Failure investigation of a protective epoxy coating by means of crosscheck between infrared spectroscopy and thermal analysis

This paper reports the failure of an epoxy coating that was applied for corrosion prevention on the inner walls of a heat exchanger. The coating became brittle and detached from the walls of the exchanger after one year of service. An investigation was performed in order to evaluate the failure cause by means of thermal analysis, optical microscopy and infrared spectroscopy. Thermal analysis excluded an incomplete curing of the detached paint. Optical microscopy highlighted sediments, pores and cracks over the detached coating surface; infrared spectroscopy revealed vibrational bands associated with thermo-oxidative phenomena. A thermo-oxidative simulation was performed on fresh coating samples, pointing out that epoxy coating starts degrading around 100-120 °C. Taking into account the temporary malfunction of the cooling system reported by the user, the failure cause was identified in an overheating that induced a thermo-oxidative degradation of the coating and its subsequent embrittlement and detachment.