Development of Remote-controlled Corrosion Monitoring System of Steels Using Electrochemical Impedance Method

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A remote-controlled monitoring system of atmospheric corrosion of steels on the basis of theory of electrochemical impedance has been developed. In the monitoring system, the impedance at two different frequencies of 10 kHz and 10 mHz is continuously and automatically measured with an Ac Corrosion Monitor (Riken Denshi). The measured data are stored in a hard disc of a computer once and regularly transferred to our laboratory using a cellular phone system.The corrosion monitoring of three different steels of ordinary carbon steel (CS), weathering steel (WS) and Ni-containing weathering steel (NiWS) was carried out at four different atmospheres, using the developed monitoring system. The comb-type probe electrodes of CS, WS and NiWS were exposed to four different sites in the distance from coastal lines. The distances were 0 km for Okinawa, 0.5 km for Futtu, 4 km for Choushi and 45 km for Tsukuba.In this atmospheric corrosion monitoring, the time of wetness (TOW) for surfaces of the ste … More els themselves was monitored from the high frequency impedance at 10 kHz, since high frequency impedance provides the solution resistance. Form the impedance difference of the low and high frequencies, the corrosion rate of the steels was monitored. The monitoring has started from September 18,2003 for Okinawa, November 11,2003 for Futtu, December 9,2003 for Choushi and December 5,2003 for Tsukuba and still continued at all sites.Both the TOW and amount of corrosion obtained from the monitoring increased in order of Tsukuba <Choushi<Futtu<Okinawa, indicating that the aggressiveness of environments increased with decreasing the distance from the coastal lines. The coupon specimens of the three steels were also exposed to the four sites together with the probes in order to measure the corrosion mass loss. The coupons were withdrawn from the exposure sites after 0.5 and 1.0 year-exposure and the mass loss was measured after removing the rusts. The results showed very high correlation between the Ac impedance monitoring data and the mass loss data. Less