Corrosion monitoring of steel in moderate corrosive environments by electrochemical noise impedance

Abstract

The corrosion monitoring of carbon steel in moderate corrosive environments was carried out using electrochemical noise impedance. For correct electrode impedance estimation, it was emphasized that data to be analyzed have a good correlations between the potential and current noises both in time and frequency domains. An ordinary three-electrode method, three identical electrodes were used for electrochemical noise measurement in aerated and deaerated 0.5 M NaCl solutions. The impedance calculated from the noise data was compared with that measured by an ordinary AC impedance method. The correlation between potential and current noises in the time domain was calculated by the correlation coefficient, and their correlation in the frequency domain was calculated by the coherence function. When both the correlation coefficient and the coherence function were high enough, the impedance at very low frequency obtained by the electrochemical noise agreed well with that obtained by AC measurement. Based on this, the measurement and calculation procedure for corrosion monitoring by electrochemical noise impedance was proposed. The procedure proposed was successfully carried out for continuous monitoring of steel corrosion rate in a moderate corrosive medium.