CN112930240A

CN112930240A - Method for welding fluid-tight membranes of cans

Info

Publication number: CN112930240A
Application number: CN201980069163.6A
Authority: CN
Inventors: N·劳伦; M·拜登百奇
Original assignee: Gaztransport et Technigaz SA
Current assignee: Gaztransport et Technigaz SA
Priority date: 2018-10-16
Filing date: 2019-10-07
Publication date: 2021-06-08
Anticipated expiration: 2039-10-07
Also published as: WO2020079347A1; KR102506520B1; KR20210075173A; FR3087141B1; CN112930240B; FR3087141A1

Abstract

The invention relates to a method for welding fluid-tight and thermally insulating tank membranes, wherein: -at least two metal edge strips (1, 2) of the fluid tight membrane; and-at least two metal welding supports, -a pair of inner rollers, -a pair of outer rollers, so as to seam weld each of the two adjacent raised side edges with a respective one of the welding supports by means of the inner and outer rollers, the welding supports being interposed between the adjacent raised edges.

Description

Method for welding fluid-tight membranes of cans

Technical Field

The object of the present invention is to produce a fluid-tight and thermally insulated tank, more particularly, but not exclusively, intended for the marine transport of liquefied gases or cryogenic liquids, and more particularly for the transport of Liquefied Natural Gas (LNG) or of Liquefied Petroleum Gas (LPG) with a high methane content. These tanks may also be mounted on land or on a floating storage structure.

The invention herein relates to a fluid-tight membrane (membrane tank) for welding such tanks, and more particularly proposes a solution for optimal welding between two adjacent edge strips of the membrane, which have raised edges, and two anchoring flanges, and welding between these two metal adjacent edge strips at the level of these raised edges.

In the following, the expressions "anchoring flange" and "welding support" will be used interchangeably to denote the same component whose function is both to provide the means of anchoring the membrane (its edge strips) to the insulating body and to serve as a welding support fixed to each of the two adjacent edge strips.

Background

Tanks for storing or transporting liquefied gases at cryogenic temperatures are known, for example, from FR 2798358, FR 2709725, FR 2549575, in which the or each fluid-tight membrane (in particular the main fluid-tight membrane in contact with the product contained in the tank) is constituted by a thin metal plate that will be supported by a heat-insulating barrier. The thin metal plates are connected to each other in a fluid-tight manner so as to achieve fluid tightness of the tank.

Fig. 1 shows a known method of fixing the metal plate to an insulating barrier in a tank of this type. In this fig. 1, the upper surface 101 of the insulating barrier comprises a groove 102 extending from the support surface 101 into the thickness of the insulating barrier. This groove 102 has a retaining area within the thickness of the thermal insulation barrier formed by an undercut 103 extending parallel to the support surface 101. This undercut 103 extends within the thickness of the insulating barrier at the level of one end of the groove 102 opposite to the support surface 101, the groove 102 having an inverted "T" shaped cross section, the base of which is formed by the undercut 103. An "L" shaped anchoring flange 104 is inserted into the groove 102. The anchoring flange 104 has a base 105 which is accommodated in the undercut 103 in such a way that the anchoring flange 104 is held on the insulating barrier in a direction perpendicular to the supporting surface 101. The anchoring flange 104 also comprises an anchoring branch 106, the lower portion 107 of which is joined to the base 105 and the upper portion 108 of which protrudes above the supporting surface 101.

Two metal plates 109 are provided on respective opposite sides of the anchoring flange 104. Each of these metal plates 109 has a planar intermediate portion 110 bearing on the support surface 101 (the support surface 101 and the metal plate 109 are shown spaced apart in fig. 1 for clarity of the drawing). These metal plates 109 also have raised side edges, referred to herein as raised edges 111. The raised edge 111 of each of two adjacent metal plates 109 is welded to each side of the anchoring branch 106 of the anchoring flange 104.

Thus, the raised edge 111 forms together with the anchoring flange 104 a bellows for absorbing forces associated with the contraction of the fluid tight membrane, e.g. during loading of cryogenic liquid into the tank.

However, such an anchoring flange 104 constitutes a fixed attachment point for each raised edge 111. In fact, the anchoring flange 104 is loaded in two opposite directions by the raised edge 111, which remains substantially stationary in the tank. Thus, the anchoring of the raised edge 111 to the support surface 101 via the anchoring flange 104 is substantially fixed in a direction perpendicular to the raised edge 111. Thus, the flexibility of the fluid tight membrane is limited.

This is why it is proposed in FR 3054872 to use two anchoring flanges, each of which has the function of anchoring a respective one of two adjacent edge strips.

However, the joint between the raised edges of two adjacent edge strips is then made up of four thicknesses of material (two raised edges of the edge strips and two anchoring flanges) so as to be welded together in a completely fluid-tight manner. Now, attaching two edge strips to two anchoring flanges becomes particularly difficult, especially in view of the raised edges of the edge strips and the thickness of the anchoring flanges, and furthermore, in view of the objective of maintaining a high flexibility or elasticity at the level of these joints, in this way makes it possible to absorb particularly thermal loads.

Methods for welding two adjacent edge strips are disclosed in FR 3054872, which are not efficient or fast enough when each of the two adjacent edge strips is welded to a respective anchoring flange.

Disclosure of Invention

The present invention aims to remedy the drawbacks of the prior art by proposing a particularly effective solution for creating a weld between two adjacent edge strips when welding each of said adjacent edge strips to an anchoring flange to connect it or attach it to an insulating body.

After various studies and analyses, the applicant has found a solution that is technically easy to implement and that is able to rapidly produce a perfect weld, i.e. a completely fluid-tight weld with very high mechanical strength, between two adjacent/adjacent edge strips of the membrane via their respective anchoring flanges.

Accordingly, the present invention relates to a method for welding fluid tight and thermally insulated tank membranes, wherein a fluid tight and thermally insulated tank comprises at least one fluid tight metallic membrane and a thermally insulating body comprising at least one thermally insulating barrier adjacent to said membrane, wherein:

-at least two metal edge strips of the fluid-tight membrane carried by the support surface of the insulating barrier are in the form of a profiled part comprising a planar middle portion resting on the support surface and two convex side edges projecting from the support surface, and

at least two metal welding supports carried by the insulating barrier protrude from the support surface between two adjacent raised side edges of two adjacent edge strips,

the method according to the invention is characterized in that:

-inserting at least one pair of inner rollers each having a first circular section between the two metal welding supports such that the circular section of each of the inner rollers is each in contact with a respective one of the metal welding supports, and

-the pairs of outer rollers, each having a second circular section, are positioned such that the circular section of each of the outer rollers is each in contact with a respective adjacent raised edge of the metal strip, and then

Due to the presence of the inner and outer rollers, each of the raised edges of two metal edge strips is simultaneously seam-welded together in a fluid-tight manner, two by two, with an adjacent respective one of the metal welding supports, which are interposed between the adjacent raised edges.

According to a preferred embodiment, the inner and outer rollers are positioned in line along the axis x' x in fig. 3. In this case, the first circular sections of each of the inner rollers also contact each other. The present embodiment is an embodiment described below with reference to the drawings. In this embodiment, one and only one current flows between all the inner and outer rollers.

However, it is contemplated that the inner rollers do not contact. In this case, there are two pairs of rollers, each pair consisting of an outer roller and an inner roller. In this embodiment, different currents flow in each of the pairs of inner/outer rollers, and welding is still performed simultaneously or nearly simultaneously in both raised edge/metal weld support assemblies by each of the two pairs of inner/outer rollers, respectively. Furthermore, the two inner/outer rolls are longitudinally offset (relative to the direction of movement of the seam welder), that is, not actually aligned with each other.

Thanks to this method according to the invention, it is now possible to automatically produce welds of optimal quality, which thus significantly reduces the time required for installing a fluid-tight and thermally insulated tank. Therefore, productivity is improved. Furthermore, the welding method according to the invention makes it possible to obtain mechanical continuity and liquid tightness of the weld bead, to weld the length of the projecting edge without stopping or restarting due to the electrical continuity, and to not fuse together the two welding supports with the two projecting edges at the level of the weld bead.

Furthermore, thanks to the method according to the invention, each of the two raised edge/welding support assemblies is welded simultaneously (at the same time).

A number of tests have been carried out to evaluate the quality of the weld between each of the anchoring flanges and the edge strip (its raised edge), and these tests prove an optimum weld quality with excellent mechanical quality (in particular without traces of the material forming the inner roller), in particular in terms of its impact resistance, its resistance to stretching/bending/compression and its thermal gradients (the joint between the anchoring flange and the edge strip must always remain fluid-tight).

"seam welding" refers to welding in which the parts are assembled by applying an electric current (continuous or discontinuous application of electric current) and pressing a knurl (in the embodiments described in detail below, in this case an outer roller) against the surfaces to be welded.

Other advantageous features of the invention are briefly described below:

before seam welding, each of the adjacent raised edges of the edge strip and each of the respective metal welding supports are advantageously distanced from each other, using an expansion device, so as to form a space for inserting the pair of inner rollers;

according to a preferred embodiment of the invention, the diameter of the first circular sections of the two inner rollers is the same, and furthermore, the diameter of the second circular sections of the two outer rollers is preferably the same;

according to a preferred embodiment of the invention, the diameter of the first circular section of the two inner rollers is smaller than the diameter of the second circular section of the two outer rollers;

here, it may be noted that the outer rollers may have a smaller diameter than the inner rollers, but in this case the service life of the outer rollers will be reduced, since these rollers are subject to greater wear, in particular since the current passes first via the outer rollers (both rollers cause each of the outer rollers to alternately form the input of the circuit when the polarity of the current is advantageously changed);

during welding, the inner roll is preferably cooled, and the outer roll is also preferably cooled. In this type of embodiment, this cooling can be advantageously achieved by circulating a refrigerant fluid in the roller;

-at least one metal welding support, preferably two, preferably comprising anchoring flanges, for anchoring the fluid tight membrane to the insulation barrier of the insulation body;

in this embodiment, according to one possibility offered by the invention, the anchoring flange is L-shaped and comprises a longitudinal portion and a lower portion reciprocally engaged with the insulating barrier, the lower portion of the anchoring flange preferably extending parallel to the intermediate portion of the metal edging in the recess of the insulating barrier of the insulating body;

according to a preferred embodiment of the invention, before welding each of said raised edges to one of said metal welding supports, said metal welding supports have been fixed together by welding in a fluid-tight manner;

thus, as shown in fig. 7, the junction of two adjacent edge strips with two metal anchoring flanges has a W-shaped profile or cross-section due to the various spot welds. In other words, this type of joint has a double bellows function, which gives it a high elasticity, enabling the fluid-tight membrane (particularly at this level) to withstand or absorb very high thermal gradients, particularly reflected by a particularly pronounced (thermal) shrinkage.

The seam welding of each of the two adjacent raised edges and of the respective one of the welding supports is advantageously carried out at a speed of between 1 meter/minute (m/min) and 2.5m/min, preferably at a speed of 1.5 m/min;

according to one embodiment of the invention, said raised edge, and preferably a metal welded support, is formed by

Made of or made of a steel comprising at least 20% manganese, preferably at least 25% manganese, even more preferably 28% manganese;

according to one embodiment, the thickness of the raised edge, and preferably of the welding support, is between 0.5 mm and 0.8 mm, preferably equal to 0.7 mm;

in the present embodiment, during seam welding, the current is between 2.5 kiloamperes and 4 kiloamperes, preferably between 3 kiloamperes and 3.5 kiloamperes, and the pressure exerted by each outer roller on the respective raised edge is between 2 bars and 3.5 bars, preferably between 2.6 bars and 2.9 bars;

according to another embodiment, the thickness of the raised edge, and preferably of the metal welding support, is between 0.9 mm and 1.2 mm, preferably equal to 1 mm;

in the present embodiment, during seam welding, the current is between 3 kiloamperes and 4 kiloamperes, preferably between 3.3 kiloamperes and 3.7 kiloamperes, and the pressure exerted by each outer roller on the respective raised edge is between 3.5 bars and 5.5 bars, preferably between 4 bars and 5 bars;

during seam welding, the welding current advantageously flows discontinuously, and the current preferably flows at a constant frequency for 60% to 80% of the time.

The invention also relates to a system for welding fluid-tight and thermally insulating tank membranes, comprising: a seam welding device having two knurls, optionally including means for retaining the knurls on a surface to be welded; and a wall of a fluid-tight and thermally insulated tank, the tank comprising:

two metal edging adjacent to the fluid-tight membrane, carried by a support surface of an insulating barrier of a wall of the fluid-tight and thermally insulated tank, in the form of a profiled part comprising a planar central portion resting on the support surface and two convex side edges projecting from the support surface, and

two metal welding supports carried by the insulating barrier, which protrude from the support surface between two adjacent convex side edges of two adjacent edge strips;

the system according to the invention is characterized in that the welding device comprises:

-a pair of inner rollers, each inner roller having a first circular section intended to be interposed between two metal welding supports, the circular sections of the inner rollers being in contact with each other and each circular section being intended to be in contact with a respective one of said metal welding supports, and

preferably, the expanding means are such that each of the raised edges of the edging and the metal welding support are movable away from each other to insert said pair of inner rollers,

a pair of outer rollers, each outer roller having a second circular section, the circular section of each of the outer rollers being intended to be in contact with a respective raised edge of each of the adjacent edge strips,

cooling means, preferably for cooling the inner roll and preferably also the outer roll,

due to the inner and outer rollers, a simultaneous seam welding of each of the two adjacent side raised edges to a respective one of the metal welded supports sandwiched between the adjacent raised edges is produced in this way.

It should be noted that all the features described above in relation to the welding method according to the invention have been found to be applicable to the welding system briefly described above.

It should be noted here that the welding device according to the invention is capable of applying a current in a very wide frequency range, from conventional frequencies such as 50Hz (hertz) to high frequencies, i.e. at least equal to 1kHz (kilohertz) and up to 2kHz or even higher. In this case, the spot welds produced during the application of current between the two outer rollers/knurls are very close along the weld line, with the result that the fluid tightness and the mechanical strength of the weld line are particularly improved.

The invention also relates to a fluid-tight and thermally insulated tank integrated into a support structure, comprising a fluid-tight and thermally insulated tank, the tank comprising: at least one fluid-tight metal membrane consisting of a plurality of metal edge strips; and a thermally insulating body comprising at least one thermally insulating barrier adjacent to the membrane, wherein:

at least two metal welding supports carried by the insulating barrier protrude from the support surface between two adjacent raised side edges of two adjacent edge strips, the two metal welding supports being welded to each other in a fluid-tight manner by spot welding.

The tank according to the invention is characterized in that each of two adjacent raised side edges of two adjacent metal bars and a respective one of said metal welding supports interposed between said adjacent raised edges are welded two by two in a fluid-tight manner by seam welding.

According to document FR 3054872, the creation of a weld between the edge strip (its raised edge) and the anchoring flange is of course known per se, but with the method according to the invention, the spot weld has a cross section of a different shape from the shape of the prior art. In fact, assuming that the pair of inner rollers is positioned on the side of (adjacent to) the anchoring flange and the knurls (or outer rollers) are positioned on the side of (adjacent to) the raised edge of the edge strip, the spot-welded section has a substantially oval (and not strictly symmetrical as in the prior art) shape, whose projecting part (projection or protuberance) is found on the side of the edge strip, that is to say on the side where the knurls (outer rollers) are positioned during welding. It should be noted that the spot welds have a symmetrical shape, provided that two identical knurls provided on respective opposite sides of the spot welds are used. This section, which is slightly different in shape with respect to the prior art (fig. 7 does not represent this shape feature of the spot weld), obviously has no negative effect on the quality of the spot weld, but it makes it possible to distinguish the spot weld produced by the method of the invention from any other welding process. Such cans, having all the features described above and featuring at least one spot weld produced by the "outer/inner roller" pair, are therefore indeed novel in the sense that the outer rollers have a different shape and/or size (diameter) than the inner rollers.

It should also be noted here that due to the device and the welding method according to the invention it is likewise possible to alternate the +/-polarity of the outer rollers at the desired frequency. In so doing, the polarity of the outer rollers/knurls is changed, since some of the electrical energy is dissipated in the form of heat, which is dissipated between the pairs of outer rollers by the joule effect (resistance to the flow of current), so that, considering the path of the current (electrons), the first outer roller forming the current input is subjected to more heat (because it is subjected to a higher current) than the second and last outer rollers forming the current output.

Finally, the invention also relates to a ship for transporting a cold liquid product, comprising a double hull and a fluid-tight and thermally insulated tank as briefly described above arranged in the double hull.

The ship according to the invention advantageously comprises at least one fluid-tight and insulated tank as described above, said tank comprising two continuous fluid-tight barriers, the main one in contact with the product contained in the tank and the auxiliary other fluid-tight barrier being arranged between the main barrier and a supporting structure, the supporting structure preferably consisting of at least one portion of a wall of the tank, the two fluid-tight barriers alternating with two thermal insulation barriers or a single thermal insulation barrier being arranged between the main barrier and the supporting structure.

In International Maritime Organization (IMO) codes, such tanks are commonly referred to as integrated tanks, such as NO

And (4) molding the tank.

The tank preferably contains Liquefied Natural Gas (LNG) or liquefied gas (LPG).

According to one embodiment, the invention also provides a method for loading or unloading a vessel of the above-mentioned type, wherein the fluid is transported from the floating or onshore storage facility to the vessel's tank or from the vessel's tank to the floating or onshore storage facility by means of an insulated pipeline.

The present invention also provides, according to one embodiment, a fluid transport system, comprising: the above-mentioned boat; an insulated pipeline arranged in such a way that a tank installed in the hull of the vessel is connected to a floating or onshore storage facility; and a pump for driving a flow of fluid from the floating or onshore storage facility to the tank of the vessel or from the tank of the vessel to the floating or onshore storage facility through the insulated pipeline.

Drawings

The following description is given by way of non-limiting illustration only with reference to the accompanying drawings, in which:

FIG. 1 is a cross-sectional view of a prior art fluid-tight metallic membrane anchoring flange anchored in an insulation barrier of a fluid-tight and insulated tank;

fig. 2 is a cross-sectional view of two metal film anchoring flanges which have been welded together before inserting them into the insulating body, showing the wall portions of the tank at the level of two adjacent edge strips before applying the welding method according to the invention;

FIG. 3 is a top view of two anchoring flanges and two raised edges of adjacent edge strips, in which the elements characteristic of the implementation of the welding method according to the invention are visible this time;

fig. 4 is a front view of the element of fig. 3 repeated on a vertical plane X' X;

FIG. 5 is a schematic view of some of the elements of the welding apparatus according to the present invention, with particular reference to the expansion means for separating the raised edge and the anchoring flange for positioning the inner roller for seam welding;

FIG. 6 is a front view of FIG. 5 in plane P;

FIG. 7 is a cross-sectional view of the elements visible in FIG. 2 in a repeating fashion, showing the tank wall portion fluid-tight and thermally insulated after the welding method according to the present invention has been performed;

fig. 8 is a schematic cross-sectional view of a methane carrier tank and a dock for loading/unloading the tank.

Detailed Description

In the following description, reference is made to a fluid-tight membrane in the context of a fluid-tight and thermally insulated tank. Such tanks comprise an internal space intended for being filled with combustible or non-combustible gases. In particular, the gas may be Liquefied Natural Gas (LNG), that is to say a gas mixture comprising mainly methane and a small proportion of one or more hydrocarbons, such as ethane, propane, n-butane, isobutane, n-pentane, isopentane, neopentane and nitrogen. The gas can also be ethane or Liquefied Petroleum Gas (LPG), that is to say a mixture of hydrocarbons produced by petroleum refining, and essentially contains propane and butane.

Generally, the fluid-tight membrane rests on a support surface formed by the thermal insulation barrier of the tank. Such a fluid-tight membrane has a repetitive structure comprising alternately on the one hand a strip of a sheet metal forming edging arranged on a support surface and on the other hand an elongated welding support connected to the support surface and extending parallel to the strip of the sheet metal over at least a part of the length of the strip of the sheet metal. The sheet metal strip includes a raised edge that is positioned against and welded to an adjacent weld support. Such structures being used, for example, in NO sold by the applicant

A methane ship tank.

At the level of the fluid-tight and thermally insulated tank, not shown as a whole in the figures, the raised edges of the strake are preferably arranged in a longitudinal direction perpendicular or parallel to the longitudinal direction of the vessel. The raised edge thus constitutes a bellows, enabling the absorption of contraction forces in the longitudinal direction of the vessel or in a transverse direction perpendicular to the longitudinal direction. The sheet metal strips and the welding supports are interrupted at the corners, for example in the manner described in document WO 2012/072906 or FR 2724623.

According to an embodiment, one of the fluid tight membrane (strake), the fluid tight membrane or the fluid tight membrane may be made of a material selected from stainless steel, aluminum, titanium,

(that is, an alloy of iron and nickel, which typically has an expansion coefficient of 1.2X 10^-6And 2X 10-6K^-1Of steel) or an iron alloy with a high manganese content (containing at least 20% manganese or even at least 28% manganese, with an expansion coefficient of 7 to 9 x 10^-6K^-1Of the order of magnitude) of metal. According to one embodiment, the coefficient of thermal contraction is selected to be less than 16 x 10^-6The material/K is used for applications in which the liquid gas temperature is between-45 ℃ and-100 ℃.

Fig. 2 to 7 show views of the wall of a fluid-tight and thermally insulated tank at the level of the connection between two adjacent metal edge strips 1, 2 of the fluid-tight membrane of the tank wall and two welded

supports

3, 4 of a thermal insulation barrier 5 anchored to the thermally insulating body of the tank wall. Such an insulating barrier 5 is formed by juxtaposed insulating elements. Suitable insulating elements are described, for example, in document W02012/072906. The insulating barrier 5 of the insulating body can be made in one or more thicknesses, so as to fulfil the function of insulating the contents of the tank from its environment. The material(s) which may also be present in such an insulating body comprise, for example, polymer foams, such as polyurethane foams, polystyrene or polyethylene, preferably very Low Density Polyethylene (LDPE), synthetic glass wool, loose glass wool, melamine foam, aerogels, polyester wadding in matt or loose form.

Typically, the insulating body is anchored to a supporting structure (not shown in the drawings), for example a ship or barge, by means of retaining members. Each of the insulating elements forming the insulating body here has the shape of a cuboid comprising two large faces or main faces and four small faces or side faces. More specifically, the adjacent metal edging 1, 2 rests on a support surface 10 of the insulating body (or insulating barrier 5). The support surface 10 is formed by the upper surface of the heat insulating barrier 5. The welded supports 3, 4 are anchored in the heat-insulating elements of the heat-insulating barrier 5 of the heat-insulating body.

In order to anchor the welding supports 3, 4 in the insulating body, the upper surface of the body (insulating barrier 5) comprises a groove 11, the section of which is inverted "T" shaped. The upper part of the insulating barrier 5 may comprise plywood or a composite material in which the grooves 11 are formed. The retaining areas 12 extend parallel to the support surface 10 within the thickness of the insulating barrier 5 of the insulating body. The welded supports 3, 4 are slid into the groove 11 of the insulating body. Thus, the welded

supports

3, 4 are anchored in a sliding manner on the insulating body 5 or within the insulating body 5 in the longitudinal direction of the welded

supports

3, 4.

The holding area 12 may likewise extend in a direction substantially inclined with respect to the support surface 10 and may comprise components parallel to the support surface 10. Here, as can be seen in fig. 2, the retaining region 12 is formed by two

undercuts

13, 14 which extend on respective opposite sides of the groove 11 at the level of the lower end of said groove 11.

The weld supports 3, 4 consist of two metal anchoring flanges, which preferably have the same shape and kind (material). These

metal anchoring flanges

3, 4 are substantially symmetrical with respect to a plane perpendicular to the support surface 10 and parallel to the longitudinal direction of the groove 11. Each

metal anchoring flange

3 or 4 has an "L" shaped cross-section comprising a base 21 and an anchoring branch 22. The base 21 corresponds to the lower part of the

metal anchoring flanges

3, 4, while the anchoring branches 22 correspond to the longitudinal parts of those same

metal anchoring flanges

3, 4.

The base 21 of each

metal anchoring flange

3, 4 is received in a respective undercut 13, 14 or recess in the groove 11. The base 21 of the

metal anchoring flanges

3, 4 extends parallel to the support surface 10. The lower portion of the anchoring branch 22 of one of the

metallic anchoring flanges

3 or 4 is joined to the other anchoring branch 22 of the

metallic anchoring flange

3 or 4. According to one possibility offered by the present invention, the lower portions of the anchoring branches 22 of the two

metallic anchoring flanges

3, 4 are therefore welded together by means of a weld line 23. The weld line 23 is preferably accommodated or located within the thickness of the insulating barrier 5 (embodiment shown in fig. 2 to 4), but the weld line 23 may be located at the level of the support surface 10, or even slightly higher than the latter surface 10. The upper part of the anchoring branch 22 of each of the

metal anchoring flanges

3, 4 protrudes from the supporting surface 10 from the groove 11 towards the inside of the tank.

In other words, two

adjacent metal strips

1, 2 are arranged on the support surface 10 on respective opposite sides of the

welding support

3, 4. Each

metal strip

1, 2 has a planar middle portion 6, 7. Each metal edging 1, 2 has two raised edges 8, 9 positioned along two opposite longitudinal edges of the planar intermediate portion 6, 7. Fig. 2 to 4 show a single raised edge 8, 9 of each of the two

metal strips

1, 2. Each raised edge 8, 9 protrudes with respect to the support surface 10.

Fig. 2 shows a situation in which the

various elements

1, 2, 3, 4, 5, 6, 7, 8, 9 are positioned before applying the welding method according to the invention, comprising two adjacent edge strips 1, 2, 6, 7, 8, 9, their intermediate portions 6, 7, their raised edges 8, 9, two anchoring flanges 3, 4 (here fixed together at the level of the spot welds 23) and the insulating body 5.

As can be seen in fig. 3 and 4, which represent the same elements in both views or in both sections, the method and welding device according to the invention make use of two

outer rollers

30, 31 which bear against the two respective raised edges 8, 9, and two

inner rollers

32, 33 which are located or positioned between each of the two welding supports 3, 4. Thus, the passage of the current from the welding device to the knurl, from one of the

outer rollers

30 or 31 to the other

outer roller

30 or 31, presents a continuity of material, i.e. one of the raised edges 8 or 9, then one of the welding supports 3 or 4, then the pair of

inner rollers

32, 33, then the other (or second) welding

support

3 or 4, the other raised edge 8 or 9 and the second

outer roller

30 or 31. Of course, these

elements

3, 4, 8, 9, 30, 31, 32, 33 have to be in contact when applying an electric current in order to achieve resistance welding, which is why the welding device applies a pressure 34 between 2 bar and 5.5 bar at each of the

outer rollers

30, 31 via the

outer rollers

30, 31 to the pair of

inner rollers

32, 33.

In order to enable a linear movement 35 of the welding device along the weld line, the

outer rollers

30, 31 and the

inner rollers

32, 33 are rotated by said device in respective opposite directions of rotation, i.e. in case one is rotated counter-clockwise and the other is rotated clockwise.

The

inner rollers

32, 33 may be mounted to rotate freely so that they are driven in rotation by the forward movement of the

outer rollers

30, 31 and the pressure 34 exerted by the latter. The

inner rollers

32, 33 may also be rotationally driven by the welding device like the

outer rollers

30, 31.

As can be seen in the figures, the diameter of the

inner rollers

32, 33 is preferably smaller than that of the

outer rollers

30, 31, so that it can be easily positioned between the two welded supports 3 or 4-raised edge 8 or 9 assemblies which have previously been distanced from each other by the expansion means 36.

In an illustrative example of one non-limiting embodiment, the

outer rollers

30, 31 have a diameter of 30 millimeters (mm) and the

inner rollers

32, 33 have a diameter of 14 mm. Therefore, the distance between the two metal welding supports 3, 4 must be 28 mm in order to accommodate the

inner rollers

32, 33, as shown in particular in fig. 3. In this configuration, the welding supports 3, 4 have a length (length protruding from the support surface 10) of 40 mm, for example, from the support surface 10 of the heat insulating body 5. The length of the welding supports 3, 4 is greater than the height of the raised edges 8, 9; in other words, the welding supports 3, 4 protrude above the raised edges 8, 9, for example by a few millimetres. Normally, the stitch-line is produced a few millimetres from the upper edge of the raised edge 8, 9, of the order of a few millimetres, for example between 4 and 8 millimetres from this edge. Of course, other sizes of the raised edges 8, 9 of the metal welding supports 3, 4 or other diameters of the

rollers

30, 31 and 32, 33 are contemplated, as long as the targeted positioning of the

inner rollers

32, 33 is achieved and the seam welding can be performed efficiently without damaging the

elements

3, 4 and 8, 9 to be welded together and/or damaging the elements used to perform the seam welding (

inner rollers

32, 33 and outer rollers 30, 31).

According to one possibility provided by the invention (not shown in the drawings), the attachment of the raised edge 8 or 9 and the

welding support

3 or 4 by seam welding can be supplemented by spot welding, for example at a higher level (above) the seam line according to conventional welding techniques. The spot weld line may advantageously be located at the level of the upper edge of the raised edge 8 or 9.

Other elements of the welding device, in particular the pressure roller 37 and the spreading device 36, can be seen in fig. 5 and 6.

The pressure roller 37 is carried by a stud 38 fixed to the welding device, which stud is not shown in its entirety in the figures. Their function is to press two by two the respective opposite sides of the metal welding supports 3, 4 and of the two raised edges 8, 9 before and after the passage of the

rollers

30, 31, 32, 33; the

latter rollers

30, 31, 32, 33 move along the raised edges 8, 9 and the metal welding supports 3, 4 at the same speed and in the same direction, since they are all connected or fixed to the welding device. Here, these pressure rollers 37 are four in number and comprise at their lower ends a rotation device 39 to facilitate the simple guiding of the welding device by the operator. The rotating discs 39 of the press rollers 37 may be freely rotatable or rotationally driven via each of the studs 38 by one or more motive forces present in the welding device.

The guide rollers, not shown in the drawings, have the same function of moving along the weld line to be produced or assisting the movement of the welding device. These guide rollers usually consist of wheels mounted to rotate freely or driven in rotation by at least one motor or the like in the welding device and supported on the planar intermediate portions 6, 7 of the edge strips 1, 2.

The rotating pressure roller 37 and/or the guide roller make it possible to provide assistance to the operator handling the welding device, on the one hand facilitating the movement of the welding device and, on the other hand, enabling the device to move at a constant speed, which has a direct effect on the quality and regularity of the stitch line.

In the embodiment chosen to illustrate the invention, as shown in fig. 5, the expansion means 36 take the form of a punch having a substantially conical section from the front to the rear of the punch, the width or length of the base of the cone corresponding substantially to the spacing required to position the

inner rollers

32, 33. Of course, this expansion device 36 connected or attached to the welding device is arranged in front of the

inner rollers

32, 33, so that when the welding device is moved forward, the point of the end of the expansion device 36 starts to separate the metal welding supports 3, 4 and the respective raised edges 8, 9 from each other by a distance to enable passage or positioning of the

inner rollers

32, 33.

In fig. 5, the raised edge 8 and a portion of the metal welding support 3 are shown as appearing transparent, so as to see the profile shape of the expansion means 36, its flared portion at the front end point. In the embodiment shown in the figures, the expansion means 36 consist of passive mechanical means, that is to say, due to the action of the welding means or to the movement of the latter during its movement, and due to its conical section shape and its passage through the end between the two metal welding supports 3, 4, the expansion means separate the raised edges 8, 9 and the welding supports 3, 4 by the distance required to enable the positioning of the

inner rollers

32, 33. Of course, any other means that can separate the raised edges 8, 9 and the welding supports 3, 4 by this distance before the seam welding operation can be envisaged, whether it is a device independent of the welding apparatus, or by the inherent ability to move the device and/or the device to produce such a separate movement according to some other mechanical or even electrical/electronic process.

Preferably, a system for cooling the rollers is provided for each of the two pairs of

inner rollers

32, 33 and

outer rollers

30, 31 to discharge or dissipate the energy from the electrical resistance resulting from the passage of the current (also enabling welding). A cooling system of this type, not shown in the figures, can consist of channels formed in the roller in which a refrigerant fluid, such as one or more components of the ethylene glycol (water + ethylene glycol mixture) or Hydrofluorocarbon (HFC) family, circulates. Of course, the choice of such a refrigerant fluid and its flow rate in the channel of the roller are particularly linked to the current used to produce the seam weld.

In the context of the present invention, the choice of current and the choice of pressure exerted by the knurls (outer rollers 30, 31) are determined after a number of experiments to ensure an optimal seam weld. The ranges of current and pressure (e.g., in bar) conform to the ranges described above for defined material thicknesses and properties.

From the point of view of the operation of the welding device according to the invention, a plurality of configurations of the polarity of the various elements can be envisaged for performing the welding operation.

It may also be noted that according to one possibility provided by the invention, it is possible to vary the polarity of the two outer rollers at a desired frequency in order to periodically vary the function of the two rollers as input and output for the current supplied by the welding device. Thus, the stitch-line is identical on each side (the spot welds on each of the two raised edge-weld support assemblies have a cross section of substantially the same shape) and the heat generated by the joule effect is distributed between the two outer rollers, instead of one of these rollers (the one forming the input for the current) being subjected to more/stronger heat.

At least at the height of the anchoring branches 22 to be welded to the respective raised edges 8, 9, the raised edges 8, 9 of the edge strips 1, 2 advantageously have a thickness of 0.7 millimeters (mm) as the anchoring

flanges

3, 4. Of course, in this way the thickness of the raised edges 8, 9 may be greater than the thickness of the anchoring

flanges

3, 4, which results in a higher applied current. The different thicknesses can equally be chosen for the raised edges 8, 9 and the anchoring

flanges

3, 4, and likewise the nature of the material or materials constituting the raised edges 8, 9 (the edge strips 1, 2) and the anchoring

flanges

3, 4 can be different.

As can be seen from fig. 7, once the welding method according to the invention has been used, the raised edges 8, 9 of each of the two

adjacent metal strips

1, 2 are welded to the respective

metal anchoring flanges

3, 4 to form a welding support. More specifically, each raised edge 8, 9 is welded to the upper portion of only one

metallic anchoring flange

3, 4 by a

weld line

40, 41.

The above described technology for creating a fluid tight membrane of a fluid tight and thermally insulated tank may be used in different types of tanks, for example in constructing a fluid tight membrane of an LNG tank in a land based facility or a floating structure such as a methane carrier or the like.

Referring to fig. 8, a cross-sectional view of a methane transport vessel 70 shows a fluid tight and insulated tank 71 of generally prismatic shape mounted in the double hull 72 of the vessel. The walls of the tank 71 comprise a main fluid containment barrier intended to be in contact with the LNG contained in the tank, a secondary fluid containment barrier arranged between the main fluid containment barrier and the double hull 72 of the ship, and two insulating barriers arranged between the main fluid containment barrier and the secondary fluid containment barrier and between the secondary fluid containment barrier and the double hull 72, respectively.

In a manner known per se, a loading/unloading line 73 provided on the upper deck of the ship may be connected to a maritime or harbour terminal by means of suitable connectors for transferring LNG cargo from the tanks 71 or for transferring LNG cargo to the tanks 71.

Fig. 8 shows an example of a marine terminal comprising a loading and unloading station 75, an underwater pipeline 76 and an onshore facility 77. The loading and unloading station 75 is a fixed onshore facility comprising a mobile arm 74 and a tower 78 supporting the mobile arm 74. The mobile arm 74 carries a bundle of insulated flexible tubes 79 that can be connected to the loading/unloading line 73. The orientable moving arm 74 is adapted to all methane carrier loading specifications. A not shown connecting line extends inside tower 78. The loading and unloading station 75 enables the methane transport vessel 70 to be loaded and unloaded from an onshore facility 77 or to an onshore facility 77. The onshore facility comprises a liquefied gas tank 80 and a connecting line 81 which is connected to the loading or unloading station 75 via the underwater line 76. The underwater pipeline 76 enables the transfer of liquefied gas over a large distance (e.g. 5km) between the loading or unloading station 75 and the onshore facility 77, which enables the methane carrier 70 to be maintained at a large distance from shore during loading and unloading operations.

Pumps on board the vessel 70 and/or pumps equipped with onshore facilities 77 and/or pumps equipped with loading and unloading stations 75 are used to generate the pressure required to deliver the liquefied gas.

Although the invention has been described in connection with several particular embodiments, it is obvious that the invention is by no means limited to these embodiments and that the invention comprises all technical equivalents and combinations of the described means if they fall within the scope of the invention as defined by the claims.

Use of the verb "comprise" or "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim.

In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim.

Claims

1. A method for welding fluid-tight and thermally insulated tank membranes, wherein a fluid-tight and thermally insulated tank comprises at least one fluid-tight metallic membrane and a thermally insulating body comprising at least one thermally insulating barrier (5) adjacent to the membrane, wherein:

-at least two metal edge strips (1, 2) of the fluid-tight membrane carried by a support surface (10) of the insulating barrier (5) are in the form of a profiled part comprising a planar intermediate portion (6, 7) resting on the support surface (10) and two convex side edges (8, 9) projecting from the support surface (10), and

-at least two metal welding supports (3, 4) carried by the insulating barrier (5) protrude from the support surface (10) between the two adjacent raised side edges (8, 9) of the two adjacent edge strips (1, 2),

the method is characterized in that:

-inserting at least one pair of inner rollers (32, 33), each having a first circular section, between the two metal welding supports (3, 4) so that the circular section of each of the inner rollers (32, 33) is each in contact with a respective one of the metal welding supports (3, 4), and

-the pairs of outer rollers (30, 31), each having a second circular section, are positioned so that the circular section of each of the outer rollers (30, 31) is each in contact with a respective adjacent raised edge (8, 9) of the metal strip (1, 2), before the metal strip is brought into contact with the respective adjacent raised edge (8, 9), and then

-thanks to the inner rollers (32, 33) and the outer rollers (30, 31), each of the convex side edges (8, 9) of the two metal edgings (1, 2) is welded together simultaneously, in a fluid-tight manner, two by two, with an adjacent respective one of the metal welding supports (3, 4) interposed between the adjacent convex edges (8, 9).

2. The method of claim 1, wherein the circular segments of each of the inner rollers (32, 33) also contact each other.

3. The method according to claim 1 or 2, wherein, before carrying out the seam welding, each of the adjacent raised edges (8, 9) of the edge strips (1, 2) and each of the respective metal welding supports (3, 4) are moved away from each other using an expansion device (36) to form a space for inserting the pair of inner rollers (32, 33).

4. The method according to any one of the preceding claims, wherein the diameter of the first circular sections of the two inner rollers (32, 33) is the same and, furthermore, the diameter of the second circular sections of the two outer rollers (30, 31) is preferably the same.

5. The method according to any one of the preceding claims, wherein the diameter of the first circular section of the two inner rollers (32, 33) is smaller than the diameter of the second circular section of the two outer rollers (30, 31).

6. The method of any one of the preceding claims, wherein the inner rollers (32, 33) and preferably the outer rollers (30, 31) are cooled during welding, preferably by circulating a refrigerant fluid in the rollers (30, 31 and 32, 33).

7. The method according to any of the preceding claims, wherein at least one metal welding support (3 or 4), preferably two metal welding supports (3, 4), comprises an anchoring flange to anchor the fluid tight membrane to the insulating barrier (5) of the insulating body.

8. A method according to claim 7, wherein the anchoring flange is L-shaped and comprises a longitudinal portion (22) and a lower portion (21) which is mutually engaged with the insulating barrier (5), the lower portion (21) of the anchoring flange (3, 4) preferably extending parallel to the intermediate portion (6, 7) of the metal edging (1, 2) in the recess (13, 14) of the insulating barrier (5) of the insulating body.

9. The method according to any one of the preceding claims, wherein the metal welded supports (3, 4) have been fixed together by welding in a fluid-tight manner before welding each of the raised edges (8, 9) to one of the metal welded supports (3, 4).

10. The method of any one of the preceding claims, wherein the seam welding of each of the two adjacent raised edges and the respective one of the welding supports is performed at a speed of between 1 meter/minute (m/min) and 2.5m/min, preferably at a speed of 1.5 m/min.

11. Method according to any one of the preceding claims, wherein the raised edges (8, 9) and preferably the metallic welding supports (3, 4) are made of invar or of steel containing at least 20% manganese, preferably at least 25% manganese.

12. The method of claim 11, wherein the thickness of the raised edges (8, 9) and preferably of the welding support is between 0.5 and 0.8 millimeters (mm), preferably equal to 0.7 mm, and wherein during seam welding the current is between 2.5 and 4 kiloamperes, preferably between 3 and 3.5 kiloamperes, and the pressure applied by each outer roller (30, 31) to the respective raised edge (8, 9) is between 2 and 3.5 bars, preferably between 2.6 and 2.9 bars.

13. The method of claim 11, wherein the thickness of the raised edges (8, 9) and preferably of the metal welding supports (3, 4) is between 0.9 and 1.2 millimeters (mm), preferably equal to 1mm, and wherein, during seam welding, the current is between 3 and 4 kiloamperes, preferably between 3.3 and 3.7 kiloamperes, and the pressure exerted by each outer roller (30, 31) on the respective raised edge (8, 9) is between 3.5 and 5.5 bar, preferably between 4 and 5 bar.

14. A method according to any preceding claim, wherein the welding current does not flow continuously during seam welding, and the current flows at a constant frequency preferably 60% to 80% of the time.

15. A system for welding fluid tight and thermally insulating tank membranes, the system comprising: a seam welding device comprising two knurls (30, 31), optionally comprising means (37) for retaining the knurls (30, 31) on a surface to be welded; and a wall of the tank that is fluid-tight and thermally insulated, the wall comprising:

-two metal edging (1, 2) adjacent to the fluid-tight membrane, carried by a support surface (10) of an insulating barrier (5) of the wall of the fluid-tight and thermally insulated tank, in the form of a profiled part comprising a planar middle portion (6, 7) resting on the support surface (10) and two convex side edges (8, 9) protruding from the support surface (10), and

-two metal welded supports (3, 4) carried by the insulating barrier (5), which metal welded supports protrude from the support surface (10) between the two adjacent raised side edges (8, 9) of two adjacent edge strips (1, 2),

characterized in that, the welding device includes:

-a pair of inner rollers (32, 33) each having a first circular section intended to be inserted between the two metal welding supports (3, 4), the circular sections of the inner rollers (32, 33) being in contact with each other and each circular section being intended to be in contact with a respective one of the metal welding supports (3, 4),

-preferably expanding means (36) enabling each of said raised edges (8, 9) of said regula-tions (1, 2) and said metal welding supports (3, 4) to be moved away from each other for inserting said pair of inner rollers (32, 33),

-a pair of outer rollers (30, 31) each having a second circular section, the circular section of each of the outer rollers (30, 31) being intended to be in contact with a respective convex edge of each of the adjacent edge strips,

preferably cooling means for cooling the inner rollers (32, 33) and preferably also the outer rollers (30, 31),

due to the inner rollers (32, 33) and the outer rollers (30, 31), a simultaneous seam welding of each of the two adjacent raised side edges (8, 9) to a respective metal welding support (3, 4) is produced in this way, the metal welding supports being sandwiched between the adjacent raised edges (8, 9).

16. A fluid-tight and thermally insulated tank integrated into a support structure, comprising a fluid-tight and thermally insulated tank, the fluid-tight and thermally insulated tank comprising: at least one fluid-tight metal film consisting of a plurality of metal edge strips (1, 2); and a thermally insulating body comprising at least one thermal barrier (5) adjacent to the membrane, wherein:

-at least two metal edge strips (1, 2) of the fluid-tight membrane carried by a support surface (10) of the insulating barrier (5) are in the form of a profiled part comprising a planar middle portion (6, 7) resting on the support surface (10) and two convex side edges (8, 9) protruding from the support surface (10), and

-at least two metal welding supports (3, 4) carried by the insulating barrier (5) protrude from the support surface (10) between the two adjacent raised side edges (8, 9) of the two adjacent edge strips (1, 2), the two metal welding supports (3, 4) being welded to each other in a fluid-tight manner by spot welding,

characterized in that each of said two adjacent convex side edges (8, 9) of said two adjacent metal strips (1, 2) and a respective metal welding support (3, 4) sandwiched between said adjacent convex edges (8, 9) are welded together in a fluid-tight manner by seam welding two by two.

17. A ship (70) for transporting cold liquid products, said ship comprising a double hull (72) and a fluid-tight and thermally insulated tank (71) according to claim 16 arranged in said double hull.

18. A fluid delivery system, the system comprising: a vessel (70) according to claim 17; -insulated piping (73, 79, 76, 81) arranged in such a way as to connect the tanks (71) installed in the hull of the vessel to a floating or onshore storage facility (77); and a pump for driving a flow of fluid from the floating or onshore storage facility to the tank of the vessel or from the tank of the vessel to the floating or onshore storage facility through the insulated pipeline.

19. A method for loading or unloading a vessel (70) according to claim 17, wherein fluid is transported from a floating or onshore storage facility (77) to the tank (71) of the vessel or from the tank of the vessel to the floating or onshore storage facility by means of insulated piping (73, 79, 76, 81).