Simulation of Crevice and Pitting Corrosion Using the Orthogonal Collocation Method

Abstract

Two dangerous forms of localized corrosion are pitting and crevice corrosion. In pitting corrosion, pits are formed as a result of differences in oxygen and ion concentration at the base of a pit compared with the surface. Crevice corrosion occurs at inaccessible locations deficient in oxygen. Elec- trochemically, both pitting and crevice corrosion may be considered equivalent. A variety of steady-state and transient models have been developed to simulate the different stages of pitting and crevice in a variety of metals. Numerical solutions have been obtained for the modeling of corrosion cells. A theoretical model simulating the propagation stage of an established pit or crevice has been developed recently. This model considers the steady state of the solution chemistry and electrochemistry within active and passive cavities, and uses the method of finite elements to solve the complex nonlinear set of mass conservation equations describing the system. In the present work, the method of orthogonal collocation is used for the solution of the steady state describing equation of this model. This results in reducing the dimensionality of the non-linear equations to be solved. Numerical results are presented to show the good performance of the solution algorithm. Only two collocation points are needed to solve the above mentioned model.