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Research Papers: Design and Analysis

Prediction of Fully Plastic Collapse Stresses for Pipes With Two Circumferential Flaws

[+] Author and Article Information
Kunio Hasegawa

 Japan Nuclear Energy Safety Organization (JNES), Toranomon 3-17-1, Minatoku, Tokyo 105-0001, Japanhasegawa-kunio@jnes.go.jp

Koichi Saito

Hitachi Works, Hitachi GE Nuclear Energy, Ltd., Saiwai-cho 3-1-1, Hitachi-shi 317-8511, Japankoichi.saito.qe@hitachi.com

Fuminori Iwamatsu

Hitachi Research Laboratory,  Hitachi, Ltd., Saiwai-cho 3-1-1, Hitachi-shi 317-8511, Japanfuminori.iwamatsu.vt@hitachi.com

Katsumasa Miyazaki

Hitachi Research Laboratory,  Hitachi, Ltd., Saiwai-cho 3-1-1, Hitachi-shi 317-8511, Japankatsumasa.miyazaki.xs@hitachi.com

J. Pressure Vessel Technol 131(2), 021209 (Jan 13, 2009) (6 pages) doi:10.1115/1.3066967 History: Received October 09, 2007; Revised June 02, 2008; Published January 13, 2009

Fully plastic collapse stress for a single circumferential flaw on a pipe is evaluated by the limit load criteria in accordance with the JSME Code S NA-1-2004 and the ASME Code Section XI. However, multiple flaws such as stress corrosion cracking are frequently detected in the same circumferential cross section in a pipe. If the distance between adjacent flaws is short, the two flaws are combined as a single flaw in compliance with combination rules. If the two flaws separated by a large distance, it is not required to combine two flaws. However, there is no evaluation method for two separated flaws in a pipe in the JSME and ASME Codes. Plastic collapse stresses for pipes with two symmetrical circumferential flaws based on net-stress approach had been proposed by one of the authors. Bending tests were performed on Type 304 stainless steel pipes with two symmetrical circumferential flaws. Consequently, it was shown that the proposed method can predict well the plastic collapse stresses for pipes with two flaws. In addition, it is also shown that this method is appropriate to use in fitness-for-service procedures, and higher plastic collapse stresses are expected, compared with current prediction methods for pipes with two flaws.

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Copyright © 2009 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Two surface flaws

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Figure 2

Two independent flaws and combined into one flaw in same circumference of a pipe

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Figure 3

Nomenclature and stress distribution of a pipe with two symmetrical flaws

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Figure 4

Limitation of plastic failure stresses for pipe with two flaws. (1) single flaw, (2) short distance between two flaws, and (3) long distance between two flaws.

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Figure 5

Full scale pipe specimens with two flaws

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Figure 6

Four-point bending apparatus

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Figure 7

Load displacement curve for DP 02 specimen

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Figure 8

Load displacement curves for pipes with two symmetrical flaws

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Figure 9

Comparison of failure bending stresses obtained from experiment and calculation using flow stress from specified properties

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Figure 10

Effect of loading capacity as a function of angle between two flaws

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