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Research Papers: Nuclear Power

Creep Effects on Design Below the Temperature Limits of ASME Section III Subsection NB

[+] Author and Article Information
T.-L. Sham

 Oak Ridge National Laboratory, 1 Bethel Valley Road, P.O. Box 2008, MS-6155, Oak Ridge, TN 37831-6155shamt@ornl.gov

Robert I. Jetter

Pebble Beach, CA 93953

Daniel R. Eno

Guilderland, NY 12084

J. Eng. Gas Turbines Power 132(1), 012904 (Oct 02, 2009) (6 pages) doi:10.1115/1.3126263 History: Received October 20, 2008; Revised November 24, 2008; Published October 02, 2009

Some recent studies of material response have identified an issue that crosses over and blurs the boundary between ASME Boiler and Pressure Vessel Code Section III Subsection NB and Subsection NH. For very long design lives, the effects of creep show up at lower and lower temperature as the design life increases. Although true for the temperature at which the allowable stress is governed by creep properties, the effect is more apparent, e.g., creep effects show up sooner, at local structural discontinuities and peak thermal stress locations. This is because creep is a function of time, temperature, and stress, and the higher the localized stress, the lower in temperature creep begins to cause damage. If the threshold is below the Subsection NB to NH temperature boundary, 700°F for ferritic steels and 800°F for austenitic materials, then this potential failure mode will not be considered. Unfortunately, there is no experience base with very long lives at temperatures close to but under the Subsection NB to NH boundary to draw on. This issue is of particular interest in the application of Subsection NB rules of construction to some high temperature gas-cooled reactor concepts. The purpose of this paper is, thus, twofold: one part is about statistical treatment and extrapolation of sparse data for a specific material of interest, SA-533 Grade B Class 1; the other part is about how these results could impact current design procedures in Subsection NB.

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References

Figures

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Figure 1

Measured versus predicted time to 1% strain for SA-533B

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Figure 2

Measured versus predicted time to start of tertiary creep for SA-533B

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Figure 3

Measured versus predicted creep rupture time for SA-533B

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Figure 4

Extrapolated minimum creep rupture stress for SA-533B

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Figure 5

Extrapolated time-dependent primary stress limits around the NB/NH temperature boundary for SA-533B

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Figure 6

Extrapolated time-dependent primary stress limits as a function of time for SA-533B

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Figure 7

Negligible creep curves for SA-533B

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