CO2 Corrosion of Mild Steel Exposed to CaCO3-Saturated Aqueous Solutions

Abstract

The behavior of CO2 corrosion of mild steel was studied in a CaCO3 saturated aqueous solution. The bulk water chemistry ([Fe2+], [Ca2+], and pH) was controlled and the mass transfer characteristics inherent to the experimental setup were well defined. A combination of weight loss and electrochemical techniques, as well as surface characterization tools, were used to assess the behavior of corrosion products over long-term experiments. Three corrosion periods were identified based on the analysis of the corrosion rates and Nyquist response values versus exposure time. Residual Fe3C was the early corrosion product; however, FexCayCO3 (x + y = 1) precipitated within its pores over the course of experiments where a favorable local water chemistry was achieved, regardless of the bulk solution. Results show that the presence of Ca2+ did not jeopardize the final protectiveness of corrosion products.