GB2597188A

GB2597188A - Continuous thermal insulation of pipes for transporting fluids

Info

Publication number: GB2597188A
Application number: GB2116063.5A
Authority: GB
Inventors: Dassonville Renaud; Dauphin Raphael; Wattez Henri-Jacques
Original assignee: Perenco SA
Current assignee: Perenco SA
Priority date: 2019-04-24
Filing date: 2020-04-21
Publication date: 2022-01-19
Anticipated expiration: 2040-04-21
Also published as: GB2597188B; CO2021014095A2; WO2020217018A1; MX2021012959A; FR3095491B1; TN2021000215A1; FR3095491A1; BR112021021249A2

Abstract

The invention consists in an insulated pipe (1) for transporting fluids, comprising at least a plurality of insulated-pipe (1) sections comprising an internal pipe (2) that is able to transport a fluid and is inserted coaxially in an external sheath (3), said external sheath (3) and said internal pipe (2) forming, between one another, an annular zone (4) for insulating the fluid transported in the internal pipe (2) from the outside environment surrounding the external sheath (3). The two ends (5; 6) of the internal pipe (2) are able to be connected mechanically to the ends (5; 6) of the internal pipes (2) of other insulated-pipe (1) sections, and the two ends (7; 8) of the external sheath (3) are able to be connected mechanically to the ends (8) of the external sheaths (3) of other insulated-pipe sections.

Description

Continuous thermal insulation of pipes for transporting fluids The present invention concerns a thermally insulated pipe enabling a fluid to be transported, for example petroleum or gas, and a method of assembly of such a pipe.

The invention applies in particular to facilities for producing crude petroleum, onshore or offshore but more generally it also applies to the transport of any effluent not exportable at ambient temperature or of which cooling would, for example, reduce the effectiveness of the treatment downstream of the production zone.

Such facilities require the installation of pipes between the wellheads and facilitates for treatment of the fluids produced (petroleum, water, gas) or injected (water, gas), and between those treatment facilities and the terminals for exporting or importing the treated effluents. These pipes may range in length from a few tens of meters to a few kilometers or possibly tens of kilometers.

According to the characteristics of the effluents transported and the ambient conditions in which the pipes are operated, it may be necessary to keep a minimum temperature within the pipe during the passage of the effluent transported in the event of stoppage of the effluent flow in the pipe.

To ensure a minimum temperature while flowing will make it possible to limit pressure losses in the pipe by maintaining the viscosity of the effluents transported to levels less than those which would result from the temperature one of the ambient environment in which the pipe is installed. Moreover, keeping the transported effluent to a sufficiently high temperature will avoid, or at least limit, solid deposits on the inside wall of the pipes. For example, by keeping the temperature in the pipe above the temperature at which paraffins appear.

Ensuring a minimum temperature in case of flow stoppage for a sufficient duration to enable either the restart of flow, or the emptying of the pipe will make it possible to avoid the blocking of the pipes. For example, this may occur in case of formation of paraffins when transporting an effluent containing hydrocarbons with a high paraffin content, or in case for formation of gas hydrates for the transport of an effluent containing gas and water under pressure.

Numerous solutions exist to keep such pipes at temperature. The known solutions consist of maintaining the temperature either by heating (these are referred to as active solution), or by insulation (these are referred to as passive solutions).

The invention relates more particularly to what are referred to as passive solutions for maintaining the temperature inside the pipe by insulation. More specifically, the invention concerns the structure and the employment of insulated submarine pipes, even though, of course, it can also be implemented onshore.

For simple submarine pipes, various passive insulation solutions exist. One of the known passive solutions consists of applying, onshore, usually in the factory, an insulating material directly on sections of steel tubes. In this case, the insulating material must resist the external environment of the pipe, in particular sea water and the external pressure applied on the pipe when it is under water. The insulation installed in the factory may be a plastic or foam type material resistant to pressure. The sections of tubes insulated in the factory are necessarily of lengths limited to approximately 12 m in general. These insulated tubes may then be pre-assembled in sections of a few tens of meters onshore. This pre-assembly is commonly carried out by welding the tube sections together then by the thermal insulation of the welded zone by adding on, for example, localized insulation. This pre-assembly makes it possible to attain the greatest length that can be manipulated by the boats or barges for the submarine pipe laying. This length depends on the selected form of laying and may be approximately 12 m, 24 m or 48 m according to the number of pre-assembled tube sections. These insulated tubes may also be assembled in sections of greater lengths in the case of what is referred to as "reel-lay", but, here too, this requires welding at each join and the reconstitution of the thermal insulation at the location of the welded joins.

Another known passive solution consists of applying, onshore, also usually in the factory, an insulator resistant neither to sea water nor to the external pressure on the sections of steel tube forming the pipe. In this case, the insulator is then encapsulated in a sleeve which is itself capable of withstanding the pressure. Most commonly, this is another steel tube forming, by welding at the ends of the tube to insulate, a fluid-tight annular space between the inside tube (the pipe) and the outside tube (the sleeve). These prefabricated insulated sections are also typically of a length of approximately 12 m, 24 m or 48 m. They may also be assembled in sections of greater lengths in the case of "reel-lay". Here too, this requires two welds at each join since it is necessary to weld between the two tubes forming the pipe and also the tubes forming the sleeve which envelopes the pipe and its insulator.

In both cases, with the exception of reel-lay, the sections of pre-assembled insulated tubes, of variable but limited length (generally of the order of 12 m, sometimes of the order of 24 m or 48 m), are next transported then assembled together on-site to from the pipe. This final assembly is carried out by welding the ends of the sections placed end-to-end. These welding operations are generally carried out on the laying boat or barge. After the pre-assembled sections of tube have been connected together by welding, it is still necessary to insulate the weld zone. The insulation of the weld zone is carried out subsequently by fastening a piece of added-on insulator or by casting the insulator piece in place around the pipe.

Document FR 3 056 628 Al describes the assembly of an insulated pipe of pipe-in-pipe type by connection together of sections of pipe. The sections of pipe are constituted by an inside envelope and by an outside envelope that are held concentrically together by devices that are anti-slip and self-centering. These devices, only when they have been deactivated, have sliding limited by shoulders between the inside envelope and the outside envelope. The ends of the inside envelope and of the outside envelope of a section of pipe are mechanically connected by welding at the respective ends of the inside envelope and of the outside envelope of another section of pipe.

Document FR 2 879 715 Al describes the assembly of an insulated pipe of pipe-in-pipe type by connection together of several sections of pipes. These sections of pipe are each constituted by an inside pipe and by an outside envelope. Their interconnection is achieved via forged joining parts assembled at the ends of the inside pipes and of the outside envelopes by welding. Next, the joining parts in facing relationship are connected together also by welding. In the case of reel-lay, sections of insulated pipe of several hundreds of meters or possibly of a few kilometers may be laid at a single time.

Nevertheless, this requires both large infrastructures onshore to prefabricate those insulated sections and store them on large reels or carrousels, and dedicated laying means which are heavy and very costly. Moreover, these heavy means are very specific and uniquely present in certain geographical zones, which makes their mobilization still more costly whenever it is required to install a pipe far from existing infrastructures.

These existing methods are both costly and long to implement. As a matter of fact, they first of all require the prefabrication of sections of pre-insulated pipes in specialized yards or factories onshore. This prefabrication includes operations of welding and installation of insulating materials. Next, it is necessary to perform the welding of these prefabricated sections on-site as described above, or implement reel-lay techniques which require specific heavy means both onshore and offshore. Lastly, it is necessary after welding to insulate the cold spots created at each welded join between the sections prefabricated or assembled offshore.

The object of the invention is to provide a solution for passive insulation of pipes that is significantly less costly and easier to implement than the known passive solutions.

To that end, a first aspect of the invention consists in a section of insulated pipe for transporting fluids comprising an inside pipe able to transport a fluid, coaxially inserted inside an outside sleeve, said outside sleeve and said inside pipe forming between them an annular zone making it possible to insulate the fluid transported in the inside pipe from the outside environment surrounding the outside sleeve. A first end and a second end of the inside pipe are each able to be assembled by mechanical connection without welding respectively to a second end of an inside pipe of a second section of insulated pipe, and to a first end of an inside pipe of a third section of insulated pipe; and a first end and a second end of the outside sleeve are each able to be assembled by mechanical connection without welding respectively to a second end of an outside sleeve of the second section of insulated pipe and a first end of the outside sleeve of the third section of insulated pipe.

Thus, the insulation is obtained in continuous manner by assembly of the tubes directly on-site, without requiring welding or creating cold spots in the main part of the pipe.

Advantageously, the first and second ends of the inside pipe have complementary configurations that can enable their insertion-based fitting respectively with the second and first ends of the inside pipes to which they are to be connected.

Preferably, the first and second ends of the outside sleeve have complementary configurations that can enable their insertion-based fitting with the second and third ends of the outside sleeves to which they are to be connected.

Preferably, the inside pipe is slidably mounted in the outside sleeve. Advantageously, the length of the outside sleeve is substantially equal to that of the inside pipe after connection.

Preferably, the annular zone located between the inside pipe and the outside sleeve is maintained by at least one spacer accommodated in the annular zone, and formed from a thermally insulating material facilitating the sliding between the inside pipe and the outside sleeve.

Advantageously, an anti-thermal radiation barrier is applied to the outside face of the inside pipe and/or the inside face of the outside sleeve.

According to a second aspect of the invention, there is provided an insulated pipe for transporting fluids which is made by successive mechanical connections of inside pipes and outside sleeves of the sections of insulated pipe as defined above.

Advantageously, the insulation is provided by the formation of a partial vacuum of air in the annular space formed by the continuous join of the annular zones separating the inside pipes from the outside sleeves of the sections of pipe assembled together.

Thus, the annular space may be partially evacuated from one of the ends of the pipe once the pipe has been laid without any submarine operation or offshore means.

Preferably, the insulated pipe further comprises an intermediate inside pipe having a first end able to be connected to the second end of the inside pipe of the last section of insulated pipe and an intermediate outside sleeve having a first end able to be connected to the second end of the last section of insulated pipe and mounted on the intermediate inside pipe so as to take up the forces of tension and compression, and of which the respective lengths are configured to accommodate the difference in length between the all the inside pipes connected together and all the outside sleeves connected together.

Advantageously, the insulated pipe also comprises an initiation section of insulated pipe able to be connected by a second end to the first end of the inside pipe and to the first end of an outside sleeve of the first section of insulated pipe in order to close in fluid-tight manner one of the ends of the annular space, and having at a first end a pipe beginning fastening flange; and a termination section of insulated pipe able to be connected by a first end to the second end of the intermediate inside pipe and to the second end of an intermediate outside sleeve in order to close in fluid-fight manner the other end of the annular space, and having at a second end a pipe termination fastening flange.

According to a third aspect of the invention, there is provided a method of assembly of an insulated pipe for transporting fluids as defined above, which comprises the following steps: a step of bringing a section of insulated pipe to assemble to one or more pre-positioned sections of pipe; * a step of connecting the inside pipe in which the first end of the inside pipe of a section of insulated pipe to assemble is mechanically connected without welding with the second end of the inside pipe of a pre-positioned section of insulated pipe; * a step of connecting the outside sleeve in which the first end of the outside sleeve of a section of insulated pipe to assemble is mechanically connected without welding with the second end of the outside sleeve of a pre-positioned section of insulated pipe; and repeating the above steps to assemble at least one section of insulated pipe to the last section of insulated pipe previously assembled.

Advantageously, the method of assembly of an insulated pipe for transporting fluids further comprises the following steps: prior to the step of connecting the inside pipe, a first step of sliding the outside sleeve of the section of pipe to assemble in order to leave clear the first end of the inside pipe to connect; and before the step of connecting the outside sleeve, a second step of sliding the outside sleeve of the section of pipe to assemble towards the outside sleeve of the section of pipe already assembled.

Preferably, the assembling method further comprises the following steps: a step of connecting a first end of the intermediate inside pipe to the second end of the inside pipe of the last section of insulated pipe; a step of inserting the intermediate outside sleeve around the intermediate inside pipe; and a step of connecting a first end of the intermediate outside sleeve to the second end of the outside sleeve of the last section of insulated pipe.

Advantageously, in the assembly method: the first step consists of assembling the first section of insulated pipe to the initiation section of pipe; and the second step consists of assembling a second end of the intermediate inside pipe and a second end of the intermediate outside sleeve to the termination section of pipe.

Preferably, the assembly method further comprises a step of establishing a partial vacuum of air in the continuous annular space formed by the connection of all the annular zones of the sections of pipe connected to each other.

It should be noted that the effectiveness of the insulation relative to its low cost of employment makes it possible to envision other applications for the insulation of pipes than those conventionally envisioned with the existing technologies which are reserved for transporting effluents not exportable at ambient temperature and having high added value. For example, the implementation of the invention may be envisioned to conserve heat and thus enable better effectiveness of a separation process downstream of the pipe. On account of the low cost of the invention, even if the effluent could be transported in a pipe not insulated without that leading to excessive head losses or deposits, it may be envisioned to envision its insulation.

Other features and advantages of the invention are shown by the following description of non-limiting embodiment examples of different aspects of the invention. The description refers to the appended drawings which are also given by way of non-limiting embodiment examples of the invention: Figure 1 is a diagrammatic representation of an insulated pipe diagram in partial cross-section; Figure 2 shows a side view in partial cross-section of a section of insulated pipe; Figure 3 shows a side view in partial cross-section of an initiation section of insulated pipe; Figure 4 shows a side view in partial cross-section of a termination section of insulated pipe; Figure 5a shows the method of assembly of a first section of insulated pipe to an initiation section of insulated pipe; Figure 5b shows a first step of the method of assembly of sections constituting an insulated pipe; Figure 5c shows a second step of the method of assembly of sections constituting an insulated pipe; Figure 5d shows a third step of the method of assembly of sections constituting an insulated pipe; Figure 5e shows a fourth step of the method of assembly of sections constituting an insulated pipe; Figure 5f shows a fifth step of the method of assembly of sections constituting an insulated pipe; Figure 6a shows a side view of an intermediate inside pipe; Figure 6b shows a side view of an intermediate outside sleeve; Figure 7a shows a method of assembly of the intermediate inside pipe to the last section of insulated pipe; Figure 7b shows a first step of the method of assembly of the intermediate outside sleeve to the last section of insulated pipe; Figure 7c shows a second step of the method of assembly of the intermediate outside sleeve to the last section of insulated pipe; and Figure 7d shows the method of assembly of the termination section of an insulated pipe to the intermediate inside pipe and to the intermediate outside sleeve.

Below, the description of the invention is given in the context of an insulated submarine pipe for transporting an effluent of petroleum origin from an extraction well to a treatment terminal. This context of implementation of the invention is only described to facilitate the understanding of the invention but cannot in any case be considered as limiting thereof. The same applies for all the other implementation examples of the different features constituting of the invention described below solely for illustrative purposes.

Figure 1 shows an insulated pipe obtained by assembly of several sections of insulated pipe 1. More particularly, a section of insulated pipe 1 has a limited length, in general between one and several tens of meters, and it is therefore necessary to connect a sufficient number of sections of insulated pipe 1 to cover the distance separating the terminals upstream and downstream of the pipe to which it is directly connected. The connection upstream of the insulated pipe, for example with the a wellhead on an offshore platform, is made by a pipe beginning fastening flange 32 which is connected to the first section of insulated pipe 1 by an initiation section of pipe 10 (see Figure 3). The connection downstream of the insulated pipe, for example with a supply point of a treatment terminal, is made by a termination flange 29 which is connected to the rest of the insulated pipe by a pipe termination section 25 (see Figure 4) Overall, the insulated pipe takes the form of an inside tube enveloped by an outside tube with an annular space formed between those two tubes. That annular space makes it possible to thermally insulate the fluid transported inside the inside tube from the ambient environment surrounding the outside tube.

More particularly, in the case of a submarine pipe, the ambient temperature around the pipe increases the viscosity of the fluid transported and may lead to the formation of solid residues, for example the paraffin contained in the fluid if the latter is a hydrocarbon, or the formation of gas hydrate, which may obstruct the pipe.

Figure 2 shows a section of insulated pipe 1 constituting the pipe before its assembly. The section of insulated pipe 1 takes the form of a double envelope tube comprising an inside pipe located coaxially inside an outside sleeve 2. An annular zone 4 is thus formed between the inside pipe 2 and the outside sleeve 3. In fact, to assemble two contiguous sections of insulated pipe 1, the two inside pipes 2 and the two outside sleeves 3 in facing relationship are mechanically connected. Thus, the join between the annular zones 4 forms a continuous annular space between the inside tube and the outside tube of the insulated pipe as illustrated in Figure 1. In order to ensure good insulation of the fluid transported in the insulated pipe, the annular space may be filled with an insulating material or as described below the insulation may also be obtained by generating a partial vacuum of air in the annular space.

The assembly of the sections of insulated pipe 1 is based on the modularity of the pipe. For this, the length of the outside sleeve 3 is substantially equal to that of the inside pipe.

The inside pipe 2 and the outside sleeve 3 are typically of steel. Nevertheless, other materials may be used, for example, according to the constraints posed by the environment in which the pipe is laid, or by the physico-chemical characteristics of the fluid to transport.

The assembly of the sections of insulated pipe 1 is made on a single assembly station, by mechanical connection without welding of the two ends with respect to the two sections of insulated pipe to assemble. As shown in Figure 2, the inside pipe has at its two distal ends 5 and 6, a female connector 5 for one of the ends and for the other a male connector 6. Similarly, the outside sleeve 3 has at its two distal ends 7 and 8, for one of the ends a female connector 7 and for the other a male connector 8. For convenience, the female connectors 5 and 7 are all at the same end of the insulated pipe section 1 and the male connectors 6 and 8 at the other end but an alternating configuration may also be envisioned.

Thus, the assembly of the sections of insulated pipe 1 is carried out by successive and alternating insertion-based fitting of the inside pipes 2 configured to transport the fluid and which thus withstand the internal pressure exerted by the transported fluid, and of the outside sleeves 3 which withstand the ambient pressure and which also make it possible to take up the installation forces of the assembly formed by the inside pipes and their outside sleeves.

The annular zone 4 formed between the inside pipe 2 and the outside sleeve 3 is made secure by spacers 9 formed from a material of low heat conductivity, for example such as polyethylene or polyurethane, which makes it possible to limit local heat losses by condition at the points of contact of the spacers 9 with the outside surface of the inside pipe 2 and with the inside surface of the outside sleeve 3. These spacers 9 are fastened to the outside surface of the inside pipe 34 and provide a low coefficient of friction with the inside surface of the outside sleeve 37 so as to enable relative movement of the inside pipe 2 in the outside sleeve 3.

As indicated above, the insulation is obtained by creating a layer of air in the annular zone 4 separating the inside pipe 2 from the outside sleeve 3.

Additionally, the insulation may be improved by creating a partial vacuum in that same annular zone 4. Additionally, the insulation is improved by installing a barrier against thermal radiation (not illustrated) which may be obtained for example, by a reinforced sheet of aluminum wound around the outside surface of the inside pipe 34, or by a suitable coating (aluminum or equivalent) applied thereon or on the inside surface of the outside sleeve 37, or on both. Other methods for producing a barrier against thermal radiation may also be envisioned.

Figure 3 shows an initiation section of pipe 10. As indicated above in relation to Figure 1, the initiation section of pipe is configured to provide the mechanical connection with the terminal by which the assembly of the pipe commences. This connection is made by the pipe beginning fastening flange 32. The initiation point of the assembly of the insulated pipe may be located upstream of the pipe or downstream according to the direction of flow of the fluid to transport depending on which will be the most practical for laying the insulated pipe. The pipe beginning fastening flange 32 is located at a distal end 12 of an initiation inside pipe 11 of the initiation section of pipe 10. The other distal end 13 of the initiation inside pipe 11 is configured for insertion-based fitting on the complementary shape configured at the opposing distal end of the inside pipe 2 of the first section of insulated pipe 1 to assemble. In Figure 3, the distal end 13 of the initiation inside pipe 11 is a male connector but this could equally well be a female connector. The initiation inside pipe 11 is partially enveloped by an initiation outside sleeve 14, of which the distal end 15 located in the region of the pipe beginning fastening flange 32 is connected to the initiation inside pipe 11 in order to provide the fluid-tightness of the annular space in the region of the insulated pipe by which its installation is initiated. The connection between the initiation outside sleeve 14 and the initiation inside pipe 11 may be produced in different manners such as welding or crimping. The other distal end 16 of the initiation outside sleeve 14 is configured for insertion-based fitting with the complementary shape configured at the opposing distal end of the outside sleeve 3 of the first section of insulated pipe 1 to assemble (see Figure 1). In Figure 3, the distal end 16 of the initiation outside sleeve 14 is also a male connector but it could equally well be a female connector. It is to be noted that the distal end 16 of the initiation outside sleeve 14 which is configured to have an insertion-based fit, is located set back relative to the corresponding distal end of the initiation inside pipe 11. As explained below, this longitudinal offset makes it possible to leave clear the connector of the distal part 13 of the initiation inside pipe 11. At least one spacer 9 makes it possible to maintain the annular zone between the initiation inside pipe 11 and the initiation outside sleeve 14.

Symmetrically, Figure 4 shows a pipe termination section 25. As indicated above in relation to Figure 1, the pipe termination section 25 is configured to provide the mechanical connection with the terminal in the region by which the assembly of the pipe terminates. This connection is made by the pipe termination flange 29. The pipe termination fastening flange 29 is located at a distal end 28 of a termination inside pipe 26 belonging to the termination section of pipe 25. The other distal end 27 of the termination inside pipe 25 is configured for insertion-based fitting with the complementary shape configured at the opposing distal end of the inside pipe 2 of the last section of insulated pipe 1 to assemble (see Figure 1). In Figure 4, the distal end 31 of the termination inside pipe 26 is a connector that is complementary to the corresponding connector of the initiation section of pipe 10. The termination inside pipe 26 is enveloped by a termination outside sleeve 30, of which the distal end 31 located in the region of the pipe termination flange 29 is connected to the termination inside pipe 11 in order to provide the fluid-tightness of the annular space in the region of the insulated pipe by which its installation is terminated. The connection between the termination outside sleeve 30 and the termination inside pipe 26 may also be produced in different manners such as welding or crimping. The other distal end 31 of the termination outside sleeve 30 is configured for insertion-based fitting on the complementary shape configured at the opposing distal end of another outside sleeve (see Figure 4). In Figure 4, the distal end 31 of the termination outside sleeve 30 is also a female connector. It is to be noted that, for the termination section 25, the distal end 31 of the termination outside sleeve 30 which is provided for insertion-based fitting extends beyond the corresponding distal end 27 of the termination inside pipe 26. This longitudinal offset between the distal end 27 of the termination inside pipe 26 and that 31 of the termination outside sleeve 30 makes it possible to compensate for the set back relationship between the distal ends 16 and 13 of the initiation section of pipe 10 (see Figure 3). At least one spacer 9 makes it possible to maintain the annular zone between the termination inside pipe 26 and the termination outside sleeve 30.

The assembly, during progression of the laying of the insulated pipe, of the inside pipes 2 and of the outside sleeves 3 is carried out mechanically without successive welds. This assembly may be carried out either using connector systems (for example connectors that are bolted, screwed, having helical or concentric threads), or by cold insertion-based fitting of the ends as used here to describe the invention. For example, the crimping systems of "ZapLok" or "SureLock" type or any other equivalent system may be used to form this insertion-based fitting system of the inside pipes 2 and/or of the outside sleeves 3. One of the advantages of this type of connection is that contrary to welding, the outside cladding of the inside pipe 2, which may be covered by the barrier against heat radiation, is preserved during the connection. The same applies for the outside sleeve 3 and the annular zone 4, which ensures their continuity along the whole length without it being needed as for the existing solutions to come to add on new insulation at each connection joint.

Figures 5a to 5f show an assembly of the different sections 1 and 10 constituting the insulated pipe with the distal ends of the different inside pipes 2 and 11 bearing male connectors pointing towards the right (in the direction of progression of the laying), but the invention is symmetrical and the male connectors could just as well be disposed in the other direction with the female connectors in the direction of laying. After the initiation section of pipe 10 has been positioned, a first section of insulated pipe 1 to assemble is brought adjacent its connectable end (see Figure 5a). Next, the inside pipe 2 of the first section of pipe 1 to assemble slides within the outside sleeve 3 towards the initiation section of pipe 10 to enable the mechanical connection of the inside pipe 2 of the first section of pipe 1 to assemble with the initiation inside pipe 11 (see Figure 5b). Next, the inside pipe 2 of the first section of pipe 1 to assemble is connected mechanically with the initiation inside pipe 11 (see Figure 5c). Next, the outside sleeve 3 of the first section of insulated pipe 1 to assemble slides towards the initiation section of pipe 10 on the inside pipe 2 which has just been connected to enable the mechanical connection of the outside sleeve 3 of the first section of insulated pipe 1 to assemble with the initiation outside sleeve 14 (see Figure 5 d). The assembly sequence of the first section of insulated pipe 1 with the initiation section of pipe 10 concludes by the mechanical connection of the outside sleeve 3 of the first section of insulated pipe 1 to assemble with the initiation outside sleeve 14 (see Figure 5 e). Next, as shown in Figure 5f, the steps described above in relation with Figures 5a to 5e are repeated to assemble the second section of insulated pipe 1 to the first section of pipe 1 assembled previously, and so forth for all other sections of insulated pipe to assemble until the desired length of insulated pipe is obtained. As shown in Figure 5e, a particular first part is assembled to the end of the insulated pipe by which the assembly of the sections of insulated pipe 1 began. This particular part is the initiation section of pipe 10 illustrated in Figure 3 which, at one end of the insulated pipe, ensures the fluid-tightness of the annular space formed by the joining of the annular zones 4 of all the sections of insulated pipe assembled to each other. Symmetrically, to close and ensure the fluid-tightness of that annular space at the other end of the insulated pipe, another particular part is assembled at the end of the insulated pipe laying sequence, which is the termination section of pipe 25 illustrated in Figure 4 and described above.

Additionally, an intermediate inside pipe 17 and an intermediate outside sleeve 21 are connected mechanically respectively between the inside pipe 2 and the outside sleeve 3 of the last assembled section of insulated pipe 1, and between the termination inside pipe 26 and the termination outside sleeve 30 (see Figure 7d). These two intermediate parts described below and illustrated in Figures 6a and 6b, ensure the take-up of the mechanical forces of tension and compression between the set of inside pipes 2 and the set of outside sleeves 3. Moreover, they make it possible to accommodate the difference in length at the end of assembly between the set of inside pipes 2 and the set of outside sleeves 3.

Figure 6a shows an intermediate inside pipe 17 which, at a first end 18, has a female connection to be connected by that first end 18 to the inside pipe 2 of the last laid section of insulated pipe 1. This could be a male connection if the end 6 of the inside pipe 2 of the last assembled section of insulated pipe is a female connection. The intermediate pipe 17 terminates with a second end 19 provided to be connected to the opposing end 27 of the termination inside pipe 26. The length of the intermediate inside pipe 17 is adapted to the difference in length identified at the end of assembly of the insulated pipe between the set of inside pipes 2 and the set of outside sleeves 3. Furthermore, a shoulder 20 is provided on the outside surface of the intermediate inside pipe 17 as well as a threaded part 35.

Figure 6b shows an intermediate outside sleeve 21 which, like the outside sleeves 3, has at each of its ends 22 and 23 a female or male connection to be connected by one end 22 to the outside sleeve 3 of the last laid section of insulated pipe 1, and by its other end 23 to the opposing end 31 of the termination outside sleeve 30. In the same way as for the intermediate inside pipe 17, the length of the intermediate inside pipe 21 is adapted to the difference in length identified at the end of assembly of the insulated pipe between the set of inside pipes 2 and the set of outside sleeves 3. At its end located adjacent the termination section of pipe 25, the intermediate outside sleeve 21 has a stop flange 24 which extends inwardly thereof. When the intermediate inside pipe 17 is mounted in the intermediate outside sleeve 21, the stop flange 24 comes to bear on a face of the shoulder 20 oriented towards the end 19 of the intermediate inside pipe 17 configured to be connected with the termination inside pipe 26. Before assembly of the termination section of pipe 25, a stop nut 36 is screwed onto the threaded part 35 to press the stop flange 24 of the intermediate outside sleeve 21 against the shoulder 20 of the intermediate inside pipe 17 (see Figure 7c).

Figures 7a to 7d show the final sequence of assembly of the insulated pipe. After the last section of insulated pipe has been assembled as shown in Figure 5f, the intermediate inside pipe is brought to the free end thereof (see upper part of Figure 7a) by its end 18 configured for female connection. Next, the intermediate inside pipe 17 is connected to the inside pipe 2 of the last section of insulated pipe 1 (see lower part of Figure 7a). After the connection of the intermediate inside pipe 17, the intermediate outside sleeve 21 is brought to the intermediate inside pipe 17 by its free end (see upper part of Figure 7b). Next, it is mounted on the intermediate inside pipe 17 until the stop flange 24 comes to bear against the shoulder 20 (see lower part of Figure 7b). A this stage, the stop nut 36 is screwed onto the threaded part 35 of the intermediate inside pipe 17 to come to press the stop flange 24 against the shoulder 20 (see Figure 7c). After the tightening of the nut 36, the termination section of pipe 25 is brought to the intermediate inside pipe 17 (see upper part of Figure 7d). Next, the female connectors 27 and 31 of the termination inside pipe 26 and of the termination outside sleeve 30 are simultaneously connected by insertion-based fitting respectively with the male connector at the end 19 of the intermediate inside pipe 17, and the male connector at the end 23 of the intermediate outside sleeve 21 and this terminates the assembly of the insulated pipe by closing the annular space in fluid-tight manner.

Once the insulated pipe has been fully assembled and laid, the evacuation of the annular space is advantageously carried out by virtue of a vacuum pump connected via a tapping made at one end of the double-envelope of the pipe, for example at the end of the termination outside sleeve 30. The insulation of the inside pipe is thus formed on site very simply once the pipe has been laid which also enables continuous verification of the integrity of the insulation starting from that tapping merely by measuring the pressure in the annular space. In fact, to form the insulation of the inside pipe, it is not necessary to produce the vacuum. A layer of air trapped in the annular space is less effective but sufficient to form insulation, for example, over a short length of pipe.

Although in the above description, the particular aspects of the invention have been described in the context of an insulated submarine pipe of "pipe in pipe" type, it could be implemented in other configurations, in particular for pipelines onshore and/or for the transport of other effluents such as gas.

Claims

CLAIMS1. Section of insulated pipe (1) for transporting fluids comprising an inside pipe (2) able to transport a fluid, coaxially inserted inside an outside sleeve (3), said outside sleeve (3) and said inside pipe (2) forming between them an annular zone (4) making it possible to insulate the fluid transported in the inside pipe (2) from the outside environment surrounding the outside sleeve; said section of insulated pipe (1) being characterized in that a first end (5) and a second end (6) of the inside pipe (2) are each able to be assembled by mechanical connection without welding respectively to a second end (6) of an inside pipe (2) of a second section of insulated pipe (1), and to a first end (5) of an inside pipe (2) of a third section of insulated pipe (1); and a first end (7) and a second end (8) of the outside sleeve (3) are each able to be assembled by mechanical connection without welding respectively to a second end (8) of an outside sleeve (3) of the second section of insulated pipe and a first end (7) of the outside sleeve (3) of the third section of insulated pipe (1).
2. Section of insulated pipe (1) for transporting fluids according to claim 1, wherein the first and second ends (5; 6) of the inside pipe (2) have complementary configurations that can enable their insertion-based fitting respectively with the second and first ends (6, 5) of the inside pipes (2) to which they are to be connected.
3. Section of insulated pipe (1) for transporting fluids according to claim 1 or 2 wherein the first and second ends of the outside sleeve (7; 8) have complementary configurations that can enable their insertion-based fitting with the second and third ends (8; 7) of the outside sleeves (3) to which they are to be connected.
4. Section of insulated pipe (1) for transporting fluids according to one of claims 1 to 3 wherein the inside pipe (2) is slidably mounted in the outside sleeve (3).
5. Section of insulated pipe (1) for transporting fluids according to one of claims 1 to 4 wherein the length of the outside sleeve (3) is substantially equal to that of the inside pipe (2) after connection.
6. Section of insulated pipe (1) for transporting fluids according to claim 4, wherein The annular zone (4) located between the inside pipe (2) and the outside sleeve (3) is maintained by at least one spacer (9) accommodated in the annular zone (4), and formed from a thermally insulating material facilitating the sliding between the inside pipe (2) and the outside sleeve (3).
7. Section of insulated pipe (1) for transporting fluids according to one of the preceding claims wherein an anti-thermal radiation barrier is applied to the outside face of the inside pipe (2) and/or the inside face of the outside sleeve (3).
8. Insulated pipe for transporting fluids characterized in that it is made by successive mechanical connections of inside pipes (2) and outside sleeves (3) of insulated pipe section (1) as defined in the preceding claims.
9. Insulated pipe for transporting fluids according to claim 8, wherein the insulation is provided by the formation of a partial vacuum of air in 15 an annular space formed by the continuous join of the annular zones (4) formed respectively between the inside pipes (2) and the outside sleeves (3).
10. Insulated pipe for transporting fluids according to one of claims 8 or 9 further comprising an intermediate inside pipe (17) having a first end (18) able to be connected to the second end of the inside pipe (2) of the last section of insulated pipe (1) and an intermediate outside sleeve (21) having a first end (22) able to be connected to the second end (8) of the last section of insulated pipe (1) and mounted on the intermediate inside pipe (17) so as to take up the forces of tension and compression, and of which the respective lengths are configured to accommodate the difference in length between the all the inside pipes (2) connected together and all the outside sleeves (3) connected together.
11. Insulated pipe for transporting fluids according to one of claims 8 or 10 comprising: -an initiation section of insulated pipe (10) able to be connected by a second end (13; 16) to the first end (5) of the inside pipe (2) and to the first end (7) of an outside sleeve (3) of the first section of insulated pipe (1) in order to close in fluid-fight manner one of the ends of the annular space, and having at a first end (12) a pipe beginning fastening flange (32); and - a termination section of insulated pipe (25) able to be connected by a first end (27; 31) to the second end (19) of the intermediate inside pipe (17) and to the second end (23) of an intermediate outside sleeve (3) in order to close in fluid-tight manner the other end of the annular space, and having at a second end (28) a pipe termination fastening flange (29).
12. Method of assembly of an insulated pipe for transporting fluids as defined in claims 8 to 11, said method comprising the following steps: a step of bringing a section of insulated pipe (1) to assemble to one or more repositioned sections of pipe; a step of connecting the inside pipe (2) in which the first end (5) of the inside pipe (2) of a section of insulated pipe (1) to assemble is mechanically connected without welding with the second end (6) of the inside pipe (2) of a pre-positioned section of insulated pipe; a step of connecting the outside sleeve (3) in which the first end (7) of the outside sleeve (3) of a section of insulated pipe (1) to assemble is mechanically connected without welding with the second end (8) of the outside sleeve (3) of a pre-positioned section of insulated pipe; and repeating the above steps to assemble at least one section of insulated pipe (1) to the last section of insulated pipe (1) previously assembled.
13. Method of assembly of an insulated pipe for transporting fluids according to claim 12, further comprising the following steps: - prior to the step of connecting the inside pipe (2), a first step of sliding the outside sleeve (3) of the section of pipe to assemble in order to leave clear the first end (5) of the inside pipe (2) to connect; and -before the step of connecting the outside sleeve (3), a second step of sliding the outside sleeve (3) of the section of pipe to assemble towards the outside sleeve (3) of the section of pipe already assembled.
14. Method of assembly according to one of claims 12 to 13 of an insulated pipe for transporting fluids according to one of claims 10 to 11, said method further comprising the following steps: - a step of connecting a first end (18) of the intermediate inside pipe (17) to the second end (6) of the inside pipe (2) of the last section of insulated pipe (1); - a step of inserting the intermediate outside sleeve (21) around the intermediate inside pipe (17); and - a step of connecting a first end (22) of the intermediate outside sleeve (21) to the second end (8) of the outside sleeve (3) of the last section of insulated pipe (1).
15. Method of assembly according to claim 14 of an insulated pipe for transporting fluids according to claim 11, wherein: - the first step consists of assembling the first section of insulated pipe (1) to the initiation section of pipe (10); and - the second step consists of assembling a second end (19) of the intermediate inside pipe (17) and a second end (23) of the intermediate outside sleeve (21) to the termination section of pipe (25).
16. Method of assembly according to one of claims 12 to 15 of an insulated pipe for transporting fluids according to one of claims 7 to 11, further comprising: a step of establishing a partial vacuum of air in the continuous annular space formed by the connection of all the annular zones (4) of the sections of pipe connected to each other.