In this paper the protective current densities for cathodic protection in marine environments were studied based on the performance surveys on steel structure, to which cathodic protection by galvanic anodes had been applied. The following results were obtaind;
(1) The values of protective current density could be charactarized by density of ammonium ion and chloride ion in sea water which surround the structures.
(2) It was proved that protective current density of a steel structure with concrete lining at tidal zone was markedly smaller thatn that without lining.
(3) The real life of anode may be shorter than the design life when two items out of the following three do not satisfy certain levels;
1 protective current density considered in design
2 water quality
3 state of steel memebers at tidal zone (bared or covered)