Effect of high temperature service on the complex through-wall microstructure of centrifugally cast HP40 reformer tube

Centrifugally cast reformer tubes are used in petrochemical plants for hydrogen production. Due to the conditions of hydrogen production, reformer tubes are exposed to high temperature which causes creep damage inside the microstructure. In this study, two different ex-service HP40 alloy reformer tubes which come from the same steam reformer unit have been compared by microstructural characterisation performed at a range of length scales from mm to μm. Analyses performed by EBSD (Electron Backscatter Diffraction), EDS (Energy Dispersive X-ray Spectroscopy) and PCA (Principal Component Analysis) show that both tubes have similar microstructural constituents, with the presence of an austenitic matrix and several phases (M23C6, G phase and M6C) at the grain boundaries. Even if both tubes have a similar microstructure, one tube due to its localisation inside the steam reformer unit presents a region with more micro cracks which may indicate that this tube has accumulated more creep damage than the other one.