreased, and corrosion was mainly controlled by H₂S. Uniform and dense needle like crystal corrosion products were generated on the surface of N80 steel, mainly FeS and FeS_1-x films. When 20<θ＜500, with the increase of θ, the corrosion current density increased, the corrosion current density first increased and then decreased. The corrosion was jointly controlled by CO₂ and H₂S, and various crystal corrosion products were generated on the surface of the steel sheet, mainly FeCO₃ and FeS_1-x films. When θ＞500, with the increase of θ, the corrosion current density increased, the corrosion reaction was controlled by CO₂, and polygonal irregular crystal corrosion products were generated on the surface of the steel sheet, mainly FeCO₃ film containing a small amount of Fe₃O₄.