Corrosion Inhibitions of Mild Steel and Copper by Oxygen Reducing Treatment Using Sealing Materials for Water Surface in Open Heat Storage Water System: Cause of Increasing Copper Corrosion Potential and Countermeasures for Its Decrease

摘要

The corrosion potential of copper electrodes increased to 220 mV (SSE) and green rusts were produced on them in some hot water tanks in which DO concentration had been kept less than 0.5 mg/L by oxygen reducing treatment. It was estimated that the cause of the potential increase can be induced by microorganisms, because of a reduction in the potential when hot water was dosed with biocide. After examination of methods for decreasing the corrosion potential of copper electrodes in order to inhibit pitting corrosion, the potential of a green rusted copper electrode was decreased by a reduction in green rust using hydrazine series water treatment chemicals; the reduced copper electrode showed immunity to an increase in the potential after that. A decrease in copper potential was also observed by injecting the chemicals into the hot water.