The series of chemical changes occurring at the onset of a localized corrosion problem is often referred to as an 'autocatalytic process' for the self aggravating modifications of an initial situation that can grow from benign to seriously severe.
Assuming that the corrosion current density is 0.010 mA cm-2 for both the anodic and cathodic processes involved in the corrosion of steel, please evaluate the corrosion penetration rate (mm y-1) in absence of crevice corrosion.
What would be the corrosion rate of the same steel in a crevice situation in which the anodic surface would be 1/20th of the cathodic surface? What if it was 1/50th?
What would be the equilibrium pH in the crevice if the solid species formed is rust or Fe(OH)3?
What would then be the corrosion rate of steel inside the crevice in mm y-1?
Read carefully the information on a crevice corrosion model.
Follow the links of all three main pages (page one, two, and three) describing this crevice model and read the information they content.