Twenty Year Field Study of The Performance of Coatings in Seawater

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The objectives of this study were to evaluate the long-term performance of various coatings on steel piles in seawater and to investigate non-destructive electrochemical corrosion testing techniques for coating evaluation in the field. Steel H piles which were 20.3 cm x 20.3 cm and 12.2 m long were installed in Buzzards Bay, Cape Cod, Massachusetts. The piles were coated with various coatings such as coal tar epoxy, polyurethane, flame sprayed zinc and aluminum. Several of the piles were left uncoated for baseline comparison. Sacrificial cathodic protection was provided by anodes to some of the bare and coated steel pilings. Corrosion rate measurements using electrochemical polarization resistance and Tafel plots were conducted periodically in the field during the twenty year study. The results of the Cape Cod, MA, corrosion study were compared with a similar study conducted at the La Costa Island, FL. The long-term coating evaluation showed that flame sprayed aluminum with a topcoat sealer performed best at the cooler temperatures in Massachusetts and polyester glass flake was the best performer in Florida. Coal tar epoxy coatings with zinc-rich primers performed well at both of the locations.