Microstructural degradation of two cast heat resistant reformer tubes after long term service exposure

• Published in: Engineering failure analysis Vol. 18; no. 1; pp. 164 - 171
• Main Authors: Mostafaei, M., Shamanian, M., Purmohamad, H., Amini, M., Saatchi, A.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 2011
• Subjects: Austenitic stainless steels; Carbides; Energy dispersive; Evolution; Failure analysis; Metals and alloys; Microstructure; Phases; Precipitation; Roofs; Scanning electron microscopy; Spectroscopy; Tubes; Scanning electron microscopy; Metals and alloys; Precipitation
• ISSN: 1350-6307; 1873-1961
• DOI: 10.1016/j.engfailanal.2010.08.017

Microstructural evolution of a gas reformer tube made of the two dissimilar heat-resistant cast alloys, 25Cr–35Ni and 28Cr–48Ni–5W, was studied using light optical microscopy and scanning electron microscopy equipped with energy dispersive spectroscopy point analysis. Specimens were cut from an ex-service, failed reformer tube aged 8 years. The phases and carbides at each section of the reformer tube were determined and compared with as-cast conditions. It was found that the specimens located far from the bottom or the roof of the reformer box had mainly meta-stable phases such as G-phase or M 23C 6 due to exposure to intermediate temperatures. Those inside the reformer box, however, had phases such as M 6C carbides which are more stable than M 23C 6, and NbC due to exposure to high temperatures above 1000 °C.