Fluidization-based chemical vapour deposition for alumina coating on tubular carbon steel substrates-Modelling and validation

The degradation of carbon steels due to corrosion and gaseous permeation phenomena can be significantly reduced by a thin alumina coating. Tubular carbon steel structures, commonly employed in nuclear establishments are particularly vulnerable to chemical degradation on the inner surface due to the flow of corrosive fluids. In the present work, a fluidization-based chemical vapour deposition process is applied as a one-step solution for simultaneous chemical passivation of both inner and outer substrate surfaces meanwhile optimizing precursor inventory by utilizing fluidized bed sublimation and induction heating techniques. The process is studied by using a 2D-1D mathematical model, which has been validated with experimental results for different carbon steel grades. It was observed that there exists an optimum fluidization velocity for a specified initial mass fraction of precursor powder at which mass of alumina deposited per unit mass of precursor sublimated is maximized.