児島湖ゲートの電気防食

Abstract

The Kojima Lake is an artificial lake. The bank was built at the narrowest point of the Kojima Gulf and it separates the sea and the lake. There are 12 watergates and one set of lockgate. These gates were painted by vinyl paint about 3 years ago. The paint is deteriorated to some extent, and rust was found on the gate surfaces from place to place. These gates are now protected by sacrificial anodes. There are some problems to be considered in this cathodic protection design. The lockgates are opened 30-40times daily, and several watergates are opened daily for a few hours to adjust the lake water level. Therefore, polarization of gates will be interrupted quite frequently. The resitivity of lake water is affected by many factors, i.e. season, weather, water depth, duration and frequency of gate opening, leakage rate of the gates, etc. Zinc anodes are used in the sea and in the lock chamber, and Mg anodes are used in the lake. Protective current density is 40mA/m2 and designed potential of the gates is -900mV referred to S.C.E. Satisfactory results are obtained in the seaside, but minimum protective potential of -770mV referred to S.C.E. is maintained in the lock chamber and in the lake.