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 um. 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 M23C6, G phase and M6C carbides at the
grain boundaries. Even if both tubes have a similar microstructure, one tube
due to it localisation inside the steam reformer unit presents a region with
more micro cracks which may indicate that this tube have accumulated more creep
damage than the other one.