EP3826796A1

EP3826796A1 - Welding a sealing membrane of a thermal insulation body of a tank

Info

Publication number: EP3826796A1
Application number: EP19761914.1A
Authority: EP
Inventors: Nicolas LAURAIN; Sylvain Karst; Michaël BIDENBACH
Original assignee: Gaztransport et Technigaz SA
Current assignee: Gaztransport et Technigaz SA
Priority date: 2018-07-26
Filing date: 2019-07-22
Publication date: 2021-06-02
Also published as: WO2020021189A1; KR20210031938A; CN112543691A; SG11202100789QA; FR3084270B1; CN112543691B; FR3084270A1

Abstract

The present invention relates to a method for welding a sealing, thermally insulating tank membrane, according to which there are present: - at least two metallic strakes (1, 2) of the sealing membrane, and - at least two metallic welding supports, a conductive strip (30) being inserted between said two welding supports, after which each of the two raised lateral edges of the two adjacent metallic strakes (1, 2) is sealingly welded, by resistance seam welding and in pairs, to one of the welding supports interposed between the adjacent raised edges.

Description

WELDING OF A SEALED MEMBRANE OF A MASSIVE

THERMAL INSULATION OF A TANK

Field of the invention

The subject of the invention is the production of sealed and thermally insulating tanks intended more particularly, but not exclusively, for the transport by sea of liquefied gases or cryogenic liquid and, more specifically, for the transport of liquefied natural gases with a high methane content (LNG). ) or petroleum (LPG). Such tanks can also be installed on the ground or on a floating structure intended for storage.

The invention relates here to the welding of a waterproof membrane of such a tank, more particularly the invention provides a solution for achieving optimal welding between two adjacent strakes of the membrane as well as two anchoring wings, said two strakes having raised edges and the welding between these two adjoining strakes being carried out at these raised edges.

In the following, the expressions “anchor wing” and “weld support” will be used interchangeably to designate the same element, the function of which is both to provide a means of anchoring the membrane (its strakes) to the block. thermal insulation and serve as a weld support for fixing with each of the two adjacent strakes.

State of the art We know for example from FR 2798358, FR 2709725, FR 2549575, storage or transport tanks for liquefied gases at low temperature including the or each waterproof membrane, in particular a primary waterproof membrane in contact with the product contained in the tank, consists of thin metal sheets which will be carried by a thermally insulating barrier. These thin metal sheets are tightly connected to each other to ensure the tightness of the tank.

FIG. 1 illustrates a known method of fixing said metal sheets to the thermally insulating barrier in this type of tank. In this FIG. 1, an upper surface 101 of the thermally insulating barrier has a groove 102 developing in the thickness of the thermally insulating barrier from the support surface 101. This groove 102 has in the thickness of the thermally insulating barrier a retaining zone formed by a groove 103 which develops parallel to the support surface 101. This groove 103 develops at one end of the groove 102 opposite the support surface 101 in the thickness of the thermally insulating barrier, the groove 102 having a cross section in the shape of an inverted "T" whose base is formed by the groove 103. An anchoring wing 104 in the shape of an “L” is inserted in the groove 102. This anchoring wing 104 has a base 105 housed in the groove 103 so as to retain the wing of anchoring 104 on the thermally insulating barrier in a direction perpendicular to the support surface 101. The anchoring wing 104 also comprises an anchoring branch 106 of which a lower part 107 is contiguous of the base 105 and an upper part 108 protrudes above the support surface 101.

Two metal sheets 109 are arranged on either side of the anchoring wing 104. These metal sheets 109 each have a flat central portion 110 bearing on the support surface 101 (for the sake of readability of the figure, the support surface 101 and the metal sheets 109 are shown in Figure 1 with a gap). These metal sheets 109 also have raised side edges, hereinafter called raised edges 111. A raised edge 111 of each of the two adjacent metal sheets 109 is welded on either side of the anchoring branch 106 of the anchor wing 104.

The raised edges 111 thus form, with the anchoring wing 104, bellows making it possible to absorb the forces associated with the contraction of the waterproof membrane, for example when loading cryogenic liquid into the tank.

However, such an anchoring wing 104 constitutes a fixed fixing point for each raised edge 111. In fact, the anchoring wing 104 being biased in two opposite directions by the raised edges 111, it remains substantially static in the tank. . Consequently, the anchoring of the raised edges 111 on the support surface 101 via the anchoring wings 104 is substantially fixed in the direction perpendicular to the raised edges 11 1. The flexibility of the waterproof membrane is therefore limited.

This is why it has been proposed, according to FR 3054872, to use two anchoring wings, each of these two anchoring wings having respectively the function of anchoring one of the two adjacent strakes. However, the junction between the raised edges of two adjacent strakes then has four thicknesses of material (two strapped edges of strakes and two anchoring wings) to be welded in a completely sealed manner between them. However, taking into account in particular the thicknesses of the raised edges of the strakes as well as those of the anchoring wings, the fixing of the two strakes to the anchoring wings is made particularly difficult to achieve, being considered moreover that an attempt is made to keep a flexibility, or elasticity, important at these tight junctions so as to be able to absorb in particular the thermal stresses. Also known are welding methods described by FR1589316 and DE44l l888.

At the present time, there is no method allowing efficient and rapid welding, that is to say at least completely sealed over the entire length of the welds, at two adjacent strakes, when the latter each have a wing d anchoring to the thermal insulation block.

Brief description of the invention

The present invention intends to remedy the shortcomings of the state of the art by proposing a particularly effective solution for carrying out the welding between two adjacent strakes, when each has or comprises an anchoring wing connecting or fixing it to the insulation block. thermal.

It has been discovered by the plaintiff, after various studies and analyzes, a technically simple solution to implement making it possible to achieve a perfect weld, namely completely waterproof and very mechanically resistant, between two adjacent / contiguous strakes of a membrane, by through their respective anchor wings and quickly.

Thus, the present invention relates to a method for welding a waterproof and thermally insulating tank membrane, in which a waterproof and thermally insulating tank comprises at least one waterproof metal membrane and a thermally insulating block comprising at least one thermally insulating barrier adjacent to said membrane, in which:

- at least two metal strakes of the waterproof membrane, carried by a support surface of the thermally insulating barrier, are in the form a profiled part comprising a flat central portion resting on the support surface and two raised lateral edges projecting from the support surface, and

- at least two metal welding supports, carried by the thermally insulating barrier, protrude from the support surface between the two adjacent raised lateral edges of the two adjacent strakes,

the method according to the invention, characterized in that a conductive strip is inserted between the two aforementioned metal welding supports and in that, subsequently, the joints are welded together, in pairs, by welding with the thumbwheel each of the two raised lateral edges of the two adjacent metal strakes respectively with one of said metallic welding supports, interposed between said adjacent raised edges.

Thanks to this process according to the invention, it is now possible to achieve optimum quality welding automatically so that the installation time of the sealed and thermally insulating tank is significantly reduced. Thus, there is a gain in productivity. Furthermore, the welding method according to the invention makes it possible to ensure the mechanical continuity and the sealing of the weld bead, to weld the length of the raised edges without stopping or resuming thanks to the electrical continuity and not to merge the two. weld supports at the welds with the two edges raised. This process is also compatible with current welding machines and therefore makes it possible to conserve existing equipment, limit investment and manage the machine fleet.

Also, thanks to the method according to the invention, a simultaneous weld (at the same time) is carried out of each of the two raised edge / weld support assemblies.

Numerous tests have been carried out to assess the quality of the weld between each of the anchoring wings and the strake (its raised edge) and these tests show an optimum weld quality (in particular no trace of the material forming the conductive strip) having d '' excellent mechanical qualities, in particular in terms of its impact resistance, its tensile / bending / compression resistance and its resistance to thermal gradients (the junction between the anchoring wing and the strake must always remain tight).

“Seam welding” is understood to mean welding in which the parts are assembled by application of an electric current (the application of direct current or not) and of pressure, knobs against the surface to be welded. Other advantageous features of the invention are briefly presented below:

- Advantageously, at least one of the welding supports, preferably both, consists of an anchoring wing so as to anchor the waterproof membrane to the thermally insulating barrier of the thermal insulation mass;

- According to one embodiment, the anchoring wing is in the form of an L and has a longitudinal portion and a lower portion engaged with the thermally insulating barrier;

- According to one embodiment, the lower portion of the anchoring wing extends, parallel to the middle portion of the metal strakes, in a recess in the thermally insulating barrier of the thermal insulation mass;

- Preferably, prior to the welding of each of the above edges raised with one of said welding supports, said welding supports have been fixed by welding in a sealed manner to each other;

Thus, as shown in FIG. 4 appended, the junction of the two adjacent strakes with the two metal anchoring wings has, thanks to the different welding points, a profile or a section in W. In other words, such a junction has a double-bellows function which gives it significant elasticity properties allowing the waterproof membrane, in particular at this level, to support or absorb very strong thermal gradients, resulting in particular in (thermal) contractions particularly significant.

Advantageously, the seam welding of each of said two adjacent raised edges with respectively one of said welding supports is carried out at a speed of between 1.5 meters per minute (m / min) and 2.5 m / min , preferably at a speed of 1.8 m / min;

- According to one embodiment of the invention, the above raised edges, preferably also the welding supports, are made of Invar® or steel containing at least 20% manganese, preferably at least 25% manganese, even more preferably 28% manganese;

- According to one embodiment, the thickness of the raised edges, preferably also the thickness of the aforementioned welding supports, is between 0.5 and 0.8 millimeter (mm), preferably equal to 0.7 mm; - when the raised edges, possibly the welding supports have such a thickness (of 0.5 and 0.8 mm), during the seam welding, the intensity of the current is between 1.8 and 3.2 kiloamperes (kA), preferably between 2.2 and 2.8 kA, and the pressure force exerted by each wheel against respectively a raised edge is between 1.2 and 2.8 bars, preferably between 2 and 2, 5 bars;

- According to another embodiment, the thickness of the raised edges, preferably also the thickness of the aforementioned welding supports, is between 0.9 and 1.2 millimeter (mm), preferably equal to 1 mm;

- when the raised edges, possibly the welding supports have such a thickness (of 0.9 and 1.2 mm), during the seam welding, the intensity of the current is between 2.7 and 3.8 kA , preferably between 3 and 3.5 kA, and the pressure force exerted by each wheel against respectively a raised edge is between 3.5 and 5 bars, preferably between 4 and 4.5 bars;

advantageously, during the seam welding, the electric current of the seam welding does not circulate continuously, preferably said electric current circulates during a time range corresponding to 60% to 80% of the time at (or for) a constant frequency, even more preferably for two thirds (2/3) of the time at (or for) a constant frequency;

- Advantageously, the conductive strip consists of a material or an alloy of materials with a high melting point, greater than the melting point of the raised edges and the welding supports. According to one embodiment, the conductive strip is (essentially comprises) copper, a molybdenum-based alloy, a tungsten-based alloy or graphite, preferably copper.

The invention also relates to a system for welding a sealed and thermally insulating tank membrane, the system comprising a seam welding device comprising two seams, optionally means for holding said seams against a surface to be welded, and a wall of a sealed and thermally insulating tank comprising:

- two adjacent metal strakes of the waterproof membrane, carried by a support surface of the thermally insulating barrier of the waterproof and thermally insulating tank, in the form of a profiled part comprising a flat central portion resting on the support surface and two raised lateral edges projecting from the support surface, and

- two metal welding supports, carried by the thermally insulating barrier, projecting from the support surface between the two adjacent raised lateral edges of the two adjacent strakes,

the seam welding device carrying out at least one welding respectively between one of the above raised edges and one of the above welding supports, the system according to the invention being characterized in that the welding device comprises a conductive blade intended to be inserted between the two welding supports so as to carry out the welding of each of the above two adjacent raised side edges with one of said welding supports respectively, interposed between said adjacent raised edges.

It should be noted that all of the characteristics presented above in connection with the welding process according to the invention are applicable to the welding system succinctly defined above.

The invention also relates to a sealed and thermally insulating tank integrated into a support structure, comprising a sealed and thermally insulating tank comprising at least one waterproof metal membrane composed of a plurality of metallic strakes and a thermally insulating block comprising at least one thermally barrier. insulator adjacent to said membrane, in which:

- At least two metal strakes of the waterproof membrane, carried by a support surface of the thermally insulating barrier, are in the form of a profiled part comprising a flat central portion resting on the support surface and two raised lateral edges making protruding from the support surface, and

The tank according to the invention is characterized in that each of the two adjacent raised lateral edges of the two adjacent metal strakes and respectively one of said weld supports, interposed between said adjacent raised edges, are welded together in pairs waterproof, by seam welding. The production of a weld between a strake (its raised edge) and an anchoring wing is certainly known as such, from the document FR 3054872, but the weld point present, with the use of the method according to the present invention, a section with a shape different from that of this prior art. Indeed, taking into account the positioning of the conductive strip on the (contiguous) side of the anchoring wing and a wheel on the (contiguous) side at the raised edge of a strake, the section of the weld point has a shape substantially oval (and not symmetrical as in the state of the art) whose protuberance (protuberance or hump) is on the side of the strake, that is to say on the side where the wheel was positioned during welding. It will be noted that, in the event that two knurls, arranged on either side of the welding point, are used, the welding point has a symmetrical shape. This section of slightly different shape - the appended FIG. 4 not being representative with regard to this characteristic of shape of the welding tip - compared to the state of the art obviously does not imply any negative consequence concerning the quality of the point of welding but it makes it possible to differentiate a welding point produced according to the process of the present invention from another welding process. Thus, such a tank, comprising all of the above-mentioned characteristics and characterized by at least one weld point produced by a “knurling / conductive blade” pair, is very new.

Finally, the invention also relates to a ship for the transport of a cold liquid product, the ship comprising a double hull and a sealed and thermally insulating tank as briefly described above, arranged in the double hull.

Advantageously, the vessel according to the invention comprises at least one sealed and insulating tank as described above, said tank comprising two successive sealing barriers, one primary in contact with a product contained in the tank and the other secondary disposed between the primary barrier and a supporting structure, preferably constituted by at least a portion of the walls of the ship, these two sealing barriers being alternated with two thermally insulating barriers or a single thermally insulating barrier disposed between the primary barrier and the load-bearing structure. Such tanks are typically designated as tanks built following code G International Maritime Organization (GMO) such as eg type tanks NO 96 ^®.

Preferably, the tank contains a Liquefied Natural Gas (LNG) or a Liquefied Gas (GL).

According to one embodiment, the invention also provides a method of loading or unloading of such a vessel, in which a fluid product is conveyed through isolated pipes from or to a floating or land storage installation towards or from the tank. of the ship. According to one embodiment, the invention also provides a transfer system for a fluid product, in particular cold liquid, the system comprising the aforementioned vessel, insulated pipes arranged so as to connect the tank installed in the hull of the vessel to an installation floating or terrestrial storage and a pump to drive a flow of fluid through the insulated pipes from or to the floating or terrestrial storage facility to or from the vessel of the ship.

Description of the appended figures The description which follows is given solely by way of illustration and not limitation with reference to the appended figures, in which:

- Figure 1 is a sectional view of a waterproof metal membrane anchor wing of the prior art, said anchor wing being anchored in a thermally insulating barrier of a sealed and thermally insulating tank; - Figure 2 is a sectional view of two metal membrane anchoring wings, the two anchoring wings having been welded together before their introduction into the thermal insulation block, this figure illustrating a portion of wall d 'a tank, at two adjacent strakes, before the application of the welding process according to the invention; - Figure 3 is a sectional view identical to Figure 2, this time the elements suitable for implementing the welding process according to the invention being visible in this figure;

- Figure 4 is a sectional view, showing the elements visible in Figures 2 and 3, of a portion of the wall of the sealed and thermally insulating tank, after the implementation of the welding process according to the invention;

- Figure 5 is a cutaway schematic representation of an LNG tank and a loading / unloading terminal of this tank.

Detailed description of embodiments of the invention

In the description below, reference is made to a waterproof membrane in the context of a sealed and thermally insulating tank. Such a tank has an internal space intended to be filled with combustible or non-combustible gas. The gas may in particular be a liquefied natural gas (LNG), that is to say a gaseous mixture mainly comprising methane as well as one or more other hydrocarbons, such as ethane, propane, n-butane, i -butane, n-pentane, i-pentane, neopentane, and nitrogen in small proportion. The gas can also be ethane or a liquefied petroleum gas (LPG), that is to say a mixture of hydrocarbons resulting from the refining of petroleum comprising essentially propane and butane.

In general, the waterproof membrane rests on a support surface formed by a thermally insulating barrier of the tank. This waterproof membrane has a repeated structure, alternately comprising, on the one hand, sheet metal strips, forming strakes, arranged on the support surface and, on the other hand, elongated welding supports linked to the support surface and s' extending parallel to the sheet metal strips over at least part of the length of the sheet metal strips. The sheet metal strips have raised side edges arranged and welded against the adjacent welding supports. Such a structure is for example used in the type of LNG tanks NO 96 ^® marketed by the Applicant.

At the sealed and thermally insulating tank, not shown as a whole in the appended figures, the raised edges of the strakes are preferably arranged in a longitudinal direction perpendicular or parallel to the longitudinal direction of the ship. Thus, the raised edges constitute bellows making it possible to absorb the contraction forces in a longitudinal direction of the ship or a transverse direction perpendicular thereto. The sheet metal strips and the welding supports are interrupted at the angles, for example as described in document WO 2012/072906 or else FR2724623.

According to one embodiment, the waterproofing membrane (strakes), one of the waterproofing membranes or the waterproofing membranes can be made of a metal chosen from stainless steel, aluminum, Invar ^® , that is to say an alloy of iron and nickel whose coefficient of expansion is typically between 1, 2.10 ⁶ and 2.10 ⁶ K ¹ or an alloy of iron with high manganese content whose coefficient of expansion is from 7 to 9.10 ⁶ K ¹ . According to one embodiment, a material having a coefficient of thermal contraction less than 16.10 ⁶ / K is chosen for applications in which the liquid gas is at a temperature between -45 ° C and -100 ° C.

Figures 2 to 4 show a sectional view of a wall of a sealed and thermally insulating tank at the connection between two adjacent metal strakes 1, 2 of a sealed membrane of the tank wall and two welding supports 3, 4 anchored on a thermally insulating barrier 5 of the thermal insulation mass of the tank wall. Such a thermally insulating barrier 5 is formed of juxtaposed insulating elements. For example, suitable insulating elements are described in document W02012 / 072906. This thermal barrier 5 of the thermal insulation mass can be produced in one or more thicknesses responding to the function of thermally isolating the contents of the tank from its environment. The material or materials which may also be present in such a thermal insulation mass consist, for example, of polymer foams, such as polyurethane foams, polystyrene or polyethylene, preferably at very low density (LDPE), manufactured glass wool, loose glass wool, melamine foams, aerogels, polyester wadding in mattresses or in bulk.

The thermal insulation block is conventionally anchored to the supporting structure, not shown in the appended figures, for example of a ship or a barge, by retaining members. Each of the insulating elements forming the thermal insulation block here has the shape of a rectangular parallelepiped having two large faces, or main faces, and four small faces, or lateral faces. More specifically, vimres 1, 2 adjacent metal rests on a support surface 10 of the thermal insulation block (or of the thermally insulating barrier 5). This support surface 10 is formed by the upper face of the thermally insulating barrier 5. The welding supports 3, 4 are anchored in the insulating element of the thermally insulating barrier 5 of the thermal insulation block.

In order to anchor the weld supports 3, 4 in the thermal insulation block, the upper face of the block (thermally insulating barrier 5) has a groove 11 which has a section in the shape of an inverted "T". The upper part of the thermally insulating barrier 5 can include a plywood or a composite material in which the groove 11 is housed. A retaining zone 12 develops in the thickness of the thermally insulating barrier 5 of the thermal insulation mass. insulator parallel to the support surface 10. The weld supports 3, 4 are inserted by sliding in the grooves 11 of the thermal insulation block. The weld supports 3, 4 are thus slidably anchored on, or in, the thermal insulation block 5, in the longitudinal direction of the weld supports 3, 4.

Provision may also be made for the retaining zone 12 to develop in a direction which is generally oblique with respect to the support surface 10 and possibly includes a component parallel to the support surface 10.

In the embodiment illustrated in Figures 2 to 4, the retaining area 12 is formed by two grooves 13, 14 developing on either side of the groove 11, at the lower end of said groove 11 .

The welding supports 3, 4 consist of two metal anchoring wings, preferably of identical shape and nature (material). These metal anchoring wings 3, 4 are essentially symmetrical with respect to a plane perpendicular to the support surface 10 and parallel to a longitudinal direction of the groove 11. Each metal anchoring wing 3 or 4 has a section in the form of “L” comprising a base 21 and an anchoring branch 22. The base 21 corresponds to the lower portion of the metal anchoring wing 3, 4 while the anchoring branch 22 corresponds to the longitudinal portion of these same metal anchor wings 3, 4.

The base 21 of each metal anchoring wing 3, 4 is housed in a groove 13, 14, or recess, respectively of the groove 11. The bases 21 of the metal anchoring wings 3, 4 develop parallel to the surface of support 10. A lower part of the anchoring branch 22 of one of the metal anchoring wings 3 or 4 is joined to the other anchor branch 22 of the metal anchor wing 3 or 4. Thus, according to a possibility offered by the invention, the lower portions of the anchor branches 22 of the two metal anchor wings 3, 4 are welded between them by a weld line 23. This weld line 23 is preferably housed, or located, in the thickness of the thermally insulating barrier 5 (mode shown in FIGS. 2 to 4) but it can be provided that this weld line 23 is situated at the level of the support surface 10, or even slightly above the latter 10. An upper part of the anchoring branch 22 of each of the metal anchoring wings 3, 4 projects from the support surface 10 from the groove 11, towards the inside of the tank.

In other words, the two adjacent metallic strakes 1, 2 are arranged on the support surface 10 on either side of the weld supports 3, 4. Each metallic strake 1, 2 has a flat central portion 6, 7. Each strake 1, 2 metallic has two raised edges 8, 9 located along two opposite longitudinal edges of the flat central portion 6, 7. A single raised edge 8, 9 of each of the two metal strakes 1, 2 is shown in Figures 2 to 4. Each raised edge 8, 9 projects from the support surface 10.

FIG. 2 illustrates the state in which the various elements 1, 2, 3, 4, 5, 6, 7, 8, 9 are positioned, that are the two adjacent strakes 1, 2, 6, 7, 8, 9, the two anchoring wings 3, 4 (fixed together here at the welding point 23) and the thermal insulation block 5, before the application of the welding process according to the invention.

FIG. 3 illustrates the elements specific to said welding process and device according to the invention, adding to the above elements of FIG. 2. Thus, compared to FIG. 2, there is present, in this FIG. 3, a conductive strip 30 (the expression “conductive strip” can also be used to designate the “conductive strip” 30) as well as two welding knobs 31, 32, said conductive strip 30 and said knobs 31, 32 being connected to a welding apparatus with the wheel, not shown in the accompanying figures. The conductive strip 30 is placed in the space defined between the two anchoring wings 3, 4, more precisely at the space between the anchoring branches 22, of each of the anchoring wings 3, 4, projecting from the support surface 10. The two knobs 31, 32 are placed contiguous against the face / external side (face / side being opposite to that where the anchoring wings are located) of each of the raised edges 8, 9 of the two strakes 1, 2. By applying a pressure of the knobs 31, 32, against each of the raised edges 8, 9, directed towards the conductive strip 30, it is possible to pass a current in the thickness constituted by a wheel 31 or 32, a raised edge 8 or 9, an anchoring wing 3 or 4 and the conductive blade 30 so as to carry out a welding with the wheel between each of the raised edges 8, 9 and the adjacent anchor wing 3, 4.

In the context of the present invention, the choice of the current intensity as well as the pressure exerted by the knurling wheels is determined, after multiple experiments, to ensure optimum seam welding. The current intensity and pressure ranges (for example expressed in bars) are in accordance with those presented above, for defined thicknesses and nature of materials.

From a point of view of the operation of the welding device according to the invention, one can envisage several configurations as for the polarity of the different elements to carry out the welding operation. Thus, we can predict that:

one knob 31 or 32 serves as a positive terminal and the other knob 31 or 32 as a negative terminal,

the two knobs 31, 32 serve as a positive terminal and the conductive strip 30 as a negative terminal,

the conductive strip 30 serves as a positive terminal and the two knobs 31, 32 as a negative terminal.

Of course, the conductive strip 30 can also be used as a (simple) electrically conductive element. Thus, in this preferred embodiment, one of the wheels 31 or 32 serves as a positive terminal and the other wheel 31 or 32 as a negative terminal, the conductive strip 30 having no polarity.

The conductive strip 30 consists of an electrically conductive material which must have a high melting point and be sufficiently resistant mechanically not to deform under the pressure forces of the knurls 31, 32. Copper is an economically advantageous material but others materials are possible, such as molybdenum (molybdenum-based alloys), tungsten (tungsten-based alloys) or graphite.

The raised edges 8, 9 of strakes 1, 2 advantageously have a thickness of 0.7 millimeter (mm) like the anchoring wings 3, 4, at least at the level of the anchoring branch 22 coming weld to the corresponding raised edge 8, 9. Of course, it can be expected that the thicknesses of the raised edges 8, 9 are greater as well as that of the anchoring wings 3, 4, which leads to the imposition of a higher current intensity. You can also choose different thicknesses for the raised edges 8, 9 and the wings anchor 3, 4, just like the nature of the material or materials constituting the raised edges 8, 9 (strakes 1, 2) and the anchor wings 3, 4 may possibly be different.

As can be seen in FIG. 4, once the welding method according to the invention has been implemented, the raised edge 8, 9 of each of the two adjacent metal strakes 1, 2 is welded to an anchoring wing respective metal 3, 4 forming a weld support. More particularly, each raised edge 8, 9 is welded by a weld line 40, 41 to the upper portion of a single metal anchoring wing 3, 4.

The technique described above for producing a waterproof membrane for a sealed and thermally insulating tank can be used in different types of tanks, for example to constitute the waterproof membrane for an LNG tank in a land installation or in a floating structure such as a LNG tanker or other.

With reference to FIG. 5, a cutaway view of an LNG tanker 70 shows a sealed and insulating tank 71 of generally prismatic shape mounted in the double hull 72 of the ship. The wall of the tank 71 comprises a primary waterproof barrier intended to be in contact with the LNG contained in the tank, a secondary waterproof barrier arranged between the primary waterproof barrier and the double hull 72 of the ship, and two insulating barriers arranged respectively between the primary waterproof barrier and the secondary waterproof barrier and between the secondary waterproof barrier and the double shell 72.

In a manner known per se, loading / unloading lines 73 arranged on the upper deck of the ship can be connected, by means of appropriate connectors, to a maritime or port terminal for transferring a cargo of LNG from or to the tank 71.

FIG. 5 represents an example of a maritime terminal comprising a loading and unloading station 75, an underwater pipe 76 and a shore installation 77. The loading and unloading station 75 is a fixed offshore installation comprising an arm mobile 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 mobile arm 74 can be adjusted to suit all LNG tankers . A connection pipe, 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 onshore installation 77. This comprises liquefied gas storage tanks 80 and connection pipes 81 connected by the underwater pipe 76 to the loading or unloading station 75. The submarine pipe 76 allows the transfer of the liquefied gas between the loading or unloading station 75 and the shore facility 77 over a long distance, for example 5 km, which makes it possible to keep the LNG carrier 70 at a long distance from the coast during loading and unloading operations.

To generate the pressure necessary for the transfer of the liquefied gas, pumps on board the ship 70 and / or pumps fitted to the shore installation 77 and / or pumps fitted to the loading and unloading station 75 are used.

Although the invention has been described in connection with several particular embodiments, it is obvious that it is in no way limited thereto and that it includes all the technical equivalents of the means described as well as their combinations if these are within the scope of the invention.

The use of the verb "to include", "to understand" or "to include" and of its conjugated forms does not exclude the presence of elements or other stages than those stated in a claim.

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

Claims

1. A method of welding a waterproof and thermally insulating tank membrane, in which a waterproof and thermally insulating tank comprises at least one waterproof metal membrane and a thermally insulating block comprising at least one thermally insulating barrier (5) adjacent to said membrane , in which :

- at least two metal strakes (1, 2) of the waterproof membrane, carried by a support surface (10) of the thermally insulating barrier (5), are in the form of a profiled part comprising a flat central portion ( 6, 7) resting on the support surface (10) and two raised lateral edges (8, 9) projecting from the support surface (10), and

- at least two metal welding supports (3, 4), carried by the thermally insulating barrier (5), protrude from the support surface (10) between the two raised lateral edges (8, 9) adjacent to the two strakes ( 1, 2) adjacent,

characterized in that a conductive strip (30) is inserted between the two aforesaid metal welding supports (3, 4) and in that, thereafter, the joints are welded together, in pairs, by welding the thumbwheel each of the two raised lateral edges (8, 9) of the two adjacent metal strakes (1, 2) with respectively one of said metallic welding supports (3, 4), interposed between said adjacent raised edges (8, 9) .

2. Method according to claim 1, in which at least one of the welding supports (3 or 4), preferably both (3, 4), consists of an anchoring wing so as to anchor the waterproof membrane to the thermally insulating barrier (5) of the thermal insulation block.

3. Method according to claim 2, in which the anchoring wing (3, 4) is in the form of an L and comprises a longitudinal portion (22) and a lower portion (21) engaged with the barrier. thermally insulating (5).

4. Method according to claim 3, wherein the lower portion (21) of the anchoring wing (3, 4) extends, parallel to the middle portion (6, 7) of the strakes (1, 2) metal, in a recess (13, 14) of the thermally insulating barrier (5) of the thermal insulation block.

5. Method according to any one of the preceding claims, in which, prior to the welding of each of the above raised edges (8, 9) with one of said welding supports (3, 4), said welding supports (3 , 4) were fixed by welding, sealingly, to each other.

6. Method according to any one of the preceding claims, in which the seam welding of each of said two raised edges (8, 9) adjacent with respectively one of said welding supports (3, 4) is carried out at a speed between 1.5 meters per minute (m / min) and 2.5 m / min, preferably at a speed of 1.8 m / min.

7. Method according to any one of the preceding claims, in which the above raised edges (8, 9), preferably also the welding supports (3, 4), are made of Invar or steel containing at least 20% manganese. , preferably at least 25% manganese. 8. The method of claim 7, wherein the thickness of the raised edges

(8, 9), preferably also the thickness of the above-mentioned welding supports, is between 0.5 and 0,

8 millimeter (mm), preferably equal to 0.7 mm.

9. The method of claim 8, wherein, during the seam welding, the intensity of the current is between 1.8 and 3.2 kiloamperes, preferably between 2.2 and 2.8 kiloamperes, and the pressure force exerted by each wheel (31, 32) respectively against a raised edge (8, 9) is between 1.2 and 2.8 bars, preferably between 2 and 2.5 bars.

10. The method of claim 7, wherein the thickness of the raised edges

(8, 9), preferably also the thickness of the above-mentioned welding supports (3, 4), is between 0.9 and 1.2 millimeter (mm), preferably equal to 1 mm.

11. The method of claim 10, wherein, during the seam welding, the intensity of the current is between 2.7 and 3.8 kiloamperes, preferably between 3 and 3.5 kiloamperes, and the force of pressure exerted by each wheel (31, 32) respectively against a raised edge (8, 9) is between 3.5 and 5 bars, preferably between 4 and 4.5 bars.

12. Method according to any one of the preceding claims, in which, during the seam welding, the electric current of the seam welding does not circulate continuously, preferably said electric current circulates during a corresponding time range of 60% to 80% of the time at a constant frequency.

13. Method according to any one of the preceding claims, in which the conductive strip (30) consists of a material or an alloy of materials with a high melting point, greater than the melting point of the raised edges (8, 9) and welding supports (3, 4).

14. A system for welding a sealed and thermally insulating tank membrane, the system comprising a seam welding device comprising two seams (31, 32), a means for holding said seams (31, 32) against a surface weld, and a wall of a sealed and thermally insulating tank comprising:

- two adjacent strakes (1, 2) of metallic waterproof membrane, carried by a support surface (10) of the thermally insulating barrier (5) of the waterproof and thermally insulating tank, being in the form of a profiled part comprising a flat central portion (6, 7) resting on the support surface (10) and two raised lateral edges (8, 9) projecting from the support surface (10), and

- two metal welding supports (3, 4), carried by the thermally insulating barrier (5), projecting from the support surface (10) between the two raised lateral edges (8, 9) adjacent to the two strakes (1, 2) adjacent,

the seam welding device producing at least one weld respectively between one of the above raised edges (8, 9) and one of the above weld supports (3, 4),

characterized in that the welding device comprises a conductive strip (30) intended to be inserted between the two welding supports (3, 4) so as to produce the welding of each of the above two adjacent raised side edges (8, 9) with respectively one of said welding supports (3, 4), interposed between said adjacent raised edges (8, 9).

15. Watertight and thermally insulating tank integrated in a supporting structure, comprising a watertight and thermally insulating tank comprising at least one watertight metallic membrane composed of a plurality of metal strakes (1, 2) and a thermally insulating block comprising at least one barrier thermally insulating (5) adjacent to said membrane, in which:

characterized in that each of the two raised lateral edges (8, 9) adjacent to the two adjacent metal strakes (1, 2) and respectively one of said weld supports (3, 4), interposed between said raised edges (8, 9 ) adjacent, are welded together in pairs, in a leaktight manner, by a welding process according to any one of claims 1 to 13.

16. Ship (70) for transporting a cold liquid product, the ship comprising a double hull (72) and a sealed and thermally insulating tank (71), according to claim 15, disposed in the double hull.

17. A transfer system for a fluid, the system comprising a ship (70) according to claim 16, insulated pipes arranged so as to connect the tank (71) installed in the hull of the ship to a floating or land storage installation and a pump for driving a flow of fluid through the isolated pipes from or to the floating or terrestrial storage installation towards or from the vessel of the ship.

18. A method of loading or unloading a ship (70) according to claim 17, in which a fluid is conveyed through insulated pipes. from or to a floating or terrestrial storage facility to or from the vessel (71).