AU2014333649A1

AU2014333649A1 - Self-supporting box for thermally insulating a fluid storage tank and method for producing such a box

Info

Publication number: AU2014333649A1
Application number: AU2014333649A
Authority: AU
Inventors: Benoit Capitaine; Bruno Deletre
Original assignee: Gaztransport et Technigaz SA
Current assignee: Gaztransport et Technigaz SA
Priority date: 2013-10-11
Filing date: 2014-10-09
Publication date: 2016-05-05
Anticipated expiration: 2034-10-09
Also published as: JP2016538488A; WO2015052446A3; EP3055606B1; EP3055606B8; CN105683645B; KR20160067899A; FR3011832A1; EP3055606A2; FR3011832B1; CN105683645A; AU2014333649B2; JP6438017B2; WO2015052446A2; KR102240250B1

Abstract

The invention concerns self-supporting insulating box intended for thermally insulating a fluid storage tank comprising: - a bottom panel and a cover panel; - a plurality of supporting webs (14), interposed between the bottom panel and the cover panel; said supporting webs (14) having a composite structure comprising a central core (17) extending in the direction of thickness and two outer skins (18) sandwiching said central core (17), said central core (17) having lower thermal conductivity than that of the outer skins (18). The outer skins (18) comprise a fibre-reinforced thermoplastic polymer matrix, the central core (17) comprises a thermoplastic polymer matrix; and the outer skins (18) and the central core (17) are linked by melting the thermoplastic matrices of the outer skins (18) and of the central core (17).

Description

1 Self-supporting case for thermally insulating a fluid storage tank and method for producing such a case Technical field The invention relates to field of fluid-tight, thermally insulated tanks with 5 membranes, for storage and/or transport of fluid such as a cryogenic fluid. Fluid-tight, thermally insulated tanks with membranes are used in particular for the storage of liquefied natural gas (LNG) which is stored at around -1620C at atmospheric pressure. These tanks may be installed on land or on a floating installation. In the case of a floating installation, the tank may be intended for the 10 transport of liquefied natural gas or to receive liquefied natural gas serving as fuel for propulsion of the floating installation. Technological background Document FR 2 877 639 describes a fluid-tight, thermally insulated tank which comprises a tank wall, is fixed to the supporting structure of a floating 15 installation and presents successively, in the thickness direction from the inside to the outside of the tank, a primary fluid-tight barrier intended to be in contact with the liquefied natural gas, a primary insulating barrier, a secondary fluid-tight barrier and a secondary insulating barrier anchored to the supporting structure. The insulating barriers comprise a plurality of adjacent, parallelepipedic, heat-insulating cases. The 20 parallelepipedic cases comprise a plywood base panel, a plywood cover panel and a plurality of bearing webs interposed between the base panel and the cover panel. The cases are also filled with heat-insulating linings extending inside the compartments arranged between the bearing webs. The bearing webs are made of a polymer-resin-based composite, for 25 example polyester resin or epoxy, reinforced with glass- or carbon-fibers, and obtained by injection molding. The bearing webs are undulating so as to ensure good resistance to compressive forces in the direction perpendicular to the base and cover panels, and thus resist the hydrostatic pressure exerted by the liquid contained in the tank. Thus, thanks to the undulations, it is possible to reduce the 30 thickness of the bearing webs and consequently reduce the heat conduction through said webs. However, the composite materials used for the production of undulating 2 webs still have a high thermal conductivity. Therefore the thermal insulation performance of the heat-insulating cases made in this way is not totally satisfactory. In addition, document DE 2441392 also describes a sealed, thermally insulating tank for the storage of liquefied natural gas. The tank comprises heat 5 insulating cases comprising a cover panel, a base panel and a plurality of bearing webs extending in the thickness direction of the cases. The bearing webs each comprise two rigid side panels made of wood or plastic and fixed to each other by cross-braces. An insulating material is injected between the two rigid side panels. Such a structure of the bearing webs offers a good compromise between firstly a 10 large support surface of the webs on the base and cover panels, in order to obtain a satisfactory resistance to compressive forces, and secondly a limited equivalent thermal conductivity of the bearing webs, i.e. good thermal insulation performance. However, the manufacture of such bearing webs is complex and does not allow the production of complicated shapes. 15 Summary An idea on which the invention is based is to propose a self-supporting insulating case which has good thermal insulation performance and which is simple to produce. According to one embodiment, the invention provides a self-supporting 20 insulating case intended for thermal insulation of a fluid-storage tank and comprising: - a base panel and a cover panel spaced apart in a thickness direction of the case; - a plurality of bearing webs interposed between the base panel and cover panel and extending in the thickness direction so as to define a plurality of compartments, 25 said bearing webs having a composite structure comprising a central core extending in the thickness direction, and two external skins surrounding said central core in the manner of a sandwich, said central core having a thermal conductivity lower than that of the outer skins; and - a heat-insulating lining extending inside said compartments arranged between the 30 bearing webs; wherein: - the outer skins comprise a matrix of fiber-reinforced thermoplastic polymer; - the central core comprises a matrix of thermoplastic polymer; and 3 - the outer skins and the central core are connected by fusion of the thermoplastic matrices of the outer skins and the central core. Thus, such a sandwich structure of the bearing webs gives both excellent flexion resistance and a limited equivalent thermal conductivity, i.e. good thermal 5 insulation capacity. The equivalent thermal conductivity of a heterogeneous material is the thermal conductivity of a homogeneous material which would produce the same equivalent thermal resistance as the heterogeneous material. Also, since the outer skins and the central core are connected by thermal diffusion of the matrices, they form a coherent assembly able to absorb compressive 10 forces without requiring cross braces ensuring the fixing of the outer skins. Furthermore, such a connection of the outer skins and the central core can easily be implemented. According to embodiments, such a case may comprise one or more of the following characteristics: 15 - the outer skins comprise a fiber fabric or mat impregnated with the thermoplastic polymer matrix, the fibers being selected from glass fibers, carbon fibers and aramide fibers. Such outer skins have excellent compressive strength and low density. - the thermoplastic polymer matrices of the outer skins and the central core 20 have a fusion temperature difference of less than 600C. This facilitates the thermal fusion of the matrices. - the thermoplastic polymer matrices of the outer skins and the central core are identical. Such an embodiment ensures excellent cohesion between the outer skins and the central core. 25 - the thermoplastic matrices of the outer skins and the central core are selected from polyethylene, polypropylene, polyethylene terephthalate, polyamide, polyoxymethylene, polyetherimide and copolymers thereof. - the thermoplastic matrix of the central core is reinforced with natural fibers. Natural fibers have a low conductivity and thus allow reinforcement of the central 30 core while limiting the equivalent thermal conductivity of the bearing webs. - the thermoplastic matrix of the central core is reinforced with insulating charges. - the thermoplastic matrix of the central core is reinforced by a felt of glass matting and has a density less than that of the outer skins, preferably less than 4 900 kg/m 3 . Such a material has excellent mechanical and thermal insulation properties. - the base panel and the cover panel each comprise at least one thermoplastic element; and the bearing webs are fixed to the base panel and 5 cover panel by thermoplastic welding in the interface zones between the bearing webs and the thermoplastic elements of the base panel and cover panel. Thus the bearing webs may be joined to the base panel and/or cover panel in a simple and reliable manner since their fixing does not degrade the structural integrity of the bearing webs, such that the strength of the latter is not reduced by the fixing 10 to the base panel and/or cover panel. - the bearing webs have a plurality of undulations, the axis of which extends perpendicular to the base panel and cover panel. According to one embodiment, the invention also proposes a method for production of a self-supporting insulating case intended for thermal insulation of a 15 fluid-storage tank, said method comprising: - production of a plurality of bearing webs; - provision of a base panel and a cover panel; - fixing the bearing webs between the base panel and the cover panel such that the base panel and the cover panel are spaced apart in a thickness direction of the case 20 and the bearing webs extend in the thickness direction; - lining a plurality of compartments arranged in the bearing webs with a heat insulating lining, wherein production of the bearing web comprises: - provision of two outer skins comprising a matrix of fiber-reinforced thermoplastic polymer; 25 - provision of a central core comprising a thermoplastic polymer matrix and having a thermal conductivity less than that of the outer skins; - positioning of the two outer skins in a mold on either side of the central core; and - joining the outer skins and the central core by fusion of the thermoplastic matrices of the outer skins and the central core. 30 According to embodiments, such a method may comprise one or more of the following characteristics: - the outer skins and the central core are joined by thermocompression, co extrusion or hot laminating.

5 - the base panel and the cover panel each comprise at least one thermoplastic element for fixing the bearing webs, and the bearing webs are fixed to the base panel and cover panel by a thermoplastic welding operation in the interface zones between the bearing webs and the thermoplastic elements of 5 the base panel and cover panel. According to one embodiment, the invention also provides a fluid-tight, thermally insulated fluid-storage tank comprising a thermal insulation barrier comprising a plurality of the above-mentioned cases arranged next to each other, and a sealing membrane resting against the thermal insulation barrier. Such a tank 10 may be produced with a single sealing membrane or with two sealing membranes alternating with two thermal insulation barriers. Such a tank may form part of a land-based storage installation, for example for storing LNG, or be installed in a floating structure in coastal waters or off-shore, in particular an LNG tanker, a floating storage and regasification unit (FSRU), a 15 floating production, storage and offloading unit (FPSO), and others. According to one embodiment, a ship for transporting a cold liquid product comprises a double hull and a tank as described above arranged in the double hull. According to one embodiment, the invention also provides a method for loading or unloading such a ship, wherein a fluid is conducted through insulated 20 pipelines from or to a floating or land-based storage installation to or from the ship's tank. According to one embodiment, the invention also provides a system for transferring a fluid, the system comprising said ship, insulated pipelines arranged so as to connect the tank installed in the ship's hull to a floating or land-based storage 25 installation, and a pump for driving a fluid through insulated pipelines from or to the floating or land-based storage installation to or from the ship's tank. Brief description of the figures The invention will be better understood and further aims, details, characteristics and advantages thereof will appear more clearly from the following 30 description of several particular embodiments of the invention, given merely for illustration and without limitation, with reference to the attached drawings.

6 e Figure 1 is a simplified perspective view of a tank wall according to one embodiment. * Figure 2 is a simplified top view of an insulating case of the tank wall from figure 1. 5 e Figure 3 is a side view of a bearing web. e Figure 4 is a cross-section view along plane IV-IV of figure 3. e Figures 5, 6 and 7 are perspective views of bearing webs according to three different embodiments, with a composite structure. 10 e Figure 8 illustrates the steps for production of composite material plates comprising a felt of glass matting impregnated with a thermoplastic matrix. e Figure 9 illustrates diagrammatically a step of forming of a bearing web by thermocompression. 15 e Figure 10 is a diagrammatic section view of a self-supporting case according to a first embodiment. e Figure 11 is a diagrammatic section view of a self-supporting case according to a second embodiment. * Figure 12 is a detailed view of the join between a bearing web and 20 a base panel according to a third embodiment. * Figure 13 is an simplified diagrammatic depiction of a tank of an LNG tanker, and of a terminal for loading and unloading this tank. Detailed description of embodiments Figure 1 shows a wall of a fluid-tight, thermally insulating tank. The general 25 structure of such a tank is well-known and has a polyhedral form. Therefore only one zone of the tank wall will be described, given that all walls of the tank may have a similar general structure. The wall of the tank, from the outside to the inside of the tank, comprises a supporting structure 1, a secondary thermal insulation barrier 2 which is formed from 30 heat-insulating cases 3 arranged adjacent to each other on the supporting structure 7 1 and anchored thereto by secondary retention elements 4, a secondary sealing membrane 5 carried by the cases 3, a primary thermal insulation barrier 6 formed by heat-insulating cases 7 arranged next to each other and anchored directly or indirectly to the supporting structure 1, for example by being anchored to the 5 secondary sealing membrane 5 by primary retention elements 8, and a primary sealing membrane 9 carried by the cases 7 and intended to be in contact with the cryogenic fluid contained in the tank. The supporting structure 1 may in particular be a self-supporting metal plate, or more generally any type of rigid partition with suitable mechanical 10 properties. The supporting structure may in particular be formed by the hull or double hull of a ship. The supporting structure comprises a plurality of walls defining the general shape of the tank. The primary 9 and secondary 5 sealing membranes are for example formed from a continuous strip of metal strakes with raised edges, said strakes being 15 welded by their raised edges to parallel weld supports fixed to the cover of the cases 3, 7. The metal strakes are for example made of Invar@: i.e. an alloy of iron and nickel, the coefficient of expansion of which is typically between 1.2.10-6 and 2.10-6

K-

1 . The cases 3 of the secondary thermal insulation barrier 2 and the cases 7 20 of the primary thermal insulation barrier 6 may have identical or different structures and the same or different dimensions. With reference to figure 2, we will now describe the general structure of a case 3, 7 of the secondary thermal insulation barrier 2 and/or the primary thermal insulation barrier 6. The case 3, 7 has substantially the form of a parallelepipedic 25 rectangle. The case 3, 7 comprises a base panel 10 and a cover panel 11 which are parallel to each other. On its inner face, the cover panel 11 has grooves 12 for housing the weld supports of the metal strakes of the sealing membrane. A plurality of spacer elements is interposed between the base panel 10 and the cover panel 11, perpendicular thereto. The plurality of spacer elements 30 comprises firstly two opposing side walls 12, 13, and secondly a plurality of bearing webs 14. The bearing webs 14 are arranged parallel to each other between the two side walls 12, 13 in a direction perpendicular to said side walls 12, 13.

8 Compartments 15 for receiving a heat-insulating lining are provided between the bearing webs 14. The heat-insulating lining may be made of any material with suitable thermal insulation properties. For example, the heat-insulating lining is selected from 5 materials such as perlite, glass wool, polyurethane foam, polyethylene foam, polyvinyl chloride foam, aerogels or other. When the heat-insulating lining is not a bulk insulating material, such as perlite or glass wool, but is formed from a foam for example, it is no longer necessary for the side walls 12, 13 to extend over the entire width of the case 3, 7. 10 Hence in an embodiment not shown, each side wall 12, 13 of the embodiment of figure 2 is replaced by two anti-tilt reinforcing webs extending along a side edge on either side of a median plane, each of the reinforcing webs extending near an end of said side edge. The bearing webs 14 shown on figure 2 are undulating and oscillate to either side of their general longitudinal direction. Each undulation thus extends 15 along an axis perpendicular to the base panel 10 and cover panel 11. In the embodiment shown, the undulations are substantially sinusoidal. However, other forms of undulation are also possible. For example, the undulations may in particular take the form of triangular teeth or rectangular notches. Thanks to their form, such undulating bearing webs 14 have a high resistance to buckling. Although 20 undulations with a periodic structure allow good uniformity of compressive strength, it is also possible to provide non-periodic undulations in order to meet to certain localized mechanical requirements. Figures 3 and 4 illustrate a bearing web 14. Along its edges extending along the base panel 10 and cover panel 11, the bearing web 14 comprises load 25 distribution plates 16a, 16b. The upper plate 16a has a flat surface intended to rest against the cover panel 11, while the lower plate 16b has a flat surface intended to rest against the base panel 10. The plates 16a, 16b have a width which is greater than the thickness of the wall of the bearing web 14 in its principal part extending between the two plates 16a, 16b. Thus the load distribution plates 16a, 16b prevent 30 a concentration of stress on a particular zone, by offering a larger support surface between the bearing web 14 and the base panel 10 and cover panel 11. The load distribution plates may have a parallelepipedic form as shown on figures 3 or 4. In this case, the width of the plates 16a, 16b may be equal to the amplitude of the 9 undulations. In other embodiments, the load distribution plates 16a, 16b may themselves have undulations. The composite structure of the bearing webs 14 is described with reference to figures 5, 6 and 7. As mentioned above, the bearing webs 14 may in particular 5 have sinusoidal undulations as depicted on figure 5, undulations in the form of teeth as depicted on figure 7, or have a smooth geometry as depicted on figure 6. The bearing webs 14 have a composite structure comprising a central core 17 and two outer skins 18 holding said central core 17 in the manner of a sandwich. The function of the central core 17 is to increase the flexion strength of the bearing 10 web by increasing its quadratic moment while only having a limited impact on the equivalent thermal conductivity of the bearing webs. Thus the central core 17 has a thermal conductivity lower than that of the outer skins 18. The thickness of the central core 17 lies between 0.5 and 10 times the thickness of the outer skin 18. 15 The outer skins 18 comprise a matrix of fiber-reinforced thermoplastic polymer. Also, the central core 17 comprises a matrix of thermoplastic polymer. Thus the join of the outer skins 18 to the central core 17 may be achieved by linking the thermoplastic matrices by thermal fusion. The central core 17 and the outer skins 18 thus form a coherent and resistant whole, capable of absorbing 20 compressive forces without separating. For example, the matrices of the outer skins 18 and the central core 17 are selected from polyethylene, polypropylene, polyethylene terephthalate, polyamide, polyoxymethylene, polyetherimide and/or copolymers thereof. In one embodiment, the matrices of the outer skins 18 and the central core 17 are different. Thus to 25 facilitate the linking of the outer skins 18 and central core 17, it is advantageous for the thermoplastic matrices to have similar fusion temperatures, the difference between their fusion temperatures being preferably less than 60 0C. In another embodiment, the matrices of the outer skins 18 and that of the central core 17 are identical. 30 The outer skins comprise a fiber fabric or mat impregnated with the thermoplastic polymer matrix, the fibers being selected from glass fibers, carbon fibers and aramide fibers. The fibers are long fibers, i.e. greater than 10 mm. Such long fibers ensure a satisfactory mechanical strength.

10 According to one embodiment, the outer skins 18 are made of a material generally known as GMT (glass fiber mat reinforced thermoplastics). Such materials have a good mechanical strength and a thermal conductivity of the order of 400 mW/m.K at 20 C. 5 According to an embodiment shown on figure 8, the GMT-type materials are initially made in the form of composite material plates. To do this, a double-belt press 19 is supplied with glass fibers 20 and thermoplastic resin 30. The thermoplastic resin 30 may be loaded into the double-belt press 19 in the form of extruded films or powder. The glass fibers 20 are provided in the form of glass fiber 10 coils cut to the desired length. The thermoplastic resin 30 and the glass fibers 20 are laminated together in the double-belt press 19. At the outlet from the double-belt press 19, a cutting device allows a plurality of plates to be obtained. In another embodiment, the GMT-type material consists of a glass mat and a matrix in the form of a thermoplastic polymer mat entangled into the glass mat and 15 thus forming a fabric intended to be hot-pressed. For example, such a material is sold by the company V6trotex under the name Twintex@. In addition, the central core 17 is also advantageously reinforced. However, in order to limit the thermal conductivity of the central core 17, the reinforcing material is selected for its thermal insulation characteristics. 20 In one embodiment, the central core 17 is reinforced by natural fibers such as fibers of linen, hemp, jute. Such natural fibers allow the creation of materials with thermal conductivities of the order of 250 mW/m.K at 20 0C. In one embodiment, the natural fibers take the form of a felt, i.e. a non-woven fabric in which the fibers are agglutinated. Such a felt has good thermal insulation characteristics. 25 In another embodiment, the central core 17 is reinforced by insulating charges. Such insulating charges are typically hollow microspheres of glass or thermoplastic for example. Finally, in another embodiment, the central core 17 is composed of a low density reinforced thermoplastic material known as LWRT (Light-Weight Reinforced 30 Thermoplastic). Such a material comprises a glass mat felt and a thermoplastic matrix comprising polypropylene fibers. For example, such a material is sold by the company Quadrant under the commercial name SymaLITE@. Such a material typically has a density lower than 900 kg/M 3 , of the order of 500 kg/M 3 . The density 11 of such a thermoplastic material depends in particular on the intensity of the compression applied to the material during production. In one embodiment, the outer skins 18 are arranged on either side of the central core 17, then the assembly is subjected to a forming operation. To achieve 5 this, as shown on figure 9, the assembly 32 comprising the central core 17 and the outer skins 18 arranged on either side of the central core 17 is heated in an oven 31, then arranged in a mold 33 in which it will be formed by application of a pressure. The bearing webs 14 are thus formed by thermocompression, by heating the composite material plates then by deep-drawing them under pressure. 10 In another embodiment, the bearing webs 14 may also be produced by thermoforming i.e. by flux of the composite material plates under conditions of temperature and vacuum. The outer skins 18 and the central core 17 may be linked by thermal fusion of their matrices during forming by thermocompression or thermoforming. According 15 to another embodiment, the outer skins 18 and the central core 17 may be linked prior to forming by thermocompression or thermoforming. To achieve this, in one variant, the assembly 32 comprising the central core 17 and the outer skins 18 is first subjected to a hot-laminating operation. In another variant, the outer skins 18 and the central core 17 are co-extruded. 20 It is also noted that to obtain a bearing web 14 with a smooth geometry as shown on figure 6, forming by thermoforming or thermocompression is not necessary. In this case, the bearing web 14 may be obtained directly after hot laminating or co-extrusion. Figure 10 illustrates the joining of the bearing webs 14 and the base panel 25 10 and cover panel 11 in one embodiment. The base panel 10 and cover panel 11 here have a body of plywood. The inner faces of the base panel 10 and cover panel 11 facing the interior of the case are covered with thermoplastic films 21, 22. In order to allow the fixing of the bearing webs 14 to the panels 10, 11, a plastic welding operation is performed in the interface zones 25 between the thermoplastic 30 films 22 and the bearing webs 14. The welding operation is for example performed by infrared radiation. It is however possible to use any other appropriate plastic welding method such as ultrasound welding, induction heating, friction welding, welding by the addition of 12 fusion material, hot air jet welding or flaming. Note that in the case of induction welding, it is necessary to provide metal inserts on the bearing webs and/or on the base panel 10 and/or cover panel 11 at the interface between the bearing webs 14 and the base panel 10 and cover panel 11, so as to allow heating of the 5 thermoplastic material. In one embodiment, before performing welding operations, protective masks are first arranged on the inner faces of the base panel 10 and cover panel 11 between the interface zones 25 between the bearing webs 14 and the panels 10, 11. When the welding operations have been performed, the protective masks may 10 then be removed. Thus the thermoplastic films 21, 22 are not damaged during the welding operations. Such protective masks are for example made of metal or ceramic material and/or glass. Such masks are advantageously fitted with a cooling circuit in which a fluid such as water, air or oil circulates in order to regulate the temperature said masks. 15 In the embodiment shown on figure 10, the outer faces of the base panel 10 and cover panel 11 are also covered with thermoplastic films 23, 24. Such an arrangement allows balancing of the flexions of the cover panels 10 and base panel 11, in particular when they are subject to high thermal stresses during chilling of the tank. 20 In the embodiment shown on figure 11, strips 29 of thermoplastic film are arranged in the interface zones 25 with the bearing webs 14. The thermoplastic films 21, 22, 23, 24, 29 are for example made of a composite material comprising a fiber-reinforced thermoplastic matrix. Thus such thermoplastic films 22, 23, 24, 29 help increase the mechanical strength of the base 25 panel and cover panel by increasing their flexion rigidity and improving their puncture resistance. Such thermoplastic films 22, 23, 24, 29 typically have a thickness of the order of 0.5 to 5 mm. In one embodiment, the thermoplastic films 21, 22, 23, 24, 29 are fixed to the body of the base panel 10 and cover panel 11 by gluing. The adhesive used is 30 for example an acrylic glue, a polyurethane glue, or an epoxy glue. In another embodiment, the thermoplastic films 21, 22, 23, 24, 29 are fixed to the body of the panels by a hot-pressing process. In such a case, it is conceivable to integrate the fixing of the thermoplastic films directly in the production process of 13 the plywood. To do this, the sheets of wood (previously coated with glue) and the thermoplastic films are superimposed then the resulting stack is subjected to a hot pressing process. For example, for such hot pressing, the stack is subjected to a temperature of the order of 190 to 200 C and to a pressure of the order of 1 to 3 5 MPa for a duration of 5 minutes. In order to facilitate the welding operations, the thermoplastic films 21, 22, 23, 24, 29 may comprise a thermoplastic matrix identical to the thermoplastic matrix of the central core 17 and/or the outer skins 18. In another embodiment (not shown), it is the actual bodies of the base 10 panel 10 and cover panel 11 which form the thermoplastic element for the fixing of the bearing webs 14. In a first variant, the base panel 10 and cover panel 11 comprise a body made of a composite material comprising a fiber-reinforced thermoplastic matrix. In a second variant, the base panel 10 and cover panel 11 are made from a 15 wooden body impregnated with a thermoplastic matrix. The body may be produced by agglomeration of fibers previously impregnated with a thermoplastic matrix. Alternatively, the body may be made of plywood, in which the inner ply and optionally the outer ply are made of wood which is sufficiently porous for diffusion of the plastic matrix inside said plies under heat and pressure. Such a wood is for 20 example selected from birch, pine, oak or other. To facilitate the impregnation of the wooden body by the thermoplastic matrix, the wooden body may have grooves or any other surface preparation improving the connection between the wooden body and the thermoplastic matrix. Figure 12 illustrates the joining of the bearing webs 14 and the base panel 25 10 and cover panel 11 in one embodiment. In this embodiment, the base panel 10 and cover panel 11, in their interface zones 25 with the bearing webs 14, comprise continuous bores through which thermoplastic studs 26 are inserted. The thermoplastic studs 26 are equipped with heads 27 resting against the outer face of the base panel 10 and cover panel 11, and distal ends extending inside bores 30 provided in the edges of the bearing webs 14. The welding of the thermoplastic studs 26 inside the bores provided in the bearing webs 14 ensures the fixing of the bearing webs 14 to the base panel 10 and cover panel 11. In one embodiment, the welding operations are performed by friction, by driving the thermoplastic studs 26 in 14 rotation. The movement of the thermoplastic studs 26 relative to the bearing webs 14 leads to a heating of the interface until local plasticization of the thermoplastic material followed by welding. In one embodiment, the base panel 10 and cover panel 11 comprise a body made of a composite material having a thermoplastic 5 matrix, such that the thermoplastic studs 26 are also welded to the base panel 10 or cover panel 11. With reference to figure 13, a simplified view of an LNG tanker 70 shows a fluid-tight and insulated tank 71 of generally prismatic form, mounted in the double hull 72 of the ship. The wall of the tank 71 comprises a primary fluid-tight barrier 10 intended to come into contact with the LNG contained in the tank, a secondary fluid tight barrier arranged between the first fluid-tight barrier and the double hull 72 of the ship, and two thermal insulation barriers arranged respectively between the primary fluid-tight barrier and the secondary fluid-tight barrier, and between the secondary fluid-tight barrier and the double hull 72. 15 In a manner known in itself, loading/unloading pipelines 73 arranged on the upper deck of the ship may be connected by means of suitable connectors to a floating or port-based terminal, in order to transfer a cargo of LNG from or to the tank 71. Figure 13 shows an example of a floating terminal comprising a loading and 20 unloading station 75, an underwater pipeline 76, and a land-based installation 77. The loading and unloading station 75 is a fixed offshore installation comprising a mobile arm 74 and a tower 78 which supports the mobile arm 74. The mobile arm 74 carries a bundle of insulated flexible hoses 79 which can connect to the loading/unloading pipelines 73. The orientable mobile arm 74 can be adapted to all 25 sizes of tanker. A connecting pipe (not shown) extends inside the tower 78. The loading and unloading station 75 allows the tanker 70 to be loaded or unloaded from or to a land-based installation 77. This comprises liquefied gas storage tanks 80 and connecting pipes 81 connected by the underwater pipeline 76 to the loading or unloading station 75. The underwater pipeline 76 allows the transfer of liquefied gas 30 between the loading or unloading station 75 and the land-based installation 77 over a great distance, for example 5 km, which allows the LNG tanker 70 to remain at a great distance from the coast during the loading and unloading operations.

15 To create the pressure necessary for the transfer of liquefied gas, on-board pumps in the ship 70 are used, and/or pumps installed in the land-based installation 77, and/or pumps fitted to the loading and unloading station 75. Although the invention has been described in connection with several 5 particular embodiments, it is evident that it is in no way limited thereto and comprises all technical equivalents of the means described and their combinations if these fall within the scope of the invention. The use of the verb "comprise" or "contain" or "include" and its conjugated forms does not exclude the presence of elements or steps other than those stated in 10 a claim. The use of the indefinite article "a" for an element of step does not, unless specified otherwise, exclude the presence of a plurality of such elements or steps. In the claims, any reference symbol in brackets should not be interpreted as a limitation of the claim.

Claims

1. A self-supporting insulating case (3, 7) intended for thermal insulation of a fluid-storage tank and comprising: - a base panel (10) and a cover panel (11) spaced apart in a thickness direction of 5 the case (3, 7); - a plurality of bearing webs (14) interposed between the base panel (10) and cover panel (11) and extending in the thickness direction so as to define a plurality of compartments (15), said bearing webs (14) having a composite structure comprising a central core (17) extending in the thickness direction, and two external skins (18) 10 surrounding said central core (17) in the manner of a sandwich, said central core (17) having a thermal conductivity lower than that of the outer skins (18); and - a heat-insulating lining extending inside said compartments (15) arranged between the bearing webs (14); wherein: 15 - the outer skins comprise a matrix of fiber-reinforced thermoplastic polymer; - the central core (17) comprises a matrix of thermoplastic polymer; and - the outer skins (18) and the central core (17) are connected by fusion of the thermoplastic matrices of the outer skins (18) and the central core (17).

2. The self-supporting insulating case (3, 7) as claimed in claim 1, wherein the 20 outer skins (18) comprise a fiber fabric or mat impregnated with the thermoplastic polymer matrix, the fibers being selected from glass fibers, carbon fibers and aramide fibers.

3. The self-supporting insulating case (3, 7) as claimed in claim 1 or 2, wherein the thermoplastic polymer matrices of the outer skins (18) and the 25 central core (17) have a fusion temperature difference of less than 60 C.

4. The self-supporting insulating case (3, 7) as claimed in claim 3, wherein the thermoplastic polymer matrices of the outer skins (18) and the central core (17) are identical.

5. The self-supporting insulating case (3, 7) as claimed in any of claims 1 to 4, 30 wherein the thermoplastic matrices of the outer skins (18) and the central core (17) are selected from polyethylene, polypropylene, polyethylene terephthalate, polyamide, polyoxymethylene, polyetherimide and copolymers thereof. 17

6. The self-supporting insulating case (3, 7) as claimed in any of claims 1 to 4, wherein the thermoplastic matrix of the central core (17) is reinforced with natural fibers.

7. The self-supporting insulating case (3, 7) as claimed in any of claims 1 to 6, 5 wherein the thermoplastic matrix of the central core (17) is reinforced with insulating charges.

8. The self-supporting insulating case (3, 7) as claimed in any of claims 1 to 7, wherein the thermoplastic matrix of the central core (17) is reinforced by a felt of glass matting and has a density less than that of the outer skins (18), preferably 10 less than 900 kg/m3.

9. The self-supporting insulating case (3, 7) as claimed in any of claims 1 to 8, wherein: - the base panel (10) and the cover panel (11) each comprise at least one thermoplastic element (22, 26, 29); and 15 - the bearing webs (14) are fixed to the base panel (10) and cover panel (11) by thermoplastic welding in the interface zones between the bearing webs (14) and the thermoplastic elements (22, 26, 29) of the base panel (10) and cover panel (11).

10. The self-supporting insulating case (3, 7) as claimed in any of claims 1 to 9, wherein the bearing webs (14) have a plurality of undulations, the axis of which 20 extends perpendicular to the base panel (10) and cover panel (11).

11. A method for producing a self-supporting insulating case (3, 7) intended to provide thermal insulation for a fluid-storage tank, said method comprising: - production of a plurality of bearing webs (14); - provision of a base panel (10) and a cover panel (11); 25 - fixing the bearing webs (14) between the base panel (10) and the cover panel (11) such that the base panel (10) and the cover panel (11) are spaced apart in a thickness direction of the case (3, 7) and the bearing webs (14) extend in the thickness direction; - lining a plurality of compartments (15) arranged in the bearing webs (14) with a 30 heat-insulating lining, wherein production of a bearing web (14) comprises: - provision of two outer skins (18) comprising a matrix of fiber-reinforced thermoplastic polymer; 18 - provision of a central core (17) comprising a thermoplastic polymer matrix and having a thermal conductivity less than that of the outer skins; - positioning of the two outer skins (18) in a mold on either side of the central core (17); and 5 - joining the outer skins (18) and the central core (17) by fusion of the thermoplastic matrices of the outer skins (18) and the central core (17).

12. The production method as claimed in claim 11, wherein the outer skins (18) and the central core (17) are joined by thermocompression, co-extrusion or hot laminating. 10

13. The production method as claimed in claim 11 or 12, wherein the base panel (10) and the cover panel (11) each comprise at least one thermoplastic element (22, 26, 29) for fixing the bearing webs (14); and wherein the bearing webs (14) are fixed to the base panel (10) and cover panel (11) by a thermoplastic welding operation in the interface zones between the bearing 15 webs (14) and the thermoplastic elements (22, 26, 29) of the base panel (10) and cover panel (11).

14. A fluid-tight, thermally insulating fluid-storage tank comprising a thermal insulation barrier comprising a plurality of cases (3, 7) as claimed in any of claims 1 to 10 arranged next to each other, and a sealing membrane resting 20 against the thermal insulation barrier.

15. A ship (70) for transporting a fluid, the ship comprising a double hull (72) and a tank (71) as claimed in claim 14, arranged in the double hull.

16. A method for loading or unloading a ship (70) as claimed in claim 15, wherein a fluid is conducted through insulated pipelines (73, 79, 76, 81) from or 25 to a floating or land-based storage installation (77) to or from the ship's tank (71).

17. A system for transferring a fluid, the system comprising a ship (70) as claimed in claim 15, insulated pipelines (73, 79, 76, 81) arranged so as to connect the tank (71) installed in the ship's hull to a floating or land-based 30 storage installation (77), and a pump for driving a fluid through insulated pipelines from or to the floating or land-based storage installation to or from the ship's tank.