EP2496400A1

EP2496400A1 - Method for producing a protective coating on a tube, and tube comprising a coating obtained by means of such a method

Info

Publication number: EP2496400A1
Application number: EP10792959A
Authority: EP
Inventors: Bernard Cavalie
Original assignee: Eupec Pipecoatings France SAS
Current assignee: Eupec Pipecoatings France SAS
Priority date: 2009-11-02
Filing date: 2010-11-02
Publication date: 2012-09-12
Also published as: BR112012010361A2; WO2011051641A1; US20120261020A1; CA2778986A1; FR2952159B1; FR2952159A1

Abstract

The invention relates to a method which comprises: moving the tube (1) in a longitudinal translation movement and simultaneously in rotation; heating the tube (1); depositing a layer of epoxy powder (9) on the outer surface of the tube (1); winding at least one strip of an adhesive material in paste form onto the epoxy layer (9); winding at least one strip of polypropylene in paste form onto said strip of adhesive material (11) such as to form a polypropylene layer (16); cooling the assembly thus obtained; heating the skin of said layer of polypropylene (16) and winding on at least one strip of non-compressible, thermally insulating elastomer in paste form such as to form an elastomer layer (22).

Description

Process for producing a protective coating on a tube and tube having a coating obtained by such a process

The present invention relates to a method for producing a protective coating on a tube, and in particular on a pipeline tube that can be immersed.

Pipeline tubes are generally used to transport hydrocarbons and it is important that the temperature of the products transported does not reach a lower limit temperature below which large deposits in the tubes are formed.

Furthermore, when in use, the tubes are in permanent contact with seawater. There is therefore a significant risk of corrosion of the tube, so that the chemical properties of the coating are also very important.

Therefore, the tubes must be coated with an insulating jacket to keep the hydrocarbons transported to the desired temperature to avoid clogging phenomena. Indeed, if the tubes are not sufficiently isolated, it can form inside these tubes a wax deposit or a hydrate deposit which slows the flow and gradually obstructs the tubes.

The insulating envelope must therefore be sufficiently sized to avoid these phenomena.

In general, the seawater in which the tubes are laid is cooler when the depth increases, the quality of the insulating coating and its behavior are therefore extremely important.

Particular problems arise when the pipeline tubes are laid in deep or deep sea, which corresponds to depths greater than about 3000 meters. Indeed, when the depth increases, the temperature of the water decreases. Therefore, to maintain the desired temperature in the tube, the coating must have better performance characteristics at greater depths than when the tube is submerged at shallower depths.

Moreover, at great depths, the tubes are subjected to a significant hydrostatic pressure, greater than 300 bar at a depth greater than 3000 meters. The material used for the coating must therefore have a higher compressive strength as depth is important.

It is known to coat the pipeline tubes with an insulating envelope formed from polypropylene foam. However, such an envelope has neither the insulating capacity nor the mechanical strength required at great depths.

Indeed, when they are subjected to significant pressure, these foamed coatings are compressed, which causes a densification of the insulating layer and therefore an increase in its thermal conductivity. Due to this compression and the entry of water into the cells of the foam, the thermal conductivity of this material tends to 0.22 Wm ^-1 .K ^-1 .

Finally, polypropylene is a very rigid material, the risk of cracks and therefore mechanical embrittlement are important.

It is also known, to improve the insulating properties of polypropylene, to charge this material with hollow glass microbeads. However, this method also has disadvantages when the tubes are laid at great depths. Indeed, because of their manufacturing process, glass microbeads are not homogeneous with respect to their resistance to pressure. As a result, at high operating pressures, a large percentage of these microbeads break, causing cracks in the insulating material. These cracks allow the passage of water and thus lead to a reduction, not only the mechanical properties of the material, but also its insulating properties.

The object of the present invention is to propose a process for obtaining a coating on a tube, and in particular on a pipeline tube, which makes it possible to overcome the drawbacks mentioned above.

The subject of the invention is therefore a method for producing a protective coating on a tube, in particular on a submergible pipeline tube, comprising the steps of:

moving the tube in longitudinal translation and simultaneously rotating said tube,

heating the tube to a temperature between 160 ° C and 230 ° C, and preferably between 180 ° and 220 ° C, - form from an epoxy powder an epoxy layer on the outer surface of the tube,

winding on the epoxy layer at least one band of adhesive in the pasty state to form an adhesive layer,

winding on said adhesive layer at least one polypropylene strip in the pasty state to form a first polypropylene layer, characterized in that it also comprises the steps of:

- Cool the assembly thus obtained to a temperature of about 80 ° C,

- heating the skin of said first polypropylene layer to a temperature of at least 110 ° C,

- Wrap at least one band of a heat insulating elastomer and incompressible in the pasty state to form a first elastomer layer.

According to other features of the invention:

after forming said first elastomer layer,

the whole obtained is cooled to a temperature of the order of 80.degree.

the skin of the first applied elastomer layer is heated to a temperature of at least 110.degree.

at least one pasty polypropylene strip is deposited on said first elastomer layer to form a second layer of polypropylene,

after forming the second layer of polypropylene,

the whole obtained is cooled to a temperature of the order of 80.degree.

the skin of the second polypropylene layer is heated to a temperature of at least 110.degree.

at least one strip of said pasty elastomer is deposited on said polypropylene layer to form a second elastomer layer.

said elastomer has a thermal conductivity of less than 0.15 Wm ^-1 .K ^-1 , said elastomer comprises at least one crosslinkable elastomer selected from butyl rubber, halobutyls and brominated copolymers of isobutylene and para-methylstyrene and at least one non-crosslinkable elastomer of low thermal conductivity,

the epoxy powder is deposited by electrostatic spraying and said powder is agglomerated by melting,

the epoxy layer has a thickness of between 10 and 800 micrometers,

the adhesive layer has a thickness of between 10 and 1000 micrometers, and preferably between 300 and 600 micrometers,

said strips of said first or second elastomer layers or said strips of said first or second polypropylene layer or said strips of said adhesive layer are obtained by lateral extrusion with respect to the direction of movement of the tube,

said strips of said first or second elastomer layers or said strips of said first or second polypropylene layers or said strips of said adhesive layer are obtained by longitudinal extrusion with respect to the direction of movement of the tube,

said strips of said first or second elastomer layers or said strips of said first or second polypropylene layer or strips of said adhesive layer are obtained by coextrusion,

said strips of said first or second elastomer layers are put under pressure by means of a pressure roller,

each of said strips of said first elastomer layer has a thickness of between 2 and 30 mm.

said strips of said first or second elastomer layers are extruded at a temperature of between 140 ° C and 230 ° C and preferably between 180 ° C and 200 ° C.

The subject of the invention is also a tube comprising a coating produced according to the method defined above, characterized in that it successively comprises an epoxy layer, an adhesive layer, a first polypropylene layer and a first layer of polypropylene. elastomer.

According to other features of the invention: the tube further comprises, above the first elastomer layer, a second layer of polypropylene,

the tube further comprises, above the second polymer layer, a second elastomer layer.

The invention will be better understood with the aid of the description which follows, given solely by way of example and with reference to the indexed drawings, in which:

FIG. 1 is a cross-sectional view of a tube coated with a coating according to a first embodiment of the invention,

FIG. 2 is a schematic view of an installation for implementing the method according to a first embodiment of the invention,

FIG. 3 is a cross-sectional view of a tube coated with a coating according to a second embodiment of the invention,

FIG. 4 is a schematic view of an installation for implementing the method according to a second embodiment of the invention,

FIG. 5 is a cross-sectional view of a tube coated with a coating according to a third embodiment of the invention, and

- Figure 6 is a schematic view of an installation for implementing the method according to a third embodiment of the invention.

According to a first embodiment of the tube comprising the coating according to the invention, represented in FIG. 1, the tube 1, which is for example a pipeline tube intended to be immersed at depths greater than 3000 m, is coated successively

an epoxy layer 9,

a layer of adhesive 11, composed of at least one strip of adhesive 12,

a polypropylene layer 16, composed of at least one polypropylene strip 17, and

an elastomer layer 22 composed of at least one elastomer strip 23.

According to the first embodiment, the epoxy layer 9 has a thickness preferably of between 10 and 800 microns and preferably between 150 and 300 microns; the adhesive layer 11 has for example a thickness of between 10 and 1000 micrometers and preferably between 300 and 600 micrometers; the polypropylene layer 16 has for example a thickness of between 1 mm and 20 mm and preferably between 3 mm and 5 mm and the elastomer layer 22 has a thickness preferably of between 2 mm and 150 mm, each of the strips of applied elastomer 23 having for example a thickness of between 2 and 30 mm.

The method according to the invention makes it possible to produce a protective coating on a tube 1, and in particular on a pipeline tube intended to be immersed at depths greater than 3000 m.

During the various steps of the method, the tube 1 is displaced in longitudinal translation and simultaneously rotated in an installation 3, at an angular speed allowing an advance of between 1 cm and 20 cm at each rotation of the tube 1 and a peripheral speed of rotation of the tube 1 preferably between 10 and 50 m / min for an average diameter of the tube 1 between 25 mm and 1500 mm.

Figure 2 shows the installation 3 which allows the implementation of the method which leads to the tube 1 comprising the coating according to the first embodiment of the invention.

The tube 1 is first heated by means of heating means 5 to a temperature of between 160 ° C. and 230 ° C. and preferably between 180 ° C. and 220 ° C. These heating means are for example at least one induction heating ring or any other appropriate heating means.

Then, an epoxy powder is deposited on the outer surface of the hot tube 1 by electrostatic spraying, for example by means of a spray box 7. This epoxy powder adheres to the hot surface of the tube 1 by electrostatic effect and melts in contact with the tube 1 hot to form on the tube 1 a homogeneous epoxy layer 9.

The epoxy layer 9 has a thickness preferably between 10 and 800 micrometers.

The epoxy layer 9 is then wound on the epoxy layer 9 and before the cooling of this epoxy layer 9, at least one band 12 of an adhesive in the pasty state to form an adhesive layer 11 using an extrusion machine. 13. The at least one adhesive strip 12 may be applied by lateral extrusion with respect to the direction of movement of the tube 1, by longitudinal extrusion or by coextrusion.

According to another embodiment of the invention, the adhesive layer 11 may also be applied by continuous spraying from an adhesive powder.

The adhesive layer 11 has a thickness of between 10 and 1000 micrometers, and preferably between 300 and 600 micrometers.

The adhesive material comprises for example by weight:

from 59 to 94% polypropylene or a propylene / ethylene or propylene / ethylene / butene 1 random copolymer, or mixtures thereof with one or more plastomeric polymers chosen from ethylene / vinyl / vinyl acetate copolymers, LDPE, HDPE, polyamide polyurethane copolymers,

from 5 to 40% of a polymer or a mixture of elastomeric polymers chosen from EPR, EPDM, SEBS and SBS block copolymers, and ethylene / ethyl acrylic copolymers,

from 1 to 10% of polypropylene modified with maleic anhydride or isophorone bis maleic acid for acrylic acid.

At the same time as the at least one adhesive strip 12 is wound up, at least one polypropylene strip 17 in the pasty state is wound on the adhesive layer 11 at least once by means of an extrusion machine 15 to obtain an polypropylene layer 16. Several extrusion machines 15 may be arranged next to each other to deposit a plurality of polypropylene strips 17 on one another to form the polypropylene layer 16.

The at least one polypropylene strip 17 may be applied by lateral extrusion with respect to the direction of movement of the tube 1, by longitudinal extrusion or by coextrusion.

The polypropylene layer 16 has a thickness of preferably between 1 mm and 20 mm and preferably between 3 mm and 5 mm.

The polypropylene used to form the polypropylene strips 17 comprises, by weight, from 92 to 100% of a thermoplastic polymer chosen from a crystalline copolymer of polypropylene containing 2 to 25% by mole of ethylene and / or C4-C10 alpha olefin, composition heterophasic comprising a polymer of the aforementioned type and one or more elastomeric olefinic copolymers.

The polymers that can be used in this process are:

an isotactic polypropylene with an isotactic index of up to 99,

a propylene / ethylene random copolymer with an ethylene content ranging from 1 to 6% by weight and preferably from 2 to 4% by weight,

a propylene / ethylene / 1-butene random copolymer with an ethylene content of 2 to 3% by weight and 1. butene of 4.5 to 5.6% by weight - a mixture of the abovementioned polymers with an EPR and EPDM elastomer, the EPR (ethylene propylene rubber) being optionally crosslinked and preferably containing from 5 to 40% by weight of elastomer,

heterophasic compositions obtained by stereospecific sequential polymerization of polypropylene with ethylene and / or alpha-olefin C4-C10, optionally in the presence of a small amount of L-diene such as butadiene, 1,4 hexadiene, 1,5 hexadiene and ethylene norbornene; 1.

Examples of C 4 -C 10 alpha olefin which may be present in the previously mentioned polymers are butene-1, 4, methylpentene-1 and hexene-1.

In the heterophasic compositions, ethylene and / or alpha olefins may be present in amounts up to 50% by weight.

The total thickness of the three layers 9, 1 1, 1 6 is between 1 mm and 30 mm and preferably between 3 mm and 6 mm.

Once the polypropylene layer 16 has been deposited, the tube 1 coated with the already formed layers 9, 11, 16 is cooled by passing through a cooling tunnel 18, where it is sprayed with water and / or of air to reach a temperature of the tube 1 of the order of 80 ° C.

At the end of this cooling step, the skin of the polypropylene layer 1 6 is heated superficially by means of a suitable heating means 19, for example by heating by infrared radiant, until a temperature is reached. of the polypropylene layer 16 at least 110 ° C. At least one band 23 of elastomer in the paste state is then immediately wound on the polypropylene layer 16 by means of an extrusion machine 21.

In order to form the elastomer layer 22, composed of several elastomer strips 23, for each new elastomer strip 23 to be applied, the tube 1 coated with the already formed layers 9, 1 1, 16 and elastomer strips 23 already deposited by passing it through a cooling tunnel 24, where it is sprayed with water and / or air until a temperature of the tube 1 of the order of 80 ° C is reached.

The skin of the last strip of elastomer is then superficially heated.

23 applied to the tube 1 via a suitable heating means, for example using infrared radiant heating, until a skin temperature of at least 110.degree. .

A band 23 of elastomer in the paste state is then wound on the last elastomer strip 23 applied using an extrusion machine 26. At the outlet of the extrusion machine 26, the temperature of the elastomer strip 23 is between 140 ° C and 230 ° C and preferably between 180 ° C and 200 ° C. During the winding of the strip 23, to allow the elastomer to be self-adhesive, the elastomer strip 23 is pressurized approximately 3 to 4 bar by means of a setting means. known type of pressure, for example by means of a silicone roll of hardness 23 Shore A.

This succession of operations is repeated until an elastomer layer 22 is obtained at the desired thickness. For this, side by side are placed as many blocks consisting of a cooling tunnel 24, a suitable heating means 25, for example an infrared radiant heating, an extrusion machine 26 and a means known type of pressing, that it is desired to deposit elastomer strips 23 to form an elastomer layer 22 to the desired thickness.

It will thus be possible to obtain a thickness of the elastomer layer 22, for example between 2 mm and 150 mm, each of the strips 23 applied having, for example, a thickness of between 2 and 30 mm.

The elastomers that can be used in this process are heat-insulating and incompressible elastomers comprising at least one elastomer crosslinkable agent selected from the group consisting of butyl rubber, halobutyls and brominated copolymers of isobutylene and para-methylstyrene and at least one non-crosslinkable elastomer of low thermal conductivity, for example of thermal conductivity less than 0.15 Wm ^-1 .K ^"1 .

In this process, the elastomer strips 23 may be applied by lateral extrusion with respect to the direction of movement of the tube 1, by longitudinal extrusion or by coextrusion.

In order to be able to apply the elastomer by extrusion, the fluidity of the elastomer is adjusted by adding a more fluid polymer.

All the steps can be performed on the same coating line.

However, if a different coating line is used for the application of the elastomer strips 23, the surface of the polypropylene layer 16 is cleaned with a solvent, in order to degrease it and remove any traces of contaminants or plasticizers, after the passage of the tube 1 coated layers already formed 9, 1 1, 16 in the cooling tunnel 18 and before the heating of the skin of the polypropylene layer 16 through the heating means 19. The solvent is by MEK (methyl ethyl ketone) deposited using a textile strip or by any other means or with another solvent applied in the vapor phase or a solvent applied in an aqueous medium. In the case where the solvent is applied in an aqueous medium, the surface of the cleaned polypropylene layer 16 is then rinsed with tap water and then dried by a hot air knife.

Once the elastomer layer 22 has reached the desired thickness, the tube 1 thus coated with the protective envelope is always kept in rotation and in translation and is transferred to a cooling tunnel 28 where it is sprayed with water. air and / or water in order to accelerate the solidification of the coating.

According to a second embodiment of the invention, represented in FIG. 3, the coating of the tube 1 according to the invention further comprises, above the elastomer layer 22, a second layer of polypropylene 30, formed of at least one polypropylene strip 31. In this second embodiment, the epoxy layer 9, the adhesive layer 11, the first polypropylene layer 16 and the elastomer layer 22 are arranged successively. on the tube 1 below the second polypropylene layer 30 and have the same characteristics as in the first embodiment.

The second polypropylene layer 30 has a thickness preferably of between 1 and 6 mm.

The installation allowing the implementation of the method resulting in the tube 1 comprising the coating according to the second embodiment is shown in FIG. 4.

To form on the tube 1 the coating according to the second embodiment, the steps of the method according to the first embodiment of the invention are reproduced until the elastomer layer 22 has been formed.

After the formation of the elastomer layer 22, the tube 1 coated with the layers 9, 1 1, 16, 22 already formed in the cooling tunnel 28 is passed until a temperature of the tube 1 of the order of 80 ° C.

The surface of the elastomeric layer 22 can then be cleaned with a solvent to degrease it and remove any traces of contaminants or plasticizers. The solvent is for example MEK (Methyl Ethyl Ketone) deposited using a textile web or by any other means or with another solvent applied in the vapor phase or a solvent applied in an aqueous medium. In the case where the solvent is applied in an aqueous medium, the surface of the elastomer layer 22 cleaned is then rinsed with tap water and dried by a hot air knife.

Then, the skin of the elastomer layer 22 is heated superficially by means of a suitable heating means 29, for example by infrared radiant heating, until a skin temperature of the elastomer layer is reached. 22 at least 110 ° C.

At least one polypropylene strip 31 is then rolled in the pasty state on the elastomer layer 22 to form the second polypropylene layer 30 by means of an extrusion machine 32.

Several extrusion machines 32 may be arranged next to each other to deposit a plurality of polypropylene strips 31 on top of one another to form the second polypropylene layer 30. The tube 1 thus coated with the layers 9, 1 1, 16, 22, 30 is transferred to a cooling tunnel 33 where it is sprayed with air and / or water in order to accelerate the solidification of the coating.

This at least one polypropylene strip 31 may be applied to the elastomer layer 22 by lateral extrusion with respect to the direction of movement of the tube 1, by longitudinal extrusion or by coextrusion.

The thickness of this second polypropylene layer 30 is preferably between 1 and 6 mm.

This second embodiment has the advantage of improving the resistance to indentation of the coating according to the invention, since polypropylene is a harder material than the elastomer.

Furthermore, the last layer of polypropylene applied plays, because of the hydrophobic nature of polypropylene, which has a water absorption coefficient of the order of 0.1%, a role of barrier to seawater, this makes it possible to avoid the diffusion of water in the elastomer layer 22 and thus the hydrolysis phenomena that may lead to a reduction in the insulating properties of the coating.

According to a third embodiment of the invention, represented in FIG. 5, the coating of the tube 1 according to the invention further comprises, above the second layer of polypropylene 30, a second layer of elastomer 35 formed at least one elastomer strip 36. In this third embodiment, the epoxy layer 9, the adhesive layer 1 1, the first polypropylene layer 16, the elastomer layer 22 and the second polypropylene layer 30 are successively arranged on the tube 1 below the second elastomer layer 35 and have the same characteristics as in the first and second embodiments.

The second elastomer layer 35 has a thickness preferably of the order of 1 mm.

The installation for implementing the method leading to the tube 1 comprising the coating according to the third embodiment is shown in FIG. To form on the tube 1 the coating according to the third embodiment, the steps of the method according to the second embodiment of the invention are reproduced until the formation of the polypropylene layer 30.

After the formation of this second layer of polypropylene 30, the tube 1 coated with the layers 9, 1 1, 16, 22, 30 already formed in the cooling tunnel 33 is passed until a temperature of the tube 1 of the tube 1 is reached. order of 80 0.

The surface of the second polypropylene layer 30 can then be cleaned with a solvent to degrease and remove any traces of contaminants or plasticizers. The solvent is for example MEK (Methyl Ethyl Ketone) deposited using a textile web or by any other means or with another solvent applied in the vapor phase or a solvent applied in an aqueous medium. In the case where the solvent is applied in an aqueous medium, the surface of the cleaned polypropylene layer is then rinsed with tap water and dried by a hot air knife.

Then, the skin of the second polypropylene layer 30 is superficially heated by means of a suitable heating means 37, for example infrared radiant heating, until a skin temperature of the second polypropylene layer 30 is reached. at least 1 10 ° C.

Next, at least one elastomer strip 36 in the paste state is rolled onto the second polypropylene layer 30 by means of an extrusion machine 38 to form a second layer of elastomer 35. At the exit of the machine, In extrusion 38, the temperature of the elastomeric strip 36 is between 140 ° C and 230 ° C and preferably between 180 ° C and 200 ° C.

To form the elastomer layer 35, composed of several elastomer strips 36, for each new elastomer strip 36 to be applied, the tube 1 coated with the already formed layers 9, 1 1, 16, 22 is first cooled. , And elastomer strips 36 already deposited by passing it through a cooling tunnel 39, where it is sprayed with water and / or air until a tube temperature of about 80 is reached. ° C.

The skin of the last elastomer strip 36 applied to the tube 1 is then superficially heated by means of heating means 41. suitable, for example by infrared radiant heating, until a skin temperature of at least 110 ° C is reached.

A band 36 of elastomer in the paste state is then wound onto the last strip 36 of elastomer applied using an extrusion machine 43. During the winding of the strip 36, to enable the elastomer to be self-adhesive, the elastomer strip 36 is pressurized to about 3 to 4 bar by means of pressurizing means of known type, for example by means of a roller in hardness silicone 23 shore A.

This succession of operations is repeated until a second layer of elastomer 35 is obtained at the desired thickness. For this purpose, one will place side by side as many blocks consisting of a cooling tunnel 39, a suitable heating means 41, for example an infrared radiant heating, an extrusion machine 43 and a means known type of pressing that is desired to deposit elastomer strips 36 to form a second elastomer layer 35 to the desired thickness.

It will thus be possible to obtain a thickness of the second elastomer layer 35 of the order of 1 mm.

Then, the tube 1 thus coated with the layers 9, 1 1, 16, 22, 30, 35 is transferred to a cooling tunnel 47, where it is sprayed with air and / or water in order to accelerate the solidification of the coating.

This at least one elastomer strip 36 may be applied to the second polypropylene layer 30 by lateral extrusion with respect to the direction of movement of the tube 1, by longitudinal extrusion or by coextrusion.

This third embodiment has the advantage, in addition to the advantages presented by the first two embodiments, to secure in the deep sea the laying of the tubes provided with their protective coating. Indeed, the elastomer has a coefficient of friction about 1 0 times higher than polypropylene, which reduces the risk of sliding of the tube out of the laying structures and therefore reduce the risk of loss of the tube.

In all embodiments, the application of the elastomer in successive strips is advantageous because the insulation can be cooled more easily, which allows the application of a greater total thickness of elastomer, since It is difficult to support a tube covered with a thick layer of hot material in the pasty state without there being deformation, sagging or ovalization of the layer.

Surprisingly, it has been found that if one simply winds successively different strips of elastomer on each other, they do not adhere to each other. The process of cooling the tube coated with the layers already formed, then heating only the skin of the last strip of elastomer applied, before applying a new elastomer strip overcomes this problem and to achieve a homogeneous layer without delamination.

Claims

1. - Process for producing a protective coating on a tube (1), in particular on a submergible pipeline tube, comprising the steps of:

moving the tube (1) longitudinally and simultaneously rotating said tube (1),

heating the tube (1) to a temperature of between 160 ° C. and 230 ° C. and preferably between 180 ° C. and 220 ° C.,

forming, from an epoxy powder, an epoxy layer (9) on the outer surface of the tube (1),

- winding on the epoxy layer (9) at least one adhesive strip (12) in the pasty state to form an adhesive layer (1 1),

winding on said layer of adhesive (1 1) at least one band (17) of polypropylene in the pasty state to form a first layer of polypropylene (16),

characterized in that it also comprises the steps of:

- Cool the assembly thus obtained to a temperature of about 80 ° C,

- heating the skin of said first polypropylene layer (16) to a temperature of at least 110 ° C, and

- Wrap at least one band of an elastomer (23) thermal insulation and incompressible in the pasty state to form a first layer of elastomer (22).

2. Method according to claim 1, characterized in that after forming said first elastomer layer (22),

the whole obtained is cooled to a temperature of the order of 80.degree.

the skin of the first applied layer of elastomer (22) is heated to a temperature of at least 110.degree.

at least one pasty polypropylene strip (31) is deposited on said first elastomer layer (22) to form a second polypropylene layer (30).

3. Method according to claim 2, characterized in that after forming the second layer of polypropylene (30), the whole obtained is cooled to a temperature of the order of 80.degree.

the skin of the second polypropylene layer (30) is heated to a temperature of at least 110.degree.

depositing at least one strip (36) of said pasty elastomer on said second polypropylene layer (30) to form a second elastomer layer (35).

4. Method according to any one of claims 1 to 3, characterized in that said elastomer has a thermal conductivity less than 0.15 Wm ^"1 .K ^{" 1}

5. Method according to any one of claims 1 to 4, characterized in that said elastomer comprises at least one crosslinkable elastomer selected from butyl rubber, halobutyls and brominated copolymers of isobutylene and para-methylstyrene and at least one non-crosslinkable elastomer of low thermal conductivity.

6. Method according to any one of the preceding claims, characterized in that the epoxy powder is deposited by electrostatic spraying and said powder is agglomerated.

7. Method according to any one of the preceding claims, characterized in that the epoxy layer (9) has a thickness of between 10 and 800 micrometers, and preferably between 150 and 300 micrometers.

8. Method according to any one of the preceding claims, characterized in that the adhesive layer (1 1) has a thickness of between 10 and 1000 micrometers, and preferably between 300 and 600 micrometers.

9. A method according to any one of the preceding claims, characterized in that said strips (23, 36) of said first or second elastomer layers (22, 35) or said strips (17, 31) of said first or second layer of polypropylene (16, 30) or said strips (12) of said adhesive layer (1 1) are obtained by lateral extrusion with respect to the direction of movement of the tube (1).

A method according to any one of the preceding claims, characterized in that said strips (23, 36) of said first or second elastomer layers (22, 35) or said strips (17, 31) of said first or second layer of polypropylene (16, 30) or said strips (12) of said adhesive layer (1 1) are obtained by longitudinal extrusion with respect to the direction of movement of the tube (1).

1 1. A method according to any one of the preceding claims, characterized in that said strips (23, 36) of said first or second elastomer layers (22, 35) or said strips (17, 31) of said first or second polypropylene layer ( 16, 30) or said strips (12) of said adhesive layer (1 1) are obtained by coextrusion.

12. A method according to any one of the preceding claims, characterized in that said strips (23, 36) of said first or second elastomer layers (22, 35) are pressurized with a pressure roller. .

13. Method according to any one of the preceding claims, characterized in that each of said strips (23) of said first elastomer layer (22) has a thickness of between 2 and 30 mm.

14. Method according to any one of the preceding claims characterized in that said strips (23, 36) of said first and second elastomer layers (22, 35) are extruded at a temperature between 140 ° C and 230 ° C and preferably between 180 ° C and 200 ° C.

15. Tube comprising a coating obtained by the process according to any one of the preceding claims, characterized in that it successively comprises an epoxy layer (9), an adhesive layer (1 1), a first layer of polypropylene ( 16) and a first elastomer layer (22).

16. Tube according to claim 15, characterized in that it further comprises above the first elastomer layer (22), a second layer of polypropylene (30).

17. Tube according to claim 16, characterized in that it further comprises above the second layer of polypropylene (30), a second layer of elastomer (35).