Studies of corrosion behaviors of a carbon steel/copper-nickel alloy couple under epoxy coating with artificial defect in 3.5 wt.% NaCl solution using the WBE and EIS techniques

[Display omitted] •Anodic reaction of the electrode at the artificial defect was accelerated.•There were electrochemical inhomogeneities of the metals during galvanic corrosion.•Difference in cathodic delamination was related to metal electrochemical activity and defect location.•Polarity reversals of the single electrodes under the coating were found. The corrosion process of a Q235 carbon steel/B10 copper-nickel alloy couple under epoxy coating with artificial defect in 3.5 wt.% NaCl solution was investigated using the wire beam electrode (WBE) and electrochemical impedance spectroscopy (EIS) techniques. The causes of the difference in the degree of coating delamination at the carbon steel area and the copper-nickel alloy area were discussed. The results showed that the anodic reaction of the electrode at the artificial defect was accelerated, while other electrodes of the WBE were protected to some extent in the whole test period. There were electrochemical inhomogeneities of carbon steel and copper-nickel alloy under epoxy coating during galvanic corrosion. The degree of cathodic delamination of the coating at the carbon steel area was obviously higher than that at the copper-nickel alloy area, which was mainly dominated by the electrochemical activity of the metal and the location of the coating defect on the WBE. Polarity reversals of the single carbon steel electrodes under the coating was found, the reasons for the phenomena were different from each other.