The electrochemical behaviour of three cermet coatings applied on low alloyed steel has been studied in artificial seawater using Zero Resistance Ammetry techniques. The evolution of corrosion potential and galvanic current with immersion time reveals the existence of two processes involved in coating corrosion. The initial stage involves pore filling by electrolyte and steel corrosion due to oxygen reduction at the cermet coating. The galvanic effect between steel and cermet coating leads to local acidification of pore bottom that decreases galvanic effect and increases steel acid corrosion. EIS measurements on individual components of the steel/coating galvanic couple reveal that the overall impedance spectrum results from the parallel combination of both anodic and cathodic reactions. Steel corrosion defines the shape of the spectrum at the low frequency range.