Overtrawling of large diameter pipeline trials JIP

Fishermen have been concerned in recent years about the laying of large diameter pipelines in the North Sea.

The perception is that these pipelines could provide an enhanced hazard to safety because they provide a larger obstacle and increase the likelihood of their fishing gear becoming snagged.

To address these concerns the DTI requested that instrumented overtrawling fishing trials with load cells and accelerometers be carried out over the Exxon-Mobil Skene pipeline to confirm that the pipeline did not present an increased hazard compared to existing pipelines, which are up to 40" diameter.

Jee set up a Joint Industry Programme (JIP) to:

• conduct the overtrawling trials, and
• perform model-scale tests that could be used to predict overtrawling behaviour.
• draw conclusions about the safety of overtrawling large diameter pipelines and the ability to simulate full scale results from model-scale tests

The final deliverable was a report that represents the culmination of a series of tasks that have been performed in consultation, and agreement, with the fishing industry and with the participation of the Fisheries Research Services Marine Laboratory.

The benefits to the sponsors and fishermen can be summarised as follows. The work carried out by the JIP showed that:

• There is no fundamental safety problem in overtrawling large diameter (46”) pipelines, and that the risks to fishermen are no greater than overtrawling smaller pipelines
• The pipeline provided no worse obstacle to the fishing gear than that from other natural features, debris and artefacts present on the seabed. It was not always evident from the fishing vessel when the fishing gear crossed over the pipeline.
• Model tests are representative of the full-scale behaviour and that model-scale testing can be used to conservatively estimate full-scale warp forces.
  

All case studies

• Trenching study for flexible pipeline subject to trawl gear interaction
• Wye piece verification
• Front-End Subsea Pipeline Conceptual Engineering Study
• Deep water pipelay capability spreadsheet
• Upheaval Buckling Analysis of a Flexible Pipeline
• Stability analysis of subsea gas pipelines using PRCI Level 2 stability analysis software
• Preparation of MathCAD sheets for pipeline stability analysis
• Goldeneye Third-Party Verification
• Overtrawling of large diameter pipeline trials JIP
• Recommended procedures and methods for design of subsea flanges
• Steady state FEA thermal analysis of a flexible pipeline in ANSYS
• Review of the Upheaval Buckling Analysis of a Pipe in Pipe System
• Investigation of data flow to foreign fishermen
• Pig impact at riser bends
• Analysis and tests of response of subsea equipment to acoustic vibrations
• Optimisation of fins on pipeline riser fairings using CFD
• Rock dump stability study
• Offshore support on pipeline inspection survey
• Pipeline design and installation procedure verification
• Study of fishing in the Gulf of Gabes
• Evaluation of the thermal properties of pipe sections and pipeline components
• Pipeline installation pull analysis
• Overtrawling capability of subsea protective structures
• Bundle towhead over-trawling – Scale model tests
• Thermal finite element analysis of a trenched umbilical
• Mattress placement study
• Pipeline stability assessment using PRCI Level 2 and Level 3 analysis tools
• Engineering critical assessment to BS 7910:2005
• Colombo harbour development
• Fishing interaction study
• Re-assessment of overtrawlability
• North Sea field development study
• Finite element analysis of mechanical connectors
• Flange leak investigation
• Spares and repairs
• Development of pipeline design sheets in MathCad
• Overtrawling of protection structures and umbilicals
• Riser ESDV leakage rate study
• Fatigue analysis of a riser in Orcaflex
• Support to BP Subsea and Pipelines Team
• Pipeline 4001 - Girth weld defect assessment
• Historical condition and lifetime prediction for Amethyst, Wollaston and Whittle
• Trawling risk assessment
• Assessment of pig run times
• Comparitive assessment of decommissioning options
• Assessment of current/ historical status of riser and bypass pipework
• Assessment of thermowell vibration fatigue due to vortex-induced vibration (VIV)
• Validation of water injection pipelines
• Defect assessment
• Unbilical stability assessment
• Technical authority and decommissioning support
• Major accident prevention document (MAPD) review and update
• General pipeline support
• Assessment of Pipeline Spares surrently held, future Spares and preservation requirements
• Creation of Technical Assessment summary sheets for North Sea pipelines
• Span and buckling assessment
• Overtrawlability trials of subsea structure
• Structural overtrawling trials
• Bend restrictor analysis
• Buoyancy module analysis
• FEA of an internally-lined pipe
• FEA of an internally-lined pipe Stage 2
• Fishing interaction
• Prediction of riser bend damage
• Pipeline decommissioning
• Fatigue analysis
• SNS decommission studies
• Riser ESDV leakage rate study
• Non-trenching study
• Span assessment and solution development
• Pipeline contingency plan
• Umbilical stability assessment
• Integrity under new flow conditions