The Effect of Electrode Size on Electrochemical Noise Measurements and the Role of Cl- on Localized Corrosion for Mild Steel in CO2 Corrosion Environment

The simultaneous fluctuation of potential noise and current noise between two nominally identical X-65 mild steel electrodes were recorded in deaerated NaCl solution at different concentrations (1wt%, 10wt% and 20wt%) at 80^oC. Electrochemical noise was obtained from two 11.6cm² and two 1cm² coupons in 1wt% NaCl solution to learn how the surface area affects electrochemical noise measurements. Small surface area coupons (1cm²) were used in 1wt%, 10wt% and 20wt% NaCl solution experiments to understand the role of Cl^- on localized corrosion processes. Linear polarization resistance measurements (LPR) were conducted in each experiment to learn the general corrosion behavior. The surface morphology of coupons was observed with SEM. The results showed that electrode area influenced the electrochemical noise signal, transients related to metastable pitting were best observed from 1cm² coupons in 1wt% NaCl solution, 10wt% NaCl solution and 20wt% NaCl solution, but such transients were not clearly obtained for 11.6cm² coupons in 1wt% NaCl solution. Both statistical analysis of being recorded current and potential noise and SEM analysis showed that increasing NaCl solution concentration did not change the localized corrosion rate.