NO171370B - SYNTACTIC HEATING INSULATION MATERIAL, PROCEDURES THEREOF MANUFACTURING THEREOF, AND INSULATING COMPANY INCLUDING SUCH MATERIAL - Google Patents

Abstract

Heat insulating material of the syntactic type comprising a filler of hollow glass microballs embedded in a matrix, and fabrication method. The matrix is selected from the family of elastomers such as natural rubber, polychloroprene, styrenebutadiene copolymers (SBR), butadiene-acrylonitrile copolymers (NBR), polynorbornenes, ethylene-propylene-diene monomers (EPDM), butyle rubbers and the like. For the fabrication of the material, hollow glass microballs are incorporated into a matrix in liquid or pulverulent phase, and the microballs and the matrix are mixed together without applying large shearing efforts and finally a cross-linking treatment is operated. The material is usable particularly for insulating underwater pipelines for the transportation of gas or oil from off-shore oil fields or urban heating conduits.

Description

The invention concerns a heat-insulating syntactic material with a relative density in the range 0.5 to 0.65 and a heat conduction coefficient X in the range 90 to 130 mWm~lK-l, which material resists a temperature of approx. 12 0°C, practically does not shrink at this temperature and under a hydrostatic pressure of approx. 40 bar, and is also sufficiently flexible to be subjected to an elongation of 7 to 10% without breaking and without losing its properties, a method for its production, and insulating means comprising such a material.

It is known that the operation of oil fields offshore requires the transport of extracted oil or gas by means of submarine channels or cables which must be thermally insulated. The materials used for this must not only exhibit good thermal insulation properties, but they must also withstand the elevated hydrostatic pressures that exist at the bottom of the sea and retain their properties at application temperatures which can be of the order of 120°C.

For this purpose, embodiments have already been proposed comprising a casing of a material of polyurethane foam or PVC foam with a low heat conduction coefficient. However, as these materials do not exhibit sufficient mechanical properties, firstly especially considering the hydrostatic pressure stresses and secondly in consideration of the hydrostatic pressure stresses and temperature, these foam materials should be combined with other means which can give the combination the necessary qualities.

It may then be possible to use other known materials, with a low heat conduction coefficient, for example a composite material comprising hollow glass microspheres in a matrix of polyester resin. Such a syntactic polyester foam is, for example, described in GB-A-1,372,845.

If such a material exhibits elevated mechanical properties, especially strength, while being significantly less heavy than ordinary materials, they can only be used in a very special way in the area of protection of submarine cables.

For applications that concern the operation of oil fields offshore or, in general, for the thermal insulation of transport channels for a fluid that exhibits a high heat gradient to the surroundings, such as for example earth channels for urban heating, the insulation means must not only exhibit the properties mentioned above, but they must moreover, it could withstand relatively strong deformations without showing damage, such as breakage, where the material is guided so that it takes the form of a surface with a weak radius of curvature.

The reason for this is that, regardless of the technique for placing underground cables, - the use of a flat-bottomed boat on which successive and adjacent pieces are connected to each other and then submersion, or instead assembly on the ground and then towing the assembled cable under water - , bending zones appear on the wire, which can lead to the destruction of the thermal insulation means when the material used for these means is not sufficiently soft.

The purpose of the present invention is therefore to provide a thermal insulation material which better corresponds to the practical requirements than the materials for the same purpose which are proposed in the state of the art.

Generally speaking, it is an aim of the invention to provide such a thermal insulation material, of a syntactic type, which satisfactorily meets the conflicting requirements mentioned above, i.e. to exhibit a low heat conduction coefficient and a high resistance to hydrostatic pressure up to temperatures of at least 115 - 120°C, at the same time as a deformation ability, so that the material can be shaped, or subjected to a deformation that locally gives it a weak radius of curvature without losing these qualities .

It is also an object of the present invention to provide a method for the industrial production of such a material comprising a matrix containing a quantity of hollow glass microspheres.

It is also an object of the invention to provide a thermal insulation agent where such syntactic material is used and which is particularly suitable for its use on channels for the operation of oil fields and/or gas fields offshore, or for underground channels for urban heating.

A syntactic thermal insulation material according to the invention comprising a charge of hollow glass microspheres in a matrix is characterized in that it is produced by the material being produced by introducing a filler of hollow glass microspheres into a matrix, the microspheres making up 40 to 80% by volume in relation to the matrix , which matrix is selected from the elastomers of the following types: natural rubber, polychloroprene, styrene butadiene copolymer (SBR), acrylonitrile butadiene copolymer (NBR), polynorbornene, ethylene-propylenediene monomers (EPDM), butyl rubbers and the like; the bond between the hollow glass spheres and the matrix being achieved with the aid of a bridging agent consisting of an isocyanate or an organo-functional silane which constitutes between 1 and 10% by weight in relation to the elastomer matrix.

The method according to the invention for producing a syntactic material, as defined above, is characterized by the filler of hollow micro-glass spheres being introduced into the matrix, by the filler and the matrix being mixed together without applying large shear forces until a uniform product is obtained, and by the product subjected to a cross-linking treatment.

In one embodiment, this crosslinking treatment is a vulcanization.

In one embodiment, the matrix is in the form of a latex.

The hollow glass microspheres are then treated using a bridging agent, such as an organo-functional silane, before they are mixed into the latex.

In another embodiment, the matrix is in the form of a solution.

The hollow glass microspheres are then mixed into the matrix simultaneously with the addition of a bridging agent for glass elastomers such as e.g. an isocyanate or an organofunctional silane.

The matrix can be in the form of a liquid.

As a variant, it is available in the form of a powder. The powder advantageously comes directly from the production of the elastomer or is obtained as a variant by cryogenic painting of an elastomer alone, or from a mixture of the elastomer and ingredients such as additives, protective agents and vulcanizing agents.

Likewise, a material of the above-mentioned type, in which the homogeneous product consists of the matrix and the charge of hollow glass spheres, can be placed in the form of a thin layer on a support, and this layer optionally subjected to coagulation, then to drying, and that these operations are repeated until a desired thickness of the material is achieved, which is then subjected to a cross-linking treatment, such as a vulcanization.

A thermal insulation agent according to the invention which is particularly useful for thermal insulation of transport channels for a liquid which exhibits a temperature gradient with the surrounding space, such as e.g. a transport line for oil or gas from an oil field offshore, or a channel for urban heating, is characterized by the fact that it comprises a sleeve made of a syntactic material, the sleeve being terminated on the front and rear end surfaces by corrugated surfaces with a complementary shape that makes it possible to put adjacent sleeves together.

In an advantageous embodiment, in which the channel is actually covered with an anti-corrosion layer known per se, the sleeves are placed slidingly one after the other on this layer and attached to this by means of a high-modulus adhesive, especially of the epoxy type, and the adjacent the sleeves are attached to each other using a low-modulus adhesive, particularly of the polyurethane, polysulphide and/or polychloroprene type.

The invention will be better understood with the help of the description that follows, in the form of an example and with reference to the accompanying drawing, in which: - Figure 1 very schematically shows a machine for producing a material according to the invention and - Figure 2 as a section shows a schematic part of a heat insulating agent according to the invention.

To obtain a syntactic material with low thermal conductivity, of the order of 90 to 130 rnWrn^K"<1>, which resists temperatures of the order of 120°C, which is practically free from shrinkage at this temperature under a hydrostatic pressure of the order of 40 bar and which is also sufficiently soft to be subjected to an elongation of 7 - 10% without breaking and without loss of these properties, according to the invention a charge of hollow microspheres is taken up in an amount of 40 to 80% by volume in a matrix selected from elastomers of the type of natural rubber, polychloroprene, styrene-butadiene copolymers (SBR), butadiene-acrylonitrile copolymers (NBR), polynorbornene, ethylene-propylene-diene monomers (EPDM), butyl rubber and the like. The matrix enables the syntactic material according to the invention to achieve the sought-after softness properties, while the use of hollow microspheres enables the introduction of gas into the matrix, which is beneficial for achieving a low heat conduction coefficient while the necessary properties in terms of resistance to pressure are ensured due to the spherical shape of the added particles to which an elevated modulus and a specific intrinsic resistance are bound.

The addition to a matrix of elastomeric material of hollow glass microspheres, with a crushing resistance below 281 kg/cm<2>, cannot, however, be carried out by means of usual techniques for mixing quantities of minerals or carbon dioxide into rubber or the like. The experiments carried out by the applicant with the BANBURY mixer or with open cylindrical mixers have all led to unacceptable products, the hollow microspheres being crushed due to the high shear forces necessary to distribute them well in the rubber.

After abandoning this experimental direction, the applicant has surprisingly established that good results are obtained by mixing the hollow microspheres into the elastomeric matrix in the form of powder or in the form of a liquid by means of a method which does not apply to the hollow microspheres elevated shear forces which can crush them them.

More precisely, the invention in a first embodiment includes carrying out the mixing of the hollow microspheres and the elastomer in liquid form by mixing the microspheres into the matrix when this is in the form of a latex.

The latter is produced according to usual methods.

Considering that it is not possible to mix dry fillers into a latex, firstly, and secondly that the adhesion of the hollow glass microspheres to the elastomeric matrix cannot be achieved directly, the invention proposes first to treat the hollow glass spheres by using a bridging agent for glass elastomers, such as an organo-functional silane and then suspend the thus treated hollow glass spheres in water to which a latex thickener has been added.

After a short resting period to promote the elimination of air from the suspension, the latex is slowly poured with stirring into the suspension of hollow glass microspheres to obtain a homogeneous mixture, but without applying pressure and without applying significant shear forces, as indicated above.

If the chosen coagulation method is a coagulation with the help of heat, then a suitable, heat-sensitive coagulant is introduced into the mixture.

Whether such an agent has been added to the homogeneous mixture or not, this is then deposited with the aid of a scraper in the form of a thin layer on a carrier, such as e.g. a metal band, or coagulation of the latex part is carried out, either by the action of an external coagulant which is previously placed on the carrier in powder form, or by the action of heat, or also by dehydration or by the action of cold.

After coagulation and possibly suspension of the latex, the deposited thin layer is dried, for example by means of a warm ventilated air stream or by means of infrared radiation.

The drying is carried out, firstly, so that it is finished within a relatively short time, and thus enables industrial fabrication on an economical level, and secondly, so that there is no discontinuity in the contact surface between the hollow glass spheres or the latex which could lead to to a porosity of the final product.

When a first thin layer has been obtained by means of this method, this is carried back again to form a new layer and so that a carpet is obtained whose thickness is chosen for the insulating material, which is then vulcanized by

of common methods for vulcanizing rubber.

In a second embodiment, according to the invention, the hollow glass balls are mixed into an elastomer solution.

In this embodiment, the elastomer which is of a type capable of forming a solution is dissolved in a suitable solvent and the hollow glass beads previously treated as indicated above, i.e. to which is bound a bridging agent for glass elastomers, for example an isocyanate or an organo-functional silane, is introduced in dry powder form into the elastomer solution, while stirring, but without pressure and without significant shear forces being created.

The procedure is then the same as described above for the latex, i.e. the deposition by means of a scraper of a thin layer of homogeneous mixture on a metal tape or the like, drying of the layer observing the conditions indicated above, deposition of a new layer of the mixture and drying of this new layer, etc. until a number of layers is obtained which is necessary to form a carpet when placed on top of each other which has a desired thickness for the insulating materials. When this thickness is achieved, the blanket is held together under pressure and the whole is then subjected to a vulcanization treatment as indicated above.

In yet another embodiment, according to the invention, the mixing of the hollow glass microspheres and the elastomeric matrix is carried out by mixing the said glass spheres, which have been previously treated to enable their final satisfactory adhesion to the matrix, in an elastomer in a liquid state.

Such a procedure can be carried out for the elastomers available in the trade in this form, which apply to mono- or bi-components, i.e. for elastomers of the type known under the name liquid nitriles, polybutadienes, etc.

After obtaining a homogeneous mixture of hollow microspheres and elastomers in a liquid state, proceed as indicated just above with reference to a solution of elastomer, without, however, using a drying operation.

In yet another embodiment, the hollow glass-

the balls in the elastomer when this is in the form of a powder.

In this embodiment, which is suitable for the production of heat-insulating material whose matrix is an elastomer of the nitrile or polynorbornene type, or SBR or natural rubber, the mixing of the hollow microspheres is carried out in a powder-mixing machine in which, in addition to the elastomer in powder form, the usual ingredients for elastomer compounds, i.e. chargers, protective agents, possibly vulcanizing agents, cross-linking agents, etc., and then little by little the hollow glass microspheres, which have been previously treated with a bridging agent, such as e.g. an organo-silane, to ensure satisfactory adhesion of the balls to the matrix.

When the powder mixture is sufficiently homogeneous, it is introduced into the filling hopper of an extrusion machine, such as a screw string sprayer. The passage of powders through the machine helps to achieve a good homogeneity of the mixture, while by choosing a suitable extrusion head, a departure from the machine of a thermal insulation material with the desired shape and dimensions is achieved.

The vulcanization of the elastomer is then carried out in the usual way, advantageously by means of a known method, such as e.g. a passage through a hot air duct, or by radiation with UHF, etc.

For the embodiment described just above, the powdered elastomer is advantageously obtained directly from the manufacturing process of the elastomer.

As a variant, powders are obtained by cryogenic grinding.

In one embodiment of this method, a mixture of elastomer and de

usual ingredients for such mixtures, then a cryogenic grinding is carried out and then the pre-treated hollow glass microspheres are mixed into the mixture, which is then introduced into the feed funnel of the string spraying machine.

For carrying out the method by means of a discontinuous process, the invention deals with the use of a machine of the type which is illustrated very schematically in figure 1. Mounted on a stand 10, it comprises an endless metal band

11 which is driven by a motor 12 by means of a chain transmission 13 and whose horizontal working arms 14 and 15, for the most part are located in a tunnel 20 equipped with ramps for infrared radiation 21 and/or heating resistors and to which an outlet channel 22 is connected with a ventilator 23 for extracting and evacuating water vapor or solvent vapors, regulation of the amount of air being achieved by means of a "papillon" 24. Above channel 22 in the direction of movement of the endless belt 11, a channel 25 opens from the tunnel 20. In electrical resistances in the form of heating ribs 26 and/or ramps for infrared radiation for the cross-linking treatment are placed on this. A ventilator 27 ensures the circulation of hot air, the quantity of which is regulated by means of "papillon" 26. In such a machine, as explained above, the homogeneous mixture of hollow microspheres and elastomer is deposited in the form of a thin layer on the upper surface 14 of the endless belt at the outside of the tunnel 20 and near the beginning of the surface 14, as shown by arrow F. A scraper 29 and a counter cylinder 19 make it possible to regulate the thickness of the deposited layer. A cylinder 18 whose distance from the band 11 can be regulated by means 17 and which is placed between the channels 22 and 25, makes it possible to regulate the thickness of the blanket obtained by producing several successive thin bands as explained above.

In a process for continuous production, work is carried out with the help of a number of adjacent tanks placed horizontally or vertically, one of which is to receive the latex, another the coagulants, etc., and which are run through by an endless conveyor belt, which passes successively through drying zones, for example with infrared radiation, vulcanization zones and then back to the latex tank, etc.

The invention is illustrated below using the following examples for the production of different thermal insulation materials according to the invention.

I - MATERIALS OBTAINED STARTING FROM A LATEX

Example 1

A latex A is produced whose quantities in percentage by weight in relation to rubber are as follows:

35 parts by weight equivalent to 48 percent by volume of hollow glass microspheres sold by the company 3M under reference B 37/2000 are added to this latex.

These microspheres have an average true density of the order of 0.37, a resistance to pressure of the order of 14 MPa and a sieve analysis such that at least 3 percent by weight of the glass microspheres is retained on a 100 mesh sieve (149 micrometers).

Before their incorporation into the latex, the hollow glass microspheres are moistened in an aqueous solution of an aminosilane, such as e.g. that sold by the company Dow Corning with the reference Z 6020, after which they are dried.

After an intimate mixing of the hollow glass microspheres and the latex is prepared using the technique indicated above, i.e. deposition with a scraper on a metal belt in the machine shown in figure 1, layer whose thickness is between 0.5 and 1 mm.

Coagulation is achieved by dewatering in an oven followed by drying for two hours at 80°C and then for 12 hours at 40°C.

For the production of a plate of heat-insulating material with a thickness of approx. 10 mm is placed between a dozen and 20 of the layers on top of each other and vulcanized at a low temperature, of the order of 115°C for about 20 min.

The obtained material has a density d = 0.57 and a heat conduction coefficient = 96 mWm^K"<1>.

Example 2

A latex B is produced with the following composition, in parts by weight in relation to rubber:

Polychloroprene (CR) latex

(one like that sold by the company Bayer below

The hollow glass microspheres used are of type B 28/750 from the company 3M with an average real density of 0.28, a resistance to pressure of 5.2 MPa and a sieve analysis such that at least 5% by weight is retained on an 80 mesh sieve (177 micrometers).

In order to carry out comparison experiments, the hollow glass microspheres that have been treated as in example 1 are mixed into lactex B in different proportions and work is then carried out as in example 1, i.e. an elementary layer is produced with a thickness of between 0.5 and 1 mm.

In this example, the coagulation is achieved in the cold and is followed by drying in an oven to constant weight.

For the production of a sheet of insulating material with a thickness of approx. 10 mm, a dozen or more elementary layers are laid on top of each other to form a carpet and the whole is vulcanized at 125°C for approx. 20 min.

The results obtained are listed in the following Table I, for Examples 2A, 2B and 2C.

II - MATERIAL OBTAINED STARTING FROM A SOLUTION

Example 3

First, the following mixture is prepared in parts by weight in relation to rubber:

Polychloroprene of the type sold by

First, a solution of rubber is prepared by mixing

2.5 parts by weight of trichlorethylene with one part by weight of the mixture.

Next, 39 parts by weight equivalent to 70% by volume of glass microspheres of the type 37/2000 sold by the company 3M and whose properties are indicated above with reference to example 1 are then added to the solution thus prepared, as well as a bridging agent, an isocyanate sold by the company Bayer under the name Desmodur RF.

The hollow microspheres are introduced into the solution while stirring and it is produced using a technique analogous to examples 1 and 2, i.e. by depositing the mixture by means of a scraper on a suitable support, of thin elementary layers which

has a thickness of the order of 0.5 to 1 mm.

The layers are dried in an oven at a temperature in the order of 70°C until a constant weight is achieved, i.e. to the weight loss in percent caused by the elimination of solvent, does not vary significantly.

After assembly of a dozen or more layers to obtain a plate of about 10 mm thickness, advantageously by means of a conventional press, the plate is subjected to a vulcanization treatment which is carried out at 150°C and for a time of about 20 min.

The properties of the heat-insulating material obtained are the following:

Density d = 0.55

Thermal conductivity coefficient:

= 97 mWm^K"<1>

As a variant, the solvent can be toluene which is used in an identical amount, i.e. 2.5 parts by weight of toluene for one part by weight of the mixture.

III - MATERIAL OBTAINED STARTING FROM A POWDERED ELASTOMER

Example 4

The rubber used is of the nitrile type with the following composition in parts by weight in relation to the rubber:

The hollow microspheres are those sold by the company 3M with reference 38/4000, i.e. hollow microspheres having an average real density of 0.38 and a pressure resistance of 28 MPa. The hollow microspheres are treated as indicated in Example 1, after which they are added to the elastomeric powder in an amount of 70 parts by weight, equivalent to 60% by volume, and the homogeneous mixture is extruded.

The obtained material is vulcanized at 150°C for approx. 20 min. Its characteristics are the following:

Density d = 0.65

Thermal conductivity coefficient:

= 110 mWm^K"<1>

Example 5

A mixture of a powder with the following composition, in parts by weight, in relation to rubber, is first prepared:

The hollow glass microspheres of the type used in example 2 and sold by the company 3M under the name B 28/750 are then added to this mixture.

The hollow glass microspheres, which have been previously treated in accordance with the method described in Example 1, are then added in an amount of 244 parts by weight, i.e.

60% by volume.

The homogeneous mixture is then formed by simple deposition with a scraper or passage through a surrounding organ.

The obtained material is vulcanized and has the following properties:

Density d = 0.65

Thermal conductivity coefficient:

= 126 mWm^K"<1>

It thus appears that the material according to the invention has good thermal insulation properties for the desired purpose, with a coefficient of the order of 90 to 130 mWm^IC<1>, as well as good properties in terms of resistance to pressure while being easily deformable.

The perfect adhesion of the hollow glass microspheres to the matrix in which they are mixed also gives the material according to the invention excellent properties as an anti-liquid barrier, and in particular a material that resists the penetration of water is obtained, at temperatures of the order of 120°C and more.

The material according to the invention thus finds a particularly advantageous application when protecting the transport of hot liquids, when it comes to water vapor in channels for urban heating or oil or gas in submarine pipelines.

In the latter case, according to the invention, sleeve 30, Figure 2, is formed from the heat-insulating material, where one front side 31 has an annular protrusion 32 and whose opposite front side 33 has an annular extension 34 of a shape that fits the shape of the protrusion 32.

For thermal insulation of a wire, the channel 40 is first covered with an anti-corrosion layer 41 known per se, on which the sleeves 30 are placed slidingly in a row and with which they are fixed, possibly by means of an adhesive of the high modulus type such as epoxy. The wavy conjugate shape of the front and rear face sides of the sleeve to which is applied glue or adhesive of a low modulus type such as polyurethane, polysulphur and/or polychloroprene for fixing the adjacent sleeves, helps to achieve the best thermal insulation properties.

In a manner known per se, the sheathing of adjacent and continuous sleeves, whose thickness can be of the order of magnitude from 5 to 40 mm, is coated, if necessary, with one or more other protective elements, for example of metal or plastic materials.

As a variant and with the softness and deformability properties of the material according to the invention, the protective covering can be produced by rolling and gluing together on the layer 41 a band of syntactic material, such as e.g. that defined above.

Claims (15)

1. Heat-insulating syntactic material with a relative density in the range of 0.5 to 0.65 and a thermal conductivity coefficient X in the range of 90 to 130 mWrn"1^!, which material withstands a temperature of about 12 0°C, practically does not shrink at this temperature and under a hydrostatic pressure of approximately 40 bar, and is also sufficiently flexible to be subjected to an elongation of 7 to 10% without breaking and without losing its properties, characterized in that the material is produced by introducing a filler of hollow microglass spheres into a matrix, the microspheres making up 40 to 80% by volume in relation to the matrix, which matrix is selected from the elastomers of the following types: natural rubber, polychloroprene, styrene butadene copolymer (SBR) , acrylonitrile butadiene copolymer (NBR), polynorbornene, ethylene-propylenediene monomers (EPDM), butyl rubbers and the like; the bond between the hollow glass spheres and the matrix being achieved with the aid of a bridging agent consisting of an isocyanate or an organo-functional silane which constitutes between 1 and 10% by weight in relation to the elastomer matrix. 2. Procedure for producing a syntactic material according to claim 1, characterized in that the filler of hollow micro-glass spheres is introduced into the matrix, in that the filler and the matrix are mixed together without applying large shear forces until a uniform product is obtained, and in that the product is subjected to a cross-linking treatment. 3. Method according to claim 2, characterized in that the cross-linking treatment takes place by vulcanisation. 4. Method according to claim 2, characterized in that a matrix in the form of a latex is used. 5. Method according to claim 4, characterized in that before introduction into the latex, the hollow microglass spheres are treated using a bridging agent such as an oranofunctional silane. 6. Method according to claim 2, characterized in that the matrix is used in the form of a solution. 7. Method according to claim 6, characterized in that the hollow microglass spheres are introduced into the matrix - at the same time as a glass - elastomer bridge-forming agent which consists of an isocyanate or an organo-functional silane which is added to these. 8. Method according to claim 2, characterized in that the matrix is used in liquid form. 9. Method according to claim 2, characterized in that the matrix is used in powder form. 10. Method according to claim 9, characterized in that the powder comes directly from the method for producing the elastomer, or is produced by cryogenic painting of an elastomer in itself or in a mixture of elastomer(s) and components such as fillers, protective agents and vulcanizing agents. 11. Method for the production of thermal insulation devices based on the material according to claim 1, characterized in that several thin layers of the material are produced in sequence, each layer being completely dry, in that these layers are joined together under light pressure, and that the cross-linking treatment is then carried out , which treatment is advantageously vulcanization. 12. Method according to claim 11, characterized in that each of the layers is deposited on a corresponding substrate using a spreader and has a thickness in the range of 0.5 to 1 mm. 13. Method according to claim 11, characterized in that it is carried out continuously in several adjacent, horizontally or vertically arranged containers with drying zones between them, followed by a final vulcanization zone. 14. Thermal insulating agents applicable in particular as insulation for pipes for transporting a liquid with a temperature gradient in relation to the surroundings, such as a pipe for transporting oil or gas from an offshore oil field or a district heating pipe, the heat insulating agent being characterized by it comprises a sleeve made of a syntactic material according to claim 1, in that the sleeve is terminated on the front and rear end surfaces by corrugated surfaces of complementary shape which enable adjacent sleeves to be joined together. 15. System for the insulation of pipes for the transport of a fluid with a temperature gradient in relation to the surroundings, such as a pipe for the transport of oil or gas from an offshore oil field, or a district heating pipe, the system being characterized in that it comprises several sleeves according to claim 14, which sleeves are attached to each other through their adjacent surfaces by means of a low-modulus adhesive or glue, preferably an adhesive or glue of the polyurethane, polysulphide and/or polychloroprene type, and attached to a common anti-corrosion layer covering the pipe using a high-modulus adhesive or glue, with the advantage of the epoxy type.