AU2016373295B2

AU2016373295B2 - Insulating block suitable for manufacturing an insulating wall in a sealed tank

Info

Publication number: AU2016373295B2
Application number: AU2016373295A
Authority: AU
Inventors: Thomas CREMIERE
Original assignee: Gaztransport et Technigaz SA
Current assignee: Gaztransport et Technigaz SA
Priority date: 2014-12-15
Filing date: 2016-12-15
Publication date: 2022-03-03
Anticipated expiration: 2036-12-15
Also published as: CN107257900A; CN108700257B; FR3030014A1; FR3030014B1; WO2016097578A2; KR102422517B1; WO2016097578A3; CN107257900B; KR20180094925A; KR102624276B1; CN108700257A; KR20170099949A; AU2016373295A1; WO2017103500A1

Abstract

The invention relates to a parallelepiped insulating block (207), which includes: a rectangular bottom plate (315); a rectangular cover plate (316) parallel to the bottom plate and separated from the bottom plate in the direction of the thickness of the insulating block; a plurality of supporting pillars (317) arranged between the bottom plate and the cover plate, the supporting pillars extending longitudinally in the thickness direction and having a small cross-section relative to a length and a width of the insulating block; and an insulating fitting arranged between the bottom plate and the cover plate and between the supporting pillars. Four corner pillars (240), which extend in the thickness direction between a corner area of the bottom plate and a corresponding corner area of the cover plate, include a first shell and a second shell perpendicular to the first shell. An outer edge of the first shell has a shoulder surface (49).

Description

INSULATING BLOCK SUITABLE FOR MANUFACTURING AN INSULATING WALL IN A SEALED TANK

Technical Field

The invention relates to the field of sealed and thermally insulating membrane-type tanks for storing and/or transporting fluid such as a cryogenic fluid.

Sealed and thermally insulated membrane-type tanks are notably used for storing liquefied natural gas (LNG) which is stored, at atmospheric pressure, at around -162°C. These tanks may be installed on land or on a floating structure.

Technological Background

In a low-temperature liquefied-gas storage tank, one essential function of the tank wall is to insulate the cargo in order to limit the heat flux that causes the cargo to evaporate, and also to protect the hull from cryogenic temperatures in the case of a ship's tank. However, the tank wall also needs to withstand the hydrodynamic loading of the cargo, which therefore entails compressive strength.

One possible option for performing these functions is to make the tank wall with a layer of homogeneous material that is both insulating and structurally resistant to compression. Examples of such tanks are available in the literature, for example from publications US-A-4116150 and WO-A-2013124573. However, the insulating material used in these examples, namely reinforced polyurethane foam, is high cost. In addition, it is difficult to find a structural insulating material that optimizes both mechanical strength and thermal insulation.

Another possible option is to make the tank wall using heterogeneous insulating units comprising mechanically strong load-bearing parts and insulating materials arranged between the load-bearing parts. Because the insulating materials are at least partially relieved of the hydrodynamic loadings in such a case, there is a wider possible choice of insulating materials. Examples of such tanks are available in the literature, for example from publications FR-A-2867831, FR-A-2989291 and WO-A-2013182776.

In FR-A-2867831, the insulating unit is a box having parallel interior partitions delimiting compartments filled with expanded perlite or aerogels. In FR-A-2989291 the insulating unit is a similar box filled with fibrous materials. In one embodiment, small cross-section columns are used in the place of the parallel partitions. In WO-A-2013182776 provision is made for an insulating foam to be poured between load-bearing columns. In every instance, the overall heat flux transmitted by such an insulating unit is the result both of the flux transmitted by the load-bearing parts and the flux transmitted by the intermediary insulating materials.

FR-A-3004512 describes a parallelepipedal insulated caisson for creating the thermally insulating barrier of a tank wall, in which caisson the cross section of the columns may be cross-shaped.

Summary

One idea underlying embodiments of the invention is that of providing an insulating unit at least certain load-bearing parts of which are made from thin materials that have good mechanical strength, so as to maximize the volume occupied by the non-structural insulating materials.

According to a first aspect of the invention, there is provided a parallelepipedal insulating unit suitable for creating an insulating wall in a storage tank for a cold liquid, the insulating unit comprising: a bottom sheet of rectangular shape, a top sheet of rectangular shape parallel to the bottom sheet and spaced away from the bottom sheet in a thickness direction of the insulating unit, a plurality of load-bearing columns arranged between the bottom sheet and the top sheet, the load-bearing columns extending longitudinally in the thickness direction and having a cross section that is small in size in comparison with a length and a width of the insulating unit, and an insulating filling arranged between the bottom sheet and the top sheet and between the load-bearing columns, the insulating unit further comprising four corner columns extending in the thickness direction between the bottom sheet and the top sheet, a corner column in each instance being arranged between a corner zone of the bottom sheet and a corresponding corner zone of the top sheet and comprising a first web and a second web perpendicular to the first web, characterized in that each first web comprises, in succession in the thickness direction of the insulating unit, a wider lower portion and a narrower upper portion, so that an external edge of the first web has a shoulder surface situated between the wider lower portion and the narrower upper portion and perpendicular or oblique to the thickness direction of the insulating unit, in which the first web is a bisecting web extending from the corner along a bisector of the corner of the bottom sheet and of the top sheet as far as an internal end situated inside the insulating unit, the external edge of the bisecting web which has the shoulder surface facing toward the corner of the bottom sheet, the second web being a bisecting-web counterweb perpendicular to the bisecting web, the bisecting-web counterweb being fixed to the internal end of the bisecting web and extending obliquely between a transverse edge and a longitudinal edge of the top sheet and of the bottom sheet, and in which the corner zone of the top sheet comprises a cutout situated in vertical alignment with the shoulder surface of the bisecting web so as to create an access opening allowing access to the shoulder surface from the top sheet in the thickness direction.

According to the embodiment, such an insulating unit may have one or more of the following features.

Various materials that exhibit suitable strength may be used for the top sheet, for example plywoods of different types or composite materials. For preference, the top sheet is made of densified plywood. Densified plywood can be obtained with wood plies that are impregnated with a large quantity of thermosetting resins, for example using beech, pine or birch wood. For preference, the density of the densified plywood is greater than or equal to 0.9. By comparison, the typical density of an ordinary plywood is of the order of 0.7. Such a densified plywood offers satisfactory properties in terms of cost price, mechanical strength and thermal insulation. For example, the thickness of the top sheet may be of the order of 5 mm. Similar considerations may be applied to the bottom sheet.

In order to minimize the heat flux by conduction, it is preferable to limit the cross section of the load-bearing columns. However, given that the load-bearing columns are intended to react a hydrostatic and hydrodynamic load and transmit it from the top sheet to the load-bearing wall, there may be a risk of the top and/or bottom sheet becoming punctured if there is an excessive concentration of the compressive stresses. In addition, the load-bearing columns are liable to create bending stresses in the top and/or bottom sheet. In order to reduce the stresses and the risk of puncturing, various load-spreading elements may be used at the connection between the load-bearing columns and the top and/or bottom sheet.

According to one embodiment, the insulating unit further comprises load spreading components of flared shape arranged between the load-bearing columns and the top or bottom sheet, the load-spreading component in each instance comprising a surface of smaller cross section facing toward the load-bearing column and a surface of larger cross section facing toward the top or bottom sheet.

According to one embodiment, the load-bearing columns are arranged in a plurality of rows extending in the length direction of the insulating unit, the insulating unit further comprising load-spreading beams arranged between the load-bearing columns and the top sheet, the load-spreading beam being oriented in the length direction of the insulating unit and in each instance resting on one of the rows of load bearing columns.

According to one embodiment, the load-spreading beam in each instance has a surface of smaller cross section facing toward the load-bearing columns and a surface of greater cross section facing toward the top sheet.

Beams may be similarly employed with the bottom sheet.

Furthermore, there are various structures that may be provided at the corners of the insulating unit. According to one embodiment, the insulating unit comprises four corner columns extending in the thickness direction between the bottom sheet and the top sheet, a corner column in each instance being arranged between a comer zone of the bottom sheet and a corresponding corner zone of the top sheet and comprising a longitudinal web extending from the corner along a longitudinal edge of the bottom sheet and of the top sheet over a portion of the length of the insulating unit, and a transverse web extending from the corner along a transverse edge of the bottom sheet and of the top sheet over a portion of the width of the insulating unit. Such a comer column has a relatively high moment of inertia in the length direction and the width direction of the insulating unit, something which is beneficial in withstanding potential shear stresses in the insulating unit parallel to the top and bottom sheets.

Alternatively, the corner column arranged in each instance between a corner zone of the bottom sheet and a corresponding corner zone of the top sheet comprises a bisecting web extending from the corner along a bisector of the corner of the bottom sheet and of the top sheet as far as an internal end situated inside the insulating unit and a bisecting-web counterweb perpendicular to the bisecting web, the bisecting web counterweb being fixed to the internal end of the bisecting web and extending obliquely between a transverse edge and a longitudinal edge of the top sheet and of the bottom sheet. By virtue of these features, the comer column has excellent resistance to buckling.

Advantageously in this case, each bisecting web comprises, in succession in the thickness direction of the insulating unit, a wider lower portion in contact with the bottom sheet and a narrower upper portion in contact with the top sheet, so that an external edge of the bisecting web facing toward the corner of the bottom sheet has a shoulder surface situated between the wider lower portion and the narrower upper portion and perpendicular or oblique to the thickness direction of the insulating unit.

For preference in this case, the corner zone of the top sheet comprises a cutout situated in vertical alignment with the shoulder surface of the bisecting web so as to create an access opening allowing access to the shoulder surface. Thus, it is possible to access a retaining member collaborating with the shoulder surface in order to fix the insulating unit in a tank wall.

According to one preferred embodiment, each bisecting web comprises an upper surface which is perpendicular to the thickness direction of the insulating unit, and the corner zone of the top sheet comprises a cutout situated in vertical alignment with the upper surface of the bisecting web so as to create a spot face surface situated in line with the upper surface of the bisecting web, whereas the upper surface of the bisecting web is fixed against the top sheet.

According to another embodiment, each bisecting web comprises an upper surface which is perpendicular to the thickness direction of the insulating unit, and the corner zone of the top sheet comprises a cutout situated in vertical alignment with an external portion of the upper surface of the bisecting web so as to create an access opening allowing access to the external portion of the upper surface of the bisecting web, whereas an internal portion of the upper surface of the bisecting web is fixed against the top sheet. Thus, it is possible to access a retaining member collaborating with the upper surface of the bisecting web in the external portion thereof so as to fix the insulating unit into a tank wall.

For preference in this case, each bisecting web has a trapezoidal shape with an upper end that is wider in the direction of the bisector of the corner of the top sheet and a lower end that is narrower in the direction of the bisector of the corner of the bottom sheet. By virtue of this progressive narrowing of the bisecting web, the corresponding thermal bridge can be reduced.

This reduction in thermal bridging can also be obtained if the trapezoidal shape does not extend as far as the ends of the bisecting web. According to one embodiment, each bisecting web of a secondary insulating unit has a trapezoidal shape with a portion that is wider in the direction of the top sheet and a portion that is narrower in the direction of the bottom sheet of the secondary insulating unit.

There are a number of different materials that can be used for the insulating filling of the insulating unit, these notably including glass wool, rockwool, cellulose wadding, fibrous materials, perlite, expanded perlite, low density polymer foams, aerogels and the like. According to one embodiment, use is made of granular or powdered insulating materials. For that, lateral walls are provided to close off the four lateral sides of the insulating unit. These lateral walls may be made from thin and lightweight materials such as fabric or very thin ply. Alternatively, these lateral walls may be made from thicker materials if they also at the same time have to perform a function of reacting load.

According to one embodiment, the bottom sheet of the insulating unit is divided into a plurality of rectangular bottom portions, the bottom portions being juxtaposed in a width direction of the insulating unit, a gap being formed in each instance between two of the bottom portions which are juxtaposed along the entire length of the insulating unit, the insulating unit further comprising a connecting piece fixed to an internal surface of the bottom sheet that faces toward the top sheet so as to connect the two juxtaposed bottom portions, the connecting piece exhibiting in succession in the width direction of the insulating unit a first end portion which is fixed to the internal surface of a first of the two juxtaposed bottom portions, an intermediate portion straddling the gap between the two juxtaposed bottom portions, and a second end portion which is fixed to the internal surface of a second of the two juxtaposed bottom portions, the connecting piece having a housing in the continuation of the gap between the two juxtaposed bottom portions, the intermediate portion of the connecting piece closing the housing in the thickness direction on the opposite side to the gap, and the gap between the two juxtaposed bottom portions and the corresponding housing are able to accept the projecting part of a sealing membrane including the projecting flange of a metal strip of the sealing membrane and the turned-up lateral edges of strakes which are welded to it.

According to a second aspect of the invention, there is provided a sealed and insulating tank comprising a tank wall held on a bearing structure, the tank wall including, in the thickness direction from the outside toward the inside of the tank, a secondary insulating barrier held on the bearing structure, a secondary sealing membrane held on the secondary insulating barrier, a primary insulating barrier held on the secondary sealing membrane and a primary sealing membrane held on the primary insulating barrier, characterized in that the secondary insulating barrier is essentially made up of a plurality of secondary insulating units juxtaposed in a repeating pattern, wherein each secondary insulating unit comprises a parallelepipedal insulating unit according to a first aspect of the invention, and in that the primary insulating barrier is essentially made up of a plurality of primary insulating units juxtaposed in the repeating pattern, the primary insulating units being aligned with the secondary insulating units in the thickness direction of the tank wall, the tank wall further comprising retaining members attached to the bearing structure at the corners of the secondary insulating units, a retaining member in each instance collaborating with four adjacent secondary insulating units to hold the adjacent secondary insulating units on the bearing structure and with four primary insulating units which are superposed with said adjacent secondary insulating units so as to hold the primary insulating units on the secondary sealing membrane.

According to a third aspect of the invention, there is provided a sealed and insulating tank comprising a tank wall held on a bearing structure, the tank wall including, in the thickness direction from the outside toward the inside of the tank, a secondary insulating barrier held on the bearing structure, a secondary sealing membrane held on the secondary insulating barrier, a primary insulating barrier held on the secondary sealing membrane and a primary sealing membrane held on the primary insulating barrier, characterized in that the secondary insulating barrier is essentially made up of a plurality of secondary insulating units juxtaposed in a repeating pattern, and in that the primary insulating barrier is essentially made up of a plurality of primary insulating units juxtaposed in the repeating pattern, wherein each primary insulating unit comprises a parallelepipedal insulating unit according to a first aspect of the invention, the primary insulating units being aligned with the secondary insulating units in the thickness direction of the tank wall, the tank wall further comprising retaining members attached to the bearing structure at the region of the comers of the secondary insulating units, a retaining member in each instance collaborating with four adjacent secondary insulating units to hold the adjacent secondary insulating units on the bearing structure and with four primary insulating units which are superposed with said adjacent secondary insulating units so as to hold the primary insulating units on the secondary sealing membrane.

The aforementioned insulating unit may be used to manufacture one and/or other of the insulating barriers in such a tank wall, notably for the secondary insulating barrier the bending stress on which is fairly modest.

According to one embodiment, the secondary insulating barrier is essentially made up of a plurality of aforementioned secondary insulating units and juxtaposed in a repeating pattern, the secondary sealing membrane comprising metal strips bent at right angles and arranged in the housings of the top sheets of the secondary insulating units, each metal strip comprising a flange projecting above the top sheet through the gap in the top sheet, the secondary sealing membrane comprising strakes made of a steel with a low coefficient of expansion, which are laid flat on the top sheets of the secondary insulating units between the metal strips, each strake having two parallel turned-up lateral edges which are welded fluidtightly to the projecting flanges of the metal strips.

According to one embodiment, mastic supports are inserted between the bottom sheets of the secondary insulating units and the bearing structure, the mastic supports comprising small-section pads of mastic arranged in vertical alignment with the load-bearing columns of the secondary insulating units.

According to one embodiment, the primary insulating barrier is essentially made up of a plurality of parallelepipedal primary insulating units juxtaposed in a repeating pattern, each primary insulating unit comprising: a bottom sheet of rectangular shape, a top sheet of rectangular shape parallel to the bottom sheet and spaced away from the bottom sheet in a thickness direction of the insulating unit, a plurality of load-bearing columns arranged between the bottom sheet and the top sheet, the load-bearing columns extending longitudinally in the thickness direction and having a cross section that is small in size in comparison with a length and a width of the insulating unit, and an insulating filling arranged between the bottom sheet and the top sheet and between the load-bearing columns.

According to one embodiment, the bottom sheet of the primary insulating unit is divided into a plurality of rectangular bottom portions, the bottom portions being juxtaposed in a transverse direction of the primary insulating unit, a gap being formed in each instance between two of the bottom portions which are juxtaposed along the entire length of the primary insulating unit, the primary insulating unit further comprising a connecting piece fixed to an internal surface of the bottom sheet that faces toward the top sheet so as to connect the two juxtaposed bottom portions, the connecting piece exhibiting in succession in the transverse direction of the primary insulating unit a first end portion which is fixed to the internal surface of a first of the two juxtaposed bottom portions, an intermediate portion straddling the gap between the two juxtaposed bottom portions, and a second end portion which is fixed to the internal surface of a second of the two juxtaposed bottom portions, the connecting piece having a housing in the continuation of the gap between the two juxtaposed bottom portions, the intermediate portion of the connecting piece closing the housing in the thickness direction on the opposite side to the gap, in which the gap between the two juxtaposed bottom portions and the corresponding housing accept the projecting flange of one of the metal strips of the secondary membrane and the turned-up lateral edges of the strakes which are welded to it.

Various materials having suitable strength can be used for the connecting piece of the bottom sheet, for example plywoods of various types or composite materials. For preference, the connecting piece is made from a material that has a thermal contraction coefficient similar to that of the bottom sheet, notably the same material as that used for the bottom sheet. According to one embodiment, the connecting piece is made of densified plywood.

There are many possible configurations for positioning the load-bearing columns of the insulating units. According to one embodiment, the load-bearing columns of a primary insulating unit are situated in vertical alignment with the load bearing columns of a secondary insulating unit. Such a configuration makes it possible to minimize the bending stresses in the top sheets of the secondary insulating units.

According to another embodiment, the load-bearing columns of a primary insulating unit are situated between the load-bearing columns of a secondary insulating unit.

According to one embodiment of the sealed and insulating tank, the secondary insulating barrier is essentially made up of a plurality of secondary insulating units which have the aforementioned comer columns and which are juxtaposed in a repeating pattern, and the primary insulating barrier is essentially made up of a plurality of primary insulating units which have the aforementioned corner columns and which are juxtaposed in the repeating pattern, the primary insulating units being aligned with the secondary insulating units in the thickness direction of the tank wall.

For preference in this case, the tank wall further comprises retaining members attached to the bearing structure at the region of the corners of the secondary insulating units, a retaining member in each instance collaborating with four adjacent secondary insulating units to hold the adjacent secondary insulating units on the bearing structure and with four primary insulating units which are superposed with said adjacent secondary insulating units so as to hold the primary insulating units on the secondary sealing membrane.

According to one embodiment, the retaining member in each instance comprises a primary bearing element kept bearing against the shoulder surface of a bisecting web of each of the four primary insulating units. According to one embodiment, the retaining member in each instance comprises a secondary bearing element kept bearing against a spot face of the top sheet of each of the four secondary insulating units, the spot face being situated in line with the upper surface of a bisecting web, or on the shoulder surface of a bisecting web of each of the four secondary insulating units.

Such a tank may form part of an on-shore storage facility, for example for storing LNG, or may be installed in a floating in-shore or off-shore structure, notably a methane tanker, a floating storage and regasification unit (FSRU), a floating production storage and offloading unit (FPSO) and the like.

According to a fourth aspect of the invention, there is provided a ship for transporting a fluid, the ship comprising a double hull and a tank according to a second or third aspect of the invention arranged in the double hull.

According to one embodiment, a ship for transporting a fluid product, notably a cold liquid, comprises a double hull and an aforementioned tank arranged in the double hull.

According to a fifth aspect of the invention, there is provided a method for loading or unloading an aforementioned ship, in which method a fluid is conveyed through insulated pipelines from or to a floating or on-shore storage facility to or from the tank of the ship.

According to a sixth aspect of the invention, there is provided a transfer system for a fluid, the system comprising an aforementioned ship, insulated pipelines arranged in such a way as to connect the tank installed in the hull of the ship to a floating or on-shore storage facility and a pump for causing a flow of fluid through the insulated pipelines from or to the floating or on-shore storage facility to or from the tank of the ship.

According to one embodiment, there is disclosed a transfer system for a fluid product, notably a cold liquid, the system comprising the aforementioned ship, insulated pipelines arranged in such a way as to connect the tank installed in the hull of the ship to a floating or on-shore storage facility and a pump for causing a flow of fluid product through the insulated pipelines from or to the floating or on-shore storage facility to or from the tank of the ship.

Brief description of the figures

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

* Figure 1 is a perspective view with partial cutaway of a sealed and insulating tank wall according to one embodiment.

• Figure 2 is a schematic perspective depiction in cross section of a primary insulating unit and of a secondary insulating unit which have been superposed and which can be used in the tank wall of figure 1.

• Figure 3 is a view in cross section of an insulating unit according to one embodiment.

• Figure 4 is an enlarged view of zone IV in figure 3.

• Figures 5, 6 and 7 are views analogous to figure 4 showing other embodiments of the top sheet.

• Figure 8 is a view similar to figure 2 showing another embodiment of the primary and secondary insulating units.

• Figure 9 is a view in longitudinal section of an insulating unit of figure 8.

• Figure 10 is a view from above of an insulating unit according to one embodiment.

• Figures 11, 12 and 13 are perspective views in cross section showing other embodiments of the top sheet of an insulating unit.

• Figure 14 is a perspective view in cross section showing the bottom sheet of a secondary insulating unit according to one embodiment.

• Figure 15 is a schematic view in cross section of the bottom sheet of a primary insulating unit according to one embodiment.

• Figure 16 is a schematic perspective view of a primary insulating unit according to one embodiment.

• Figure 17 is a schematic depiction with cutaway of a methane tanker tank and of a terminal for loading/unloading this tank.

• Figure 18 is a schematic depiction in perspective of superposed primary and secondary insulating units that can be used in the tank wall of figure 1.

• Figure 19 is a schematic depiction in perspective and in cross section of superposed primary and secondary insulating units that can be used in the tank wall of figure 1.

• Figure 20 is a perspective view of a secondary insulating unit according to another embodiment.

• Figure 21 is an enlarged perspective view of a detail of a tank wall produced with the secondary insulating unit of figure 20.

• Figure 22 is a view from above of the detail of figure 21.

• Figure 23 is a perspective view of a retaining member used in the tank wall of figure 21.

• Figure 24 is a perspective view of a primary insulating unit according to another embodiment.

• Figure 25 is an enlarged perspective view of a detail of a tank wall produced with the primary insulating unit of figure 24.

• Figure 26 is a perspective view of a retaining member used in the tank wall of figure 25.

• Figure 27 is a view from above of the detail of figure 25.

Detailed description of embodiments

Figure 1 depicts a wall of a thermally insulating sealed tank. The overall structure of such a tank is well known and has a polyhedral shape. Only one zone of the wall of the tank will therefore be described here given that all the walls of the tank may exhibit a similar general structure.

As a result, irrespective of the actual orientation of the tank wall in the earth's gravitational field, the terms "on" and "above" will be used to denote a position situated toward the inside of the tank in the thickness direction of the tank wall and the terms "under" and "below" will be used to denote a position situated toward the outside of the tank, namely toward the bearing structure.

The tank wall comprises, from the outside toward the inside of the tank, a bearing wall 1, a secondary thermally insulating barrier 2 which is formed of insulating units 3 juxtaposed on the bearing structure 1 and anchored thereto by secondary retaining members 4, a secondary sealing membrane 5 supported by the insulating units 3, a primary thermally insulating barrier 6 formed of insulating units 7 juxtaposed and anchored on the secondary sealing membrane 5 by primary retaining members 8 and a primary sealing membrane 9 supported by the insulating units 7 and intended to be in contact with the cryogenic fluid contained in the tank.

The bearing structure comprises a plurality of bearing walls defining the overall shape of the tank. The bearing structure may notably be formed by the hull or double hull of a ship. The bearing wall 1 may notably be a self-supporting sheet of metal or, more generally, any type of rigid partition exhibiting suitable mechanical properties.

The primary 9 and secondary 5 sealing membranes are, for example, made up of a continuous layer of metal strakes with turned-up edges, said strakes being welded by their turned-up edges to parallel welding supports held on the insulating units 3, 7. The metal strakes are, for example, made of Invar @, namely an alloy of iron and nickel the expansion coefficient of which is typically comprised between 1.2.10-6 and 2.10-6 K-1, or from an iron alloy with a high manganese content the expansion coefficient of which is typically of the order of 7.10-6 K-1. In the case of a ship's tank, the strakes preferably run parallel to the longitudinal direction 10 of the ship.

The secondary insulating units 3 and the primary insulating units 7 may have identical or different structures and equal or different dimensions.

Figure 2 is a half view of a secondary insulating unit 3 surmounted by a primary insulating unit 7, the sealing membranes having been omitted for the sake of simplicity.

Each of the insulating units 3 and 7 has a rectangular parallelepipedal shape with two large faces, or main faces, and four small faces, or lateral faces. The two insulating units have the same length and the same width. The secondary insulating unit 3 is thicker than the primary insulating unit 7.

The secondary insulating unit 3 comprises a bottom sheet 15 and a top sheet 16 which are parallel and spaced apart in the thickness direction. The bottom sheet 15 and the top sheet 16 define the main faces of the secondary insulating unit 3.

The top sheet 16 has an exterior support surface able to accept the secondary sealing membrane 5. The top sheet 16 furthermore has housings to accept welding supports 11 that allow the metal strakes 12 of the secondary sealing membrane 5 to be welded, as will be explained later on. By convention, the longitudinal direction of the secondary insulating unit 3 is the direction parallel to the welding supports 11.

Load-bearing columns 17 extend in the thickness direction of the secondary insulating unit 3 and are fixed, firstly, to the bottom sheet 15 and, secondly, to the top sheet 16. The load-bearing columns 17 are able to react compressive load. The load bearing columns 17 are aligned in a plurality of rows and arranged in a staggered configuration. The distance between the load-bearing columns 17 is determined in such a way as to allow good distribution of compressive load. In one embodiment, the load-bearing columns 17 are distributed equidistantly. The load-bearing columns 17 are fixed to the bottom sheet 15 and to the top sheet 16 by any suitable means, by screwing, clipping and/or bonding for example.

In the embodiment depicted in figure 2, the load-bearing columns 17 have a solid cross section which is square in shape. At the four corners of the bottom sheet 15 and of the top sheet 16 there is also a corner column 18. The corner column 18 in each instance comprises a longitudinal web 19 and a transverse web 20 which meet at the corner. The longitudinal web 19 and the transverse web 20 are rectangular in shape here. As an alternative, they can have a trapezoidal shape as sketched out in figure 11.

The load-bearing columns 17 and the corner columns 18 may be made from numerous materials. They may notably be made from ordinary or densified plywood, or from a plastics material such as polyvinyl chloride (PVC), polyethylene terephthalate (PET), polyethylene (PE), the copolymer acrylonitrile-butadiene-styrene (ABS), polyurethane (PU) or polypropylene (PP), optionally fiber-reinforced.

An insulating filling, not depicted, extends in the spaces formed between the load-bearing columns 17. The insulating filling is, for example, glass wool, cellulose wadding, a polymer foam, such as polyurethane foam, polyethylene foam or polyvinyl chloride foam. Such a polymer foam can be applied between the load-bearing columns 17 using an injection operation at the time of manufacture of the secondary insulating unit 3. Alternatively, it is possible to create the insulating filling by forming, in a precut block of polymer foam, glass wool or cellulose wadding, orifices to accommodate the load-bearing columns 17.

The primary insulating unit 7 has an overall structure analogous to the secondary insulating unit 3, apart from a few differences which will be explained later on. For the sake of simplicity, elements that make up the primary insulating unit 7 that are analogous to those of the secondary insulating unit 3 will be denoted by the same reference numeral increased by 100.

In a configuration such as in figure 2 in which the primary columns 117 are superposed with the secondary columns 17, the primary bottom sheet 115 and the secondary top sheet 16 are substantially unstressed both in terms of bending and in terms of shear. Essentially, under hydrodynamic loading, it is therefore the primary top sheet 116 that works in bending whereas the load-bearing columns 17 and 117 and the corner columns 18 and 118 work in compression.

By contrast, the primary bottom sheet 115, the secondary top sheet 16 and the secondary bottom sheet 15 are less heavily loaded, namely essentially by the loading of ballast in the ship, although these cause stress loadings that are far weaker in comparison with those associated with the weight of the cargo. The working thickness of these structural elements can therefore be reduced in order to allow more volumetric space for the insulating filling and thus improve the thermal performance of the wall.

In the case of the primary bottom sheet 115, the secondary top sheet 16 and the secondary bottom sheet 15, it is therefore particularly advantageous to use structurally strong thin materials such as densified plywoods or composite materials.

Examples of suitable densified plywoods are notably the materials marketed by the RANCAN srl company under the tradename RANPREX@, for example references ML15 and ML20. These materials may notably be used in thicknesses of between 4 and 9 mm.

The secondary top sheet 16 will now be described more specifically with reference to figures 3 to 7 in which elements which are analogous are denoted by the same reference numeral despite variations in form.

Figure 3 is a view in cross section of the secondary insulating unit 3. It may be seen that the top sheet 16 has two longitudinal housings 21 spaced across the width of the insulating unit to accept welding supports 11. For that, the top sheet 16 is divided into three successive portions across the width of the insulating unit. This is because the small thickness of the secondary top sheet 16 does not allow the housings to be machined in the conventional way into the thickness thereof. Therefore, a housing 21 is formed here by the gap 22 between two successive portions of the top sheet 16 and by a connecting piece 23 fixed in line with the gap 22 on the internal surface of the top sheet 16.

As best visible in the enlarged view of figure 4, the connecting piece 23 here takes the form of a profiled rod of trapezoidal cross section the large base of which faces toward the top sheet 16 and the small base of which faces toward the bottom sheet 15. A central portion of the large base is hollowed out by a groove of rectangular cross section 26, whereas two end portions 24 of the large base are fixed to the internal surface of the top sheet 16 one on each side of the gap 22. The intermediate portion 25 of the connecting piece 23 thus straddles the gap 22 some distance therefrom. It may be seen that the groove 26 extends under a marginal portion 28 of the top sheet 16 on each side of the gap 22. In reality, all that would be required would be for the groove 26 to extend on just one side of the gap 22 so as to be able to accept the horizontal flange 30 of the welding support 11, as depicted in figure 6.

In the embodiment of figure 5, which is notably suitable for a thicker top sheet 16, the housing 21 comprises a spot face 27 formed in the internal surface of the top sheet 16 in the region of the marginal portion 28. The connecting piece 23 in this instance is a simple flat plate.

The embodiment of figure 6 is analogous to figure 4 except for the exterior shape of the connecting piece 23 which here is rectangular rather than trapezoidal.

The embodiment of figure 7 is analogous to figure 6 except for the cross section of the groove 26 which in this instance is in the shape of an inverted T, thereby increasing the surface area of the end portion 24 available for attaching to the top sheet 16.

In figures 3 to 7, the connecting piece may in each instance be a profiled component extending over the entire length of the secondary insulating unit 3. Other configurations may be appropriate depending on the position of the load-bearing columns 17. Figure 8 thus shows another embodiment of the secondary insulating unit 3 in which the elements analogous or identical to those of figure 2 are denoted by the same reference numeral. In this case, load-bearing columns 17 are very close to the gaps 22 intended for the passage of the welding supports and the connecting piece 23 is interrupted in the region of these load-bearing columns 17. In other words, a housing 21 is made up here of a plurality of connecting pieces 23 juxtaposed along the gap 22 and spaced apart from one another in the length direction of the insulating unit in order to allow the load-bearing columns 17 to pass between them. This situation is best visible in figure 9 which is a view in longitudinal section of the secondary insulating unit 3 of figure 8, in which three connecting pieces 23 are juxtaposed in the length direction of the insulating unit.

The two situations discussed hereinabove are summarized in figure 10 which is a view from above of a secondary insulating unit 3 the top sheet 16 of which comprises three rectangular portions separated by two longitudinal gaps 22. By way of example, this secondary insulating unit 3 comprises fourteen load-bearing columns 17 arranged in five longitudinal rows. In comparison with the central row, the row situated to the right in the figure is relatively well spaced away from the corresponding gap 22 and the connecting piece 23 is formed continuously over the entire length of the insulating unit. By contrast, the row situated to the left in the figure is closer to the corresponding gap 22 and four connecting pieces 23 are arranged along the left-hand gap 22, with mutual spacings in the region of the load-bearing columns 17.

The connecting pieces 23 are fixed to the top sheet 16 by any suitable means, for example clipping, nailing, screwing, insertion of a non-return pin, bonding or several of these solutions at once. The machining of the gaps 22 and of the housings 21 can be done before or after the connecting pieces 23 are assembled to the top sheet 16.

In figures 3 and 9, the load-bearing columns 17 bear directly on the bottom sheet 15 and on the top sheet 16. To improve the distribution of the load of the load bearing columns, there are a number of structures that may be provided in the region of the connection between the load-bearing columns 17 and the bottom sheet 15 and/or the top sheet 16. Examples of load-spreading structures are illustrated in figures 11 to 13 in the case of the top sheet 16. The load-spreading structure may in each instance be produced in the form of a separate component or produced as one with the top sheet 16, or produced as one with the load-bearing column 17.

In figure 11, a pyramid-shaped block 31 is placed at the top of each load bearing column 17 in the manner of an architectural capital. In an alternative form that has not been depicted, the block is a flattened parallelepiped rather than a pyramid. In figures 12 and 13, a longitudinal beam 32 is positioned at the top of each row of load-bearing columns 17. In figure 12, the beam 32 has a trapezoidal cross section. In figure 13, the beam 32 has a square cross section.

The manufacture of a large-sized bearing wall 1 such as the hull of a ship does not allow surfaces that are perfectly planar to be obtained. It is therefore generally necessary to provide polymerizable mastic supports under the bottom sheet 15 of a secondary insulating unit 3 in order to compensate for defects in flatness of the bearing wall 1 and to thus align the secondary insulating units 3 to a tight tolerance, so as to obtain a highly uniform supporting surface for the secondary membrane 5.

There are various configurations that these polymerizable mastic supports can adopt. Figure 14 illustrates an exemplary embodiment in which the polymerizable mastic supports comprise square pads 33 situated in vertical alignment with the load bearing columns 17 and L-shaped corner strips 34 situated in vertical alignment with the corner columns 18. It is thus possible to minimize the bending loads in the bottom sheet 15 while at the same time offering a total mastic-support cross section that is fairly small, thereby limiting the thermal conduction through the mastic supports. In a version which has not been depicted, the cross section of the mastic pads is circular.

All of the foregoing description relating to the secondary insulating units 3 can also apply to the primary insulating units 7. Nevertheless, the primary insulating unit 7 may have certain differences compared with the secondary insulating unit 3, notably in terms of the bottom sheet 115. Thus, there is no need for the bottom sheet 115 to comprise mastic supports. By contrast, the bottom sheet 115 does need to be adapted to suit the projecting parts of the secondary membrane 5, namely the turned up edges of the strakes 12 and the vertical flange of the welding supports 11.

For that, as figure 15 illustrates, it is possible to subdivide the bottom sheet 115 in a similar way to the top sheet 16 so as to allow the projecting parts of the secondary membrane 5 to pass through the gaps 36. In order for the bottom sheet 115 to maintain a certain bending strength, connecting pieces 35 may be used in a similar way to the connecting pieces 23. The connecting piece 35 for the bottom sheet is, for example, a profiled rod fixed straddling two successive portions of the bottom sheet 115 in line with the gap 36 and having a longitudinal groove 37 in the continuation of the gap 36.

As forthe top sheet 116 of the primary insulating unit 7, this may be produced in a similar way to the top sheet 16 of the secondary insulating unit 3. However, because the bending loads are generally higher at the primary top sheet 116, it is preferable for this to be made from a stronger and/or thicker material than the secondary top sheet 16. If appropriate, if the primary top sheet 116 is thick enough, the housing for the welding support for the primary sealing membrane 9 can be machined into its thickness in the known way.

Figure 16 depicts a primary insulating unit 7 with comer columns 40 according to another embodiment, the top sheet and the insulating filling being omitted from the depiction. The bottom sheet 115 is subdivided into three portions by two longitudinal gaps 36. It bears fourteen load-bearing columns 117 arranged in five longitudinal rows.

The corner column 40 has a T-shaped cross section made up of two perpendicular webs:

- a bisecting web 41 oriented at 45 between the longitudinal side 43 and the transverse side 44 of the bottom sheet 115 and extending from the corner of the bottom sheet 115 over approximately half of the distance to the gap 36 of the portion, - a bisecting-web counterweb 42 oriented perpendicular to the bisecting web 41 and extending tangentially to the internal end 45 of the bisecting web 41 from the longitudinal side 43 to the transverse side 44 of the bottom sheet 115.

The corner column 40 can also be used in the secondary insulating unit 3 as visible in figures 3 and 9.

In one embodiment, the bisecting web 41 is made from plywood 9 to 10 mm thick with a length of 100 mm and a height adapted to suit the thickness of the insulating barrier. The bisecting-web counterweb 42 is made from plywood 12 mm thick with a length of 200 mm. Such plywood thicknesses are standard and therefore readily available. Alternatively, a densified plywood may also be used.

Figure 18 illustrates another embodiment of the primary and secondary insulating barriers of the tank wall, with the sealing membranes omitted. Elements analogous or identical to those described previously are denoted by the same reference numeral increased by 200. The depiction used fictitiously positions the tank wall on a bearing structure that is transparent or invisible, so that the bottom sheets 215 of the secondary insulating units 203 and the secondary retaining member 204 are viewed slightly from beneath, something which is generally impossible in a real construction.

Figure 18 shows three secondary insulating units 203, two of them only very partially, each of which has a corner adjacent to the secondary retaining member 204. A fourth secondary insulating unit, not depicted, could be inserted in the same way so that the secondary retaining member 204 situated at the level of the adjacent comers of the four secondary insulating units collaborates simultaneously with each of these in order to hold them on the bearing structure. The same is true of the primary retaining member 208. The secondary retaining member 204 and the primary retaining member 208 may be produced in different ways, for example in accordance with the teachings of publications FR-A-2798902 and FR-A-2973097.

In the secondary insulating unit 203 of figure 18, it may be seen that the bisecting web 241 of the corner column 240 is trapezoidal in shape with a wider upper end and a narrower lower end, such that the external edge 46 of the bisecting web is oblique. A rectangular cutout is formed in each comer of the top sheet 216 in a portion of the thickness of the top sheet 216 so as to form a spot face 50 in the top sheet. The horizontal upper end of the bisecting web is covered by the top sheet. The horizontal upper end of the bisecting web 241 is situated below the spot face 50. This spot face 50 allows a metal plate 51 of the secondary retaining member 204 to bear against it.

In an alternative form that has not been depicted, the corner of the top sheet 216 could be completely cut away to partially uncover the horizontal upper end of the bisecting web 241, so that an uncovered horizontal surface at the upper end of the bisecting web 241 can have bearing directly against it a metal plate of the secondary retaining member 204.

In the primary insulating unit 207 of figure 18, it may be seen that the bisecting web 241 of the corner column 240 has a different shape, with a wider lower portion 47 and a narrower upper portion 48, so that the external edge of the bisecting web has a horizontal shoulder surface 49 between the portions 47 and 48. A rectangular cutout 53 is formed in each corner of the top sheet 316 so as to uncover the horizontal shoulder surface 49 of the bisecting web 241. This uncovered horizontal shoulder surface is able to have a metal plate 52 of the primary retaining member 208 bearing against it. The surface 49 could perform the same function if it were oblique.

The rectangular cutouts 53 formed in the corners of the top sheets 316 allow access to be gained to the retaining members to make these easier to fit. Following this fitment, these openings may be plugged, for example using the teaching of publication FR-A-2973097.

Just like the columns 317 and 217, the corner columns 240 of the primary insulating units 207 are also superposed with the corner columns 240 of the secondary insulating units 203.

Figure 19 is a view analogous to figure 2 showing yet another embodiment of the tank wall. Reference numerals that are identical to figure 18 are used to denote the elements that are analogous or identical. In the secondary insulating unit 203 of figure 19, the top sheet 416 is continuous and thick enough that L-section grooves 55 can be cut therein to accept the welding supports 11. For the remainder, the construction is similar to figure 18.

Another embodiment of the secondary insulating unit 203 and of the secondary retaining member 204 is now described with reference to figures 20 to 23. Reference numerals identical to figure 19 are used to denote elements that are analogous or identical.

The secondary insulating unit 203 is notable here in that, in the case of the four corner columns 340 extending in the thickness direction between a comer zone of the bottom sheet 215 and a corresponding corner zone of the top sheet 416, the bisecting web 341 comprises a shoulder surface 349 on its external edge. The shoulder surface 349 performs the same function as the shoulder surface 49 of the primary insulating unit 207, namely that it has bearing against it a metal plate 51 of the secondary retaining member 204 so as to anchor the secondary insulating unit 203 to the bearing wall, as can be seen best in figure 21.

More specifically, the bisecting web 341 here has a trapezoidal lower portion 346 in contact with the bottom sheet 215 and a rectangular upper portion 348 in contact with the top sheet 416. The shoulder surface 349 is located at the boundary between the trapezoidal lower portion 346 and the upper portion 348 and, because the trapezoidal lower portion 346 widens in the direction of the top sheet 416, the shoulder surface 349 corresponds to the longest width of the trapezoidal lower portion 346, which is therefore wider than the upper portion 348.

Incidentally, the smallest width of the trapezoidal lower portion 346, at the level of the bottom sheet 215, may be more or less wide than the upper portion 348. The small width of the bisecting web 341 at its base offers the advantage of freeing up space to make the base 83 of the retaining member 204 easier to position (fig. 21). For the same reason, the bottom sheet 215 has rectangular cutouts 94 at its four corners.

The top sheet 416 also has rectangular cutouts 353 formed in the four corners to allow for the passage of the secondary retaining members 204 and to allow the operator access for erecting the tank wall.

More specifically, the layout of the secondary insulating units 203 on the bearing wall is depicted in figure 21, which is a partial perspective view in the region of the adjacent comers of three secondary insulating units 203 arranged around a secondary retaining member 204 and in figure 22 which is a view of the same region, from above. The fourth secondary insulating unit has been omitted to improve legibility. It may be seen that the secondary insulating units 203 are almost in contact with one another along their longest sides, which in this instance are the sides parallel to the grooves 55, and spaced apart by a small gap 95 between their shortest sides, which in this instance are the sides perpendicular to the grooves 55. It may also be seen that the bottom sheet 215 extends slightly beyond the top sheet 416 at the shortest sides, whereas their edges are aligned at the longest sides.

As may also be seen in figure 23, the secondary retaining member 204 in this instance comprises a hollow base 83 which is fixed, for example welded, to the bearing wall, an anchor rod 84, a lower portion of which is held in the base 83, preferably with a small degree of angular freedom in order to make it easier to compensate for build tolerances, and an upper portion of which bears the metal plate 51, which in this instance is square in shape.

More specifically, the following are engaged in succession on the upper portion of the anchor rod 84: the metal plate 51, a stack of conical spring washers 85, a nut 86 and a stop plate 87 secured to the nut 86, for example by a weld. The tightening of the nut 86 allows the metal plate 51 to be pressed firmly against four shoulder surfaces 349 of four secondary insulating units 203 surrounding the secondary retaining member 204. The conical spring washers 85 give the secondary retaining member 204 elasticity, particularly so as to absorb small deformations of the bearing wall caused by the variation in load according to the degree of fullness of the tank and, in the case of a ship, by the conditions in which the ship is sailing.

After these elements have been fitted, the secondary retaining member 204 is supplemented by a metal top plate 88, placed on top of the metal plate 51, with the interposition of a block of insulating material 90, for example made of wood or of synthetic material and which is intended to align with the upper surface of the top sheets 416 (fig. 25) in order to offer a substantially planar support surface to accept the secondary sealing membrane (which has been omitted from the drawings).

The metal top plate 88 and the block of insulating material 90 are fixed to the metal plate 51 by means of two screws 89 (fig. 23). The two screws 89 and/or the block of insulating material 90 also prevent the stop plate 87 from rotating, thus preventing unwanted loosening of the nut 86.

Now that the embodiment of a secondary insulating barrier has been described, a description will be given of a primary insulating barrier that can be superposed with it, making reference to figures 24 to 27.

The primary insulating unit 207 of figure 24 is extremely similar to that of figure 18, except for the number and exact positioning of the bearing columns 317, which can be modified according to the particular requirements of the application, and the orientation of the gaps 236 and connecting pieces 235 for housing the projecting parts of the secondary membrane (which has not been depicted). In figure 24, seven bearing columns 317 are provided, each one surmounted by a square load-spreading plate 132 fixed under the top sheet 316 by means of five screws 97.

Figure 26 depicts one embodiment of the primary retaining member 208, comprising a flanged stud 91, the base of which is screwed into a tapped bore 96 in the top metal plate 88, and the threaded upper portion of which bears, in succession, the metal plate 52 bearing against the shoulder surfaces 49, a washer 93 and a nut 92.

Figures 25 and 27 are views analogous to figures 21 and 22, after the fitting of two primary insulating units 207. The tightening of the nut 92 allows the metal plate 52 to be pressed firmly against four shoulder surfaces 49 of four primary insulating units 207 surrounding the primary retaining member 208.

Figure 27 particularly shows that the cutout 53 in the primary insulating unit 207 can be wider than the cutout 353 in the secondary insulating unit 203 and can be bordered by a lip 82 formed in the thickness of the top sheet 316 to accept a closure plate, as described in publication FR-A-2973097.

The technique described hereinabove for creating a sealed and insulating wall can be used in various types of reservoir, for example to constitute the wall of an LNG reservoir in an on-shore facility or in a floating structure such as a methane tanker or the like.

The structures described hereinabove for creating the primary insulating barrier and the secondary insulating barrier can be used independently of one another. In other words, the primary insulating barrier of the embodiments described hereinabove can also be combined with a secondary insulating barrier produced in a different way. Reciprocally, the secondary insulating barrier of the embodiments described hereinabove can also be combined with a primary insulating barrier produced in a different way. Finally, the primary insulating barrier of the embodiments described hereinabove could also be omitted, in order to create a tank wall having a single insulating barrier, notably for storing products that are not as cold as LNG, for example LPG or ethylene.

With reference to figure 17, a cutaway view of a methane tanker 70 shows a sealed and insulated tank 71 of prismatic overall 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 way known per se, loading/unloading pipelines 73 arranged on the top deck of the ship can be coupled, by means of suitable connectors, to a maritime or harbor terminal to transfer a cargo of LNG from or to the tank 71.

Figure 17 depicts an example of a maritime terminal comprising a loading and unloading station 75, an underwater pipe 76 and an on-shore facility 77. The loading and unloading station 75 is a fixed off-shore facility comprising a mobile arm 74 and a turret 78 supporting the mobile arm 74. The mobile arm 74 carries a bundle of insulated flexible hoses 79 which can be connected to the loading/unloading pipelines 73. The orientable mobile arm 74 adapts to suit all sizes of methane tanker. A connecting pipe, not depicted, extends up inside the turret 78. The loading and unloading station 75 allows the methane tanker 70 to be loaded and unloaded from or to the on-shore facility 77. The latter comprises liquefied-gas storage tanks 80 and connecting pipes 81 connected by the underwater pipe 76 to the loading or unloading station 75. The underwater pipe 76 allows the liquefied gas to be transferred between the loading or unloading station 75 and the on-shore facility 77 over a long distance, for example 5 km, which allows the methane tanker 70 to be kept standing a long way off the shore during the loading and unloading operations.

In order to generate the pressure necessary fortransferring the liquefied gas, use is made of pumps on board the ship 70 and/or of pumps with which the on-shore facility 77 is equipped and/or of pumps with which the loading and unloading station 75 is equipped.

Although the invention has been described in conjunction with a number of particular embodiments, it is quite clear that it is not in any way restricted thereto and that it comprises all the technical equivalents of the means described and combinations thereof where these fall within the scope of the invention.

The use of the verbs "comprise", "include" or "have" and of the conjugated forms thereof does not exclude the presence of elements or steps other than those listed in a claim. The use of the indefinite article "a"or "an" for an element or step does not, unless mentioned otherwise, exclude there being a plurality of such elements or steps.

The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

In the claims, any reference sign between parentheses should not be interpreted as imposing a limit on the claim.

Claims

1. A parallelepipedal insulating unit suitable for creating an insulating wall in a storage tank for a cold liquid, the insulating unit comprising: a bottom sheet of rectangular shape, a top sheet of rectangular shape parallel to the bottom sheet and spaced away from the bottom sheet in a thickness direction of the insulating unit, a plurality of load-bearing columns arranged between the bottom sheet and the top sheet, the load-bearing columns extending longitudinally in the thickness direction and having a cross section that is small in size in comparison with a length and a width of the insulating unit, and an insulating filling arranged between the bottom sheet and the top sheet and between the load-bearing columns, the insulating unit further comprising four corner columns extending in the thickness direction between the bottom sheet and the top sheet, a corner column in each instance being arranged between a corner zone of the bottom sheet and a corresponding corner zone of the top sheet and comprising a first web and a second web perpendicular to the first web, characterized in that each first web comprises, in succession in the thickness direction of the insulating unit, a wider lower portion and a narrower upper portion, so that an external edge of the first web has a shoulder surface situated between the wider lower portion and the narrower upper portion and perpendicular or oblique to the thickness direction of the insulating unit, in which the first web is a bisecting web extending from the corner along a bisector of the corner of the bottom sheet and of the top sheet as far as an internal end situated inside the insulating unit, the external edge of the bisecting web which has the shoulder surface facing toward the corner of the bottom sheet, the second web being a bisecting-web counterweb perpendicular to the bisecting web, the bisecting-web counterweb being fixed to the internal end of the bisecting web and extending obliquely between a transverse edge and a longitudinal edge of the top sheet and of the bottom sheet, and in which the corner zone of the top sheet comprises a cutout situated in vertical alignment with the shoulder surface of the bisecting web so as to create an access opening allowing access to the shoulder surface from the top sheet in the thickness direction.

2. A sealed and insulating tank comprising a tank wall held on a bearing structure, the tank wall including, in the thickness direction from the outside toward the inside of the tank, a secondary insulating barrier held on the bearing structure, a secondary sealing membrane held on the secondary insulating barrier, a primary insulating barrier held on the secondary sealing membrane and a primary sealing membrane held on the primary insulating barrier, characterized in that the secondary insulating barrier is essentially made up of a plurality of secondary insulating units juxtaposed in a repeating pattern, wherein each secondary insulating unit comprises a parallelepipedal insulating unit as claimed in claim 1, and in that the primary insulating barrier is essentially made up of a plurality of primary insulating units juxtaposed in the repeating pattern, the primary insulating units being aligned with the secondary insulating units in the thickness direction of the tank wall, the tank wall further comprising retaining members attached to the bearing structure at the corners of the secondary insulating units, a retaining member in each instance collaborating with four adjacent secondary insulating units to hold the adjacent secondary insulating units on the bearing structure and with four primary insulating units which are superposed with said adjacent secondary insulating units so as to hold the primary insulating units on the secondary sealing membrane.

3. The tank as claimed in claim 2, in which the retaining member in each instance comprises a secondary bearing element kept bearing against the shoulder surface of a bisecting web of each of the four secondary insulating units.

4. The tank as claimed in claim 2 or 3, in which each primary insulating unit comprises a parallelepipedal insulating unit as claimed in claim 1, and in which the retaining member in each instance comprises a primary bearing element kept bearing against the shoulder surface of a bisecting web of each of the four primary insulating units.

5. A sealed and insulating tank comprising a tank wall held on a bearing structure, the tank wall including, in the thickness direction from the outside toward the inside of the tank, a secondary insulating barrier held on the bearing structure, a secondary sealing membrane held on the secondary insulating barrier, a primary insulating barrier held on the secondary sealing membrane and a primary sealing membrane held on the primary insulating barrier, characterized in that the secondary insulating barrier is essentially made up of a plurality of secondary insulating units juxtaposed in a repeating pattern, and in that the primary insulating barrier is essentially made up of a plurality of primary insulating units juxtaposed in the repeating pattern, wherein each primary insulating unit comprises a parallelepipedal insulating unit as claimed in claim 1, the primary insulating units being aligned with the secondary insulating units in the thickness direction of the tank wall, the tank wall further comprising retaining members attached to the bearing structure at the region of the comers of the secondary insulating units, a retaining member in each instance collaborating with four adjacent secondary insulating units to hold the adjacent secondary insulating units on the bearing structure and with four primary insulating units which are superposed with said adjacent secondary insulating units so as to hold the primary insulating units on the secondary sealing membrane.

6. The tank as claimed in claim 5, in which the retaining member in each instance comprises a primary bearing element kept bearing against the shoulder surface of a bisecting web of each of the four primary insulating units.

7. The tank as claimed in either of claims 5 and 6, in which each of the secondary insulating units is a parallelepipedal insulating unit comprising: a bottom sheet of rectangular shape, a top sheet of rectangular shape parallel to the bottom sheet and spaced away from the bottom sheet in a thickness direction of the insulating unit, a plurality of load-bearing columns arranged between the bottom sheet and the top sheet, the load-bearing columns extending longitudinally in the thickness direction and having a cross section that is small in size in comparison with a length and a width of the insulating unit, and an insulating filling arranged between the bottom sheet and the top sheet and between the load-bearing columns, in which the insulating unit further comprises four corner columns extending in the thickness direction between the bottom sheet and the top sheet, a corner column in each instance being arranged between a corner zone of the bottom sheet and a corresponding corner zone of the top sheet and comprising a bisecting web extending from the corner along a bisector of the comer of the bottom sheet and of the top sheet as far as an internal end situated inside the insulating unit and a bisecting-web counterweb perpendicular to the bisecting web, the bisecting-web counterweb being fixed to the internal end of the bisecting web and extending obliquely between a transverse edge and a longitudinal edge of the top sheet and of the bottom sheet, in which each bisecting web of a secondary insulating unit comprises an upper surface which is perpendicular to the thickness direction of the secondary insulating unit, and in which the corner zone of the top sheet of the secondary insulating unit comprises a cutout situated in vertical alignment with the upper surface of the bisecting web so as to create a spot face surface situated in line with the upper surface of the bisecting web, whereas the upper surface of the bisecting web is fixed against the top sheet of the secondary insulating unit, the retaining member in each instance comprising a secondary bearing element kept bearing against the external portion of the upper surface of a bisecting web of each of the four secondary insulating units.

8. The tank as claimed in claim 7, in which each bisecting web of a secondary insulating unit has a trapezoidal shape with an upper end that is wider in the direction of the bisector of the corner of the top sheet and a lower end that is narrower in the direction of the bisector of the corner of the bottom sheet of the secondary insulating unit.

9. The tank as claimed in one of claims 2 to 7, in which each bisecting web of a secondary insulating unit has a trapezoidal shape with a portion that is wider in the direction of the top sheet and a portion that is narrower in the direction of the bottom sheet of the secondary insulating unit.

10. A ship for transporting a fluid, the ship comprising a double hull and a tank as claimed in one of claims 2 to 9 arranged in the double hull.

11. A method for loading or unloading a ship as claimed in claim 10, in which method a fluid is conveyed through insulated pipelines from or to a floating or on-shore storage facility to or from the tank of the ship.

12. A transfer system for a fluid, the system comprising a ship as claimed in claim 10, insulated pipelines arranged in such a way as to connect the tank installed in the hull of the ship to a floating or on-shore storage facility and a pump for causing a flow of fluid through the insulated pipelines from or to the floating or on shore storage facility to or from the tank of the ship.