Both organic coatings and SACP (Sacrificial Anode Cathodic Protection) system have been used to
protect the steel surface from the corrosion in the water ballast tanks of ships and offshore structures.
This study was aimed at the effectiveness of SACP added to the epoxy coated steels. It is also found
that the EIS parameters would be represented electrochemical characteristics of epoxy coated steel
with or without the artificial defect and under CP. Despite the intact coating, the epoxy coated steel is
cathodically polarized below -0.79V/SCE by sacrificial anode after several hours for the beginning of
the immersion. EIS spectrum of epoxy coated steel under CP shows a two time constants and AC
impedance modulus decreases. Consequently, the cathodic reaction at coating/substrate interface can
effectively control the rust of substrate under the coating in spite of fact that epoxy coatings are sound
and intact.