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EVALUATION OF TECHNICAL FEASIBILITY ON APPLYING CALCAREOUS DEPOSIT COATINGS TO SHIP BALLAST TANKS

This study evaluated the technical feasibility of applying a combination of calcareous deposit coating and cathodic protection (anodes) in lieu of completely coating ship ballast tanks with high-performance coatings (epoxy). As an initial step to achieve this goal, batches of calcareous deposits were formed on A3 6 grade carbon steel plates, induced by cathodic polarization (CP) in natural seawater. The effects of deposition parameters such as CP current density, potential, and coating time on the coating's characteristics were evaluated to establish the optimum coating condition. Results showed that good overall calcareous coating can be achieved by lowering the current density as much as possible in the range 0.1-0.5mA/cm and by increasing coating formation time. Optimum number and arrangement of CP anodes for calcareous coating of a 3-dimensional structure such as a ballast tank were also evaluated by using Finite Element Method (FEM) analysis of potential distribution under CP. The results were fairly consistent with the experimental data obtained from coating tests made on the inner surface of a box-type, mock-up structure.