Electrochemical Noise Analysis For Estimation Of Corrosion Rate Of Carbon Steel In Bicarbonate Solution

Corrosion Science 45 (2003) 2093–2104 www.elsevier.com/locate/corsci

Electrochemical noise analysis for estimation of corrosion rate of carbon steel in bicarbonate solution
Takumi Haruna *, Yasuyuki Morikawa, Shinji Fujimoto, Toshio Shibata 1
Department of Materials Science and Processing, Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita, Osaka 565-0871, Japan Received16 January 2003; accepted 24 January 2003

Abstract We have investigated the electrochemical noise behavior of carbon steel in fully deaerated aqueous bicarbonate solutions, and discussed the optimum conditions of the noise analysis for estimating corrosion rate of the steel. Noise of the potential difference and of the short-circuit current between two identical steel coupons were successfullymeasured. The time-series noise patterns were transformed into frequency domain by fast Fourier transformation, and then their power spectrum densities (PSDs) at a frequency were determined to be compared with the corrosion rate. The PSDs of the potential and of the current varied with changing environmental factors of bicarbonate concentration, pH, and immersion time. The factors also controlledthe corrosion rate of the steel. The PSDs were associated with the corrosion rate, and then it was found that the PSDs of the potential and of the current showed linear correlation with the corrosion rate in log–log scale. There was also linear relationship between the corrosion rate and a spectral noise resistance obtained from the PSDs of the potential and the current. The linearities of thethree correlations were better at a lower analyzed frequency. Furthermore, the PSDs of the current and the noise resistance indicated more linear correlation with the corrosion rate than that of the potential. As the simplicity of the measurement system is additionally considered, it is concluded that the PSD of the current noise at an

Corresponding author. Tel.: +81-6-6879-7470; fax:+81-6-6879-7471. E-mail address: haruna@mat.eng.osaka-u.ac.jp (T. Haruna). 1 Present address: Department of Mechanical Engineering, Fukui University of Technology, 3-6-1 Gakuen, Fukui, Fukui 910-8505, Japan. 0010-938X/03/$ - see front matter Ó 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0010-938X(03)00031-3

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T. Haruna et al. / Corrosion Science 45 (2003) 2093–2104

analyzedfrequency of 3 mHz is the optimum conditions for estimating the corrosion rate from 10À2 to 100 A mÀ2 in this study. Ó 2003 Elsevier Science Ltd. All rights reserved.
Keywords: A. Carbon steel; B. Electrochemical noise; Hydrocarbonate solution; Corrosion rate

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