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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

## Abstract

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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## Figures

Fig. 1

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

Fig. 2

Typical pressure layer geometry

Fig. 3

Pressure armor cross section profile

Fig. 4

Stress versus strain curve of the internal plastic layer material

Fig. 5

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

Fig. 6

Cutting regions in the full 3D model

Fig. 7

Fig. 8

Boundary conditions applied to the pressure armor layer

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.

Fig. 10

Contact regions considered in the full 3D model

Fig. 11

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

Fig. 12

Fig. 13

Axial and symmetry boundary conditions applied to each ring quarter

Fig. 14

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

Fig. 15

Free body diagram for a thin-walled pressure vessel

Fig. 16

Bilinear material model used in the nonlinear analytical model

Fig. 17

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

Fig. 18

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

Fig. 19

Fig. 20

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

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