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