Abstract:
The disclosure relates to a corner structure which is suitable for a sealed and thermally insulating tank for storing a fluid comprising a secondary thermal insulation barrier which is retained on a carrier structure, a secondary sealing membrane, a primary thermal insulation barrier and a primary sealing membrane which is intended to be in contact with the fluid contained in the tank, the corner structure comprising: a first panel and a second panel forming a corner of the secondary thermal insulation barrier, and comprising an external face intended to move opposite the carrier structure and an internal face; a corner arrangement of the secondary sealing membrane, which arrangement is fixed to the first and second panels; a first insulating block and a second insulating block of a primary thermal insulation barrier which are fixed to the first and second panels, respectively, and which rest against the corner arrangement of the secondary sealing membrane; and a corner of a primary sealing barrier comprising a first wing and a second wing which are fixed to the first and second insulating blocks, respectively.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is the National Stage of, and therefore claims the benefit of, International Application No. PCT/FR2014/050793 filed on Apr. 3, 2014, entitled “CORNER STRUCTURE OF A SEALED AND THERMALLY INSULATING TANK FOR STORING A FLUID,” which was published in French under International Publication Number WO 2014/167214 on Oct. 16, 2014. International Application No. PCT/FR2014/050793 claims priority to FR Application No. 1353322 filed on Apr. 12, 2013. Both of the above applications are commonly assigned with this National Stage application and are incorporated herein by reference in their entirety. 
     TECHNICAL FIELD 
     The disclosure relates to the field of sealed and thermally insulating tanks having membranes for storing and/or transporting a fluid, such as a cryogenic fluid. 
     The disclosure more particularly relates to a corner structure of such a sealed and thermally insulating tank. 
     BACKGROUND 
     Document FR 2 691 520 describes a sealed and thermally insulating tank successively having, in the direction of the thickness, from the inner side to the outer side of the tank, a primary sealing membrane, in contact with the fluid contained in the tank, a primary thermal insulation barrier, a secondary sealing membrane, a secondary thermal insulation barrier and a carrier structure which is constituted by metal sheets which form the hull or the double hull of a merchant tanker, such as a methane tanker. 
     The corner zones of the tank are produced from preassembled corner structures, in the form of a dihedron, which are illustrated in FIG. 3 of the document FR 2 691 520. Such a preassembled corner structure comprises two beveled insulating plates which form the secondary thermal insulation barrier, a flexible membrane resting on the insulating plates of the secondary thermal insulation barrier and constituting the secondary sealing barrier, a plurality of insulating blocks of the primary thermal insulation barrier which are adhesively bonded to the secondary sealing membrane and metal corners of a primary sealing membrane which are fixed to the insulating blocks of the primary thermal insulation barrier. 
     The adhesive bonding of the insulating blocks of the primary thermal insulation barrier to the secondary sealing barrier is not completely satisfactory. In particular, the bonding operations of the insulating blocks are complex to carry out. 
     Given this complexity, the adhesive bonding of the insulating blocks of the primary thermal insulation barrier to the secondary sealing membrane is brought about in the workshop and the corner structures are integrally preassembled. However, such preassembled corner structures are heavy, making the transport and handling thereof to and at the installation site of the tank difficult. 
     SUMMARY 
     A notion on which the disclosure is based is to propose a corner structure which is easy to assemble. 
     According to an embodiment, the disclosure provides for a sealed and thermally insulating tank for storing a fluid comprising a secondary thermal insulation barrier which is retained on a carrier structure, a secondary sealing membrane, a primary thermal insulation barrier and a primary sealing membrane which is intended to be in contact with the fluid contained in the tank, the tank comprising a corner structure comprising: 
     a first panel and a second panel forming a corner of the secondary thermal insulation barrier and comprising an external face opposite the carrier structure and an internal face; 
     a corner arrangement of the secondary sealing membrane, which arrangement is fixed to the first and second panels; 
     a first insulating block and a second insulating block of primary thermal insulation barrier which are fixed to the first and second panels, respectively, and which rest against the corner arrangement of the secondary sealing membrane; and 
     a corner of a primary sealing barrier comprising a first wing and a second wing which are fixed to the first and second insulating blocks, respectively; wherein: 
     the first and second panels each comprise a metal plate which is fixed to the internal face thereof and which carries a fixing member for an insulating block; and 
     the corner arrangement of the secondary sealing membrane is of metal, has openings for the introduction of the fixing members of the insulating blocks and is welded, at the periphery of the openings, to the metal plates which carry the fixing members so as to ensure the sealing of the secondary sealing membrane. 
     Therefore, such a corner structure does not require any adhesive bonding operation for the insulating blocks of the primary thermal insulation membrane. In this manner, the fixing of insulating blocks to the corner structure can be carried out more easily in situ. 
     Furthermore, the mechanical securing of the insulating blocks to the corner structure ensures greater mechanical strength than securing by adhesive bonding. 
     According to embodiments, such a tank may comprise one or more of the following features: the fixing members of the insulating blocks are threaded pins which cooperate with nuts, the insulating blocks each comprising an opening for the introduction of a pin and a recess which communicates with the opening for the introduction of a pin and which has an abutment surface for a nut bounding the opening for the introduction of a pin; the first and second insulating blocks comprise a lateral edge adjacent to the tank corner, a lateral edge opposite the tank corner, and an internal face which cooperates with the corner of a primary sealing barrier and in which the recesses open at the lateral edge opposite the tank corner and/or in an internal face portion which is contiguous with the lateral edge opposite the tank corner and which is not covered by the corner of a primary sealing barrier; the corner structure comprises insulating elements for closing the recesses; the recesses are formed by indentations comprising a base which forms the abutment surface of a nut and which opens at a portion of the internal face of the insulating blocks extending, in the direction toward the lateral edge opposite the tank corner of the insulating blocks, beyond an edge of the corner of a primary sealing barrier; the corner has edges which are provided with cut-outs which are arranged opposite the indentations which open at the internal face of the first and second insulating blocks; the recess is formed by a recess of the lateral edge opposite the tank corner, providing a lug which carries the abutment surface of a nut; the corner arrangement of the secondary sealing membrane comprises a first metal sheet which is fixed to the first panel, a second metal sheet which is fixed to the second panel and a metal corner which is welded to the first and second metal sheets; the wings of the corner of a primary sealing barrier each comprise an external face which is provided with a pin, projecting outward, for fixing the corner to the first and second insulating blocks; the corner structure comprises a plurality of first and second insulating blocks which are distributed over the first and second panels, respectively, and a plurality of corners of a primary sealing barrier which are each fixed to a first insulating block and a second insulating block; the tank comprises a planar wall, at the end of which the corner structure is arranged, the secondary sealing membrane of the planar wall being welded to the corner arrangement of the secondary sealing membrane and the primary sealing membrane of the planar wall being welded to a wing of the corner of a primary sealing barrier; the secondary sealing membrane of the planar wall comprises a plurality of metal plates comprising undulations extending in two perpendicular directions; the secondary thermal insulation barrier of the planar wall comprises a plurality of heat-insulating panels, between which gaps are provided, the undulations of the metal plates of the secondary sealing membrane projecting toward the outer side of the tank and being inserted in the gaps. 
     Such a tank may be part of a ground-based storage installation, for example, in order to store LNG or to be installed in a floating structure, at the coast or in deep water, in particular a methane tanker, a floating storage and regasification unit (FSRU), an offshore floating production and storage unit (FPSO) and the like. 
     According to an embodiment, the disclosure relates to an assembly method for a corner structure as mentioned above, comprising: the assembly of a plurality of preassembled modules each comprising a corner of a primary sealing barrier and a first insulating block and a second insulating block, the assembly step comprising, for each preassembled module, the fixing of a corner of a primary sealing barrier to a first insulating block and a second insulating block; and the fixing of the plurality of preassembled modules to the first and second panels forming a corner of the secondary thermal insulation membrane. 
     According to an embodiment, a first plurality of preassembled modules are fixed to the first and second panels in the workshop and a second plurality of preassembled modules are fixed to the first and second panels in situ in the tank. Thus, the transport and handling of the corner structure are made easier. 
     According to an embodiment, a tanker for transporting a fluid comprises a double hull and an above-mentioned tank, in which the double hull forms the external carrier structure of the tank. 
     According to an embodiment, the disclosure also provides for a method for loading or unloading such a tanker, wherein a fluid is conveyed through the insulated channels from or toward a floating or ground-based storage installation toward or from the tank of the tanker. 
     According to an embodiment, the disclosure also provides for a transfer system for a fluid, the system comprising the above-mentioned tanker, insulated channels which are arranged so as to connect the tank which is installed in the hull of the tanker to a floating or ground-based storage installation and a pump for driving a flow of fluid through the insulated channels from or toward the floating or ground-based storage installation toward or from the tank of the tanker. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will be better understood and other objectives, details, features and advantages thereof will be appreciated more clearly from the following description of several specific embodiments of the disclosure, given purely by way of non-limiting illustration, with reference to the appended drawings, in which: 
         FIGS. 1, 3, 5, 7 and 9  are perspective views illustrating the successive assembly steps for a corner structure of a sealed and thermally insulating tank. 
         FIG. 2  is a detailed view of  FIG. 1 , illustrating a metal plate, which is fixed to the internal face of one of the panels which forms the corner of the secondary thermal insulation barrier and which carries fixing pins for insulating blocks of the primary thermal insulation barrier. 
         FIG. 4  is a detailed view of  FIG. 3 , illustrating the introduction of pins for fixing insulating blocks of the primary thermal insulation barrier, through a metal sheet of the secondary sealing membrane. 
         FIG. 6  is a detailed view of  FIG. 5 , illustrating a corner arrangement of the secondary sealing membrane. 
         FIG. 8  is a detailed view of  FIG. 7 , in which, for a better understanding, two insulating blocks and a corner of the primary sealing membrane are illustrated in a transparent manner so as to visualize the fixing members of the corner with respect to the insulating blocks and the fixing members of the insulating blocks with respect to the secondary thermal insulation barrier. 
         FIG. 10  is a detailed view of  FIG. 9 , more specifically illustrating insulating elements for filling a recess which is formed in an insulating block or a joint between two adjacent insulating blocks, before the positioning of the insulating elements. 
         FIG. 11  is a perspective view of a corner structure according to a second embodiment. 
         FIG. 12  is a detailed view of  FIG. 11 . 
         FIG. 13  is a perspective view of a corner structure according to a third embodiment. 
         FIG. 14  is a perspective cut-away view of the elements of a wall of a sealed and thermally insulating tank. 
         FIG. 15  is a cross-section of a wall of a sealed and thermally insulating tank. 
         FIG. 16  is a cut-away schematic view of a tank of a methane tanker and a loading/unloading terminal of this tank. 
     
    
    
     DETAILED DESCRIPTION 
     In conventional manner, the terms “external” and “internal” are used to define the relative position of one element in relation to another, with reference to the inner side and outer side of the tank. 
     The sealed and thermally insulating tank comprises, from the outer side toward the inner side of the tank, a carrier structure, a secondary thermally insulating barrier, a secondary sealing membrane, a primary thermally insulating barrier and a primary sealing membrane which is intended to be in contact with the cryogenic fluid contained in the tank. 
     The carrier structure may particularly be a self-supporting metal sheet or, more generally, any type of rigid partition which has suitable mechanical properties. The carrier structure may in particular be formed by the hull or the double hull of a tanker. The carrier structure comprises a plurality of walls defining the general form of the tank. 
       FIG. 1  illustrates the secondary thermal insulation barrier, having a corner structure which is intended to be arranged at the intersection between two walls of the carrier structure. The secondary thermal insulation barrier comprises two heat-insulating panels  1 ,  2 . The panels  1 ,  2  have an external face which is intended to be fixed against the walls of the carrier structure. The panels  1 ,  2  further have a cross-section in the form of a rectangular trapezium and are connected to each other, for example, by adhesive bonding, via the chamfered lateral edge  3 ,  4  thereof. The panels  1 ,  2  thereby form a corner of the secondary thermal insulation barrier. 
     In the embodiment illustrated, the heat-insulating panels  1 ,  2  comprise a layer of insulating polymer foam which is engaged in a sandwich between two internal and external rigid plates, which are adhesively bonded to the foam layer. The internal and external rigid plates are, for example, of plywood. The polymer foam may in particular be a high-density polyurethane foam, which may optionally be reinforced with glass fibers. 
     The panels  1 ,  2  have cylindrical indentations  5  which open at the internal face thereof and which are intended to receive the end of a threaded pin, which is welded to the carrier structure, in order to ensure securing of the panels  1 ,  2 . The cylindrical indentations  5  communicate with openings for the introduction of the pins (not illustrated) which open at the external face of the panels  1 ,  2 . The cylindrical indentations  5  have a diameter greater than that of the openings for the introduction of the pins so that the bases of the cylindrical indentations  5  define an abutment surface which is intended to cooperate with a nut which is screwed to the threaded pin. When the fixing of the panels  1 ,  2  to the carrier structure have been carried out, plugs of an insulating material (not illustrated) can be introduced into the cylindrical indentations  5  so as to ensure continuity of the secondary thermal insulation barrier. 
     In addition to the securing of the panels  1 ,  2  by pins which are welded to the carrier structure, beads of polymerizable resin may be arranged between the carrier structure and the external face of the panels  1 ,  2 . 
     The panels  1 ,  2  are provided with a plurality of metal plates  6 , which are fixed to the internal rigid plate thereof by screws, rivets or staples, for example. The metal plates  6  carry threaded pins  7  which project toward the inner side of the tank, and which are intended to ensure the fixing of the primary thermal insulation barrier to the panels  1 ,  2 . 
       FIGS. 3 to 6  illustrate the corner arrangement of the secondary sealing membrane. The corner arrangement comprises two metal sheets  8 ,  9  which are each fixed to a panel  1 ,  2  by screws, rivets or staples, for example. The metal sheets  8 ,  9  are provided with openings  11  for the introduction of the pins  7 . In order to ensure the sealing of the secondary sealing membrane, the metal sheets  8 ,  9  are welded, at the periphery of the openings  11 , to the metal plates  6 . 
     In an embodiment, the welding of the metal sheets  8 ,  9  to the plates  6  is carried out by an orbital welding process. The orbital welding equipment is advantageously capable of being secured to the pins  7  in such a manner that the welding can be carried out in an automated manner. 
     The corner arrangement of the secondary sealing membrane also comprises a metal corner  10  which is illustrated in  FIGS. 5 and 6 . The metal corner  10  is lap-welded to the metal sheets  8 ,  9  so as to ensure the sealing of the secondary sealing membrane in the corner zone. The welding of the metal corner  10  to the metal plates  8 ,  9  is brought about by a piece of continuous welding equipment. Such welding equipment is advantageously capable of being secured to the pins  7 . 
     In the embodiment illustrated, the openings  11  for the introduction of the pins  7  are bores which are provided in the metal sheets  8 ,  9 . However, it may be envisaged to produce the openings for the introduction of the pins by any other means. In particular, such openings may be formed by means of cut-outs which are formed in an edge of the corner and/or in the edge of the metal sheets adjacent to the corner. In this manner, it is not necessary to perforate the corner  10  or the metal sheets  8 ,  9  in order to allow the pins  7  to pass. In a similar manner, it is also possible to provide for a plurality of metal sheets which rest on each of the panels  1  and  2  and to form cut-outs in the adjacent edges of the metal sheets so as to form the introduction openings for the pins  7 . 
     Subsequently, as illustrated in  FIGS. 7 and 8 , insulating blocks  13 ,  14  of the primary thermal insulation barrier and metal corners  15  of the primary sealing barrier are fixed to the panels  1 ,  2 . 
     In an advantageous embodiment, the insulating blocks  13 ,  14  and the metal corners  15  are assembled beforehand in the form of modules  12   a ,  12   b ,  12   c ,  12   d . Each preassembled module  12   a ,  12   b ,  12   c ,  12   d  comprises two insulating blocks  13 ,  14  of a primary thermal insulation barrier and a corner  15  which is fixed to the two insulating blocks  13 ,  14 . 
     The insulating blocks  13 ,  14  are of generally rectangular parallelepiped form. They comprise an internal face on which the corner  15  rests and an external face which rests against one of the metal sheets  8 ,  9 . The insulating blocks  13  and  14  are fixed to the panels  1  and  2 , respectively. The insulating blocks  13 ,  14  may be integrally produced from plywood or have a composite structure similar to that of the panels  1 ,  2 , that is to say, comprising a layer of insulating polymer foam engaged in a sandwich-like manner between two internal and external rigid plates which are adhesively bonded to the layer of foam. 
     The corners  15  are metal corners, for example, produced from stainless steel. The corners  15  have two wings  15   a  and  15   b , which are perpendicular in the embodiment illustrated, resting against the internal face of the insulating blocks  13  and  14 . The wings  15   a ,  15   b  have pins  16  which are for fixing to the insulating blocks  13 ,  14 , are illustrated in  FIG. 8 , welded to the external face of the wings  15   a ,  15   b  and project toward the inner side of the tank. The insulating blocks comprise openings  17  which are for the introduction of the pins  16  and which are formed at the internal face thereof. The openings  17  for the introduction of the pins communicate with cylindrical indentations  18  which open at the external face of the insulating blocks  13 ,  14 . Nuts which are screwed to the pins  16  press against the base of the cylindrical indentations  18  and thus bring about the connection of the corner  15  to the insulating blocks  13 ,  14 . In the  FIGS. 7 to 12 , the wings  15   a ,  15   b  also have pins  19  which are welded to the internal face thereof. Such pins  19  allow a piece of welding equipment to be secured during the welding of the primary sealing membrane elements to the corners  15 . 
     Furthermore, a corner connector  46  of insulating material, such as a polymer foam, is arranged between the adjacent edges at the tank corner of two insulating blocks  13 ,  14  and thereby ensures continuity of the thermal insulation in the region of the corner of the tank. 
     In order to ensure the fixing of the insulating blocks to the pins  7  which are carried by the panels  1 ,  2 , the insulating blocks  13 ,  14  are provided with openings  20  for the introduction of the pins  7 , which openings are provided in the internal face thereof. In the embodiment illustrated in  FIGS. 7 to 10 , the openings  20  for the introduction of the pins  7  communicate with cylindrical indentations  21  which open at the internal face of the insulating blocks  13 ,  14 . The bases of the cylindrical indentations  21  define abutment surfaces for nuts which cooperate with the threaded ends of the pins  7 . 
     In order to ensure the fixing of the insulating blocks  13 ,  14  to the pins  7 , whilst corners  15  have been fixed beforehand to the insulating blocks  13 ,  14 , the cylindrical indentations  21  open in portions of the internal face of the insulating blocks  13 ,  14 , which portions are not covered by the corners  15 . To this end, in the embodiment illustrated in  FIGS. 7 to 10 , the insulating blocks  13 ,  14  project, in the opposite direction to the tank corner, beyond the edges of the corners  15 . Furthermore, the cylindrical indentations  21  are provided in the portions of the insulating blocks  13 ,  14  projecting beyond the edge of the corners  15 . Thus, it is possible to gain access to the cylindrical indentations  21  in order to ensure the fixing of the insulating blocks  13 ,  14  to the pins  7  while the corner  15  is positioned on the insulating blocks  13 ,  14 . 
     When the insulating blocks  13 ,  14  have been secured to the pins  7 , the cylindrical indentations  21  are closed by plugs  22  of insulating material, in particular illustrated in FIGS.  9  and  10 . Furthermore, insulating joining elements  23  are inserted between the insulating blocks  13 ,  14 . 
     The arrangement of the insulating blocks  13 ,  14  and the corners  15  in the form of preassembled modules  12   a ,  12   b ,  12   c ,  12   d  is particularly advantageous and allows different assembly and transport methods for the corner structures. In an embodiment, the panels  1 ,  2  of the corner structure are assembled, in situ, at the installation site of the tank by fixing a plurality of preassembled modules  12   a ,  12   b ,  12   c ,  12   d  to the panels  1 ,  2 . In another embodiment, the panels  1 ,  2 , the corner arrangement of the secondary sealing membrane and a portion or the whole of the preassembled modules  12   a ,  12   b ,  12   c ,  12   d  are assembled at the workshop. In an advantageous variant, there is provision for there to be fixed to the panels  1 ,  2  at the workshop only a number of preassembled modules  12   a ,  12   b ,  12   c ,  12   d  necessary for ensuring the mechanical strength of the corner structure during the transport and handling thereof, the remainder of the preassembled modules subsequently being fixed at the installation site of the tank. Such an assembly method limits the weight of the corner structure during the transport and handling thereof, without for all that impairing the ergonomics of the assembly in situ of the tank. 
       FIGS. 11 and 12  set out a corner structure according to another embodiment. The insulating blocks  13 ,  14  also have openings for the introduction of the pins provided in the internal face thereof. In this embodiment, however, the openings communicate with recesses  24 , which are formed in the insulating blocks  13 ,  14  and which open at the lateral edge thereof opposite the tank corner. The recesses  24  are formed by recesses which are formed in the lateral edge opposite the tank corner. The recesses provide lugs  25  which carry the abutment surface of the nuts which cooperate with the threaded end of the pins  7 . The recesses  24  are advantageously formed in the region of the corners of the insulating blocks  13 ,  14 . In this manner, the recesses  24  open at the gap between two adjacent insulating blocks  13 ,  14  and the filling of a gap between two adjacent insulating blocks  13 ,  14  and two recesses  24  which bound the gap can be carried out by a single insulating joining element  26 . It may be noted that such recesses  24  also allow fixing of the insulating blocks  13 ,  14  to the pins  7 , when corners  15  have been fixed to the insulating blocks  13 ,  14  beforehand. 
       FIG. 13  illustrates another embodiment. In this embodiment, the corners  15  have edges having cut-outs  27 . The insulating blocks  13 ,  14  comprise cylindrical indentations  28  which communicate with introduction openings for the pins  7 , which openings are provided at the external face of the insulating blocks  13 ,  14  and of which the base cooperates with a nut which is screwed onto a pin  7 . The cylindrical indentations open at the internal face of the insulating blocks  13 ,  14  opposite the cut-outs  27  which are formed in the edges of the corners  15  in such a manner that the fixing of the insulating blocks  13 ,  14  to the pins  7  can be brought about in spite of the presence of the corner  15 . The cylindrical indentations  28  are closed by plugs. 
       FIGS. 14 and 15  illustrate, by way of example, the structure of the walls of a sealed and thermally insulating tank which is provided with a corner structure as described above. 
     The secondary thermal insulation barrier comprises a plurality of heat-insulating panels  29  which are secured to the carrier structure  30  by means of resin beads  31  and pins  32  which are welded to the carrier structure  1 . The panels  29  are substantially in the form of a rectangular parallelepiped and have, in accordance with the two axes of symmetry thereof, a metal connection strip  33 , which is positioned in a recess and which is fixed therein by screws, rivets, staples or adhesive. In the intersection zone of the metal connection strips, there is provided a pin  34  which projects toward the inner side of the tank and which allows the primary thermal insulation barrier to be fixed. 
     The secondary sealing membrane is obtained by assembling a plurality of metal plates  35  which are butt-welded and which have a substantially rectangular form. The metal plates  35  comprise, in accordance with each of the two axes of symmetry of this rectangle, an undulation  36  which forms a relief in the direction of the carrier structure  30 . The metal plates  35  are in this instance arranged in an offset manner in relation to the panels  29  so that each of the metal plates  35  extends so as to straddle four adjacent panels  29 . Furthermore, the undulations  36  are received in gaps  37  of the secondary thermal insulation barrier which are provided between two adjacent panels  29 . The adjacent metal plates  35  are lap-welded to each other. The securing of the metal plates  35  to the panels  29  is brought about by means of the metal connection strips  33  to which at least two edges of the metal plates  35  are welded. 
     In the region of the corner zone, the metal plates  35  of the secondary sealing barrier are lap-welded to the metal sheets  8 ,  9  of the corner arrangement of the secondary sealing membrane. 
     The primary thermal insulation barrier comprises a plurality of heat-insulating panels  38  which are of substantially rectangular parallelepiped form and which cover the secondary sealing membrane. The panels  38  of the primary thermal insulation barrier also comprise at the internal face thereof metal connection strips  39  which allow the primary sealing barrier to be secured by welding. 
     The primary sealing membrane is obtained by assembling a plurality of metal plates  40 , which are welded to each other along the edges thereof. The metal plates  40  comprise undulations  41  which extend in two perpendicular directions. The undulations  41  of the primary sealing membrane project from the side of the internal face of the metal plates  40 . The metal plates  40  are, for example, produced from sheet metal of stainless steel or aluminum, which is formed by bending or by stamping. The metal plates  40  are offset in relation to the panels  38 , each of the metal plates  40  extending so as to straddle four adjacent panels  38 . 
     In the region of the corner zone of the primary sealing membrane, the metal plates  40  are welded to the corners  15 . Furthermore, corner components which are not illustrated are positioned in a straddling manner between two adjacent corners  35 . Such corner components comprise in their central zone an undulation which extends in the continuation of an undulation of the metal plate  40  and are lap-welded to the metal sheets  40  which extend at one side and the other of the corner structure and to the two corners  35  which they straddle. 
     With reference to  FIG. 16 , a cut-away view of a methane tanker  70  shows a sealed and insulated tank  71  which is of generally prismatic form and which is mounted in the double hull  72  of the tanker. The wall of the tank  71  comprises a primary sealed barrier which is intended to be in contact with the LNG which is contained in the tank, a secondary sealed barrier which is arranged between the primary sealed barrier and the double hull  72  of the tanker, and two insulating barriers which are arranged between the primary sealed barrier and the secondary sealed barrier and between the secondary sealed barrier and the double hull  72 , respectively. 
     In a manner known per se, loading/unloading channels  73  which are arranged on the upper bridge of the tanker may be connected, by means of suitable connectors, to a sea-based or port-based terminal in order to transfer a cargo of LNG from or toward the tank  71 . 
       FIG. 16  shows an example of a sea-based terminal which comprises a loading and unloading station  75 , an underwater conduit  76  and a ground-based installation  77 . The loading and unloading station  75  is a fixed off-shore installation comprising a movable arm  74  and a tower  78  which supports the movable arm  74 . The movable arm  74  carries a bundle of flexible insulated pipes  79  which can be connected to the loading/unloading channels  73 . The movable arm  74  which can be orientated is adapted to all the gauges of methane tankers. A connection conduit which is not illustrated extends inside the tower  78 . The loading and unloading station  75  enables the loading and unloading of the methane tanker  70  from or to a ground-based installation  77 . This comprises storage tanks  80  for liquefied gas and connection conduits  81  which are connected via the underwater conduit  76  to the loading or unloading station  75 . The underwater conduit  76  enables liquefied gas to be transferred between the loading or unloading station  75  and the ground-based installation  77  over a great distance, for example, 5 km, which enables the methane tanker  70  to be kept at a great distance from the coast during the loading and unloading operations. 
     In order to produce the pressure required for the transfer of the liquefied gas, there are used pumps which are on-board the tanker  70  and/or pumps with which the ground-based installation  77  is provided, and/or pumps with which the loading and unloading station  75  is provided. 
     Although the disclosure has been described in connection with several specific embodiments, it is clearly evident that it is by no means limited thereto and that it comprises all the equivalent techniques of the means described and their combinations if they are included within the scope of the disclosure. 
     It should be noted in particular that, if the disclosure is described in relation to an embodiment in which the tank comprises two sealing and thermal insulation levels, it is in no way limited thereto and also applies to sealed tanks comprising only a single sealing and thermal insulation level. 
     The use of the verb “comprise”, “contain” or “include” and the conjugated forms thereof does not exclude the presence of elements or steps other than those set out in a claim. The use of the indefinite article “a” or “an” for an element or a step, unless otherwise stated, does not exclude the presence of a plurality of such elements or steps. 
     In the claims, any reference numeral in brackets should not be interpreted to be a limitation of the claim.