Page 49: of Maritime Reporter Magazine (October 2002)

Marine Coatings

The Navy realized it was financially impractical to require that all edges be rounded. They choose instead to devel- op a test protocol for extremely high or 100 percent solids coatings that exhibit- ed "edge retentive" properties for the edges of the stiffeners in their vessels, thus making them easier to coat. They decided that approved products needed to maintain at least 70 percent of the film thickness that was applied to the flat surface on the edge. Initially, only one coating manufacturer made a com- mercially available product that met the

Navy's requirement. Now, however, there are several approved coatings manufacturers, including at least two

U.S. approved suppliers.

Currently there is much interest in the ship owner and ship builder community regarding the tributyltin (TBT) ban.

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TBT is currently used to protect the bot- toms of nearly 75 percent of the com- mercial vessels. For years TBT has been the primary and most cost-effec- tive biocide used on the underside of ships to provide antifouling protection.

However, since TBT causes mutations in certain marine organisms, it is sched- uled to be removed from the list of approved products. The TBT ban begins to take effect in 2003, with the complete ban scheduled to be effective date in 2008.

Currently, alternative technologies under consideration as replacements for

TBT include "easy release" coatings based on silicone or fluoropolymer technology, and ablative self-polishing coatings with biocides that are well established and with known perfor- mance (i.e. Cu20 and CuSCN) or the less established and metal free organic and reduced metal metallo-organic bio- cides. At this point, some ship owners have voiced considerable concern that the commercially available replace- ments for TBT are far more expensive (up to two times more costly) and do not last nearly as long as TBT. Five year projections for marine antifouling coat- ings predict that demand for these prod- ucts will double by 2008. If past response to environmental regulations holds true, the coating manufacturers will develop products that meet the demands of both the regulators and the owners.

On the process side, ship owners rec- ognized the importance of removing soluble salts before painting or coating surfaces. The traditional method of abrasive blasting previously painted tanks and ship surfaces did not remove the non-visible soluble salts. More sig- nificantly, when these non-visible salts are blasted into the surface they result in a significant reduction in the service life of coatings, especially in immersion conditions. Owners recognized they needed test methods for nonvisible con- taminants and began to develop these.

The second generation of chloride tests (i.e. the Bresle Cell and Bresle Kit) is currently being used by the U.S. Navy and others. This method consists of placing a patch on the surface, injecting a liquid beneath the patch using a syringe, massaging the liquid on the surface, extracting the liquid with the syringe, and then testing the solution with a titration test strip. According to some published literature, because the

Bresle Test Method extracts only 45 = 60 percent of the salts on the tile sur- 48 Maritime Reporter & Engineering News