EP0543686A1 - Fluid-tight and heat-insulating tank integrated in a ship's hull structure - Google Patents

Abstract

The invention relates to a fluid-tight and insulating tank integrated in the hull structure of a ship. This tank comprises two impermeability barriers alternating with two insulating barriers. The boxes 3 of the secondary insulating barrier are attached to the hull structure of the ship by tabs 5 fixed in line with thick internal partitions, said partitions supporting longitudinally the means of attaching the primary barrier. These fastening means are constituted by a sliding joint with a double fold arranged between two plates 21 of the primary insulating barrier, the plates 21 being held in position by angles welded on a welding support 18 which constitutes a part of the fastening means. …<IMAGE>…

Description

The present invention relates to the production of sealed and thermally insulating tanks intended for the transport by sea of liquefied gases and, in particular, for the transport of liquefied natural gases with a high methane content.

In French patents 1,438,330, 2,105,710 and 2,146,612, the production of a sealed and insulating tank has already been described, integrated into the carrying structure of a ship and constituted by two successive sealing barriers, one primary, in contact with the transported liquefied gas, and a secondary, disposed between the primary barrier and the ship's supporting structure, these two sealing barriers being alternated with two layers of thermal insulation called "insulating barriers". In these embodiments, the primary and secondary insulating barriers are constituted by parallelepipedic boxes filled with a particulate insulation and the primary and secondary sealing barriers are constituted by metallic strakes, for example, invar, welded with raised edges and on the other side of a welding wing.

In French patent 2,462,336, a tank has been proposed in which the secondary insulating barrier is produced by a thick layer of cellular material fixed against the load-bearing structure of the ship, the primary insulating barrier consisting of a rigid plate having in particular an advantage in terms of mechanical strength. Indeed, the rigidity of the plates of the primary insulating barrier allowed better resistance to shocks produced on the walls of the tank by the movements of the liquid during transport, movements which are due to the roll and pitch of the ship. In this embodiment, the primary barrier was hung on the secondary barrier without any connection with the carrying structure of the ship, which was very advantageous for the insulation characteristics; but the main disadvantage came from the fact that the construction was practically impossible in an automated way so that the cost of realization proved prohibitive despite the good performance that we obtained. In addition, at the level of the primary insulating barrier, a watertight partition was created between two adjacent elements of said barrier, which made it very difficult to purge the primary barrier by circulation of inert gas or to check the tightness by injection of tracer gas.

In French patent 2 504 882, an embodiment of this type of tank has been proposed in which the secondary insulating barrier consists of parallelepipedic boxes filled with thermal insulation and the primary insulating barrier consists of plates formed by a cellular layer assembled to a panel. rigid. This type of structure has the advantage of essentially retaining the benefit of the rigidity of the primary insulating barrier as it was proposed in the aforementioned patent 2 462 336; unfortunately this device also has a serious defect: in fact, the primary barrier is hung directly on the load-bearing structure of the ship by anchoring members which pass through the secondary sealing barrier. However, it has been found that this technique is capable of generating, under certain conditions, zones of concentration of stresses, which is unfavorable from the security point of view; in addition, a direct thermal bridge is established by the anchoring members between the primary barrier and the ship's supporting structure, which is very unfavorable in terms of insulation performance.

In French patent 2,629,897, an embodiment of such a type of tank has been proposed in which, on the one hand, rigid plates are provided as part of the primary insulating barrier, providing good mechanical resistance to the impacts of the liquid. during transport, on the other hand, the creation of a direct thermal bridge between the primary barrier and the ship's supporting structure is avoided and, finally, it is allowed to be set up by automatic means, which limits the cost of production of the tank. This embodiment uses a secondary insulating barrier consisting, in a known manner, of rigid boxes filled with heat-insulating particulate material; the secondary sealing barrier consists of invar strakes welded with raised edges, on either side of a weld support retained on the cases of the secondary insulating barrier and this same weld support is used to maintain the elements of the primary insulating barrier. However, this embodiment has a drawback due to the fact that the elements of the secondary insulation barrier are fixed by their angles and that the pulls exerted on the welding supports apply in areas remote from the fixing angles, whence may result from a dynamic deformation of the elements of the secondary insulation barrier during service. In addition, the attachment of the primary barrier is exclusively carried out by means of a welding support retained by an angled folding on the face of the boxes of the secondary insulation barrier, which supports the secondary sealing barrier. ; this way of operating does not give a tear resistance as high as that which could be desired for maximum security and, moreover, it requires ensuring a fastening by screw between the face which supports the attachment and the reinforced internal partition, which is located at the right of said hanging, hence a significant increase in the cost price. Finally, as in the above-mentioned prior embodiments, the same retaining member cooperates with four adjacent elements, which makes it difficult to put in place.

The present invention therefore relates to the new industrial product that constitutes a sealed and thermally insulating tank integrated into the carrying structure of a ship, said tank comprising two successive sealing barriers, one primary in contact with the product contained in the tank and the other secondary disposed between the primary barrier and the ship's supporting structure, these two sealing barriers being alternated with two thermally insulating barriers, the primary insulating barrier being resiliently supported on the secondary sealing barrier by to hooking means arranged linearly in a substantially continuous manner and mechanically linked to the secondary insulating barrier, the primary insulating barrier consisting of rigid substantially parallelepiped plates between which pass said attachment means, the secondary insulating barrier being constituted by a set of substantially parallelepipedal and internally partitioned insulating boxes, fixed against the carrying structure of the ship by retaining members integral with said carrying structure, which cooperate with fasteners arranged in edge of the boxes of the secondary insulating barrier, said boxes being separated from each other by substantially rectilinear joint zones where the aforementioned retaining members are arranged, each box comprising, in line with each groove intended for the installation of '' a hooking means, a thick internal partition fixed to the faces delimiting the box, characterized in that outside the tank angles, the retaining members used to maintain the secondary insulating barrier on the ship's supporting structure are aligned to the right of the grooves where the l are inserted es means of attachment.

In known manner, each retaining member comprises, on the one hand, a threaded stud welded by its base to the carrying structure of the ship, and, on the other hand, a nut, which rests on a fixing integral with a secondary insulating barrier box; said attachment is, according to an interesting embodiment, the edge folded at right angles to a tab fixed on the edge of each box at the right of the straight end section of each thick partition of the box, this square fold being elastically deformable; provision can be made for the support of a nut on said edge folded at right angles by means of a plate bearing simultaneously on the edges of two legs belonging to two adjacent boxes, thus constituting an elastic connection between the caissons and the carrying structure of the ship.

According to this technique, the boxes are fixed two by two, which is simpler than four by four, as was the case in the prior art. But above all the tensile forces transmitted by the attachment means are transmitted by a thick partition just below the retaining members, which limits the dynamic deformations of the boxes during service. Finally, two successive retaining members on the same alignment perpendicular to the hooking means are spaced apart by a half-width of the box, as soon as the thick partitions of a box are arranged at a quarter of the width from each longitudinal edge of the box; in the prior art, the spacing in question was of a box width; for caissons of constant surface, there are therefore retaining members less distant from each other and the forces on the tank in service are therefore better transferred to the supporting structure of the ship.

Advantageously, the secondary sealing barrier consists of metal strakes with edges raised towards the inside of the tank, said strakes being made of thin sheet metal with a low coefficient of expansion and being welded edge to edge, by their raised edges, on the two faces of a weld support, which is mechanically retained on the elements of the secondary insulating barrier by a sliding joint; each attachment means consists of a first and a second part, a weld support constituting a first part of an attachment means and having its free end set back relative to the plane of the sealing barrier primary, the rigid plates of the primary insulating barrier comprising, opposite each weld support and over their entire length, a fixing tab, two square strips being welded on either side of said weld support and s 'pressing elastically, by their non-welded wing, on said tabs, to constitute a second part of a hooking means.

In a preferred embodiment of the sliding joint, which retains the weld support on the boxes of the secondary insulating barrier, said joint is of the known type consisting, on the one hand, of a first U-shaped fold formed on a longitudinal edge of the weld support and, on the other hand, of a second U-shaped fold formed on a fixing strip, the two folds being fitted one inside the other, each fixing strip being put in place and maintained in a grooves made at the right of each thick partition of the boxes, the width of said groove being only slightly greater than that of the two nested folds; maintaining a band fixing in its groove can be achieved by holding means, which cross transversely at the level of the groove the thick partition, where said fixing strip is disposed; the above-mentioned holding means are advantageously staples.

In known manner, each box of the secondary insulating barrier can be made of plywood, the boxes being filled with a particulate heat-insulating material such as perlite; outside the tank angles, the elements of the secondary insulating barrier are preferably rectangular parallelepipeds, all identical.

In a known manner, it is possible to ensure that the boxes of the secondary insulating barrier rest on the load-bearing structure of the ship by means of strands of polymerizable resin, these strands reconstituting, by discontinuous elements, a defined, independent geometric surface. random deviations of the support structure in the static state with respect to its theoretical surface. A plastic film is advantageously interposed between the support structure and said resin tubes to prevent them from sticking to said structure, which allows dynamic deformation of the support structure between the retaining members, without the insulating barrier secondary is disturbed.

In known manner, it is advantageous for the secondary insulating barrier to be under a reduced pressure of between 0.1 and 300 millibars since this improves the insulation characteristics of the secondary insulating barrier. There are, of course, joint zones between the boxes of the secondary insulation barrier due to the presence of the tabs and the retaining members: it is advantageous to provide that these joint zones are filled with insulating material. This insulating material may be in the form of a strip, the thickness of which corresponds to that of the joint area to be filled, said strip having laterally at least one longitudinal groove, closed in leaktight manner at its ends. These grooves make it possible to establish a reduced pressure in the secondary insulating barrier; the non-tight closure of the ends allows the reduction of pressure but prevents a natural convection is established between the area adjacent to the supporting structure and the groove, which would increase the heat exchange.

To ensure continuous support of the primary sealing barrier, one can provide, at the level of each weld support and of the tabs of the plates of the primary insulating barrier with which it cooperates, a joint cover, the side of which faces towards the he interior of the tank is at the level of the faces of the plates of the primary insulating barrier, which supports the primary sealing barrier. According to an advantageous embodiment leading to benefit from good mechanical resistance of the primary insulating barrier, the rigid plates constituting said primary insulating barrier are formed of a layer of cellular material, such as a polyurethane foam by example, sandwiched between two rigid panels, for example of plywood, and possibly surrounded on its edges by means of rigid elements having the thickness of the layer of cellular material. It is advantageously possible to provide for the primary insulating barrier to be swept by a neutral gas such as nitrogen; the overpressure necessary for sweeping, when it is maintained while the tank is empty, or that due to the injection of tracer gas for the detection of leaks, poses no problem for the attachment of the primary barrier because the sliding joint with double U-shaped fold used in a preferred embodiment, the invention is capable of supporting several tonnes per linear meter, when the weld support and the fixing strip are made of invar sheet 0.5 mm thick .

In a preferred embodiment, the primary sealing barrier is formed by metal strakes with edges raised towards the inside of the tank, said strakes being made of thin sheet metal with a low coefficient of expansion, for example invar, and being welded edge on board, by their raised edges, on both sides of a welding wing, which is mechanically retained by a joint cover of the primary insulating barrier; the welding wing advantageously has a square profile, the short side of which is engaged in a groove formed over the entire length of the joint cover.

According to a technique previously described by the applicant company, the angle of connection of the elements of the primary and secondary barriers in the zones, where the transverse partitions of the ship join the double hull, is produced in the form of a ring, the structure of which remains constant all along the curve of intersection of said transverse partition with the double hull of the ship. In an angle formed by the double hull of the ship and a transverse partition, it is proposed, according to the invention, to hang on the perpendicular load-bearing walls, by a unidirectional connection, two perpendicular anchoring strips connected by angles at right angles to the two secondary sealing barriers, said angle brackets being interconnected by a connecting strip perpendicular to the bisector plane of the angle in question, at least one of the anchoring strips extending, substantially in its plane, beyond of the angle iron angle, which is linked to it, to join the primary sealing barrier associated with one of the bearing walls of the angle considered, the primary sealing barrier associated with the other bearing wall being connected, by watertight welding of a square strip, with its aforementioned counterpart and, optionally, with the anchoring strip located in its plane; the unidirectional connection of an anchor strip may include threaded studs fixed to the support structure and an anchor angle with a square profile, one wing of which is held on each stud by the nut associated with it and whose the other wing is welded to the anchoring strip, said anchoring angle being free to move in approaching its associated bearing wall.

To better understand the object of the invention, we will now describe, by way of purely illustrative and non-limiting example, an embodiment shown in the accompanying drawing.

• la figure 1 représente, en perspective, avec arrachement les barrières primaire et secondaire d'une cuve selon l'invention ;
• la figure 2 représente, en élévation, le chant d'un caisson de la barrière isolante secondaire ;
• la figure 3 représente la zone de joint entre deux caissons de la barrière isolante secondaire au droit des organes de retenue fixés sur la structure porteuse du navire ;
• la figure 4 représente, en perspective avec arrachement, la structure de la bande d'isolation mise en place entre deux caissons adjacents de la barrière isolante secondaire au droit des organes de retenue ;
• la figure 5 représente schématiquement la mise en place des bandes en équerre par soudure par point sur le support de soudure pour fixer les plaques de la barrière isolante primaire sur la barrière d'étanchéité secondaire ;
• la figure 6 représente, en coupe perpendiculairement au plan des barrières d'étanchéité de la cuve, la structure des plaques de la barrière isolante primaire et les fixations des deux barrières d'étanchéité au droit d'un support de soudure ;
• la figure 7 représente la réalisation d'un angle de cuve vu en coupe dans un plan perpendiculaire à l'arête du dièdre formée par ledit angle ;
• la figure 7a représente, en détail, la réalisation d'une liaison unidirectionnelle utilisée pour l'angle de cuve de la figure 7 ;
• la figure 8 représente, en détail, la zone de raccordement des barrières d'étanchéité primaire et secondaire pour l'angle de cuve de la figure 7 ;
• la figure 9 représente une variante de réalisation de la zone de raccordement de la figure 8.

On this drawing :

• Figure 1 shows, in perspective, with cutaway the primary and secondary barriers of a tank according to the invention;
• Figure 2 shows, in elevation, the edge of a box of the secondary insulating barrier;
• FIG. 3 represents the joint area between two boxes of the secondary insulating barrier in line with the retaining members fixed to the carrying structure of the ship;
• Figure 4 shows, in perspective with cutaway, the structure of the insulating strip placed between two adjacent boxes of the secondary insulating barrier to the right of the retaining members;
• FIG. 5 schematically represents the positioning of the angled strips by spot welding on the welding support to fix the plates of the primary insulating barrier on the secondary sealing barrier;
• FIG. 6 represents, in section perpendicular to the plane of the sealing barriers of the tank, the structure of the plates of the primary insulating barrier and the fastenings of the two sealing barriers in line with a weld support;
• Figure 7 shows the embodiment of a tank angle seen in section in a plane perpendicular to the edge of the dihedral formed by said angle;
• FIG 7A shows in detail the embodiment of a unidirectional link used for tank angle of Figure 7;
• Figure 8 shows, in detail, the connection area of the primary and secondary sealing barriers for the tank angle of Figure 7;
• FIG. 9 represents an alternative embodiment of the connection zone of FIG. 8.

Referring to the drawing, it can be seen that the carrier structure of a tank according to the invention has been designated by 1. This carrier structure can be, or the inner wall of the double hull of the ship, in which case it has been designated by the reference 1a, or a transverse bulkhead of the vessel, in which case it is designated by reference 1 b . For the rest, when there is no need to distinguish between these two types of supporting structure, we will only use the generic reference 1.

On the wall 1, retaining members have been welded consisting of threaded studs 2. These threaded studs are aligned in two perpendicular directions, one of which is perpendicular to the center line of the ship; on this line, the studs are spaced by 500 mm and two successive alignments of studs on such a line perpendicular to the axis of the ship are spaced by 1 200 mm. The studs 2 are used to fix on the supporting structure 1 boxes, which constitute the elements of the secondary insulation barrier of the tank according to the invention. Each box is designated by 3 as a whole: it consists of a parallelepipedal plywood box with a width of 1 m and a length of 1.20 m. Inside this box, longitudinal partitions have been arranged extending between the two large rectangular faces of the box; the thickness of the box is 430 mm. The internal transverse partitions of each box are of two types: some are relatively thin and designated by 4 a ; the others are relatively thick and are designated by 4 b . The thin walls 4 b are 250 mm of the longitudinal edges of the box 3. The box 3 comprises 7 regularly spaced internal baffles. The interior of the box 3 is filled with a heat-insulating particulate material such as that known under the name of "perlite". On the edges of the box 3 which are perpendicular to the internal partitions , a tab 5 has been fixed in the median plane of the thick partitions 4 b ; said tab 5 has an edge folded at right angles; the fixing of the legs 5 on the edge of each box 3 is carried out by screwing in the median plane of each thick partition 4 b . The edges folded at right angles 5 a cooperate with a plate 6 held by means of a nut 7, which is screwed onto each threaded stud 2. Two boxes 3, the bearing faces of fixing lugs 5 are facing each other, are fixed by the same two studs 2. It can therefore be seen that the boxes 3 are placed two by two, which is simpler than in the prior art where they were placed four by four. The edges 5a have an inherent elasticity due to the folding of the bracket 5, which allows a degree of independence between the deformation of the carrier wall and that of the pedestal 3.

The installation of the box 3 is carried out using the interposition of strands 9 of polymerizable resin; these sausages are arranged longitudinally on that of the large faces of the box 3, which faces the supporting structure 1, and the box is pressed in the direction of the supporting structure until wedges 8 of predetermined size fixed at the four angles of the box come to bear against said supporting structure 1. In this position, the strands of polymerizable resin 9 are more or less flattened and this technique makes it possible to make up for the defects that the carrying partition 1 has in the static state relative to the surface theoretical. The dimensioning of the shims 8 is calculated after a precise reading of the spatial positioning of the internal face of the load-bearing partition 1. When this positioning of a box is carried out, the box 3 is fixed by means of the studs 2 and the polymerizable tubes 9 harden in a few hours by polymerization, which then makes it possible to remove the shims 8. Before applying the box 3 against the load-bearing partition 1, a polyane film 10 is interposed between the latter and the tubes 9, to prevent the resin of the flange 9 does not stick to the load-bearing partition 1 and thus allow dynamic deformation of the load-bearing partition 1 without the box 3 being subjected to the forces due to said deformation between the retaining members 2.

In line with the studs 2, the boxes 3 are spaced apart by a joint zone of approximately 60 mm in width. In this joint zone, there is interposed a strip 11 made of a thermal insulating material such as a polyurethane foam. This strip 11 has the shape of a rectangular parallelepiped; its height is 400 mm and its length is 1.20 m. On these longitudinal edges corresponding to the thickness of the strip, a slit 12 of approximately 3 mm wide has been made, arranged in the median plane of the strip: this slit 12 gives a certain elasticity when it is put in place. and participates in maintaining the strip 11 in the joint area. The height of the strip 11 is such that one of its narrow longitudinal edges is located exactly at the level of the face of the boxes 3, which is turned towards the inside of the tank. On each of the large lateral faces of the strip 11, a groove 13 has been formed along the center line, which is plugged in a leaktight manner at each end of the strip 11 by an adhesive tape 14, which covers the entire transverse end of the strip 11.

In the upper face of the boxes 3, in line with the thick internal partitions 4 b , a groove 15 extending over the entire length of the box was made. In this groove 15, a fixing strip 16 has been put in place, a longitudinal edge of which is folded back into a U to form a fold 16 a . The fastening strip 16 is held inside the groove 15 by clips 17 arranged transversely. With the fastening strip 16 cooperates a weld support 18, a border of which is folded in a U to form a fold 18 a . The two folds 16 a and 18 a are fitted one into the other so that the welding support 18, which is, in fact, a strip of invar sheet, is retained on the fixing strip 16 and, by Consequently, either secured to the boxes 3 of the secondary insulating barrier, the method of fixing adopted nevertheless allowing the weld support 18 to slide relative to the box 3 in the longitudinal direction of these boxes, that is to say parallel to the internal partitions. boxes. To ensure good resistance of the attachment 16/18, it is made so that the width of the groove 15 is only slightly greater than the overall thickness of the two folds 16 a , 18 a , which prevents the opening of the folds and increases the tensile force that can support the weld support 18.

The secondary insulating barrier being thus constituted, the secondary sealing barrier is put in place, which is formed of strakes made of invar sheet 19 of 0.5 mm thickness with raised edges 19 a . These invar strakes 19 constitute bands, which are substantially 50 cm wide between two raised edges and which are welded by their raised edges on either side of the welding supports 18. The raised edges 19 a and the support of weld 18 protrude above the surface formed by the strakes 19. The welds of the raised edges 19 a being sealed, a secondary sealing barrier is thus pressed against the secondary insulating barrier.

Given the presence of the fixing strips 16 and the welding supports 18, it is necessary to provide transversely, in the insulation strips 11, grooves 20 arranged every 50 cm on those of the thick longitudinal edges, which are in the immediate vicinity of the secondary sealing barrier, these grooves 20 allowing the passage of the sliding joint 16/18.

The secondary barrier being thus formed, is placed between the welding supports 18 of the plates designated by 21 as a whole, said plates 21 constituting the elements of the primary insulating barrier. Each plate 21 is constituted by a rectangular parallelepiped of polyurethane foam having a specific mass of 80 kg / m³. These plates are 40 cm wide and 3 m long. They are placed on a plywood sole 22 and surmounted by a plywood cover panel 23. The foam parallelepiped is bordered on its thick faces by peripheral plywood strips 24 and the sole 22 overflows with respect to the strips 24 over the entire length of the plates 21, so as to constitute a tongue which, when the plate 21 is placed between two welding supports 18, comes in the vicinity of the raised edges 19 a of the secondary sealing barrier. The cover panel 23 stops slightly behind the peripheral strips 24, so as to allow the installation of a joint cover 25, which is a plywood plate making the connection between the cover panels 23 of two adjacent plates 21. The joint cover 25 rests on the two peripheral strips 24 of two adjacent plates 21 and is fixed there by staples 26. The joining of the peripheral strips 24 with the sole 22 is also obtained by staples 27. The joining of the parallelepipedal core of polyurethane foam with the cover panel 23 and the sole 22 is obtained by gluing.

When the plates 21 have been placed between the welding supports 18, they are secured to the secondary barrier as indicated in FIG. 5: to do this, with an automatic machine of known type, one presses on both sides other of the welding support 18 two angle brackets 28 made of invar sheet, one of the wings being applied against a tongue 22 a and the other wing coming into contact with the welding support 18. The positioning machine comprises inclined rollers 29, which enclose the welding support 18 and exert a force on it in the direction of the arrow F (see FIG. 5 ) while the rollers 30 of the machine exert on the angle iron 28 a force according to the arrows F1 aimed at applying the angle iron 28 against the tongue 22 a on which it rests. In this way, any clearance between the plate 21 and the secondary sealing barrier constituted by the strakes made of invar sheet metal is eliminated. The positioning machine then performs spot welding using the electrodes 31, so that the relative position of the angle iron 28 and the weld support 18 is fixed; of course this operation is carried out simultaneously on either side of the welding support 18. The distance between the two peripheral strips 24 of two adjacent plates 21 is approximately 80 mm, which is sufficient for the passage of the machine spot welding. After this welding has been carried out, a strip of polyurethane foam 32 which is substantially the same thickness as that of the weld is placed between the two adjacent peripheral strips 24 and above the weld support 18 associated with its angles 28. block of parallelepipedal foam which constitutes the core of the plate 21 and this strip 32 is covered, which fills the joint area, by the joint cover 25, which is fixed by staples 26. The surface of the joint cover 25, which faces the inside of the tank, is located at the external surface of the cover panels 23. The thickness of the primary insulating barrier thus formed is 70 mm.

According to the median longitudinal line of the joint covers 25, a continuous groove 33 having a T profile was made. In this groove, a welding wing 34 is put in place, which is bent at right angles to form an L profile, whose short side is engaged in one of the transverse branches of the T-groove while the long side crosses the web of the T of said groove and protrudes above the joint cover. Between the welding flanges 34, there are set up strakes of invar sheet 35 having raised edges 35 a . The width of the strakes 35 is approximately 50 cm, so that the has raised edges 35 come on either side of a wing of solder 34; one can then carry out in known manner, by means of an automatic machine, a sealed continuous weld between the edges 35 a and the flange weld 34. This produces the establishment and maintenance of the primary sealing barrier .

It is preferred that the secondary insulating barrier be placed under reduced pressure, for example under an absolute pressure of 2 millibars. Given its thick thickness of 430 mm, the secondary insulating barrier then has very high insulation characteristics. To establish the reduced pressure of 2 millibars, the air is pumped into the secondary insulation layer; the boxes 3 may have orifices in their transverse edges, to facilitate the aspiration of air into the boxes; the grooves 13 of the strips 11 allow circulation of the air sucked in despite the presence of the ribbons 14 which are not placed in a sealed manner. The ribbons 14 are intended to avoid a circulation of the residual gas by natural convection between the grooves 13 and the space between the boxes 3 and the support structure 1: in fact, such a circulation would lead to a significant thermal loss.

In Figure 7, there is shown the structure adopted in a tank angle, that is to say in the area where a transverse partition 1 b of the ship is connected with the internal wall 1 a of the double hull of the ship. The intersection 36 of the partitions 1 a and 1 b forms a closed polygon along which the structure which will be described constitutes a ring; FIG. 7 represents a cross section of this ring zone.

The edge of the dihedral formed by the angle of the vessel is designated by 36. About 530 mm from the edge 36, an alignment of threaded studs 37 is provided, parallel to the edge 36 on each of the load-bearing partitions 1 a and 1 b . On these studs, an angle bracket 38 is put in place, one wing of which is positioned on the studs 37 and is retained there by means of a bar 39, which has the same length as the angle 38 and increases the resistance thereof, by means of the nuts 40 associated with the studs 37. The studs 37 have, in the vicinity of the load-bearing partitions which support them, a smooth surface on which the angle iron 38 can slide freely. It is therefore seen that this assembly establishes a unidirectional connection, which allows the angle iron 38 to approach the load-bearing partition, which supports it, but which establishes by the nut 40 a limitation of the position of the angle iron in the direction of the inside of the tank.

The wing of the angle iron 3 8, which does not cooperate with the studs 37, is connected by welding with a connecting strip 41, which consists of an invar sheet 2 mm thick located substantially in the plane of the primary sealing barrier associated with that of the supporting partitions, which do not support the bracket 38 of the strip 41 considered. Before the establishment of the connecting strips 41, there is, in the edge dihedral 36, a secondary box 42 of substantially square section which rests on the partitions 1 a and 1 b by means of resin tubes 9; the box 42 is filled with a particulate thermal insulator like the boxes 3. The connecting strips 41 and the brackets 38 are then put in place on the two faces of the box, which are opposite to the partitions 1 a and 1 b . The angle of the box 42, which is opposite the edge 36, is cut down to form a cutaway.

On the angle thus prepared, we just put in place a prefabricated composite beam shown in detail in Figure 8. This beam has a dihedral shape, the two planes of the dihedron being perpendicular and connected by a cut-off area at 45 ° . The beam is formed in the following way: a sheet of invar 43 2 mm thick receives two sheets of invar 44 and 45 1.5 mm thick perpendicular to sheet 43 and welded to it by their edges readings; the sheets 44 and 45 are parallel and spaced 70 mm apart. On its other face, the sheet 43 supports an invar sheet 46 1.5 mm thick arranged at 45 ° relative to the sheet 43 and folded in line with the sheet 45 to become again parallel to the sheet 43. The sheet 46 is welded to sheet 43 at the same level as sheet 44 and a U-shaped angle iron 47 is welded by its two wings on the one hand, to sheet 43 in line with the welding of sheet 45 but on the opposite side by relative to this sheet, and on the other hand, on the sheet 46, the core of this angle iron 47 being in the plane of the sheet 45. On the side of the sheet 46, where the angle iron 47 is not found, and in the plane of the sheet 45, a sheet of invar 48 48 1.5 mm thick has been welded onto the sheet 46, with raised edges. In the prismatic space of triangular section defined by the sheets 43, 46 and by the core of the angle iron 47, a plywood beam 49 of substantially triangular section has been put in place which is kept in its sheet housing by screws 50 passing through the sheet 43 in the space between the sheets 44 and 45. In each of the spaces included on the one hand, between the sheets 43, 44 and 45 and on the other hand, between the sheets 43 and 46 and the core of the angle iron 47, plywood beams 54, 55 of substantially rectangular section have been put in place, these beams being held relative to the sheets, which surround them, by screws 51 disposed respectively, on the center side of the tank, on the sheets 45 and 43. To complete the joining of the beams with their sheet envelopes, screws 52 and 53 are put in place, which, respectively, join the beam 55 with the beam 49 by passing through the of the angle iron 47, on the one hand, and the beam 49 av ec the beam 54 passing through the sheet 43, on the other hand.

The composite beam, which has just been described, is brought against the box 42, the sheet 46 bearing against the cutaway of said box. In this position, the sheets 43 and 48 come to rest on the connecting strips 41 and a continuous tight seal is provided on the edge of the covering. In this position, the sheet 43 is located substantially in the plane of the primary sealing barrier and the sheet 46 in the plane of the secondary sealing barrier parallel to the load-bearing partition 1 a ; in the same way, the sheet 44 is located substantially in the plane of the secondary sealing barrier and the sheet 45 in the plane of the primary sealing barrier parallel to the load-bearing partition 1b . It therefore suffices to connect these sheets of the composite beam by leaktight welding with the invar strakes which constitute the primary and secondary sealing barriers. The end edges of the sheets constituting the primary sealing barrier have been designated by 350; we see that these sheets cover the areas where the screws 51 are located, so that the seal is not destroyed by the presence of said screws 51. The area where the screws 52 and 53 are located does not require sealing since this corresponds to the thickness of the primary insulating barrier.

It can be seen that this structure makes it possible to perfectly transfer the forces exerted on the primary and secondary barriers to the load-bearing partitions. By using studs 37 15 mm in diameter at the rate of 10 studs per linear meter, it is without difficulty to absorb the static forces due to the cooling of the tanks and the dynamic forces during navigation. The static forces apply alone to the strip 41 parallel to the transverse partition while the strip 41 parallel to the double shell supports both the static and dynamic forces. The use of a unidirectional connection at the angles 38 allows the recoil under load of said angles at the time of loading the tanks: the angle structure, which has just been described, makes it possible to collect easily significant tensile forces being exerted on the sealing barriers but would not allow compression forces to be absorbed since the sheets of the composite beams would risk buckling, which would cause destruction of the welds and a loss of sealing.

In Figure 9, there is shown an alternative embodiment of the angle ring defined in Figures 7 and 8, Figure 9 showing only the corner area of the composite beam without showing the primary and secondary boxes which adapt to it appreciably as for the first realization. In this variant, the composite beam allows a better distribution of the static and dynamic forces applied to the strip 41 parallel to the double shell thanks to a symmetrical connection (43, 46) established by the triangular zone of the beam between said strip 41 and the primary 350 and secondary 190 sealing barriers parallel to the double hull. The efforts in the longitudinal direction being the greatest, the asymmetry parallel to the transverse partition is not a problem. The same reference numbers were used for the different elements of the beam as for the first embodiment; the constituent sheets of the beam are invar sheets 1.5 mm thick except sheet 43 which is 2 mm thick. The three compartments defined by these sheets are occupied by wooden beams 49, 54, 56. The connection, with the primary and secondary sealing barriers, of the composite assembly thus formed is carried out as indicated above for the variant of the Figures 7 and 8.

It can be seen that the tank structure described above eliminates any crossing of the secondary sealing barrier by members intended to retain the primary insulation and sealing barriers on the supporting partition: a thermal bridge is therefore avoided. Furthermore, the fixing of the boxes 3 by legs with folded edges makes it possible to tolerate a greater dynamic deformation of the shell than in the past. Finally, the fact of attaching the primary barrier just in line with the retaining members, which hold the secondary barrier on the load-bearing partition, makes it possible to reduce the deformation of the caissons during navigation.

It is understood that the embodiment described above is in no way limiting and may give rise to any desirable modification, without departing from the scope of the invention.

Claims (18)

1 - Watertight and thermally insulating tank integrated into the carrying structure of a ship, said tank comprising two successive sealing barriers, one primary in contact with the product contained in the tank and the other secondary disposed between the primary barrier and the supporting structure of the ship, these two sealing barriers being alternated with two thermally insulating barriers, the primary insulating barrier being resiliently supported on the secondary sealing barrier by means of hooking means arranged linearly in a substantially continuous manner and mechanically linked to the secondary insulating barrier, the primary insulating barrier consisting of rigid plates (21) substantially parallelepiped between which said hooking means pass, the secondary insulating barrier consisting of a set of insulating boxes (3) substantially parallelepiped and internally t partitioned, fixed against the carrying structure of the ship by retaining members (2, 7) integral with said carrying structure, which cooperate with fasteners (5) arranged on the edge of the boxes of the secondary insulating barrier, said boxes (3) being separated from each other by substantially rectilinear joint zones where the aforementioned retaining members (2, 7) are arranged, each box (3) comprising in line with each groove (15) intended for the installation of a hooking means, a thick interior partition (4b) fixed to the faces delimiting the box (3), characterized in that outside the tank angles, the retaining members (2) used to hold the barrier secondary insulation on the supporting structure of the ship are aligned vertically with the grooves (15) where the attachment means are inserted. 2 - Tank according to claim 1, wherein each retaining member comprises, on the one hand, a threaded stud (2) welded by its base to the support structure (1) of the ship and, on the other hand, a nut ( 7), based on an integral attachment of a box (3) of the secondary insulating barrier, characterized in that said fastener is folded edge (5a) elastically deformable with a tab (5) fixed on the edge of each box (3) to the right of the straight end section of each thick partition (4b) of the box (3). 3 - tank according to claim 2, characterized in that the support of the nut (7) on a tab (5) is effected by means of a plate (6) which is supported simultaneously on two legs (5) belonging to two adjacent boxes (3). 4 - Tank according to one of claims 1 to 3, characterized in that the secondary sealing barrier consists of metal strakes (19) with raised edges (19 a ) towards the inside of the tank, said strakes being made of thin sheet metal with low dilatation coefficient and being welded edge to edge, by their raised edges (19 a) on both faces of a weld support (18) which is held mechanically on the elements of the insulating barrier secondary by a sliding joint. 5 - Tank according to claim 4, characterized in that each attachment means consists of a first and a second part, the weld support (18) constituting a first part of an attachment means and having its free end set back relative to the plane of the primary sealing barrier, the rigid plates (21) of the primary insulating barrier comprising, facing each weld support (18) and over their entire length, a fixing tab (22 a ), two angled bands (28) being welded on either side of said welding support (18) and bearing elastically, by their non-welded wing, on said tongues (22 a ) for constitute a second part of a hooking means. 6 - tank according to claim 5, characterized in that the sliding seal, which retains the weld support (18) on the boxes (3) of the secondary insulating barrier, is of the known type consisting on the one hand, of a first U-shaped fold (18 a ) formed on a longitudinal edge of the weld support (18) and, on the other hand, a second U-shaped fold (16 a ) formed on a fixing strip (16), the two folds (16 a / 18 a ) being nested one inside the other, each fixing strip (16) being put in place and held in one of the grooves (15) formed in line with each thick partition (4 b ) boxes (3), the width of said groove (15) being only slightly greater than that of the two nested folds (16 a / 18 a ). 7 - Tank according to claim 6, characterized in that the maintenance of a fixing strip (16) in its groove (15) is achieved by holding means (17), which cross transversely at the level of the groove ( 15) the thick partition (4b), or is disposed said fixing strip (16). 8 - Tank according to one of claims 1 to 7, characterized in that the boxes (3) of the secondary insulating barrier are supported on the supporting structure (1) of the ship by means of tubes (9) of polymerizable resin, these tubes reconstituting, by discontinuous elements, a defined geometric surface, independent of the random deviations of the supporting structure in the static state with respect to its theoretical surface. 9 - tank according to claim 8, characterized in that a plastic film (10) is interposed between the support structure (1) and the tubes (9) of resin. 10 - Tank according to one of claims 1 to 9, characterized in that the joint zones between the boxes (3) of the secondary insulation barrier are filled with an insulating material. 11 - Tank according to one of claims 1 to 10, characterized in that the secondary insulating barrier is under a reduced pressure of between 0.1 and 300 millibars. 12 - Tank according to claims 10 and 11 taken simultaneously, characterized in that the insulating material filling the joint areas is in the form of a strip (11), the thickness of which corresponds to that of the joint area to be filled , said strip (11) laterally comprising at least one longitudinal groove (13) closed in leaktight manner at its ends. 13 - A tank according to claim 5, characterized in that, in line with each weld support (18) and the tongues (22 a ) of the plates (21) of the primary insulating barrier, with which it cooperates, is arranged a joint cover (25), the side facing inward of the tank is at the faces of the plates (21) of the primary insulating barrier, which supports the primary sealing barrier. 14 - tank according to one of claims 1 to 13, characterized in that the plates (21) constituting the primary insulating barrier are formed of a layer of foam material sandwiched between two rigid panels (22, 23) . 15 - Tank according to one of claims 1 to 14, characterized in that the primary insulating barrier is swept by a neutral gas. 16 - Tank according to one of claims 1 to 15, characterized in that the primary sealing barrier is formed by metal strakes (35) with raised edges (35 a ) towards the inside of the tank, said strakes (35) being made of thin sheet metal with a low coefficient of expansion and being welded edge to edge, by their raised edges (35 a ), on the two faces of a welding wing (34), which is mechanically retained by a cover -joint (25) of the primary insulating barrier. 17 - Tank according to one of claims 1 to 16, characterized in that, in an angle formed by the double hull ( 1a ) and a transverse partition ( 1b ) of the ship are hung on the perpendicular load-bearing walls, by a unidirectional connection, two perpendicular anchoring strips (41) connected by sheets bent at an angle (43, 48) to the two secondary sealing barriers, said sheets (43, 48) being connected together by a connecting strip (46 ) perpendicular to the bisector plane of the angle in question, at least one of the anchoring strips (41) extending, substantially in its plane, beyond the sheet (44) folded in an angle which is linked to it to join the primary sealing barrier associated with one (1a) of the load-bearing walls of the angle in question, the primary sealing barrier associated with the other support wall (1b) being connected, by sealed welding of a sheet (45 ) folded square, with its homol ogue above and possibly with the anchor strip (41) located in its plane. 18 - Tank according to claim 17, characterized in that the unidirectional connection of an anchoring strip (41) comprises threaded studs (37) fixed to the carrying structure of the ship and an anchoring angle (38) having a square profile, one wing of which is held on each stud (37) by the nut (40) associated with that -this and whose other wing is welded to the anchoring strip (41), the anchoring angle (38) being free to move by approaching its associated bearing wall.

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