The electrode was monitored for the next five days and although the cap increased in size no further noise activity was observed. On examination a single pit was found, approx. 1 mm in diameter and of a similar depth. No other corrosion was found on this electrode. The results indicate that systems undergoing pitting or crevice corrosion may be monitored by sensitive measurements of the electrode potential, Pit initiation occurs when the environmental conditions become aggressive, i.e. after chloride ion addition.
Initiation continues as long as there are latent pit sites available.
Crevice corrosion progresses in well defined cycles, a rapid propagation stage followed by a longer interval of comparative inactivity. The crevice system appears to be very stable and the cyclic oscillations observed continued at a constant frequency over considerable periods of time. This phenomenon has been generally observed in practice. The results reported here have been duplicated on other systems undergoing these two forms of attack. Work is in progress to investigate the crevice oscillations in detail, using reference electrodes situated within the crevice.