Corrosion Evaluation with Atmospheric Corrosion Monitoring Sensors and Corrosion Rate Map Development
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Electric power facilities such as steel towers, poles, transmission and distribution lines, substation and power plant facilities have been exposed in various atmospheric environments. These steel structures have been corroded by thin water films on them formed by high humid weather conditions such as acid rain, dew, fog snow. Atmospheric corrosion is accelerated by the range and quantity of deposition on them. Therefore it is important to evaluate the corrosivity of atmospheric environment and corrosion rates of metals and alloys for the application of corrosion control and protection methods and the decision of appropriate maintenance interval against the corrosion of facilities. Atmospheric Corrosion Monitor type sensors (ACM sensors) have been developed to evaluate the corrosivity of atmospheric environments and corrosion rates of metals and alloys. ACM sensor outputs galvanic current between silver (Ag) and carbon steel (Fe) related to corrosion rates of metals and alloys to be used as a measure of corrosion. The current depends upon relative humidity, RH, and time of wetness, TOW, such as the presence of thin water film from rain, fog, dew or snow, and the quantity of depositions such as adhered sea salt and the other contaminants, which correspond to the severity of atmospheric corrosion. In this study, Fe/Ag-pair type ACM (Fe-ACM) and Zn/Ag-pair type ACM (Zn-ACM) sensors had been installed on around 150 transmission steel towers at various site for around several years to get corrosion rates and evaluate the atmospheric corrosivity. Moreover, the corrosion rate maps of carbon steel and zinc in various atmospheric environments in Japan were developed using these corrosion data and statistical methods. Multiple regression analysis method was applied to evaluate the relationship between corrosion rates and topographic or meteorological factors.