Corrosion pits on stainless steel often grow in such a way as to undermine the original surface, and, consequently, a thin layer of metal and oxide is left over the growing pit cavity. These pit covers develop a porous, lacelike structure, and a model for the development of this structure is described. Calculations based on this model produce pit morphologies showing the main features of real pits observed in the scanning electron microscope and also produce theoretical current transients resembling those recorded experimentally.