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 longterm 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.