Application of corrosion monitoring to power plant

The technique which directly and continuously measures the rate of corrosion, that is, the corrosion monitoring technique, has been desired earnestly amid the strong need of high plant reliability, and the investigations in this field have been advanced. The authors have been developing a fast and continuous, automatic corrosion monitoring system which can measure corrosion even in low conductivity solutions. As a result, the authors have succeeded to develop an automatic and microcomputer assisted corrosion monitoring system to which Coulostat method, one of electro-chemical techniques, has been applied. The principle of Coulostat method is to determine corrosion rate by the ion current flowing from metal into water at their interface or electric current value. The system utilized that the corrosion current is inversely proportional to the polarization resistance. In this paper, the measurement and data analysis method and the outline of the monitoring system are described, and the monitored results obtained in Chita thermal power plant, Japan, are reported. The monitoring was carried out in the shaft cooling water system of the actual plant with carbon steel and aluminium bronze probes, of which corrosion was feared. The continuous monitoring for about a month revealed that corrosion rate changed due to a very little variation in water quality (change of inhibitor concentration) and it was sufficiently detectable, and anti-corrosion management can be done on the safe side. Therefore, the monitoring system was decided to be applicable to power generating plants. (Wakatsuki, Y.)