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Research Papers: Design and Analysis

Failure Bending Moment for Pipes With an Arbitrary-Shaped Circumferential Flaw

[+] Author and Article Information
Yinsheng Li

Seismic Safety Division, Japan Nuclear Energy Safety Organization, Toranomon 4-3-20, Minato-ku, Tokyo 105-0001, Japanli-yinsheng@jnes.go.jp

Kunio Hasegawa

Nuclear Energy System Safety Division, Japan Nuclear Energy Safety Organization, Toranomon 3-7-11, Minato-ku, Tokyo 105-0001, Japanhasegawa-kunio@jnes.go.jp

Akira Shibuya

Seismic Safety Division, Japan Nuclear Energy Safety Organization, Toranomon 4-3-20, Minato-ku, Tokyo 105-0001, Japanshibuya-akira@jnes.go.jp

Nathaniel G. Cofie

 Structural Integrity Associates, 5215 Hellyer Avenue, Suite 210, San Jose, CA 95138ncofie@structint.com

J. Pressure Vessel Technol 133(4), 041207 (May 17, 2011) (7 pages) doi:10.1115/1.4002927 History: Received April 26, 2010; Revised October 13, 2010; Published May 17, 2011; Online May 17, 2011

When a flaw is detected in a stainless steel piping system, an evaluation has to be performed to determine its suitability for continued operation. The failure bending moment of the flawed pipe can be predicted by limit load criterion in accordance with Appendix E-8 in the JSME S NA-1-2008 and/or Appendix C in the ASME Code Section XI. However, in these current codes, the limit load criterion is only calculated for the case of pipes containing a single flaw with constant depth, although the actual flaw depth is variable along the circumferential direction. Particularly, geometrical shapes of stress corrosion cracks are generally complex. The objective of this paper is to propose a method by formula for predicting the load-carrying capacity of pipes containing a circumferential surface flaw with any arbitrary shape. The failure bending moment is obtained by dividing the surface flaw into several subflaw segments. Using this method, good agreement is observed between the numerical solution and the reported experimental results. Several numerical examples are also presented to show the validity of the proposed methodology. Finally, it is demonstrated that three subflaw segments are sufficient to determine the collapse bending moment of a semi-elliptical surface flaw using the proposed methodology.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Flaw characterization in current codes

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Figure 2

Nomenclature and stress distribution of a pipe with a constant-depth flaw

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Figure 3

Flaw characterization by segmented subflaws

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Figure 4

Nomenclature and stress distribution of a pipe with a flaw characterized by segmented subflaws

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Figure 5

Nomenclature of a pipe with a flaw characterized by nonsymmetrical segmented subflaws

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Figure 6

A pipe with a circumferential semi-elliptical flaw

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Figure 7

Relation between ratio of collapse moment and flaw angle for different flaw depths

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Figure 8

Relation between ratio of collapse moment and flaw angle for different membrane stresses

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Figure 9

The flaw shape used in experiment

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Figure 10

(a) Specimen no. EXP1, comparison between predicted values and experimental result, (b) specimen no. SYM160, comparison between predicted values and experimental result, and (c) specimen no. SYM180, comparison between predicted values and experimental result

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Figure 11

Relation between ratio of collapse moments and divided number of segmented subflaws

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Figure 12

Sample of relative difference of collapse moment between m=3 and m=200

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