Many steel structures built in marine environment were mainly protected by organic coatings. For saving the life cycle cost (LCC) of these structures, it is very important to predict the lifetime of those. About 25 kinds (n=2) of organic coated steel pipes were exposed at seashore at Miyakojima Island in OKINAWA for 20 years and were evaluated the degradation of coated materials. The obtained results are as follows:
1) Some monitoring techniques measured at exposure site were not effective for predicting the degradation of organic coating materials. A new monitoring technique to evaluate degradation will be expected.
2) A correspondence between the exposure results and laboratory acceleration test results was examined. It is shown that the rusted area spread from scratched portion exposed at splash zone correlates the rust width in SST, and also changes in adhesion strength of the tidal and submerged zone correlate with those of rotating immersion test. So, the preferable acceleration test can predict the degradation of organic coatings, in the case of having the similar environmental condition.
3) Maximum corrosion depth under the defect portion of organic coating was measured after removal the coating and rust. The maximum depth of submerged zone was deeper than those of tidal and splash zone. These phenomena were affected by macro cell formation, which consisted of sound coating as cathode and defect part as anode.
The degradation of organic coated steel in marine environment should be considered the effect of macro cell formation.