As the corrosion protection method for marine steel structures, a cathodic protection method is applied in the submerged zone and below the sea bottom, a protective oating method is applied above the tidal zone. For these two methods, the establishment of the following methods is needed: 1) the performance verification method at the design stage, 2) the estimation method of protection performance at the present and the future.
On the other hand, the cathodic protection method and various protective coating methods are applied to the steel pipe piles in Hazaki oceanographical laboratory station. The long-term exposure test was started since 1984 and 30 years have passed in fiscal year 2014. In this study, to estimate the durability of each corrosion protection methods and to establish the performance verification method, various investigations were carried out. Main conclusions are below:
(1) The outlines in the protective coatings are below: For painting and underwater cured coating, some deterioration was started after 20 year. For polyethylene coating, no apparent deterioration was observed. For petrolatum coating, some slight corrosion was observed inside some kind of protective cover after 20 year. For concrete coating, no deterioration was observed on the surface.
(2) The electrochemical property such as impedance, insulation resistance and volume resistivity can be an index of the performance evaluation for painting and organic coating.
(3) For the petrolatum and the concrete coating, some subjects in establishment of the deterioration index were picked out.