PURPOSE:To enable simultaneously corrosion prevention and destaticization of a cargo tank by connecting electrically a heating pipe disposed in the cargo tank to the wall of the tank only by electric discharge tubes to block the flow of electrolytic corrosion current. CONSTITUTION:A heating pipe 2 consisting of a heating coil part 6 and a vertical pipe part 7 is disposed in a cargo tank 1 and the required parts of the pipe 2 are electrically insulated from a side wall 4 and a bottom wall 3. The insulated parts are electrically connected via electric discharge tubes 26 to the bottom wall 3, the side wall 4 and a top wall 5. When sea water ballast is loaded into the tank 1, the potential difference between the walls 3, 4, 5 of the tank 1 and the heating coil part 6 is smaller than the set voltage of the tubes 26 and therefore the tubes 26 do not generate discharge and insulate electrically the coil part 6 from the wall of the tank 1. When the sea water ballast is not loaded into the tank, the accumulation of static electricity in the part 6 is prevented by the tubes 26.
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