Corrosion Behavior of 16Mn Steel under Different CO₂ Partial Pressure in Oil Field Gathering and Transportation System

The corrosion behavior of 16Mn steel in the stimulating environment of oil field gathering and transporting system with different CO₂ partial pressure was investigated by dipping test and electrochemical test. The results show that the corrosion rate of 16Mn steel increased first then decreased with the increase of CO₂ partial pressure. The corrosion product scale was not formed on the surface of 16Mn steel when CO₂ partial pressure was 0 and the type of corrosion was uniform corrosion. The corrosion product scale was complete and compact at the CO₂ partial pressure of 0.15 MPa and the type of corrosion was uniform corrosion. When CO₂ partial pressure was 0.30 MPa, the corrosion product scale became thinner and defects occurred,and the type of corrosion was platform corrosion. The main corrosion product on the surface of 16Mn steel was FeCO₃. The major corrosion behavior of 16Mn steel was anodic active dissolution. The middle frequency inductive loop of electrochemical impedance spectroscopy was related to the dissolution and absorption of corrosion products. The low frequency capacitive loop was related to the active dissolution of corrosion scale covered area.