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Research Papers: Codes and Standards

# Application of Negligible Creep Criteria to Candidate Materials for HTGR Pressure Vessels

[+] Author and Article Information
R. I. Jetter

1106 Wildcat Canyon Road, Pebble Beach, CA 93953

T.-L. Sham1

Materials Science and Technology Division, Oak Ridge National Laboratory, 1 Bethel Valley Road, P.O. Box 2008, MS-6155, Oak Ridge, TN 37831-6155shamt@ORNL.gov

R. W. Swindeman

Cromtech Inc., 125 Amanda Drive, Oak Ridge, TN 37830

1

Corresponding author.

J. Pressure Vessel Technol 133(2), 021103 (Feb 14, 2011) (7 pages) doi:10.1115/1.4001919 History: Received April 11, 2009; Revised May 11, 2010; Published February 14, 2011; Online February 14, 2011

## Abstract

Two of the proposed high temperature gas reactors (HTGRs) under consideration for a demonstration plant have the design object of avoiding creep effects in the reactor pressure vessel during normal operation. This work addresses the criteria for negligible creep in subsection NH, Division 1 of the ASME Boiler and Pressure Vessel Code, Sec. III, other international design codes, and some currently suggested criteria modifications and their impact on permissible operating temperatures for various reactor pressure vessel materials. The goal of negligible creep could have different interpretations depending on what failure modes are considered and associated criteria for avoiding the effects of creep. It is shown that for the materials of this study, consideration of localized damage due to cycling of peak stresses results in a lower temperature for negligible creep than consideration of the temperature at which the allowable stress is governed by the creep properties. In assessing the effect of localized cyclic stresses, it is also shown that consideration of cyclic softening is an important effect that results in a higher estimated temperature for the onset of significant creep effects than would be the case if the material were cyclically hardening. There are other considerations for the selection of vessel material besides avoiding creep effects. Of interest for this review are (1) the material’s allowable stress level and impact on the wall thickness (the goal being to minimize the required wall thickness) and (2) ASME code approval (inclusion as a permitted material in the relevant section and subsection of interest) to expedite regulatory review and approval. The application of negligible creep criteria to two of the candidate materials, SA533 and Mod 9Cr–1Mo (also referred to as Grade 91), and to a potential alternate, normalized and tempered $214$ Cr–1Mo, is illustrated, and the relative advantages and disadvantages of the materials are discussed.

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## Figures

Figure 1

SA533 allowable primary stresses (1)

Figure 2

Figure 3

Negligible creep curves for ferritic and austenitic steels based on 1.5Sm and a creep strain of 0.03% (6)

Figure 4

SA533 negligible creep curves based on Eq. 2(1)

Figure 5

SA533 cyclic hardening data at 482°F(250°C)

Figure 6

Grade 91 negligible creep curves based on Eq. 2

Figure 7

N&T 214 Cr–1Mo allowable primary stresses

Figure 8

N&T 214 Cr–1Mo negligible creep curves based on Eq. 2

Figure 9

PBMR RPV temperature distribution during normal operation (in °C) (17)

Figure 10

Negligible creep curves for wall sizing

Figure 11

Negligible creep curves based on Eq. 2 for selected s parameters

Figure 12

Expected minimum rupture stress at 600,000 h for SA533 and N&T 214 Cr–1Mo

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