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

TL;DR

This study compares microstructural damage in two high-temperature reformer tubes using advanced microscopy techniques, revealing localized creep damage despite similar overall microstructures.

Contribution

It provides detailed microstructural analysis of ex-service reformer tubes, highlighting localized creep damage through advanced characterization methods.

Findings

Similar microstructures with carbides and austenitic matrix in both tubes

One tube shows more micro cracks indicating higher creep damage

Microstructural analysis can identify localized damage in service tubes

Abstract

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.