Installation for storing a liquefied gas

Abstract

The invention relates to a storage facility comprising a supporting structure comprising an upper supporting wall and the tank comprising a ceiling wall fixed to the upper supporting wall, the supporting structure comprising a dome structure comprising dome walls projecting from the upper supporting wall and each having an upper end, the dome structure comprising a seat wall fixed to the upper ends, the dome structure comprising a cover which covers the passage and is sealed welded to the seat wall, the cover comprising a peripheral edge having a bevel oriented such that the cover tapers from an upper face of the cover to a lower face of the cover, the peripheral edge being welded to an intermediate frame by a lap weld located in a space between the bevel of the peripheral edge and an upper face of the intermediate frame.

Description

Domaine technique

[0001] The invention relates to a liquefied gas storage installation comprising a sealed and thermally insulating tank arranged in a supporting structure.

[0002] In particular, the invention relates to the field of sealed and thermally insulating tanks for the storage and / or transport of liquefied gas at low temperature, such as tanks for the transport of Liquefied Petroleum Gas (also called LPG) having for example a temperature between -50°C and 0°C, or for the transport of Liquefied Natural Gas (LNG) at approximately -162°C. 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.

[0003] The invention relates more particularly to a storage installation of the aforementioned type comprising a dome structure projecting upwards from an upper load-bearing wall of the load-bearing structure and intended to be crossed by at least one pipe intended for loading or unloading the tank. Arrière-plan technologique

[0004] Document WO2022 / 253615 discloses a liquefied gas storage facility comprising a supporting structure, consisting of the double hull of a ship, and a sealed and thermally insulating tank arranged in the supporting structure. The facility comprises a dome structure, shown in the figure 1 of the aforementioned document, which serves as a penetration point for various equipment of the tank, such as pipes intended for loading or unloading the tank. The dome structure comprises a vertical load-bearing wall, projecting upwards from an upper load-bearing wall of the load-bearing structure, and a horizontal wall which is positioned at the top of the vertical load-bearing wall as shown in figure 7 of the aforementioned document. The horizontal wall comprises a seat wall and a metal cover wall welded tightly to the latter.

[0005] To fix the horizontal wall of the dome structure and the metal cover wall and ensure the sealing of the dome structure, it is known to fix the metal cover wall to an intermediate frame by means of a weld line and to weld said intermediate frame to the horizontal wall of the dome structure by means of one or more other weld lines. When the pressure prevailing inside the tank is higher than atmospheric pressure, this pressure differential exerts on the cover a force directed towards the outside of the tank which stresses the metal cover wall in bending. Such stresses are likely to degrade the aforementioned weld lines and thus cause problems of sealing of the dome structure, in particular when the tank is intended to store the gas at pressures higher than those of traditional membrane tanks.

[0006] Such a dome structure arrangement is therefore not fully satisfactory. Résumé

[0007] One idea behind the invention is therefore to propose a liquefied gas storage installation comprising a dome structure which offers better pressure resistance.

[0008] To this end, according to one embodiment, the invention provides a liquefied gas storage facility comprising a supporting structure and a sealed and thermally insulating tank arranged in the supporting structure, the supporting structure comprising an upper supporting wall and the tank comprising a ceiling wall fixed to the upper supporting wall, the upper supporting wall and the ceiling wall being interrupted locally so as to delimit an opening, the supporting structure comprising a dome structure projecting vertically towards the outside of the tank from the upper supporting wall around the opening and defining a passage intended to be crossed by at least one pipe intended for loading or unloading liquefied gas from the tank, the dome structure comprising: dome walls projecting from the upper supporting wall and each comprising an upper end,a seat wall attached at the upper ends and extending horizontally, a cover which covers the passage, and has a peripheral edge an intermediate frame located between the seat wall and the peripheral edge the peripheral edge having a first bevel oriented so that the cover tapers from an upper face of the cover to a lower face of the cover, the peripheral edge being welded to the intermediate frame by a weld located in a space between the first bevel and an upper face of the intermediate frame, the intermediate frame being welded to the seat wall, the intermediate frame having an outer peripheral end which is welded to the seat wall by a second weld.,

[0009] Thus, thanks to the bevel, with constant dimension between the peripheral edge of the cover and the external peripheral end of the intermediate frame, the throat depth of the first weld can be greater, which improves its hold.

[0010] For example, one or all of the welds are lap welds. In particular, the weld between the bevel and an upper face of the intermediate frame is a lap weld in a particular embodiment.

[0011] Furthermore, the bevel allows the cover to be positioned on the intermediate frame with greater adjustment latitude.

[0012] Furthermore, for a constant actual throat depth of the first weld, the horizontal dimension of said weld is reduced. Thus, while maintaining a gap between the first and second welds that is sufficient to prevent them from amalgamating during welding operations, the majority of the volume of the first lap weld is closer to the second weld. The inventors have found that such a bringing together of the aforementioned welds allows for better distribution of stresses in said welds, which makes it possible to improve their strength and, in fine, to improve the fixing of the cover on the dome.

[0013] According to embodiments, such an installation may comprise one or more of the following features.

[0014] According to one embodiment, the intermediate frame has a second bevel oriented such that the intermediate frame tapers from the upper face of the intermediate frame to a lower face of the intermediate frame, the second weld being located in a space between the bevel and an upper face of the seat wall.

[0015] According to one embodiment, a distance between an outer peripheral end of an upper face of the intermediate frame and an upper end of the peripheral edge of the cover is between 5 and 40 mm, for example between 10 and 20 mm.

[0016] According to one embodiment, an angle of the first bevel is between 45 and 90°, limits not included, the angle being located between the upper face of the cover and a face of the first bevel connecting the upper face of the cover to the lower face of the cover and / or the angle being located between the upper face of the intermediate plate and a face of the first bevel connecting the upper face of the cover to the lower face of the cover.

[0017] According to one embodiment, the first weld has an actual throat depth of between 5 and 25 mm.

[0018] According to one embodiment, a distance between an outer end of the first weld and the outer peripheral end of an upper face of the intermediate frame is between 1 and 20 mm; the distance being measured in a plane of the intermediate frame.

[0019] This allows the first and second welds to be positioned sufficiently close to each other without the risk of them amalgamating, which would have the effect of significantly degrading their strength.

[0020] According to one embodiment, a distance between an outer end of the lower face of the cover and the outer peripheral end of an upper face of the intermediate frame is between 5 and 25 mm.

[0021] Likewise, this allows the first and second welds to be positioned sufficiently close to each other without the risk of them amalgamating, which would have the effect of significantly degrading their strength, while allowing the stress to be distributed in such a way that the welds work together.

[0022] According to one embodiment, the dome structure comprises a frame formed by frame walls which are welded against the upper face of the cover and reinforcing gussets which are each positioned in abutment against an external face of a frame wall and against the upper face of the cover.

[0023] Thus, the frame and the gussets make it possible to reinforce the rigidity of the cover, which limits its bending and thus improves the pressure resistance of the welds ensuring the attachment of the cover to the seat wall.

[0024] According to one embodiment, the reinforcing gussets comprise a body arranged perpendicular to the frame wall, the body comprising a heel by which said body bears against the upper face of the cover and a chamfered portion extending from the heel, the reinforcing gusset further comprising a reinforcing plate positioned on the chamfered portion perpendicular to a plane of the body.

[0025] According to one embodiment, a lower end of the reinforcement plate extends to an upper end of the heel.

[0026] According to one embodiment, the dome structure further comprises a plurality of horizontal stiffeners positioned in abutment against an upper face of the cover, each horizontal stiffener being aligned with a reinforcing gusset in the same plane normal to the cover.

[0027] According to one embodiment, the dome structure further comprises a plurality of vertical stiffeners positioned in abutment against an external face of a frame wall and against a lower face of the seat wall, each vertical stiffener being aligned with a reinforcing gusset in the same plane.

[0028] According to one embodiment, a distance between a lower end of the reinforcement plate and the upper face of the cover is between 10 and 100 mm.

[0029] According to one embodiment, the reinforcement plate is generally rectangular in shape and includes upper corners each having a chamfer. In this embodiment, the rectangle forming the generally rectangular shape has sides measuring 400 mm or less. The chamfered corners facilitate handling operations. For example, they facilitate the passage of a welding torch.

[0030] It is also possible to provide a general shape that is not rectangular. For example, the reinforcement plate can be generally elliptical, square, triangular, or trapezoidal.

[0031] Furthermore, here too, the dimensions of the general shape - whatever it may be - are less than 200 mm; the dimensions being measured from a neutral fiber of the chamfered portion.

[0032] According to one embodiment, a distance between the heel and an upper end of the peripheral edge of the cover is between 10 and 75 mm.

[0033] According to one embodiment, a thickness of the intermediate frame is between 5 and 40 mm and / or a thickness of the cover is between 15 and 40 mm.

[0034] According to one embodiment, the invention relates to a ship for transporting a fluid which comprises an installation of the aforementioned type.

[0035] According to one embodiment, the vessel comprises a double hull which forms the supporting structure.

[0036] According to one embodiment, the invention also provides a transfer system for a fluid, the system comprising the aforementioned vessel, insulated pipes arranged to connect the vessel tank to a floating or land-based storage facility and a pump for driving a flow of fluid through the insulated pipes from or to the floating or land-based storage facility to or from the vessel tank.

[0037] According to one embodiment, the invention also provides a method of loading or unloading such a vessel, in which a fluid 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

[0038] 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 figure 1 is a schematic perspective view of a supporting structure intended to support a sealed, thermally insulated tank for storing liquefied gas. fig.2 ] There figure 2 is a schematic view of the multi-layer structure of the tank walls. fig.3 ] There figure 3 is a top perspective view of the dome structure. fig.4 ] There figure 4 is a schematic sectional view illustrating the attachment of the dome structure cover to the seat wall via the intermediate frame. fig.5 ] There figure 5 is a perspective view of the dome structure frame and reinforcing gussets. fig.6 ] There figure 6 is a top perspective view of the dome structure (reinforcing gussets are not shown). fig. 7 ] There figure 7 is a diagram of the geometry of the weld of the cover without bevel on the intermediate frame. [ fig. 8 ] There figure 8 is a diagram illustrating, for comparison, the geometry of the weld when the bevel of the cover has an angle of 45°, on the one hand, and when the bevel has an angle of 60°, on the other hand. fig. 9 ] There figure 9 is a diagram illustrating an alternative embodiment in which the intermediate frame has a bevel. fig.10 ] There figure 10 is a schematic cutaway representation of an LNG tank and a loading / unloading terminal for this tank. Description des modes de réalisation

[0039] In relation to the figure 1 , a supporting structure 1 is described against which a sealed and thermally insulating tank 2 for storing a liquefied gas is intended to be fixed. The supporting structure 1 is, for example, formed by the double hull of a ship. The supporting structure 1 has a generally polyhedral shape. It has two front and rear supporting walls 120, here octagonal in shape, of which only the rear supporting wall is shown in the figure 1 . The front and rear walls 120 are, for example, cofferdam walls of the ship which extend transversely to the longitudinal direction of the ship. The supporting structure 1 also comprises an upper supporting wall 3 to which a tank ceiling wall 2 is fixed, a lower supporting wall 40 and side supporting walls 50, 60, 110, 180, 90, 100.

[0040] The sealed and thermally insulating tank for storing liquefied gas comprises a plurality of tank walls which are each anchored against one of the load-bearing walls 120, 3, 50, 60, 110, 180, 90, 100 of the load-bearing structure 1.

[0041] As shown in the figure 2 , each wall of the tank 2 successively has, from the outside to the inside, along the thickness direction of the wall, a secondary thermally insulating barrier 12 comprising insulating elements 13 fixed to the supporting structure 1, a secondary sealing membrane 14 anchored to the insulating elements 13 of the secondary thermally insulating barrier 12, a primary thermally insulating barrier 15 comprising insulating elements 16 fixed to the insulating elements 13 of the secondary thermally insulating barrier 12 or to the supporting structure 1 and resting against the secondary sealing membrane 14 and a primary sealing membrane 17 anchored to the insulating elements 16 of the primary thermally insulating barrier 15 and intended to be in contact with the liquefied gas contained in the tank 2.

[0042] As shown in the figures 1 And 6, the upper load-bearing wall 3 as well as the ceiling wall are interrupted locally so as to delimit an opening 18. The load-bearing structure 1 comprises a dome structure 19 which projects upwards from the upper load-bearing wall 3 around the opening and which defines a passage 24 intended to be crossed by one or more pipes 20, 21, 47 intended for loading or unloading the tank 2.

[0043] The dome structure 19 comprises vertical dome walls 22. The dome walls 22 are, for example, four in number when the dome structure 19 has a square or rectangular cross-section. The dome walls 22 project upwards from the upper load-bearing wall 3 and here rise above the deck of the ship. The dome structure 19 also comprises, at the top of the dome walls 22, a seat wall 23 which extends horizontally all around the passage 24 formed by the dome walls 22 and thus forms, with the dome walls 22, a coaming. The seat wall 23 supports a cover 25 through which the pipe(s) 20, 21 intended for loading or unloading the tank 2 pass. As illustrated in the figures 3 et 6 , according to one embodiment, the cover 25 comprises a network of stiffeners 48 which are each formed by metal plates welded against the upper face of the metal cover plate 25.

[0044] Furthermore, the supporting structure 1 also comprises stiffeners 49 which are fixed under the seat wall 23 and bear against the seat wall 23 and against the dome walls 22.

[0045] The multi-layer structure of tank 2, described above in relation to the figure 2 , is also present against the dome walls 22 but is not present at the cover 25 of the dome structure 19.

[0046] According to one embodiment, each of the pipes 20, 21, 47 is hollow, passes through the cover 25 of the dome structure 19 and forms: a pipe which is intended for loading tank 2 with liquefied gas, a pipe which is intended for unloading liquefied gas from tank 2 and which is for this purpose associated with an unloading pump fixed to the lower end of said pipe, or an emergency well allowing the descent of an emergency pump and an unloading line in the event of failure of an unloading pump.

[0047] In relation to the figure 4 , the fixing of the cover 25, and more particularly of its metal plate, to the seat wall 23 is described below.

[0048] The cover 25 is fixed in a sealed manner to the seat wall 23. To do this, the cover 25 is sealed welded to a metal intermediate frame 28, which is itself previously sealed welded to the seat wall 23. Advantageously, the intermediate frame 28 is sealed welded to the seat wall 23 by means of two continuous lap weld lines 29, 30 which extend respectively along the inner peripheral edge of the intermediate frame 28 and along the outer peripheral edge of the intermediate frame 28. An actual groove depth of the weld 30 is between 5 and 25 mm. For example, the actual groove depth of the weld 30 measures 16.5 mm.

[0049] Furthermore, the cover 25 rests against the upper face of the intermediate frame 28 and is welded, in a sealed manner, by means of a continuous lap weld line 8, on said upper face of the intermediate frame 28. To do this, a peripheral end 282 of the intermediate frame 28 projects, in the plane of the intermediate frame 28, relative to an upper end of the peripheral edge 33 in order to be able to accommodate the lap weld 8. According to one embodiment, a distance d6 between the peripheral end 282 of the intermediate frame 28 and the upper end of the peripheral edge 33 of the cover 25 is between 10 and 20 mm. For example, the distance d6 is 15 mm.

[0050] In the embodiment shown, the intermediate frame 28 rests at least partly against an outer zone 32 of the seat wall 23, i.e. an area which is positioned, relative to the passage 24, outside the dome walls 22. This outer zone 32 also projects, in the plane of the intermediate frame 28, relative to the intermediate frame 28 in order to accommodate the weld 30. A distance d3 between the peripheral end 282 of the intermediate frame 28 and one end of an outer zone 32 of the seat wall 23 is at least 5 mm. For example, the distance d3 is 55 mm. This distance d3 is marked in the plane of the seat plate 23.

[0051] Additionally, as illustrated in the figure 4 , the peripheral edge 33 is beveled, i.e. has a bevel 6 oriented so that the cover 25 narrows from its upper face 331 towards its lower face 332. The bevel 6 is characterized by an angle α located between the upper face 331 of the cover 25 and a face of the bevel 6. The angle α is between 45° and 90°, upper limit not included. For example, it can be 60° or 70°.

[0052] This bevel 6 forms a space 5 between the peripheral edge 33 of the cover 25 and an upper face 281 of the intermediate frame 28. A distance between the bottom of the space 5 - i.e. the point of contact between the lower face 332 of the peripheral edge 33 and the upper face 281 of the intermediate frame 28 - and one end of the peripheral edge 33 is greater than this same distance measured in the absence of a bevel 6.

[0053] The bevel 6 makes it possible, for a constant actual groove depth of the weld 8 between the cover 25 and the intermediate frame 28, to reduce the distance d6 between the peripheral end 282 of the intermediate frame 28 and the upper end of the peripheral edge 33 of the cover 25. The actual groove depth of the weld 8 is advantageously between 5 and 25 mm and for example 16.5 mm.

[0054] Since, in general, chamfered plates, i.e. having a bevel at their end, have better welding resistance, the bevel 6 makes it possible to reduce a distance d5 between an external end of the lower face 332 of the cover 25 and the external peripheral end 282 of the intermediate frame 28. Generally, the distance d5 is greater than 25 mm. Thanks to the bevel 6, the distance d5 is less than or equal to 25 mm, preferably less than or equal to 20 mm.

[0055] The bevel 6 also makes it possible to reduce the distance d1 between an external end of the first weld 8 and the external peripheral end 282 of an upper face 281 of the intermediate frame 28 (the distance being measured in a plane of the intermediate frame). Generally, the distance d1 is 10 mm.

[0056] THE figures 7 à 9 illustrate the reduction of the distance d6 thanks to the bevel 6 according to different values of the angle α according to a first example of illustration.

[0057] An angle α of 90 degrees corresponds to the absence of bevel 6 and thus serves as a reference to illustrate the reduction in distance d5. At the figure 7 , a weld 8, having an actual weld throat G and weld toes P, is shown. The actual throat depth G is 16.5 mm in this illustrative example. The weld toe P, i.e. the width of the weld, is approximately 23.3 mm.

[0058] To the figure 8 , a distance d6 defined by a bevel 6 having an angle α of 45 degrees is compared with a distance d6 defined by a bevel 6 having an angle α of 60 degrees. It can therefore be seen that, at a constant throat depth (for example 16.5 mm), the horizontal weld root P located on the upper face 281 of the intermediate frame 28 reduces as the angle α decreases. For example, the horizontal weld root P is 23.3 mm with an angle α of 90 degrees, 19 mm with an angle α of 60 degrees, 20 mm for an angle α of 70° and 17.9 mm for an angle α of 45 degrees.

[0059] Furthermore, at the figure 8 , a chamfer angle β, complementary to the angle α, is represented. This angle β is defined by the normal to the intermediate frame 28 passing through the upper end of the peripheral edge 33 and the face of the bevel 6. It is also possible to define the bevel 6 with the angle β. Thus, it is therefore noted that at a constant throat depth (for example 16.5 mm), the horizontal weld root P located on the upper face of the intermediate frame 8 reduces as the angle β increases.

[0060] A reduction in the distances d5, d6 and the weld root P is thus observed when the chamfer angle β = (90°- α) increases and this for an identical throat depth.

[0061] By reducing the horizontal welding foot P, it is then possible to reduce the distance d6 and in fine to bring the internal end of weld 8 closer to weld 30.

[0062] This allows for a better distribution of the stresses along the two weld lines 8 and 30. Indeed, the two welds 8 and 30 being closer to each other, without however joining, they cooperate with each other in order to offer better bending resistance to the forces acting on the metal cover wall 25.

[0063] In addition, the bevel 6 and the resulting space 5 also allow the cover 25 to be positioned on the intermediate frame 28 with more adjustment latitude. Indeed, thanks to the geometry of the bevel, a gain in flexibility due to the tolerance play is observed during assembly.

[0064] According to an embodiment illustrated in the figure 9 , the intermediate frame 28 has a bevel 61 oriented so that the intermediate frame 28 tapers from the upper face 281 of the intermediate frame 28 to a lower face 283 of the intermediate frame 28, the second weld 30 being located in a space 51 between the second bevel 61 and an upper face of the seat wall 23.

[0065] The bevel 61 is characterized by an angle α2 located between the upper face 281 of the intermediate frame 28 and a face of the bevel 61. The angle α2 is between 45° and 90°, excluding the upper limit. For example, it can be 60° or 70°. figure 9 , angle α2 is approximately 45°, just like angle α. However, angle α2 is not necessarily equal to angle α.

[0066] Furthermore, as shown in the figures 3 And 5, the dome structure 19 comprises a profiled frame 9. The profiled frame 9 is welded to the upper face 331 of the cover 25, continuously all around it in order to stiffen it.

[0067] As shown in the figure 5 , the frame 9 has an I-shaped section, that is to say that it comprises a wing 91 which is perpendicular to the cover 25. The wing 91 extends vertically, relative to the cover 25.

[0068] According to an embodiment variant shown in the figures 4 And 5 , the dome structure 9 comprises reinforcing gussets 10 which each have a first edge bearing against the wing 91 of the frame 9 and a second edge bearing against the cover 25.

[0069] As illustrated in the figure 5 , the reinforcing gussets 10 comprise a body arranged perpendicular to the frame wall 9. The body comprising a heel 102 by which it bears against the upper face 331 of the cover 25 and a chamfered portion 101 extending from the heel 102.

[0070] In addition, the reinforcing gussets 10 comprise a reinforcing plate 103 positioned on the chamfered portion 101 perpendicular to a plane of the body.

[0071] The heel 102 of the body of a reinforcement gusset 10 corresponds to the portion of the body that is not chamfered. As illustrated in figure 4 , the heel 102 has a height d2 between the lower end of the reinforcing plate 103 and the upper face 331 of the cover 25. The height d2 of the heel 102 is between 10 and 100. The height of the heel 102 is determined or determines the chamfering angle of the body of the reinforcing plate 103 and thus the inclination of the reinforcing plate 103 relative to the frame 9 and the reinforcing gusset 10.

[0072] As illustrated in the figure 5 , the reinforcing plate 103 is of generally straight parallelepiped shape. It extends along the entire length of the chamfered portion 101 so that a lower end of the reinforcing plate 103 extends to an upper end of the heel 102.

[0073] The reinforcement plate 103 has dimensions less than or equal to 200 mm; the dimensions being measured from a neutral fiber of the chamfered portion.

[0074] It is also possible to provide a general shape of the reinforcement plate 103 which is not rectangular. For example, the reinforcement plate 103 may be of a general shape which is elliptical, square, triangular or trapezoidal.

[0075] In these cases also, the dimensions of the general shape - whatever it may be - are less than 200 mm; the dimensions being measured from a neutral fiber of the chamfered portion.

[0076] The reinforcement plate 103 also includes a chamfer at each of its upper corners. In other words, the upper corners of the reinforcement plate 103 each have a chamfer. These chamfered corners make it easier to weld the reinforcement gusset 10 and the reinforcement plate 103 to the frame 9.

[0077] In addition, a distance d4 between a peripheral end of the heel 102 and the peripheral edge 33 of the cover 25 is between 10 and 75 mm. For example, the distance d4 is 25 mm. Thus, the body of the reinforcement gusset 10 does not reach the peripheral edge 33, which makes it possible to carry out the welding operations.

[0078] The reinforcing gussets 10 contribute with the frame 9 to reinforcing the rigidity of the cover 25.

[0079] The reinforcing gussets 10 are located in the extension of the horizontal stiffeners 48. The horizontal stiffeners 48 are aligned with the reinforcing gussets 10 in the same plane, called the alignment plane. This alignment plane is normal to the cover 25.

[0080] Furthermore, the reinforcing gussets 10 are aligned with the vertical stiffeners 49. In other words, each vertical stiffener 49 which is positioned in abutment against an external face of the wall 22 of the frame 9 and against the lower face 231 of the seat wall 23 is aligned with a reinforcing gusset 10 in the same plane perpendicular to the cover 25. In other words, the vertical stiffeners 49 are positioned in the extension of the reinforcing gussets 10.

[0081] The stiffeners 49 being in abutment against the lower face of the seat wall 23 and the reinforcing gussets 10 being in abutment against the upper face of the cover 25, the stiffeners 49 are located under the reinforcing gussets 10.

[0082] For better visibility of the figures, the reinforcement gussets 10 are not shown in the figure 6 and the stiffeners 49 are not shown in the figure 4 .

[0083] The reinforcing plate 103 makes it possible to improve the reinforcement provided by the reinforcing gusset 10 to the frame 9 and thus to improve the rigidity of the cover 25, without increasing the thickness of the body of the gusset 10. Indeed, it increases the moment of inertia of the reinforcing gusset 10 when taking up the bending forces exerted on the cover 25 and the frame 9.

[0084] Furthermore, according to a variant of the invention, the intermediate frame 28 may also have a bevel (as shown in figure 9 ), similar to bevel 6, at its outer peripheral end 282.

[0085] As a reminder, the intermediate frame 28 is welded, in a sealed manner, to the seat wall 23 by means of two continuous lap weld lines 29, 30 which extend respectively along the internal peripheral edge of the intermediate frame 28 and along the external peripheral edge of the intermediate frame 28.

[0086] Thus, the weld 30 located along the peripheral end 282 can then benefit from the same advantages conferred by the bevel 6 to the weld 8 presented above.

[0087] According to one embodiment, the portion of the lower face 281 of the cover 25 which rests against the intermediate frame 28 is previously machined in order to guarantee the flatness of the contact between the cover 25 and the intermediate frame 28. In such a case, said portion of the cover 25 has a recess.

[0088] To achieve such a step, operators machine a thicker plate. However, it has been found that it can be complicated to comply with the flatness requirement and the intended thickness of the step. Often greater thicknesses are therefore often accepted. However, it is sometimes difficult to know what size groove to provide for the weld 8 between the cover 25 and the intermediate frame 28 due to the thickness variations observed on the edge of the cover 25. However, as explained previously, this weld 8 greatly contributes to the proper attachment of the cover 25 to the dome structure. In addition, the machining area of the thicker plate to be machined is often complex to machine.

[0089] Thus, according to another embodiment, said portion of the cover 25 is not previously machined and therefore does not have a recess.

[0090] Thus, in the absence of a step of machining the cover 25, the following advantages are obtained: Constant cover plate sheet thickness 25; and No machining.

[0091] The liquefied gas to be stored in the tank may in particular be liquefied natural gas (LNG), i.e. a gas mixture comprising mainly methane and one or more other hydrocarbons. The liquefied gas may also be ethane or liquefied petroleum gas (LPG), i.e. a mixture of hydrocarbons produced by oil refining, comprising mainly propane and butane.

[0092] In reference to the figure 7 , a cutaway view of an LNG carrier 70 shows the sealed and insulated tank 2 of generally prismatic shape mounted in the double hull 72 of the ship. The wall of the tank 71 comprises a primary sealed barrier intended to be in contact with the LNG contained in the tank, a secondary sealed barrier arranged between the primary sealed barrier and the double hull 72 of the ship, and two insulating barriers arranged respectively between the primary sealed barrier and the secondary sealed barrier and between the secondary sealed barrier and the double hull 72.

[0093] In a manner known per se, loading / unloading pipelines 73 arranged on the upper deck of the ship can be connected, by means of appropriate connectors, to a maritime or port terminal to transfer a cargo of LNG from or to the tank 2.

[0094] There figure 10represents an example of a maritime terminal comprising a loading and unloading station 75, a subsea pipeline 76 and a land-based installation 77. The loading and unloading station 75 is a fixed offshore installation comprising a mobile arm 74 and a tower 78 which supports the mobile arm 74. The mobile arm 74 carries a bundle of insulated flexible pipes 79 which can be connected to the loading / unloading pipes 73. The orientable mobile arm 74 adapts to all sizes of LNG carriers. A connecting pipeline (not shown) extends inside the tower 78. The loading and unloading station 75 allows the loading and unloading of the LNG carrier 70 from or to the land-based installation 77. The latter comprises liquefied gas storage tanks and connecting pipelines 81 connected by the subsea pipeline 76 to the loading or unloading station 75.The subsea pipeline 76 allows the transfer of liquefied gas between the loading or unloading station 75 and the onshore installation 77 over a long distance, for example 5 km, which makes it possible to keep the LNG carrier 70 at a great distance from the coast during loading and unloading operations.

[0095] To generate the pressure necessary for the transfer of the liquefied gas, pumps on board the ship 70 and / or pumps equipping the onshore installation 77 and / or pumps equipping the loading and unloading station 75 are used.

[0096] Although the invention has been described in connection with several particular embodiments, it is quite obvious that it is in no way limited thereto 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, as defined by the claims.

[0097] The use of the verb "comprise", "comprise" or "include" and its conjugated forms does not exclude the presence of other elements or other steps than those set out in a claim.

[0098] In the claims, any reference sign in parentheses cannot be interpreted as a limitation of the claim.

Claims

1. A liquefied gas storage facility comprising a supporting structure (1) and a sealed and thermally insulating tank (2) arranged in the supporting structure (1), the supporting structure (1) comprising an upper supporting wall (3) and the tank (2) comprising a ceiling wall fixed to the upper supporting wall (3), the upper supporting wall (3) and the ceiling wall being interrupted locally so as to delimit an opening (18), the supporting structure (1) comprising a dome structure (19) projecting vertically towards the outside of the tank (2) from the upper supporting wall (3) around the opening (18) and defining a passage (24) intended to be crossed by at least one pipe (20, 21, 47) intended for loading or unloading liquefied gas from the tank (2), the dome structure (19) comprising: - dome walls (22) projecting from the upper supporting wall (3) and each having an upper end,- a seat wall (23) fixed at the upper ends and extending horizontally, - a cover (25) which covers the passage (24), and has a peripheral edge (33), and - an intermediate frame (28) located between the seat wall (23) and the peripheral edge (33), the peripheral edge (33) having a first bevel (6) oriented so that the cover (25) tapers from an upper face (331) of the cover (25) to a lower face (332) of the cover (25), the peripheral edge (33) being welded to the intermediate frame (28) by a first weld (8) located in a space (5) between the first bevel (6) and an upper face (281) of the intermediate frame (28), the intermediate frame (28) being welded to the seat wall (23); the intermediate frame (28) having an outer peripheral end (282) which is welded to the seat wall (23) by a second weld.

2. Installation according to claim 2, wherein the intermediate frame (28) has a second bevel (61) oriented so that the intermediate frame (28) tapers from the upper face (281) of the intermediate frame (28) towards a lower face (283) of the intermediate frame (28), the second weld (30) being located in a space (51) between the second bevel (61) and an upper face of the seat wall (23).

3. Installation according to claim 1, in which a distance (d6) between the external peripheral end (282) of an upper face of the intermediate frame (28) and an upper end of the peripheral edge (33) of the cover (25) is between 5 and 40 mm.

4. Installation according to any one of claims 1 to 3, in which an angle (α) of the first bevel (6) is between 45° and 90°, upper limit not included, the angle being located between the upper face (331) of the cover (25) and a face of the first bevel (6) connecting the upper face (331) of the cover (25) to the lower face (332) of the cover (25).

5. Installation according to any one of claims 1 to 4, in which the first weld (8) has an actual throat depth of between 5 and 25 mm.

6. Installation according to any one of claims 1 to 5, in which a distance (d1) between an external end of the first weld (8) and the external peripheral end (282) of an upper face (281) of the intermediate frame (28) is between 1 and 20 mm; the distance being measured in a plane of the intermediate frame (28).

7. Installation according to any one of claims 1 to 6, in which a distance (d5) between an external end of the lower face (332) of the cover (25) and the external peripheral end (282) of an upper face of the intermediate frame (28) is between 5 and 25 mm.

8. Installation according to any one of claims 1 to 7, in which the dome structure (19) comprises a frame (9) formed by frame walls which are welded against the upper face (331) of the cover (25) and reinforcing gussets (10) which are each positioned in abutment against an external face of a frame wall and against the upper face (331) of the cover (9).

9. Installation according to claim 8, in which the reinforcing gussets (10) comprise a body arranged perpendicular to the frame wall, the body comprising a heel (102) by which said body bears against the upper face (331) of the cover (25) and a chamfered portion (101) extending from the heel (102), the reinforcing gussets (10) further comprising a reinforcing plate (103) positioned on the chamfered portion (101) perpendicular to a plane of the body.

10. Installation according to claim 9, in which a lower end of the reinforcement plate (103) extends to an upper end of the heel (102).

11. Installation according to claim 9 or 10, in which a distance (d2) between a lower end of the reinforcing plate (103) and the upper face (331) of the cover (25) is between 10 and 100 mm.

12. Installation according to any one of claims 9 to 11, in which the reinforcing plate (103) is of generally rectangular shape and comprises upper corners each having a chamfer.

13. Installation according to any one of claims 9 to 12, in which a distance (d4) between the heel (102) and an upper end of the peripheral edge (33) of the cover (25) is between 10 and 75mm.

14. Installation according to any one of claims 8 to 13, in which the dome structure (19) further comprises a plurality of horizontal stiffeners (48) positioned in abutment against an upper face (331) of the cover (25), each horizontal stiffener being aligned with a reinforcing gusset (10) in the same plane normal to the cover (25).

15. Vessel (70) for transporting a fluid, the vessel (70) comprising an installation according to any one of claims 1 to 14.

16. A transfer system for a fluid, the system comprising a vessel (70) according to claim 15, insulated pipes (73, 79, 76, 81) arranged to connect the vessel tank (2) to a floating or land-based storage facility (77) and a pump for driving a fluid through the insulated pipes (73, 79, 76, 81) from or to the floating or land-based storage facility (77) to or from the vessel tank (2).

17. A method of loading or unloading a ship (70) according to claim 15, wherein a fluid is conveyed through insulated pipes (73, 79, 76, 81) from or to a floating or land-based storage facility (77) to or from the tank (2) of the ship.

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