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Observed changes to the stability of a subsea pipeline caused by seabed mobility

Observed changes to the stability of a subsea pipeline caused by seabed mobility
Observed changes to the stability of a subsea pipeline caused by seabed mobility
High resolution bathymetry combined with structural modelling is used to estimate changes in the on-bottom stability of an offshore pipeline due to scour and sedimentation over an 11 year period. Detailed observations of post-lay embedment changes have been combined with the pipeline structural characteristics and an elastic-plastic model of soil resistance to estimate the vertical and horizontal stability of the pipeline using a finite difference solution to the beam bending equation. Application of the design approach indicates that post-lay increases to the critical (break-out) velocity of 1 – 2 m/s occur along the full 19 km of surveyed pipeline due to scour and sedimentation, which act to reduce load and increase soil resistance. The rate at which this increase in stability occurs with time is found to vary along the pipeline, and is dependent on the mechanism of pipeline lowering (i.e. whether the pipe lowered due to sagging into widely spaced scour holes, or by sinking into the shoulders between many closely spaced scour holes). By incorporating sediment transport into the pipeline design, the present results suggest potential for significant improvements in pipeline on-bottom stability and associated reductions in minimum required specific gravity and/or secondary stabilisation.
0029-8018
159-176
Leckie, Simon H.F.
2f62ed53-abf1-461d-879f-9b9e0134cb0f
Draper, Scott
efe46b7d-3989-403b-8b19-0b17dd54194f
White, David J.
a986033d-d26d-4419-a3f3-20dc54efce93
Cheng, Liang
0ce99dcc-f682-4ec6-97aa-59fd87174385
Griffiths, Terry
24b3e648-f03d-4597-a69b-c2f90c2f70eb
Fogliani, Antonino
10bd8e2f-fda7-4f3b-94af-93047361164f
Leckie, Simon H.F.
2f62ed53-abf1-461d-879f-9b9e0134cb0f
Draper, Scott
efe46b7d-3989-403b-8b19-0b17dd54194f
White, David J.
a986033d-d26d-4419-a3f3-20dc54efce93
Cheng, Liang
0ce99dcc-f682-4ec6-97aa-59fd87174385
Griffiths, Terry
24b3e648-f03d-4597-a69b-c2f90c2f70eb
Fogliani, Antonino
10bd8e2f-fda7-4f3b-94af-93047361164f

Leckie, Simon H.F., Draper, Scott, White, David J., Cheng, Liang, Griffiths, Terry and Fogliani, Antonino (2018) Observed changes to the stability of a subsea pipeline caused by seabed mobility. Ocean Engineering, 169, 159-176. (doi:10.1016/j.oceaneng.2018.07.059).

Record type: Article

Abstract

High resolution bathymetry combined with structural modelling is used to estimate changes in the on-bottom stability of an offshore pipeline due to scour and sedimentation over an 11 year period. Detailed observations of post-lay embedment changes have been combined with the pipeline structural characteristics and an elastic-plastic model of soil resistance to estimate the vertical and horizontal stability of the pipeline using a finite difference solution to the beam bending equation. Application of the design approach indicates that post-lay increases to the critical (break-out) velocity of 1 – 2 m/s occur along the full 19 km of surveyed pipeline due to scour and sedimentation, which act to reduce load and increase soil resistance. The rate at which this increase in stability occurs with time is found to vary along the pipeline, and is dependent on the mechanism of pipeline lowering (i.e. whether the pipe lowered due to sagging into widely spaced scour holes, or by sinking into the shoulders between many closely spaced scour holes). By incorporating sediment transport into the pipeline design, the present results suggest potential for significant improvements in pipeline on-bottom stability and associated reductions in minimum required specific gravity and/or secondary stabilisation.

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AM Observed changes to the stability of a subsea pipeline caused by seabed mobility - Accepted Manuscript
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Accepted/In Press date: 31 July 2018
e-pub ahead of print date: 22 September 2018
Published date: 1 December 2018

Identifiers

Local EPrints ID: 423114
URI: http://eprints.soton.ac.uk/id/eprint/423114
ISSN: 0029-8018
PURE UUID: e436e563-aff3-428d-9039-e874d52a806f
ORCID for David J. White: ORCID iD orcid.org/0000-0002-2968-582X

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Date deposited: 14 Aug 2018 16:30
Last modified: 07 Oct 2020 04:48

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Contributors

Author: Simon H.F. Leckie
Author: Scott Draper
Author: David J. White ORCID iD
Author: Liang Cheng
Author: Terry Griffiths
Author: Antonino Fogliani

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