The cathodic protection method with adequate sacrifice anodes (i.e., galvanic coupling protection)has generally been applied as an anticorrosion measure for the submerged parts of harbor steel structures. The effectiveness of this method has been confirmed with calcareous films electrodeposited on the steel surface. Electro-deposition Technique has already been developed in which this calcareous film is compulsorily produced by an external power. In this study, the combination of above two methods “combined cathodic protection method is considered. This new method is composed of the two steps: first, an external power is applied in order to produce enough thickness of calcareous films;second, cathodic protection is subsequently continued with an adequate sacrifice anode in the absence of the external power. The effectiveness of the method was examined by three steps experiments, 1)experiments in the laboratory-scale quiescent seawater, 2) experiments in a tank filled with natural seawater, and 3) experiments in an actual marine environment. The test results obtained in this study are as follows,
1) Laboratory experiments showed that the calcareous film with 100μ in thickness is at least necessary for reducing the protective current of the cathodic protection.
2) It was proved that by the combination method, the required current density can be reduced to the level of 20% at H・W.L. and to the level of 5% below H.W.L., of the value for the usual cathodic protection solo.
3) The experimental results in actual environment showed that no corrosion was recognized on the steel structures after 5 months exposure in the environment, and the protective current densitycould be reduced to the level of21% of the value for the usualcathodic protection.
4) From these results, it can be concluded that the combined cathodic protection method can be effective as a protection method of steel in the marine environment.