Determining the coupling current as a means of detecting crevice activation and inhibition

A simple crevice corrosion monitor was developed to monitor crevice corrosion in 1018 mild steel, Type 304 SS, and Type 410 SS in DI water and in NaCl solutions with and without 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 Cl^-. The crevice initiation time is typically very short, but appears to depend upon the chloride concentration and possibly on the inhibitor concentration. In addition, amines are effective corrosion inhibitors of crevice corrosion of mild steel and stainless steels in NaCl solutions, provided that they are present in sufficiently high concentrations.