Manufacturing Science and Technology(CEASE PUBLICATION) Vol. 3(4), pp. 155 - 159
DOI: 10.13189/mst.2015.030413
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Investigation of Micro-structure and Creep Life Analysis of Centrifugally Cast Fe–Cr–Ni Alloy Reformer Tubes

Amitava Ghatak ^*, P.S. Robi
Department of Mechanical Engineering, Indian Institute of Technology Guwahati, India

ABSTRACT

Reformer furnace tubes are designed for exposure to high temperatures and pressures for prolonged time. HP grade steels which are cast austenitic Fe–Cr–Ni alloys are used as reformer tubes for service temperatures in the range of 950℃ to 1000℃. This paper reports an investigation on the results of analysis of service exposed HP40Nb steel micro-alloyed with Ti. Microstructural investigation of the service exposed tube revealed carbides rich in Cr, Nb and Ti at grain boundary regions which are typical features of the cast material. No evidence of creep deformation was observed in this material indicating absence of degradation in structure and properties. Accelerated stress rupture tests at temperatures in the range of 850℃ - 1050℃ and stress in the range of 47 MPa - 80 MPa on samples machined from tubes exposed for 11 years at 650℃ was carried out to assess the life of the tube for various combinations of temperature and stress by Larson-Miller parameter. Observation of the fractured samples after accelerated stress rupture tests revealed nucleation and growth of voids at Cr rich phases as the main mechanism of damage at elevated temperatures. This paper also discusses the need for using the Larson-Miller constant (C_L-M) as a function of stress rather than considering it as a constant value.

KEYWORDS
Reformer Tube, HP40Nb, Larson-Miller Parameter, Stress Rupture Test

Cite This Paper in IEEE or APA Citation Styles
(a). IEEE Format:
[1] Amitava Ghatak , P.S. Robi , "Investigation of Micro-structure and Creep Life Analysis of Centrifugally Cast Fe–Cr–Ni Alloy Reformer Tubes," Manufacturing Science and Technology(CEASE PUBLICATION), Vol. 3, No. 4, pp. 155 - 159, 2015. DOI: 10.13189/mst.2015.030413.

(b). APA Format:
Amitava Ghatak , P.S. Robi (2015). Investigation of Micro-structure and Creep Life Analysis of Centrifugally Cast Fe–Cr–Ni Alloy Reformer Tubes. Manufacturing Science and Technology(CEASE PUBLICATION), 3(4), 155 - 159. DOI: 10.13189/mst.2015.030413.