Wavelet Transform Modulus Maxima and Holder Exponents Combined with Transient Detection for the Differentiation of Pitting Corrosion Using Electrochemical Noise

Abstract

A potentially powerful tool to detect and classify corrosion mechanisms is the analysis of electrochemical noise (EN). Data analysis in the time-frequency domain using e.g. continuous wavelet transform (CWT) allows the extraction of localized frequency information, providing information on the type of corrosion, i.e. uniform or localized corrosion, from the EN signal. The CWT provides the opportunity to analyse changes in frequency behavior of electrochemical noise signals over time. In the presence of transients generated by pitting corrosion that occur only during short instants of time, this is an important property. This paper introduces the combination of automated transient detection with wavelet transform modulus maxima (WTMM) and the Holder exponent. WTMM enhances the determination of transient frequencies by indicating the ridges of a CWT spectrum. The Holder exponent, a measure of singularity of an EN signal, provides a single parameter discrimination tool based on WTMM and serves to differentiate between general corrosion and two types of pitting corrosion of stainless steel AISI304 exposed to aqueous HCl solutions of different concentrations and as such at different pH values.

Electrochemical Noise Analysis of the Corrosion of Titanium Alloys in NaCl and H2SO4 Solutions

“…Moreover, Ti alloys do not present damage on the surface [7,77]. Researchers have also found that titanium is not affected by pitting corrosion in salt media when the temperature is under 90 • C, that Cl − ions will not penetrate the surface of alloys, and that the alloy shows passivation [17,46,[78][79][80][81][82][83][84][85].…”

Interpreting Electrochemical Noise and Monitoring Local Corrosion by Means of Highly Resolved Spatiotemporal Real-Time Optics

“…The electrochemical potential noise (EPN) monitored in parallel with the optical analysis serves as a basis for the time-frequency electrochemical analysis using CWT as previously shown for steel. 19 The in-situ combination of optical and electrochemical analysis allowed for the first time to directly assign electrochemical signals to specific corrosion processes (e.g. de-alloying, trenching, pitting and oxide formation).…”

An integral non-intrusive electrochemical and in-situ optical technique for the study of the effectiveness of corrosion inhibition

“…to keep the lowest frequency constant. Where applicable, transients in the EPN signals were located using an automated transient analysis technique based on modulus maxima in the CWT spectrum, which was published in earlier work [37] . Modulus maxima effectively indicate the locations of ridges, and therefore singularities or transients, in CWT spectra [37] .…”