Effect of CO₂ Partial Pressure on Corrosion Resistance of X80 Pipeline Steel

The effect of CO2 partial pressure on corrosion resistance of X80 pipeline steel was investigated in high temperature and pressure autoclave simulating the downhole environment of an oil field, using the weight loss method, SEM and XRD. The results showed that with increasing CO2 partial pressure , the corrosion rate of X80 pipeline steel showed the tendency of fluctuation, and the maximum rate appeared at the CO2 partial pressure of 1.5 MPa. Uniform corrosion occurred when the CO2 partial pressure was 0 MPa and 0.5 MPa. When the CO2 partial pressure was 1.5 MPa and 2 MPa, localized corrosion occurred. The corrosion product was composed of noncrystalline substance at partial pressure of 0 MPa, and mainly composed of FeCO3 at other partial pressures. With increasing the CO2 partial pressure, the combination between corrosion product and substrate was increasingly close, and the thickness of corrosion product showed the tendency of fluctuation, corresponding to the change in corrosion rate.