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.
Coatings for offshore structures are subjected to highly corrosive environments. Because of this, several test protocols have been developed to evaluate them for this type of service. Cyclic tests, such ASTM (1) D5894, NACE(2) TM0304, and ISO (3) 20340 Annex A, have been shown to correlate more closely to exterior exposures compared to continuous salt fog such as ASTM B117. 1-10
In this study, various surface preparations, panel designs, and coating chemistries are being examined to determine what effect these variables have on the performance of the coatings for offshore service.
In addition, electrochemical impedance spectroscopy (EIS) and permeance per ASTM D165311 are being used in an effort to correlate quantitative values obtained from these methods with visual evaluations. FTIR is also being used to note any chemical changes in the films. Accelerated corrosion in the laboratory per NACE TM0303/0404 along with two highly corrosive exterior sites are being used to further substantiate correlation of these exposure methods.