Influence of Temperature on Corrosion Behavior of N80 Steel in CO₂/O₂ Co-existing Environment

The corrosion behavior of N80 steel in CO2/O2 co-existing environment at different temperatures was studied using high temperature and pressure autoclave, weight loss method, X-ray diffraction, scanning electron microscopy and energy dispersive spectrometer. The results showed that the corrosion rate of N80 steel increased rapidly first and then decreased slowly with temperature increasing in CO2/O2 co-existing environment. The maximum corrosion rate arrived when temperature was 90 ℃. From the results of XRD, the corrosion products formed in CO2/O2 co-existing environment were composed of FeCO3, Fe2O3 and Fe3O4 at three temperatures. The surface of N80 steel was closely covered by corrosion products mainly composed of FeCO3 which can prevent the corrosion process at low temperature. With temperature increasing, the oxide content of the corrosion products increased gradually which produced a loose film with weak protection. When the temperature reached 120 ℃, the iron oxide products became dense gradually, so the film had certain protective effect.