Electrochemical Noise Analysis of Pitting Corrosion of Type 304L Stainless Steel

Electrochemical current and potential noise were simultaneously acquired from Type 304L stainless steel (UNS S30403) in 0.05 M ferric chloride (FeCl3) using a three-electrode configuration. Power spectral, statistical, and wavelet analyses have been used to know the uniqueness of the parameters proposed for the identification of various types of corrosion processes. Roll-off slopes derived from power spectral analysis and statistical parameters such as standard deviation, localization index, and kurtosis corroborated with pitting as the corrosion mechanism. Energy distribution plots (EDP) obtained from wavelet analysis of current noise was found to be useful to derive mechanistic information on the progress of corrosion. Discrete wavelet transform was used to decompose the signals into a D-1, D-2, D-3...D-8, S-8 set of coefficients. The EDP showed that the contribution from the medium time scale crystal, D-5, prevailed over the smaller time scale crystals and larger time scale crystals during the initial stages of immersion. With an increase in the time of immersion, the energy deposition on the larger time scale crystals increased and the maximum energy was concentrated on the D8 crystals, indicating that the dominant process occurring on the specimen surface was stable pitting. The results of the investigation are detailed in the paper.