Effect of Calcium on the Formation and Protectiveness of Iron Carbonate Layer in CO_2 Corrosion

摘要

Among the known options in carbon capture and storage (CCS), the injection and storage of CO_2 in deep saline aquifers has the potential to cause casing corrosion due to the direct contact between injected CO_2 and the saline aquifer, containing highly concentrated aqueous salts such as NaCl and CaCl_2. Thus, in the present study, the effect of Ca~(2+) on the CO_2 corrosion behavior of mild steel was investigated in simulated saline aquifer environments (1 wt.% NaCl, 80°C, pH 6.6) with different concentrations of Ca~(2+) (10, 100, 1,000 and 10,000 ppm). Electrochemical methods (open circuit potential (OCP) and linear polarization resistance (LPR) measurements) were used to measure the corrosion rate. Surface analysis techniques (scanning electron microscope (SEM), X-ray spectroscopy (EDS) and X-ray diffraction (XRD)), were used to characterize the morphology and identity of the corrosion products. The results show that with low concentrations of Ca~(2+) (10 and 100 ppm), the corrosion rate decreased with time due to the formation of protective FeCO_3 and/or Fe_xCayCO_3 (x + y =1). However, the presence of high concentrations of Ca~(2+) (1,000 and 10,000 ppm) resulted in the change of corrosion product from protective FeCO_3 to non-protective CaCO_3, and an increasing corrosion rate with time. While the general corrosion rate was high for both 1,000 and 10,000 ppm Ca~(2+), surface analysis data revealed a different steel surface morphology with pitting observed in the presence of 10,000 ppm Ca~(2+).