Study On Performance Of Protective Coatings Applied To High-pressure Pipelines On Semi-submersible Platform

As semi-submersible platforms often serve under severely corrosive environment, corrosion problems frequently occur on the platforms. The organic coating technique is one of the most frequently used protection methods for steel structure in marine atmospheric zone. With the advancement of modern technology, arc spraying aluminium coating technology has become one of the most important means to guarantee long-term protection of steel structure in the marine environment and has been successfully applied all over the world. Additionally, if the sealing agent and porosity-sealed process are properly selected, arc-spraying coatings could substantially increase the service life of composite coatings, which is of great significance in practical production.The resistance to salt fog corrosion and aging is the most important factor that affects the service life of coatings in marine atmospheric zone. In this paper, two kinds of organic coating systems used in marine environment were selected and prepared respectively. Then, the phenolic epoxy coating system was used to seal the arc-spraying aluminum coating. The corrosion resistance of different coatings under salt fog and artificial aging conditions was surveyed by electrochemical impendence spectrum (EIS) and others means such as SEM and FTIR.The EIS results showed that the organic coatings can keep high corrosion resistance before the penetrating of corrosive medium into the interface between coating and steel substrate, while the sealed aluminum coating that has low corrosion resistance can provide effective protection for the substrate in salt spray or aging test because of the sacrificial anodic protection. SEM observation and FTIR analysis revealed that the damage of organic coatings in salt fog environment was mainly caused by the corrosion of substrate or the increase of porous defects. The aging mechanism of the studied organic coatings was the breakage of the C-H bonds (methyl and methylene group) and C-O bonds (polyester) in cross-link position thus tend to promote the oxidation and the generation of small molecules, which led to powdering and flaking of the coatings.The corrosion resistance of sealed aluminum coating in salt fog and aging environment is much higher than that of organic coatings, therefore, it can be concluded that arc-spraying aluminum coating sealed with phenolic epoxy paint system is a new way of preparing protective coatings with long service life to apply in high-pressure pipelines on sub- submersible platform.