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Research Papers: Piper and Riser Technology

Velocity-Dependent Soil Resistance in Finite Element Analysis of Pipeline Walking

[+] Author and Article Information
Daniel Carneiro

Mem. ASME
Wood Group,
432 Murray Street,
Perth, WA 6000, Australia
e-mail: daniel.carneiro@woodgroup.com

Andrew Rathbone

Wood Group,
432 Murray Street,
Perth, WA 6000, Australia
e-mail: andrew.rathbone@woodgroup.com

Kok Siong Soon

Wood Group,
432 Murray Street,
Perth, WA 6000, Australia
e-mail: koksiong.soon@woodgroup.com

Graham Viecelli

Wood Group,
432 Murray Street,
Perth, WA 6000, Australia
e-mail: musoe81@hotmail.com

1Corresponding author.

2Present address: Fugro Roames, 53 Brandl Street, Brisbane, QLD 4113, Australia.

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received February 27, 2015; final manuscript received September 5, 2016; published online October 20, 2016. Editor: Solomon Yim.

J. Offshore Mech. Arct. Eng 139(2), 021701 (Oct 20, 2016) (7 pages) Paper No: OMAE-15-1019; doi: 10.1115/1.4034695 History: Received February 27, 2015; Revised September 05, 2016

Soil resistance to pipeline axial displacement plays a key role in the ratcheting process known as “pipeline walking.” Still, it is not yet fully understood. New frameworks to address the different geotechnical aspects involved have recently been published. However, the current practice has been to lump all the time-dependent effects back into a single “equivalent” friction factor, based on a representative pipeline velocity. This paper argues that defining a single velocity as representative of the pipeline expansion (or contraction) is not trivial. While the pipeline ends might move a couple of meters in the few hours it takes to heat up, somewhere close to the middle it will move a few millimeters only. As a result, different levels of soil drainage, for example, are observed along the same pipeline, during the same loading. This paper presents the results of “true” velocity-dependent pipeline walking analyses and compares them to those obtained using constant equivalent friction factors. For the particular cases analyzed, the difference between the results obtained with the two approaches ranged from negligible up to about 30%. Examples show that the results of velocity-dependent pipeline walking analyses are significantly influenced by how the temperature changes over time along the pipeline length. The velocity-dependent model employed describes the axial soil resistance as a hyperbolic function of the pipe velocity. Additional aspects which are expected to influence the soil response (e.g., consolidation time between movements, progressive compression, and consolidation hardening) have been neglected.

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References

Figures

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Fig. 1

Velocity-dependent soil resistance curve

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Fig. 2

Velocity-dependent soil resistances curves for different consolidation rates

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Fig. 3

Effective axial force diagram at design temperature for different constant soil resistances and velocity-dependent soil resistances for different consolidation rates

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Fig. 4

Effective axial force diagram at design temperature and back to ambient temperature for constant and velocity-dependent soil resistance

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Fig. 5

Walking per cycle for different constant soil resistances and velocity-dependent soil resistances for different consolidation rates

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Fig. 6

Effective axial force diagram at design temperature for different constant soil resistances and fixed velocity-dependent soil resistance curve with different heat up times

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Fig. 7

Walking per cycle for different constant soil resistances and fixed velocity-dependent soil resistance curve with different heat up times

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Fig. 8

Effective axial force diagram at design temperature and back to ambient temperature for velocity-dependent soil resistance—cool down time equal to and ten times longer than heat up time

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Fig. 9

Idealized temperature change curves—linear and logarithmic

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Fig. 10

Effective axial force diagram at design temperature and back to ambient temperature for velocity-dependent soil resistance—linear and logarithmic heat up

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Fig. 11

Idealized constant gradient heat up transient

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Fig. 12

Effective axial force diagram at design temperature and back to ambient temperature for constant and velocity-dependent soil resistance—transient heat up

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Fig. 13

Effective axial force diagram during transient heat up with velocity-dependent resistance—percentages refer to total heat up time

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