Method for sealing a sealing membrane for a sealed and thermally insulated tank

Description

Domaine technique

[0001] The invention relates to the field of sealed tanks and more particularly to sealed and thermally insulating tanks with membranes, and more particularly to a method for closing a sealing membrane for a sealed tank and to a welding assembly, see claims 1 and 16. In particular, the invention relates to the field of sealed and thermally insulating tanks for storing liquefied gas at low temperature, such as tanks for storing 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 intended for the transport of liquefied gas or for receiving liquefied gas used as fuel for the propulsion of the floating structure. Arrière-plan technologique

[0002] Well known in the prior art are sealed and thermally insulating tanks integrated into supporting structures to serve as a land storage facility, comprising a secondary thermally insulating barrier, a secondary sealing membrane, a primary thermally insulating barrier and a primary sealing membrane. The tank comprises a plurality of tank walls assembled together.

[0003] In this type of structure, the waterproofing membranes are required to be closed at the end of the wall or at an opening in order, for example, to allow loading / unloading pipes to pass through.

[0004] In these closures, the secondary waterproofing membrane or the primary waterproofing membrane is connected in a watertight manner to the supporting structure. These connections are made using a 90° bent part which is generally welded on one side to the supporting structure and connected on the other side to the waterproofing membrane.

[0005] These welding operations are carried out manually.

[0006] JP S48 25012 U describes a welding assembly, and WO 2019 / 239048 A1 describes a method of closing a sealing membrane for a sealed tank in accordance with the preamble of claim 1. Résumé

[0007] One idea behind the invention is to simplify the welding operation in a closing area of ​​the waterproofing membrane

[0008] According to one embodiment, the invention provides a method for closing a sealing membrane for a sealed tank, said tank being in particular thermally insulating, in accordance with claim 1, the method comprising the following steps: providing a tank wall fixed to a load-bearing wall, the tank wall comprising in a thickness direction a thermally insulating barrier and a sealing membrane fixed to the thermally insulating barrier, the thermally insulating barrier comprising an end portion located at one end of the thermally insulating barrier in a first direction, fixing a metal connecting angle at the end portion, the metal connecting angle comprising a first wing and a second wing connected to the first wing, by welding the first wing using a weld bead to a metal part secured to the load-bearing wall, and by connecting the second wing to the sealing membrane, wherein the step of welding the first wing is carried out using an automatic welding machine moving on a welding support, the welding support comprising a fixing surface and a support surface perpendicular to the fixing surface, the support surface comprising a guide means, in particular a guide rail, extending in a second direction perpendicular to the first direction and to the thickness direction, the welding machine comprising a movement system cooperating with the guide means and being configured to move the welding machine in a feed parallel to the second direction, the welding machine also comprising a welding torch, and wherein during the welding of the first wing, the fixing surface of the welding support is fixed on the end portion of the thermally insulating barrier so that the support surface is perpendicular to the first direction.

[0009] Thanks to these features, it is possible to use an automatic welding machine in a waterproofing membrane closing area, thus simplifying the welding operation and limiting costs. In addition, the welding support allows the automatic welding machine to be guided and held by attaching to elements of the tank already mounted in it, namely an end portion of the thermally insulating barrier. As a result, it is not necessary to have space allocated to the welding support and the machine when closing the waterproofing membrane.

[0010] According to embodiments, such a method may comprise one or more of the following features.

[0011] According to one embodiment, the welding machine also comprises a hook bar attached to the movement system and comprising a first end remote from the movement system and a second end remote from the movement system, the first end and the second end being located on either side of the movement system in the thickness direction, the welding torch being attached to the first end, and a counterweight being attached to the second end.

[0012] According to one embodiment, the first wing is formed in a plane perpendicular to the first direction while the second wing is formed in a plane perpendicular to the thickness direction.

[0013] According to one embodiment, the metal part secured to the load-bearing wall is an anchoring plate projecting from the load-bearing wall in the thickness direction and extending in the second direction, the end portion of the thermally insulating barrier being adjacent to the anchoring plate.

[0014] The end portion is thus either located against the anchor plate or separated from the anchor plate by a plywood plate.

[0015] According to one embodiment, the metal part secured to the load-bearing wall is a metal portion of the load-bearing wall.

[0016] According to one embodiment, the thermally insulating barrier comprises a plurality of insulating blocks juxtaposed to each other and the end portion of the thermally insulating barrier comprises an end insulating block.

[0017] According to one embodiment, the weld bead is a first weld bead, a metal closure plate being fixed on at least a part of a surface of the end portion of the thermally insulating barrier opposite the load-bearing wall, one end of the sealing membrane being fixed to the metal closure plate, and in which during the step of fixing the connecting angle, the second wing is welded using a second weld bead to the metal closure plate.

[0018] According to one embodiment, the weld bead is a first weld bead, a metal closure plate being fixed on at least part of a surface of the end portion of the thermally insulating barrier opposite the load-bearing wall, and in which during the step of fixing the connecting angle, the second wing is welded to the metal closure plate, one end of the sealing membrane also being welded to the second wing.

[0019] Preferably, only the welding of the end of the waterproofing membrane to the second wing of the connecting angle is carried out using the automatic welding machine and thus constitutes a second weld bead. The welding of the second wing to the metal closing plate is manual welding.

[0020] According to one embodiment, the closure plate comprises fixing orifices, the closure plate being fixed to the end portion of the thermally insulating barrier using anchoring devices inserted into the fixing orifices, and in which when producing the first weld bead, the fixing surface of the welding support is fixed using anchoring devices inserted into fixing orifices left free by the anchoring devices of the closure plate.

[0021] According to one embodiment, the fixing surface of the welding support is a first fixing surface and the welding support comprises a second fixing surface perpendicular to the first fixing surface and parallel to the support surface, and wherein when producing the second weld bead, the second fixing surface of the welding support is fixed against the load-bearing wall so that the support surface is parallel, preferably coplanar, to the waterproofing membrane, the second weld bead being produced using said automatic welding machine moving on the guide means of the welding support, said welding support being used for both producing the first weld bead and the second weld bead.

[0022] Thus, the same welding support and the same welding machine can be used both to weld the first leg of the connecting angle to the load-bearing wall and to weld the second leg of the connecting angle to the closing plate or the waterproofing membrane.

[0023] According to one embodiment, the load-bearing wall comprises fixing orifices, the insulating blocks being anchored to the load-bearing wall using anchoring devices inserted into the fixing orifices, and in which when producing the second weld bead, the second fixing surface of the welding support is fixed using anchoring devices inserted into fixing orifices of the load-bearing wall left free by the anchoring devices of the insulating blocks.

[0024] According to one embodiment, the tank wall is inclined relative to the horizontal, preferably the tank wall is a vertical wall.

[0025] According to one embodiment, the second end of the hanging bar is equipped with a wheel provided with a spring so that the wheel is constantly pressed against the support surface of the welding support when the welding bead is being produced.

[0026] According to one embodiment, the welding torch is an electric arc welding torch, advantageously without material input and with inert gas flow, such as for example a torch with a tungsten electrode and argon flow.

[0027] According to one embodiment, the thermally insulating barrier is a secondary thermally insulating barrier and the sealing membrane is a secondary sealing membrane, and in which the tank wall comprises in the thickness direction a primary thermally insulating barrier arranged at least partially on the secondary sealing membrane, and a primary sealing membrane fixed on the primary thermally insulating barrier and intended to be in contact with a liquefied gas.

[0028] According to one embodiment, the secondary waterproofing membrane is formed from a composite material comprising an aluminum sheet sandwiched between two sheets of fiberglass fabric.

[0029] According to one embodiment, one end of the secondary sealing membrane is glued to the metal closure plate or to the second wing.

[0030] According to one embodiment, the thermally insulating barrier is a primary thermally insulating barrier and the sealing membrane is a primary sealing membrane, and wherein the tank wall comprises in the thickness direction a secondary thermally insulating barrier arranged between the primary thermally insulating barrier and the load-bearing wall, a secondary sealing membrane arranged between the secondary thermally insulating barrier and the primary thermally insulating barrier, a first portion of the primary thermally insulating barrier being arranged on the secondary sealing membrane and a second portion arranged against the load-bearing wall, said end portion of the primary thermally insulating barrier being located in the second portion of the primary thermally insulating barrier,the first part and the second part of the primary thermally insulating barrier being adjacent to each other at an end portion of the secondary thermally insulating barrier.,

[0031] According to one embodiment, the invention also provides a welding assembly according to claim 16, the assembly comprising a welding support and an automatic welding machine, wherein the welding support comprises a planar fixing surface and a planar support surface perpendicular to the fixing surface, the support surface carrying a guide means, for example a guide rail, extending in one direction, the welding machine comprising a movement system cooperating with the guide means and being configured to move the welding machine in the direction of the guide rail, the welding machine also comprising a hook bar fixed to the movement system and comprising a first end remote from the movement system and a second end remote from the movement system,the first end and the second end being located on either side of the displacement system in a direction parallel to the support surface and perpendicular to the direction of the guide means, a welding torch being fixed to the first end, and a counterweight being fixed to the second end to cooperate with the support surface at a distance from the guide means.,

[0032] According to one embodiment, the attachment surface of the welding support is a first attachment surface and the welding support further comprises a second attachment surface perpendicular to the first attachment surface and parallel to the support surface. Brève description des figures

[0033] The invention will be better understood, and other objects, details, characteristics and advantages thereof will appear more clearly during the following description of several particular embodiments of the invention, given solely for illustrative and non-limiting purposes, with reference to the accompanying drawings. [ Fig.1 ] There [ Fig.1 ] is a cutaway schematic representation of a land-based storage facility. Fig.2 ] There [ Fig.2 ] is an exploded view of detail II of the [ Fig.1 ]. [ Fig.3 ] There [ Fig.3 ] is an exploded view of detail III of the [ Fig.1 ]. [ Fig.4 ] There [ Fig.4 ] is a schematic side view of a secondary membrane closure zone according to a first embodiment, during a first welding operation. Fig.5 ] There [ Fig.5 ] is a schematic side view of a secondary membrane closure zone according to a second embodiment, during a first welding operation. [ Fig.6 ] There [ Fig.6 ] is a schematic side view of a primary membrane closure zone according to the first embodiment, during a first welding operation. Fig.7 ] There [ Fig.7 ] is a schematic side view of a secondary membrane closure area, during a second welding operation. Description des modes de réalisation

[0034] The invention will be described below in connection with a liquefied gas storage facility which bears the reference 1 in the description which follows. The facility 1 is capable of storing a liquefied gas, in particular liquefied natural gas (LNG) at a temperature of approximately -162°C and at atmospheric pressure or other liquefied gases. The facility 1 may also be capable of storing other types of liquid, in particular at ambient temperature.

[0035] The installation 1 mainly comprises a supporting structure 10 and a sealed and thermally insulating tank 20 installed in the internal space of the supporting structure 10.

[0036] The supporting structure 10 comprises a bottom supporting wall 11 and a vertical supporting wall 12.

[0037] The installation 1 may be designed to be located on land. The bottom load-bearing wall 11 is then typically horizontal, i.e. located in a plane perpendicular to the direction of the acceleration of gravity, within dimensional tolerances. The bottom load-bearing wall 11 may be located at ground level or possibly below ground level. The supporting structure 10 is, for example, made of concrete.

[0038] Alternatively, the installation 1 may be intended to be installed on board a floating structure, such as a ship. In this case, the supporting structure 10 is a portion of a double hull belonging to the floating structure. The bottom supporting wall 11 may optionally be non-horizontal, and even be located in a plane parallel to the direction of the acceleration of gravity within dimensional tolerances when the floating structure is at rest.

[0039] The remainder of the description will focus more particularly on a land-based storage installation 1. The outline of the bottom load-bearing wall 11 is designed to have the shape of a regular polygon with N sides, where N is an integer greater than or equal to 3. Preferably, N is even. An installation 1 where N is equal to 8 or 56 is more particularly interesting.

[0040] As can be seen better on the [ Fig.1 ], the vertical load-bearing wall 12 forms a polygonal cylindrical surface, with the polygonal contour of the bottom load-bearing wall 11 as its directrix. The vertical load-bearing wall 12 extends in a vertical direction, that is to say in a direction perpendicular to the plane of the bottom load-bearing wall 11 within dimensional tolerances.

[0041] At the end of the vertical load-bearing wall 12 opposite the bottom load-bearing wall 11, the load-bearing structure 10 comprises a cover load-bearing wall 13 closing the internal space delimited by the bottom load-bearing wall 11 and the vertical load-bearing wall 12. This cover load-bearing wall can support various equipment usable for conveying liquefied gas from or to this internal space.

[0042] The sealed and thermally insulating tank 20 is installed in the internal space of the supporting structure 10. The tank 20 comprises a bottom wall 21 arranged on the bottom supporting wall 11, and a vertical wall 22 arranged on the vertical supporting wall 12.

[0043] The bottom wall 21 and the vertical wall 22 comprise, going from the supporting structure towards the interior space of the tank 20, a secondary thermally insulating barrier 23, a secondary sealed membrane 24, a primary thermally insulating barrier 25, and a primary sealed membrane 26 intended to be in contact with the liquefied gas contained in the tank 20.

[0044] The bottom wall 21 and the vertical wall 22 can be made using modular elements. In the embodiment described here, these modular elements correspond to the GST ® technology marketed by the applicant, for example. Reference may also be made to document US 6,035,795 for the description of certain modular elements.

[0045] Also by way of example, such membrane tanks are described in particular in patent applications WO2019239048, WO14057221, FR2691520 and FR2877638.

[0046] Two particular zones of the vertical wall 22 will be described more particularly below, namely the closure zone of the secondary sealing membrane 24 and the closure zone of the primary sealing membrane 26. On the vertical wall 22 of the terrestrial storage installation 1 shown in [ Fig.1 ], the secondary waterproofing membrane 24 and the secondary thermally insulating barrier 23 are intended to extend only from a lower end of the vertical wall up to a predetermined height of the vertical wall 22 extending at a distance from the upper end of the vertical wall. This predetermined height is for example of the order of 5m.

[0047] Thus, the secondary sealing membrane 24 is closed at the predetermined height so as to be connected to the vertical load-bearing wall 12. After this predetermined height of the vertical wall 22 and up to the vicinity of the cover load-bearing wall 13, the vertical wall 22 only comprises the primary thermally insulating barrier 25 which is directly fixed to the vertical load-bearing wall 12 and the primary sealing membrane 26. Therefore, in the vicinity of the cover load-bearing wall 13, the primary sealing membrane is also provided to be closed so as to connect it to the vertical load-bearing wall 12.

[0048] There [ Fig.2 ] more particularly represents the closing zone of the secondary sealing membrane 24 while the [ Fig.3 ] more particularly represents the closing zone of the primary sealing membrane 26.

[0049] As partially represented in [ Fig.2 ], the secondary thermally insulating barrier 23 comprises a plurality of secondary insulating blocks 231 juxtaposed with each other and an end secondary insulating block 232 located at one end of the secondary thermally insulating barrier 23 formed at the predetermined height of the vertical wall 22. As shown in the [ Fig.2 ], in this embodiment, the secondary insulating blocks 231 are pre-assembled with a portion of the secondary sealing membrane 24 as well as one or more primary insulating blocks 251. These portions of the secondary sealing membrane 24 are then connected to each other using flexible strips (not shown).

[0050] The closure of the secondary sealing membrane 24 is carried out at the level of the secondary end insulating block 232. The closure is carried out using a metal connecting angle 30 comprising a first wing 31 which is welded to a part of the vertical load-bearing wall 12 and a second wing 32 connected to the secondary sealing membrane 24. The first wing 31 and the second wing 32, as shown in [ Fig.2 ], forms a right-angled part which is positioned at the level of an edge of the secondary end insulating block 232. In the first embodiment shown in particular in figures 2 à 4 , said part of the vertical load-bearing wall 12 is an anchoring plate 14 projecting from the vertical load-bearing wall 12 in the thickness direction of the vertical wall 22 and extending parallel to a lateral edge of the secondary end insulating block 232.

[0051] A metallic secondary closure plate 27 is fixed to a surface of the secondary end insulating block 232, opposite the vertical load-bearing wall 12, using fixing devices (not shown) passing through orifices 29 provided in the secondary closure plate 27. One end of the secondary sealing membrane 24 is fixed to the metallic secondary closure plate 27, by gluing or welding depending on the type of sealing membrane used.

[0052] The second wing 32 of the connecting angle 30 is thus welded to the secondary closing plate 27 so as to tightly connect the connecting angle 30 and the secondary sealing membrane 24.

[0053] The welding of the first wing 31 to the anchor plate 14 is carried out using a first weld bead 33, the welding step of which is explained below in connection with the [ Fig.4 ]. The welding of the second wing 32 to the secondary closing plate 27 is carried out using a second weld bead 34, the welding step of which is explained below in connection with the [ Fig.7 ].

[0054] As partially represented in [ Fig.3 ], the primary thermally insulating barrier 25 comprises a plurality of primary insulating blocks juxtaposed to each other and an end primary insulating block 252 located at one end of the primary thermally insulating barrier 25 formed near the cover-bearing wall 13.

[0055] In a manner similar to the secondary sealing membrane 24, the primary sealing membrane (not shown) is closed at the primary end insulating block 252. The closure is also achieved using a metal connecting angle 30 comprising a first wing 31 which is welded to an anchoring plate 14 of the vertical load-bearing wall 12 and a second wing 32 welded to a primary metal closing plate 28. The primary closing plate 28 is fixed to a surface of the primary end insulating block 252, opposite the vertical load-bearing wall 12.

[0056] As shown in [ Fig.3 ] but which is also valid at the level of the secondary sealing membrane 24, connecting angles 30 are welded to each other so as to form a continuous closure on the vertical wall 22 all around the bottom wall 21.

[0057] THE figures 4 And 5present the step of producing the first weld bead 33, between the first wing 31 and the part of the vertical load-bearing wall 12 according to two embodiments, so as to produce the closure of the secondary sealing membrane 24.

[0058] To carry out the welding, a welding support 50 and an automatic welding machine 40 are used. The welding support 50 comprises a first planar fixing surface 51, a second planar fixing surface 52 which is connected perpendicularly to the first fixing surface 51, and a planar support surface 53 which is connected perpendicularly to the first fixing surface 51 so as to be parallel to the second fixing surface 52. According to the first embodiment shown in [ Fig.4 ], the support surface 53 is equipped with a guide rail 54 extending parallel to the anchoring plate 14.

[0059] The automatic welding machine 40 comprises a movement system 41 cooperating with the guide rail 54, which is configured to move the welding machine 40 in a feed parallel to the direction of the guide rail 54. The welding machine 40 also comprises a hook bar 42 fixed to the movement system 41 and comprising a first end remote from the movement system 41 and a second end remote from the placement system 41. The first end and the second end are located on either side of the movement system 41. A welding torch 43 is fixed to the first end while a counterweight 44 is fixed to the second end of the hook bar 42. The second end of the hook bar 42 is also equipped with a wheel 45 provided with a spring so that the wheel 45 is constantly pressed against the support surface 53 of the welding support 50.

[0060] When producing the first weld bead 33, the first fixing surface 51 of the welding support 50 is fixed on the secondary end insulating block 232 so that the support surface 53 is perpendicular to the vertical load-bearing wall 12. As shown in figures 4 And 5 , one or more anchoring devices 60 fix the first fixing surface 51 to the secondary end insulating block 232 by passing through the orifices 29 of the secondary closing plate 27. Thus, the welding machine 40 moves on the support surface 53 so that the welding torch 43 is located close to the area to be welded between the first wing 31 and the anchoring plate 14.

[0061] The second embodiment illustrated in [ Fig.5 ] differs from the embodiment of the [ Fig.4 ] in that the first wing 31 is not welded to an anchor plate but to a metal portion 15 fixed parallel to the vertical load-bearing wall 12. In the case where the vertical load-bearing wall 12 is metallic, this metal portion 15 is simply a portion of the vertical load-bearing wall 12. Thus, in this embodiment, the first wing 31 has a folded end, an end distant from the second wing 32, so as to extend parallel to the metal portion 15. The folded end and the metal portion 15 are thus welded to each other by the first weld bead 33.

[0062] This welding step is carried out in a similar manner to the primary waterproofing membrane, whether for the first embodiment, represented in [ Fig.6 ], or the second embodiment (not shown). Indeed, the welding machine 40 is also used to weld a first wing 31 of a connecting angle 30 to an anchoring plate 14 using a first weld bead 33, at the primary end insulating block 252 of the primary thermally insulating barrier 25. The welding support 50 is also fixed at the first fixing surface 51 to a surface of the primary end insulating block 252, opposite the vertical load-bearing wall 12, using one or more anchoring devices 60. The second wing 32 is welded to a primary closure plate 28. One end of the primary sealing membrane is then welded to the second wing 32, or alternatively to the primary closure plate 28.

[0063] There [ Fig.7 ] presents the step of producing the second weld bead 34 between the second wing 32 and the secondary closing plate 27, so as to produce the closing of the secondary sealing membrane 24.

[0064] When producing the second weld bead 34, the second fixing surface 52 of the welding support 50 is fixed to the vertical load-bearing wall 12 so that the support surface 53 is parallel to the surface of the secondary end insulating block 232, opposite the vertical load-bearing wall 12. As shown in [ Fig.7], one or more anchoring devices 60 fix the second fixing surface 52 to the vertical load-bearing wall 12 by passing through orifices 16 provided in the vertical load-bearing wall 12. In addition, the welding support 50 may comprise a fixing leg 55 fixed on the one hand to the support surface 53 and on the other hand to the vertical load-bearing wall 12 at other orifices 16 in order to increase the number of anchoring points. Thus, the welding machine 40 moves on the support surface 53 so that the welding torch 43 is located close to the area to be welded between the second wing 32 and the secondary closure plate 27.

Claims

1. Method of closing a sealing membrane (24, 26) for a sealed tank, said tank being in particular thermally insulative, the method including the following steps: - furnishing a tank wall (22) fixed to a support wall (12), the tank wall including in a direction of thickness a thermally-insulating barrier (23, 25) and a sealing membrane (24, 26) fixed to the thermally-insulating barrier (23, 25), the thermally-insulating barrier (23, 25) including an edge portion (232, 252) situated at one edge of the thermally-insulating barrier (23, 25) in a first direction, the method being characterised in that: - fixing a metal connecting angle-iron (30) at the level of the edge portion (232, 252), the metal connecting angle-iron (30) including a first flange (31) and a second flange (32) connected to the first flange (31), by welding the first flange (31) by means of a weld bead (33, 34) to a metal part (14, 15) on the support wall, and by connecting the second flange (32) to the sealing membrane (24, 26), in which the step of welding the first flange is carried out using an automatic welding machine (40) moving on a welding support (50), the welding support (50) including a fixing surface (51) and a support surface (53) perpendicular to the fixing surface (51), the support surface (53) including a guide means (54), in particular a guide rail, extending in a second direction perpendicular to the first direction and to the direction of thickness, the welding machine (40) including a displacement system (41) cooperating with the guide means (54) and configured to move the welding machine (40) in a forward movement parallel to the second direction, the welding machine (40) also including a welding torch (43), and in which during welding of the first flange the fixing surface (51) of the welding support (50) is fixed to the edge portion (232, 252) of the thermally-insulating barrier so that the support surface (53) is perpendicular to the first direction.

2. Closing method according to claim 1, in which the welding machine also includes an attachment bar (42) fixed to the displacement system (41) and having a first end remote from the displacement system (41) and a second end remote from the displacement system (41), the first end and the second end being situated on respective opposite sides of the displacement system in the direction of thickness, the welding torch (43) being fixed to the first end and a counterweight (44) being fixed to the second end.

3. Closing method according to claim 1 or claim 2, in which the first flange (31) is formed in a plane perpendicular to the first direction and the second flange (32) is formed in a plane perpendicular to the direction of thickness.

4. Closing method according to any one of claims 1 to 3, in which the metal part on the support wall (12) is an anchor flat (14) projecting from the support wall in the direction of thickness and extending in the second direction, the edge portion (232, 252) of the thermally-insulating barrier being adjacent to the anchor flat.

5. Closing method according to any one of claims 1 to 3, in which the metal part on the support wall is a metal portion (15) of the support wall (12).

6. Closing method according to any one of claims 1 to 5, in which the thermally-insulating barrier (23, 25) includes a plurality of insulating blocks (231) juxtaposed to one another and the edge portion of the thermally-insulating barrier includes an edge insulating block (232, 252).

7. Closing method according to any one of claims 1 to 6, in which the weld bead is a first weld bead (33), a metal closing plate (27, 28) being fixed to at least a portion of a surface of the edge portion (232, 252) of the thermally-insulating barrier opposite the support wall (12), an edge of the sealing membrane (24, 26) being fixed to the metal closing plate (27, 28), and in which during the step of fixing the connecting angle-iron (30) the second flange (32) is welded by means of a second weld bead (34) to the metal closing plate (27, 28).

8. Closing method according to claim 7, in which the closing plate (27, 28) includes fixing orifices (29), the closing plate (27, 28) being fixed to the edge portion (232, 252) of the thermally-insulating barrier by means of an anchoring device coming to be inserted in the fixing orifices, and in which during the production of the first weld bead (33) the fixing surface (51) of the welding support (50) is fixed by means of anchor devices (60) that come to be inserted in the fixing orifices (29) left free by the devices anchoring the closing plate (27, 28).

9. Closing method according to claim 7 or claim 8, in which the fixing surface of the welding support (50) is a first fixing surface (51) and the welding support (50) includes a second fixing surface (52) perpendicular to the first fixing surface and parallel to the support surface (53), and in which during the production of the second weld bead (34) the second fixing surface (52) of the welding support (50) is fixed against the support wall (12) so that the support surface (53) is parallel to, preferably coplanar with, the sealing membrane (24, 26), the second weld bead being produced by means of said automatic welding machine (40) moving on the guide means of the welding support (50), said welding support (50) being used to produce both the first weld bead and the second weld bead.

10. Closing method according to claim 9 in combination with claim 6, in which the support wall (12) includes fixing orifices (16), the insulating blocks (231) being anchored to the support wall by means of anchor devices that come to be inserted in the fixing orifices (16), and in which during the production of the second weld bead (34) the second fixing surface (52) of the welding support (50) is fixed by means of anchor devices (60) that come to be inserted in the fixing orifices (16) of the support wall (12) left free by the devices anchoring the insulating blocks (231).

11. Closing method according to any one of claims 1 to 10, in which the tank wall is inclined relative to the horizontal and the tank wall is preferably a vertical wall (22).

12. Closing method according to any one of claims 1 to 11, in which the welding torch (43) is an electric arc welding torch, advantageously with no addition of material and with a flow of inert gas, such as for example a tungsten electrode torch with flow of argon.

13. Closing method according to any one of claims 1 to 12, in which the thermally-insulating barrier is a secondary thermally-insulating barrier (23) and the sealing membrane is a secondary sealing membrane (24) and in which the tank wall (22) includes in the direction of thickness a primary thermally-insulating barrier (25) disposed at least partly on the secondary sealing membrane and a primary sealing membrane fixed to the primary thermally-insulating barrier (25) and intended to be in contact with a liquefied gas.

14. Closing method according to claim 13, in which the secondary sealing membrane (24) is made of a composite material including a sheet of aluminium sandwiched between two glass fibre sheets.

15. Closing method according to any one of claims 1 to 12, in which the thermally-insulating barrier is a primary thermally-insulating barrier (25) and the sealing membrane is a primary sealing membrane and in which the tank wall (22) includes in the direction of thickness a secondary thermally-insulating barrier (23) arranged between the primary thermally-insulating barrier and the support wall and a secondary sealing membrane (24) arranged between the secondary thermally-insulating barrier and the primary thermally-insulating barrier, a first part of the primary thermally-insulating barrier (25) being disposed on the secondary sealing membrane (24) and a second part being disposed against the support wall (12), said edge portion (252) of the primary thermally-insulating barrier (25) being situated in the second part of the primary thermally-insulating barrier (25), the first part and the second part of the primary thermally-insulating barrier (25) being adjacent to one another in line with an edge portion (232) of the secondary thermally-insulating barrier (23).

16. Welding system including a welding support (50) and an automatic welding machine (40), in which the welding support (50) includes a plane fixing surface (51) and a plane support surface (53) perpendicular to the fixing surface, the support surface (53) carrying a guide means (54) extending in a direction, the welding machine (40) including a displacement system (41) cooperating with the guide means (54) and configured to move the welding machine (40) in the direction of the guide means (54), the welding machine (40) also including an attachment bar (42) fixed to the displacement system (41) and having a first end remote from the displacement system (41) and a second end remote from the displacement system, the first end and the second end being situated on respective opposite sides of the displacement system (41) in a direction parallel to the support surface and perpendicular to the direction of the guide means, a welding torch (43) being fixed to the first end and a counterweight (44) being fixed to the second end to cooperate with the support surface at a distance from the guide means.

17. System according to claim 16, in which the fixing surface of the welding support (50) is a first fixing surface (51) and the welding support (50) further includes a second fixing surface (52) perpendicular to the first fixing surface and parallel to the support surface (53).