Application of Electrochemical Impedance Spectroscopy to evaluate cathodically protected coated steel in seawater

Two types of organic coated carbon steel (S235JR2 grade) electrodes were exposed to artificial seawater environment. One prepared type was defect free while the other one had an intentionally introduced ϕ0.5 cm coating defect. Both kinds of samples were polarized during the exposure to four potentials corresponding to four different cathodic protection levels. Evolution of their EIS spectra is presented in this paper. Results obtained in the experiment indicate that protective organic coating condition could be estimated and monitored in time based on EIS investigations. If a sample is defected EIS allows recognition of overprotected and unprotected sample. Distinguishing a fully protected sample from partially protected sample based on EIS was troublesome.