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Research Papers: Piper and Riser Technology

Simplified Finite Element Models to Study the Wet Collapse of Straight and Curved Flexible Pipes

[+] Author and Article Information
Alfredo Gay Neto

Department of Structural and
Geotechnical Engineering,
University of São Paulo,
São Paulo, SP 05505-010, Brazil

Clóvis de Arruda Martins

Department of Mechanical Engineering,
University of São Paulo,
São Paulo, SP 05505-010, Brazil

Eduardo Ribeiro Malta

Department of Naval Architecture and
Ocean Engineering,
University of São Paulo,
São Paulo, SP 05505-010, Brazil

Rafael Loureiro Tanaka, Carlos Alberto Ferreira Godinho

Prysmian Cables and Systems,
Santo André, SP 09110-900, Brazil

1Corresponding author.

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received December 8, 2015; final manuscript received June 9, 2017; published online September 11, 2017. Assoc. Editor: Ioannis K. Chatjigeorgiou.

J. Offshore Mech. Arct. Eng 139(6), 061701 (Sep 11, 2017) (10 pages) Paper No: OMAE-15-1125; doi: 10.1115/1.4037291 History: Received December 08, 2015; Revised June 09, 2017

When the external sheath of flexible pipes experiences damage, seawater floods the annulus. Then, the external pressure is applied directly on the internal polymeric layer, and the load is transferred to the interlocked carcass, the innermost layer. In this situation, the so-called wet collapse failure of the interlocked carcass can occur. Simplified methodologies to address such a scenario, using restricted three-dimensional (3D) finite element models, are presented in this work. They are compared with full 3D models, studying both straight and curved flexible pipes scenarios. The curvature of the flexible pipe is shown to be important for wet collapse pressure predictions.

Copyright © 2017 by ASME
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References

Figures

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Fig. 1

Boundary conditions of the model: pilot nodes (Adapted from Ref. [1])

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Fig. 2

Geometry description example of the full model (Adapted from Ref. [1])

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Fig. 3

Internal polymeric layer material curve (Adapted from Ref. [10])

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Fig. 4

External polymeric layer material curve (Adapted from Ref. [10])

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Fig. 5

Some contact regions of interlocked carcass and internal polymeric layer

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Fig. 6

Geometry of the model A. From inside to outside of the pipe: carcass layer, internal polymeric layer, and pressure armor layer (as an equivalent ring): (a) xz view and (b) xy view

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Fig. 7

Center of curvature of the approximated collapse models (exaggerated curvature—small r)

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Fig. 8

A mesh example of the wet collapse model with 38,270 nodes: (a) whole view and (b) detailed view

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Fig. 9

Contact regions considered in model A

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Fig. 10

External pressure loading

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Fig. 11

Displacement couplings assumed

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Fig. 12

Different integration areas in which the external pressure acts in a curved flexible pipe, presenting a non-null resultant R (Adapted from Ref. [1])

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Fig. 13

Boundary conditions “CC1”

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Fig. 14

Boundary conditions “CC2”

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Fig. 15

Boundary conditions “CC3”

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Fig. 16

Model B mesh example (1788 nodes and 720 elements; Adapted figure from Ref. [1])

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Fig. 17

API ovalization versus external pressure for the 2.5-in flexible pipe wet collapse

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Fig. 18

API ovalization versus external pressure for the 4.0-in flexible pipe wet collapse

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Fig. 19

API ovalization versus external pressure for the 2.5-in flexible pipe wet collapse. Comparison between models.

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Fig. 20

API ovalization versus external pressure for the 4.0-in flexible pipe wet collapse. Comparison between models.

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Fig. 21

(a) “Heart mode” shape obtained by model A with 1.0 MBR and (b) “eight mode” shape obtained by model A with 100.0 MBR. Both for the 4.0-in flexible pipe showed in 10× scaled plot.

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Fig. 22

“Transition mode” obtained in the wet collapse full model of a straight flexible pipe—2.5 in (displacements are 10 times scaled)—obtained using Ref. [10] model

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