A reasonable prediction of the service life of structures or equipment operating at high-temperatures in aggressive atmospheres requires a full understanding of the degradation mechanisms of the material due to mechanical loading and corrosion. The overall objective of this study is to simulate high-temperature corrosion processes under near-service conditions, which require both, a thermodynamic model to predict phase stabilities for given conditions and a mathematical description of the kinetic process, i.e., solid state diffusion. A computer program was developed in which the thermodynamic program library ChemApp is integrated into a numerical finite-difference diffusion calculation to treat internal oxidation, nitridation and sulfidization processes in various commercial alloys. The model is capable of simulating multi-phase internal corrosion processes controlled by solid-state diffusion into the bulk metal as well as intergranular corrosion occurring in low-alloy steels by fast inward oxygen transport along the grain boundaries of the substrate. In this article, dilute and monophase solutions are considered.
Internal nitridation; oxidation; computational thermodynamics; ChemApp; InCorr; finite difference
