Characteristics of N80 steel corrosion scales forming under different CO₂ pressures

Corrosion experiments of N80 steel were conducted under different CO₂ pressures by a high temperature and high pressure autoclave. The corrosion rate of N80 steel was calculated by the mass-loss method, the micrograph, thickness and Ca content of the corrosion scales were observed by scanning electron microscopy, and the electrochemical properties were measured and analyzed by electrochemical impedance spectra and potentiodynamic polarization. The shear strengths between the corrosion scale and the N80 steel substrate were measured. The results show that with the increase of CO₂ pressures the corrosion rate of N80 steel increases, the grain sizes of the corrosion scales show no obvious difference, and the amount of microcosmic flaws in the corrosion scales increases gradually. The resistance of the corrosion scale and the reaction resistance show the increase tendency. The shear strength between the corrosion scale and the N80 steel substrate decreases with the increase of CO₂ pressure, leading to the increase in corrosion rate.