Changes in Corrosion of X70 Steel in Water-Saturated Supercritical CO<sub>2</sub> System Caused by Impurity

Abstract

During the process of Carbon Capture and Storage, some impurity may be found in the supercritical CO2fluid. The changes in corrosion of X70 Steel in water-saturated supercritical CO2system caused by impurity has been studied by the simulation experiment. The average corrosion rate was got from weight loss measurement. The morphologies and compositions of corrosion products were analyzed by SEM, EDS and XRD. It was observed that the existence of separate impurity would aggravate the corrosion of X70 steel in the water-saturated supercritical CO2system. The average corrosion rate was the highest when NO2or SO2was included, followed by H2S, and the average corrosion rate was the smallest when O2was contained. Among them, X70 steel suffered local corrosion when NO2was contained. The corrosion scale was monolayer structure of FeCO3under the supercritical CO2-H2O system. After the addition of O2, Fe2O3appeared in the corrosion scale, indicating that the oxygen corrosion process occurred. While with the addition of H2S, corrosion scales were double layers. FeS was mainly present in the outer layer. The corrosion process was controlled by CO2and H2S. The corrosion products were mostly FeSO3·xH2O and a spot of FeCO3when SO2was contained. SO2mainly governed the corrosion process. Besides, corrosion product was Fe2O3without FeCO3in the supercritical CO2-H2O-NO2system, NO2completely controlled the corrosion process.