To obtain an orientation for the evaluation of abilities of protective coating films, the electrochemical parameters determined by electrochemical impedance spectroscopy (EIS), current interrupter method (CI), and scanning vibrating electrode technique (SVET), were compared with each other, and the relation and the characteristics of each method were discussed. The interrelations of the parameters were found. The limitations of measurements were discussed fully by the interrelations : The upper limits of film resistance (R
f) measured were about 10
10 ·cm
2 in CI, 5×10
8Ω·cm
2 in EIS, and 1×10
7 Ω·cm
2 in SVET. Many parameters were determined in CI method. It was thought not only the abilities of protective coating films could be evaluated, but also the mechanisms of the deterioration of films and the corrosion of steels could be analyzed. In the relation between electrochemical measurement and actual observation, R
f of the coating steel having corrosion area of 0.3 to 1% was 5×10
5 to 1×10
6 Ω· cm
2.
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