Piper and Riser Technology

A Comparative Wet Collapse Buckling Study for the Carcass Layer of Flexible Pipes

[+] Author and Article Information
Alfredo Gay Neto, Clóvis de Arruda Martins

 Department of Mechanical Engineering, University of São Paulo, São Paulo, SP 05508-970, 01000 Brazil

J. Offshore Mech. Arct. Eng 134(3), 031701 (Feb 01, 2012) (9 pages) doi:10.1115/1.4005185 History: Received September 27, 2010; Revised August 04, 2011; Published February 01, 2012; Online February 01, 2012

When there is a failure on the external sheath of a flexible pipe, a high value of hydrostatic pressure is transferred to its internal plastic layer and consequently to its interlocked carcass, leading to the possibility of collapse. The design of a flexible pipe must predict the maximum value of external pressure the carcass layer can be subjected to without collapse. This value depends on the initial ovalization due to manufacturing tolerances. To study that problem, two numerical finite element models were developed to simulate the behavior of the carcass subjected to external pressure, including the plastic behavior of the materials. The first one is a full 3D model and the second one is a 3D ring model, both composed by solid elements. An interesting conclusion is that both the models provide the same results. An analytical model using an equivalent thickness approach for the carcass layer was also constructed. A good correlation between analytical and numerical models was achieved for pre-collapse behavior but the collapse pressure value and post-collapse behavior were not well predicted by the analytical model.

Copyright © 2012 by American Society of Mechanical Engineers
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Figure 1

Typical flexible pipe internal layers (virtual prototype developed by Numerical Offshore Tank – USP)

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Figure 2

Typical interlocked carcass geometry

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Figure 3

Self contact regions of carcass layer in Full 3D and in 3D Ring models

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Figure 4

Stress versus strain curve for the carcass layer steel

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Figure 5

Stress versus strain curve of the internal plastic layer material

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Figure 6

Parameterized carcass profile

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Figure 7

Three dimensional mesh of full 3D model, (a) Whole view and (b) Detailed view

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Figure 8

Pressure loading applied to the carcass in the 3D full model

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Figure 9

Faces involved in coupling of DOFs considered in the Full 3D Model

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Figure 10

Boundary conditions applied to the internal polymeric layer in the Full 3D Model (a) Nodes fixed only in y direction (b) Nodes fixed in all directions

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Figure 11

Three dimensional mesh of 3D ring model, (a) Whole view and (b) Detailed view

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Figure 12

Boundary conditions considered in 3D Ring Model (a) symmetry condition (b) symmetry condition and constraint in all directions of a line of nodes in polymeric layer

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Figure 13

Coupling details considered in 3D Ring Model

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Figure 14

Maximum ovalization normalized by inner radius versus loading parameter

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Figure 15

Lines in which the reference nodes are contained (for radial displacement calculation in both the numerical models). Measurement of superposed length and pitch of carcass cross section profiles.

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Figure 16

Results for w1  = 0.5% of inner radius of carcass (Ri )

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Figure 17

Results for w1  = 1.0% of inner radius of carcass (Ri )

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Figure 18

Results for w1  = 2.0% of inner radius of carcass (Ri )




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