Effect of through-life changes in soil strength and axial pipe-seabed resistance for HPHT pipeline design

Abstract

Axial pipe-seabed resistance is a key input parameter in the design of HTHP subsea pipelines. This paper describes a calculation procedure that captures the through-life changes in the strength of soil around a pipeline to quantify the available peak and residual axial soil resistances throughout the operational life. This paper illustrates the effects of pipeline pre-commissioning loading history, cyclic operational displacements and soil characteristics on the axial resistance over typical operational life, through which the axial friction might vary by a factor of two or more. The described calculation procedure is verified by published model test data. Practical application of these tools can improve pipeline design by considering specifically the varying soil states around a pipeline at different stages of its design life. Only the likely ranges of friction factors at each design ‘instant’ need to be considered, rather than the full range of friction factors potentially applying throughout the entire design life. This will facilitate pipeline design by reducing lateral buckling and axial walking mitigation measures and providing appropriate pipeline-related inputs to subsea structure design.

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ORCID for D.J. White: orcid.org/0000-0002-2968-582X

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