Assessment of Embrittlement of VHTR Structural Alloys in Impure Helium Environments Page: 5 of 63
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The specimen cross-sectional area of WxT = 3.2x3.125 mm2 was chosen based on considerations
of the anticipated strength of the alloys and the capacity of the load cell (more discussion to
Design values (mm):
Figure 2 Geometry of tensile specimens as defined by ASTM standard E8, along with the design values
2.2 Creep Crack Growth (CCG) Testing and Apparatus
To carry out the objectives of this project, we developed an apparatus for conducting CCG
experiments on candidate alloys at elevated temperatures and in controlled environments,
including impure helium. Design of the CCG testing apparatus was performed considering the
requirements established in ASTM standard E 1457-07 for performing CCG measurements on
metals and alloys. The apparatus was designed for testing three CT specimens in series within an
environmental chamber and under dead-weight loading (Figure 3), and the direct current
potential drop (DCPD) technique was employed to monitor crack growth continuously during
testing. The capability of testing three specimens simultaneously is important for efficiently
evaluating variability of CCG behavior under identical conditions. The composition of the
impure helium used for these CCG studies is presented in Table 2.
Gas Composition (ppm)
Carbon monoxide 12
Carbon Dioxide 1.5
Water vapor 0.2
As described in a published
conference proceeding , a
carbon steel frame, standing
approximately six feet tall,
constitutes the overall structure
of the CCG testing apparatus. A
retort tube, fabricated with
Inconel 600 alloy, was designed
to withstand elevated
Table 2 Composition of impure helium used for these studies. temperatures and to be isolated
environmentally from the
ambient conditions. Access ports at the top and bottom of the retort tube were positioned to
allow the tension rods (Figure 3b), fabricated with Inconel 617 alloy, to deliver a constant load to
the specimens throughout the testing duration. Inconel 625 was machined to make the clevises
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Crone, Wendy; Cao, Guoping & Sridhara, Kumar. Assessment of Embrittlement of VHTR Structural Alloys in Impure Helium Environments, report, May 31, 2013; United States. (digital.library.unt.edu/ark:/67531/metadc836772/m1/5/: accessed May 23, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.