Ultra-Supercritical Steam Corrosion Page: 4 of 6
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Three types of oxidation experiments are planned: cyclic oxidation in air plus steam at atmospheric
pressure, thermogravimetric analysis (TGA) in steam at atmospheric pressure, and exposure tests in
supercritical steam up to 650 C (1202 F) and 34.5 MPa (5000 psi). The atmospheric pressure tests,
combined with supercritical exposures at 13.8, 20.7, 24.6, and 34.5 MPa (2000, 3000, 4000, and 5000
psi) are designed to determine the effect of pressure on the oxidation process.
Cyclic oxidation tests will measure how the material reacts to rapid changes in temperature. In
particular, differences in the thermal expansion coefficients of the base alloy and its oxide scale can lead
to the spallation of the scale and possible erosion of downstream components, i.e., turbine blades and
buckets. Cyclic oxidation tests will be conducted at atmospheric pressure in air at temperatures up to
800 C (1472 F).
The apparatus is shown in Fig. 1. It consists of a
vertical tube furnace fitted with an upper end cap
attached to a linear slide. Seven samples can be
attached to the upper end cap. The linear slide is
programmed to move the samples in and out of the
furnace at regular (hourly) cycles. The samples
are temporarily removed and weighed at periodic
intervals, then replaced in the furnace. A metering
pump injects water into a heated tube to produce
steam at the bottom of the furnace and create an
air plus steam environment.
The TGA tests in steam provide information on
the mechanism of oxidation in terms of kinetics
and activation energies. The apparatus is shown in
Fig. 2. A single sample is suspended from a
balance into a vertical tube furnace. Steam is
injected into the base of the tube furnace with a
metering pump. It is condensed and collected
from a side port above the furnace. A dissolved
oxygen (DO) sensor measures the oxygen content
of the input water. Bubbling nitrogen gas through
the input water, containing a known percentage of
oxygen, fixes the input water at a particular DO
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Fig. 1: Cyclic oxidation apparatus.
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Holcomb, G. R.; Alman, D. E.; Bullard, S. B.; Covino, B. S., Jr.; Cramer, S. D. & Ziomek-Moroz, M. Ultra-Supercritical Steam Corrosion, article, April 22, 2003; Pittsburgh, Pennsylvania. (digital.library.unt.edu/ark:/67531/metadc787689/m1/4/: accessed December 15, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.