To estimate a proper anodes arrangement in the cathodic protection of a gigantic marine structure, quite a simple method was proposed, and the validity and applicability of the method was examined. The method was based on the assumption that the electric resistance between an anode and the structure mainly come from the part of seawater in catholic protection of a gigantic marine structure. To examine the validity of this assumption, the potentials of the anode and cathode under the catholic protection at a constant current density were measured using seawaters diluted to various salinities. The results showed that the dilution method is valid for the estimation of the anodes arrangement in the catholic protection of gigantic marine structures.
To show how to apply the dilution method to a concrete design problem in protecting a gigantic marine structure cathodically, the electric current distributions on a structure during catholic protection were measured in seawater diluted to 1/10 with fresh water. A close relation was found between the distribution of current density and that of accompanying calcareous deposit amount. The current density data were treated statistically, and a dimensionless number was introduced to evaluate quantitatively the unevenness of the calcareous deposit distribution. It was found that the dimensionless number is very useful for designing the arrangement of electrodes for the catholic protection of a gigantic marine structure accompanied with calcareous deposition.
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