Session: 04-04-06 Pipe-Soil Interaction

Paper Number: 127231

127231 - Local Scour Around the Touchdown Zone of a Cryogenic Pipeline-Riser System for Lng Offloading 

This paper presents the results from a series of physical model tests that investigated local scour around the touchdown zone of a cryogenic pipeline-riser system used for LNG offloading. The local scour around a J-shape pipeline-riser system may be influenced by several parameters, including the J-curve radius to pipeline-riser diameter ratio (R/D), normalised pipe embedment (e/D), flow intensity (defined by the ratio of the Shields parameter to the critical Shields parameter, θ/θ_cr), and flow direction (α). The model tests were conducted in an O-tube facility using a model pipe with a diameter of D = 0.07 m and R/D = 5. Eight different flow directions (α = 0° to 180°) and six normalised pipe embedment depths (e/D = 0.5, 0.75, 1, 1.5, 2 and 3) were examined.

The results indicate that flow direction α affects the equilibrium scour depth significantly for e/D = 3.0. When α ranges between 0° and 122.5°, the curvature  of the model pipe appears to intensify the local scouring process. For larger α values, the scour depth is less than that observed around a vertical pile. For e/D = 3.0, local scour is seen to be a constrained process, and the horizontal pipeline remains buried. The equilibrium scour depth diminishes as e/D reduces from 3.0 to 0.75; and, no scour propagation is observed along the pipeline on the seabed within this range. For e/D = 0.5, local scour continuously expands in the spanwise direction of the pipeline, leading to the formation of free spans. Critical e/D value for the development of free spans lies between 0.5 and 0.75.

Presenting Author: Hongwei An The University of Western Australia

Presenting Author Biography: Hongwei An is a senior lecturer at the University of Western Australia. He got his PhD from UWA in 2010 and since then he has been working there as an academic staff. His research area covers flow-structure interaction and local scour with applications in offshore engineering.

Authors:

Hongwei An The University of Western Australia
Muhammad Hossain The University of Western Australia
Youngho Kim The University of Western Australia
Young Tae Kim DoAZ
Kyung Tae Bae Daewoo E&C
Ian Golabek The University of Western Australia
Jake Tabram The University of Western Australia