Corrosion monitoring in marine environments using electrochemical impedance

Electrochemical impedance (EIS) has been applied to study the corrosion behavior of carbon steels in the marine environment. The marine environment was reproduced to simulate three environments: marine atmosphere, tidal zone and underwater zone. The polarization resistance and solution resistance were monitored, and the corrosion rate of the carbon steel was estimated from the reciprocal of the polarization resistance. Furthermore, in order to examine the corrosion behavior of carbon steel in the tidal zone, the surface was continuously observed by a digital microscope under the wet-dry cycle. The carbon steel exposed to marine atmosphere showed very low corrosion rate, because the surface of carbon steel was not wet at all in this environment. The carbon steel gave approximately constant corrosion rate in the underwater zone. Meanwhile, the corrosion rate of the carbon steel exposed to tidal zone increased as the frequency of wet-dry cycles increased and was much higher than those exposed to the other environment. The EIS technique employed in this study is useful for the corrosion monitoring in marine environment.