Anodic pit generation and pit growth of stainless steel at constant potential in a sulphuric acid solution containing chloride ion have been investigated by use of a rotating electrode. The electrode rotation makes the generation and growth of pits very stable and enables the pit generation frequency and the pitting current from a single pit to be measured potentiostatically. The pits break out at constant frequency and the rate of pit generation is a linear function of the potential, suggesting that the pit generation proceeds electromechanically rather than electrochemically. An incubation time, probably associated with the initial adsorption of chloride ion, is found before the linear pit generation commences, which differs from the induction time for opening an initial pit.
The pitting current is in proportion to the area of pit mouth with the current density (8 A/cm²) which is independent of the potential, indicating that the mass transfer is rate-limiting. The pit grows following a parabolic law and the rate constant is an exponential function of the potential, from which a pit model is proposed in which the transpassive film continuously forming and breaking down on the inner pit surface assumes a high electric field.