Modelling Crevice Corrosion

Abstract An improved mathematical technique has been developed for the numerical simulation of the incubation period of crevice corrosion. The model utilizes an iterative fully-implicit finite difference method coupled with a modified fractional- step decoupling technique to solve the mass transport section of the model. This produces an unconditionally stable algorithm permitting time step considerations to be centered around the desired accuracy of the solution. All chemical equilibria are solved simultaneously by the use of a multiple Newton-Raphson technique. Two test cases were explored. The simulation of a Ag+/K+/NO3− moving boundary experiment, without chemical reaction, produced excellent agreement between numerical simulation and the experimental results of others demonstrating that the transport algorithm produces an accurate simulation of migration and diffusion processes. The second test case was the simulation of the incubation period of crevice corrosion of titanium. The results show that mass transfer processes coupled with chemical reaction can be used to determine the changes in the composition of the crevice solution. As expected, the critical pH was not obtained at 25°C and the crevice attained a steady state with the metal remaining in the passive state.