A marine structure is located in the severe corrosive environment more than other structures. Corrosion of steel structures and corrosion of steel in the concretes structure tend to develop as a result. To prevent this corrosion, various prevention methods are carried out for both structures. This paper describes the current state of the corrosion and recent topic about the prevention methods in the port structures among the marine structure.
The objective of this research is to purpose a new method of predicting the depassivation of PC steel. This is achieved by making clear the characteristics of the passivation film on PC steel in the transition state from passivation to depassivation using polished PC steel samples and electrodes immersed in an alkaline environment that simulated the interior of concrete. The new method is proposed here based on the following results. Firstly, it has been possible to judge the presence of corrosion from the change in the immersion potential of PC steel electrodes in an alkaline environment, but information about the degradation of the passivation film with time has not been obtained. Next, to clarify, it was shown that depassivation of PC steel can be predicted based on the decline in film resistance on the low frequency range in electrochemical impedance with the lapse of time. Under the experimental conditions used in this study, it was observed that depassivation could occur when the passivation film resistance was less than 2.0 MΩ・cm2. In addition, results obtained by spectroscopic ellipsometry confirmed that a correlation exists between this resistance on the low frequency range and passivation film thickness.
For the development of a method to evaluate the residual lifetime of a heavy-duty coating on the surfaces of the internal bottom plates of oil storage tanks， the impedance characteristics of the coating were investigated by the laboratory immersion test of the coated steel panel in a 3 wt. % NaCl solution for 85 days and the field study of an actual oil storage tank that had stored oil over 266 months. As a result， the impedance spectra of the coating could be analyzed with the electrical equivalent circuit of one CPE (Constant-phase element). It was found that the CPE behavior in the impedance spectra is caused by the electrolyte solution permeation in the coating. In addition， it was suggested that the degradation with age of the coating can be evaluated quantitatively by using the fitted parameter values of the CPE.
Electrochemical trials and efforts have been made to clarify mechanism of the ant's nest-like pitting attacks which had been observed on the copper tube used in air-conditioning units. It has been known and pointed out that the attacks require some conditions such as wet atmosphere, oxygen and formic acid. Experimental researchs were made on corrosion variables of corrosion potential and pH values in 102 ppm formic acid solution for about one month exposure. The corrosion reactions composed the ant's nest-like pitting attacks were thermodynamically estimated and its process was conveniently considered as two stages; in early corrosion stage and in steady stage. A kinetic study by polarization resistance curves revealed that reactions in alkaline atmosphere played important role and showed characteristics with fast rate reaction system. It is also indicated that the pitting attacks will occur not only on phosphorus-deoxidized copper tubes but also oxygen-free high purity copper tubes.