Evaluation of New Surface Preparation and Coating Repair Techniques in Ballast Tanks

: Ship ballast tanks offer unique corrosion control challenges. Being subjected to intermittent wet and dry cycles of aerated sea water places an extreme demand on corrosion control methods. Harsh service environments are coupled with necessarily complex tank geometries, especially in Navy combatants where weight and hull designs dictate small, irregular tanks with limited accessibility. These difficulties equate to costly corrosion control techniques. The NSRP SP-3 Panel recognized these problems and formulated a series of research and development projects to investigate alternate, cost effective corrosion control solutions for the preservation of ballast tanks. The first project began in 1980 and was entitled "Cathodic Protection/Partial Coatings Versus Complete Coating in Tanks." A series of steel mock-up ballast tanks were constructed which duplicate tank geometries. The tanks were also large enough to allow access for surface preparation and installation of the various corrosion control methods. In 1988, the project was redirected to evaluate maintenance procedures and techniques. At that time the tanks had been under test for six years. In 1990, funding was approved to extend the project for an additional two years. This report contains the results of five years of testing under the new program. After eleven years of testing, the inorganic preconstruction primer with zinc anode has finally failed. The VOC compliant surface tolerant epoxy "A" applied over both the power tool cleaned and abrasive blast cleaned surfaces was essentially equal in performance for the first three years, but the power tool cleaned system was somewhat inferior after five years. Both systems require extensive repair.