Active heating systems have been successfully installed since 2007, culminating with the world's deepest "Direct Electrical Heating" (DEH) system in 1100m water depth installed in 2015 by a major offshore contractor. The company, with its market-leading track record in the design, fabrication and installation of pipe-in-pipe (PIP) solutions, is now collaborating on the qualification of the most efficient active heating technology – complementary to DEH systems – the "Electrically Heat Traced Flowline" (EHTF). This technology was originally introduced in 2000, and has undergone tests and improvements since 2009 within the framework of a cooperation between a major offshore contractor and a PiP design and manufacturing company. The low power consumption EHTF Technology is based on a field-proven, high performance PiP system. A specific insulation material arrangement (mineral/silica based microporous pre-compressed insulation), combined with a reduced pressure environment, provides extremely competitive thermal performances, unmatched by other usual dry insulation materials. Heating is supplied via a combination of multiple bundles of three-phase low voltage wires, continuously laid all along the inner pipe (flowline) under the insulation. The EHTF system provides the following advantages: Low power heating requirements thanks to the thermal efficiency of the insulation system: typically in the order of kilowatts rather than megawatts for competing high-voltage systems; High level of operational flexibility, reliability and redundancy thanks to the multiplicity of cables in the cross-section, which allows to face different heating level scenarios: both fluid preservation and permanent heating are envisaged during the operating field life. This paper describes a typical EHTF system, and provides examples of applications to future project developments. An overview of vessel capabilities in safely installing EHTF systems (focusing on, but not limited to reeling) demonstrates that the EHTF is not only a competitive and suitable in-place solution compared to other systems available in the subsea market, but also a very effective solution from an operational point of view. The current status of the EHTF qualification programme is also described. It includes the flowline components, the corresponding structures, termination modules and electrical connections to surface using wet-mateable connectors. The paper also shows how the advantages of an EHTF system can improve the economics of field developments by providing significant modification of CAPEX ("SURF+SPS+Topside"), OPEX (less consumables, maintenance and intervention than classical preservation methods) and production (shorter start-up times and higher production turndown ratios allowed). It opens up a whole range of new developments, by improving access to thermally demanding reserves, bringing flexibility and redundancy, and also allowing permanent heating and long tie-backs of up to 30km or more.

Active heating technologies are for the moment based on topsides power distribution, limiting by default, the length of the flowline that can be heated. It is proposed to extend the range of active heating technologies by utilizing a field architecture that enables production for very long tie-backs by combining subsea electrical power distribution with the most efficient active heating technology the "Electrically Heat Traced Flowline" (EHTF) technology. The paper will present typical field architectures that require such combinations of subsea electrical power distribution and efficient active heating technology, typically brown fields with remote tie-backs that could not be developed with available technologies. EHTF Technology is based on a field proven high performance thermally insulated pipe-in-pipe, limiting the heat loss. Multiple high voltage wires, connected as three phase circuits, laid under the insulation along the entire length of the fluid carrier pipe, are used to provide heating. The heating wires extend typically 20km each side of a small in-line structure allowing safe penetrations into the pipe-in- pipe annulus. This small structure is powered on by a power cable, laid alongside the flowline, via a subsea electrical power distribution unit, which can be combined with a subsea transformer, to distribute the power to the multiple heating circuits within the annulus. Exceptional thermal efficiency of the insulation system generates lower heating power requirements, meaning that subsea distribution systems can be designed with reliable and off the shelf components, easily retrievable and maintained with low operational expenditures. Multiple circuits in the cross-section offer a greater operational flexibility and improved reliability of the system. Different power outputs can be provided from simple switching control depending on the heating requirement. Combining an efficient, reliable and flexible active heating technology with a simple and robust subsea power distribution allows development of remote fields that can be tied-back to existing facilities, virtually without limitation in length.

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.