The simultaneous fluctuations of potential noise and current noise between two nominally identical X-65 mild steel electrodes were recorded in deaerated aqueous sodium chloride solutions with concentration ranging between 1 and 20 wt % at 80°C. Electrochemical noise (EN) was obtained from both 11.6 cm2 and 1 cm2 coupons in 1 wt % NaCl solution to learn how the surface area affects EN measurements. Only small surface area coupons (1 cm2) were used in 10 wt % and 20 wt % NaCl solution experiments to understand the role of Cl− on localized corrosion processes. Linear polarization resistance measurements were conducted in each experiment to investigate the general corrosion behavior. The surface morphology of coupons was observed with a scanning electrochemical microscope (SEM). The results showed that the electrode area influenced the EN signal. Transients related to metastable pitting were best observed with 1 cm2 coupons in 1, 10, and 20 wt % NaCl solutions, but such transients were not clearly obtained for 11.6 cm2 coupons in the 1 wt % NaCl solution. Both statistical analysis of recorded current and potential noise and SEM analysis showed that increasing the NaCl solution concentration did not change the localized corrosion rate.

Subject
Electric current, Films, Electrochemical noise, Steel coupons, Corrosion products, Sodium chloride solution, Current noise, Salt concentration, Pitting, Corrosion coupons, Localized corrosion, Electrodes, Electrode potential
Keywords:
Localized CO2 corrosion, mild steel, electrochemical noise, electrode size, NaCl concentration
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2009
Association for Materials Protection and Performance (AMPP)
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