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Research Papers: Pipeline Systems

The Effect of Prestrain on Ductile Fracture Toughness of Reeled Pipeline Steels

[+] Author and Article Information
Tomasz Tkaczyk1

Offshore Engineering Division, Technip, Westhill, Aberdeenshire AB32 6TQ, UKttkaczyk@technip.com

Noel P. O’Dowd

Department of Mechanical and Aeronautical Engineering, Materials and Surface Science Institute, University of Limerick, Limerick, Ireland

Kamran Nikbin

Department of Mechanical Engineering, Imperial College London, London SW7 2AZ, UK

1

Corresponding author.

J. Pressure Vessel Technol 133(3), 031701 (Apr 04, 2011) (8 pages) doi:10.1115/1.4002280 History: Received September 17, 2009; Revised July 14, 2010; Published April 04, 2011; Online April 04, 2011

The reel-lay method is a cost efficient alternative to the S-lay and J-lay methods for small to medium size steel offshore pipelines. The quality of the pipeline construction is enhanced by on-shore welding and inspection under controlled conditions. However, reeled pipelines are subjected to at least two symmetrical plastic strain cycles during installation. The plastic straining associated with reeled installation modifies the axial tensile response of the pipe material. Also, it has been suggested that plastic straining may reduce fracture toughness. In this work, small scale tests representative of conditions experienced under reeling of steel pipelines have been carried out. The fracture resistance curves obtained for the material in the as-received and strained conditions have been compared. No significant effect of the reeling strain cycle on the fracture toughness during subsequent straining was observed.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 2

Models to represent the effect of prestrain on fracture toughness: (a) loss of memory model (2), (b) memory model (10), and (c) history dependent model (9). Note: Δa is the crack growth in the current loading cycle, R is the crack growth resistance, and Δa1 is the crack growth after the first tensile load.

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Figure 5

Cyclic response of: (a) parent material and (b) weld material

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Figure 7

Servo hydraulic testing machine with hydraulic grips

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Figure 10

Silicon impression technique: (a) silicon replica and (b) sectioned silicon replica

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Figure 11

Fracture resistance of as-received and strained weld materials: (a) CTOD resistance curve a/W=0.25, (b) J resistance curve a/W=0.25, (c) CTOD resistance curve a/W=0.5, and (d) J resistance curve a/W=0.5. Note: Δa is the crack growth in the current loading cycle.

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Figure 12

Regions investigated using SEM: (a) as-received material and (b) strained material

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Figure 13

Results of SEM examination

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Figure 9

Fracture resistance of as-received weld material: (a) CTOD-R and (b) J-R

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Figure 8

Position of knife edges

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Figure 6

Geometry of SEN(T) specimens

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Figure 4

Tensile response of X70 parent and weld materials

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Figure 3

Profile of weld bevel and weld passes

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Figure 1

Schematic of pipe installation by reeling

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