Detection of microbiologically influenced corrosion by electrochemical noise transients

•Electrochemical current noise transients can reflect the occurrence of pitting.•The development of transients over time can be investigated using Hilbert spectra.•MIC can be detected early by transient analysis through Hilbert spectra.•Sulphate-reducing bacteria cause ennoblement of carbon steel.

This work investigates the electrochemical processes involved in pitting corrosion induced by microbiologically influenced corrosion by using time-resolved instantaneous frequency information of electrochemical current noise (ECN) transients obtained from Hilbert spectra. In addition to the time-frequency analyses, also the open corrosion potential is investigated and microscopic examinations of the specimens are performed after the tests. Hilbert spectra of the ECN signals indicated the development of transients in one of the two electrochemical cells containing sulphate-reducing bacteria with a different instantaneous frequency decomposition as compared to the background ECN signal, which resulted from the anaerobic general corrosion process. After day 13, the transients in the ECN signals developed towards consistent instantaneous frequency decompositions in the Hilbert spectra that are typical for relatively fast pitting corrosion processes. Post-exposure microscopic observations confirmed the existence of pits underneath the attached biofilms at the working electrodes.