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Research Papers: Piper and Riser Technology

Radial Buckling of Tensile Armor Wires in Subsea Flexible Pipe—Numerical Assessment of Key Factors

[+] Author and Article Information
Alireza Ebrahimi, Amgad Hussein

Faculty of Engineering and Applied Science,
Memorial University of Newfoundland,
St. John's, NL A1B 3X5, Canada

Shawn Kenny

Department of Civil and Environmental
Engineering,
Faculty of Engineering and Design,
Carleton University,
Ottawa, ON K1S 5B6, Canada

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received May 20, 2015; final manuscript received February 14, 2016; published online April 6, 2016. Assoc. Editor: Myung Hyun Kim.

J. Offshore Mech. Arct. Eng 138(3), 031701 (Apr 06, 2016) (8 pages) Paper No: OMAE-15-1039; doi: 10.1115/1.4032894 History: Received May 20, 2015; Revised February 14, 2016

Flexible pipes can be used as risers, jumpers, and flowlines that may be subject to axial forces and out-of-plane bending motion due to operational and environmental loading conditions. The tensile armor wires provide axial stiffness to resist these loads. Antibirdcaging tape is used to provide circumferential support and prevent a loss of stability for the tension armor wires, in the radial direction. The antibirdcaging tape may be damaged where a condition known as “wet annulus” occurs that may result in the radial buckling (i.e., birdcaging mechanism) of the tensile armor wires. A three-dimensional continuum finite element (FE) model of a 4 in. flexible pipe is developed using abaqus/implicit software package. As a verification case, the radial buckling response is compared with similar but limited experimental work available in the public domain. The modeling procedures represent an improvement over past studies through the increased number of layers and elements to model contact interactions and failure mechanisms. A limited parameter study highlighted the importance of key factors influencing the radial buckling mechanism that includes external pressure, internal pressure, and damage, related to the percentage of wet annulus. The importance of radial contact pressure and shear stress between layers was also identified. The outcomes may be used to improve guidance in the engineering analysis and design of flexible pipelines and to support the improvement of recommended practices.

Copyright © 2016 by ASME
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References

Figures

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Fig. 1

Layers and element distribution in the cross section

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Fig. 2

The pipe after birdcaging (radial buckling)

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Fig. 3

Global axial force versus axial strain at the reference point

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Fig. 4

Global axial force versus twist per unit length at the reference point

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Fig. 5

Global axial compression versus axial stress in mid of the tensile armors

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Fig. 6

Local compressive strain versus global axial shortening per unit length

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Fig. 7

Global axial force versus displacement per unit length at the reference point for different external pressures

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Fig. 8

Global axial force versus twist per unit length at the reference point for different external pressures

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Fig. 9

Global axial force versus local radial expansion at the midlength of the pipe for different external pressures

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Fig. 10

Local compressive strain versus global axial shortening per unit length

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Fig. 11

Global axial force versus local twist at the midlength of the pipe for different external pressures

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Fig. 12

Global axial compression versus axial stress in mid of the external armors

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Fig. 13

Global axial compression versus axial stress in mid of the internal armors

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Fig. 14

Influence of external hydrostatic pressure on axial buckling force, axial strain, and torsional response

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Fig. 15

Influence of external hydrostatic pressure on the effective stiffness behavior

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Fig. 16

Normalized shear stress versus global axial force

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Fig. 17

Damaged area applied in the middle of pipe length

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Fig. 18

Global axial force versus axial shortening per unit length at the reference point for different damage lengths

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Fig. 19

Global axial force versus twist per unit length at the reference for different damage lengths

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