Corrosion under insulation (CUI) is a common phenomenon caused by ingressed water and corrosive species on insulated metal piping and equipment. The severity of CUI is strongly influenced by process parameters such as temperature, types of insulation, types, and concentration of contaminants in the ingressed moisture. The primary mitigation strategy of CUI is the application of protecting coatings. However, protective coatings may still degrade over time due to numerous factors including the development of thermal stresses induced by the thermal expansion coefficients mismatch between coating and underlying substrates, which could ultimately lead to coating failures such as cracks or delamination depending on the generated stress states. This study has conducted a numerical analysis of thermal stresses generated in a commercial epoxy coating deposited on carbon steel and stainless-steel substrates with Finite Element Analysis using ANSYS. Thermomechanical properties of thermally aged coatings were obtained after continuous exposure to 150 °C for 8 weeks. The acquired residual stresses of coatings were further cross-examined with the coating’s protective and adhesive properties through electrochemical impedance spectroscopy and pull-off adhesion tests, respectively.