Characterization of the oxide scale formed on external surface of HP reformer tubes

• Published in: Journal of materials research and technology Vol. 7; no. 4; pp. 578 - 583
• Main Authors: Silveira, Rosa Maria Sales da, Arenas, Mónica P., Pacheco, Clara Johanna, Rocha, Adriana da Cunha, Eckstein, Carlos Bruno, Bruno, Antonio Carlos, Pereira, Gabriela Ribeiro, de Almeida, Luiz Henrique
• Format: Journal Article
• Language: English
• Published: Elsevier Editora Ltda 01.10.2018; Elsevier
• Subjects: High temperature oxidation; Modified HP steel; Oxide scale; Steam reforming tubes; Steam reforming tubes; Oxide scale; Modified HP steel; High temperature oxidation
• ISSN: 2238-7854
• DOI: 10.1016/j.jmrt.2018.08.001

This work presents the characterization of the external oxide scale of a centrifugally cast HP steel tube, modified with Nb and Ti, after 90,000h of operation in a steam reforming furnace, showing different aging states as a function of the column height and exposure temperature. The objective was to relate the oxide microstructural morphology to its magnetic response for three different microstructural aging states. The morphological and compositional characterization was performed by high resolution scanning electron microscopy, energy dispersive spectrometer and X-ray diffraction. The magnetic response of the external surface was analyzed by magnetic force microscopy and scanning magnetic susceptometer. The results showed the formation of a multilayer oxide scale with different compositions along its thickness. In addition, a microstructural modification was identified in the scale-matrix interface, due to the depletion of chromium. It was also observed that the magnetic response is dependable both on the oxide scale thickness and the chromium carbides depleted zone. Magnetic force microscopy was able to identify the origin of the magnetic response resulted from the steel tube surface.