A novel approach to characterizing localized corrosion within a crevice

A method of experimentally simulating crevice corrosion was developed that allows the nominal current density to be determined in a straightforward ma nner, in contrast to a gap crevice. The apparatus involves placing a crevic e cover with a hole oriented perpendicular to the specimen and then measuri ng the current between the specimen and a counter electrode with a zero res istance ammeter and the potential versus a reference electrode. The effects of diffusion and polarization can be largely separated by the presence or absence of a crevice cover and the resistance to transport in the crevice c an be controlled by the depth of the crevice cover. Test specimens were mad e of nickel aluminum bronze (NAB) materials that are used in marine applica tions. For this material the corrosion rate was influenced by the cathodic rate in a straightforward manner and by diffusion effects caused by the cre vice. The presence of a crevice produced a positive shift in the specimen p otential that is consistent with an increase in the potential of the contro lling anodic reaction due to higher concentrations of dissolution products at the metal surface. Surface roughness observations after exposure suggest a correlation with the skewness of the current density. The skewness measu rements of the de-trended current density of the five NAB samples examined suggest the following: (i) a crevice increases the propensity of a NAB towa rds localized corrosion. (ii) a longer crevice length increases the propens ity of NAB towards localized corrosion and (iii) laser treatment can greatl y reduce the propensity of NAB towards localized corrosion in a crevice. Cr own Copyright (C) 2001 Published by Elsevier Science Ltd.