Evaluation of atmospheric corrosive environment in okinawa by using ACM sensors

摘要

The lifetime of metallic materials used for telecommunication facilities can be estimated using the corrosion rate when the materials are generally corroded. The corrosion rate differs not only due to local weather and/or atmospheric corrosive factors where the material is but also due to whether the material is directly exposed to rain even in the same location. To evaluate the differences in corrosion rates of steel and zinc due to rain exposure, we placed ACM sensors consisting of Fe/Ag-galvanic and Zn/Ag-galvanic couples in Nago city, Okinawa and measured corrosion currents as output of the sensors. The skyward-facing Fe/Ag sensor responded to rainfall quicker and more stably than the groundward-facing Fe/Ag sensor. This suggests that when a stable electrically conductive water layer was formed should affect the evaluation of the corrosion rate. The annual corrosion rate of steel was estimated to be about 0.09 mm/year, which was equivalent to the reported value in Nishihara, also in Okinawa. The corrosion current of the skyward-facing Zn/Ag sensor showed a tendency to decrease gradually. This made it difficult to estimate the corrosion rate of zinc by using the ACM sensor.