2016 Volume 65 Issue 8 Pages 350-357
The distribution of electric potential and current density was numerically analyzed by the finite element method with 8 noses iso-parametric elements during crevice corrosion process of SUS304 at E=399mV in the artificial seawater. The crevice corrosion propagation mechanism before and after arrival of the corrosion tip to the edge of crevice was proposed by the results of this numerical analysis. The main results were as follows: (1)Before the corrosion tip reached to the edge of crevice, the electric potential of the passive area decreased linearly from the edge of crevice to the corrosion tip due to the IR drop even though under the constant potential condition. (2) The electric potential dropped greatly and the current density increased discontinuously at the corrosion tip. (3) The current density in the corroded area decreased from the corrosion tip to the initiation site of corrosion. (4) The current density of the corrosion tip at the edge side was predominantly larger than that at the crevice center side. For this reason, the migration speed of the corrosion tip at the edge side was accelerated as compered with that at the crevice center side. It was considered that the pH in front of the corrosion tip at the crevice edge side remarkably dropped because of the much dissolved metallic ions.(5) When the corrosion tip reached to the crevice edge, the electric potential and current density of the tip increased furthermore. However, the metallic ions diffused to outside the crevice and water came into the crevice from the outside. The movement of the corrosion tip to the outside of crevice stopped by this mitigation of corrosive solution.
