A simple crevice corrosion monitor was developed to monitor crevice corrosion in 1018 mild steel, Type 304 SS, and Type 410 SS in NaCI solutions with and witliout the addition of a chemical corrosion inhibitor. The monitor, which measures the electron coupling current, accurately followed the evolution of crevice activity in a manner that can be understood in terms of the cathodic process that occurs on the external surface and the partial anodic process that develops within the crevice, due to the accumulation of H~+ and CI~-. The crevice initiation time is typically very short, but appears to depend upon the chloride concentration and possibly on the inhibitor concentration. The coupling current increases with time after initiation, passes through a maximum and then decreases, eventually changing sign to mark crevice inversion. The inversion is attributed to the gradual build-up of H~+ in the crevice to the extent that proton reduction within the crevice becomes the principal cathodic reaction in the system, while the anodic reaction moves to the external surfaces. In addition, amines are effective corrosion inhibitors of crevice corrosion of mild steel and stainless steels in NaCI solutions, provided that they are present in sufficiently high concentrations.
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