Research Papers: Gas Turbines: Microturbines and Small Turbomachinery

Comparison of Three Microturbine Primary Surface Recuperator Alloys

[+] 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

MicroTurbine is a registered trademark of Capstone Turbine Corporation.

J. Eng. Gas Turbines Power 132(2), 022302 (Nov 05, 2009) (6 pages) doi:10.1115/1.3157094 History: Received March 19, 2009; Revised March 23, 2009; Published November 05, 2009; Online November 05, 2009

Extensive work performed by Capstone Turbine Corporation, Oak Ridge National Laboratory, and various others has shown that the traditional primary surface recuperator alloy, type 347 stainless steel, is unsuitable for applications above 650°C(1200°F). Numerous studies have shown that the presence of water vapor greatly accelerates the oxidation rate of type 347 stainless steel at temperatures above 650°C(1200°F). Water vapor is present as a product of combustion in the microturbine exhaust, making it necessary to find replacement alloys for type 347 stainless steel that will meet the long life requirements of microturbine primary surface recuperators. It has been well established over the past few years that alloys with higher chromium and nickel contents than type 347 stainless steel have much greater oxidation resistance in the microturbine environment. One such alloy that has replaced type 347 stainless steel in primary surface recuperators is Haynes Alloy HR-120 (Haynes and HR-120 are trademarks of Haynes International, Inc.), a solid-solution-strengthened alloy with nominally 33 wt % Fe, 37 wt % Ni and 25 wt % Cr. Unfortunately, while HR-120 is significantly more oxidation resistant in the microturbine environment, it is also a much more expensive alloy. In the interest of cost reduction, other candidate primary surface recuperator alloys are being investigated as possible alternatives to type 347 stainless steel. An initial rainbow recuperator test has been performed at Capstone to compare the oxidation resistance of type 347 stainless steel, HR-120, and the Allegheny Ludlum austenitic alloy AL 2025+Nb (AL 20–25+Nb is a trademark of ATI Properties, Inc. and is licensed to Allegheny Ludlum Corporation). Evaluation of surface oxide scale formation and associated alloy depletion and other compositional changes has been carried out at Oak Ridge National Laboratory. The results of this initial rainbow test will be presented and discussed in this paper.

Copyright © 2010 by American Society of Mechanical Engineers
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Figure 1

Primary surface recuperator (PSR) core with individual aircell (inset)

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Figure 2

HR-120 sample from rainbow PSR: (a) BSE image, (b) Cr map, (c) Fe map, and (d) O map

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Figure 3

AL 20–25+Nb sample from rainbow PSR: (a) BSE image, (b) Cr map, (c) Fe map, and (d) O map

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Figure 4

347SS sample from rainbow PSR: (a) BSE image, (b) Cr map, (c) Fe map, and (d) O map

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Figure 5

HR-120 profile scan location

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Figure 6

HR-120-EPMA O, Cr, Fe, and Ni profiles

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Figure 7

AL 20–25+Nb profile scan location

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Figure 8

AL 20–25+Nb: EPMA O, Cr, Fe, and Ni profiles

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Figure 9

347SS profile scan location

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Figure 11

Comparison of postexposure Cr profiles of HR-120, AL 20–25+Nb, and 347SS

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Figure 10

347SS-EPMA O, Cr, Fe, and Ni profiles



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