Sealed and thermally insulating tank

Abstract

The invention relates to a sealed and thermally insulating tank for storing a fluid, integrated into a load-bearing structure, having a secondary insulating block and a primary insulating block anchored to the secondary insulating block by a primary anchoring system (97) having a movable part (102) disposed in a housing formed in a cover plate (10), the movable part having an upper face flush with the support surface, a retaining part (101) fixed to the cover plate keeping the movable part in the housing in a thickness direction, the movable part being able to move at least parallel to a longitudinal direction of the welding flange, the movable part having a sliding layer (106) covering at least one surface of the body, the sliding layer being in contact with the retaining part and having a coefficient of friction lower than that of the movable part.

Description

Domaine technique

[0001] The invention relates to the field of leak-proof and thermally insulated membrane tanks. In particular, the invention relates to the field of leak-proof and thermally insulated tanks for the storage and / or transport of liquefied gases at low temperatures, such as tanks for transporting Liquefied Petroleum Gas (LPG) at temperatures ranging, for example, from -50°C to 0°C, or for transporting Liquefied Natural Gas (LNG) at approximately -162°C at atmospheric pressure. These tanks can be installed on land or on a floating structure. In the case of a floating structure, the tank can be used for transporting liquefied gas or for receiving liquefied gas to serve as fuel for the propulsion of the floating structure.

[0002] In one embodiment, the liquefied gas is LNG at atmospheric pressure. Other liquefied gases can also be considered, including ethane, propane, butane, hydrogen, or ethylene. Arrière-plan technologique

[0003] The tanks of ships transporting liquefied natural gas generally comprise a double wall consisting, from the inside to the outside of the tank, of a primary watertight membrane, a primary thermally insulating barrier, a secondary watertight membrane, and a secondary thermally insulating barrier. The secondary insulating barrier includes a secondary insulating block comprising a cover plate that forms a support surface for the secondary watertight membrane.

[0004] French patent application FR 3 090 810 describes a watertight and insulating tank wall in which an anchoring system allows a primary insulating block to be anchored to the secondary insulating block. The anchoring system comprises a base fixed to the lid plate. A movable part is retained in the base along a wall thickness direction and mounted freely within the base. The movable part has a tapped hole opening onto its upper surface. The upper surface of the movable part is flush with the upper surface of the lid plate, and the movable part is mounted in the free base in translation at least parallel to the longitudinal direction of the weld flange.

[0005] However, the proposed anchoring system is not entirely satisfactory. Indeed, the moving part is prone to seizing, caused in particular by an excessively high coefficient of friction of the metal part and by the lack of homogeneity of the coefficient of friction on the surface of an untreated metal part. Résumé

[0006] One idea behind the invention is to limit the seizing of the moving part present in the primary anchoring system of a sealed and thermally insulating tank.

[0007] Another idea underlying the invention is to promote sliding of the moving part only in the desired directions.

[0008] According to one embodiment, the invention provides a sealed and thermally insulating tank for the storage of a fluid, the tank comprising a tank wall successively comprising, in a thickness direction, a secondary insulating barrier retained to a load-bearing wall, a secondary waterproof membrane resting against the secondary insulating barrier, a primary insulating barrier resting against the secondary waterproof membrane and a primary waterproof membrane resting against the primary insulating barrier, in which the secondary insulating barrier comprises a secondary insulating block including a cover plate forming a support surface for the secondary waterproof membrane, in which said secondary waterproof membrane comprises a plurality of metal strakes, the metal strakes having edges raised towards the interior of the tank, said metal strakes being welded in pairs, by their raised edges on two faces of a weld flange mechanically retained on the secondary block, said weld flange being partially engaged in a groove formed in the cover plate and extending in a longitudinal direction, in which the primary insulating barrier comprises a primary insulating block anchored to the secondary insulating block by a primary anchoring system, the primary anchoring system comprising: a housing formed in the cover plate and opening onto said support surface,a movable part disposed in the housing, the movable part comprising a body having an upper face flush with the support surface, and a retaining part fixed to the cover plate and cooperating with the movable part so as to stop the movable part in the housing in the thickness direction, the housing and the retaining part being configured to permit movement of the movable part at least parallel to the longitudinal direction of the weld flange, in which the movable part comprises a sliding layer covering at least one surface of the body, the sliding layer being in contact with the retaining part and having a coefficient of friction lower than said body,

[0009] Thanks to these characteristics, the sliding layer improves the durability of the primary anchoring system. Indeed, by having a lower coefficient of friction than the body, the moving part can move within the body while minimizing friction between the two parts. This reduces the stress on the welds between the primary anchor and the secondary membrane, thus increasing the lifespan of the primary anchoring system. It also ensures that the moving part only moves in the desired direction, preventing it from jamming.

[0010] According to embodiments, such a tank may include one or more of the following characteristics.

[0011] In one embodiment, a compressible material is inserted into gaps located between the retaining element and the moving part, or between the moving part and the walls of the housing. The compressible material is insulating and is chosen, for example, from polymer foams and mineral wools. Thanks to the compressibility of the material, it is possible to adjust the initial position of the moving part to a centered position, allowing the moving part a good degree of freedom of movement in either direction during commissioning.

[0012] According to one embodiment, the compressible material can be a low-stiffness spring.

[0013] According to one embodiment, the sliding layer is made of polymer.

[0014] According to one embodiment, the sliding layer is chosen from the following polymers: PTFE (polytetrafluoroethylene), PCTFE (polychlorotrifluoroethylene), POM (polyoxymethylene) preferably of type H for homopolymer, PEI (polyetherimide), PAEK (polyaryletherketone), PEEK (polyetheretherketone).

[0015] In one embodiment, the polymer is reinforced with fibers, for example with glass fibers. This has the advantage of increasing the material's resistance to creep and reducing the coefficient of thermal contraction of the sliding layer.

[0016] In one embodiment, the polymer sliding layer is made of a polymer loaded with particulate fillers, preferably nanofillers. This has the advantage of increasing, depending on the materials used, either the polymer's hardness or its sliding capacity during contact between the stressed surfaces. A nanofiller is defined by its size, which is between 1 and 100 nanometers. The shape of the particulate fillers, particularly the nanofillers, can be chosen, for example, from: sheets, fibers, granules, and spheres.

[0017] According to one embodiment, the particulate charges are made of at least one material chosen from: carbon, graphite, glass, cellulose and bronze.

[0018] According to one embodiment, the sliding layer is obtained by surface treatment of said at least one surface of the body.

[0019] According to one embodiment, the surface treatment is a nitriding treatment.

[0020] According to one embodiment, the sliding layer is disposed on a surface of the retaining part in contact with the moving part.

[0021] According to one embodiment, the sliding layer is disposed on a surface of the retaining part in contact with the moving part and on the moving part.

[0022] According to one embodiment, the housing has a depth in the thickness direction such that the moving part is flush with the support surface and a length in the longitudinal direction and a width in a transverse direction such that the moving part can move at least parallel to the longitudinal direction of the metal strakes.

[0023] According to one embodiment, the cover plate has a counterbore on the edge of the housing, the counterbore receiving the retaining piece, the counterbore having a depth such that the retaining piece is flush with the support surface, in which the retaining piece completely covers the housing and the counterbore and has an opening, the upper face of the body being flush through said opening.

[0024] According to one embodiment, the moving part has a base having a width greater than that of the opening in the retaining part.

[0025] According to one embodiment, the movable part comprises an upper part having a width equal to that of said opening, the upper part being flush with an upper surface of the retaining part.

[0026] According to one embodiment, at least the base of the moving part includes the sliding layer.

[0027] In one embodiment, an upper surface of the base is covered by the sliding layer. This reduces friction between the moving part and a lower surface of the retaining part.

[0028] In one embodiment, one side of the upper part is covered by the sliding layer. This reduces friction between the moving part and an edge of the opening in the retaining part.

[0029] In one embodiment, the retaining piece is a retaining plate. In another embodiment, the retaining piece is made of steel, for example stainless steel and / or cryogenic steel.

[0030] According to one embodiment, the retaining plate is fixed to the cover plate by fasteners placed around the periphery of the retaining plate, so that the fasteners are arranged outside the housing around the housing and / or by gluing.

[0031] Thanks to these features, fasteners, for example screws or rivets, are not at risk of coming into contact with the moving part.

[0032] According to one embodiment, the moving part has a tapped hole opening onto said upper face of the moving part and the primary anchoring system further comprises a stud having a threaded lower part screwed into the tapped hole.

[0033] According to one embodiment, the stud has a collar extending above the moving part, in which the collar is welded around the periphery to the secondary sealing membrane in a watertight manner.

[0034] Such a tank can be part of an onshore storage facility, for example for storing LNG, or be installed in a floating structure, whether coastal or deep-water, including an LNG carrier, a floating storage and regasification unit (FSRU), a floating production and storage unit (FPSO), and others. Such a tank can also serve as a fuel tank in any type of vessel.

[0035] According to one embodiment, the primary anchoring system further comprises at least one washer and at least one nut cooperating with threaded upper portions of said stud to retain said washer in support on a base plate of the primary insulating block.

[0036] According to one embodiment, a ship for the transport of a cold liquid product comprises a double hull and the aforementioned tank arranged in the double hull.

[0037] According to one embodiment, the invention also provides a transfer system for a cold liquid product, the system comprising the aforementioned vessel, insulated pipes arranged to connect the tank installed in the hull of the vessel to a floating or land-based storage facility, and a pump to drive a flow of cold liquid product through the insulated pipes from or to the floating or land-based storage facility to or from the vessel's tank.

[0038] According to one embodiment, the invention also provides a method for loading or unloading such a vessel, in which a cold liquid product is conveyed through insulated pipes from or to a floating or land-based storage facility to or from the vessel's tank. Brève description des figures

[0039] The invention will be better understood, and other objects, details, features and advantages thereof will become more apparent from the following description of several particular embodiments of the invention, given solely by way of illustration and not limitation, with reference to the accompanying drawings. [ Fig.1 ] There [ Fig.1 ] is a cutaway perspective view of a tank wall. Fig.2 ] There [ Fig.2 ] is a schematic cross-sectional view of detail II of the [ Fig.1 illustrating an anchoring system cooperating with a stud according to a first embodiment. Fig.3 ] There [ Fig.3 [ ] is a schematic top view of the anchoring system according to the first embodiment, including a movable part and a retaining part. ] Fig.4 ] There [ Fig.4 ] is a schematic perspective view of the moving part of the [ Fig.3 ]. Fig.5 ] There [ Fig.5 ] is a schematic perspective view of the moving part according to a second embodiment. Fig.6 ] There [ Fig.6 ] is a schematic perspective view of the moving part according to a third embodiment. Fig.7 ] There [ Fig.7 ] is a schematic perspective view of the moving part according to a fourth embodiment [ Fig.8 ] There [ Fig.8 ] is a schematic perspective view of the moving part according to a fifth embodiment [ Fig.9 ] There [ Fig.9 ] is a schematic perspective view of the moving part according to a sixth embodiment. Fig.10 ] There [ Fig.10 ] is a schematic perspective view of the moving part according to a seventh embodiment. Fig.11 ] There [ Fig.11 ] is a schematic perspective view of a retaining piece according to a first variant. Fig.12 ] There [ Fig.12 ] is a schematic perspective view of the retaining piece according to a second variant. Fig.13 ] There [ Fig.13 ] is a schematic cutaway representation of a tank on an LNG carrier and a loading / unloading terminal for that tank. Description des modes de réalisation

[0040] On the [ Fig.1 [ ] The multilayer structure of a sealed and thermally insulated tank 1 for storing a liquefied fluid, such as liquefied natural gas (LNG), is shown. Tank 1 has a generally polyhedral shape and comprises several walls. The wall of tank 1 consists successively, in the thickness direction, from the outside to the inside of tank 1, of a secondary thermally insulating barrier 2 attached to a supporting structure 3, a secondary sealed membrane 4 resting against the secondary thermally insulating barrier 2, a primary thermally insulating barrier 5 resting against the secondary sealed membrane 4, and a primary sealed membrane 6 intended to be in contact with the liquefied natural gas contained in tank 1.

[0041] The supporting structure of tank 1 can notably be formed by the hull or double hull of a ship. The supporting structure comprises a plurality of load-bearing walls 3 defining the general shape of the view, usually a polyhedral shape.

[0042] The secondary thermal insulation barrier 2 comprises a plurality of secondary insulating blocks 7 which are anchored to the load-bearing wall 3 by means of secondary anchoring systems 98. The secondary insulating blocks 7 are generally parallelepiped in shape and are arranged in parallel rows. Three rows are designated by the letters A, B, and C. Sealant strips (not shown) are interposed between the secondary insulating blocks 7 and the load-bearing wall 3 to compensate for deviations of the load-bearing wall 3 from a flat reference surface. Kraft paper can be inserted between the sealant strips and the load-bearing wall 3 if desired to prevent the sealant strips from adhering to the load-bearing wall 3.

[0043] It is observed that the secondary watertight membrane 4 comprises a continuous layer of metallic strakes 21 with raised edges 32 facing inwards towards the tank. The strakes 21 are welded in pairs, by their raised edges 32, on the two faces of a weld flange. The weld flanges have an L-shaped cross-section. The raised edges 32 of the strakes 21 are welded to one arm of the L-shape, while the other arm is engaged in a groove 20 formed on the cover plates 10 of the secondary insulating blocks 7. The cover plates 10 comprise a plurality of parallel grooves 20, the distance between two grooves 20 corresponding to the width of a strake 21, while the distance between a free edge of a block and an adjacent groove 20 corresponds to the width of a strake 21, so that a strake forms the joint between two adjacent insulating blocks 7. Thus, the secondary waterproof membrane 4 is retained on the secondary thermally insulating barrier 2.The weld wings and grooves 20 form sliding joints allowing the strakes 21 to contract and deform relative to the secondary insulating blocks 7.

[0044] The primary thermal insulation barrier 5 comprises a plurality of primary insulation blocks 22 superimposed across two rows of secondary insulation blocks 7. The primary insulation blocks 22 are anchored to the secondary insulation blocks 7 by means of primary anchoring systems 97. The primary anchoring systems 97 are separate and offset from the secondary anchoring systems 98. The primary insulation blocks 22 have a generally parallelepiped shape and are arranged in parallel rows. Furthermore, they have the same dimensions as the primary insulation blocks 22 except for their thickness along the thickness direction of the tank wall 1, which may be different, and in particular, less. The primary thermal insulation barrier 5 is topped with a corrugated metal sealing barrier.Alternatively, the thermally insulating barrier 5 could be surmounted by a metallic sealing barrier composed of strakes.

[0045] There [ Fig.2 [ ] represents the primary anchoring system 97, according to a first embodiment. The primary anchoring system 97 comprises a movable part 102 held in place by a retaining part 101. The movable part 102 is disposed in a recess 108 cut into the cover plate 10 and the retaining part 101 is disposed in a counterbore 109, so that the retaining part 101 is flush with a top surface of a cover plate 10. The retaining part 101 is fixed to the cover plate 10 by means of fasteners 34 and / or by bonding.

[0046] In a preferred embodiment, the cover plate 10 includes in particular a layer of plywood with a thickness between 15 and 24 millimeters, in which the housing is hollowed out.

[0047] At a tapped hole 104 in the moving part 102, the waterproof membrane 4 is pierced to allow the passage of a stud 35. The stud 35 subsequently allows the secondary insulating block 7 to be fixed to the primary insulating block 22.

[0048] There [ Fig.3 ] represents the primary anchoring system 97, according to the first embodiment, viewed from above. An opening 103 where the movable part 102 is flush is also filled with a piece of compressible insulating material 105. On the [ Fig.3 ], the compressible insulating piece 105 is shown on only one side of the movable part 102, but another identical piece can also be placed on the other side to initially center the movable part 102 with respect to the opening 103. A sliding layer 106 covers at least one side of the movable part 102.

[0049] The pre-positioning of the movable part 102, for example a centered pre-positioning, obtained thanks to the compressible insulating material parts 105 ensures that a certain range of mobility exists in one direction or the other in the longitudinal direction of the strakes 21. This mobility makes it possible to adjust the position of the stud 35, if necessary, either during the welding of the secondary sealing membrane 4 to compensate for positioning tolerances, or during the operation of the tank to absorb deformations which may have various causes.

[0050] THE figures 4 à 10 represent different embodiments of the moving part 102-702 of the primary anchoring system, while the figures 11 et 12 represent two variant embodiments of the retaining piece 101-201.

[0051] There [ Fig.4 [ ] represents the moving part 102 according to the first embodiment. The moving part 102 comprises an upper portion 114 and a lower portion 110. The lower portion 110 is a rectangular parallelepiped base, and the upper portion 114 has a rectangular cross-section and is shorter than the lower portion 110. The moving part 102 includes a tapped hole 104 in an upper surface of the upper portion 114, which allows the passage of a stud 35. The moving part 102 is surrounded by a sliding pad 106, which is a polymer layer. The lower portion 110 and the upper portion 114 are, for example, made of stainless steel. The sliding pad 106 is disposed on an edge of the upper surface of the upper part 114, on sides 115 of the upper part 114 and on an upper surface 111 of the lower part 110 not covered by the upper part 114.The 106 sliding pad can be made from a single block.

[0052] According to an unrepresented variant, the sliding pad 106 can be replaced by a nitriding treatment applied to the moving part 102 on the sides 115 of the upper part 114 and on the upper surface 111 of the lower part 110.

[0053] There [ Fig.5 [ ] represents the moving part 202 according to a second embodiment. The second embodiment differs from the first embodiment in that the upper part 214 is cylindrical with a tapped hole 204. The lower part 210 is a base with a rectangular cross-section. In this embodiment, an upper surface 211 of the lower part 210 has a sliding layer. One side 215 of the upper part 214 may also have a sliding layer. The sliding layer 206 is obtained either by surface treatment of the upper surface 211 (and optionally of the side 215), or by covering the upper surface 211 (and optionally the side 215) with a sliding pad.

[0054] There [ Fig.6 ] represents the moving part 302 according to a third embodiment. The third embodiment differs from the second embodiment in that the upper part 314 has a rectangular cross-section with rounded edges, with dimensions in a longitudinal and transverse direction smaller than those of the lower part 310. In this embodiment, the sliding layer 306 is obtained by surface treatment of an upper surface 311 of the lower part 310 and, optionally, of the sides 315 of the upper part 314 or by covering said upper surface 311 and optionally said sides 315 with a sliding pad.

[0055] There [ Fig.7 ] represents the moving part 402 according to a fourth embodiment. The fourth embodiment differs from the second embodiment in that the upper part 414 has a rectangular cross-section and has a dimension in a longitudinal direction identical to that of the lower part 410. In this embodiment, the sliding layer 406 is obtained by surface treatment of an upper surface 411 of the lower part 410 and, optionally, of the sides 415 of the upper part 414, or by covering said upper surface 411 and optionally said sides 415 with a sliding pad.

[0056] There [ Fig.8 [ ] represents the moving part 502 according to a fifth embodiment. The fifth embodiment differs from the fourth embodiment in that the upper part 514 has rounded edges. In this embodiment, the sliding layer 506 is obtained by surface treatment of an upper surface 511 of the lower part 510 and, optionally, of the sides 515 of the upper part 514, or by covering said upper surface 511 and optionally said sides 515 with a sliding pad.

[0057] There [ Fig.9 [ ] represents the moving part 602 according to a sixth embodiment. The sixth embodiment differs from the first embodiment in that the polymer sliding pad 606 has dimensions in the longitudinal and transverse directions greater than those of the lower part 610.

[0058] There [ Fig.10 [ ] represents the moving part 702 according to a seventh embodiment. The seventh embodiment differs from the second embodiment in that the sliding pad 706 is made of polymer and is parallelepiped in shape with rounded edges and has a dimension in the longitudinal direction identical to that of the lower part 710. The lower part 710 is also covered by the sliding pad 706.

[0059] According to variants not shown, the sliding pad 606 or 706 can be replaced by a surface treatment of an upper surface of the lower part 610 or 710 and, optionally, of the side of the upper part 614 or 714.

[0060] There [ Fig.11 ] represents the retaining piece according to a first variant. According to this first variant, the retaining piece 101 is a rectangular retaining plate, with a rectangular opening where the movable part 102-702 is flush and with four tapped holes 119 at the ends for attaching the fasteners 34

[0061] There [ Fig.12 ] represents the retaining piece according to a second variant. This second variant differs from the first in that the retaining plate 201 is circular in shape.

[0062] The two retaining part variants are notably compatible with all embodiments of the moving part.

[0063] In other variants not shown, the retaining piece can be made in various other ways, for example by having a different shape and a different number of tapped holes.

[0064] With reference to the [ Fig.13 [ ], a cutaway view of a methane tanker 70 shows a sealed and insulated tank 71 of generally prismatic shape mounted in the double hull 72 of the ship. The wall of the tank 71 comprises a primary watertight barrier intended to be in contact with the LNG contained in the tank, a secondary watertight barrier arranged between the primary watertight barrier and the double hull 72 of the ship, and two insulating barriers arranged respectively between the primary watertight barrier and the secondary watertight barrier and between the secondary watertight barrier and the double hull 72.

[0065] As is known per se, loading / unloading pipelines 73 arranged on the upper deck of the ship can be connected, by means of suitable connectors, to a marine or port terminal to transfer a cargo of LNG to or from the tank 71.

[0066] There [ Fig.13Figure 75 represents an example of a marine terminal comprising a loading and unloading berth 75, a subsea pipeline 76, and an onshore facility 77. The loading and unloading berth 75 is a fixed offshore installation comprising a movable arm 74 and a tower 78 that supports the movable arm 74. The movable arm 74 carries a bundle of insulated flexible pipes 79 that can be connected to the loading / unloading pipelines 73. The steerable movable arm 74 accommodates all LNG carrier sizes. A connecting pipeline (not shown) extends inside the tower 78. The loading and unloading berth 75 allows the loading and unloading of the LNG carrier 70 to and from the onshore facility 77. The onshore facility comprises liquefied gas storage tanks 80 and connecting pipelines 81 linked by the subsea pipeline 76 to the loading or unloading berth 75.The subsea pipeline 76 allows the transfer of liquefied gas between the loading or unloading station 75 and the onshore facility 77 over a long distance, for example 5 km, which allows the LNG carrier 70 to be kept a long distance from the coast during loading and unloading operations.

[0067] To generate the pressure necessary for the transfer of the liquefied gas, pumps on board the ship 70 and / or pumps equipping the land installation 77 and / or pumps equipping the loading and unloading station 75 are used.

[0068] Although the invention has been described in connection with several particular embodiments, it is clearly evident that it is by no means limited to them and that it includes all technical equivalents of the means described as well as their combinations if these fall within the scope of the invention.

[0069] The use of the verb "comporter", "comprendre" or "include" and its conjugated forms does not exclude the presence of other elements or steps than those stated in a claim.

[0070] In claims, any reference sign in parentheses shall not be interpreted as a limitation of the claim.

Claims

1. Sealed and thermally insulating tank (1) for storing a fluid, the tank (1) including a tank wall including in succession, in the direction of the thickness thereof, a secondary insulating barrier (2) secured to a load-bearing wall (3), a secondary sealing membrane (4) resting against the secondary insulating barrier (2), a primary insulating barrier (5) resting against the secondary sealing membrane (4) and a primary sealing membrane (6) resting against the primary insulating barrier (5), in which said secondary insulating barrier (2) includes a secondary insulating block (7) comprising a cover plate (10) forming a supporting surface for the secondary sealing membrane (4), in which said secondary sealing membrane (4) comprises a plurality of metal strakes (21), the metal strakes (21) having edges (32) raised towards the inside of the tank, said metal strakes (21) being welded in pairs, by their raised edges (32), on two faces of a welding flange mechanically secured to the secondary insulating block (7), said welding flange being partially engaged in a groove (20) made in the cover plate (10) and extending in a longitudinal direction, in which the primary insulating barrier (5) includes a primary insulating block (22) anchored to the secondary insulating block (7) by a primary anchoring system (97), the primary anchoring system (97) including: - a recess made in the cover plate and emerging onto said supporting surface, - a movable part (102, 202, 302, 402, 502, 602, 702) positioned in the recess, the movable part including a body, and - a securing part (101, 201) fastened to the cover plate (10) and interacting with the movable part (102, 202, 302, 402, 502, 602, 702) so as to immobilize the movable part in the recess in the thickness direction, the recess and the securing part (101, 201) being configured to allow the movement of the movable part (102, 202, 302, 402, 502, 602, 702) at least parallel to the longitudinal direction of the metal strakes, in which the securing part (101) has an opening (103), the body including a base (110, 210, 310, 410, 510, 610, 710) and an upper portion (114, 214, 314, 414, 514, 614, 714), the upper portion having an upper surface flush with an upper surface of the securing part through said opening, the base having a larger width than the opening in the securing part (101, 201), in which the movable part (102, 202, 302, 402, 502, 602, 702) includes a polymer sliding layer (106, 206, 306, 406, 506, 606, 706) covering at least an upper surface (111, 211, 311, 411, 511) of the base (110, 210, 310, 410, 510, 610, 710) of the body, the sliding layer (106, 206, 306, 406, 506, 606, 706) being in contact with the securing part (101, 201) and having a lower coefficient of friction than said body, characterized in that the cover plate (10) includes a counterbore on the edge of the recess, the counterbore receiving the securing part (101), the counterbore having a depth such that the securing part (101) is flush with the supporting surface, the securing part (101) completely covering the recess and the counterbore, and in that the polymer sliding layer (106, 206, 306, 406, 506, 606, 706) also covers a side (115, 215, 315, 415, 515) of the upper portion of the body.

2. Tank according to Claim 1, in which the polymer sliding layer is made from a polymer filled with particulate fillers, the particulate fillers preferably including nanofillers.

3. Tank according to Claim 2, in which the particulate fillers are made from at least one material selected from: carbon, graphite, glass, cellulose and bronze.

4. Sealed and thermally insulating tank (1) for storing a fluid, the tank (1) including a tank wall including in succession, in the direction of the thickness thereof, a secondary insulating barrier (2) secured to a load-bearing wall (3), a secondary sealing membrane (4) resting against the secondary insulating barrier (2), a primary insulating barrier (5) resting against the secondary sealing membrane (4) and a primary sealing membrane (6) resting against the primary insulating barrier (5), in which said secondary insulating barrier (2) includes a secondary insulating block (7) comprising a cover plate (10) forming a supporting surface for the secondary sealing membrane (4), in which said secondary sealing membrane (4) comprises a plurality of metal strakes (21), the metal strakes (21) having edges (32) raised towards the inside of the tank, said metal strakes (21) being welded in pairs, by their raised edges (32), on two faces of a welding flange mechanically secured to the secondary insulating block (7), said welding flange being partially engaged in a groove (20) made in the cover plate (10) and extending in a longitudinal direction, in which the primary insulating barrier (5) includes a primary insulating block (22) anchored to the secondary insulating block (7) by a primary anchoring system (97), the primary anchoring system (97) including: - a recess made in the cover plate and emerging onto said supporting surface, - a movable part (102, 202, 302, 402, 502, 602, 702) positioned in the recess, the movable part including a body, and - a securing part (101, 201) fastened to the cover plate (10) and interacting with the movable part (102, 202, 302, 402, 502, 602, 702) so as to immobilize the movable part in the recess in the thickness direction, the recess and the securing part (101, 201) being configured to allow the movement of the movable part (102, 202, 302, 402, 502, 602, 702) at least parallel to the longitudinal direction of the metal strakes, in which the securing part (101) has an opening (103), the body including a base (110, 210, 310, 410, 510, 610, 710) and an upper portion (114, 214, 314, 414, 514, 614, 714), the upper portion having an upper surface flush with an upper surface of the securing part through said opening, the base having a larger width than the opening in the securing part (101, 201), characterized in that the movable part (102, 202, 302, 402, 502, 602, 702) includes a sliding layer (106, 206, 306, 406, 506, 606, 706) in contact with the securing part (101, 201) and having a lower coefficient of friction than said body, the sliding layer (106, 206, 306, 406, 506, 606, 706) being obtained by surface treatment of at least one surface of the body, and in that the sliding layer (106, 206, 306, 406, 506, 606, 706) forms an upper surface (111, 211, 311, 411, 511) of the base (110, 210, 310, 410, 510, 610, 710) of the body and a side (115, 215, 315, 415, 515) of the upper portion of the body, and in that the cover plate (10) includes a counterbore on the edge of the recess, the counterbore receiving the securing part (101), the counterbore having a depth such that the securing part (101) is flush with the supporting surface, the securing part (101) completely covering the recess and the counterbore.

5. Tank according to Claim 4, in which the surface treatment is a nitriding treatment.

6. Tank according to one of Claims 1 to 5, in which a compressible material (105) is inserted into gaps situated between the securing part (101, 201) and the movable part (102, 202, 302, 402, 502, 602, 702) or between the movable part and walls of the recess.

7. Tank according to one of Claims 1 to 6, in which the recess has a depth in the thickness direction such that the movable part (102, 202, 302, 402, 502, 602, 702) is flush with the supporting surface and a length in the longitudinal direction and a width in a transverse direction such that the movable part can move at least parallel to the longitudinal direction of the metal strakes.

8. Tank according to one of Claims 1 to 7, in which the upper portion (114, 214, 314, 414, 514, 614, 714) with the sliding layer is the same width as said opening.

9. Tank according to one of Claims 1 to 8, in which the securing part (101, 201) is a retaining plate.

10. Tank according to Claim 9, in which the retaining plate is fastened to the cover plate (10) by fasteners (34) placed on the periphery of the cover plate, so that the fasteners (34) are positioned outside the recess around the recess, and / or by adhesive bonding.

11. Tank according to one of Claims 1 to 10, in which the movable part (102, 202, 302, 402, 502, 602, 702) includes a tapped hole (104, 204, 304, 604, 704) emerging onto said upper face of the movable part (102, 202, 302, 402, 502, 602, 702) and the primary anchoring system (97) further includes a stud (35) having a threaded lower portion screwed into the tapped hole (104).

12. Tank according to Claim 11, in which the stud (35) includes a collar extending above the movable part (102, 202, 302, 402, 502, 602, 702), in which the periphery of the collar is sealably welded to the secondary sealing membrane (4).

13. Tank according to Claim 11 or 12, in which the primary anchoring system (97) further comprises at least one washer and at least one nut interacting with threaded upper portions of said stud (35) in order to secure said washer pressing on a bottom plate of the primary insulating block (22).

14. Vessel for transporting a cold liquid product, the vessel comprising a double hull and a tank positioned in the double hull, the tank being a tank according to one of Claims 1 to 13.

15. System for transferring a cold liquid product, the system including a vessel according to Claim 14, insulated pipes arranged so that they connect the tank installed in the hull of the vessel to a floating or onshore storage installation and a pump for conveying a stream of cold liquid product through the insulated pipes from or to the floating or onshore storage installation to or from the tank of the vessel.

16. Method for loading or unloading a vessel according to Claim 14, in which a cold liquid product is conveyed through insulated pipes from or to a floating or onshore storage installation to or from the tank of the vessel.

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