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The influence of sea state on as-laid pipeline embedment: A case study

The influence of sea state on as-laid pipeline embedment: A case study
The influence of sea state on as-laid pipeline embedment: A case study

The as-laid embedment of an offshore pipeline is an important parameter for design as it affects lateral and axial stability, exposure to environmental loads, and thermal insulation. For soft clay seabeds, the as-laid embedment can be significantly higher than predicted using methods based on the static penetration resistance due to dynamic lay effects. There are very few published field surveys showing the as-laid embedment of a pipeline following installation. Back-analysis of field survey data has the potential to improve existing design methods, as well as gain insights into the effects of the installation conditions, including the vessel response, the lay angle and tension, weather and sea state, and downtime events. This study describes the as-laid field survey carried out for a 12-inch flowline installed on a soft clay seabed in the North Sea. The dynamic lay effects are examined by studying the influence of sea state, manifested through the vessel response which leads to pipeline motions at the seabed. The findings show that a clear correlation exists between sea state and pipeline embedment. The ratio between the mean observed embedment and the embedment that would be predicted using a conventional static penetration analysis (termed the dynamic embedment factor, Fdyn) ranged from 2.5 up to 4 for normal pipelay conditions, increasing with wave height. Downtime events, during which pipelay is temporarily suspended, significantly increase the embedment. In this study they led to maximum embedment values greater than one diameter, corresponding to Fdyn of up to 10, due to the larger numbers of cyclic pipeline motions at the seabed.

Dynamic embedment, Offshore pipelay, Pipe-soil interaction, Sea state
0141-1187
321-331
Westgate, Z.J.
983a044b-1644-4a5c-895d-6b7c83501ab9
Randolph, M.F.
75caa33a-e630-4ae8-84cd-758797bf9633
White, D.J.
a986033d-d26d-4419-a3f3-20dc54efce93
Li, S.
969bf9fe-bb11-44e3-8135-e71fb95d6f6f
Westgate, Z.J.
983a044b-1644-4a5c-895d-6b7c83501ab9
Randolph, M.F.
75caa33a-e630-4ae8-84cd-758797bf9633
White, D.J.
a986033d-d26d-4419-a3f3-20dc54efce93
Li, S.
969bf9fe-bb11-44e3-8135-e71fb95d6f6f

Westgate, Z.J., Randolph, M.F., White, D.J. and Li, S. (2010) The influence of sea state on as-laid pipeline embedment: A case study. Applied Ocean Research, 32 (3), 321-331. (doi:10.1016/j.apor.2009.12.004).

Record type: Article

Abstract

The as-laid embedment of an offshore pipeline is an important parameter for design as it affects lateral and axial stability, exposure to environmental loads, and thermal insulation. For soft clay seabeds, the as-laid embedment can be significantly higher than predicted using methods based on the static penetration resistance due to dynamic lay effects. There are very few published field surveys showing the as-laid embedment of a pipeline following installation. Back-analysis of field survey data has the potential to improve existing design methods, as well as gain insights into the effects of the installation conditions, including the vessel response, the lay angle and tension, weather and sea state, and downtime events. This study describes the as-laid field survey carried out for a 12-inch flowline installed on a soft clay seabed in the North Sea. The dynamic lay effects are examined by studying the influence of sea state, manifested through the vessel response which leads to pipeline motions at the seabed. The findings show that a clear correlation exists between sea state and pipeline embedment. The ratio between the mean observed embedment and the embedment that would be predicted using a conventional static penetration analysis (termed the dynamic embedment factor, Fdyn) ranged from 2.5 up to 4 for normal pipelay conditions, increasing with wave height. Downtime events, during which pipelay is temporarily suspended, significantly increase the embedment. In this study they led to maximum embedment values greater than one diameter, corresponding to Fdyn of up to 10, due to the larger numbers of cyclic pipeline motions at the seabed.

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More information

Accepted/In Press date: 9 December 2009
e-pub ahead of print date: 4 February 2010
Published date: July 2010
Keywords: Dynamic embedment, Offshore pipelay, Pipe-soil interaction, Sea state

Identifiers

Local EPrints ID: 420155
URI: http://eprints.soton.ac.uk/id/eprint/420155
ISSN: 0141-1187
PURE UUID: 2cfb847b-3386-4ee0-b778-62403640b8e9
ORCID for D.J. White: ORCID iD orcid.org/0000-0002-2968-582X

Catalogue record

Date deposited: 27 Apr 2018 16:30
Last modified: 03 Dec 2019 01:26

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Contributors

Author: Z.J. Westgate
Author: M.F. Randolph
Author: D.J. White ORCID iD
Author: S. Li

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