Monitoring the Early Stage of Degradation of Epoxy-Coated Steel for Ballast Tank by Electrochemical Impedance Spectroscopy

Abstract

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 (R f) and the coating capacitance (C f). In addition, the water volume fraction (X V) and the diffusion coef cient (D H2O) in the coating were determined from the C f 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 190 th day, R f decreasing, C f and X V increasing started. Underlying corrosion also initiated between 80 th and 190 th day. On the other hand D H2O did not indicate the clear change associated with the degradation. The changes in R f , C f , and X V were closely correlated with the progress of the degradation of the coated steels.

Coating Condition Detection and Assessment on the Steel Girder of a Bridge through Hyperspectral Imaging

“…The electrochemical impedance spectroscopy (EIS) technique has been studied to detect coating integrity as well as substrate corrosion occurrence. Impedance values can effectively reflect the coating status before the presence of macroscopic degradations, but EIS does not give local information and thus a vague location of the impaired coating spots [16,17]. Spectroscopic techniques, including Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and Mossbauer spectroscopy, have been performed to evaluate the coating conditions but are generally limited to lab experiments [11,[18][19][20].…”

In Situ Evaluation of Carbon Steel Corrosion under Salt Spray Test by Electrochemical Impedance Spectroscopy

“…Electrochemical impedance spectroscopy (EIS) is another powerful method to monitor the corrosion of metallic materials in various environments [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] because of its ability to estimate instantaneous CRs. This method offers the advantage of allowing bulk materials to be used as working electrodes (corrosion monitoring sensors).…”