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Research Papers: Piper and Riser Technology

End Fitting Effect on Stress Evaluation of Tensile Armor Tendons in Unbonded Flexible Pipes Under Axial Tension

[+] Author and Article Information
Leilei Dong

School of Naval Architecture,
Dalian University of Technology,
No. 2 Linggong Road,
Dalian 116024, China
e-mail: leilei.dong@dlut.edu.cn

Qi Zhang

School of Naval Architecture,
Dalian University of Technology,
No. 2 Linggong Road,
Dalian 116024, China
e-mail: zhangqi@dlut.edu.cn

Yi Huang

School of Naval Architecture,
Dalian University of Technology,
No. 2 Linggong Road,
Dalian 116024, China
e-mail: huangyi@dlut.edu.cn

Gang Liu

School of Naval Architecture,
Dalian University of Technology,
No. 2 Linggong Road,
Dalian 116024, China
e-mail: liugang@dlut.edu.cn

Zhiyuan Li

School of Naval Architecture,
Dalian University of Technology,
No. 2 Linggong Road,
Dalian 116024, China
e-mail: lizhiyuan@dlut.edu.cn

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 July 17, 2017; final manuscript received February 27, 2018; published online April 24, 2018. Assoc. Editor: Myung Hyun Kim.

J. Offshore Mech. Arct. Eng 140(5), 051701 (Apr 24, 2018) (8 pages) Paper No: OMAE-17-1116; doi: 10.1115/1.4039524 History: Received July 17, 2017; Revised February 27, 2018

This paper deals with the effect of termination restraint due to end fitting on the stress evaluation of tensile armors in unbonded flexible pipes under axial tension. The problem is characterized by one single armoring tendon helically wound on a cylindrical supporting surface subjected to traction. The deviation from the initial helical angle is taken to describe the armor wire path as the pipe is stretched. The integral of this angle change gives the lateral displacement of the wire, which is determined by minimizing the energy functional that consists of the strain energy due to axial strain, local bending and torsion, and the energy dissipated by friction, leading to a variational problem with a variable endpoint. The governing differential equation of the wire lateral displacement, together with the supplementary condition, is derived using the variational method and solved analytically. The developed model is verified with a finite element (FE) simulation. Comparisons between the model predictions and the FE results in terms of the change in helical angle and transverse bending stress show good correlations. The verified model is then applied to study the effects of imposed tension and friction coefficient on the maximum bending stress. The results show that the response to tension is linear, and friction could significantly increase the stress at the end fitting compared with the frictionless case.

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References

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Figures

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Fig. 1

Example of a flexible-pipe end fitting [1]

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Fig. 2

Original and strained helix together with actual wire path

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Fig. 3

Principal axes orientation of wire cross section

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Fig. 4

Element of original and strained helix

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Fig. 5

Finite element mesh of wire and supporting layer

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Fig. 6

Radial constraint imposed using MPC184 rigid beam element

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Fig. 7

Change in helical angle

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Fig. 8

Transverse bending stress in wire (x3=−w/2)

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Fig. 9

Stress increase at end fitting against pipe strain (x3=−w/2 and μi=0.10)

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Fig. 10

Distributions of helical angle change under different pipe tensions

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Fig. 11

Stress increase at end fitting against friction coefficient (x3=−w/2 and εTEN=0.10%)

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Fig. 12

Distributions of helical angle change with different friction coefficients

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