Selection of Electrode Area for Electrochemical Noise Measurements to Monitor Localized CO2 Corrosion

The simultaneous fluctuations of potential noise and current noise between two nominally identical X-65 mild steel electrodes were recorded using a ZRA (Zero Resistance Ammeter) to monitor localized CO2 corrosion in CO2-saturated 1 wt % NaCl solution at 80C. Electrochemical noise (EN) was obtained from both 11.6 cm and 1 cm specimens to understand how the surface area affects EN signals. Linear polarization resistance (LPR) measurements were conducted to investigate the general CO2 corrosion behavior. Surface morphologies and pit depths were observed by scanning electron microscopy (SEM) and infinite focus microscopy (IFM) for 3D optical analysis. The results showed that the electrode area significantly influenced the EN signals of localized CO2 corrosion. Transients related to metastable pitting were best observed with 1 cm specimens but not clearly obtained for 11.6 cm specimens.