Microstructural and Performance Analyses of Thermal-Sprayed Electric Resistance Heating Systems Deposited onto Steel Pipes as De-Icing Elements

The freezing of water in piping systems is a widespread phenomenon that can lead to internal pressurization and rupture of pipes, causing noticeable financial losses. Multi-layered functional coatings that consist of different materials with favorable electrical properties, namely alumina/alumina-titania, nickel-chromium, and copper, were fabricated by using flame spray (FS), suspension plasma spray (SPS), and cold gas dynamic spray processes in an effort to develop a de-icing system. Internal morphology and elemental composition of the fabricated coatings were examined by using a scanning electron microscope. The correlation between the deposited coating microstructure, electrical performance, and strain tolerance were analysed and both mechanical and electrical failure mechanisms of the developed coating systems were investigated. Furthermore, phase composition of the alumina coatings that were deposited by both FS and SPS processes were evaluated. Compared to the porous flame-sprayed coatings, the intermediary alumina layer that was produced by the SPS process was found to be more reliable due to its cauliflower-like structure, higher content of corundum, and better hygroscopic properties. The results suggest that further study on material selection and choice of thermal spraying technique can improve the heating performance and increase the resistance of coating-based heating systems against electrical and mechanical failure modes.