The finite volume method has been used to good effect in the course of research into the simulation of atomic diffusion that occurs in service conditions of post-weld heterogeneous welded joints. This paper reports on the subsequent analysis of the algorithms that supported this investigation and detail additional constants necessary to account for supposed grain boundary diffusion due to changes in microstructure. The paper reports on the methodology used to conduct the initial simulations and concludes with a number of suggested simplified equations that will assist practitioners in predicting atomic diffusion for a number of materials.