A test protocol was developed to provide an assessment of the effects of various film defects as well as to perform post-exposure qualitative and quantitative evaluations on eight different coatings systems. A variety of film defects were created; linear scribe, X-scribe, impact, and a welded U-channel. After exposure, the analysis consisted of visual evaluations (blister, rust, scribe creepage), as well as EIS, moisture permeability, and FTIR. The exposures were performed in an accelerated corrosion cycle (NACE TM0404/0304), as well as exterior exposure in 3 environments; Near-Ocean in both northerly and subtropical latitudes (Newfoundland and Florida) as well as light industrial (Cleveland, Ohio). The coatings were applied over a variety of surfaces preparations as well. It was found that EIS used in conjunction with accelerated cyclic exposure can predict a coating’s behavior in exterior. Angular surfaces (U-channel) was found to provide good visual information not observed in flat panels. Film thickness only seems to play a role if particularly high, but a thin film of highly UV resistant fluoropolymer may significantly retard corrosion.
Key words: Offshore, Epoxy, urethane, zinc, fluoropolymer, zinc, acrylic, waterborne corrosion, EIS, permeability, FTIR, salt, SP10, SP11, UHP, NACE TM0304, ISO 20340, ASTM D5894, ASTM B117