Cathodic Protection to Prevent Crevice Corrosion of Stainless Steels in Halide Media

Crevice corrosion greatly restricts the use of stainless steels in chloride media. To aid in overcoming this difficulty a laboratory study was made of the stages of development of naturally occurring crevice corrosion. Also studied were the response of crevice and bulk specimen to cathodic polarization. The development of naturally occurring crevice corrosion was followed by measuring the potential within the crevice. Typically, there were three relatively rapid changes in potential separated by plateaus in the potential-time curve. These changes are postulated to correspond to (1) oxygen depletion in the crevice, (2) passivity breakdown in the crevice, and (3) acidification in the crevice. It was shown that crevice corrosion can be stopped by extended polarization somewhat more noble than the protection potential, and that on specimens with multiple active crevices some will be stifled at lower current densities than others. The findings indicate that intermittent application of cathodic protection can suppress crevice corrosion with a consequent power saving compared with the cost of continuous protection.