Technical Note: Measuring Corrosiveness with a Dual Galvanic/Surface Film Resistance Sensor Available to Purchase

A galvanic sensor system designed to measure atmospheric corrosiveness within an aircraft was modified to also measure surface film resistance. Its response to four laboratory conditions was compared to the mass loss of an aircraft alloy, UNS A92024. The experimental factors were relative humidity (RH) and level of sodium chloride (NaCl). The amount of salt added was equivalent to the cumulative deposition of salt aerosols at a marine site for one week. The four conditions were (a) low RH with no salt added, (b) high RH with no salt added, (c) low RH with salt added, and (d) high RH with salt added. The mass loss of UNS A92024 plates was above that due to cleaning alone for conditions (b), (c), and (d), whereas the galvanic sensor only responded to the most severe condition (d). The galvanic current declined with time when exposed to the same environment in a manner consistent with the development of mass-transfer limitations of oxygen for the cathodic reaction. Implications for improving the design of a galvanic sensor to minimize both of these deficiencies were discussed.