AU2014286010A1

AU2014286010A1 - Lagging element suited to the creation of an insulating barrier in a sealed and insulating tank

Info

Publication number: AU2014286010A1
Application number: AU2014286010A
Authority: AU
Inventors: Thomas CREMIERE; Benoit Morel; Nicolas THENARD
Original assignee: Gaztransport et Technigaz SA
Current assignee: Gaztransport et Technigaz SA
Priority date: 2013-07-02
Filing date: 2014-06-26
Publication date: 2016-01-28
Anticipated expiration: 2034-06-26
Also published as: WO2015001230A3; JP2016529168A; CN105378368B; KR20160026990A; EP3017234A2; JP6415550B2; EP3017234B1; FR3008163A1; AU2014286010B2; CN105378368A; KR102206805B1; FR3008163B1; WO2015001230A2

Abstract

A lagging element suited to the creation of an insulating barrier in a sealed and insulating tank the lagging element comprising a flat cover panel, a thermal insulation lining (10) arranged parallel to the cover panel and load bearing elements which extend through the thickness of said thermal insulation lining from the cover panel to react compressive loadings, the load bearing elements comprising a plurality of pillars (4) the cross section of which is small in comparison with the dimensions of the cover panel and which are fit into recesses (11) in the thermal insulation lining and are fixed to the cover panel, in which, at normal temperature, a cross-sectional dimension of each pillar is smaller than a corresponding dimension of the recess in which the pillar is fitted. Application to the manufacture of a tank wall with a membrane for storing or transporting LNG.

Description

1 LAGGING ELEMENT SUITED TO THE CREATION OF AN INSULATING BARRIER IN A SEALED AND INSULATING TANK Technical field The invention relates to the field of the construction of lagging elements 5 making it possible to produce a modular insulating wall, in particular a tank wall for storing or transporting a cold liquid, notably in a membrane tank for liquefied natural gas. Technological background 10 In a membrane tank for liquefied natural gas, lagging elements are employed to transmit the hydrodynamic loading of the cargo from the sealed membrane to the double hull, which implies a function of resistance to compression, and to insulate the cargo from the hull of the ship, in order to limit the flow of heat leading to evaporation of the cargo, but also to protect the hull from the cryogenic 15 temperatures. There is known from FR-A-2877638 a sealed and thermally insulated tank including a tank wall fixed to the hull of a floating structure. The tank wall includes successively, in the direction of the thickness from the interior toward the exterior of said tank, a primary sealed barrier, a primary insulating barrier, a secondary sealed 20 barrier and a secondary insulating barrier. The insulating barriers essentially consist of juxtaposed lagging elements. Each lagging element includes a bottom panel, a cover panel and a thermal insulation lining disposed in the form of a layer parallel to the tank wall. Loadbearing elements are erected through the thickness of said thermal insulation lining to absorb the compression forces. The loadbearing 25 elements of a lagging element include pillars the cross section of which is small in comparison with the dimensions of the lagging element in a plane parallel to the tank wall. Summary of the invention 30 One idea on which the invention is based is to provide a lagging element that is relatively easy to manufacture, having good thermal performance and in 2 which the thermal insulation lining can be made from a material able to contract more than its environment on cooling, for example a low-density, non-structural polyurethane foam. Some aspects of the invention start from the idea of producing the thermal 5 insulation lining using a single block of such a material. Some aspects of the invention start from the idea of limiting the establishing of stresses of thermal origin in the insulation lining on cooling the wall. Some aspects of the invention start from the idea of providing a thermal insulation lining retained with the possibility of sliding relative to loadbearing elements and one or more flat panels to allow thermal 10 contractions of different amplitude as a function of the materials from which those elements are constructed. In accordance with one embodiment, the invention provides a lagging element suited to the creation of an insulating barrier in a sealed and insulating tank, the lagging element comprising a flat cover panel, a thermal insulation lining 15 arranged parallel to the cover panel and loadbearing elements which extend from the cover panel through the thickness of said thermal insulation lining to absorb compression forces, the loadbearing elements comprising a plurality of rigid pillars the cross section of which is small in comparison with the dimensions of the cover panel engaged in voids of the thermal insulation lining and fixed to the cover panel, 20 in which, at a normal temperature, for at least one of said pillars, a cross-sectional dimension of the pillar is smaller than a corresponding dimension of the void in which the pillar is engaged so as to provide a gap between the pillar and the wall of the void. In accordance with embodiments, such a lagging element may include one 25 or more of the following features. In accordance with one embodiment, the lagging element further includes a flexible material filling element disposed in the gap between the pillar and the wall of the void. The filling element is made from a material that is much less rigid than the thermal insulation lining so as to absorb itself most of the deformations induced by 30 the differential thermal contraction between the rigid structure and the thermal insulation lining. In accordance with embodiments, the filling element is made from a material chosen from very low density polymer foams, glass wool products, loose 3 glass wool, melamine foams, aerogels, polystyrene, blocks of polyester wadding or loose polyester wadding. In accordance with one embodiment, the pillars include a first pillar engaged in a first void situated in a central area of the thermal insulation lining and a 5 second pillar engaged in a second void of the thermal insulation lining situated at a distance from the central area of the thermal insulation lining, and in which a cross sectional dimension of the second void is greater than a corresponding dimension of the first void to allow differential thermal contraction between the thermal insulation lining and the cover panel, and in which a flexible material filling element is disposed 10 in the second void and no flexible material filling element is disposed in the first void. In accordance with one embodiment, the pillars include a first pillar engaged in a first void of the thermal insulation lining and a second pillar identical to the first pillar engaged in a second void of the thermal insulation lining, the second void being situated at a greater distance from the center of the thermal insulation 15 lining than the first void, and in which a cross-sectional dimension of the second void is greater than a corresponding dimension of the first void to allow differential thermal contraction between the thermal insulation lining and the cover panel. These dimensional features of the voids may be applied at the level of some pillars or at the level of all the pillars. In accordance with one embodiment, all 20 the voids in which identical pillars are engaged have a cross-sectional dimension increasing, for example proportionally, with the distance between the void and the center of the thermal insulation lining. In accordance with one embodiment, at a normal temperature one pillar or each pillar is disposed in the void so as to be nearer a wall of the void facing toward 25 the center of the thermal insulation lining than a wall of the void facing away from the center of the thermal insulation lining. In accordance with one embodiment, the lagging element further includes a flat bottom panel parallel to the flat cover panel and the thermal insulation lining is disposed between the bottom panel and the cover panel, the loadbearing elements 30 extending through the thickness of said thermal insulation lining as far as the bottom panel, the cross section of the pillars being moreover small in comparison with the dimensions of the bottom panel and the pillars moreover being fixed to the bottom panel.

4 The pillars may be produced with various shapes and orientations. In accordance with one embodiment, the pillars are perpendicular to the cover panel and, where appropriate, to the bottom panel. Oblique pillars may also be employed. In one embodiment, a pillar or each pillar may have a uniform section, 5 which facilitates the production and the installation of the pillar. In accordance with one embodiment, a pillar or each pillar may have a cross-sectional dimension varying along the thickness of said thermal insulation lining, the cross-sectional dimension decreasing in the direction of the cover panel. Because the cover panel corresponds in use to the side facing toward the interior of 10 the tank at which the temperature is the lowest, this disposition leaves more room for the contraction of the thermal insulation lining where its amplitude tends to be the greatest. The voids may be produced with various shapes and orientations. In one embodiment, a void or each void has a uniform section, which facilitates the 15 production of the void. In accordance with one embodiment, a void or each void has a cross sectional dimension varying along the thickness of said thermal insulation lining, the cross-sectional dimension increasing in the direction of the cover panel. This disposition also makes it possible to leave more room for the contraction of the 20 thermal insulation lining where its amplitude tends to be the greatest. In accordance with one embodiment, the thermal insulation lining includes a polymer foam block, notably a polyurethane foam block. In accordance with one embodiment, the thermal insulation lining includes a relaxation slot extending in the thickness of the polymer foam block. 25 The cover panel and the bottom panel may be made from various materials, for example plywood, composite material or other material able to transmit the forces whilst retaining acceptable thermal properties. In accordance with one embodiment, the thermal insulation lining is retained by the loadbearing elements with a possibility of sliding relative to the 30 loadbearing elements and to the cover panel. In accordance with one embodiment, the invention also provides a sealed and insulating tank disposed in a supporting structure, the tank including a tank wall 5 fixed to the supporting structure, said tank wall including successively, in the direction of the thickness from the interior toward the exterior of said tank, a primary sealed barrier, a primary insulating barrier, a secondary sealed barrier and a secondary insulating barrier, the primary insulating barrier and/or the secondary 5 insulating barrier including a plurality of juxtaposed lagging elements as referred to above. Such a tank may form part of a storage installation on land, for example for storing LNG, or be installed in a coastal or deep water floating structure, notably a methane tanker, a floating storage and regassification unit (FSRU), a floating 10 production storage and offloading (FPSO) unit, etc. In accordance with one embodiment, a ship for the transportation of a cold liquid product includes a double hull and a tank as referred to above disposed in the double hull. In accordance with one embodiment, the invention also provides a method 15 of loading or offloading such a ship, in which a cold liquid product is routed through insulated pipes from or to a floating storage installation or a storage installation on land to or from the tank of the ship. In accordance with one embodiment, the invention also provides a transfer system for a cold liquid product, the system including the aforementioned ship, 20 insulated pipes arranged in such a manner as to connect the tank installed in the hull of the ship to a floating storage installation or a storage installation on land and a pump for driving a flow of cold liquid product through the insulated pipes from or to the floating storage installation or the storage installation on land to or from the tank of the ship. 25 Brief description of the figures The invention will be better understood, and other objects, details, features and advantages thereof will become more clearly apparent in the course of the following description with reference to the appended drawings of particular 30 embodiments of the invention, given by way of nonlimiting illustration only. * Figure 1 is a perspective view of a rigid structure suited to the production of a lagging box of rectangular parallelepiped shape.

6 * Figure 2 is a view in section in a plane parallel to the cover panel of a lagging box at a normal temperature. e Figure 3 is a view analogous to figure 2 showing the lagging box at a low temperature. 5 e Figure 4 is a view to a larger scale of the area IV in figure 2. * Figures 5 to 10 are perspective views of a void that can be used in the thermal insulation lining from figure 2, showing different geometries of the void. e Figure 11 is a view analogous to figure 2, showing a thermal 10 insulation lining in accordance with another embodiment. * Figure 12 is a view analogous to figure 2, showing part of a thermal insulation lining in accordance with another embodiment at the normal temperature and at the low temperature. * Figure 13 is a diagrammatic cutaway representation of a tank of a 15 methane tanker including an insulating barrier and of a terminal for loading/offloading that tank. e Figure 14 is a perspective view of a lagging box of rectangular parallelepiped shape. 20 Detailed description of embodiments Referring to figure 1, there is represented a parallelepipedal lagging box 1, the insulating lining of which has been omitted to allow only the rigid structure to be seen. Such lagging boxes can be juxtaposed in accordance with a regular pattern to produce the primary insulating layer and/or the secondary insulating layer, with the 25 result that the lagging boxes therefore form a substantially flat surface able to support a sealed membrane. The rigid structure of the box 1 includes a flat rectangular cover panel 2, a flat rectangular bottom panel 3 parallel to the cover panel and pillars 4 disposed between and perpendicular to the cover panel 2 and the bottom panel 3. The pillars 30 are disposed in a plurality of rows, in which each row of pillars 4 rests on the bottom panel 3 via a lath 5 disposed between the bottom panel 3 and the lower end of the 7 pillars of the row. The assembly of the pillars 4, laths 5 and panels 2 and 3 is effected with the aid of fixing elements, for example staples, nails or screws. The pillars 4 notably enable the transmission of stresses exerted on the cover panel 2 and therefore have a function of resistance to compression. A lagging 5 lining, not represented in figure 1, is disposed between the bottom panel 3 and the cover panel 2 and fills the space between the pillars 4. The pillars may be arranged in various manners. In figure 1, the successive rows of pillars are offset relative to each other. To be more precise, the pillars 4 of one row are spaced with a regular spacing and two successive rows are offset in the 10 direction of their length by half the spacing. Such a disposition enables a good compromise to be achieved between the number of pillars 4 in the box 1 and the proper distribution of the load. In figure 2, the rows of pillars are instead aligned. Other dispositions of the pillars 4 are also possible. The figure 1 cover panel 2 is a reinforced cover panel that includes an 15 upper panel 6 and a lower panel 7 that are spaced by a series of parallel solid beams 8. In particular, the beams 8 extend parallel to the longitudinal sides of the box 1. Each beam 8 is positioned along and above a row of pillars 4. The beams 8 have a rectangular section. The beams 8 and the panels 6 and 7 are rigidly joined together, for example glued or stapled together. Such a reinforced cover panel 20 structure makes it possible to obtain good stiffness and an efficient distribution of the load in the case of localized stress. Each beam 8 is spaced from the other beams 8 in such a manner as to delimit spaces 9 between the beams 8 and between the panels 6 and 7. These spaces 9 form channels parallel to the longitudinal sides of the box 1 that can be 25 used, for example, to circulate a fluid between the two sides of the lagging box. The juxtaposition of the lagging boxes therefore makes it possible to form a circuit in a wall of the tank into which it is possible to inject a neutral gas to neutralize the wall of the tank and therefore to prevent all risk of explosion in the event of a leak in the presence of oxygen. 30 The rigid structure that has just been described can be made from wood or from composite materials, for example from polymer resin with or without reinforcing fibers. In accordance with other embodiments, the cover panel 2 may be made 8 differently, for example in the form of a solid panel. In accordance with other embodiments, the bottom panel 3 and/or the laths 5 may be omitted. Figure 2 represents diagrammatically a view of a lagging box in section on a plane intersecting the pillars 4 at mid-height. A thermal insulation lining of the box 5 consists of a block 10 of insulating material, for example polyurethane foam, having a rectangular parallelepiped shape the dimensions of which substantially correspondent to the space between the bottom panel and the cover panel of a box. The box includes a rigid structure similar to that from figure 1, with a modified position of the pillars 4. 10 Figure 2 shows that the insulating material block 10 is pierced by a plurality of square section cylindrical voids 11 the axis of which is parallel to the pillars 4 and each of which receives one of the pillars 4. The cross-sectional dimensions of the voids 11 are in each case greater than the corresponding dimensions of the pillar 4, which leaves a clearance 12 to facilitate the insertion of the pillar and most 15 importantly to allow differential thermal contraction between the insulating material block 10 and the cover panel 2 to which the pillars 4 are fixed. This point will be explained by comparing figures 2 and 3. Figure 2 represents the box at a normal temperature, representative of the manufacturing conditions, namely an ambient temperature between 100C and 300C 20 inclusive, for example. Figure 3 represents the box at a cryogenic usage temperature, for example between 00C and approximately -1000C if the box is employed in the secondary barrier of an LNG tank and between approximately -100 C and -160 C if the box is employed in the primary barrier of an LNG tank. In figure 3, the contour 100 represents diagrammatically the dimensions of 25 the insulating material block at the normal temperature and the contour 10 represents the insulating material block at the cryogenic use temperature. It is seen that in this cold state the voids 11 have contracted more than the pillars 4 so that the clearances 12 are greatly reduced (they are no longer visible in figure 3). To this end, the dimensions and the positions of the voids 11 in figure 2 have been defined 30 in the following manner: - to take into account the local thermal contraction of the block 10, each void 11 has cross-sectional dimensions greater than the corresponding dimensions of the pillar 4; 9 - to take into account the overall thermal contraction of the block 10, the cross-sectional dimensions of a void 11 increase in proportion to the distance of the void from the center of the insulating material block 10, represented here by the point of intersection of the diagonals 13; 5 indeed, the overall thermal contraction of the insulation occurs in the direction of the center 13 of the insulating block 10. Moreover, for the clearances 12 to be substantially eliminated in the figure 3 contracted state, it is seen that the position of the center of the void 11 is initially offset relative to the center of the pillar, so that the pillar 4 is in each case nearer the 10 walls of the void 11 that face toward the center 13 of the insulating material block 10. In other words, by defining holes piercing the insulating block with geometries which at ambient temperature are wider than the pillar itself, the gap between the face of the pillar and the facing face of the insulating material is 15 compensated at low temperature by the contraction of the insulating block. Under thermal loading, the internal faces of the holes in the insulating block will come into contact with the pillar or come very close to it without this generating stresses in this block, or at worst stresses of an acceptable level enabling the insulating material to remain intact over a long service life. 20 To implement this principle, more precise dimensioning rules are proposed hereinafter, by way of example, with reference to figures 2 and 4. The longitudinal axis of the box is denoted x and the rows of pillars perpendicular to this axis are numbered by the index m, with the result that m varies from 1 to 5 in the figure 2 box. In the same way, the lateral axis of the box is 25 denoted y and the rows of pillars perpendicular to that axis are numbered by the index n, with the result that n varies from 1 to 4 in the figure 2 box. A pillar situated at the intersection of the rows m and n is designated Pmn, this pillar having a rectangular section with dimensions Lmn and in along the axes x and y, respectively. The center of the pillar Pn is designated cn and the coordinates 30 of cn considered relative to the center 13 of the box are designated Xn and Yn. These quantities further depend on the coordinate h in the direction of the height in the situation where the section of the pillar varies along this direction.

10 The coefficients of thermal expansion of the insulating material 10 in the directions x and y are respectively designated ax and ay. The coefficients of thermal expansion of the material used for the rigid structure of the box and the pillars 4 in the direction x and y are respectively 5 designated apx and apy. The temperature variation between the manufacturing temperature and the temperature of use for a point in the insulation situated at a height h of the lagging box is designated ATh. This temperature variation is substantially invariant in the plane x, y. 10 The temperature variation for a point in the pillar in the lower part of the lagging box at which the temperature variation is the smallest is designated AThot. The temperature variation for a point in the pillar in the upper part of the lagging box at which the temperature variation is the greatest is designated ATCOId. The overall manufacturing tolerance for the pillar 4, including the tolerance 15 for the positioning of the pillar and the dimensional tolerance on the section of the pillar, is designated Vp. The overall manufacturing tolerance for the insulating material block 10, including the tolerance for the positioning of the void 11 and the dimensional tolerance for the section of the void 11, is designated Vi. 20 The dimensions of the void 11 for a pillar Pmn in the directions x and y are respectively designated Dxmn and Dymn. The center of the section of the void 11 for a pillar Pmn is designated Cmn and the coordinates of Cmn considered relative to the center 13 of the box in the directions x and y are respectively designated XCmn, YCmn. These quantities further depend on the coordinate h in the direction of the 25 height in the situation where the section of the void varies along this direction. e Through-holes of rectangular section with ax>> apx and ay>> apy: For variable section voids 11, the following rule can be used for the position and the dimensions of the through-hole: 30 Dxmn,h=(Xmn+1Lmn/2)*ax*ATh+Vp+Vi+Lmn Dymn,h=(Ymn+fmn/ 2 ) *ay*ATh+Vp+Vi+mn 11 XCmnh=Xmn+Dxmn,hi 2 YCmnh=Ymn+Dymn,hi 2 For voids 11 of constant section, the following rule can be used for the 5 position and the dimensions of the through-hole: Dxmn=maXh (DXmn,h) Dymn=maXh (Dymn,h) XCmn=Xmn+Dxmn/2 YCmn=Ymn+Dymn/2 10 e Situation in which the coefficients of thermal expansion of the insulation and of the material used for the rigid structure of the box are fairly similar: For variable section pillars 4 and voids 11, the following rule can be used for the position and the dimensions of the through-hole: 15 Dxmn,h=(Xmn,h+mn,h/2)*ax*ATh+Vp+Vi+Lmn,h [(Xmnh+Lmnh/2)*apx*AThot)+(Xmn,h+Lmnh/2)*apx*(ATcoId-AThot)*h/H] Dymn,h=(Ymn,h+fmn,h/ 2 )Y*ATh+Vp+Vi+mn,h [(Ymnh+fmnh/2)*py*AThot)+(Ymnh+lmnh/2)*py*(ATcold-AThot)*h/H] XCmnh=Xmnh+Dxmn,h/ 2 20 YCmn,h=Ymnh+Dymn,h/2 For voids 11 of constant section, the following rule can be used for the position and the dimensions of the through-hole: Dxmn=maxh((Xmn,h+1Lmnh/2)*ax*ATh+Vp+Vi+1Lmn,h-[(Xmnh+1Lmnh/2)*Qpx*AThot]) 25 Dymn=maxh((Ymn,h+fmn,h/2)Y*ATh)+Vp+Vi+mn,h-[(Ymn,h+fmn,h/2)pY*AThot XCmn=Xmn+Dxmn/2 YCmn=Ymn+Dymn/2 12 In one embodiment, the insulating material block 10 is made of a polyurethane foam without fibers and with a density of 50 kg/m3. The coefficient of thermal expansion of this foam is typically between 40.10-6 K- 1 and 60.10-6 K-1 inclusive. For a block with dimensions of 1.2 m x 1 m, a maximum contraction is 5 obtained of the order of 3.3 mm to 5 mm. For a rigid plywood structure, the contraction under the same conditions is of the order of 0.7 mm maximum. The cross-sectional shape of the voids 11 may be designed in different ways according to the dimensions of the boxes, notably their length and width, and the dimension, shape and number of the pillars 4. In figures 5 to 10, there is 10 represented a portion of the insulating material block 10 with in each case a void 11 and a pillar 4 to show multiple possible shapes of the voids. In figure 5, the void 11 has a uniform section over all its height, of square shape. In figure 6, the void 11 has a section increasing continuously over all its height, of square shape, resulting in a square base pyramid general shape. In figure 15 7, the void 11 includes a plurality of successive stages in the direction of the height, of increasing section and of square shape. In figure 8, the void 11 has a uniform section over all its height, of circular shape. In figure 9, the void 11 has a section varying continuously over all its height, of circular shape, resulting in a frustoconical general shape. In figure 10, the void 11 includes a plurality of successive stages in 20 the direction of the height, of increasing section and of circular shape. In cases where the section of the void 11 varies along the height, the widest section is placed on the coldest side, namely the side of the cover panel in an LNG tank wall application. In a variant embodiment the principle described above is reversed by 25 having voids 11 of constant section in the insulating material and varying the section of the pillar 4. This solution has the advantage of facilitating the cutting of the insulating material by avoiding the complex geometries that are difficult to produce. This solution may be particularly suitable in the case of composite material pillars. In cases where the section of the pillar 4 varies along the height, the 30 narrowest section is placed on the coldest side, namely on the side of the cover panel in an LNG tank wall application. In the figure 11 embodiment, the insulating material block 20 includes a plurality of vertical relaxation slots 21, which makes it possible to segment the block 13 20 into a plurality of portions able to contract independently of one another and therefore to limit the size of the voids 11. In the figure 12 embodiment, a flexible material lining 30 is inserted to fill the clearance 12 between the pillar 11 and the insulating material block 10 in order 5 to eliminate or to limit the convection movements of gas in this gap. In addition to being anti-convection and insulative, the flexible material lining 30 must be sufficiently flexible to absorb the reduction in the distance between the pillar 4 and the wall of the void 11 or to compensate the increase in this distance during temperature variations. This point is illustrated in figure 12, which represents 10 superimposed the pillar 4, the void 11 and the insulating block 10 in dashed outline in the state of use at low temperature and in solid outline at a normal temperature. The materials that can be used to produce the lining 30 notably include very low density polymer foams, glass wool products, loose glass wool, melamine foams, aerogels, polystyrene, polyester, blocks of polyester wadding or loose 15 polyester wadding. For the manufacture of such a lagging box, the insulating block 10 may be cut or drilled with appropriate tools and machines, for example by means of a punch, a rotary machine or waterjet cutting. The punching process consists in punching through the foam with sharp steel tube or blade tools. The foam may be retained on 20 a cutting table that possibly incorporates female imprints complementary to the tools to facilitate cutting. A plurality of passes may be necessary, possibly with different tools, to arrive at the required geometry of the voids 11. Moreover, waterjet cutting makes it possible to produce any type of geometry by freely programming the trajectory of the cutting nozzles. 25 The steps of assembling the lagging box including the rigid structure and the insulating material block 10 may be carried out in various orders. Two solutions are: Assembly procedure A: - Introducing the pillars into the pierced insulating material block 30 - Fixing the bottom panel to the pillars by techniques such as stapling, screwing, gluing, heat-welding Assembly procedure B: 14 - Fixing the bottom panel to the pillars by techniques such as stapling, screwing, gluing, heat-welding - Threading the pierced insulating material block over the pillars For the figure 12 embodiment in which the spaces between the insulation 5 and the pillars are filled in, two solutions are: - Prefabricating pillars wrapped in, coated with, threaded into or molded with the flexible material lining 30, or - Subsequently mounting the flexible material lining 30 by threading, projection or injection of material into the clearances 12. 10 These solutions can be integrated into the two assembly procedures A and B described above. Figure 14 is a perspective view of a parallelepipedal lagging box 101 the insulating lining of which has been omitted to show the rigid structure as in figure 1. Elements analogous or identical to those of the preceding figures bear the same 15 reference numbers increased by 100. The lagging box 101 includes a rigid structure built on a flat rectangular bottom panel 103. The pillars 104 are disposed in thirteen transverse rows regularly spaced along the lengthwise direction of the box 101. The number of pillars 104 per transverse row is successively: 6, 5, 6, 7, 6, 7, 6, 7, 6, 7, 6, 5 and 6. Each transverse 20 row of pillars 104 rests on the bottom panel 103. The cover panel 102 is parallel to the bottom panel 103 and rests on the upper ends of the pillars 104 that are disposed perpendicularly to the panels 102 and 103. The cover panel 102 is a reinforced cover panel that includes an upper panel 106 and a lower panel 107 that are spaced by a series of solid beams 108. 25 The beams 108 extend in a widthwise direction of the box 101 and are situated in line with each transverse row of rigid pillars 104. There are also thirteen of them in the box 101. Each beam 108 is therefore positioned along and above a transverse row of pillars 104. The beams 108 have a square section, for example. The beams 108 and the panels 106 and 107 are rigidly joined together, for example glued or 30 stapled together.

15 The upper panel 106 may include two parallel grooves (not shown) to receive two welding supports adapted to retain a sealed membrane consisting of plane strakes with raised edges, in accordance with the known technique. The pillars 104 shown have a square section and each pillar 104 is entirely 5 surrounded by a flexible material insulating sheath 130 that has a circular external shape, for example. The section of the pillar 104 could have other shapes. An insulating polymer foam block not shown in figure 14 has a shape complementary to the structure that can be seen in figure 1, so as to fill substantially all of the space between the panels 103 and 102. In other words, the insulating polymer foam block 10 is a rectangular parallelepiped pierced by a series of identical circular holes through the foam block to receive in each case a pillar 104 surrounded by the sheath 130. The diameter of a circular hole in the insulating foam block is greater than the diagonal of the section of the pillar 104 and, for example, substantially equal to or slightly less than the outside diameter of the sheath 130 at rest, so that each of the 15 sheaths 130 inserted in the hole is slightly compressed against its wall. The sheath 130 makes it possible to absorb relative movements between the foam block and the pillars, given the greater thermal contraction of the polymer foam, at the same time as preventing convection movements in the holes in the insulating foam block. The pillars 104 disposed at the peripheral edges of the box 101 are 20 received in holes that open laterally onto the peripheral lateral surface of the insulating polymer foam block that is not shown. At these locations, a modified sheath 230 is provided that does not surround the pillar 104 completely but is interrupted in line with the peripheral lateral surface of the insulating polymer foam block, i.e. in line with the peripheral lateral surface of the box 101. 25 In a variant embodiment, the sheath 130 is eliminated for the pillars 104 that are disposed in a central area 113 of the box, i.e. in an area in which the overall thermal contraction of the foam block causes smaller movements relative to the pillars 104. This area 113 may cover approximately 10 to 20% of the surface of the box 101, for example. In the central area 113 in which the sheath 130 is absent, the 30 holes in the foam block may be produced with a smaller diameter than the other holes situated outside the central area 113. For example, a lagging box 1.2 m long and 1 m wide includes seven rows of pillars distributed along its length and thirteen rows of pillars distributed along its 16 width. The pillars have a 21 mm square section. The square voids have at ambient temperature a section between 21 mm and 23 mm inclusive according to their position relative to the center of the box. The thickness of the box is 230 mm for the primary and 300 mm for the secondary. The cover panel makes a thickness of 5 60 mm at the primary and 48 mm at the secondary. The bottom panel is made of plywood 9 mm thick. The lagging boxes of rectangular parallelepiped general shape described above may also be produced with other contour shapes, for example any regular or 10 irregular polygonal shape. Moreover, in accordance with a variant that is not shown, a plurality of series of pillars having different properties, notably of shape and/or of size, may be employed in the same box. The technique described above for producing a lagging element may be used in different types of tank, for example to constitute the primary or secondary 15 insulating barrier of an LNG tank in an installation on land or in a floating structure such as a methane tanker or other ship. Referring to Figure 13, a cutaway view of a methane tanker 70 shows a sealed and insulated tank 71 of prismatic general shape mounted in the double hull 72 of the ship. The wall of the tank 71 includes a primary sealed barrier intended to 20 be in contact with the LNG contained in the tank, a secondary sealed barrier arranged between the primary sealed barrier and the double hull 72 of the ship, and two insulating barriers respectively arranged between the primary sealed barrier and the secondary sealed barrier and between the secondary sealed barrier and the double hull 72. 25 In accordance with the known technique, the primary sealed barrier and the secondary sealed barrier consist of parallel invar strakes with raised edges, that alternate with elongate welding supports, also made of invar. To be more precise, the welding supports are perpendicular to the wall and each is secured to the underlying insulating layer, example by being lodged in inverted T-shape grooves 30 produced in the cover panels of the boxes. The raised edges of the strakes are welded along the welding supports.

17 In a manner that is known in itself, loading/offloading pipes 73 disposed on the upper deck of the ship may be connected by means of appropriate connectors to a maritime or harbor terminal to transfer an LNG cargo from or to the tank 71. Figure 13 shows an example of a maritime terminal including a loading and 5 offloading station 75, a submarine pipeline 76 and an installation 77 on land. The loading and offloading station 75 is a fixed offshore installation including a mobile arm 74 and a tower 78 that supports the mobile arm 74. The mobile arm 74 carries a bundle of insulated flexible pipes 79 that can be connected to the loading/offloading pipes 73. The orientable mobile arm 74 fits all methane tanker loading gauges. A 10 connecting pipeline that is not shown extends inside the tower 78. The loading and offloading station 75 makes it possible to load and to offload the methane tanker 70 from or to the installation 77 on land. The latter includes liquefied gas storage tanks 80 and connecting pipelines 81 connected by the submarine pipeline 76 to the loading or offloading station 75. The submarine pipeline 76 enables the transfer of 15 the liquefied gas between the loading or offloading station 75 and the installation 77 on land over a great distance, for example 5 km, which makes it possible for the methane tanker 70 to remain at a greater distance from the coast during the loading and offloading operation. Pumps onboard the ship 70 and/or pumps equipping the installation 77 on 20 land and/or pumps equipping the loading and offloading station 75 are used to generate the pressure necessary to transfer the liquefied gas. Although the invention has been described in connection with a number of particular embodiments, it is obvious that it is no way limited to them and that it encompasses all the technical equivalents of the means described and their 25 combinations if they are within the scope of the invention. The use of the verbs "include", "comprise" and their conjugate 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 indicated. 30 In the claims, any reference sign between parentheses should not be interpreted as a limitation of the claim.

Claims

1. A lagging element (1, 101) suited to the creation of an insulating barrier in a sealed and insulating tank, the lagging element comprising a flat cover panel (2, 102), a thermal insulation lining (10, 20) arranged parallel to the cover 5 panel and loadbearing elements which extend from the cover panel through the thickness of said thermal insulation lining to absorb compression forces, the loadbearing elements comprising a plurality of rigid pillars (4, 104) the cross section of which is small in comparison with the dimensions of the cover panel engaged in voids (11) of the thermal insulation lining and fixed to the cover panel (2, 102), 10 in which, at a normal temperature, for at least one of said pillars, a cross-sectional dimension of the pillar is smaller than a corresponding dimension of the void in which the pillar is engaged so as to provide a gap (12) between the pillar (4, 104) and the wall of the void, the lagging element further including a filling element (30, 130) disposed in the gap (12) between the pillar (4, 104) and the wall of the void, the 15 filling element (30, 130) being made from a more flexible material than the thermal insulation lining.

2. The lagging element as claimed in claim 1, in which the filling element (30, 130) is made from a material chosen from very low density polymer foams, glass wool products, loose glass wool, melamine foams, aerogels, 20 polystyrene, blocks of polyester wadding or loose polyester wadding..

3. The lagging element as claimed in either one of claims 1 or 2, in which the pillars include a first pillar (104) engaged in a first void (11) situated in a central area (113) of the thermal insulation lining and a second pillar (104) engaged in a second void (11) of the thermal insulation lining situated at a distance from the 25 central area (113) of the thermal insulation lining, and in which a cross-sectional dimension (Dx, Dy) of the second void is greater than a corresponding dimension (Dx, Dy) of the first void to allow differential thermal contraction between the thermal insulation lining (10, 20) and the cover panel (102), and in which a flexible material filling element (30, 130) is disposed in the second void and no flexible material filling 30 element (30, 130) is disposed in the first void.

4. The lagging element as claimed in any one of claims 1 to 3, in which the pillars include a first pillar (4) engaged in a first void (11) of the thermal insulation lining and a second pillar (4) identical to the first pillar engaged in a 19 second void (11) of the thermal insulation lining, the second void being situated at a greater distance from the center (13) of the thermal insulation lining than the first void, and in which a cross-sectional dimension (Dx, Dy) of the second void is greater than a corresponding dimension (Dx, Dy) of the first void to allow differential thermal 5 contraction between the thermal insulation lining (10, 20) and the cover panel (2).

5. The lagging element as claimed in claim 4, in which all the voids (11) in which identical pillars are engaged have a cross-sectional dimension (Dx, Dy) increasing with the distance between the void and the center of the thermal insulation lining. 10

6. The lagging element as claimed in any one of claims 1 to 5, in which at the normal temperature one pillar (4) or each pillar (4) is disposed in the void (11) so as to be nearer a wall of the void facing toward the center (13) of the thermal insulation lining than a wall of the void facing away from the center of the thermal insulation lining. 15

7. The lagging element as claimed in any one of claims 1 to 6, further including a flat bottom panel (3, 103) parallel to the flat cover panel, and in which the thermal insulation lining (10, 20) is disposed between the bottom panel and the cover panel, the loadbearing elements extending through the thickness of said thermal insulation lining as far as the bottom panel, the cross section of the pillars 20 (4, 104) being moreover small in comparison with the dimensions of the bottom panel (3, 103) and the pillars being furthermore fixed to the bottom panel.

8. The lagging element as claimed in any one of claims 1 to 7, in which the pillars are perpendicular to the cover panel (2, 102).

9. The lagging element as claimed in any one of claims 1 to 8, in 25 which a pillar or each pillar has a cross-sectional dimension varying along the thickness of said thermal insulation lining, the cross-sectional dimension decreasing in the direction of the cover panel.

10. The lagging element as claimed in any one of claims 1 to 9, in which a void (11) or each void (11) has a cross-sectional dimension varying along 30 the thickness of said thermal insulation lining, the cross-sectional dimension increasing in the direction of the cover panel. 20

11. The lagging element as claimed in any one of claims 1 to 10, in which the thermal insulation lining includes a block (10, 20) of polymer foam.

12. The lagging element as claimed in claim 11, in which the thermal insulation lining (20) includes a relaxation slot (21) extending in the thickness of the 5 polymer foam block.

13. The lagging element as claimed in any one of claims 1 to 12, in which the cover panel (2, 102) is made of plywood.

14. The lagging element as claimed in any one of claims 1 to 13, in which the thermal insulation lining (10, 20) is retained by the loadbearing elements 10 (4, 104) with a possibility of sliding relative to the loadbearing elements and to the cover panel (2, 102).

15. A sealed and insulating tank (71) disposed in a supporting structure, the tank including a tank wall fixed to the supporting structure, said tank wall including successively, in the direction of the thickness from the interior toward 15 the exterior of said tank, a primary sealed barrier, a primary insulating barrier, a secondary sealed barrier and a secondary insulating barrier, the primary insulating barrier and/or the secondary insulating barrier including a plurality of juxtaposed lagging elements (1, 101) as claimed in any one of claims 1 to 14.

16. A ship (70) for the transport of a cold liquid product, the ship 20 including a double hull (72) and a tank (71) as claimed in claim 15 disposed in the double hull.

17. A use of a ship (70) as claimed in claim 16, in which a cold liquid product is routed via insulated pipes (73, 79, 76, 81) from or to a floating storage installation or a storage installation on land (77) to or from the tank (71) of the ship 25 to load or to offload the tank of the ship.

18. A transfer system for a cold liquid product, the system including a ship (70) as claimed in claim 16, insulated pipes (73, 79, 76, 81) arranged in such a manner as to connect the tank (71) installed in the hull of the ship to a floating storage installation or a storage installation on land (77) and a pump for driving a 30 flow of cold liquid product through the insulated pipes from or to the floating storage installation or the storage installation on land to or from the tank of the ship.