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Research Papers: Design and Analysis

Applicability of Net-Section Collapse Load Approach to Multiple-Cracked Pipe Assessment: Numerical Study

[+] Author and Article Information
Myeong-Woo Lee

Mechanical Engineering,
Korea University,
Anam-Dong, Sungbuk-Ku,
Seoul 136-701, Korea
e-mail: lee-mw@korea.ac.kr

So-Dam Lee

Mechanical Engineering,
Korea University,
Anam-Dong, Sungbuk-Ku,
Seoul 136-701, Korea
e-mail: faireunshow@korea.ac.kr

Yun-Jae Kim

Mechanical Engineering,
Korea University,
Anam-Dong, Sungbuk-Ku,
Seoul 136-701, Korea
e-mail: kimy0308@korea.ac.kr

1Corresponding author.

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received October 12, 2016; final manuscript received April 26, 2017; published online May 26, 2017. Assoc. Editor: Haofeng Chen.

J. Pressure Vessel Technol 139(4), 041208 (May 26, 2017) (9 pages) Paper No: PVT-16-1192; doi: 10.1115/1.4036656 History: Received October 12, 2016; Revised April 26, 2017

In this paper, applicability of net-section collapse load approach to circumferential multiple-cracked pipe assessment is investigated using finite element (FE) damage analysis. The FE damage analysis based on the stress-modified fracture strain model is validated against limited fracture test data of two circumferential surface-cracked pipes. Then, the systematic parametric study is performed using the FE damage analysis for symmetrical and asymmetrical surface-cracked pipes. It is found that predictions using the net-section collapse load approach tend to be more accurate with increasing the distance between two symmetrical cracks. For asymmetrical cracks, it is found that the deeper crack plays a more important role and that the existing net-section collapse load expression can be potentially nonconservative. Idealization to symmetrical cracks based on the deeper crack is proposed.

Copyright © 2017 by ASME
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References

Figures

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Fig. 1

Schematic diagram of a circumferential cracked pipe with: (a) two asymmetrical surface cracks, (b) two symmetrical surface cracks, and (c) single surface crack

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Fig. 2

(a) True and engineering stress–strain curve and (b) comparison of experimental collapse moments with predicted ones using Eq. (3)

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Fig. 3

(a) Determined multi-axial fractures strain locus for 304 stainless steel and (b) the effect of the element size on the critical damage ωc

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Fig. 4

Comparison of experimentally measured maximum moments with FE predicted ones

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Fig. 5

Typical FE meshes to simulate pipe test with: (a) a single crack and two symmetrical surface cracks and (b) two asymmetrical cracks

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Fig. 6

(a) FE moment–rotation curves for single surface crack cases from FE damage analysis (θ = 60 deg) and (b) comparison of FE maximum moments with predicted ones using Eq. (4)

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Fig. 7

Fracture surface from FE damage analysis at the maximum moment: (a) and (b) θ = 45 deg with a/t = 0.3 and 0.73; and (c) and (d) θ = 60 deg with a/t = 0.3 and a/t = 0.73. Ductile tearing regions are shown in black.

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Fig. 8

Outside of cracked surface at the maximum moment: (a) θ = 45 deg with a/t = 0.3 and (b) θ = 60 deg with a/t = 0.73. Cracked and necked regions are shown in black.

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Fig. 9

FE moment–rotation curves for two symmetrical crack cases from FE damage analysis: (a)α = 15 deg and (b) α = 30 deg at θ = 60 deg

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Fig. 10

Fracture surface from FE damage analysis at the maximum moment: (a) θ = 45 deg, a/t = 0.3 and α = 15 deg or α = 30 deg and (b) θ = 60 deg, α = 15 deg and a/t = 0.3 or 0.73. Ductile tearing regions are shown in black.

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Fig. 11

Outside of cracked surface at the maximum moment: (a) θ = 45 deg, a/t = 0.3 and α = 15 deg and (b) θ = 45 deg, a/t = 0.3 and α = 30 deg. Cracked and necked regions are shown in black.

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Fig. 12

Comparison of FE maximum moments with predicted ones using Eq. (3) for two symmetrical crack cases: (a) a/t = 0.3, (b) a/t = 0.5, and (c) a/t = 0.73

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Fig. 13

FE moment–rotation curves for two asymmetrical crack cases: (a) case 1 and 2 at α = 30 deg, (b) case 3 and 4 at α = 15 deg, and (c) case 5 and 6 at α = 5 deg

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Fig. 14

Fracture surface from FE damage analysis at the maximum moment: (a) case 1 at α = 15 deg, (b) case 2 at α = 30 deg, (c) case 3 at α = 15 deg, (d) case 4 at α = 30 deg, (e) case 5 at α = 5 deg, and (f) case 6 at α = 30 deg. Ductile tearing regions are shown in black.

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Fig. 15

Comparison of FE maximum moments with predicted ones for two asymmetrical crack cases: (a) case 1 and 2, (b) case 3 and 4, and (c) case 5 and 6 using Eq. (1) and (d) case 3–6 using Eq. (3)

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