Application of AC impedance method to atmospheric corrosion monitoring of low alloy steels

The electrochemical impedance method has been applied to monitor the corrosion rate of pure iron, Fe-Ni alloys and Fe-Cr alloys, exposed to outdoors. Corrosion monitoring was carried out using the concentric ring-type corrosion sensor consisting of the pin and ring electrodes, and the atmospheric corrosion rate of corrosion sensor was monitored by the continuous impedance measurement at 10kHz and 10mHz. All specimens were subjected to high corrosion rate at night of both dry and rainy days. The corrosion rate of iron based binary alloys was lower than that of the pure iron and was inclined to decrease with an increase in the content of alloying elements. Moreover, the corrosion loss measured after the exposure test also showed similar values to those values calculated from the corrosion monitoring. It is concluded that the addition of Ni and Cr inhibits the atmospheric corrosion of iron. The corrosion monitoring system employed in this study is useful to evaluate the atmospheric corrosion performance of low alloy steels in coastal areas.