Study of corrosion of carbon steel API 5L (X60) in NaHCO₃/NaCl solutions by electrochemical noise and impedance measurements

Abstract

Electrochemical noise (EN) measurement and electrochemical impedance spectroscopy (EIS) were employed to study the corrosion behaviour of carbon steel API 5L (X60). The base solution was deaerated aqueous 0·5M bicarbonate to which chloride ion (NaCl) was added in concentrations ranging from 0·05 to 0·3M; potentiodynamic polarisation measurements were made in parallel. The time series current and potential noise were transformed into the frequency domain by fast Fourier transformation and their power spectral densities (PSDs) at specified frequencies were determined and compared with the EIS and polarisation results. The PSDs of the potential and of the current and roll-off slope varied with the concentration of Cl⁻ ion. Parameters such as noise resistance R _n and the skewness and kurtosis of potential and current fluctuations have been determined from the statistical analysis in the time domain. The relationship between polarisation resistance and noise resistance has been investigated. The comparison of R _p and R _n showed that R _n was generally much smaller than R _p. The characteristic charge and characteristic frequency increased and decreased respectively with the addition of Cl⁻ ion.

Keywords:

• CARBON STEEL CORROSION
• ELECTROCHEMICAL NOISE
• ELECTROCHEMICAL IMPEDANCE
• POTENTIODYNAMIC POLARISATION