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Research Papers: Materials and Fabrication

Fracture Response of Girth-Welded Pipeline With Canoe Shape Embedded Crack Subjected to Large Plastic Deformation

[+] Author and Article Information
Lie Seng Tjhen

School of Civil and Environmental Engineering,
Nanyang Technological University,
50 Nanyang Avenue,
Singapore 639798, Singapore
e-mail: cstlie@ntu.edu.sg

Zhang Yao

School of Civil and Environmental Engineering,
Nanyang Technological University,
50 Nanyang Avenue,
Singapore 639798, Singapore
e-mail: zhangyao@ntu.edu.sg

Zhao Hai Sheng

School of Civil and Environmental Engineering,
Nanyang Technological University,
50 Nanyang Avenue,
Singapore 639798, Singapore
e-mail: hzhao006@e.ntu.edu.sg

1Corresponding author.

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received February 22, 2016; final manuscript received November 16, 2016; published online January 11, 2017. Assoc. Editor: Xian-Kui Zhu.

J. Pressure Vessel Technol 139(2), 021406 (Jan 11, 2017) (9 pages) Paper No: PVT-16-1026; doi: 10.1115/1.4035313 History: Received February 22, 2016; Revised November 16, 2016

Long-distance offshore pipelines always suffer large plastic deformation during installation and operation. Accompanied by high internal pressure, potential flaws are found to initiate from the girth welds, and this brings a significant challenge to the structural integrity of the pipelines. The currently used procedures for fracture assessment of pipelines are usually stress based, which are unsuitable for application to cracked pipeline subjected to large plastic deformation. Therefore, the aim of this paper is to investigate the fracture assessment of pipeline subjected to large plastic deformation and identify and understand the critical parameters influencing the fracture responses under actual loading conditions. The evolution of crack tip opening displacement (CTOD) of a pipeline segment with an embedded canoe shape crack located in the middle of the girth weld is investigated under pure bending and biaxial loading through 3D elastic–plastic finite-element simulations. The effects of crack width, crack length, pipeline thickness, material hardening, and internal pressure on fracture response are discussed. Finally, a strain-based failure assessment diagram (FAD) is developed, and comparison between fracture assessment by BS7910:2013 and finite-element simulations concludes that the former produces conservative predictions for deep crack.

Copyright © 2017 by ASME
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References

Figures

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Fig. 1

Configurations of canoe shape crack embedded in a pipeline

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Fig. 2

Design of the grid mesh along the crack front

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Fig. 3

Different loading situations: (a) pure bending and (b) bending with internal pressure

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Fig. 4

Definition of CTOD when crack is in the middle of the weld

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Fig. 5

Comparisons of CTOD values for different crack length to perimeter ratios: (a) l = 0.05 mm, (b) l = 0.1 mm, (c) l = 0.2 mm, and (d) l = 0.3 mm

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Fig. 6

CTOD–global strain curves for different crack widths under pure bending load: (a) d/t = 0.1 mm, (b) d/t = 0.2 mm, and (c) d/t = 0.3 mm

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Fig. 7

Comparisons of CTOD values for different crack depth (a) ce = 8 mm, (b) ce = 10 mm, and (c) ce = 12 mm

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Fig. 8

Effect of diameter to thickness ratio on the evolution of CTOD

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Fig. 9

Effect of welding mismatch on the evolution of CTOD

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Fig. 10

Effect of internal pressure on the evolution of CTOD: (a) d/t = 0.1 mm, l = 0.1 mm and (b) d/t = 0.2, l = 0.1

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Fig. 11

Geometrical configurations of crack at the interface between weld and back steel

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Fig. 12

Definition of CTOD when crack is at interface between weld and back steel

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Fig. 13

CTOD for crack in the weld and at interface under pure bending: (a) even-match, (b) over-match, and (c) under-match

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Fig. 14

The actual stress distribution along the wall of unflawed girth weld (εg = 3%)

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Fig. 15

Comparison of the CTOD toughness requirement based on FEM and BS 7910:2013 [3] (a) d/t = 0.2, l = 0.1 and (b)d/t = 0.3, l = 0.1

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Fig. 16

FAD for cracked pipeline under pure bending (εg = 3%)

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