AU2017261679A1 - Heating device for transporting a multiphase mixture of hydrocarbons, and associated method - Google Patents

Abstract

There is a need to provide a heating device for transporting a multiphase mixture of hydrocarbons which is able to supply thermal energy for a duration which may last as long as 20 years under severe pressure and temperature conditions and which makes it possible to dispense with the need for a heavy and expensive thermally insulating outer jacket. To that end, the present invention proposes a heating device for transporting a multiphase mixture of hydrocarbons that is notable in that its at least one peripheral space (7) is permeable to the water of the said expanse of water (3) and in that the main layer of electrical insulation is configured to form a water-resistant jacket around the at least one internal electrical element, the said main electrical insulation layer containing a fluorinated organic polymer. The invention also relates to the method for implementing said device.

Description

HEATING DEVICE FOR TRANSPORTING A MULTIPHASE MIXTURE OF HYDROCARBONS, AND ASSOCIATED METHOD

DESCRIPTION

Technical field of the invention

The present invention relates to a heating device for transporting a multiphase mixture of hydrocarbons comprising a structure submerged in a body of water capable of conveying said multiphase mixture of hydrocarbons. The invention also relates to the method implementing said heating device for transporting said multiphase mixture of hydrocarbons.

The general technical field of the invention is that of the extraction and transport of a multiphase mixture of hydrocarbons in the context of subsea oil and gas exploitation.

Background of the invention

Multiphase mixtures of hydrocarbons from subsea oil and gas deposits are conveyed over several kilometers through subsea structures that may in particular be flexible or rigid pipes within increasingly deep bodies of water.

Deep or even ultra deep water are reflected by an increase in the hydrostatic pressure between 200 bar and 500 bar and a drop in temperature that may reach -5°C, for example. Thus, during transport, heat exchanges with the surrounding environment cause temperature drops within the pipes and solid deposits may partially or completely obstruct the pipes.

Indeed, the oil and gas deposits comprise a multiphase hydrocarbon mixture in particular comprising hydrocarbons in liquid and gaseous form, water as well as solid particles, in particular sand. The multiphase hydrocarbon mixture may also comprise nonhydrocarbon gases such as nitrogen or hydrogen disulfide. Under the aforementioned high-pressure and low-temperature conditions, the water molecules in the presence of gas contained in the multiphase hydrocarbon mixture tend to form hydrates. Therefore, under these same conditions, the oils contained in multiphase hydrocarbon mixture tend to form paraffin crystals. The temperature drop is also responsible for the formation of blocks of ice within the pipes, causing a slowing of the flow rate, or even a total stop of production. Furthermore, the solid deposits such as hydrates, paraffins and ice may create pressure differentials along the pipes and/or block moving elements in the underwater structures, of the valve, pump or other type, and may thus cause irreversible damage on the infrastructure, leading to substantial economic losses. Therefore, tragic environmental consequences may occur and operator safety may be compromised.

One of the strategies making it possible to offset these drawbacks during transport of the multiphase hydrocarbon mixture therefore consists of maintaining a threshold temperature within the pipes higher than the solidification temperature of the paraffins, hydrates and ice under the high-pressure conditions.

First, it has been proposed to thermally isolate the pipes in order to minimize the heat exchanges between the pipe and the surrounding environment and thus to offset a temperature drop inside the pipes. For example, it is well known in the prior art to use double-jacketed pipes (called PiP for “pipe in pipe”). In this type of pipe, the double jacket is formed by two coaxial steel tubes. More particularly, this type of pipe comprises an inner tube in which the fluid is transported and an outer tube. Between the inner tube and the outer tube is a completely watertight peripheral space comprising air, gas or vacuum that makes it possible to provide passive thermal insulation of the inner tube.

However, the multiphase hydrocarbon mixture is transported over several kilometers. Thus, although PiPs are an effective solution in terms of thermal insulation, there are nevertheless heat losses, which, over large distances, cause a temperature drop allowing solid deposits to form as previously mentioned. Passive thermal insulation is therefore not fully satisfactory over large transport distances.

Thus, structures such as PiPs typically comprise at least one heating cable arranged within the peripheral space intended to heat the inner tube, temporarily or continuously. This type of heating device is commonly called ETH-PiP (Electrically Trace Heated Pipe in Pipe). One example embodiment of such a heating device is in particular shown schematically in figure 1. The device (100) in particular comprises a pipe (500) submerged in a body of water (300) and arranged on the seabed (400). The device (100) also comprises an outer tube (600) around the pipe (500) forming a peripheral space (700) on the perimeter of the pipe (500). One or several heating cables (800) is (are) arranged within said peripheral space (700) that is or are intended to heat the pipe (500) over at least part of its length.

In this type of configuration, the pipe (500) and the outer tube (600) define a watertight peripheral space (700) in which the heating cables (800) are arranged. The peripheral space (700) comprises air, gas or vacuum. Thus, the heating cables (800), which are in particular intended to operate under temperatures between 20°C and 170°C over at least a cycle of 30 minutes, are preserved from the outside environment by the pipe (500) and the outer tube (600) together forming a tight peripheral space (700).

However, ETH-PiP is expensive and the steel double jacket of this heating device represents a relatively heavy weight, which makes installation difficult, in particular at great depths. Aside from the weight of the ETH-PiP, the steel double jacket creates a particularly rigid, bulky assembly that is difficult to manipulate using traditional placement means. The double jacket therefore restricts the placement capacities to pipes having outer diameters of about 45 cm (18 inches) or 48 cm (19 inches).

An alternative solution is for example described in document US 6,940,054. This document describes a heating device comprising a thermally insulated pipe commonly called ETH-SP (Electrically Trace Heated Single Pipe). The pipe comprises a thermally insulating outer jacket lighter than the steel outer tube intended to reduce heat exchanges with the outside environment. This thermally insulating outer jacket comprises at least one insulating layer made from polyvinyl chloride (PVC) arranged on the perimeter of the pipe. The PVC insulating layer forms channels defining a peripheral space on the perimeter of the pipe. Heating means intended to heat the pipe are arranged within these channels. According to document US 6,940,054, the heating means assume the form of tubes in which a hot fluid supplying heat to the pipe flows. An alternative according to this prior art consists of heating means assuming the form of heating cables arranged within the peripheral space.

Like the peripheral space of the ETH-PiP, the peripheral space of the ETH-SP, in particular delimited by the thermally insulating outer jacket made from PVC, and the pipe must be free of water. To that end, the installation of this type of pipe is done using specific and complex placement means compatible with the PVC outer jacket, which is particularly fragile relative to a steel outer jacket as used in a PiP-type pipe.

Indeed, the PVC thermally insulating outer jacket for example is significantly less strong than the steel outer tube of the ETH-PiP. During a traditional installation, the pipe is passed through conventional placement means, exerting gripping forces on the outer jacket of the pipe, such as tensioners or gripping collars. The gripping force applied to the pipe and in particular to the thermally insulating outer jacket tends to weaken the latter. As a result, the thermally insulating outer jacket undergoes impacts when the pipe reaches the seabed. The pipe therefore experiences stresses that tend to weaken or damage the thermally insulating outer jacket. As a result, cracks within this jacket may form and water from the body of water may infiltrate and flood the peripheral space. The presence of water within the peripheral space damages the insulating performance of the thermally insulating outer jacket. Furthermore, this infiltration of water is highly problematic for the heating of the pipes using heating cables.

Indeed, conventional heating cables comprise an inner electrical element configured to generate thermal energy primarily by Joule Effect when it is subject to an electric current and an electrically insulating outer layer. The electrically insulating outer layer typically comprises a polymer that may for example be a cross-linked or non-cross-linked polyethylene. Under the effect of a high temperature in particular related to the temperature of the hydrocarbons leaving wells, this electrically insulating outer layer tends to deteriorate by thermolysis or by thermo-oxidation and in fine to lose its dielectric resistance properties. As a result, the outer electrically insulating layer is subject to electrical fields greater than 1 kV/m generating partial discharges and preferred current leak paths generating a water tree or an electrical tree through the insulation causing the erosion or oxidation of the outer electrically insulating layer.

Furthermore, in the presence of water, in particular saltwater, and under high pressure, the hydrolysis of the outer electrically insulating layer is even more greatly favored.

Furthermore, the outer electrically insulating layer generally has surface irregularities and/or flaws related to the method for manufacturing said layer. In the presence of water, these flaws and irregularities constitute crack onsets in which water may infiltrate. The hydrolysis or intrusion of water lead to premature cracking of the outer electrically insulating layer. The outer electrically insulating layer therefore no longer performs its electrical insulation role and the heating of the pipe is quickly no longer provided.

There is therefore a need to provide a heating device for transporting a multiphase mixture of hydrocarbons that is light, inexpensive, able to be installed using conventional installation means, and able to deliver thermal energy over a duration of up to 20 years in a subsea environment.

Brief description of the invention

To that end, the invention relates to a heating device for transporting a multiphase mixture of hydrocarbons comprising: - a structure submerged in a body of water capable of conveying a multiphase mixture of hydrocarbons; - at least one peripheral space arranged on the perimeter of said structure; - at least one heating cable arranged within said at least one peripheral space comprising: - at least one inner electrical element configured to generate thermal energy when it is subjected to an electric current; and - at least one primary electrically insulating layer.

The heating device for transporting a multiphase mixture of hydrocarbons is remarkable in that said at least one peripheral space is permeable to the water from said body of water and in that said primary electrically insulating layer is configured to form a jacket resistant to said water around said at least one inner electrical element, said primary electrically insulating layer comprising a fluorinated organic polymer.

The devices of the prior art did not appear to be able to operate after their installation by conventional placement means in light of the presence of water within the peripheral space responsible for the deterioration of the thermal insulation performance of the device. Faced with this state of affairs, one skilled in the art sought to take advantage of a thermally insulating outer jacket able to withstand the impacts and the forces experienced during installation in order to benefit from a tight peripheral space and therefore a functional heating device. Against the technical prejudices related to the insulating performance when the peripheral space comprises water, the work by the Applicants made it possible to show that the heating device according to the invention comprising a peripheral space comprising water was compatible with the insulating performance expected from such a device.

Furthermore, while one skilled in the art is strongly discouraged in general from using electrical cables in an environment where they could be in contact with water, the heating cables of the Applicant are stripped of a rigid sealing jacket leaving the main electrically insulating layer in direct contact with the seawater. Indeed, the work by the Applicant has made it possible to show that the dielectric resistance properties of the fluorinated organic polymers are preserved when they are in contact with water for at least 20 years and when they are subject to temperature peaks of at least 30 minutes between 20°C and 170°C. As a result, when the temperature favors the deterioration of the polymer layers under such conditions, fluorinated organic polymers are particularly resistant when they are subject to such temperatures, even under a pressure between 10 bars and 500 bars, and more particularly between 200 bars and 500 bars. Against technical prejudices related to the use of cables under these conditions, the heating cables according to the invention are compatible with the pressure, temperature, humidity and usage duration conditions related to offshore oil exploitation.

Owing to the present invention, it is henceforth possible to benefit from a heating device for transporting a multiphase mixture of hydrocarbons that is light, inexpensive, able to be installed using conventional installation means and compatible with a subsea environment.

Furthermore, the device according to the invention may comprise one or more of the following features, considered alone or according to any technically combination.

According to one advantageous feature of the invention favoring the mechanical holding of the main electrically insulating layer for a duration of at least 20 years in particular under operating pressures between 10 bars and 500 bars, more particularly between 200 bars and 500 bars and under temperature peaks of at least 30 minutes between 20°C and 170°C and in particular between 100°C and 170°C, said primary electrically insulating layer has a thickness of at least 1 mm, advantageously at least 10 mm, still more advantageously at least 100 mm.

According to one advantageous feature of the invention making it possible to improve the heating of said structure, said at least one heating cable comprises at least one additional layer.

According to one advantageous feature of the invention making it possible to favor the sustainability of said additional layer for a duration of at least 20 years in particular under operating pressures between 10 bars and 500 bars, more particularly between 200 bars and 500 bars and under temperature peaks of at least 30 minutes between 20°C and 170°C and in particular between 100°C and 170°C, said at least one additional layer comprises a fluorinated organic polymer.

According to one advantageous feature of the invention relating to the homogenization of the electrical fields within the primary electrically insulating layer, said at least one additional layer comprises conductive particles.

Advantageously, said at least one additional layer is arranged between said at least one inner electrical element and said primary electrically insulating layer or around said primary electrically insulating layer. Thus, said additional layer, in addition to the electrical functions it may perform when it is charged with conductive particles, may advantageously reinforce the mechanical holding of the primary electrically insulating layer and its cohesion with the primary electrically insulating layer.

The fluorinated organic polymers particularly making it possible to achieve the aim of the invention are chosen from among ethylene tetrafluoroethylene (ETFE), perfluoroalkoxy (PFA), fluorinated ethylene propylene (FEP), polytetrafluoroethylene (PTFE) or mixtures thereof.

According to one advantageous feature of the invention, said fluorinated organic polymer comprises a volumetric uptake of water of less than 1%, less than 0.5% and preferably less than 0.1% according to standard ASTM D570. The low volumetric uptake of the fluorinated organic polymers in particular favors the water resistance of the primary layer.

According to one advantageous feature of the invention making it possible to optimize the electrical insulation properties of the primary electrically insulating layer, said primary electrically insulating layer comprises at least 50 wt% of the fluorinated organic polymer, preferably at least 70 wt% of the fluorinated organic polymer, advantageously exclusively a fluorinated organic polymer.

According to one particular embodiment of the invention allowing the transport of a multiphase mixture of hydrocarbons within a light structure while being heated under conditions where the heating cable is in contact with saltwater and subject to operating pressures comprised between 10 bars and 500 bars, more particularly between 200 bars and 500 bars, and temperature peaks of at least 30 minutes between 20°C and 170°C and in particular between 100°C and 170°C for at least 20 years, the device comprises: - at least one pipe submerged in a body of water capable of conveying a multiphase mixture of hydrocarbons; - a thermally insulating jacket comprising: - at least one channel extending over at least part of the pipe; - said at least one peripheral space being arranged within said at least one channel.

Advantageously, said thermally insulating jacket comprises at least two adjacent parts forming at least one longitudinal channel.

According to one particular embodiment of the invention making it possible to confine the heat delivered to said structure and thus to avoid heat losses leading to a temperature drop of the multiphase mixture of hydrocarbons, the heating device comprises: - at least one pipe submerged in a body of water capable of conveying a multiphase mixture of hydrocarbons; - at least one removable lid arranged facing the pipe comprising an inner face facing said pipe; - said inner face comprises at least one channel extending over at least one part of the length of said at least one removable lid; - said at least one peripheral space being arranged within said at least one channel.

According to one particular embodiment of the invention, said structure comprises a mean for collecting and/or distributing a multiphase mixture of hydrocarbons.

Owing to the present invention, the heating cables can operate with no outer sealing jacket making it possible to preserve the inner electric element from water. The primary electrically insulating layer made from fluoropolymer is particularly water-resistant. The properties of the latter are preserved in contact with water and the inner electrical element remains functional under these conditions. Thus, owing to the present invention, such a structure may henceforth benefit from active heating enabling an effective circulation of a multiphase mixture of hydrocarbons while being light and inexpensive.

The invention also relates to a method for implementing the heating device for transporting a multiphase mixture of hydrocarbons comprising the following steps: - (a) providing a structure capable of conveying a multiphase mixture of hydrocarbons comprising at least one water-permeable peripheral space arranged on the perimeter of said structure; - (b) providing at least one heating cable by: - (b1) providing at least one inner electrical element configured to generate thermal energy when it is subjected to an electric current; - (b2) arranging at least one primary electrically insulating layer around said at least one inner electrical element (81), said layer comprising a fluorinated organic polymer configured to form a water-resistant jacket around said at least one inner electrical element; - (c) arranging said at least one heating cable within said at least one peripheral space: - (d) submerging said structure within a body of water.

The methods for implementing heating devices according to the prior art comprise supplying a steel double jacket that is difficult to place due to its weight, its volume and the rigidity of the steel double jacket, and represent a substantial economic investment. The method according to the invention makes it possible to do away with a steel double jacket while benefiting from active heating of subsea structures. Henceforth, owing to the method according to the present invention, it is possible to provide a lighter, inexpensive device having active heating.

Description of the figures

The invention will be better understood upon reading the following description, provided solely as an example and done in reference to the appended drawings, in which: - figure 1 is a schematic cross-sectional view of a heating device of the prior art, - figure 2 is a schematic cross-sectional view of a heating device according to the invention, - figure 3 is a schematic cross-sectional view of a heating cable equipping the device according to the invention, - figure 4 is a schematic cross-sectional view of a heating cable equipping the inventive device according to a first specific embodiment of the cable, - figure 5 is a schematic cross-sectional view of a heating cable equipping the inventive device according to a third specific embodiment of the cable, - figure 6 is a schematic cross-sectional view of a heating cable equipping the inventive device according to a fourth specific embodiment of the cable, - figure 7 is a schematic longitudinal view of an element of a heating cable equipping the device according to the invention, - figure 8 is a schematic cross-sectional view of the heating device according to a first specific embodiment of the invention, - figure 9 is a schematic cross-sectional view of the heating device according to a second specific embodiment of the invention, - figure 10 is a schematic perspective view of the heating device according to a third specific embodiment of the invention.

Detailed description of the invention A heating device (1) for transporting a multiphase mixture of hydrocarbons according to the invention is illustrated schematically by figure 2 and figures 8 to 10.

The heating device (1) for transporting a multiphase mixture of hydrocarbons comprises a structure (2) submerged in a body of water (3) capable of conveying a multiphase mixture of hydrocarbons.

The structure (2) can for example rest on the bottom (4) of the body of water (3), be embedded or extend through the body of water (3) from the bottom (4) toward the surface. The body of water (3) can for example be a river, lake, sea or ocean. The depth of the body of water (3) is generally greater than 10 m, and is for example comprised between 200 m and 5000 m. The structure (2) can therefore be subject to a hydrostatic pressure of at least 10 bars, and more generally between 200 bars and 500 bars. The structure (2) is intended to be submerged for at least 20 years. Furthermore, when the structure (2) is located in a sea or ocean, it resides in a particularly corrosive environment in light of the salt content.

Within the meaning of the present invention, the structure (2) may comprise a pipe (5) or a set of pipes (5) intended to transport a multiphase mixture of hydrocarbons from an undersea installation such as a well toward a surface unit or installation. The surface unit or installation may in particular be a Floating Production, Storage and Offloading (FPSO) unit, or a Floating Liquefied Natural Gas (FLNG) unit, or a Single Point Anchor

Reservoir (SPAR), or a Tension Leg Platform (TLP). The pipe (5) may also extend between undersea installations. The pipe (5) may be of the rigid or flexible type.

In combination with or as an alternative to the pipe (5), the structure (2) may comprise a means for collecting and/or distributing (11) a multiphase mixture of hydrocarbons such as a manifold, a pump, a separator or any other equipment intended for the storage and distribution of a multiphase mixture of hydrocarbons in the offshore oil environment.

The heating device (1) may also comprise a thermally insulating jacket (6) in order to limit the heat exchanges with the surrounding environment and thus favor the heating of the structure (2), and in particular of the pipe (5).

The thermally insulating jacket (6) may be of the fixed type. It then comprises at least one layer with at least two adjacent insulating parts (60) arranged on the circumference of the pipe (5). Alternatively, the thermally insulating jacket (6) may be movable and assume the form of a removable lid (10) arranged along the pipe (5) or on at least part of its length.

Furthermore, the oil and gas deposit comprises a multiphase mixture of hydrocarbons comprising a gaseous phase and at least one carbonaceous liquid phase. Generally, the deposit also comprises an aqueous liquid phase and a solid phase comprising impurities such as sand or sediments. Thus, a mixture of gaseous phases, liquid phases and solid phases hereinafter referred to generically as multiphase mixture of hydrocarbons circulates inside the structure (2) at a temperature between 60° and 200° at the well output and at a pressure of at least 50 bars. The structure (2) provides the circulation of a multiphase mixture of hydrocarbons under these conditions over a period of at least 20 years. The circulation may be continuous, i.e., without circulation stoppage over this period, or temporary, i.e., with circulation stoppages that may be longer or shorter, in particular from several hours to several weeks.

Furthermore, the heating device (1) comprises at least one peripheral space (7) arranged on the perimeter of said structure (2).

In general, the peripheral space (7) is comprised between the outer surface of the structure (2) and a fictitious jacket (70) separated by a distance D from the outer surface of the structure (2) in an outer direction relative to the structure (2). The distance D is generally between 6 cm and 100 cm, preferably between 6 cm and 15 cm.

Said at least one peripheral space (7) is permeable to water from the body of water (3) and thus comprises water from the body of water (3) when the heating device (1) is submerged in the body of water (3). When the body of water (3) is seawater or ocean water, it comprises a saltwater content between 30 g/l and 40 g/l. The peripheral space (7) is also subject to a hydrostatic pressure of at least 10 bars, generally between 200 bars and 500 bars.

Furthermore, the heating device (1) comprises at least one heating cable (8) arranged within said at least one peripheral space (7).

Within the meaning of the present invention, heating cable refers to a medium, high voltage electric cable comprising at least one inner electrical element (81) and at least one primary electrically insulating layer (80).

Within the meaning of the present invention, medium voltage, high voltage refers to a voltage across the terminals of a electric cable at least greater than 1 kV. The medium voltage cables are generally configured to operate under a voltage across their terminals between 1 kV and 50 kV, and the high voltage cables are typically configured to operate under a voltage across their terminals greater than 50 kV.

More specifically, the voltage applied to the heating cable (8) depends on the distance from the structure (2) needing to receive the heating and the type of signal injected, DC current or AC current. In the case at hand, the heating cable (8) is subject to a voltage across its terminals of at least 1 kV.

Furthermore, the intensity of the current passing through the heating cable (8) is typically between 0.1 A and 320 A.

The consumed power is generally between 50 W/m and 200 W/m.

The heating cable (8) can be supplied with single-phase or three-phase DC current or AC current.

In particular, the heating cable (8) is powered by a power source located on the surface of the body of water (3) by the FPSO, for example, and the electric current can be transmitted to the heating cable (8) through an umbilical. Generally, the umbilical comprises, near the heating cable (8), a point of contact with the water from the body of water (3) making it possible to collect, toward the electrical power supply source, the leakage currents and the fault currents related to the electrical insulation faults of the heating cable (8) generally between 1 mA/m and 10 mA/m. The point of contact is for example located at a distance of less than 500 m relative to the end of the heating cable (8) and may for example be an anode.

Alternatively, the pipe (5) comprises a riser extending to the surface installation facility or unit. The heating cable (8) may in this case extend along said riser to the surface installation and may be directly connected to a power source located on the FPSO.

Generally, the heating cable (8) operates during production stoppages or during transitional phases between the production stoppages and production. The heating cable (8) may also operate when production is in progress, i.e., during the circulation of the multiphase mixture of hydrocarbons.

As previously cited and in particular shown in figure 3, the heating cable (8) comprises at least one inner electrical element (81) configured to generate thermal energy when it is subjected to an electric current and at least one primary electrically insulating layer (80).

The inner electrical element (81), also called "strand", comprises a set of conductive elements, such as metal wires. The metal wires are preferably made from an aluminum- and/or copper-based alloy. The outer surface of the inner electrical element (81) can also comprise a layer of tin in order to preserve the integrity of the inner electrical element (81) during a period of at least 20 years.

Typically, the inner electrical element (81) comprises a set of 6 to 500 wires, or even 600 wires, or even 800 wires. The number of wires is in particular chosen based on the need for flexibility of the heating cable (8) for its installation, linear resistance characteristics and wire-drawing capacities. For inner electrical elements (81) with a same section, a large number of wires with a small diameter is favored compared to a small number of wires with a large diameter in order to limit the interstitial spaces between the wires and optimize the regularity and rotundness of the outer surface of the inner electrical element (81). Thus, the number of wires forming the inner electrical element (81) is typically greater than 100.

The inner electrical element (81) can be of the simple, segmented, compact, hollow or braided type. Preferably, the inner electrical element (81) is of the compact type in order to optimize the regularity and rotundness of the inner electrical element (81).

The compactness rate of the inner electrical element (81) is advantageously at least 60%, preferably at least 80%, and still more advantageously at least 90%. The compactness rate is in particular defined as the ratio of sections of the wires making up the inner electrical element (81) to the section of the circle delineated at the inner electrical element (81).

The heating cable (8) is subject to a hydrostatic pressure between 10 bars and 500 bars, and more particularly between 200 bars and 500 bars. The compactness rate makes it possible to limit, or even eliminate the risks of collapse of the inner electrical element (81) under such pressures. Thus, by improving the architecture of the inner electrical element (81), and in particular its regularity and rotundness, the pressure content of the inner electrical element (81) is optimized. As a result, the risks of creep of the primary layer (80) that surrounds the inner electrical element (81) are decreased.

Typically, the section of the inner electrical element (81) is dimensioned so as to generate sufficient thermal energy primarily by Joule Effect when the inner electrical element (81) is subject to an electrical current. The section of the inner electrical element (81) is for example between 0.5 mm2 and 75 mm2. Such a section in particular makes it possible to generate a linear resistance between 0.01 mOhm/m and 20 mOhm/m. Preferably, the section of the inner electrical element (81) is between 6 mm2 and 25 mm2.

The thermal energy is transferred in the form of heat to the surrounding environment, and in particular to the structure (2), and through it to the multiphase mixture of hydrocarbons. This in particular results in melting of the solid deposits and/or a temperature increase of the multiphase mixture of hydrocarbons that may be between 2°, temperature at which the blocks of ice resorb, and 65°C, temperature at which the paraffins are fluidified. The melting temperature of the hydrates is generally between 20°C and 30°C.

The primary electrically insulating layer (80) is in particular in contact with the water from the body of water (3). The primary electrically insulating layer (80) is also subject to the hydrostatic pressure between 10 bars and 500 bars, more particularly between 200 bars and 500 bars, and to temperatures between 20°C and 170°C.

The primary electrically insulating layer (80) is configured to form a water-resistant jacket around the inner electrical element (81), and it comprises a fluorinated organic polymer making it possible to satisfy the conditions to which it is subjected. A fluorinated organic polymer refers to any polymer having, in its chain, at least one monomer chosen from among compounds containing a vinyl group capable of opening to polymerize and which contains, directly attached to said vinyl group, at least a fluorine atom, a fluoroalkyl group or a fluoroalkoxy group.

Fluorinated organic polymers have the property of withstanding temperatures that may reach up to 170°C, or even 200°C. Unexpectedly, the Applicant has shown that in contact with water and under these temperature conditions, the fluorinated organic polymers were retaining their integrity and dielectric properties for at least 20 years, unlike the polymers of the prior art, which tend to break down under such conditions. The primary electrically insulating layer (80) is thus a remarkable electrical insulator in that it is water-resistant. Water-resistant means that the primary electrically insulating layer (80) minimizes the infiltration of water by permeation within the primary electrically insulating layer (80) even under temperatures between 20°C and 170°C and pressures between 10 bars and 500 bars, more particularly between 200 bars and 500 bars for at least 20 years.

Advantageously the fluorinated organic polymer comprises a volumetric uptake of water of less than 1%, less than 0.5% and preferably less than 0.1% according to standard ASTM D570.

Advantageously, the primary electrically insulating layer (80) comprises at least 50 wt% of the fluorinated organic polymer, preferably at least 70 wt% of the fluorinated organic polymer, and preferably exclusively a fluorinated organic polymer.

Preferably, the fluorinated organic polymer is chosen from among ethylene tetrafluoroethylene (ETFE), perfluoroalkoxy (PFA), fluorinated ethylene propylene (FEP), polytetrafluoroethylene (PTFE) or mixtures thereof.

When the primary electrically insulating layer (80) does not exclusively comprise a fluorinated organic polymer, it comprises a mixture of fluorinated organic polymer and thermoplastic polymer such as polyethylene (PE) or polyamide (PA).

The primary electrically insulating layer (80) may comprise typical additives such as antioxidant or anti-UV fillers or any other type of additive suitable for the targeted application. However, the chemical stability of the fluorinated materials previously cited is particularly advantageous and generally does not require additives.

Advantageously, the primary electrically insulating layer (80) has a thickness of at least 1 mm, preferably a thickness of at least 10 mm, still more advantageously a thickness of at least 100 mm. The thickness of the primary electrically insulating layer (80) favors the holding of its temperature and prevents or at least minimizes the swelling and/or hydrolysis of the primary electrically insulating layer (80) in contact with the water. Therefore, such a thickness allows the mechanical holding of the primary electrically insulating layer (80). Indeed, when the inner electrical element (81) has surface irregularities, the primary electrically insulating layer (80) tends to creep within said irregularities and no longer perform its electrical insulation role. When the thickness of the primary electrically insulating layer (80) is at least 1 mm, a portion of the primary electrically insulating layer (80) may creep within the irregularities, the second portion of the thickness not having creeped providing the electrical insulation of the inner electrical element (81).

The primary electrically insulating layer (80) is preferably obtained by extrusion. The melt flow and cooling rates of the primary electrically insulating layer (80) are slow enough to optimize the compactness of the material and to allow the creation of long fluorinated chains while minimizing the risk of air bubble formation in the fluorinated organic polymer. The melt flow rate is for example between 0.5 g/10 min and 8 g/10 min.

The melt flow temperature is above the melting point of the fluorinated organic polymer. Generally, the melt flow temperature is between 260°C and 330°C.

The crystallinity of the fluorinated organic polymer is advantageously greater than 40%.

The volume resistivity of the primary electrically insulating layer (80) is greater than 1 Gohm per kilometer of cable according to standard ASTM D257.

Furthermore, the heating cable (8) may comprise an additional layer (82).

The additional layer (82) may for example comprise a thermoplastic polymer such as polyethylene or polypropylene.

Preferably, the additional layer (82) comprises a fluorinated organic polymer. Advantageously, the fluorinated organic polymer is chosen from among the fluorinated organic polymers making up the primary electrically insulating layer (80).

The additional layer (82) may also comprise conductive particles such as carbon black, metal particles or graphites intended to perform the semi-conductive function of the additional layer (82) and thus to homogenize the electrical fields around the inner electrical element (81) and therefore to reduce the stresses induced within the primary electrically insulating layer (80).

Advantageously, the resistivity of the additional layer (82) comprising a fluorinated organic polymer filled with conductive particles is typically between 5 Ohm.cm and 50 Ohm.cm according to standard ASTM D527. The additional layer (82) according to the invention thus allows a better distribution of the electrical fields.

Generally, the thickness of the additional layer (82) is between 0.1 mm and 0.8 mm.

In a first specific embodiment of the heating cable (8) shown in figure 4, the additional layer (82) is arranged between the inner electrical element (81) and the primary electrically insulating layer (80).

The additional layer (82) makes it possible to compensate the outer surface irregularities of the inner electrical element (81). In this case, the additional layer (82) therefore has a thickness at least equal to the height of said irregularities. Generally, this thickness is between 0.2 mm and 0.4 mm.

In a second specific embodiment of the heating cable (8), not shown, the additional layer (82) is arranged around the primary electrically insulating layer (80).

According to this second example, the additional layer (82) guarantees the transfer of electric charges related to the leakage currents and fault currents toward the marine environment.

According to a third specific embodiment of the heating cable (8) shown in figure 5, the heating cable (8) comprises two additional layers (82, 82'), a first additional layer (82) being arranged between the inner electrical element (81) and the primary electrically insulating layer (80) and a second additional layer (82') being arranged around the primary electrically insulating layer (80).

In a manner well known by those skilled in the art, the heating cable (8) may comprise mechanical reinforcements (not shown) arranged around the primary electrically insulating layer (80) or the additional layer (82) when the latter is arranged around the primary electrically insulating layer (80). The mechanical reinforcements may for example be metal armors making it possible to react to axial forces experienced during the installation of the device (1).

Preferably and as shown in figure 2 and figures 8 to 10, several heating cables (8) can be arranged on the perimeter of the structure (2) in order to optimize heating thereof.

Advantageously and as in particular shown in figure 6, several heating cables (8, 8”, 8”’) like those previously described can be grouped together in a single bundle (888).

Advantageously, at least three substantially aligned heating cables (8’, 8”, 8”’) are grouped together in a bundle (888). Substantially aligned means that the center of each heating cable in the bundle (888) is aligned along a same axis with a possible misalignment of several millimeters. Alternatively, the heating cables (8’, 8”, 8”’) may be aligned so as to form a triangular bundle (888).

More particularly, the bundle (888) comprises at least one outer sheath (83) making it possible to secure the heating cables (8’, 8”, 8”’) in a single bundle (888).

Advantageously, the outer sleeve (83) is polymeric. The polymer for example comprises a thermoplastic such as a polyamide (PA), a polyethylene (PE) or a polyvinylidene fluoride (PVDF) or an elastomer such as an ethylene-propylene-diene monomer (EPDM).

The thickness of the outer sheath (83) is for example comprised between 0.1 mm and 5 mm.

The outer sheath (83) comprises at least one means for infiltration (86) of water from said body of water (3). Advantageously, several water infiltration means (86) are arranged over the length of the outer sheath (83) every 1 m, or even every 100 m or every 500 m. The infiltration means (86) are in particular arranged along the outer sheath (83) such that water penetrates the interstitial spaces (84) during the installation of the device (1) without damaging said outer sheath (83) by erosion, for example. The water infiltration means (86) may for example be a piercing formed in the thickness of the outer sheath (83) as shown in figure 6 or any other equivalent means suitable for one skilled in the art allowing the passage of water through the outer sheath (83).

Grouping several heating cables (8) together in a single bundle (888) makes it possible to reduce the couplings by magnetic field between the heating cables (8) and between the heating cables (8) and the structure (2). Furthermore, the number of heating cables (8) to be installed is reduced by three, which makes it possible to install them by conventional means, such as a spiral winder. Thus, the installation of the heating cables (8) is made significantly easier.

Furthermore, the heating cables (8) may have a length greater than 10 m, greater than 100 m, greater than 1 km or even greater than 4 km and advantageously extend over the entire length of the structure (2) or over a part of the structure (2) where heating is necessary. Typically, the heating cables (8) have a length of 1.1 km corresponding to the length of a stalk (5). Advantageously, the structure (2) may comprise several heating cables (8) arranged in series on at least part, or even all, of the length of the structure (2). The heating cables (8) are then connected via connectors (85) every 100 m, 1 km or even every 4 km as a function of the length of the heating cable (8). A connector (85) connecting the free end of a heating cable (8a) to the free end of an adjacent heating cable (8b) is for example shown in figure 7. It in particular comprises a male portion (850) and a female portion (851) cooperating with one another to form the connector (85).

Preferably, the male portion (850) has a conical surface so as to minimize the potential air bubbles at the interface of the male (850) and female (851) portions. The risk of partial discharges or preferential current leakage paths is thus limited.

The connector (85) further comprises a means for attaching the male portion (850) on the female portion (851) by bolting on a flange, screwing, gluing or any other fastening means known by one skilled in the art. More particularly, when it involves fastening by screwing, the means comprises a connecting ring (853) comprising, on the one hand, an inner shoulder intended to engage on an outer shoulder respectively arranged on the male (850) and female (851) portion and, on the other hand, a tapping intended to engage on a thread arranged on the female portion (851) and on the male portion (850), so as to constrain the male portion (850) against the female portion (851) by screwing of the connecting ring (853).

In light of the marine environment, a sealing gasket (852) of the single or double type may be arranged between the male (850) and female (851) portion so as to minimize the risks of water infiltration.

Furthermore, the connector (85) comprises an electrically insulating means (857) as well as a means making it possible to react the radial forces related to the outside pressure exerted on the connector (85). Thus, the connector (85) responds to the same pressure resistance, electrical insulation, and sealing specificities as the heating cable (8).

Thus, the connector (85) comprises a housing (854) bearing against a metal gripping ring (855) arranged around the free end of the heating cable (8a, 8b). Preferably, the housing (854) is made from metal and thus provides the mechanical holding of the connector (85). The support (854) is for example made from stainless steel of type SS316L, Super Duplex or Inconel 825 in order to withstand corrosion.

Furthermore, the electrical insulation (857) is for example a cylindrical molded part arranged within the connector (85). The electrical insulation (857) is arranged around the free end of the primary electrically insulating layer (80a, 80b) of the heating cable (8a, 8b) and is in contact with the inner electrical element (81a, 81b). Preferably, the upper electrically insulating layer (857) is inserted at a conical fastening ring (859) attached on the free end of the primary electrically insulating layer (80a, 80b). The upper electrically insulating layer (857) is for example made from a thermoplastic material such as a polyether either ketone (PEEK), or an elastomeric material such as an ethylene-propylene-diene monomer (EPDM) or a HNBR, or a fluorinated thermoplastic, such as a PTFE or a fluorocarbon elastomer (FKM).

Advantageously, and in particular when the heating cable (8) comprises an additional layer (82), the connector (85) comprises a semiconductor element (858) that may for example be a cylindrical molded part, arranged within the connector (85).

Preferably, the additional layer (82a, 82b) has an excess length at the free end of the heating cable (8) around which the semiconductor element (858) is arranged. Thus, the additional layers (82a) and (82b) easily cooperate with the electrical connection within the connector.

Likewise, the free end of the inner electrical element (81a, 81b) of the heating cable (8a, 8b) comprises an excess length relative to the primary insulating layer (80a, 80b) thus facilitating the electrical connection at the connector (85).

Furthermore, the electrical connection within the connector (85) allowing the passage of current between two heating cable sections (8a, 8b) connected via the connector (85) can be done using any means known by one skilled in the art, such as a connection by bush or lug. For example, the male (850) and female (851) portions may respectively comprise at least one electrical strip (859) engaging on a ring (859') arranged around the inner electrical element (81a, 81b) and providing the passage of current by contact between the electrical strips (859). Advantageously, the electrical strips (859) have a copper base.

The length of the connector (85) is preferably less than 300 mm, and its thickness is preferably less than 30 mm.

Lastly, the connection between the male portion (850) and the female portion (851) of the connector (85) can be done on shore or at sea.

Other specific embodiments of the invention will now be described, provided for information but non-limitingly.

According to a first embodiment of the invention shown in figure 8, the structure (2) comprises a rigid pipe (5) able to convey a multiphase mixture of hydrocarbons. A rigid pipe may in particular be characterized by its minimum bend radius (MBR). A rigid pipe typically has a MBR of about 8 m to 10 m. Such a MBR makes it possible to keep the rigid pipe at an elongation threshold of less than 3%.

The rigid pipe (5) comprises a metal tube for example made from steel, stainless steel and another type of steel with a variable nickel content, or any other combination of these materials. Typically, the metal tube forming the rigid pipe (5) has an inner diameter between 10 cm and 50 cm, or even higher depending on the applications, and a thickness between 5 mm and 100 mm, or even higher depending on the applications.

The rigid pipe (5) may also comprise a liner making it possible to protect the metal tube from the corrosion phenomenon. For example, the liner may be of the corrosion-resistant metal type such as an alloy of type 316L, Super 13cr, 22 Cr duplex, alloy 28, alloy 825, alloy 2550, alloy 625 or any other corrosion-resistant alloy. Typically, the thickness of the metal coating is between 0.5 mm and 10 mm, or even greater.

Alternatively, the inner coating may be of the polymeric type. In particular, the polymer is chosen from among thermoplastics that are inert with respect to the multiphase mixture of hydrocarbons and temperature-resistant, such as cross-linked polyethylene (PEX). Typically, the thickness of the polymeric coating is between 0.5 mm and 50 mm, or even greater.

The rigid pipe (5) is intended to be and/or is submerged in a body of water (3). It is therefore in contact with the water from the body of water and the metal pipe is thus subject to corrosion. Thus, in order to prevent corrosion of the metal tube, the rigid pipe (5) is preferably provided with an outer protective coating such as a layer of fusion-bonded epoxy or a layer of polypropylene, between 2 mm and 5 mm. Such a thickness in particular makes it possible to guarantee the integrity of the protective layer up to temperatures of 130°C. Advantageously, a protective means of the cathode type with sacrificial anode may be provided in order to improve the corrosion protection of the pipe (5) .

The heating device (1) may further comprise a thermally insulating jacket (6) arranged on the circumference of the rigid pipe (5).

According to this first specific embodiment of the invention shown in figure 8, the thermally insulating jacket (6) is of the fixed type.

More particularly, the thermally insulating jacket (6) comprises at least one layer of two adjacent portions (60), generally at least one layer of 3 adjacent portions arranged on the circumference of the rigid pipe (5). Here, a layer of 4 adjacent portions (60) is shown.

The adjacent portions (60) comprise a thermally insulating material, such as a polyolefin or polyurethane or a mixture of insulating material. When the insulating jacket (6) comprises a superposition of layers of adjacent portions (60), it may comprise different materials depending on the layers. The insulating portions may be straight or helical.

The thickness of the insulating portions (60) is generally between 10 mm and 90 mm.

The insulating jacket (6) further comprises at least one channel extending over at least part of the rigid pipe (5).

More particularly, at least two adjacent portions (60) may form at least one longitudinal channel.

Furthermore, the insulating jacket (6) may comprise separate portions (61) located between the adjacent portions (60) and the rigid pipe (5). The separate portions (61) comprise an insulating or non-insulating material and are arranged in spirals or straight lines. The separate portions (61) may form at least one longitudinal channel intended to receive a heating cable (8).

Around the insulating jacket (6), a maintaining layer (9) is wound by taping. The maintaining layer (9) is advantageously formed by a nonmetallic strip intended to maintain the adjacent portions (60) around the rigid pipe (5). The maintaining layer (9) is for example made up of a polymer material such as polyethylene comprising fibrous reinforcements of the aramid or poly(p-phenyleneterephthalamide) (PPD-T) type. The width of the nonmetallic strip of the maintaining layer (9) is generally between 50 mm and 400 mm and may comprise superposition zones with a width between 0 mm and 320 mm, or a superposition between 0% and 80%.

Furthermore, the heating device (1) comprises at least one peripheral space (7) arranged on the perimeter of the rigid pipe (5). The peripheral space (7) is in particular arranged within the longitudinal channel, and at least one heating cable (8) according to the invention is arranged therein. The heating cable (8) is in particular wound in a spiral within the peripheral space (7) along the rigid pipe (5).

The water from the body of water (3) can diffuse through the maintaining layer (9) and infiltrate within the insulating jacket (6) and the peripheral space (7). The superposition zones of the nonmetallic strip of the maintaining layer (9) participate in the inertia of the water within the insulating jacket (6). Thus, the water is confined and the insulation of the rigid pipe (5) persist despite the diffusion of water. The heating cables (8) are in contact with the water from the body of water (8) having infiltrated within the peripheral space (7). The primary electrically insulating layer (80) made from fluorinated organic polymer forms a tight electrically insulating jacket around the inner electrical element (81) and thus sees to the operation of the heating cables (8) for at least 20 years.

Furthermore, the maintaining strip (9) and/or the thermally insulating jacket (6) may comprise flooding means that may for example be an orifice, a porous membrane or a gate opening out within the peripheral space (7). More specifically, the flooding means are arranged on the thickness of the maintaining strip (9) every 2 m and distributed on the perimeter of the structure (2), thus facilitating the flooding of the peripheral space (7).

According to a second specific embodiment of the invention shown in figure 9, comprising a rigid pipe (5) submerged in a body of water (3) capable of conveying a multiphase mixture of hydrocarbons of the type described in the preceding example, the thermally insulating jacket (6) is of the movable type. More particularly, the thermally insulating jacket (6) comprises at least one removable lid (10) arranged across from the rigid pipe (5), on at least part of the rigid pipe (5).

Typically, the removable lid (10) has a thickness between 50 mm and 100 mm.

The removable lid (10) is suitable for allowing winding and unwinding without significant plastic deformation around a spool, in particular for storage on a surface unit or platform. The removable lid (10) may for example be made from a resilient material such as an elastomer of the rubber or polyurethane type or a syntactic foam, for example with a base of polypropylene with glass microspheres. Preferably, the removable lid (10) is thermally insulating. It for example has a thermal conductivity below 0.3 W/m.K, and in particular between 0.1 W/m.K and 0.3 W/m.K.

The removable lid (10) comprises an outer face and an inner face across from the rigid pipe (5). At the inner face of the removable lid (10), at least one channel is arranged extending over at least part of the length of the removable lid (10). The channel extends parallel to the axis of the removable lid (10) or extends in a zigzag along the removable lid (10).

When the removable lid (10) is facing the rigid pipe (5), the channel comprises water from the body of water (3). The channel is also subject to the operating pressure between 100 bars and 500 bars.

At least one peripheral space (7) is arranged within the channel.

Furthermore, at least one heating cable (8) according to the invention is arranged within the peripheral space (7) on a portion or all of the length of the lid (10). The heating cable (8) is advantageously secured to the removable lid (10). The heating cable (8) is then kept in position on the removable lid (10) using metal or plastic rings or any other suitable means. The heating cable (8) may advantageously be mounted gripped in the channel arranged on the inner face of the removable lid (10). The heating cable (8) is then kept in the channel by friction with or without additional fastening means. The frictional contact is in particular done by contact between the outer surface of the heating cable (8) and the side walls of the channel.

In a third particular embodiment of the invention shown in figure 10, the structure (2) comprises a means for collecting and/or distributing (11) a multiphase mixture of hydrocarbons. The collection and/or distributing means (11) may for example be a manifold arranged on the seabed (4). A manifold is a structure made up of a set of pipes and valves that make it possible to collect and distribute a multiphase mixture of hydrocarbons coming from and/or intended for one or several pipes of flexible or rigid types.

The heating device (1) comprises a peripheral space (7) arranged on the perimeter of the structure (2). In the case at hand, the peripheral space (7) is located on the outer face of the collection and/or distributing means (11) and thus comprises water from the body of water (3). The outer face may be coated with a thermally insulating jacket (6) of the fixed or removable type. In figure 10, the thermally insulating jacket (6) is shown partially in order to simplify and clarify the figure. Advantageously, the thermally insulating jacket (6) completely covers the outer face of the collecting and/or distributing means (11) in order to limit the heat exchanges with the body of water (3). If the invention is implemented with a thermally insulating jacket (6) of the removable type, preferably a removable lid (10) will be used of the type previously described.

The heating device (1) further comprises at least one heating cable (8) according to the invention that may be wound around the collecting and/or distributing means (11) or arranged sinusoidally on the outer face of the collecting and/or distributing means (11) and maintained by rings or fastening collars for example.

If the invention is implemented with a thermally insulating jacket (6), the latter is advantageously arranged between the body of water (3) and said at least one heating cable (8), in order to reduce the heat losses toward the body of water (3) and thus to increase the output of the electrical heating of the collection and/or distributing means (11). When the invention is implemented with a removable lid (10), the heating cables (8) are advantageously secured to the removable lid (10). A method for implementing the heating device (1) for transporting a multiphase mixture of hydrocarbons will now be described.

The method in particular comprises the following steps: - (a) providing a structure (2) capable of conveying a multiphase mixture of hydrocarbons comprising at least one water-permeable peripheral space (7) arranged on the perimeter of said structure (2); - (b) providing at least one heating cable (8) by: - (b1) providing at least one inner electrical element (81) configured to generate thermal energy when it is subjected to an electric current; - (b2) arranging at least one primary electrically insulating layer (80) around said at least one inner electrical element (81), said layer comprising a fluorinated organic polymer configured to form a water-resistant jacket around said at least one inner electrical element (81); - (c) arranging said at least one heating cable (8) within said at least one peripheral space (7); - (d) submerging said structure (2) within a body of water (3).

In particular, the method may comprise sub-steps or additional steps as described in detail below.

During step (a), when the structure (2) comprises a rigid pipe (5) as previously described, the latter is provided in a single segment or several segments.

Preferably, a liner is formed on the inner surface of each segment. To that end, the inside of the rigid pipe (5) is pressurized, for example using a pump making it possible to inject a fluid such as water, oil or any other suitable fluid, in order to press the liner against the inner surface of a segment.

Furthermore, if there are multiple segments to be assembled, one end of a second segment is placed across from one end of a first segment. Then, a junction is done between these two tube segments, for example by welding. Next, an outer liner and inner liner is made at the junction in order to provide thermal insulation as well as corrosion resistance at the welding area.

When the heating device (1) comprises a thermally insulating jacket (6), a sub-step may consist of arranging a thermally insulating jacket (6) around the rigid pipe (5).

In particular, when the thermally insulating jacket (6) is of the fixed type, it is arranged around the rigid pipe (5) during step (a).

When the thermally insulating jacket (6) is of the movable type, more particularly a removable lid (10), it is arranged around the rigid pipe (5), in particular after the step (f) for submersion of the rigid pipe (5).

During a step (b), at least one heating cable (8) is provided. More particularly, the heating cable (8) is provided by carrying out at least sub-steps (b1) and (b2).

During sub-step (b1), at least one inner electrical element (81) configured to generate thermal energy when it is subjected to an electric current is provided. To that end, a set of conductive elements, such as 6 to 500 wires, or even 600 wires, or even 800 wires, made from aluminum- and/or copper-based alloy, are assembled by rolling and wire-drawing. The inner electrical element (81) may further be of the simple, segmented, compact, hollow or braided type. Preferably, the wires are compacted so as to obtain a compactness rate of at least 60%, preferably at least 80%, and still more advantageously at least 90%. A tin deposition may also be done on the outer surface of the inner electrical element (81).

Next, during step (b2), at least one primary electrically insulating layer (80) is arranged around said at least one inner electrical element (81), comprising a fluorinated organic polymer configured to form a water-resistant jacket around said at least one inner electrical element (81).

In a first alternative, the primary electrically insulating layer (80) is extruded in one or several passes so as to form a tube at least 1 mm thick, at least 10 mm thick or at least 100 mm thick around the inner electrical element (81).

In a second alternative, the primary electrically insulating layer (80) is coextruded with an additional layer (82) around the inner electrical element (81). The additional layer (82) can be coextruded in the inner position, i.e., around the inner electrical element (81) or in the outer position, i.e., the primary electrically insulating layer (80) is coextruded around the inner electrical element (81).

Alternatively, each of the layers can be extruded alone. The primary insulating layer (80) can be extruded first around the inner electrical element (81). Then, in a second extrusion step, the additional layer (82) can be extruded around the primary insulating layer (80). Conversely, the additional layer (82) can be extruded first around the inner electrical element (81). Then, in a second extrusion step, the primary insulating layer (80) can be extruded around the additional layer (82).

The melt flow and cooling rates of the primary electrically insulating layer (80) are slow enough to optimize the compactness of the material and to allow the creation of long fluorinated chains while minimizing the risk of air bubble formation in the fluorinated organic polymer. The melt flow rate is for example between 0.5 g/10 min and 8 g/10 min.

The melt flow temperature is above the melting point of the fluorinated organic polymer. Generally, the melt flow temperature is between 260°C and 330°C.

The crystallinity of the fluorinated organic polymer is advantageously greater than 40%.

Then, during step (c), the heating cable (8) is arranged within said at least one peripheral space (7). The heating cable (8) is arranged in a helix or parallel to the axis of the rigid pipe (5) using a taper, for example. Alternatively, the heating cable (8) can be arranged within the peripheral space (7) in S-Z by carrying out the following steps: - depositing said cable along a first helix portion in a rotation direction by a predetermined angle, then - depositing said cable along a second helix portion in a rotation direction opposite the previous direction by a rotation angle equal to the preceding angle, - repeating the two previous steps as many times as necessary.

When several heating cables (8’, 8”, 8”’) are grouped together in a bundle (888), step (b) comprises an additional sub-step (b2’) carried out after step (b2) consisting of arranging an outer sheath (83) around at least two heating cables (8’, 8”) and advantageously at least three heating cables (8’, 8”, 8”’).

During step (b2’), the outer sheath (83) his extruded around at least two heating cables (8’, 8”) and advantageously at least three heating cables (8’, 8”, 8”’). Then, infiltration means (86) are formed by perforating the outer sheath (83) every 1 m, or even every 100 m or every 500 m.

When the method comprises sub-step (b2’), step (c) can be carried out using conventional installation means, such as a spiral winder, thus simplifying the installation of the heating cables (8).

During step (d), the structure (2) is submerged in a body of water (3) from an installation boat, for example. During this step, the structure (2), and in particular the rigid pipe (5), is passed through conventional retaining means, such as tensioners. The tensioners henceforth support a lighter pipe (5), and the gripping pressure needing to be exerted on the pipe (5) is lessened in comparison to that necessary for a PiP. Furthermore, the peripheral space being intentionally flooded, the lack of deterioration on the surface of the pipe (5) during its manipulation is no longer a predominant factor. Indeed, for such pipes (5), surface deterioration can be tolerated. The pipe (5) can therefore be manipulated more easily and be placed within deeper bodies of water (3) relative to the structures of the prior art.

Claims (14)

1. A heating device for transporting a multiphase mixture of hydrocarbons comprising: - a structure (2) submerged in a body of water (3) capable of conveying a multiphase mixture of hydrocarbons; - at least one peripheral space (7) arranged on the perimeter of said structure (2); - at least one heating cable (8) arranged within said at least one peripheral space (7) comprising: - at least one inner electrical element (81) configured to generate thermal energy when it is subjected to an electric current; and - at least one primary electrically insulating layer (80); characterized in that said at least one peripheral space (7) is permeable to water from said body of water (3) and in that said primary electrically insulating layer (80) is configured to form a jacket resisting to said water around said at least one inner electrical element (81), said primary electrically insulating layer (80) comprising a fluorinated organic polymer.

2. The device according to claim 1, characterized in that primary electrically insulating layer (80) has a thickness of at least 1 mm, advantageously at least 10 mm, still more advantageously at least 100 mm.

3. The device according to any one of the preceding claims, characterized in that said at least one heating cable (8) comprises at least one additional layer (82).

4. The device according to claim 3, characterized in that said additional layer (82) comprises a fluorinated organic polymer.

5. The device according to claim 3 or 4, characterized in that said additional layer (82) comprises conductive particles.

6. The device according to one of claims 3, 4 or 5, characterized in that said at least one additional layer (82) is arranged between said at least one inner electrical element (81) and said primary electrically insulating layer (80) or around said primary electrically insulating layer (80).

7. The device according to any one of the preceding claims, characterized in that said fluorinated organic polymer is chosen from among ethylene tetrafluoroethylene (ETFE), perfluoroalkoxy (PFA), fluorinated ethylene propylene (FEP), polytetrafluoroethylene (PTFE) or mixtures thereof.

8. The device according to any one of the preceding claims, characterized in that said fluorinated organic polymer comprises a volumetric uptake of water of less than 1%, less than 0.5% and preferably less than 0.1% according to standard ASTM D570.

9. The device according to any one of the preceding claims, characterized in that said primary electrically insulating layer (80) comprises at least 50 wt% of the fluorinated organic polymer, preferably at least 70 wt% of the fluorinated organic polymer, advantageously exclusively a fluorinated organic polymer.

10. The device according to any one of the preceding claims, characterized in that it comprises: - at least one pipe (5) submerged in a body of water (3) capable of conveying a multiphase mixture of hydrocarbons; - a thermally insulating jacket (6) comprising: - at least one channel extending over at least part of the pipe (5); - said at least one peripheral space (7) being arranged within said at least one channel.

11. The device according to claim 10, characterized in that said thermally insulating jacket (6) comprises at least two adjacent parts (60) forming at least one longitudinal channel.

12. The device according to any one of claims 1 to 9, characterized in that it comprises: - at least one pipe (5) submerged in a body of water (3) capable of conveying a multiphase mixture of hydrocarbons; - at least one removable lid (10) arranged facing the pipe (5) comprising an inner face facing said pipe (5); - said inner face comprises at least one channel extending over at least one part of the length of said at least one removable lid (10); - said at least one peripheral space (7) being arranged within said at least one channel.

13. The device according to any one of the preceding claims, characterized in that said heating structure (2) comprises at least one means (11) for collecting and/or distributing a multiphase mixture of hydrocarbons.

14. A method for implementing the heating device for transporting a multiphase mixture of hydrocarbons comprising the following steps: - (a) providing a structure (2) capable of conveying a multiphase mixture of hydrocarbons comprising at least one water-permeable peripheral space (7) arranged on the perimeter of said structure (2); - (b) providing at least one heating cable (8) by: - (b1) providing at least one inner electrical element (81) configured to generate thermal energy when it is subjected to an electric current; - (b2) arranging at least one primary electrically insulating layer (80) around said at least one inner electrical element (81), said layer comprising a fluorinated organic polymer configured to form a water-resistant jacket around said at least one inner electrical element (81); - (c) arranging said at least one heating cable (8) within said at least one peripheral space (7); - (d) submerging said structure (2) within a body of water (3).