Research Papers: Codes and Standards

Extension of Fatigue Exemption Rules in Section VIII, Division 2 Slightly Into the Creep Regime

[+] Author and Article Information
Charles Becht

 Becht Engineering Co., Inc., Liberty Corner, NJ 07960

J. Pressure Vessel Technol 134(2), 021101 (Jan 19, 2012) (5 pages) doi:10.1115/1.4003457 History: Received May 01, 2009; Accepted December 07, 2010; Published January 19, 2012; Online January 19, 2012

A number of alloys have applications slightly into the creep range that are in cyclic service, such as process reactors. The 2007 edition of Section VIII, Division 2 (2007, ASME Boiler and Pressure Vessel Code, Section VIII, Division 2, The American Society of Mechanical Engineers) provides allowable stresses for these materials, which may be controlled by creep properties. However, the fatigue design rules and fatigue exemption rules are not applicable, precluding the construction of vessels using these materials at temperatures above 370C (700F). This paper provides a simplified approach for the exemption of low chrome alloys that are slightly into the creep range from fatigue analysis. Part 1 of this paper (Becht, C., 2009, “Elevated Temperature Shakedown Concepts,” ASME J. Pressure Vessel Technol. 133 , p. 051203) describes shakedown concepts, which are the basis for the criteria evaluated in this paper.

Copyright © 2012 by American Society of Mechanical Engineers
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Figure 9

Stress, plastic and creep strain, strain limit ratio, and damage after ten cycles with 2 year hold time [9]

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Figure 8

Nozzle subjected to internal pressure with high peak stress at the acute corner [9]

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Figure 7

Creep-fatigue interaction diagram

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Figure 6

9Cr−1Mo−V data point plotted versus fatigue data for 9Cr−1Mo−V steel [13]

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Figure 5

9Cr−1Mo−V data point plotted versus fatigue data for 9Cr−1Mo−V steel (see Appendix D in Ref. [7])

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Figure 4

2.25Cr−1Mo−V data point plotted versus fatigue data for 2.25Cr−1Mo−V steel [12]

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Figure 3

2.25Cr−1Mo class 2 data point plotted versus fatigue data for 2.25Cr−1Mo steel class 2. Note: HAZ stands for heat effected zone [11].

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Figure 2

Relaxation/damage accumulation curves for 1.25Cr−0.5Mo class 1 material

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Figure 1

2.25Cr−1Mo class 2 data points at 482∘C(900∘F) plotted versus fatigue data for PWHT and QT (both bainitic) material condition. Tension or compression hold times in hours tabulated [3].



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