AU2014255598B2

AU2014255598B2 - Tight and thermally insulating vessel

Info

Publication number: AU2014255598B2
Application number: AU2014255598A
Authority: AU
Inventors: Sebastien Delanoe; Bruno Deletre; Florent OUVRARD; Raphael Prunier; Mohamed Sassi; Nicolas WALKER
Original assignee: Gaztransport et Technigaz SA
Current assignee: Gaztransport et Technigaz SA
Priority date: 2013-04-15
Filing date: 2014-03-25
Publication date: 2017-11-30
Anticipated expiration: 2034-03-25
Also published as: FR3004512A1; KR20150143776A; EP2986885B1; WO2014170572A1; EP2986885A1; CN105164459A; CN105164459B; ES2636265T3; KR102112775B1; FR3004512B1; AU2014255598A1

Abstract

The invention relates to a tight and thermally insulating vessel built into a carrier structure for containing a fluid, wherein a vessel wall comprises, from the outside of the vessel towards the inside of the vessel: a carrier wall, a heat insulation barrier consisting of a plurality of adjacently arranged heat-insulating elements (30), and a sealing barrier, a heat-insulating element comprising: a heat insulator (21a, 21b), a plurality of carrier elements (33) crossing the heat insulator in a thickness direction perpendicular to the vessel wall and a cover panel (34) and a bottom panel (31), and an anti-buckling plate (40) parallel to the cover panel (34) and the bottom panel, crossed by the plurality of carrier elements (33) in a plurality of openings of the anti-buckling plate. A tight and thermally insulated vessel can be used especially in a methane carrier.

Description

SEALED, THERMALLY INSULATED TANK

Technical field

The invention relates to the field of sealed, thermally insulated tanks arranged in a support structure for containing a cold fluid, and notably to membrane tanks for containing liquefied gases. Liquefied gases are stored at very low temperatures of about -160°C. This form of storage is affected by an evaporation phenomenon, depending on the degree of thermal insulation of the tank. In order to reduce this evaporation, it is necessary to improve the thermal insulation of tanks.

Prior art

There are known sealed, thermally insulated tanks which are arranged in the hulls of ships for transporting liquefied natural gas (LNG) with a high methane content. An example of such a tank is disclosed in FR-A-2798902. In this known tank, a primary insulating barrier and a secondary insulating barrier are constructed in modular form, using juxtaposed parallelepipedal wooden box structures. FR-A-2877638 discloses another LNG tank arranged in the hull of a ship, in which a secondary insulating barrier comprises insulating blocks arranged in a repeated pattern. The insulating block comprises a generally parallelepipedal slab of low-density polymer foam sandwiched between a base panel and a cover panel. The insulating block comprises pillars arranged between the base panel and the cover panel. The pillars are distributed in the insulating block to bear the compressive forces that cannot be withstood by the low-density foam.

Summary

An idea on which the invention is based is that of providing insulating blocks suitable for constructing an insulating barrier of a sealed, thermally insulating tank in a relative simple way, while providing high insulating capability.

According to one embodiment, the invention provides a sealed, thermally insulated tank incorporated into a support structure for containing a fluid, in which a tank wall comprises, from the outside of the tank toward the inside of the tank: a load-bearing wall, a thermal insulation barrier retained on the load-bearing wall, the thermal insulation barrier being formed from a plurality of insulating elements juxtaposed to form a support surface, and a sealing barrier bearing on the support surface, an insulating element having a generally flattened prismatic shape, and comprising: a thermal insulating material, a plurality of load-bearing elements passing through the thermal insulating material along a direction of thickness perpendicular to the tank wall, and a cover panel and a base panel parallel to the tank wall and arranged at the first ends and the second ends, respectively, of the load-bearing elements of the insulating element, so as form exterior walls of the insulating element, the first ends of the load-bearing elements being fastened to the cover panel and the second ends of the load-bearing elements being fastened to the base panel, and an anti-buckling plate, parallel to the cover panel and to the base panel, sandwiched between a first and a second portion of the thickness of said thermal insulating material, the anti-buckling plate having a plurality of load-bearing elements passing through it in a plurality of openings in the anti-buckling plate, the openings being spaced apart from one another so as to provide a distance between two neighboring load-bearing elements, in a plane defined by the anti-buckling plate.

Because of these characteristics, a load-bearing element subjected to a significant stress is supported by a force which is opposed to the buckling and which is transmitted by the anti-buckling plate.

According to embodiments, this tank may have one or more of the following characteristics.

According to one embodiment, an opening in the anti-buckling plate has dimensions greater than the dimensions of a cross section of the load-bearing element engaged in the opening, so as to leave an assembly clearance.

Because of these characteristics, manufacturing is facilitated.

According to one embodiment, the assembly clearance is less than three millimeters.

Because of these characteristics, when a pillar buckles, the anti-buckling plate distributes the force to the other pillars which oppose this force.

According to one embodiment, the anti-buckling plate is positioned halfway between the base panel and the cover panel.

Because of these characteristics, the pillar is supported at three points, thus creating two equal pillar portions.

According to one embodiment, the thermal insulating material comprises a second anti-buckling plate parallel to the base panel and the cover panel, sandwiched between the second and a third portion of the thickness of said thermal insulating material, the second anti-buckling plate having the plurality of loadbearing elements passing through it in a plurality of openings positioned in alignment with the openings in the first anti-buckling plate.

Because of these characteristics, very thick insulating elements can be formed, with the addition of as many anti-buckling plates as are required.

According to one embodiment, an insulating element comprises a plurality of anti-buckling plates, the number of anti-buckling plates being greater than or equal to a theoretical number defined in such a way that the distance between two successive support points of a load-bearing element according to the longitudinal orientation of the load-bearing element is less than a predetermined critical height He, said critical height being equal to:

where: • E: Young’s modulus of the load-bearing element, • S: cross-sectional surface area of the load-bearing element, • σ is an ultimate compressive stress of the material, where the support points are the second end of the load-bearing element fastened to the base panel, the first end of the load-bearing element fastened to the cover panel, and each portion of the load-bearing element engaged in an opening of the anti-buckling plates.

Because of these characteristics, it is possible to determine the number of plates required for a given thickness of an insulating element.

According to one embodiment, the insulating element comprises a plurality of anti-buckling plates positioned in an equidistant way in the thickness of the insulating element.

Because of these characteristics, a force acting on a load-bearing element is distributed identically across all the sections of the load-bearing element defined by the positions of the anti-buckling plates.

According to one embodiment, an insulating element comprises positioning means capable of positioning the anti-buckling plate in the thickness of the insulating element.

Because of these characteristics, the anti-buckling plate does not crush a non-structural insulating material.

According to one embodiment, the positioning means are arranged on the load-bearing elements, to prevent the translation of the anti-buckling plate in a longitudinal direction of the plurality of load-bearing elements.

Because of these characteristics, the number of components is reduced.

According to one embodiment, the positioning means comprise a shoulder formed by a difference in cross section between two adjacent longitudinal segments of one load-bearing element of the plurality of elements.

According to one embodiment, for the shoulder capable of supporting the anti-buckling plate, the dimensions of the plurality of openings in the anti-buckling plate lie between cross-sectional dimensions of a first of the two segments and cross-sectional dimensions of the second segment of the load-bearing element.

Because of these characteristics, the anti-buckling plate rests on the shoulder.

According to one embodiment, the positioning means comprise a spacer tube fitted onto a load-bearing element, the spacer tube having an outside diameter greater than the dimensions of the opening in the anti-buckling panel so as to provide, at one end of the spacer tube, a bearing point for the anti-buckling panel, and, at the other end of the spacer tube, a bearing point for the base panel of the insulating element or another anti-buckling plate.

Because of these characteristics, positioning is provided in a simpler way.

According to one embodiment, the positioning means is a flanged clip on the load-bearing element which prevents the translational movement of the antibuckling plate in a direction along the direction of the load-bearing elements. In a variant, the anti-buckling plate is held between two clips, preventing any movement in the longitudinal direction of the load-bearing elements.

According to one embodiment, the positioning means comprise a longitudinal portion of a load-bearing element which is flared and in which the dimensions of an opening in the anti-buckling plate substantially correspond to the cross-sectional dimensions of the longitudinal portion of the load-bearing element.

Because of these characteristics, the same load-bearing element can be used to create insulating elements having plates positioned at different heights, by adapting the dimensions of the opening in the plate.

According to one embodiment, the positioning means comprise supporting pillars orthogonal to the base panel, a first end of each pillar being fastened to the base panel, while the other end serves as a bearing point for said anti-buckling plate.

According to one embodiment, the invention also provides a sealed, thermally insulated tank positioned in a support structure, the tank comprising, from the outside of the tank toward the inside of the tank: a primary thermal insulation barrier bearing on and retained on the sealing barrier, the primary thermal insulation barrier being formed by a plurality of insulating elements juxtaposed to form a primary support surface, a primary sealing barrier bearing on the primary support surface, a primary insulating element having the same characteristics as the indicated secondary insulating element. A tank of this type may form part of a land-based storage installation, for storing LNG for example, or may be installed in a floating structure in coastal or deep waters, notably in a gas carrier ship, a floating storage and regasification unit (FSRU), a floating production and storage and offloading unit (FPSO), or others.

According to one embodiment, a ship for transporting a refrigerated liquid product comprises a double hull, and a storage tank of the aforesaid type positioned in the double hull.

According to one embodiment, the invention also provides a method for loading or unloading a ship of this type, in which a refrigerated liquid product is conveyed through insulated pipes from or toward a floating or land-based storage installation toward or from the ship’s tank.

According to one embodiment, the invention also provides a transfer system for a refrigerated liquid product, the system comprising the aforesaid ship, insulated pipes arranged so as to connect the tank installed in the ship’s hull to a floating or land-based storage installation and a pump for propelling a flow of refrigerated liquid product through the insulated pipes from or toward the floating or land-based storage installation toward or from the ship’s tank.

Some aspects of the invention are based on the idea of increasing the insulating capability of an insulating block. Some aspects of the invention are based on the idea of increasing the thickness of the insulating block, by increasing the length of the support elements. Some aspects of the invention are based on the idea of reinforcing the insulating block. Some aspects of the invention are based on the idea of opposing the effects of buckling of the support elements.

Brief description of the drawings

The invention will be better understood and other objects, details, characteristics and advantages thereof will be more fully apparent from the following description of some specific embodiments of the invention, provided solely for illustrative purposes and in a non-limiting way, with reference to the attached drawings. • Figure 1 is a partial perspective cut-away view of a wall of a sealed, thermally insulated tank using insulating box structures. • Figure 2 is a schematic side view of an insulating element which can be used in the tank wall of Figure 1, showing stresses and deformations to which it is subjected. • Figure 3 is a partially transparent perspective view of an insulating element having a reinforced cover panel. • Figure 4 is a schematic view showing the effects of the buckling of a pillar subjected to a force greater than the maximum force which can be withstood by this pillar. • Figure 5 is a partial perspective cut-away view of a wall of an insulated box structure comprising an anti-buckling plate positioned between two layers of thermal insulating material. • Figure 6 is a perspective view of a pillar comprising a shoulder for the positioning of a plate according to Figure 5. • Figures 7a to 7g are top views of a pillar that can be used in a box structure according to Figure 5. • Figure 8 is a schematic cutaway view of a tank of a natural gas carrier, comprising an insulating barrier composed of box structures according to Figure 5, and of a terminal for loading and/or unloading this tank.

Detailed description of embodiments

In this description, the terms “above”, “upper”, or “on” refer to anything nearer the inside of the tank, and the terms “below”, “lower” or “under” refer to anything nearer the outside of the tank, regardless of the gravitational field.

In the different variants shown in the drawings, components which have the same function are denoted by the same reference numerals, even if their construction has been modified to some extent.

Figure 1 shows a sealed insulating wall of a tank incorporated into a support structure of a ship.

The support structure of the tank is, in this case, formed by the inner hull of a double-hulled ship, the wall of which is indicated by the number 1.

On the wall 1 of the support structure, a corresponding tank wall is formed by superimposing, in succession, a secondary insulation layer 2, a secondary sealing barrier 3, a primary insulation layer 4 and a primary sealing barrier 5.

The primary insulation layer 4 and the secondary insulation layer 2 are formed by insulating elements, and more particularly by parallelepipedal insulating box structures 6 and 7 juxtaposed in a regular pattern. The primary box structures 7 and the secondary box structures 6 thus form a substantially flat surface which carries the primary sealing barrier 5 and the secondary sealing barrier 3, respectively.

The primary sealing barrier 5 and the secondary sealing barrier 3 are formed by parallel strakes 8 made of Invar®, with raised edges, which are positioned in alternation with elongated weld supports (not shown), also made of Invar®. More precisely, the weld supports extend perpendicularly to the wall and are retained by the underlying insulation layer 2 or 4 in each case, for example by being housed in inverted T-shaped groove 10 formed in cover panels 11 of the box structures 6 and 7. The raised edges of the strakes 8 are welded along the weld supports.

The primary insulating box structures 7 and the secondary insulating box structures 6 are held on the support structure by means of securing members 12. In particular, the securing members 12 of the secondary insulating layer 2 are fastened to the tank wall 1 by means of studs 13 welded perpendicularly to the wall 1. FR-A-2973097 describes a tank of this type, and notably the securing members 12 used to fasten the primary insulating box structures 7 and the secondary insulating box structures 8.

Figure 2 shows the construction of a box structure 15 which can be used in a tank wall of this type.

The box structure 15 has a base panel 16 on which are placed ladder-like structures 17 formed by rows of pillars 18 extending perpendicularly to the base panel 16, a batten 19 and a beam 20. Each row of pillars 18 bears on the base panel 16 via the batten 19, and carries the beam 20 which supports the cover panel 11 and is fastened thereto. The ladder structures 17 are assembled and fastened to the panels by means of fastening elements, by stapling for example. An insulating filling 21 is placed between the base panel 16 and the cover panel 11, and surrounds the pillars 18.

The beams 20 can be used to stiffen the cover panel 11 and to distribute the load when the panel is subjected to stresses such as those exerted by the fluid present in the tank, these stresses being shown schematically here by the arrows 22, and being due, for example, to the surging of the fluid in the tank.

However, if the insulating element is subjected to these stresses, the cover panel 11 tends be deformed and to warp between two ladder structures 17, under the effect of pressure, in curves indicated schematically by the curves 24. This deformation tends to cause the rotation of the lateral beams 20 located on either side of the mid-plane of the box structure 15. This rotation is illustrated by the lines 23. This deformation and this rotation result in the bending of the lateral pillars 18 located on the ladder structures on either side of the mid-plane of the insulating element 15 toward the outside of the box structure, as illustrated by the curve 25. The pillar is therefore embrittled by this bending 25, which is additional to the compressive stresses exerted on the pillars 18.

The fastening elements between the beams and the various elements of the box structure 15 are thus strongly stressed, which may cause them to become detached. Furthermore, this deformation causes poor distribution of the load across the pillars 18. In fact, as indicated by the arrows 26 and 27, the load 26 exerted by the pillars at the center of the box structure 15 is much greater than the load 27 exerted by the lateral pillars 20.

To overcome these problems, the box structure 15 may be replaced with a reinforced box structure 30 as illustrated in Figure 3. A box structure 30 of this type has a base panel 31 to which battens 32 are fastened. A row of pillars 33 is positioned and fastened above a corresponding batten 32 in each case. A reinforced cover panel 34 is attached to the pillars 33. The pillars 33 can be used, notably, to transmit the stresses exerted on the cover panel 34 to the wall 1, and therefore serve the purpose of resisting compression. An insulating filling (not shown) fills the space between the pillars, and may, for example, consist of an insulating foam cast between the pillars 33 or a block of foam machined to fit the pillars 33.

The successive rows of pillars 33 are offset from one another. In fact, the pillars 33 of the two successive rows 29 and 39 comprise pillars 33 spaced at the same regular interval, but the two rows of pillars 33 are offset in their longitudinal direction by a half-space. This arrangements provides a good compromise between the number of pillars 33 in the box structure 30 and the satisfactory distribution of the load.

The reinforced cover panel 34 has an upper panel 35 and a lower panel 36, each having a thickness of 15 mm, spaced apart by a series of parallel solid beams 37. In particular, the beams 37 extend parallel to the longitudinal sides of the box structure 30. In each case, a beam 37 is positioned along and above a row of pillars 33. The beams 37 have a rectangular cross section and a thickness of 15 mm. However, these beams may also have a trapezoidal cross section. The beams 37 and the panels 35 and 36 are connected rigidly; thus, when the upper panel 35 is subjected to the stresses exerted by the fluid and tends to warp, the lower panel 36 acts by traction, thereby preventing the rotation of the beams 37. Additionally, since the beams 37 are immobilized by the lower panel 36, the deformation of the upper panel 35 is reduced.

As described above, the mechanical characteristics of a box structure 6 or a box structure 7 are related not only to those of the cover panel 11 or 34, but also to those of the pillars 33 subjected to the compressive force. In order to increase the insulating capability of a box structure 6 or 7, either a material having a greater insulating capability is used, or the thickness of the box structure is increased. In the second case, this results in an increase in the length of the pillars 33. Beyond a certain length, the pillar 33 is exposed to a risk of buckling or breakage. The case of breakage corresponds to a stress on the pillar 33 much greater than that required to cause buckling. For a pillar 33 made of plywood, the break is more like a delamination between the different layers. If there is a force which is below the breakage threshold of the pillar 33, but above the buckling threshold, the box structure 6 or 7 may be locally deformed. It is therefore necessary to determine the critical buckling height of a pillar made from a given material. This critical height He is calculated by the following formula:

where: • E: Young’s modulus of the load-bearing element; • S: cross-sectional surface area of the load-bearing element; • σ is an ultimate compressive stress of the material of the loadbearing element.

For example, the critical height He can be evaluated, as a function of the surface area of the load-bearing element, with the aid of the data in Table 1. It should be noted that the critical height depends on the temperature at which the material is used.

Table 1: characteristics of materials for examples of load-bearing elements.

Thus, for a thickness of the box structure 6 and 7 chosen on the basis of its thermal insulation capability, it is possible to determine whether the pillars 33 have a length greater than the critical height.

Figure 4 shows the effects of a load 45 which is variable at different points of the surface of a box structure 30. This load 45 is not uniformly distributed over the surface of the cover panel 34 of the box structure 30. The load 45 is smaller with a force 45a at the outside of the surface of the box structure in the alignment of the pillar 33a, and increases up to the maximum force 45c. This force 45c, located at right angles to the pillar 33c, causes the pillar 33c to buckle. As shown in Figure 4, the effects of buckling on the pillar 33c are greatest at a point halfway along the distance between two fastening points of the pillar 33c. In this schematic illustration, the fastening points are the fastening to the cover panel 34 and the fastening to the base panel 31, which is not shown in this case.

Containing the buckling is therefore a matter of preventing the lateral movement to which the pillar 33c is subjected under the action of the force 45c. By interposing a plate 40 between the pillars 33, the lateral movements can be limited. Each pillar 33 passes through this plate 40 in openings 41. The plate 40 fixes the pillars 33 to one another in order to avoid movements in the plane. The force exerted by a pillar 33c on the plate 40 under a force 45c is borne by all the other pillars 33a.

This plate 40 is preferably placed halfway between the two securing points of the pillar 33. Thus the plate 40 is placed at the point of maximum observed deformation of the pillar 33 in the buckling mode 1.

In a variant, the plate can be positioned at other locations along the longitudinal direction of a pillar 33. However, in order to improve its effectiveness, it is preferably to ensure that the length of one of the segments of the pillar 33 between the plate and the base or cover panel does not exceed the critical height He of buckling of this pillar 33.

The size of the openings 41 is slightly greater than that of the pillars 33, creating a clearance 42. This clearance 42 is intended to facilitate the assembly of the plate 10 onto the pillars 33. The presence of this clearance 42 provides the plate with a degree of freedom. Under the effect of a force exerted by the pillar 33c at the contact point 47, the plate is translated in the direction of the buckling 46 to which the pillar 33c is subjected. The openings 41 in the plate 40 then bear on the pillars 33a in contact areas 47. The set of pillars 33a then opposes the buckling force with an opposite force 48.

For correct action, the clearance 42 must be small. For example, the clearance is less than 3 millimeters, and preferably more than 1 millimeter.

According to a variant, the holes are adjusted on the pillars 33. If there is no assembly clearance, there is no floating of the plate 40.

An anti-buckling plate 40 of this type can be arranged in a box structure 15 shown in dotted lines in Figure 2.

Figure 5 shows a box structure 30 in which an anti-buckling plate 40 is inserted between two layers 21a and 21b of insulating filling 21.

The insulating filling 21 can be made using various insulating materials such as polyurethane foam or mineral wool. If a very unstructured insulating material, such as perlite, is used, the insulating material subsides under the weight of the plate 40. In this case, positioning means which prevent the sliding of the plate 40 on the pillars 33 must be provided. Thus this makes it possible to prevent the plate 40 from crushing the insulating filling 21, or, in the case of a powdered insulating material, from creating transfer effects between the compartments of the box structure 30 delimited by the plate 40.

As shown in Figure 6, this function is then provided with the aid of a positioning pillar 60 comprising a shoulder 61, separating two portions 62 and 63 of the positioning pillar 60. The two portions 62 and 63 have different square cross sections. The opening 41 corresponding to the positioning pillar 60 has dimensions lying between the dimensions of the two sections of the positioning pillar 60. Thus, the plate can slide during assembly until it is stopped at the change of cross section defined by the shoulder 61.

The shoulder 61 can be produced in the body of the positioning pillar 60, on all or part of its periphery. It can also be produced by using an applied piece held on the pillar by any known means. For example, the applied piece is glued. In a variant, the applied piece is assembled by a threaded fastening with screwing and gluing.

To ensure that the plate 40 is supported, it is simply necessary to fit three positioning pillars 60 to stabilize the plate. For this purpose, it is preferable to place the positioning pillars 60 so as to define a triangle whose surface area inscribed in the surface of the box structure 15 or 30 is largest.

With the small assembly clearance relative to the size of a box structure 15 or 30, two positioning pillars 60 in a diagonal arrangement are equally suitable. It is also possible to support the plate 40 by means of the set of pillars fitted in the box structure 15 or 30. In a preferred embodiment, the positioning pillars 60 are placed at the corners of the box structure. In the case of box structures 15 or 30 which are particularly stressed, the center of the plate 40 is also supported.

On a ceiling wall, the shoulder 61 is turned toward the base panel 16 or 31, that is to say upward in terms of the gravitational field. For a box structure 15 or 30 positioned on a lateral wall, the box structure 15 or 30 is, for example, fitted with two sets of pillars. The shoulders of the first set are turned toward the base panel 16 or 31 and the pillars 60 fastened to the cover panel 11 or 34. Conversely, the pillars 60 of the second set are fastened to the base panel 16 or 31, with the shoulders turned toward the cover panel 11 or 34.

In a variant of the shoulder 61, the support is provided with the aid of a spacer tube. This tube is fitted over the pillars 33 placed at the support positions, such as the corners and the center. This spacer then acts as an applied shoulder. The shoulder 61 or the applied spacer prevent the movement of the plate 40 along the longitudinal axis of the pillars 33 in one direction. In some cases, it may be useful to lock the plate 40 in both directions. It is then simply necessary, after fitting the plate 40 at the bearing position, to fit a second spacer tube corresponding to the remaining length of the pillar 33 in order to immobilize the plate 40 in both directions.

In a variant, the plate 40 is fixed to at least three pillars 33. It can no longer move in the direction of the thickness to crush the insulating lining 21. A plate 40 of this type is made, for example, by molding.

The cross section of the pillars of Figure 6 is square, but, with reference to Figures 7a to 7g, any pillar shape, whether circular, polygonal, solid or hollow, in an H-shape or in the shape of a cross, is suitable and can be supported by an antibuckling plate 40. The anti-buckling function of the plate 40 is provided by adapting the shape of the opening 41 to the shape of the pillar.

In a variant of Figure 5, in the case of a very thick box structure 30, as many plates 40 as necessary may be added. In this case, it is preferable for the distance between a plate 40 and a base panel 16 or cover panel 34, or between two consecutive plates 40, to be less than the critical height of buckling of the pillar 33.

If a support is required for a box structure 30 with a plurality of plates 40, if a positioning pillar 60 is used, the latter comprises a shoulder 61 for each plate 40. It then has three portions, with three different cross-sectional dimensions. In this case, each plate 40 has openings 41 whose dimensions depend on the cross section of the positioning pillar 60 at its intended height in the box structure 15 or 30. In a variant, the box structure 15 or 30 has two types of positioning pillars 60 made with a shoulder 61. The first type of positioning pillar 60 has a shoulder height 61 which differs from the height of the shoulder 61 of the second type of positioning pillar 60. The box structure 15 or 30 is then fitted with two plates 40 which are distinguished by openings 41 whose dimension at right angles to each pillar 33 of the box structure 15 or 30 is adapted on the basis of the location of the plate 40 in the thickness of the box structure 15 or 30.

The placing of the plates 40 in terms of height relative to the pillar 33, or in the direction of the thickness of the box structure 15 or 30, is free and is a function of the conditions of use of the box structure 15 or 30. Preferably, the distribution is uniform and regular over the thickness. The plate or plates 40, the base panel 16 and the cover panel 11 or 34 are equidistant in pairs.

In a variant of the pillars 33 with a constant cross section, the pillar has a cross section which increases from the top toward the base of the pillar, over all or part of its length. For example, it is flared from a square cross section toward the base, to form a truncated pyramid. In a variant, the cross section of the pillar is a disk, and the pillar takes the form of a truncated cone. This solution with an increasing cross section has the further advantage of enabling a box structure 15 or 30 to be made with a plurality of plates whose height is simply adjusted by the dimension of the openings 41 present in each plate 40.

The anti-buckling plate 40 can be manufactured from any material, notably from plywood with a thickness of less than 20 mm, or from composite or metallic materials. For a plywood plate, the wood used may be birch or any other species.

The openings 41 can be formed by any known means, notably water jet cutting, laser cutting, punch cutting (or die cutting), or milling cutting.

In the case of a pillar 33 with a rectangular cross section, for example, the plate 40 may, for example, be made of metal with swaged openings. The swaged part forms an edging to increase the bearing area 47 of the plate 40 in contact with the pillar 33.

In a variant, the plate 40 is made of a plastic material, by molding.

An insulating element can be assembled in various ways. For example, the manufacture begins with the assembly of the base panel 16 with the battens 19 serving as sole plates on which the pillars 33 are placed. The lower layer of insulating material 21a is then fitted on the structure of pillars 33, followed by the pierced plate 40. A second layer of insulating material 21b is fitted in the upper structure of the pillars 33. Finally, the cover panel 11 or 34 is fastened to the pillars 33.

In a variant, the assembly begins with the fastening of the battens 19 to the base panel 16. The lower segment of insulating material 21a is then added, followed by the pierced plate 40 and the upper segment of insulating material 21b. The pillars are then fitted, using a template for positioning the pillars 33. Finally, the box structure 15 or 30 is completed with the cover panel 34.

The method described above for the production of an insulating layer can be used in various types of reservoirs, for example in order to form the primary and/or secondary insulating membrane of an LNG reservoir in a land-based installation or in a floating structure such as a gas carrier or other ship.

With reference to Figure 8, a cutaway view of a gas carrier ship 70 shows a sealed insulated tank 71 of generally prismatic shape mounted in the double hull 72 of the ship. The wall of the tank 71 comprises a primary sealing barrier intended to be in contact with the LNG contained in the tank, a secondary sealing barrier arranged between the primary sealing barrier and the double hull 72 of the ship, and two insulating barriers arranged, respectively, between the primary sealing barrier and the secondary sealing barrier, and between the secondary sealing barrier and the double hull 72.

In a known way, loading/unloading pipes 73 positioned on the upper deck of the ship can be connected, using appropriate connectors, to a marine or port terminal for transferring a cargo of LNG from or to the tank 71.

Figure 8 shows an example of a marine terminal comprising a loading and unloading station 75, a submarine pipe 76 and a land-based installation 77. The loading and unloading station 75 is a fixed off-shore installation comprising a movable arm 74 and a tower 78 supporting the movable arm 74. The movable arm 74 carries a bundle of insulated flexible hoses 79 that can be connected to the loading/unloading pipes 73. The movable arm 74, which can be oriented as required, is suitable for all sizes of gas carriers. A connecting pipe which is not shown extends inside the tower 78. The loading and unloading station 75 enables the gas carrier 70 to be loaded and unloaded from or to the land-based installation 77. The latter comprises liquefied gas storage tanks 80 and connecting pipes 81 linked by the submarine pipe 76 to the loading and unloading station 75. The submarine pipe 76 enables the liquefied gas to be transferred between the loading and unloading station 75 and the land-based installation 77 over a long distance, for example 5 km, allowing the gas carrier ship 70 to be kept at a long distance from the shore during the loading and unloading operations.

In order to generate the pressure required for transferring the liquefied gas, pumps on board the ship 70 and/or pumps fitted in the land-based installation 77 and/or pumps fitted in the loading and unloading station 75 are used.

Although the invention has been described with reference to particular embodiments, it is evidently not limited in any way to these embodiments, and comprises all the technical equivalents of the means described and their combinations where these fall within the scope of the invention.

The use of the verb “to have”, “to comprise” or “to include” and any of its conjugated forms does not exclude the presence of elements or steps other than those stated in a claim. The use of the indefinite article “a” or “an” for an element or a step does not exclude the presence of a plurality of such elements or steps unless otherwise specified.

In the claims, any reference symbol in brackets is not to be interpreted as a limitation of the claim.

Claims

1. A sealed, thermally insulated tank incorporated into a support structure for containing a fluid, in which a tank wall comprises, from the outside of the tank toward the inside of the tank: a load-bearing wall (1), a thermal insulation barrier (2, 4) retained on the load-bearing wall, the thermal insulation barrier being formed from a plurality of insulating elements (15, 30) juxtaposed to form a support surface, and a sealing barrier (3, 5) bearing on the support surface, an insulating element having a generally flattened prismatic shape, and comprising: a thermal insulating material (21), a plurality of load-bearing elements (33) passing through the thermal insulating material along a direction of thickness perpendicular to the tank wall, the loadbearing elements (33) each having a first end and second end, and a cover panel (11, 34) and a base panel (16, 31) parallel to the tank wall and arranged at the first ends and the second ends, respectively, of the load-bearing elements of the insulating element, so as form exterior walls of the insulating element, the first ends of the load-bearing elements being fastened to the cover panel and the second ends of the load-bearing elements being fastened to the base panel, and an anti-buckling plate (40), parallel to the cover panel (11, 34) and to the base panel, sandwiched between a first (21a) and a second (21b) portion of the thickness of said thermal insulating material (21), the anti-buckling plate having a plurality of load-bearing elements (33) passing through it in a plurality of openings (41) in the anti-buckling plate, the openings being spaced apart from one another so as to provide a distance between two neighboring load-bearing elements, in a plane defined by the anti-buckling plate.

2. The tank as claimed in claim 1, wherein an opening (41) in the anti-buckling plate is larger than a cross section of the load-bearing element engaged in the opening, so as to leave an assembly clearance (42).

3. The tank as claimed in claim 2, wherein the assembly clearance (42) is less than three millimeters.

4. The tank as claimed in any of claims 1 to 3, wherein the antibuckling plate (40) is positioned halfway between the base panel and the cover panel.

5. The tank as claimed in any of claims 1 to 4, wherein the thermal insulating material comprises a second anti-buckling plate parallel to the base panel and the cover panel, sandwiched between the second and a third portion of the thickness of said thermal insulating material, the second anti-buckling plate having the plurality of load-bearing elements passing through it in a plurality of openings positioned in alignment with the openings in the first anti-buckling plate.

6. The tank as claimed in any of claims 1 to 5, wherein a said insulating element comprises a plurality of anti-buckling plates (40), the number of anti-buckling plates being greater than or equal to a theoretical number defined in such a way that the distance between two successive support points (47) of a loadbearing element according to the longitudinal orientation of the load-bearing element is less than a predetermined critical height He, said critical height being equal to:

where: E: Young’s modulus of the load-bearing element, S: cross-sectional surface area of the load-bearing element, σ is an ultimate compressive stress of the material where the support points are the second end of the load-bearing element fastened to the base panel, the first end of the load-bearing element fastened to the cover panel, and each portion of the load-bearing element engaged in an opening of the anti-buckling plates, such that each anti-buckling plate provides a single support point for the load-bearing element.

7. The tank as claimed in any of claims 1 to 6, wherein the insulating element comprises a plurality of anti-buckling plates (40) positioned in an equidistant way in the thickness of the insulating element.

8. The tank as claimed in any of claims 1 to 7, wherein an insulating element comprises positioning means capable of positioning the anti-buckling plate in the thickness of the insulating element.

9. The tank as claimed in claim 8, wherein the positioning means are arranged on the load-bearing elements, to prevent the translation of the antibuckling plate in a longitudinal direction of the plurality of load-bearing elements.

10. The tank as claimed in claim 9, wherein the positioning means comprise a shoulder (61) formed by a difference in cross section between two adjacent longitudinal segments of one load-bearing element of the plurality of loadbearing elements.

11. The tank as claimed in claim 10, wherein, for the shoulder (61) capable of supporting the anti-buckling plate, the size of the plurality of openings in the anti-buckling plate lies between crosssectional size of a first of the two segments and cross-sectional size of the second segment of the load-bearing element.

12. The tank as claimed in claim 9, wherein the positioning means comprise a spacer tube fitted onto a load-bearing element, the spacer tube having an outside diameter greater than the dimensions of the opening in the anti-buckling panel so as to provide, at one end of the spacer tube, a bearing point for the antibuckling panel, and, at the other end of the spacer tube, a bearing point for the base panel of the insulating element or another anti-buckling plate.

13. The tank as claimed in claim 9, wherein the positioning means comprise a longitudinal portion of a load-bearing element which is flared from the first end of the load-bearing element toward the second end of the load-bearing element, and wherein the size of an opening in the anti-buckling plate substantially corresponds to the cross-sectional size of the longitudinal portion of the load-bearing element.

14. The tank as claimed in claim 8, wherein the positioning means comprise supporting pillars orthogonal to the base panel, a first end of each pillar being fastened to the base panel, while the other end serves as a bearing point for said anti-buckling plate.

15. A ship (70) for transporting a refrigerated liquid product, the ship comprising a double hull (72) and a tank (71) as claimed in any of claims 1 to 14 positioned in the double hull.

16. A method for loading or unloading a ship (70) as claimed in claim 15, wherein a refrigerated liquid product is conveyed through insulated pipes (73, 79, 76, 81) from or to a floating or land-based storage installation (77) to or from the tank of the ship (71).

17. A transfer system for a refrigerated liquid product, the system comprising a ship (70) as claimed in claim 15, insulated pipes (73, 79, 76, 81) arranged so as to connect the tank (71) installed in the ship’s hull to a floating or land-based storage installation (77), and a pump for propelling a flow of refrigerated liquid product through the insulated pipes from or to the floating or land-based storage installation to or from the ship’s tank.