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Research Papers: Gas Turbines: Manufacturing, Materials, and Metallurgy

Comparison of Recuperator Alloy Degradation in Laboratory and Engine Testing

[+] Author and Article Information
Bruce A. Pint

Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6156pintba@ornl.gov

Karren L. More, Rosa Trejo, Edgar Lara-Curzio

Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6156

J. Eng. Gas Turbines Power 130(1), 012101 (Dec 13, 2007) (7 pages) doi:10.1115/1.2436565 History: Received June 20, 2006; Revised July 03, 2006; Published December 13, 2007

In order to increase the efficiency of advanced microturbines, durable alloy foils are needed for their recuperators to operate at 650700°C. Prior work has demonstrated that water vapor in the exhaust gas causes more rapid consumption of Cr from austenitic alloys, leading to a reduction in lifetime for the thin-walled components in this application. New commercial alloy foils are being tested in both laboratory tests in humid air and in the exhaust gas of a modified 60kW microturbine. Initial results are presented for a commercial batch of 80μm alloy 120 foil. The Cr consumption rates in laboratory testing were similar to those observed in previous testing. The initial results from the microturbine indicate a faster Cr consumption rate compared to the laboratory test, but longer term results are needed to quantify the difference. These results will help to verify a Cr consumption model for predicting lifetimes in this environment based on classical gas transport theory.

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Figures

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Figure 1

Light microscopy of polished cross sections of as-received 80μm alloy 120 foil

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Figure 2

Specimen mass gains for various foil materials during 100hr cycles in humid air at 650°C

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Figure 3

Light microscopy of polished cross sections of 80μm alloy 120 foil oxidized in humid air for (a) 1000hr at 650°C, (b) 5000hr at 650°C, (c) 1000hr at 700°C, (d) 5000hr at 700°C, (e) 1000hr at 800°C, and (f) 5000hr at 800°C

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Figure 4

Light microscopy of polished cross sections of 90μm alloy 120 foil oxidized for 10,000hr at 700°C in (a) humid air and (b) laboratory air

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Figure 5

Secondary electron images of polished cross sections of alloy 120 foil exposed for 1000 in the exhaust gas of a 60kW microturbine. The specimens were exposed at (a) 720°C, (b) 690°C, (c) 670°C, and (d) 600°C.

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Figure 6

EPMA Cr profiles from three scans across the cross section of alloy 120 foils after laboratory exposures in humid air for (a) 5000hr at 650°C, (b) 1000hr at 700°C, (c) 5000hr at 700°C, and (d) 1000hr at 800°C

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Figure 7

EPMA Cr profiles from two scans across the cross section of alloy 120 foil after exposures in a microturbine recuperator for 1000hr at 720°C. The side exposed to the exhaust gas is marked.

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Figure 8

EPMA Cr (a,c,e) and O (b,d,f) maps of 80μm alloy 120 foil after 1000hr exposures in exhaust gas at (a,b) 720°C, (c,d) 690°C, and (e,f) 670°C. The exhaust gas side is up in these images.

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Figure 9

Chromium mass losses from alloy 120 foil specimens as a function of time after exposures to air+10%H2O (solid lines) at 650–800°C and exhaust gas at 720°C. Values for 800°C exposures in laboratory air (dashed line) are shown for comparison.

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Figure 10

Comparison of the calculated and measured Cr loss from alloy 709 foils exposed to humid air at 800°C

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Figure 11

Calculated Cr loss fluxes as a function of (v∕l)1∕2 for air+5%H2O at 650–800°C. Vertical dashed lines mark conditions in the laboratory test compared to the approximate conditions in a recuperator.

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