LAUSR

The early stages of the degradation of thick epoxy-coated steels used for water ballast tanks were monitored by electrochemical impedance spectroscopy (EIS). 200-μm-thick epoxy-coated steels were exposed to accelerated corrosion tests containing humid air at 70°C for 246 days before immersion in a NaCl solution at 70°C for 79 days. They were removed from the corrosion test chamber during the test so that EIS measurements could be performed in order to determine the coating resistance (Rf) and the coating capacitance (Cf). In addition, the water volume fraction (XV) and the diffusion coef cient (DH2O) in the coating were determined from the Cf vs. t 1/2 curves during the water desorption process. These parameters were compared with the degradation morphology of the coated steel after a pull-off test. Only “physical aging” of coating was observed for rst 80 days. After 190th day, Rf decreasing, Cf and XV increasing started. Underlying corrosion also initiated between 80th and 190th day. On the other hand DH2O did not indicate the clear change associated with the degradation. The changes in Rf, Cf, and XV were closely correlated with the progress of the degradation of the coated steels. [doi:10.2320/matertrans.M2017243]