Abstract
The ACM (Atmospheric Corrosion Monitor) type corrosion sensor which consists of a Fe-Ag galvanic couple was developed and applied for the evaluation of corrosivity of marine atmosphere. The sensors were exposed at two different sites, Shimizu in Shizuoka prefecture and Nishihara in Okinawa prefecture, and renewed every month. The temperature, relative humidity (RH) and the outputs of the sensors, I, were recorded in the microcomputer. Some sensors were exposed for more than one month at Shimizu. The sensor was found to be functional at least for two months. By analyzing magnitude and time variation of I, rain, dew and dry periods could be distinguished and their duration could be determined. By referencing to the empirically determined I-RH calibrating curve, the amount of deposited sea salt, Ws, could also be estimated. After the deposited sea salt was washed away by the rainfall, the sea salt was redeposited and Ws increased with time until reaching a stationary value. At Shimizu, a stationary value of 1.3×10-3mg/cm2 was reached after 3-4 days, while at Nishihara, a stationary value of 1.9×10-2mg/cm2, which is about ten times as much as that of Shimizu, was reached after 1-2 days. It is considered that the corrosivity of each site can be evaluated with these environmental parameters.
