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Research Papers: Materials Technology

Prediction of Burst in Flexible Pipes

[+] Author and Article Information
Alfredo Gay Neto

e-mail: alfredo.neto@gmail.com

Eduardo Ribeiro Malta

Department of Mechanical Engineering,
University of São Paulo,
São Paulo, SP, Brazil

Carlos Alberto Ferreira Godinho

Prysmian Cables and Systems,
Santo André, SP, Brazil

1Corresponding author.

Contributed by the Ocean Offshore and Arctic Engineering Division of ASME for publication in the JOURNALOF OFFSHORE MECHANICSAND ARCTIC ENGINEERING. Manuscript received December 2, 2010; final manuscript received May 4, 2012; published online February 22, 2013. Assoc. Editor: Pingsha Dong.

J. Offshore Mech. Arct. Eng 135(1), 011401 (Feb 22, 2013) (9 pages) Paper No: OMAE-10-1114; doi: 10.1115/1.4007046 History: Received December 02, 2010; Revised May 04, 2012

Usually when a large internal fluid pressure acts on the inner walls of flexible pipes, the carcass layer is not loaded, as the first internal pressure resistance is given by the internal polymeric layer that transmits almost all the loading to the metallic pressure armor layer. The last one must be designed to ensure that the flexible pipe will not fail when loaded by a defined value of internal pressure. This paper presents three different numerical models and an analytical nonlinear model for determining the maximum internal pressure loading withstood by a flexible pipe without burst. The first of the numerical models is a ring approximation for the helically rolled pressure layer, considering its actual cross section profile. The second one is a full model for the same structure, considering the pressure layer laying angle and the cross section as built. The last numerical model is a two-dimensional (2D) simplified version, considering the pressure layer as an equivalent ring. The first two numerical models consider contact nonlinearities and a nonlinear elastic-plastic material model for the pressure layer. The analytical model considers the pressure armor layer as an equivalent ring, taking into account geometrical and material nonlinear behaviors. Assumptions and results for each model are compared and discussed. The failure event and the corresponding stress state are commented.

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References

Zhu, X. K., and Leis, B. N., 2007, “Theoretical and Numerical Predictions of Burst Pressure of Pipelines,” ASME J. Pressure Vessel Technol., 129, pp.644–652. [CrossRef]
American Petroleum Institute, 1999, API 17J - Specification for Unbonded Flexible Pipe, 2nd ed, Washington, D.C.
Fernando, U. S., Sheldrake, T., Tan, Z., and Clements, R., 2004, “The Stress Analysis and Residual Stress Evaluation of Pressure Armor Layers in Flexible Pipes Using 3D Finite Element Models,” Proceedings of ASME 23rd International Conference on Offshore Mechanics and Arctic Engineering. [CrossRef]
American Petroleum Institute, 2002, API 17B Recommended Practice for Flexible Pipe, 3rd ed, Washington, D.C.
ANSYS INC., 2009, ANSYS Help, Version 12.0.
Gay Neto, A., and Martins, C. A., 2012, “A Comparative Wet Collapse Buckling Study for the Carcass Layer of Flexible Pipes,” ASME J. Offshore Mech. Arct. Eng., 134 (3), p. 031701. [CrossRef]
Martins, C. A., Pesce, C. P., and Aranha, J. A. P., 2003, “Structural Behavior of Flexible Pipe Carcass During Launching,” Proceedings of the ASME 22nd International Conference on Offshore Mechanics and Arctic Engineering. [CrossRef]
Timoshenko, S. P., and Goodier, J. N., 1951, Theory of Elasticity, McGraw-Hill, New York.

Figures

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Fig. 1

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

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Fig. 2

Typical pressure layer geometry

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Fig. 3

Pressure armor cross section profile

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Fig. 4

Stress versus strain curve of the internal plastic layer material

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Fig. 5

Mesh in the full 3D model (250,340 nodes)

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Fig. 6

Cutting regions in the full 3D model

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Fig. 7

Internal pressure loading in the full 3D model

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Fig. 8

Boundary conditions applied to the pressure armor layer

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Fig. 9

Boundary conditions applied to the internal polymeric layer. (1) All DOFs fixed in the outer diameter line and y direction fixed in the areas; (2) axial cutting regions area constrained in z direction; and (3) the nodes located in the y = 0 plane are restrained to move only in this plane.

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Fig. 10

Contact regions considered in the full 3D model

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Fig. 11

Mesh in the 3D ring model (86,006 nodes)

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Fig. 12

Internal pressure loading in the 3D ring model

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Fig. 13

Axial and symmetry boundary conditions applied to each ring quarter

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Fig. 14

DOF couplings considered in each cross section of pressure layer in the 3D ring model

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Fig. 15

Free body diagram for a thin-walled pressure vessel

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Fig. 16

Bilinear material model used in the nonlinear analytical model

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Fig. 17

Mesh used in the 2D equivalent ring model (3530 nodes)

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Fig. 18

Maximum von Mises stress in the pressure armor; flexible pipe subjected to internal pressure loading

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Fig. 19

Average radial displacement in the pressure armor; flexible pipe subjected to internal pressure loading

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Fig. 20

Maximum circumferential stress in the pressure armor; flexible pipe subjected to internal pressure loading

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