Effect of O2 Concentration on Corrosion Rate of Steels in Supercritical CO2

Abstract

The carbon capture and storage (CCS) in geological reservoirs is now considered to be one of the main options for achieving deep reductions in CO2 emissions. Generally, the purity of captured CO2 is only about 95% and can contain trace gases such as O2, CO, SOx and NOx. In the presence of a water phase, these trace gases can contribute to the corrosiveness of high pressurehigh temperature CO2 (supercritical CO2) systems. In this study, corrosion experiments of supercritical CO2 with various amounts of O2 were carried out to study the effect of small concentrations of O2 on the corrosion rate of two kinds of carbon steels C75 and X65 and three kinds of stainless steels 13Cr, 2205 and 904L in aqueous supercritical CO2 at 80 °C under 12 MPa. The decay kinetics of small starting O2 concentrations were investigated and used for the experiments with continuous replenishment of used-up O2. The results indicated that constant O2 concentrations in supercritical CO2, even trace of O2 (1.50×10), could enhance the corrosion rate of carbon steels tremendously (more than 100 mm/a). Under this condition, even the corrosion rate of 13Cr stainless steel obviously increased. However, surprisingly, with high O2 concentrations seemed to exhibit passivation effect and the corrosion rates for carbon steels and 13Cr stainless steel were relatively low. The 2205 and 904L stainless steels were unaffected by addition of O2 and showed high resistance (< 0.01 mm/a) to the aqueous supercritical CO2 corrosion.