OA19031A - Procédé d'installation en mer d'une conduite sous-marine préchauffée à double enveloppe pour le transport de fluides - Google Patents

Abstract

L'invention concerne un procédé d'installation en mer d'une conduite sous- marine préchauffée à double enveloppe pour le transport de fluides, comprenant successivement, pour chaque nouvelle section de conduite (2) à assembler sur la conduite déjà installée en mer, une étape de préchauffage de l'élément unitaire d'enveloppe interne à l'intérieur de l'élément unitaire d'enveloppe externe de la nouvelle section de conduite, une étape d'assemblage de l'élément unitaire d'enveloppe interne de la nouvelle section de conduite à l'enveloppe interne (4') de la conduite (10) déjà installée en mer, une étape d'assemblage de l'élément unitaire d'enveloppe externe de la nouvelle section de conduite à l'enveloppe externe (6') de la conduite (10) déjà installée en mer, une étape de descente en mer de la nouvelle section de conduite, et la répétition des étapes précédentes pour d'autres nouvelles sections de conduite à assembler de sorte à assurer une mise en précontrainte de la conduite au cours de son installation en mer

Description

Title of invention

Method for installing at sea a pre-heated double-jacket underwater pipe for transporting fluids

Invention background

The present invention relates to the general field of installation at sea of underwater pipes lying at the bottom of the sea or ensuring the bottom-surface connection for the transfer of hydrocarbons, for example oil and gas, from wells submarine production.

More precisely, it relates to submarine pipes with a double jacket of the “Pipe In Pipe” or PIP type, that is to say “pipe in a pipe”, in which an internal jacket transports the fluids and an external jacket coaxial with the internal envelope is in contact with the ambient environment, that is to say with sea water.

The annular space between the two envelopes can be filled with an insulating material or even be emptied of any gas so as to provide thermal insulation for the fluids circulating in the internal conduit. Such submarine coaxial pipes are particularly used in the context of installations at great depths where the water temperature is typically 4 ° C.

Generally, submarine jackets with double shells are assembled ashore in a plurality of pipe sections called "oars", each pipe section being produced from one or more unitary pipe elements, of the order of 10 at 1000m depending on the load carrying capacity of the installation system. These pipe sections are then transported at sea on a laying vessel where they are connected to each other as they are laid at sea (by laying in J, S, unrolled or in float sections).

Laying techniques require connecting each new pipe section to the pipe already installed at sea before lowering this new pipe section into the sea by moving the laying vessel forward. This connection step is typically carried out by butt welding the free steel ends of the respective internal and external envelopes of the new pipe section and of the pipe already installed at sea.

During installation, the internal envelopes of the various pipe sections compress under their own weight and transmit these forces to the external envelope of the pipe. This prestressing induced during the installation in J limits the resistance of the pipe during its passage in the bending zone before resting on the seabed. The addition of mechanical connection elements (“bulkhead” type) is then necessary to limit this prestress. However, the addition of these mechanical connection parts has many drawbacks. In particular, the addition of these parts lengthens the ship time by the need to assemble half-shells on the external envelope of the pipe at the location of the mechanical connection parts. In addition, these half-shells are typically assembled together by means of a weld bead, the quality of which is not optimal. Furthermore, the presence of these mechanical connection elements on the pipe adds cold spots along the latter.

Furthermore, when the pipe installed at the bottom of the sea is in service and the temperature of the fluid it transports reaches moderate to high temperatures (of the order of 50 to 150 ° C), the increase in temperature causes an expansion of the internal envelope of the different sections of the pipe compared to their colder external envelope (because in contact with sea water at a low temperature of the order of 3 to 5 ° C). This expansion of the internal envelope of the pipe sections results in a compression of the internal envelope, the latter being in fact blocked at each end of the underwater pipe by the closing elements of the annular space between the two envelopes. This buckling, if it is concentrated in a section of the pipe, induces bending forces which can cause the ruin of the structure. It is therefore necessary to ensure that the expansion of the pipe is distributed in buckling zones to avoid such concentration.

Document WO 2007/096548 discloses a method of manufacturing a coaxial pipe element comprising an internal pipe and an external pipe with an annular space formed between these pipes and closed at each of its ends. This manufacturing process is characterized in that the internal pipe is subjected to a mechanical tensile stress between the closed ends of the annular space when the internal pipe is out of service.

This manufacturing process applies more specifically to coaxial pipes in which the annular space between the internal pipe and the external pipe is closed, either by cracking, that is to say by deformation of the terminal part of the external pipe. to connect it directly to the surface of the internal pipe, either by connection to a connecting piece directly or through two half-shells forming a tubular sleeve interposed between the ends of the external pipe and the connecting piece. Once the tensile stress has been applied to one end of the internal pipe, the annular space at this end is closed.

The manufacturing process described in this document therefore applies to coaxial pipes necessarily needing to use fasteners between the internal and external pipes of each pipe section.

Document GB 2,492, 883 also discloses a method of installing a pipe in which the prestressing of the individual elements of the internal envelope is effected during the assembly on the ground of the sections of pipe (or oars). However, such an installation method has the drawback that it is necessary to use mechanical connection elements between the different pipe sections with all the drawbacks that these mechanical connection elements have.

Subject and summary of the invention

The main object of the present invention is therefore to propose a method of installing an underwater pipe at sea which does not have the aforementioned drawbacks.

In accordance with (Invention, this object is achieved by a method of installing at sea a preheated underwater pipe with a double jacket for transporting fluids, said pipe comprising a plurality of pipe sections assembled successively at sea to the others, each section of pipe being obtained by assembling on the ground between them at least two unitary elements of internal envelope intended to receive the fluid to be transported and at least two unitary elements of external envelope assembled around the unitary elements of internal envelope by being coaxial with them, the assembly of the unitary elements of external envelope around the unitary elements of internal envelope being carried out without addition of element of mechanical connection, the method comprising successively, for each new section of pipe to be assembled on the pipe already installed at sea:

a step of preheating the unitary inner shell elements inside the unitary outer shell elements of the new pipe section;

a step of assembling one end of the unitary elements of the internal envelope of the new pipe section with the internal envelope of the pipe already installed at sea;

a step of assembling one end of the unitary outer shell elements of the new pipe section with the outer shell of the pipe already installed at sea;

a stage of descent at sea from the new pipe section; and the repetition of the previous steps for other new sections of pipe to be assembled so as to ensure a prestressing of the pipe during its installation at sea.

The method according to the invention is remarkable in particular in that it provides for inducing in the pipe a prestressing force in tension as it is installed at sea by the preheating of the unitary elements of internal envelope of the new sections. driving. This prestressing force is thus applied successively to all or some of the pipe sections at the same time as their installation at sea directly from the laying ship.

The preheating of the individual elements of the internal envelope of the pipe sections is applied so as to initiate a tension preload in the pipe during its laying. In this way, during the production phases (that is to say when the internal envelope of the pipe is traversed by the fluids to be transported), this tension preload makes it possible to reduce the compression of the pipe, and thus minimize the risk of it buckling. qÇ

By minimizing the risk of pipe buckling, we can reduce or even eliminate buckling control systems. Similarly, it is possible to reduce (or even eliminate) the excess thicknesses of the pipe sections subject to buckling. The duration of the offshore campaign can also be reduced.

In addition, the method according to the invention makes it possible to simplify the management of the differential settlement created between the two envelopes of the pipe. In fact, the reduction in the length of the internal envelope under the effect of its own weight relative to the elongation of the external envelope under the combined effect of the weight of the two envelopes can be reduced.

One end of the unitary inner shell elements of each new pipe section can be kept centered inside the corresponding outer shell unitary elements by means of a non-slip and self-centering device. .

In this case, after the descent at sea step of each new pipe section, the anti-slip and self-centering device is advantageously activated.

The preheating of the unitary internal shell elements of each new pipe section can be carried out by induction heating of said unitary internal shell elements.

In an alternative embodiment, the installation at sea of the pipe is carried out by means of a laying vessel comprising a J-laying tower;

the step of preheating the unitary inner shell elements of each new pipe section takes place in a substantially horizontal position of the unitary inner shell elements, the step of assembling the unitary inner shell elements of each new section of pipe to the internal envelope of the pipe already installed at sea comprises the lifting of said unitary elements of internal envelope in the J-laying tower to tilt them into a substantially vertical position;

the step of assembling the unitary outer shell elements of each new pipe section with the outer shell of the pipe already installed at sea comprises beforehand the relative sliding of the unitary outer shell elements with respect to the unitary elements d 'internal envelope; and the step of descent at sea of each new pipe section comprises advancing the forward of the laying vessel with an advance corresponding substantially to the length of the pipe section.

Advantageously, the unitary elements of the internal envelope of certain pipe sections can be assembled with the internal envelope of the pipe already installed at sea without being subjected beforehand to preheating. In the production phase, the pipe sections whose unitary inner shell elements have not been preheated (i.e. which have not been prestressed in tension during its installation) compression at an axial force level lower than the preheated pipe sections. Such non-prestressed pipe sections will have a critical buckling force which will be less than that of the prestressed pipe sections. By not preheating the individual elements of the internal envelope of certain sections of pipe, it is possible to trigger the buckling of the pipe at predefined points during the design, and thus distribute the operating thermal elongations in zones of controlled buckling, at regular intervals across the board. In this way, we can get rid of particularly expensive structures or auxiliary parts which are commonly added along the pipe to cause the pipe to buckle.

In another alternative embodiment, the step of preheating the unitary elements of the internal envelope of each new pipe section is carried out by electric heating of the unitary elements of the internal envelope by means of electric heating cables extending over the entire length of the unitary internal envelope elements.

In this variant, prior to the step of assembling a free end of the unitary elements of the outer casing of each new section of pipe to the outer casing of the pipe already installed at sea, the method may include a step of electrical connection of the electric heating cables of the unitary internal envelope elements to the electric heating cables of the unitary internal envelope element of the preceding pipe section.

In this case, the electrical heating of the unitary elements of the internal envelope of the pipe sections installed during the entire installation at sea of the pipe is advantageously maintained, then this electric heating is deactivated once the pipe has been completely carried out on board the poses then installed at the bottom of the sea.

Brief description of the drawings

Other characteristics and advantages of the present invention will emerge from the description given below, with reference to the appended drawings which illustrate an embodiment thereof devoid of any limiting character. In the figures:

- Figures 1 to 5 show the application of the installation method according to one embodiment of the invention to the installation in J of an underwater pipe.

Detailed description of the invention

The invention applies to the laying (or installation at sea) of an underwater pipe with a double jacket of the “Pipe in Pipe” (or “PIP”) type, that is to say a pipe which comprises an internal envelope intended to transport hydrocarbons coming from production wells and an external envelope arranged around the internal envelope by being coaxial with it and intended to be in direct contact with the surrounding sea water.

This type of underwater pipe is typically used in the offshore production of hydrocarbons at great depths. In the framework of such installations, the jacketed pipes can be assembled on the ground in several pipe sections, each pipe section being formed from several elements of unit length (we also speak of "oars"), order of 10 to 100 m depending on the holding capacity of the laying system, these unitary pipe elements being assembled without the need for mechanical connection elements of the “bulkhead” type (forged connection piece).

During installation (in J or S), the pipe sections are connected to each other on board the ship and as they are installed at sea. More precisely, with J installation, the pipe under -marine is typically descended from the laying ship practically ^ vertical (between + 30 ° and -10 ° relative to the vertical). This quasi-vertical inclination of the pipe decreases as it moves downwards until it follows the slope of the seabed. With the S-pose, the underwater pipe is typically lowered from the laying vessel practically horizontal and then curves to reach the seabed.

Figures 1 to 5 illustrate the different stages of a J-shaped installation according to one embodiment of the installation process at sea according to the invention.

In Figure 1, is shown in a horizontal position a new pipe section 2 intended to be assembled on the pipe portion already installed at sea.

This pipe section 2 comprises several unitary inner casing elements 4 made of steel intended to receive the fluid to be transported and several unitary outer casing elements 6 assembled around the unitary inner casing elements while being coaxial with them.

This pipe section 2 is obtained by sliding the unitary inner shell elements 4 inside the unitary outer shell elements 6 by interposing between these elements at one of their ends an anti-slip device and self-centering 8, this device being in a deactivated state. At the other end of the unitary inner casing elements 4, an installation assistance collar 9 makes it possible to retain the pipe section 2, the latter being able in fact to slide relative to the unitary outer casing elements

6.

An example of such an anti-slip and self-centering device is described in patent application WO 2016/128655. Typically, this device 8 comprises a ring of elastomeric material 8a sandwiched between two metallic annular plates 8b whose internal diameter corresponds substantially to the diameter of the unitary elements of internal envelope and an external diameter corresponds substantially to the diameter of the unitary elements of envelope external. Clamping means (of the screw / nut type 8c for example) of the plates between them make it possible to compress the ring of elastomeric material.

In the next step of the process (FIG. 2), provision is made to preheat the unitary inner envelope elements 4 of the pipe section 2 thus obtained.

This preheating step is carried out on board the laying vessel, when the new pipe section is assembled on the pipe portion already installed at sea.

The preheating of the unitary inner casing elements 4 of steel can be carried out by induction heating of said unitary inner casing elements. It will thus be possible to use an electric heater disposed inside the unitary elements of internal envelope, this heating causing an expansion, and therefore an axial elongation F, of the unitary elements of internal envelope with respect to the unitary elements of external envelope. (which are not subject to preheating).

For example, electric induction heating takes the form of one or more carriages, each carrying a wound ferrite core which is supplied with electricity, the carriages being moved inside the unitary internal pipe elements to heat them. this thanks to the magnetic field that the coiled ferrite core generates. With this type of device, to obtain a rise of 130 ° C. in the temperature of unitary elements of internal steel envelope having a length of 48 m, an outside diameter of 273 mm and a thickness of 20 mm, the preheating time is about 30 min.

For example, preheating will be applied to obtain a temperature of the unitary elements of the internal envelope of the order of approximately 150 ° C., which generates an elongation of said elements of 0.075 m for a pipe section of 48 m. long. In terms of prestressing, this elongation is equivalent to a tensile tension of the unitary internal envelope elements of 323 MPa. For a steel with API 5L X60 grade, i.e. a yield strength of 413 MPa, a tensile working rate of 78% is thus obtained.

During the next step (FIG. 3), once the unitary internal envelope elements 4 of the new pipe section 2 are preheated to the desired temperature, they are assembled to the internal envelope 4 'of the pipe 10 already installed at sea.

For this purpose, the unitary internal envelope elements of the pipe section 2 are placed in the J-shaped laying tower (not shown in the figures) to be tilted there in a substantially vertical position (typically between + 30 ° and -10 ° relative to the vertical).

Once in the laying tower, the lower end of the unitary inner casing elements 4 is welded to the upper end of the unitary inner casing element 4 'of the pipe 10 already installed at sea (the bead of solder 13 is visible in Figure 3). This welding operation is known per se and is therefore not detailed here. It is carried out between the unitary internal envelope elements 4, 4 '. During this stage, the heat loss of the unitary elements of internal envelope 4 which have been preheated is typically 1 Kelvin per hour (with unitary elements of internal steel envelope having a length of 48m, an external diameter of 273 mm and a thickness of 20 mm, as well as a heat exchange factor of 1 Watt per square meter per Kelvin).

As shown in FIG. 4, and in a known manner, the unitary outer shell elements 6 of the new pipe section 2 are then slid down (relative to the unitary inner shell elements) to allow it to be assembled by welding to the unitary outer casing element 6 ′ of the pipe 10 already installed at sea (the weld bead 14 is visible in FIG. 4).

Once the unitary outer shell elements 6 of the new pipeline section 2 are welded to the unitary outer shell element of the pipeline already installed at sea, the new pipeline section 2 is lowered vertically into the sea by moving the vessel laying forward a distance equal to the length of this pipe section 2 (Figure 5).

Before repeating the steps previously described in connection with FIGS. 1 to 5 with a new pipe section to be assembled to the previous one, the anti-slip and self-centering device 8 as described in the patent application WO 2016/128655 to anchor one end of the unitary internal shell elements to the unitary external shell elements, is activated, that is to say that the plates of the device are tightened together to compress the ring in elastomeric material at the required level, this clamping force allowing the anti-slip and self-centering device to take up the force which will be exerted during the cooling of the unitary internal envelope elements to the temperature of the bottom of the sea (4 ° C). .

More specifically, means are provided to allow the anti-slip and self-centering device 8 to take up the force which will be exerted during the cooling of the unitary element of internal envelope. For example, an internal annular shoulder 11 carried by the unitary inner casing element 4 and an external annular shoulder 12 carried by the unitary external casing element 6 make it possible to secure the anti-axial device in axial position. -sliding and self-centering 8 once the unitary inner envelope element has cooled (see Figure 4 in particular).

The example of application of the method according to the invention described above applies to the installation in J of an underwater pipe. Of course, the invention also applies to the installation in S, in place or in floating sections of such a pipe. In known manner, with in particular the S-shaped laying, the underwater pipe is typically lowered from the laying ship almost horizontally and then bends to reach the seabed.

In another embodiment of the invention (not illustrated in the figures), the preheating of the unitary internal envelope elements of each new section of pipe to be assembled on the pipe already installed at sea is carried out by electric heating of these elements inner casing units via a plurality of electric heating cables extending over the entire length of the unitary inner casing elements.

More specifically, these electric heating cables are cables which are typically positioned in the annular space between the internal and external envelopes of the pipe by making them run along the internal envelope over its entire length. These cables are thus electric cables wound around the internal envelope to heat it by Joule effect. This technique, called “heat tradng”, keeps the fluids transported in underwater pipes at a temperature above a critical threshold throughout their journey from the production well to surface installation (and thus avoid the appearance of annoying phenomena in the pipes for the maintenance of good traffic conditions).

In the case of the present invention, it is advantageous to use these electric heating cables to heat the unitary elements of the internal envelope of each new pipe section in order to lengthen them by expanding them during their installation at sea.

To this end, prior to the step of assembling one end of the unitary outer shell elements of each new pipe section with the outer shell of the pipe already installed at sea, the method according to the invention comprises a step of electrically connecting the electric heating cables of the unitary elements of the internal envelope to the electric heating cables of the unitary element of the internal envelope of the pipe already installed at sea.

Preferably, this connection can be made using male and female connectors as described in patent application WO 2016/128656. The use of such connectors ensures electrical continuity between the cables of each new pipe section and the cables of the pipe already installed at sea which is simple, quick and efficient.

During this installation process, the electrical heating of the individual elements of the internal envelope of the various pipe sections installed during the entire installation at sea of the pipe is maintained (the internal envelope of the pipe is prestressed during the entire pipe laying). Once the pipe is completely manufactured on the laying vessel, the electric heating can be deactivated so as to interrupt the electrical supply for maintaining the temperature of the unitary internal envelope elements. Of course, the heating cables can again be used in the production phase to maintain the fluids transported at a temperature above a critical threshold as usually practiced.

It will be noted that the installation method according to this embodiment by electric heating could also be applied to the installation of a pipe with a single envelope (that is to say without an external envelope). Indeed, in this case, the electric preheating of the various pipe sections as they are laid makes it possible to ensure that the pipe is prestressed, this prestressing being taken up again at the end of the laying operation by the ground on which the pipe rests.

It will also be noted that the unitary elements of the internal envelope of certain pipe sections can be assembled with the internal envelope of the pipe already installed at sea without being subjected to preheating beforehand (only certain pipe sections are subjected to prestressing. of their internal envelope). This alternative embodiment makes it possible to obtain a controlled buckling trigger.

For example, for a coaxial pipe of diameter 8 inches internally and 14 inches externally with a length of 8.5 km by a depth of 1300 m, an initial prestress of approximately 0.02% of deformation is introduced during the installation process according to the invention. If the internal pressure of the 260bara operating system and the temperature of 100 ° C are applied, the structure requires 3 buckling mitigation systems, typically in the form of 16-ton metallic structures triggering buckling at this position. . The application of different prestresses according to defined sections makes it possible to eliminate such structures, their function being fulfilled by zones where the installation prestress is maintained, thus becoming zones of instability privileged for buckling. For a project comprising 3 sections of this type, this method also makes it possible to reduce the number of mechanical connection pieces (“bulkheads”) to 6 instead of 11 evenly distributed. The removal of mitigation works simplifies the installation phases of underwater pipes by eliminating the preparatory phases for installation of these structures. The reduction in the number of mechanical connection parts also makes it possible to reduce the time spent at sea to build the pipe and therefore its cost.

The invention described here and its use for finely controlling the allowable bending can also be used in areas where the natural terrain is heckled. Some seabed are damaged and induce significant free ranges of driving. In the case of double-walled pipes, the problem of these free spans is amplified by the weight of the coaxial pipe, and possibly requires expensive retaining structures or riprap. The skillfully selected prestressing of certain zones of the pipe therefore makes it possible to reduce the criticality of the free spans, by controlling the critical bending of the two tubes, and therefore to skillfully limit the retaining structures.

This is particularly advantageous in the case of passing underwater cliffs for example. The same invention and the same principle also apply to areas subject to fishing where the possible grip of gear subjects the pipe to a significant bending or triggers the uncontrolled buckling of the pipe.

It will also be noted that the limitation of the bending induced by the buckling of the pipe and therefore the management of the buckling of this pipe becomes particularly critical in the particular case of the jacketed tubes. In order to reinforce the corrosion resistance properties, it is known to use coaxial conduits, the inner tube of which is lined with a thin layer of materials with particular properties, for example alloys of type 625 or 825. A method of construction of these tubes consists in introducing a jacket into the internal pipe, mechanically linked to this pipe as well as at its ends. The problems of collapse of this shirt are well known. This limitation in bending also applies to the operating phase when the flow in the pipe is stopped. The internal pressure in the pipe drops although the buckling pipe is still subject to bending due to the temperature of the walls which decreases much more slowly than the pressure. This effect can lead to an irreversible collapse of the inner liner, which can make the structure inoperable. The invention described here therefore makes it possible to skillfully limit the bending of the line by fine management of the prestress.

Claims (9)

1. A method of installing at sea a pre-heated double-jacket submarine pipe for transporting fluids, said pipe comprising a plurality of pipe sections (2) assembled at sea one after the other, each pipe section being obtained by assembling on the ground between them at least two unitary elements of internal envelope (4) intended to receive the fluid to be transported and at least two unitary elements of external envelope (6) assembled around the elements unitary inner casing being coaxial to them, the unitary outer casing elements being assembled around the unitary inner casing elements being carried out without adding any mechanical connection element, the method comprising successively, for each new pipe section to be assembled on the pipe already installed at sea: a step of preheating the unitary inner shell elements inside the unitary outer shell elements of the new pipe section; a step of assembling a free end of the unitary internal envelope elements of the new pipe section with the internal envelope (49 of the pipe (10) already installed at sea; a step of assembling a free end of the unitary outer shell elements of the new pipe section with the outer shell (6 ') of the pipe (10) already installed at sea; a stage of descent at sea from the new pipe section; and the repetition of the preceding steps for other new sections of pipe to be assembled so as to ensure a prestressing of the pipe during its installation at sea. 2. Method according to claim 1, in which one end of the unitary inner shell elements of each new pipe section is kept centered inside the corresponding outer shell unitary element by means of a device. (8) anti-slip and self-centering. 3. The method of claim 2, wherein, after the step of descent at sea of each new pipe section, the anti-slip and self-centering device is activated. 4. Method according to any one of claims 1 to 3, wherein the preheating of the unitary inner shell elements of each new pipe section is carried out by induction heating of said unitary inner shell elements. 5. Method according to any one of claims 1 to 4, wherein the installation at sea of the pipe is carried out by means of a laying vessel comprising a J-laying tower; the step of preheating the unitary inner shell elements of each new pipe section takes place in a substantially horizontal position of the unitary inner shell elements, the step of assembling the unitary inner shell elements of each new section of pipe to the internal envelope of the pipe already installed at sea comprises the lifting of said unitary elements of internal envelope in the J-laying tower to tilt them into a substantially vertical position; the step of assembling the unitary outer shell elements of each new pipe section with the outer shell of the pipe already installed at sea comprises beforehand the relative sliding of the unitary outer shell elements with respect to the unitary elements d 'internal envelope; and the step of descent at sea of each new pipe section comprises advancing the forward of the laying vessel with an advance corresponding substantially to the length of the pipe section. 6. Method according to any one of claims 1 to 5, in which the unitary elements of internal envelope of certain sections of pipe are assembled with the internal envelope of the pipe already installed at sea without being subjected beforehand to a preheating. . 7. The method of claim 1, wherein the step of preheating the unitary inner shell elements of each new pipe section is carried out by electric heating of the unitary inner shell elements via electric heating cables s 'extending over the entire length of the unitary internal envelope elements. 8. Method according to claim 1, in which, prior to the step of assembling a free end of the unitary elements of the external envelope of each new section of pipe to the external envelope of the pipe already installed at sea, the method comprises a step of electrical connection of the electric heating cables of the unitary elements of internal envelope to the electric heating cables of the unitary element of internal envelope of the preceding pipe section. 9. The method of claim 8, wherein maintaining the electrical heating of the unitary inner envelope elements of the pipe sections installed during the entire installation at sea of the pipe, then deactivating this electric heating once the pipe is completely completed on board the laying vessel and then installed at the bottom of the sea.