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Research Papers: Design and Analysis

Determination of Shakedown Boundary and Failure-Assessment-Diagrams of Cracked Pipe Bends

[+] Author and Article Information
Mostafa S. Elsaadany

Department of Bioengineering,
College of Engineering,
University of Toledo,
2801 W Bancroft Street,
Toledo, OH 43606
e-mail: mostafa.elsaadany@utoledo.edu

Maher Y. A. Younan

Professor of Mechanics and Design
Associate Dean for Undergraduate Studies
School of Sciences and Engineering,
The American University in Cairo,
AUC Avenue, P.O. Box 74,
New Cairo 11835, Egypt
e-mail: myounan@aucegypt.edu

Hany F. Abdalla

Assistant Professor of
Mechanical Design and Solid Mechanics
Department of Mechanical Engineering,
School of Sciences and Engineering,
The American University in Cairo,
AUC Avenue, P.O. Box 74,
New Cairo 11835, Egypt
e-mail: hany_f@aucegypt.edu

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received January 3, 2013; final manuscript received August 3, 2013; published online December 12, 2013. Assoc. Editor: Osamu Watanabe.

J. Pressure Vessel Technol 136(1), 011209 (Dec 12, 2013) (9 pages) Paper No: PVT-13-1003; doi: 10.1115/1.4025614 History: Received January 03, 2013; Revised August 03, 2013

Determination of shakedown (SD) boundaries of 90-degree plain smooth pipe bends has recently received substantial attention by several researchers. However, scarce or almost no solid information is found within the literature regarding the determination of the shakedown boundary of cracked pipe bends. The current research presents two additions to the literature, namely, determination of shakedown boundary for a circumferentially cracked 90-degree pipe bend via a simplified technique utilizing the finite element (FE) method and introduction of failure-assessment diagrams (FADs) in compliance with the API 579 failure-for-service assessment of pressure vessel and piping components. The analyzed cracked pipe bend is subjected to the combined effect of steady internal pressure spectrum and cyclic in-plane closing (IPC) and opening (IPO) bending moments. Line spring elements (LSEs) are embedded in quadratic shell elements to model part-through cracks. FAD is obtained through linking the J-integral fracture mechanics parameter with the shakedown limit moments of the analyzed cracked 90-degree pipe bend. The LSE outcomes illustrated satisfactory results in comparison to the results of two verification studies: stress intensity factor (SIF) and limit load. Additionally, full elastic-plastic (ELPL) cyclic loading finite element analyses are conducted and the outcomes revealed very good correlation with the results obtained via the simplified technique. The maximum load carrying capacity (limit moment) and the elastic domain are also computed thereby generating a Bree diagram for the cracked pipe bend. Finally, Crack growth analysis is presented to complement the FAD.

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References

Figures

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Fig. 1

Full model of the plate with central surface crack

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Fig. 9

Normalized limit, SD, and elastic moments of QM120C subjected to IPC bending moment and internal pressure

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Fig. 11

Comparison between elastic and SD limits of QM120C-IPO and QM120C-IPC models (b/t = 0.75)

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Fig. 10

Comparison between elastic and SD limits of defect-free and QM120C models subjected to IPC bending moment and internal pressure

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Fig. 7

Representative sample moment end-rotation curve for the model QM120C-IPO at 30%Py used for limit load determination using TES method

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Fig. 8

Comparison between elastic and SD limits of defect-free-IPO, QM45C-IPO, and QM120C-IPO models

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Fig. 2

Quarter model of pipe bend that is used to introduce external circumferential crack on the extrados

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Fig. 3

Full model of the pipe bend that is used to introduce external axial crack on the crown

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Fig. 4

Deformed shape of the quarter model with external circumferential crack

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Fig. 5

Deformed shape of the full model with external axial crack on the crown

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Fig. 6

Normalized limit, shakedown, and elastic moments of pipe bend with 120 deg circumferential crack subjected to IPO bending moment and internal pressure

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Fig. 12

Elastic shakedown behavior exhibited for the case of 15%Py using the shakedown limit obtained using the simplified technique

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Fig. 13

Reversed plasticity behavior exhibited for the case of 0%Py (QM120C-IPO) upon slightly exceeding the shakedown limit obtained using the simplified technique

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Fig. 14

Elastic J-integral versus applied moment for the case of QM120C-IPO at 0%Py

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Fig. 15

Total J-integral versus applied moment for the case of QM120C-IPO at 0%Py

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Fig. 16

Failure-assessment diagram of QM120C model (P = 0%Py) and (b/t = 0.75)

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Fig. 17

Failure-assessment diagram of QM120C-IPO model (P = 15%Py) and (b/t = 0.75)

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Fig. 18

Failure-assessment diagram of QM45C-IPO model (P = 20%Py) and (b/t = 0.5)

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Fig. 19

Failure-assessment diagram of QM120C-IPC model (P = 40%Py) and (b/t = 0.75)

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Fig. 20

Crack growth analysis for the pipe bend models with circumferential crack at the intrados under the combined effect of IPO bending moment and internal pressure

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