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Research Papers: Gas Turbines: Microturbines and Small Turbomachinery

Long-Term Microturbine Exposure of an Advanced Alloy for Microturbine Primary Surface Recuperators

[+] Author and Article Information
Wendy J. Matthews

 Capstone Turbine Corporation, Chatsworth, CA 91311

Karren L. More, Larry R. Walker

 Oak Ridge National Laboratory, Oak Ridge, TN 37831

J. Eng. Gas Turbines Power 131(3), 032301 (Feb 06, 2009) (6 pages) doi:10.1115/1.2966419 History: Received March 28, 2008; Revised April 08, 2008; Published February 06, 2009

Haynes alloy HR-120 (Haynes and HR-120 are trademarks of Haynes International, Inc.) forms a protective oxide scale when exposed to the harsh operating environment of a microturbine primary surface recuperator. Primary surface recuperators manufactured from HR-120 are currently in use on the Capstone C65 MicroTurbine (MicroTurbine is a registered trademark of Capstone Turbine Corporation). Long-term microturbine tests of this alloy are currently being conducted at an elevated turbine exit temperature (100°F higher than that in a normal operation) at Capstone Turbine Corporation. Alloy samples that have been tested under steady-state microturbine operating conditions are removed after predetermined exposure intervals for characterization by Capstone Turbine Corporation in collaboration with Oak Ridge National Laboratory. Such evaluations include the characterization of surface oxide scales and the associated alloy compositional changes following a steady-state operation ranging from 1800 h to 14,500 h. Results from the microstructural and compositional analyses of these long-term steady-state engine-tested HR-120 samples are used to illustrate the progression of alloy oxidation in the microturbine operating environment.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Aircell assembly

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Figure 3

Recuperator with a removable aft dome

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Figure 4

Steady-state elevated TET engine testing of Haynes HR-120 alloy; tack-welded sample shown in the inset

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Figure 5

HR-120 alloy exposed for 5548 h: (a) BSE image, (b) Cr map, (c) Fe map, (d) Ni map, (e) Mn map, and (f) O map

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Figure 6

HR-120 alloy exposed for 14,501 h: (a) BSE image, (b) Cr map, (c) Fe map, (d) Ni map, (e) Mn map, and (f) O map

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Figure 7

Typical locations used for the measurement of the oxide scale, Cr-depleted zone, and unaffected alloy

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Figure 8

Cr-loss from starting reservoir as a function of EOH: HR-120 at ∼720°C and ∼666°C, and 347SS at ∼666°C

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Figure 9

5548 h: EPMA O, Cr, Fe, and Ni profiles

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Figure 10

14,501 h: EPMA O, Cr, Fe, and Ni profiles

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