Four types of corrosion tests were carried out to determine a relationship corrosion rate, CR (Fe), carbon steel and ACM sensor output. Test 1-1 and 1-2 were laboratory tests under controlled relative humidity, RH, and amount of deposited sea salt, Ws Test 2-1 and 2-2 were outdoor exposed tests in Shimizu city, Shizuoka prefecture, and Nishihara town, Okinawa prefecture, respectively under conditions sheltered from rainfall.
Corrosion rate of carbon steel coupons was determined by conventional mass loss method in the tests except in Test 1-2 for lower corrosion rate, to which QCM (Quartz Crystal Microbalance) technique was applied.
The output of the ACM sensor, galvanic current, I, between carbon steel and silver, was recorded every ten minutes with temperature and relative humidity, and analyzed to be related to the corrosion rate, CR (Fe), as a formula:
log CR(Fe)[mm/y]=0.378logQ[C/day]-0.636 (1)
Where Q is daily average electricity, integral of ACM output I over a day.
The ACM sensor can predict corrosion rates as low as 2μm/y through the equation (1), being slightly short of 0.2μm/y of QCM technique.