Research Papers: Codes and Standards

Recommended Revisions to Nuclear Piping Thermal Expansion Stress Limits

[+] Author and Article Information
Gerry Slagis

 G C Slagis Associates, 258 Hillcrest Place, Pleasant Hill, CA 94523slagisg@asme.org

J. Pressure Vessel Technol 133(2), 021102 (Jan 31, 2011) (7 pages) doi:10.1115/1.4002256 History: Received July 13, 2007; Revised December 16, 2009; Published January 31, 2011; Online January 31, 2011

Piping thermal expansion stress limits for ASME Section III Class 2 and 3 piping are directly based on the original thermal expansion rules for B31.1 piping published in 1955. Temperature limits for B31 piping are much higher than for Class 2/3 nuclear piping. The fundamental concern in 1955 for piping design was to prevent cyclic creep strains, and the thermal expansion rules were based on a strain range criterion. Fatigue was also a concern, and a stress-range reduction factor for cyclic conditions was incorporated into the strain-based rule. The history and development of the B31.1 thermal expansion rules are summarized. After review of the technical basis, it becomes evident that the nuclear Class 2/3 rules can be simplified and improved by changing to an explicit fatigue-based rule rather than the strain-based rule of B31.1. Recommended Section III code revisions are provided with discussion of related technical issues.

Copyright © 2011 by American Society of Mechanical Engineers
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Figure 1

Typical Markl fatigue tests (from Ref. 4)

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Figure 2

Effect of relaxation upon reactions and stresses (from Ref. 5)

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Figure 3

Stress-range reduction factor (from Ref. 5)

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Figure 4

Fatigue safety factor (from Ref. 5)



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