OA16564A - Rigid thermal insulation and / or buoyancy material for underwater piping. - Google Patents

Abstract

The present invention provides a material for thermal insulation and / or rigid buoyancy characterized in that it consists of a mixture of: - (a) a matrix of a homogeneous mixture of crosslinked elastomeric polymer and a liquid insulating plasticizer compound, said insulating plasticizer compound being chosen from compounds derived from mineral or vegetable oil, said insulating plasticizer compound not being a phase change type material at a temperature of 10 ° to + 150 ° C. , the mass proportion of said insulating plasticizer compound in said matrix being at least 50%, preferably at least 60%, and - (b) hollow beads, preferably glass microbeads, dispersed within said matrix of said homogeneous mixture of said polymer and said insulating plasticizer compound, in a volume proportion of at least 35% of the total volume of the mixture of said beads with said matrix, preferably from 40 to 65% of said total volume. Said rigid insulating material according to the invention can be used for the insulation and / or the buoyancy of an underwater pipe or underwater pipe element.

Description

The present invention relates to a material for thermal insulation and / or rigid buoyancy for an underwater pipe and accessories, such as valves and flow or pressure regulators, in particular for an underwater pipe conveying hot or cold fluids. , preferably an underwater pipe intended for great depths, or also bottom-to-surface connections between underwater wellheads and a storage and processing vessel anchored to the surface.

In the majority of industrial fields, efficient insulation systems are sought to maintain the fluids conveyed in the piping at constant temperature, so that transfers between equipment can be made possible over long distances, reaching for example several hundreds of meters or even several kilometers. Such distances are common in industries such as petroleum refineries, liquefied natural gas installations (-165 ° C), submarine oil fields which extend over several tens of kilometers. Such oil fields are developed by increasingly deep water depths which can reach 2000 m to 3000 m, or even more.

The present invention relates in particular to isolated submarine pipes, installed on oil fields at very great depths, or to bottom-to-surface connection pipes in suspension between the seabed and a surface vessel anchored on said oil field, as well as as all types of accessories, such as valves, flow or pressure regulators, etc.

Crude oil usually leaves well heads at temperatures of 45 to 75 ° C or more, and well heads are often horizontally several kilometers away from the surface support which receives and processes the crude oil, while the wellhead The water is around 3-5 ° C. In addition, the water depth reaches and exceeds 2000 to 3000m, and we try to keep the crude oil until it reaches the surface, at a temperature above 30-35 ° C, so as to avoid the formation paraffin or gas hydrate plugs, which would block production. This therefore requires continuous efficient thermal insulation of the bottom-surface connection pipe conveying the crude oil.

Thus, multiple types of insulated pipes have been developed and in particular pipes of the Pipe In Pipe or PiP type, that is to say pipe in a pipe, in which an internal pipe conveys the fluid and an external pipe coaxial with the pipe. above, also called the outer shell, is in contact with the surrounding environment, that is to say water. The annular space between the two pipes can be filled with an insulating material or else be emptied of all gas.

These systems have been developed to achieve a high level of thermal performance and specific versions have been developed to respond more appropriately to the deep sea, that is to say to withstand the pressure of the seabed. water pressure being substantially 0.1 MPa, i.e. approximately 1 bar for 10 m of depth, the pressure to which the pipe must withstand is then approximately 10 MPa, i.e. approximately 100 bars for 1000 m of depth and approximately 30 MPa, or approximately 300 bars for 3000 m.

Means are known for insulating external conduits resistant to high hydrostatic pressures and therefore suitable for use at high immersion depths, consisting of coatings of virtually incompressible solid polymer materials based on polyurethane, polyethylene, polypropylene, etc. which may be in the form of a solid tubular sleeve. However, these materials exhibit fairly average thermal conductivity and thermal insulation properties, insufficient to avoid the drawbacks of the formation of plugs mentioned above in the event of

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V 'for stopping production for underwater pipes conveying hydrocarbons.

There are also known rigid insulating materials exhibiting, in addition, an advantageous buoyancy, made up of synthetic materials comprising micro-spheres (with a diameter of less than 0.1 mm) or hollow macro-spheres (with a diameter of 1 to 10 mm) containing a gas and resistant to external pressure, embedded in binders such as an epoxy resin or polyurethane resin, known to those skilled in the art under the name of syntactic foam. These syntactic foam insulating materials are used mainly for the insulation of submarine pipes at great depth, of the riser or multi-rtser tower type, as described for example in WO 00/29276, WO 2006/136960, WO 2009 / 138609 or also WO 2010/097528. These foams are extremely expensive to manufacture when they are intended for depths greater than 1000 m, that is to say when they must withstand pressures of the order of 100 bars, that is to say 10 MPa. , because the necessary microspheres must be sorted and tested to withstand these pressures. In addition, the manufacturing process is very delicate when trying to manufacture very thick elements, because the crosslinking of chemicals is a strongly exothermic reaction. Indeed, the main problem is to slow down the physicochemical reaction and simultaneously to evacuate the calories produced, so as to prevent the reaction from racing, thus risking cooking, or even burning the material in the mass, this which generally leads to a material unfit for the use for which it was intended.

In addition, in general the main manufacturing defects encountered result from a lack of control of the crosslinking process, leading to internal degradation of the polymer matrix, said defects not always being detectable before installation and commissioning. underwater pipes. This then results, after a few months of operation at high temperature, in particular for the transfer of oil at a temperature of

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at 90 ° C and at very high external pressure (10 MPa per section of 1000 m of water), cracking of the polymer matrix and degradation of the micro-spheres, which not only leads to losses of insulation significant losses and buoyancy losses, but above all to the creation of cold spots, the latter being particularly feared in the event of production stoppage, because then the crude oil very quickly begins to set, forming very localized plugs of paraffin and 'gas hydrates that are almost impossible to absorb simply.

These high performance rigid syntactic foam insulating materials are used for pipe insulation of standard lengths, both for pipes resting on the seabed and for bottom-to-surface connection pipes. On the other hand, these rigid insulating materials are not easy to use for the singular junction elements, called spool pieces, or connecting pieces, or even bent junction pipes, because these pipe elements generally have complicated shapes, comprising a plurality of bends or bends, as described in WO 2010/063922, and must be manufactured after laying the subsea pipes and installing the bottom-to-surface connections.

Furthermore, insulating materials are known with a superior thermal insulation property, that is to say with lower thermal conductivity, coupled with phase change properties. Phase change insulating materials (PCM) are implemented in particular in WO 00/40886 and WO 2004/003424, but these PCM insulating materials which can adopt a liquid state require confinement in an absorbent material, as described in WO 00 / 40886 or containment in pockets, as described in WO 2004/003424.

Phase change materials (PCM) behave like heat accumulators. They restore this energy during their solidification by crystallization or absorb this energy * L · during their fusion, in a reversible manner. These materials can therefore make it possible to increase the duration of production stoppages without risking the clogging of the pipes by premature cooling of their contents. However, these phase change materials have the drawback that their viscous liquid state promotes heat losses by convection. Another drawback of these phase-change insulating materials is that they induce a necessary variation in the volume of the material during these phase changes, which has consequences on their confinement envelope, which must be capable of accept these variations in volume.

These confined thermal insulating coatings are coated with a continuous tubular semi-rigid outer shell. But in the prior art, the embodiments described are limited to the manufacture of straight pipes and cannot be easily adapted, either, to manufacture elbow pipes as described above. These embodiments are not easily adaptable for the realization of thermal insulation of elbow junction pipes by the structure of the outer casings, which as described cannot be deformed concentrically with respect to the internal pipe and would not allow d 'obtain a substantially constant thickness of insulating material, in particular in the bent areas.

Other insulating materials in gel form have been described, in particular in patents FR 2 809 115, FR 2 820 426 and FR 2 820 752, by the applicant and WO 02/34809. More particularly, these insulating gels consist of a complex comprising a first compound having superior thermal insulation properties, as well as a plasticizing character, which is mixed with a second compound having a structuring effect, in particular by crosslinking, such as a polyurethane compound, said mixture ultimately forming, after crosslinking of the second compound, an insulating gel consisting of a matrix of said second compound confining said first insulating compound, the final insulating gel obtained radically reducing convection phenomena in the case where the first compound is a phase change material in particular.

Indeed, said first compound can itself be a phase change compound such as paraffin, other compounds of the alkane family, such as waxes, bitumens, tars, fatty alcohols, glycols, and more particularly still any compound whose melting point is between the temperature t ₂ of the hot effluents circulating the internal pipe and the temperature t ₃ of the environment surrounding the pipe in operation, that is in fact, in general a melting temperature of between 20 and 80 ° C.

However, said first compound may be an insulating material without phase change such as kerosene in a homogeneous intimate mixture with a polyurethane polymer, the whole being in the form of a gel, as described in WO 02/34809.

In previous embodiments, these insulating gels, by virtue of their extremely flexible elastomeric structure and their relatively fragile mechanical strength, are entirely confined by a flexible or semi-rigid protective envelope, in particular between an internal steel pipe and an external pipe made of material. thermoplastic, for portions of straight pipes as well as for portions of elbow pipes, in particular the elbow junction pipes described above.

To do this, preconstituted tubular envelopes are prepared, which are placed by threading on a coaxial internal pipe, and the gel is injected into the annular space after having blocked the ends of said annular space between said tubular envelopes and internal pipes. Other methods of making coaxial angled connection pipes of the PiP type are described in patent WO 2010/063922.

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These insulating gels therefore have the advantage of improved thermal insulation properties, while allowing easier implementation than for solid insulating materials, in particular in the context of bent junction pipes or in thermal insulation sleeves. as described in WO 2010/049627.

However, the mechanical strength of these gels is insufficient for them to be able to withstand on their own the mechanical stresses of the pipes during their handling during manufacture, transport and installation on site and throughout their lifetime.

Another drawback of these insulating gels is that said first compound, such as kerosene, has a tendency to exude outside the crosslinked polymeric matrix, during its lifetime.

The aim of the present invention is to provide a novel thermal insulation material exhibiting improved thermal insulation and, where appropriate, buoyancy properties.

Another aim of the present invention is to provide a new material for thermal insulation and / or buoyancy exhibiting high mechanical strength, such as the syntactic foams of the prior art, which are mats that do not present any risk of cracking and degradation over time. due to possible crosslinking defects, as described above.

Another object of the present invention is to provide a thermal insulation material having great ease of manufacture and implementation, in particular by casting in situ in a mold, to form molded parts in a preconstituted protective envelope, suitable for be arranged around an underwater pipe or cast directly into the annular space of coaxial pipes, such as the insulating gels described in the prior art mentioned above, and more generally having the appropriate advantages for an application to insulation thermal of an elbow junction pipe.

Another object of the present invention is to provide a thermal insulation material and / or buoyancy material exhibiting improved stability of composition and mechanical and thermal properties over time.

According to the present invention, it has been discovered that it is possible to obtain a thermal insulation and buoyancy material, rigid, having a quasi-incompressibility similar, or even greater, to that of sea water, and having in addition to the improved properties of thermal insulation, buoyancy and ease of use, in accordance with the aim of the present invention, from a viscous composition of insulating gel, as described in WO 02/34809, in the mixing with hollow microbeads, before crosslinking of said gel, subject to selecting the components of said insulating gel and their proportions by mass with respect to the microbeads, as defined below.

More specifically, the present invention provides a rigid thermal insulation and / or buoyancy material characterized in that it consists of a mixture of:

- (a) a matrix of a homogeneous mixture of crosslinked elastomeric polymer and a liquid insulating plasticizer compound, said insulating plasticizer compound being chosen from compounds derived from mineral oils, preferably from hydrocarbons, and from compounds derived from of vegetable oils, preferably esters of vegetable oils, said insulating plasticizer compound not being a phase change type material at a temperature of -10 ° to + 150 ° C, the mass proportion of said compound insulating plasticizer in said matrix being at least 50%, preferably at least 60%, and

- (B) hollow beads, preferably glass microbeads, dispersed within a matrix of said homogeneous mixture of said polymer and said insulating plasticizer compound, in a volume proportion of at least 35% of the total volume of the mixture of said beads with said matrix, preferably 40 to 65% of the total volume.

A material according to the present invention exhibits properties of thermal insulation, of buoyancy and of resistance to cracking increased as well as a lower cost compared to a syntactic foam material made up of the same constituents but without a plasticizing compound as will be explained below. -after.

The insulating gels described in document WO 02/34809 have the essential function of providing thermal insulation while exhibiting high compressive strength due to their almost incompressible nature whatever the pressure level, that is to say. say as far as the abyss (- 10,000 m), or even beyond.

Consequently, it was not obvious to add hollow microspheres within an insulating gel of the type of WO 02/34809 insofar as said hollow microbeads are subject to implosion when their mechanical resistance limit pressure is exceeded. Indeed, the mixture of the insulating gel of WO 02/34809 with hollow microbeads in accordance with the material defined in claim 1 of the present application has a certain rigidity and loses its incompressible character due to the presence of the hollow microbeads.

Moreover, it was not obvious that a material according to the present invention would exhibit an improvement in thermal insulation properties compared to a syntactic foam comprising the same polymer and the same level of hollow microbeads as demonstrated according to the present invention with hollow microbeads in accordance with the subject of the present invention.

In fact, the inventors accidentally discovered that the mixture of an insulating gel and hollow microbeads had an unexpected and non-obvious advantage in that its buoyancy does not decrease, or even increases with depth, whereas conversely, the buoyancy of a syntactic foam material (similar material

U but without plasticizer compound) decreases very significantly with water depth.

This increased buoyancy as a function of depth results from the fact that the compressibility modulus of said rigid insulating material according to the invention is greater than the compressibility modulus of water, namely greater than 2200 MPa, the compressibility modulus of water being around 2000 MPa.

In other words, the increase in buoyancy of said material results from the fact that the density of water increases more than that of said material depending on the depth at which the material is found.

Consequently, a rigid insulating material according to the invention or CBG is much more efficient in terms of buoyancy at great depth, in particular for depths of 1000 to 3500 m and beyond, in comparison with a syntactic foam of the prior art ( similar material without plasticizer compound) whose compressibility modulus does not exceed 1600 MPa (see example 3 below).

In addition, as explained in the description, in a syntactic foam, in the event of significant compression at great depth, cracks in the matrix and breakage of the microbeads which come into contact with one another are observed, while in the material according to the present invention the breakage of the microbeads occurs for a compression value therefore a water depth of 15 to 30% greater than that of traditional syntactic foam.

The advantageous technical effects of the plasticizer compound with regard to the properties of the microbeads constitute new technical effects of the plasticizer compound which were neither described nor suggested in either of the two documents WO 02/34809 and FR 2587934.

Although the inventors do not want to be bound by this theory, they believe that these advantageous techniques can be explained by the fact that a film of plasticizing compound always remains on the surface of the microbeads: the microbeads are always separated by a thin layer of mixture. polymer / plasticizer compound which then acts as a cushion or shock absorber in the case of significant pressure variations, so that the phenomenon of stress concentration existing in the syntactic foam and resulting in cracks of the matrix and breakage microbeads does not occur in the material according to the invention.

Finally, the cost of a material according to the present invention is much lower than that of the syntactic foams of the prior art insofar as the said plasticizing compound is of a cost much lower than that of the said polymer constituting the matrix.

All in all therefore the material according to the present invention provides better mechanical properties of resistance to cracking and increased buoyancy at great depth as well as a lower cost than a comparable syntactic foam material (similar components without plasticizer compound).

The very important and unexpected advantages resulting from the new composition of the material according to the present invention described above will be explained below.

By thermal insulator is meant here a material whose thermal conductivity properties are less than 0.25 W / m / K and by positive buoyancy a density of less than 1.

By rigid material is meant here a material which holds its shape by itself and does not substantially deform due to its own weight when it is preformed by molding or confined in a flexible envelope, and whose Young's modulus λ is greater than 200 MPa, unlike a gel which remains extremely flexible and whose Young's modulus is almost zero.

It is understood that the molecules of said plasticizer compound are miscible, therefore compatible in terms of polarity and chemically inert with said polymer and the mono or plurîfunctional and / or monomeric pre-polymer components when they are mixed before crosslinking, the whole forming a crosslinkable composition. by reacting said components of said polymer by mixing them with one another, the molecules of said insulating plasticizer compound being trapped and dispersed within a three-dimensional crosslinked network of said polymer as the network is crosslinking after mixing of said components, preventing or, at the very least, reducing sweating and / or convection and / or percolation of said insulating plasticizer compound out of the matrix after crosslinking.

It is also understood that, in a known manner, said matrix of homogeneous mixture of polymer and plasticizer compound fills all of the interstices between the microbeads.

The term “mineral oil” is understood here to mean a hydrocarbon-based oil obtained from fossil material, in particular by distillation of petroleum, coal, and certain bituminous shales and vegetable oil, an oil obtained from plants by extraction, in particular in the case of oils rapeseed, sunflower or soybean, and more particularly by treatment in the case of esters of these vegetable oils.

In a known manner, the hollow balls are filled with a gas and resist the hydrostatic external pressure underwater. They have a diameter of 10 µm to 10 mm, and, for microspheres, 10 to 150 µm, preferably 20 to 50 µm and have a thickness of 1 to 2 microns, preferably about 1.5 µm. Such glass microspheres are available from the company 3M (France).

More particularly, to produce an insulating material according to the present invention, hereinafter abbreviated as GBG (Glass Bubble Gum), that is to say gum of glass beads, resistant to 2,500 m, or approximately 25 MPa, Advantageously, a selection of microspheres is used, the Gaussian distribution of which is centered on 20 μm, while for a depth of 1250 m, a Gaussian distribution centered around 40 μm is suitable.

The phase stability of the plasticizer compound according to the invention at temperature values of -10 ° to + 150 ° C, makes it compatible with the temperature values of sea water and oil production fluids at deep sea.

As explained below, a rigid insulating material according to the present invention, although relatively rigid within the meaning of the present invention, exhibits a mechanical behavior in terms of compressibility which is similar to an elastomeric rubber due to the low value of its modulus. de Young, whereas a syntactic foam behaves like a solid.

The rigidity within the meaning of the present invention of the insulating material results essentially from the high mass content of said microbeads, said microspheres also providing a gain in buoyancy and thermal insulation compared to an insulating gel of the same composition.

A rigid thermal insulation and / or buoyancy material according to the present invention has properties of buoyancy, thermal insulation and mechanical strength, in particular of quasi-incompressibility, superior to the traditional syntactic foams and insulating gels of the prior art, because higher thermal insulation properties and lower density values of said constituent insulating plasticizer compound which it contains in the polymer matrix.

In addition, due to the plasticizing nature of said insulating plasticizing compound, the crosslinking reaction of the polymer of the matrix exhibits an attenuated exothermic character or, at the very least, the convexion and evacuation of the heat released during the crosslinking process does not cause no degradation and / or inhomogeneity in the mass C of the matrix during the crosslinking process or subsequently and, in particular on large thicknesses of material.

In this regard, it should be noted that an essential advantageous technical function of said polymer of the matrix is to reduce convection phenomena, by preventing the displacement of molecules of said insulating plasticizer compound.

Another essential advantage of the thermal insulation and / or rigid buoyancy material according to the present invention is its relative cost which is much lower than that of the syntactic foams of the prior art, insofar as the use of said insulating plasticizer compound represents a significant reduction in costs compared to a material comprising exclusively a polymeric matrix, due to the fact that said crosslinked polymeric materials are more expensive than the liquid plasticizer compound according to the present invention.

Finally, due to the properties of said insulating plasticizer component in the temperature range indicated, as well as the glass transition values of said polymer, the thermal insulation material according to the present invention can be used to convey hot fluids, such as , in particular, production oils at temperatures ranging from -10 ° C to 150 ° C and, therefore, in cold seas, as is the case in deep seas, where the temperature of l the water is about 2 to 4 ° C.

Another advantage of the rigid material according to the present invention, compared in particular with the insulating gel of the prior art, lies in that said plasticized insulating compound is more trapped in the polymer matrix, which exhibits increased stability over time in terms of composition. , said plasticizer compound exuding less outside the matrix because said insulating plasticizer compound is more trapped in said solidified polymeric matrix than in the insulating gel of the prior art. This results in a reduced thermal convection property of said rigid insulating material compared to the insulating gel of the prior art.

It should be observed that homogeneous mixtures of polymers and insulating plasticizing compounds, used in the rigid material according to the present invention, had already been implemented in the form of insulating gels in WO 02/34809, but it is not 'had never been envisaged, nor suggested, that it is possible to formulate them as a mixture with hollow microbeads, to obtain advantageous rigid materials in accordance with the present invention, all the more so since these insulating gels were sought essentially for their character of high resistance to compression due to their quasi-incompressible nature whatever the pressure level, that is to say up to the abyss (- 10,000 m), which incompressibility disappears in the rigid material according to the present invention due to the presence of hollow microbeads subject to implosion when their mechanical resistance limit pressure is exceeded.

More particularly, the rigid insulating material according to the present invention has a density of less than 0.7, preferably less than 0.6, and a thermal conductivity of said material of less than 0.15 W / m / K, preferably less than 0 , 13 W / m / K, and a Young's modulus or triaxial compressive modulus of said material of 100 to 1000 MPa, preferably 200 to 500 MPa and a compressibility modulus of said rigid insulating material greater than 2000 MPa, of preferably greater than 2200 MPa, that is to say a compressibility modulus greater than that of water.

It should be noted that no prior art thermal insulation and / or buoyancy material exhibits the combined characteristics of buoyancy, thermal insulation and compressibility as defined above.

Comparatively, the same material without microbeads is in the form of an insulating gel with a thermal conductivity greater than 0.13 W / m.k.

More particularly still, the rigid insulating material according to the present invention, hereinafter abbreviated as GBG, has an elastic modulus in triaxial compression, or Young's modulus, of between 100 and 1000 MPa, preferably between 200 and 500 MPa. , the compressibility modulus of the GBG (bulk modulus in English) being similar or even greater than that of sea water, the compressibility of which is of the order of 2,100-2,200 MPa depending on salinity and temperature. Thus, at great depth, the density of seawater increases faster than that of GBG and therefore the buoyancy of said GBG is either independent of the depth of water, or increases slightly with the depth of water. On the other hand, a syntactic polyurethane or epoxy foam of the prior art exhibits a Young's modulus close to its compressibility modulus of a value of approximately 1500 1600 MPa and its buoyancy therefore decreases significantly with increasing pressure. water depth. Consequently, the rigid insulating material according to the invention or GBG is much more efficient in terms of buoyancy and insulation than the syntactic foams of the prior art, this being all the more accentuated as the water depth becomes greater. , ie for depths of 1000 to 3500 m, or even more.

The best performance of the GBG according to the invention is due to the fact that the compressibility modulus of the plasticizer compound is very high, while that of the elastomeric polymer is rather low, which therefore drastically increases said compressibility modulus of the GBG. Thus, a syntactic foam behaves like a solid, while the rigid insulating material or GBG according to the present invention behaves like a flexible elastomer due to the low value of its Young's modulus.

A rigid insulating material according to the present invention therefore resists compression better than a syntactic foam of the same polymer composition and proportion of the same microbeads at stress levels of submarine hydrostatic pressure where a said syntactic foam degrades and cracks. . It seems that this is linked to the physicochemical properties of said plasticizer compound. More specifically, the oily plasticizer compound increases the adhesion of the matrix to the surface of said microspheres and said microbeads are permanently covered with a film of matrix of said polymer and said plasticizer compound, and, this, even in the event of significant compression. . Thus, a rigid insulating material according to the present invention is more resistant to compression than a syntactic foam, without cracking and without loss of thermal insulation and / or buoyancy due to the breakage of the microbeads, that is to say without breaking. microbeads for a compression value, therefore a water depth, 15 to 30% greater than that of traditional syntactic foam. In the syntactic foam, it is observed, in the event of significant compression and cracking of the matrix, that the adjacent microspheres come into direct contact with one another and break, whereas, in the material according to the invention, this phenomenon requires greater compressions probably because the microspheres remain fully coated on all their surfaces with a layer of the mixture of said matrix.

The mechanical behavior of the rigid insulating material according to the present invention, hereinafter referred to as GBG (Glass Bubble Gum), is radically different from that of a syntactic polyurethane or epoxy foam. In fact, in a syntactic foam, the glass microspheres trapped in the polymer matrix are mainly used to create perfectly spherical microcavities, these microcavities resistant to implosion thanks to the rigidity of the impregnation resin, either a polyurethane or epoxy. Thus, during the impregnation of the microsphere, the latter are in point contact with each other. When the polymer foam is subjected to a strong external pressure, this results in significant deformations of this rigid resin which behaves like a solid, leading to local stress concentrations, the latter generally occurring very locally and leading to destruction of the microspheres of said zone, then deformation of the microcavities, and finally the collapse of the structure of the syntactic foam in this restricted localized zone. The process then generally propagates over distances which can be large and, in the case of isolated pipes, localized collapses or cracks appear in the insulating coating, said cracks being able to be several centimeters, or even several decimeters, s 'sometimes extending over the entire circumference of said pipe.

On the other hand, the behavior of the rigid insulating material according to the present invention or GBG is radically different, because it behaves like a flexible elastomer and not like a solid, due to the high proportion of plasticizing compound in the final product and its physico-chemical property as a compound derived from mineral or vegetable oil. Indeed, the rigid insulating material retains a high internal flexibility, therefore a high capacity for local deformation. Thus, when the external pressure P increases, the entire internal volume of said matrix of rigid insulating material or GBG is found substantially at said pressure P and each of the microspheres is in intimate contact with the matrix compound, polymer - plasticizer compound. . Direct contacts between two or more microspheres are no longer punctual, as is the case in syntactic foam, because the microspheres are always separated by the plasticizer compound polymer mixture which then plays the role of cushion or shock absorber in the case. sudden pressure variations, for example variations due to an external shock under pressure P corresponding to the depth at which said insulating material or GBG is located. Thus, in the rigid insulating material according to the invention or GBG, the stress concentration phenomenon existing in the syntactic foam does not occur. The insulating plasticizer compound fulfills, in the rigid insulating material according to the present invention, a new technical effect.

More particularly therefore, said microspheres are in direct contact with one another, but their external surfaces remain entirely coated with at least one film of mixture of said matrix, said mixture occupying all of the interstices between said microbeads. This matrix film is easily deformable.

More particularly, said plasticizing compound has a compressibility modulus greater than that of said polymer, preferably greater than 2000 MPa, a thermal conductivity, as well as a density, lower than that of said polymer, preferably a thermal conductivity less than 0, 12 W / m / K and a density of less than 0.85, more preferably 0.60 to 0.82.

More particularly, a rigid insulating material according to the present invention has the following characteristics:

- the mass ratio of said crosslinked polymer and of said insulating plasticizer compound is 15/85 to 40/60, preferably 20/80 to 30/70, and

the volume ratio of said microbeads relative to the volume of said matrix of crosslinked polymer and of said insulating compound is 35/65 to 65/35, preferably 40/60 to 60/40, more preferably 45/55 to 57/43.

Beyond 85% of plasticizer compound in the matrix, the latter risks exuding outside it.

Also advantageously, said polymer has a glass transition temperature of less than -10 ° C., its phase stability thus being compatible with the temperature values of sea water and of petroleum production fluids at deep sea levels.

More particularly, these compressibility properties and thermal insulation properties and comparative density of said plasticizer compound and said polymer are observed when, in accordance with a preferred embodiment, said crosslinked polymer is of polyurethane type and said liquid plasticizer compound is a product. oil tanker, said to be light cut fuel type.

Insulating plasticizing compounds of this type have the additional advantage of being approximately 5 to 10 times less expensive than that of polymers such as polyurethane used in traditional syntactic foams.

More particularly still, said plasticizer compound is chosen from kerosene, gas oil, gasoline and white spirit.

These fuels, with the exception of gasolines, also have the advantage of having a flash point above 90 ° C, thus eliminating any risk of fire or explosion in the manufacturing process.

Kerosene has a thermal conductivity of about 0.11 W / m / K.

In another embodiment, a plasticizing compound derived from vegetable oil of the biofuel type is used, preferably an oil ester of vegetable origin, in particular an alcoholic ester of vegetable oil, rapeseed, sunflower or soy.

More particularly, said polymer is a polyurethane resulting from the crosslinking of polyol and poly isocyanate, said polyol preferably being of the branched type, more preferably at least in a 3-branched star, and the polyisocyanate being an isocyanate prepolymer and / or polyisocyanate polymer.

More particularly still, said polyurethane polymer results from the crosslinking by polyaddition of hydroxylated polydiene, preferably hydroxylated polybutadiene, and of aromatic polyisocyanate, preferably 4,4'-diphenyl-methane isocyanate (MDI) or a polymeric MDI.

Preferably, the NCO / OH molar ratio of the two polyol and polyiscocyanate components is from 0.5 to 2, preferably greater than 1, more preferably from 1 to 1.2. An excess of NCO ensures that all of the OH has reacted and that crosslinking is complete or, at the very least, optimal.

Advantageously, said rigid material is confined in a protective envelope.

The outer casing can be made of metal, such as iron, steel, copper, aluminum and metal alloys, but also can also be of polymeric synthetic material, such as polypropylene, polyethylene, PVC, polyamides , polyurethanes or any other polymer convertible into tubes, plates or envelopes, or else obtained by rotational molding of thermoplastic powders, or else into composite materials. The option of envelopes made of polymeric materials mentioned above is an option which is all the more practical and effective as the solution of the invention, allowing a rigid insulating material according to the invention to be obtained, makes the use possible. envelope materials that are less rigid, lighter and less difficult to use and, consequently, less expensive overall.

The outer casing may preferably be a more or less rigid thick layer, from a few millimeters to several centimeters in thickness, but may also be in the form of a flexible or semi-rigid film.

The free space between the fluid transport pipe and the outer casing, where the rigid insulating material according to the invention will be applied, can be variable and will be defined as a function of the desired degree of insulation, calculated from the coefficient d insulation of the rigid insulating material according to the invention and the temperatures to be maintained, or the desired buoyancy calculated from the density of the rigid insulating material according to the invention.

More particularly, said rigid insulating material is in the form of a pre-molded part, preferably suitable for being applied around an underwater pipe or an underwater pipe element to ensure thermal insulation and / or buoyancy and resistant to subsea hydrostatic pressure, preferably at a great depth of at least 1000 m.

According to another embodiment, said rigid insulating material according to the invention is not pre-molded but molded in situ, by casting before crosslinking as explained in the process according to the invention below.

In a manner known to those skilled in the art, the setting time, which is the time necessary for the composition according to the present invention to be completely crosslinked, can vary to a large extent. However, this setting time can be adjusted, in particular by using a certain proportion of crosslinking catalyst to obtain an adequate setting time.

The present invention also provides a process for preparing a rigid insulating material according to the invention, characterized in that the following steps are carried out in which:

1 / - said insulating liquid compound is mixed with the monomers and / or prepolymer capable of reacting in particular by polyaddition, to form said crosslinked polymer, until a homogeneous mixture is obtained, preferably by evacuating, namely by sucking the 'air and other gas vapors by vacuuming, to obtain a degassed mixture, and

2 / - a homogeneous mixture from step 1 / - is mixed with said microspheres to obtain a homogeneous mixture, in particular of fluid to pasty consistency, preferably by evacuation, and

3 / - said mixture from step 2 / - is left to stand so that the reaction until complete crosslinking forms a said rigid thermal insulating material, preferably baked at a temperature of 18 to 30 ° C and for at least 24 hours, more preferably 24 to 72 hours.

The suction of the air by vacuuming makes it possible to obtain a degassed mixture which is advantageous because the rigid insulating material according to the invention is then almost incompressible and has a compressibility modulus of the order of 2200 MPa, whereas the presence of air or gas micro-bubbles would lead to a drastic reduction of the material as soon as it is subjected to an external pressure, therefore as soon as it is at great depth below sea level.

More particularly, as mentioned previously, in step 3 / -, the successive steps are carried out in which:

3a / - said mixture of step 2 / - is poured or injected into an envelope serving as a mold or into a space formed by (a) the outer surface of a pipe element or submarine pipe to be insulated and / or whose buoyancy is desired, and (b) the inner surface of a said protective envelope, then

3b / - said mixture is left to stand in said envelope until crosslinking and complete solidification in situ.

Advantageously, said envelope is made of polyethylene, polypropylene, polyamide and / or PVDF, preferably by rotational molding or extrusion.

A subject of the present invention is therefore also the use of a thermal insulation and / or rigid buoyancy material according to the invention, for the insulation and / or the buoyancy of an underwater pipe or underwater pipe element. .

More particularly, said subsea pipe element is an elbow junction coaxial pipe element.

More particularly still, said pipe conveys a hot fluid at a temperature of 20 to 80 ° C in sea water the temperature of which is less than 20 ° C, preferably less than 4 ° C, preferably at a great depth of water. at least 1000 m.

More particularly still, the present invention provides a thermally insulated submarine junction pipe, consisting of coaxial pipes of the PiP type, as described in WO 2010/063922, ensuring the junction between two portions of thermally insulated submarine pipes, said junction pipe comprising a rigid bent internal pipe, preferably made of steel and having a radius of curvature of 3 to 10 times its external diameter, preferably 4 to 5 times its external diameter, coated with a thermal insulating material, comprising:

- an outer casing surrounding said inner pipe, made of flexible or semi-rigid material following the bent shape of said inner pipe, concentrically,

the tubular wall of said outer casing comprising structural reinforcing elements of annular or helical shape capable of allowing the curvature of said tubular wall of the outer casing while maintaining its substantially uniform cross section, preferably substantially circular, and concentric with the cross section of said inner pipe, despite its curvature to follow the bent contour of said inner pipe according to its said radius of curvature, and

- a plurality of support elements called centralizing elements in rigid plastic or composite materials interposed between said inner pipe and said outer casing so as to keep the cross sections of said outer casing and inner pipe substantially concentric, said centralizing elements being spaced apart in the direction axial of said pipe every at least 1 m, preferably every 3 to 10 m, and

a plurality of longitudinal guide elements made of rigid or semi-rigid material, arranged at a substantially constant distance, preferably constant, from the surface of the bent internal pipe, extending between two successive centralizing elements on the periphery of which the ends of said longitudinal guide elements preferably rest at least four said guide elements regularly distributed over the periphery of said centralizing elements, and

a rigid thermal insulating material according to the invention, completely filling the annular space between said internal pipe and said external envelope.

Other characteristics and advantages of the present invention will become apparent in the light of the detailed description which follows, with reference to the following FIGS. 1 to 4 in which:

- Figure 1 shows a bottom-surface connection between a floating support 22 on the surface 20 and an underwater pipe 4 resting on the seabed 21, consisting of a hybrid tower 1 consisting of at least one riser 2, consisting of a rigid pipe, and at least one flexible pipe 3 ensuring the connection between the upper end of said riser (s) and said floating support 22, the junction between the submarine pipe 4 and the lower end of the (or ) said riser (s) 2 being produced using bent junction pipe (s) 5;

- Figure 2 shows an example of a portion of a bent junction pipe, consisting of coaxial pipes;

- Figure 3A shows a buoyancy module 8, able to slide along said riser (s) 13 or 14, optionally comprising a central tendon 13, said buoyancy module 8 being equipped with shell-shaped buoyancy elements of cylindrical section 9;

- Figure 3B shows a longitudinal sectional view of a said shell of buoyancy elements 9, made of a rigid insulating material according to the invention 11 protected by a protective envelope 10, filled entirely with said rigid insulating material 11 by casting through a closed orifice 12 of a plug 12a, said shell being shown empty on the left and full and plugged on the right;

FIG. 4A represents an installation comprising an export pipe 16 between a floating support 22 and an unloading buoy 23, said export pipe 16 being equipped with coaxial floats 15;

- Figure 4B shows in longitudinal section the pipe 16 equipped with coaxial floats 15, completely filled with rigid insulating material according to the invention 11 cast before crosslinking in the chamber 17 of the float, the left casing being assembled in a sealed manner on the pipe 16, empty and having a filling orifice 19, the right one being full and blocked at 19a.

A general method for preparing and installing a rigid insulating material according to the invention, or CBG, comprises the following successive steps:

1- mixing polyol with kerosene, and

2- is added with stirring iso cyanate in a polyol / iso cyanate mass ratio of 30/1 to 35/1, corresponding to an NCO / OH molar ratio of 1 to 1.2, the polymer / kerosene mass ratio being from 23/77 to 27/73, the above mixtures being carried out intimately under vacuum suction to obtain a homogeneous mixture of fluid to pasty, then

3- the homogeneous uncrosslinked mixture above is thickened with glass microspheres in a mass ratio of 75/25 to 65/35, under vacuum suction to obtain a mixture of fluid to pasty, saturated with microbeads, then

4- said mixture is poured into an envelope serving as a mold and surrounding the element to be insulated or lightened (buoyancy), and the whole is left to stand, if necessary steamed at a temperature of 18-25 ° C, to a period of 24 to 72 hours, until complete crosslinking of the whole.

The function of the casing is to isolate the rigid insulating material from the ambient seawater at great depth so as to prevent the migration of the plasticizing compound, if applicable kerosene, into the ambient environment throughout the service life of the installation, that is to say for 25 to 30 years or more.

In embodiments 1 and 2 described below, the following constituents were used:

- PolyBd®45HTLO = hydroxylated polybutadiene with a number-average molecular weight Mn equal to 2,800 with a polydispersity Mw / Mn = 2.5, exhibiting a hydroxyl number of 47.1 mg KOH / g, a viscosity of 8,000 mPa. s at 23 ° C and a specific gravity of 0.925, and a glass transition temperature of -75 ° C. This product is marketed by the company CRAYVALLEY (France).

- Isonate® 143L = sold by the company DOW CHEMICAL = polymeric MDI having an NCO content equal to 29.2%, a viscosity at 25 ^Q C equal to 33 cps (33 mPa.s).

- Ketrul® 211 = aromatized kerosene marketed by the company TOTAL Fluides of the TOTAL group (France),

- microbeads of commercial references S38XHS from the company 3M, made of sodium alumino-silicate glass of pyrex® type, with an average diameter of 10 to 40 μm, a wall thickness of approximately 1.5 μm, and of true density 0.38, and of which more than 90% are able to withstand an external pressure of 5500 PSI, that is to say substantially 38 MPa. By true density is meant the density of the microbeads alone and not the density of a volume of 11 filled with beads: - in fact, these

W last being in contact with each other, there then remains within this volume of 1 I, a free volume between said microspheres: - the density in this case is an apparent density (bulk density) which is then much lower than the true density, but does not really make sense with respect to the final compound according to the invention.

Example 1:

To obtain 1 m ³ of a fluid to pasty mixture of the insulating material according to the invention, before crosslinking, obtained in step 4 / - below, the consistency of which is sufficiently liquid for its placement in the envelope, it is necessary to performs the following successive steps, in which:

1 / - 116.5 kg of PolyBd® are mixed with 350 kg of Ketrul® with a density of 0.81, then evacuated and stirred for a few minutes, then

2 / - 19.2 kg of Inosate® are added, and mixing is continued under vacuum for several minutes, then

3 / - 162 kg of glass microbeads are incorporated and mixing continues under vacuum for several minutes until the material is in the form of a fluid paste, and

4 / - the fluid paste from step 3 / - is poured into an envelope, then the whole is left to stand for several hours, or even several days, until complete crosslinking.

The corresponding volume ratios are 42.6% microspheres for 57.4% gel.

The crosslinked insulating material according to the present invention thus obtained, hereinafter referred to as GBG, has a density of 0.648 with respect to fresh water, which then gives a buoyancy of 352 liters / m ³ of GBG, ie a positive buoyancy of 363 kg / m ³ of GBG, for seawater density 1.03.

The thermal conductivity of this rigid insulating material according to the invention or GBG is approximately λ = 0.13 W / m / K.

Comparatively, an insulating gel made of the same polyurethane based on PolyBd® and Inosate® with the same ratio of Ketrul® 211, would have a thermal conductivity of λ = 0.14 W / m / K, and an insulating material of the syntactic foam type consisting of the same polyurethane based on PolyBd® and Inosate® (without Ketrul®), with the same ratio of the same glass microspheres, would have a thermal conductivity of λ = 0.17-0.18 W / m / K.

Example 2:

In the same way, 1 m ³ of pasty mixture is obtained before crosslinking in step 3 / - above with a more viscous consistency by mixing, according to the same process as above, 91.5 kg of PolyBd® with 274.5 kg of Ketrul®, then 15.1 kg of Inosate®, then 209 kg of glass microbeads. The corresponding volume ratios are 55% microspheres for 45% gel.

The insulating material according to the invention, called GBG, obtained after crosslinking, then has a density of 0.590 with respect to fresh water, which then gives a buoyancy of 410 liters / m ³ of GBG, ie buoyancy of 422.5 kg / m ³ of GBG for seawater with a density of 1.03. An increase in buoyancy of 16.4% is thus observed compared to the more fluid formulation of Example 1.

The thermal conductivity of this rigid insulating material according to the invention or GBG, is λ = 0.12 W / m / K.

Comparatively, an insulating gel and an insulating material of syntactic foam type consisting of the same polyurethane based on PolyBd® and Inosate®, (without Ketrul® and) with the same ratio of the same glass microspheres with regard to the syntactic foam), would exhibit thermal conductivities of λ = 0.13 W / m / K for the gel and λ = 0.17-0.18 W / m / K for the syntactic foam.

Example 3:

For the two rigid insulating materials according to the invention or GBG of Examples 1 and 2, a Young's modulus of close to 400 MPa is obtained at the end of the crosslinking process, then it decreases asymptotically towards 250-300 MPA after 10 or 20 years (accelerated aging tests).

The compressibility modulus of the GBG (bulk module) is of the order of 2250 MPa.

In comparison, an insulating material of the syntactic foam type made up of the same polyurethane based on PolyBd® and Inosate®, without Ketrul® 211, with the same ratio of the same glass microspheres, would have a Young's modulus of 200 to 600 MPa and a modulus compressibility of a value of about 1600 MPa.

In comparison, an insulating gel made up of the same polyurethane based on PolyBd® and Inosate®, with the same ratio of Ketrul® 211, would have a compressibility modulus of a value of approximately 1900 MPa and an almost zero Young's modulus, because it then behaves like a fluid.

Example 4:

The relatively more fluid formulation of the pasty mixture of step 3 / - of Example 1 is more suitable for filling envelopes delimiting small thicknesses of insulating materials, in particular from 3 to 10 cm and / or long lengths. of insulating materials, in particular from 5 to 20 m, as required for the insulation of coaxial elbow junction pipes described in patent WO 2010/063922 and in Figures 1 and 2. In this case, in fact, the casing of the insulating material is formed by the outer surface of the inner pipe 5a and the inner surface of the outer pipe 5b, the annular space 5c being closed at its longitudinal ends by plugs 6. And, the centralizing elements 7 are perforated to leave said pasty mixture from step 3 / - to flow off before crosslinking.

It should be noted that, in this very particular type of application, the insulating character of the GBG is sought more than its performance in terms of buoyancy, which justifies the use of a GBG of rather fluid consistency. And, it is necessary to achieve a compromise in terms of fluidity and thermal performance so as to guarantee good placement of the GBG in this space of small thickness and great length.

Example 5:

The insulating materials or GBGs according to the present invention, obtained in Example 2, are more particularly useful for preparing buoyancy modules 8, as described in Figures 1 and 3A-3B, comprising preconstituted shells 9, comprising an insulating material according to invention 11 cast in and protected by a casing 10. The buoyancy modules 8 are intended to slide around and isolate the risers 2, 13, 14, of an installation shown in FIG. 1, as described in WO 2010/097528. These buoyancy modules 8 make it possible to obtain positive buoyancies distributed over portions of the length of pipes with a greater thickness of insulating material 11, in particular from 10 to 30 cm, but over reduced lengths with regard to the buoyancy elements. 9, namely from 1 to 10 m. The buoyancy modules 8 can be implemented on pipes, both in a vertical position and in a horizontal position.

Example 6:

According to another embodiment, as shown in FIGS. 4A and 4B, the pasty mixture of step 3 / - of Example 2 is poured in situ in a float chamber 15, consisting of a flexible or rigid tubular outer wall. 17 closed and fixed in a sealed manner at its longitudinal ends 18 around the outer surface of an export pipe 16, thus forming a sealed enclosure between the pipe 16 and the inner wall of the casing 17. The pasty mixture of the 'step 3 / - is cast into said chamber of floats 15 through an orifice 19 closed by a plug 19a. This type of export conduct 16 has been described in more detail in WO 2006/120351 and WO 2009/138609.

In this type of export pipe, the said pipe is located at a shallow depth, generally between 50 and 100 m below the surface of the water: - the pressure of the ambient environment is then 0.5 to 1 MPa. It is then advantageous to use microspheres having a lower resistance to pressure than in the previous examples 1 and 2. For this purpose, use will advantageously be made of microspheres referenced K20 (3M France). The latter have a true density of 0.2, therefore considerably reduced, but also a maximum implosion pressure reduced to 500 PSI (~ 3.5 MPa), which is perfectly suited to the installation depth of said lines of export. Thus, 1 m ³ of a pasty mixture of viscosity similar to that of Example 2 is prepared with 91.5 kg of PolyBd® with 274.5 kg of Ketrul®, then 15.1 kg of Inosate®, then 110 kg of K20 type glass microbeads (3M France). The corresponding volume ratios are 55% microspheres for 45% gel.

The insulating material according to the invention, called GBG, obtained after crosslinking, then has a density of 0.491 with respect to fresh water, which then gives a buoyancy of 509 liters / m ³ of GBG, i.e. buoyancy of 524.5 kg / m ³ of GBG for seawater with a density of 1.03. An increase in buoyancy of 44.5% relative to the more fluid formulation of example 1 is thus observed, and an increase in buoyancy of 24.1% relative to the pasty formulation of example.

2.

Example 7:

Likewise, for a bottom-surface connection as described with reference to FIG. 1, the buoyancy elements of the lower part of the riser will be advantageously produced using high pressure microspheres (type S38XHS from 3M France) and the upper elements will advantageously be produced using low pressure microspheres (type K20 from 3M France), the intermediate elements being advantageously produced using intermediate pressure microspheres available from this same supplier. The cost of the buoyancy required for such an installation is thus optimized.

Example 8:

Preferably, the casing 10 and 17 of Examples 4 and 5 is produced by rotational molding or by extrusion, so as to minimize the connections by welding, gluing or by mechanical assembly, these methods being a source of leakage, and therefore of pollution of the environment. ambient by migration of kerosene. For this purpose, thermoplastic materials are preferably used which limit the migration by percolation of the plasticizer compound and more particularly kerosene, for example polyamide (PA) or PVDF, the latter being particularly well suited to the production of said envelopes.

In the case of rotational molding with a polyamide or a PVDF, due to the high cost of the raw material, a rotational molding is preferably carried out in two stages, but continuously. First, the envelope is rotomoulded with polyethylene (PE) or polypropylene (PP), so as to form the resistant wall of the envelope (75 to 90% of the thickness of said wall), then, Once the PE / PP wall has been completely melted and adhered to the wall of the mold, the second charge of PA / PVDF is then introduced and the rotational molding is continued until the wall is entirely made of a bilayer having l '' outside towards the inside: - a first external layer of PE / PP representing approximately 75 to 90% of the final thickness, and - a second internal layer of PA / PVDF representing approximately 25 to 10% of the thickness final. Thus, the envelope is produced at a lower cost and has optimum mechanical strength (PE / PP) as well as a barrier limiting, or even eliminating, the percolation of the plasticizing compound and more particularly of the kerosene to the outside, thus respecting the ambient environment. , ie the seabed and its fauna.

Example 9:

The use of kerosene as a liquid plasticizing insulating compound has been described above, but a lighter fuel, such as gasoline, can also be used, since the latter has a lower density of 0.75, a modulus of compressibility of about 2100 MPa, therefore similar to that of kerosene, and a thermal conductivity of 0.07 W / m / K, therefore extremely low, which leads to a rigid insulating compound according to the invention with similar mechanical performance , insulation performance mats and greatly improved buoyancy. On the other hand, due to the flash point of gasoline, the latter being very low (-43 ° C), the manufacturing process is more dangerous due to the risks of explosion and, therefore, does not constitute the preferred version of the invention.

Claims (3)

1. Material of thermal insulation and / or rigid buoyancy characterized in that it consists of a mixture of: - (a) a matrix of a homogeneous mixture of polymer 5 crosslinked elastomer and a liquid insulating plasticizer compound, said insulating plasticizer compound being chosen from compounds derived from mineral oil, preferably from hydrocarbons, and compounds derived from vegetable oils, preferably esters of vegetable oils, said insulating plasticizer compound not being a phase change type material at a temperature of -10 ° to + 150 ° C, the mass proportion of said plasticizer compound in said matrix being at least 50%, preferably at least 60%, and - (b) hollow beads, preferably glass microbeads, dispersed within a said matrix of said homogeneous mixture of said 15 polymer and said insulating plasticizer compound, in a volume proportion of at least 35% of the total volume of the mixture of said beads with said matrix, preferably 40 to 65% of said total volume. 2. Thermal insulation and / or buoyancy material according to claim 1, characterized in that said plasticizer compound has A modulus of compressibility greater than that of said polymer, preferably greater than 2000 MPa, and a thermal conductivity, as well as a density, lower than that of said polymer, preferably a thermal conductivity of less than 0.12 W / m / K and a density of less than 0.85, more preferably 0.60 to 0.82. 25 3. Material of thermal insulation and / or buoyancy according to claim lou 2, characterized in that: - the mass ratio of said crosslinked polymer and said insulating plasticizer compound is from 15/85 to 40/60, preferably from 20/80 to 30/70, and ï t - the volume ratio of said microbeads relative to the volume of said matrix of crosslinked polymer and of said insulating compound is 35/65 to 65/35, preferably 40/60 to 60/40, more preferably 45/55 to 57/43. 4. Material of thermal insulation and / or buoyancy according to one of claims 1 to 3, characterized in that said crosslinked polymer is of the polyurethane type and said liquid plasticizer compound is a petroleum product, said of light cutting of the fuel type. . 5. Thermal insulation and / or buoyancy material according to one of claims 1 to 4, characterized in that said plasticizing compound is chosen from kerosene, gas oil, gasoline and white spirit. 6. Material of thermal insulation and / or buoyancy according to one of claims 1 to 5, characterized in that said crosslinked polymer is a polyurethane resulting from the crosslinking by polyaddition of hydroxylated polydiene, preferably hydroxylated polybutadiene, and of polyisocyanate. aromatic, preferably 4,4'-diphenyl-methane diisocyanate (MDI) or a polymeric MDI. 7. Thermal insulation and / or buoyancy material according to one of claims 1 to 6, characterized in that said material is confined in a protective envelope. 8. Thermal insulation and / or buoyancy material according to one of claims 1 to 7, characterized in that said material is in the form of a pre-molded part, preferably suitable for being applied around an underwater pipe. or a subsea pipe element to provide thermal insulation and / or buoyancy thereof and resistant to subsea hydrostatic pressure, preferably to a great depth of at least 1000 m. 9. Material for thermal insulation and / or buoyancy according to one of claims 1 to 8, characterized in that said rigid material has a density less than 0.7, preferably less than K ♦ 0.6, and a thermal conductivity of said material less than 0.15 W / m / K and a Young's modulus or triaxial compressive modulus of said material of 100 to 1000 MPa, preferably 200 to 500 MPa, and a compressibility modulus of said rigid insulating material greater than 2000 MPa, preferably greater than 2200 MPa. 10. Thermal insulation and / or buoyancy material according to one of claims 1 to 9, characterized in that said microspheres are in direct contact with each other, said microspheres being fully coated on all their external surfaces with at least one film of mixture of said matrix, said mixture occupying all of the interstices between said microbeads. 11. Process for preparing a material according to one of claims 1 to 10, characterized in that the following steps are carried out in which: 1 / - said insulating liquid compound is mixed with the monomers and / or prepolymer capable of reacting to form said crosslinked polymer, until a homogeneous mixture is obtained, preferably by evacuating to obtain a degassed mixture, and 2 / - a homogeneous mixture from step 1 / - is mixed with said balls to obtain a homogeneous mixture, preferably by evacuating, and 3 / - said mixture of step 2 / - is left to stand until complete crosslinking to form a said rigid thermal insulating material, preferably baked at a temperature of 18 to 30 ° C and for at least 24 hours, more preferably 24 to 72 hours. 12. The method of claim 11 characterized in that in step 3 / -, the successive steps are carried out in which: 3a / - said mixture of step 2 / - is poured or injected into a casing (5a-5b, 10, 17) serving as a mold or in a space formed by (a) the outer surface of a pipe element or underwater pipe to be insulated and / or whose buoyancy is to be increased, and (b) the inner surface of said protective casing, then 3b / - said mixture is left to stand in said envelope 5 until crosslinking and complete solidification in situ. 13. Use of a thermal insulation and / or buoyancy material according to one of claims 1 to 10, for the insulation and / or buoyancy of an underwater pipe or underwater pipe element. 14. Use of a thermal insulation and / or buoyancy material according to claim 13, characterized in that said subsea pipe element is an elbow joint coaxial pipe element. 15. Use according to claim 13 or 14, characterized in that said pipe conveys a hot fluid at a temperature of 20 to 80 ° C in sea water the temperature of which is less than 20 ° C, preferably less than 4. ° C, preferably at a great depth of at least 1000 m.