Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

VIV Fatigue Assessment of a PIP (Pipe-in-Pipe) Pipeline in Sand Wave Area in South China Sea
Lianfeng Yang, Chao Luo

Offshore Oil Engineering Co., Ltd.
Tianjin, China

Zhipeng Zang

State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin UniversityTianjin, ChinaCong Wang
CNPC Engineering Technology Research Co., Ltd.
Tianjin, ChinaABSTRACTof 24 km. The LF14-4 DPP to LF13-2 DPP pipeline crosses a large
sand wave field which leads to free spanning. The bathymetry along thepipeline route is presented in Figure 1. The pipeline route is taken fromthe Client supplied bathymetry data.

Many large sand waves are formed on the sea bottom along the pipeline
routes in Lufeng oilfields. The free spans and the resultant VIV fatigue
are analyzed for the pipeline on sea bottom with sand waves. The VIV
onset screening assessment identified a significant number of freespans which are larger than the VIV onset span lengths for temporary
and operating conditions, and are therefore susceptible to VIV fatigue.
The analyses show that the pipe is not acceptable for VIV fatigue for a
non-trenched seabed, and will require trenching to meet VIV fatigue
requirements during operation.

KEY WORDS: VIV; fatigue assessment; submarine pipeline;
sand waves.
INTRODUCTION
Submarine sand waves are large rhythmic bedforms developed on
sandy bottoms on continental shelves, with characteristic wavelengths
ranging from tens of meters to hundreds of meters and wave heightsreaching a few meters or more. Any continental shelf with a directional
flow, such as estuaries, coasts, and tidal channels, is suitable for thedevelopment of sand waves (Németh et al., 2002; Sterlini et al., 2009;
Zang et al., 2010). Moving sand waves can cause instability of offshore
platforms, silting of navigation channels and exposure and breakdownof submarine pipelines or cables (Morelissen et al., 2003; Tonnon et al.,2007).

Figure 1. Elevation view of Pipeline Route LF14-4 DPP to LF13-2
Free spans of offshore pipelines has been the topic of a number of
researches over the past three decades due to its engineeringsignificance. Free spans can be by the local scour at a number oflocations along the pipeline as the results of either the piping
mechanism (Zang et al., 2009) or uneven seabed after installation of thepipeline (Cheng et al., 2009). Once a local scour is initiated somewherealone a pipeline, it spreads along the pipeline to form free spans. Free
spans were often identified as causes for pipeline failures in pipeline
industry because free-spanned pipelines are more susceptible tostructural damages related to over-stressing, fatigue and humanactivities (Palmer, 1996). Cheng et al. (2009, 2014) conducted
experimental investigations on the propagation of scour along pipelines
subject to steady currents and combined current and waves under livebed conditions. Effects of various parameters such as pipeline
embedment depth, incoming flow Shields parameter and flow incident
angle to the pipeline on scour propagation velocities along the pipeline
were investigated.

Lufeng oilfields are located in the Pearl River Mouth Basin, SouthChina Sea. The LF14-4 oilfield is located at about 216 km southeast ofHong Kong in a water depth of about 145 m. LF13-2 DPP is theexisting facility of Lufeng regional development project, which is acentral processing platform with wellhead and deals with the fluids
produced on this platform. The new LF14-4 DPP (Drilling ProductionPlatform) is used to develop Lufeng 14-4 oilfield. The processed waterbearing crude oil is transported by booster pump to the inlet of thesubsea pipeline from LF14-4 DPP to LF13-2 DPP, which has a length2594