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Research Papers: Materials and Fabrication

Methodology for Assessment of Surface Defects in Undermatched Pipeline Girth Welds

[+] Author and Article Information
Aurélien Pépin

Offshore Engineering Division,
Technip,
Westhill, Aberdeen AB32 6TQ, UK
e-mail: apepin@technip.com

Tomasz Tkaczyk

Offshore Engineering Division,
Technip,
Westhill, Aberdeen AB32 6TQ, UK
e-mail: ttkaczyk@technip.com

Noel O'Dowd

Department of Mechanical,
Aeronautical and Biomedical Engineering,
Materials and Surface Science Institute,
University of Limerick,
Limerick, Ireland
e-mail: noel.odowd@ul.ie

Kamran Nikbin

Department of Mechanical Engineering,
Imperial College,
London SW7 2AZ, UK
e-mail: k.nikbin@imperial.ac.uk

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received April 1, 2014; final manuscript received November 4, 2014; published online February 27, 2015. Assoc. Editor: Xian-Kui Zhu.

J. Pressure Vessel Technol 137(5), 051402 (Oct 01, 2015) (11 pages) Paper No: PVT-14-1053; doi: 10.1115/1.4029190 History: Received April 01, 2014; Revised November 04, 2014; Online February 27, 2015

The demand for subsea transport of highly corrosive constituents has noticeably increased in recent years. This has driven the requirement for high strength pipelines with enhanced corrosion resistance such as chromium stainless steel or bimetal pipes. The latter are carbon steel pipes with a corrosion resistant alloy lining. Reeling is a cost effective installation method for small to medium size subsea pipelines, up to 457.2 mm (18 in.) in diameter. However, plastic straining associated with reeling has an effect on weld defect acceptance criteria. The maximum acceptable defect sizes are typically developed using engineering critical assessment (ECA), based on the reference stress method, which requires that the weld metal is equal to or stronger than the parent metal in terms of the stress–strain curve. However, evenmatch/overmatch cannot always be achieved in the case of subsea stainless or bimetal pipelines. In this work, a parametric finite-element (FE) study was performed to assess the effect of weld metal undermatch on the crack driving force, expressed in terms of the crack tip opening displacement (CTOD). Subsequently, the fracture assessment methodology for reeled pipes was proposed, where the ECA as per BS7910 is first carried out. These acceptable defect sizes are then reduced, using an analytical formula developed in this work, to account for weld undermatch.

Copyright © 2015 by ASME
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References

Figures

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Fig. 1

Illustration of reeling installation

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Fig. 3

Equivalent width for V-bevel weld with center line defect

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Fig. 4

Weld geometry: (a) actual and (b) equivalent

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Fig. 5

Stress–strain curves with yield plateau, E = 210 GPa, σy = 450 MPa, and n = 16.8

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Fig. 6

Stress–strain curves with continuous yielding, E = 210 GPa, σy = 450 MPa, and n = 5.7

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Fig. 8

Effect of yield plateau on crack driving force: Evenmatch case

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Fig. 9

Effect of undermatch on crack driving force: Yield plateau scenario

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Fig. 10

Effect of undermatch and defect depth: Materials with continuous yielding

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Fig. 11

Effect of undermatch and defect length: Materials with yield plateau

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Fig. 12

Parent metal stress–strain curves with yield plateau

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Fig. 13

Parent metal stress–strain curves with continuous yielding

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Fig. 14

Equivalent stress–strain curve

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Fig. 15

Normalized maximum acceptable defect depths: 168.3 mm × 7.11 mm pipe material with yield plateau

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Fig. 16

Normalized maximum acceptable defect depths: 168.3 mm × 7.11 mm pipe material with continuous yielding

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Fig. 17

Normalized maximum acceptable defect depths: 323.9 mm × 15.9 mm pipe material with yield plateau

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Fig. 18

Normalized maximum acceptable defect depths: 323.9 mm × 15.9 mm pipe material with continuous yielding

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Fig. 19

Normalized maximum acceptable defect depths: 323.9 mm × 25.4 mm pipe material with continuous yielding

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Fig. 20

Normalized maximum acceptable defect depths: 406.4 mm × 17.6 mm pipes

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Fig. 21

Normalized maximum acceptable defect depths: 406.4 mm × 25.4 mm pipes

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