Video: Development of Detailed Reeling Analysis for Electrically Heat Traced Flowline EHTF System
- Sabesan Rajaratnam (Subsea 7) | Arek Bedrossian (Subsea 7) | Alan Roy (Subsea 7) | Narciso Lacerda (Subsea 7) | Saad Cherkaoui (Subsea 7) | Sonia Giraudbit (Subsea 7) | Leonardo Gitahy (Subsea 7)
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- Offshore Technology Conference
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- 2020. Copyright is retained by the author. This document is distributed by OTC with the permission of the author. Contact the author for permission to use material from this document.
- 4.2 Pipelines, Flowlines and Risers, 2.1.3 Completion Equipment, 7.4.3 Market analysis /supply and demand forecasting/pricing, 7 Management and Information, 4.2 Pipelines, Flowlines and Risers, 7.4 Energy Economics, 4.3.1 Hydrates
- Finite element, electrical wires, EHTF, optical cables, Reeling
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- 2 since 2007
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The Electrically Heat Traced Flowline (EHTF) is characterised by a combination of high performance dry annular thermal insulation of Pipe-in-Pipe (PiP) with a restricted electrical heating capability provided by helically wound copper wires laid between the inner pipe and the insulation in the annulus. The main advantage of EHTF are: future tie-back integration, unlock marginal reserves, access to HPHT pipeline, extend field life and maximise economic recovery and reduction in chemical and energy usage operational flexibility in controlling the flowline temperature and preventing the formation of wax and hydrates in shutdown conditions. Fibre optic cables are deployed in the EHTF system to measure the temperature of the flowline.
This paper presents the development of a detailed finite element model to predict the mechanical behaviour of the helically wound cabling during reeling operations. The wires and cables were represented explicitly in the model as initially straight and then wound helically around the inner pipe with specified pre-tension. The EHTF PiP system was then cyclically deformed against a former to simulate the reeling process. A fibre optic cable (FOC) containing a local imperfection due to denting was included in the model to assess the impact of reeling process on the continued acceptability of accidentally dented FOC.
The effects of friction between the cabling and the inner pipe and insulation surfaces, the pre-tensioned helical winding process and helix pitch, and the restraint provided by the thermal insulation layer and centralizers, were all investigated. Physical tests were conducted to establish the cyclic material properties of the electrical wires and results from these tests were used to calibrate the FE model.
This paper details Subsea 7's technical expertise in modelling the highly complex behaviour of the EHTF cabling system as it experiences multiple bending cycles due to reeling. The paper highlights some important key results describing the behaviour of the wires and consequent predictions of integrity which have since been verified through full scale physical tests. The FE modelling also contributed to the insight gained regarding the overall behaviour of the system.