Guguloth, K and Swaminathan, J and Bagui, Sumanta and Ray, Ashok K (2012) Remnant Life Assessment and Microstructural Studies on Service Exposed Primary Reformer Tubes of a Catalytic Converter of an Ammonia Plant. High Temperature Materials Proceedings, 31 . pp. 759-767.
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13.5 year service exposed (SE) catalyst primary reformer tube material made of H39WM micro-paralloy grade used in feritilizer plant was assessed for remaining life. The investigation includes mechanical properties evaluation; microstructural analysis and accelerated stress rupture tests. Failed tube portions showed coarsening prim-ary carbides of Chromium and Niobium along the grain boun-daries. Degradation of Niobium carbide (NbC) into Ni-Nb-Si phase and partial conversion this phase back to NbC was observed. Secondary carbides within grains were almost absent. Degradation in tensile strength for a range of temperature from 1123 to 1223 K was also observed but they were within the specified limits. Premature failures within 3–5 years service exposure are more common in reformer tubes. The failure was attributed to localized overheating leading to creep damage. The cast tube material may undergo microstructural changes during ser-vice exposure which is the main cause of degradation in strength and hardness changes. Accelerated stress rupture tests were performed in the range of 1173– 1248 K on samples machined from 13.5 years at 1191 K and 15.4 MPa exposed reformer steel tubing, did not reveal any degra-dation of rupture behavior compared to that of the virgin alloy. An additional life of at least 10.6 years is predicted at the operating stress-temperature conditions.
|Uncontrolled Keywords:||Reformer tubes; remaining life; mechanical properties; accelerated stress rupture; microstructure|
|Divisions:||Material Science and Technology|
|Deposited By:||Sahu A K|
|Deposited On:||17 Dec 2012 16:41|
|Last Modified:||13 Nov 2013 16:14|
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