Research Papers: Materials Technology

Flexible Pipes: Influence of the Pressure Armor in the Wet Collapse Resistance

[+] Author and Article Information
Alfredo Gay Neto

Department of Structural
and Geotechnical Engineering,
University of São Paulo,
São Paulo, SP, Brazil
e-mail: alfredo.gay@usp.br

Clóvis de Arruda Martins

Department of Mechanical Engineering,
University of São Paulo,
São Paulo, SP, Brazil
e-mail: cmartins@usp.br

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 September 29, 2011; final manuscript received April 17, 2014; published online May 19, 2014. Assoc. Editor: John Halkyard.

J. Offshore Mech. Arct. Eng 136(3), 031401 (May 19, 2014) (8 pages) Paper No: OMAE-11-1085; doi: 10.1115/1.4027476 History: Received September 29, 2011; Revised April 17, 2014

When submitted to high external pressure, flexible pipes may collapse. If the external sheath is damaged, all the external pressure is directly applied on the internal polymeric layer that transmits the loading to the carcass layer, which can fail due to this effect, leading to wet collapse. This failure mode must be taken into account in a flexible pipe design. A model can be set up neglecting the influence of the pressure armor, but this assumption may underestimate the wet collapse pressure value. This work aims to include the pressure armor effect in the numerical prediction of wet collapse. The main contribution of the pressure armor to the flexible pipe resistance to collapse is to be a constraint to the radial displacement of the carcass and the internal polymeric layers. Two models were developed to find the wet collapse pressure in flexible pipes. A first study was done using a ring approximation three-dimensional (3D) finite element method (FEM) model. Comparisons are made with more simplified models using a 3D FEM equivalent ring approximation. The aim is to clarify the mechanical behavior of the pressure armor in the wet collapse scenario. Parametric studies of initial ovalization of carcass and initial gaps and interference between polymeric layer and pressure armor are made and discussed.

Copyright © 2014 by ASME
Topics: Pressure , Pipes , Collapse , Armor
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Fig. 1

Typical flexible pipe (virtual prototype developed by numerical offshore tank—USP)

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Fig. 3

Eight-shape (a) and heart shape (b) collapse modes represented schematically by three layers of a cross section of flexible pipe. From innermost to outermost layers: carcass, polymeric layer, and pressure armor.

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Fig. 4

Pressure armor cross section profile

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Fig. 5

Model A mesh (143,432 nodes)

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Fig. 6

Symmetry boundary conditions and pressure loading

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Fig. 8

Couplings between DOFs in the axial cutting regions and additional couplings for implying a constant pitch

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Fig. 9

Contact regions in model A

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Fig. 10

Model B mesh (91,035 nodes)

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Fig. 11

Lines in which the reference nodes are contained (for maximum radial displacement evaluation). Figure from Ref. [3].

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Fig. 12

Results for the cases A1 and B1 (0.5% of initial ovalization)

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Fig. 13

Results for the cases A2 and B2 (1.0% of initial ovalization)

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Fig. 14

Results for the cases A3 and B3 (2.0% of initial ovalization)

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Fig. 15

Von Mises stress distribution just after the limit point occurrence for case A1 (values in MPa)

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Fig. 16

Case B1 (some values of equivalent thickness of pressure armor and the corresponding obtained wet collapse pressures)

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Fig. 17

Results for the cases A1, B1, A5, B5, A4, and B4 (0.5% of initial ovalization)

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Fig. 18

Results for the cases A1 and A6 to A10 (0.5% of initial ovalization)

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Fig. 19

Results for the cases B1 and B6 to B10 (0.5% of initial ovalization)




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