Failure analysis of enamel-coated carbon steel heating elements of gas-gas heater for flue gas desulfurization system

A premature failure of enamel-coatings applied to low carbon steel heating elements of a heat exchanger used for the flue gas desulfurization system was analyzed and reported in this work. Some parts of heating elements were severely destroyed and some other parts were found to be sound. Theses parts and newly prepared samples were visually and microscopically inspected. According to the analysis results, in the damaged parts the interface between the coating and the carbon steel substrate was attacked noticeably. In the coating of heating elements used for the system no Ni (or NiO), an adhesion-strengthening element, was detected, and some fish-scales and detachment of coatings from the substrate were also found. As these fish-scales were not found in the newly prepared samples containing some NiO in the coating, it was concluded that the premature failure of the heating elements was mostly attributed to the poor adhesion of enamel coatings to the substrate.