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Research Papers: Materials and Fabrication

Failure Mode and Failure Strengths for Wall Thinning Straight Pipes and Elbows Subjected to Seismic Loading

[+] Author and Article Information
Kunio Hasegawa1

Nuclear System Division,  Hitachi, Ltd., Saiwai-cho 3-1-1, Hitachi-shi, 317-8511 Ibaraki-ken, Japanhasegawa-kunio@jnes.go.jp

Katsumasa Miyazaki

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

Izumi Nakamura

 National Research Institute for Earth Science and Disaster Prevention, Miki-shi, Hyogo-ken 673-0515, Japanizumi@bosai.go.jp

1

Present address: Japan Nuclear Energy Safety Organization.

J. Pressure Vessel Technol 130(1), 011404 (Jan 17, 2008) (8 pages) doi:10.1115/1.2826425 History: Received February 09, 2006; Revised January 08, 2007; Published January 17, 2008

It is important to assess the failure strengths for pipes with wall thinning to maintain the integrity of the piping systems and to make codification of allowable wall thinning. Full-scale fracture experiments on cyclic loading under constant internal pressure were performed for 4in. diameter straight pipes and 8in. diameter elbow pipes at ambient temperature. The experiments were low cycle fatigue under displacement controlled conditions. It is shown that a dominant failure mode under cyclic loading for straight pipes and elbows is crack initiation∕growth accompanying swelling by ratchet or buckling with crack initiation. When the thinning depth is deep, the failure mode is burst and crack growth with ratchet swelling. In addition, failure strengths were compared with the design fatigue curve of the ASME Code Sec. III. It is shown that pipes with wall thinning less than 50% of wall thickness have sufficient margins against a seismic event of the safety shutdown earthquake.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Straight pipe specimens with full circumferential wall thinning. (1) 50% thinned specimen (EC02, 05, 06). (2) 75% thinned specimen (EC07). (3) 25% thinned specimen (EC08). (4) 60% thinned specimen (EC09).

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Figure 2

Elbow specimens with wall thinning. (1) Elbow specimen. (2) Longitudinal section. (3) Wall thinning geometry at circumferential cross: (a) No defect, (b) 50% full defect, (c) 50% partial defect, and (d) 70% partial defect.

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Figure 3

Four-point bending test apparatus for straight pipe specimens

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Figure 4

(a) Test apparatus for elbow with in-plane cyclic bending load: (1) schematic illustration; (2) pin-pin supported elbow. (b) Test apparatus of pin-fixed support for elbow with cyclic bending load: (3) in-plane loading, (4) out-of-plane loading, (5) in- and out-of-plane loading, and (6) pin-fixed support elbow.

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Figure 5

Time histories of input displacement. (1) Sinusoidal wave for straight pipe (one block is 26cycles). (2) Sinusoidal wave for elbow (one block is 5cycles). (3) Sinusoidal wave for elbow (one block is 20cycles).

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Figure 6

Failure mode of the EC07 specimen

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Figure 7

Failure mode of the ELMB-01 specimen

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Figure 8

Example of pressure blowout occurring at thermal power plant piping

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Figure 9

Elastic strain-based moment for elbow

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Figure 10

Comparison of low cycle fatigue strengths for wall thinned straight pipes, seismic regime, and design fatigue curve

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Figure 11

Comparison of low cycle fatigue strengths for wall thinned elbows, seismic regime, and design fatigue curve

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