CREVICE CORROSION AND MICROTHROWING POWER

The two concepts of crevice corrosion and electrolytic microthrowing power seem to have been connected very seldom, in spite of the fact that, on a closer look, microthrowing power would be expected to be a decisive factor in crevice corrosion of stainless steels. Whereas the electrolyte resistance is the predominating factor for the macrothrowing power, i. e. an even current distribution on macro-scale electrodes, the microthrowing power, i. e. an even current distribution on small-scale electrodes, like crevices, is governed by the product, vertical kappa multiplied by (times) d eta /di vertical , of the electrolyte conductivity kappa and of the slope d eta /di of the polarization curve. Calculations are presented for the distribution of current and electrode potential on the crevice walls and of total crevice current and ohmic potential drop from the bottom to the mouth of a thin (h equals 0. 01 cm) and deep (L equals 10 cm) metal/metal crevice of type 316 stainless steel in the preinitiation, initiation and propagation stages of crevice corrosion.