Integral Tank For Transporting Liquefied Gas

Abstract

Methane tanker comprises two heat insulating barriers and two fluid-tight barriers, positioned alternately with a fluid-tight barrier innermost and the outermost insulating barrier attached to the hull of the ship. The other fluid-tight barrier is positioned between the two insulating barriers and comprises vertical plates joined together by welding to horizontal metallic strips. One edge of each strip is slidably connected to the outer insulating barrier and the other edge is resiliently connected to the inner insulating barrier.

Description

SUMMARY OF THE INVENTION

This invention relates to the transportation of liquefied gas by sea, and in particular to the transportation of liquefied natural gases having a high methane content.

In French Pat. No. 1,438,330, an isothermic fluid-tight tank is described, which tank is integrated into the framework of a ship and comprises two successive fluid-tight barrier layers, the first of which is in contact with the liquefied gas being carried, and the second of which is positioned between the first barrier and the hull of the ship. These two fluid-tight barrier layers are alternated with two thermal insulating layers hereinafter referred to as insulating barriers. In the embodiment described, the secondary insulating barrier consists of boxes filled with a heat insulating material and attached directly to the double hull or double wall of the ship by means of threaded studs welded to these walls. These boxes may be gas permeable and are so positioned that an open space between the boxes assures free circulation of the gas. The secondary fluid-tight barrier layer consists of thin metal sheets having edges bent toward the inside of the ship, which sheets have a height substantially equal to the height of the boxes of heat insulating material and which are welded together. The sheets are attached to the insulating barrier by sliding joints. The primary insulating barrier also consists of boxes filled with heat insulating material. Arrangements analogous to those made for the secondary insulating barrier permit a free circulation of gas therethrough.

These boxes are attached by screws to a series of vertical bars positioned between the vertical stacks of boxes. These bars are attached by supporting members passing in a fluid-tight manner through the secondary fluid-tight barrier to yokes attached from point to point along horizontal wooden planks, which are themselves supported and attached from point to point by brackets welded to the supporting hull. The primary fluid-tight barrier is made like the secondary fluid-tight barrier from sheets having edges bent inwardly for a distance equal to those of the boxes of heat insulating material. The assembly of the sheets is welded together and in the secondary fluid-tight barrier the attachment of the sheets to the insulating barrier is made by sliding joints. It has been found that the embodiment of an integrated tank such as the one described in the French Pat. No. 1,438,330 gives rises to difficulties resulting from the mechanical connections between the two fluid-tight barriers and the hull of the ship. In particular, the primary insulating barrier and the fluid-tight barrier corresponding to it are mechanically attached to the double hull of the ship by means of vertical bars connected to the hoirzontal planks by anchoring means which pass through the secondary fluid-tight barrier. It is obvious that the provision of these mechanical connections comprising horizontal planks and vertical bars is rather complicated and therefore expensive, as is the sealing of the points at which the means which connect the planks and bars pass through the secondary fluid-tight barrier.

It is the object of the present invention to avoid the above disadvantages by providing, on the one hand, a mechanical connection between the secondary barrier and the double hull of the ship and, on the other hand, an elastic mechanical connection between the secondary insulating barrier and the primary insulating barrier, without having these connections pass through the metallic plates constituting the secondary fluid-tight barrier.

It is a further object of the present invention to provide as a new article of manufacture a fluid-tight isothermal tank integrated into the supporting structure of a ship and comprising two successive fluid-tight barriers, the first of which is in contact with the product contained in the tank, and the second of which is situated between the primary barrier and the supporting structure of the ship, said two fluid-tight barriers being alternated between two insulating barriers, with the secondary insulating barrier consisting of boxes filled with an insulating material and attached directly to the double hull or double partition of the ship by means of thread studs attached to its walls. The second fluid-tight barrier consists of metallic plates having edges bent inwardly of the tank, the height of which is substantially equal to the height of the boxes of heat insulating material. These plates are welded edge to edge to the two sides of a metallic strip which is slidable with respect to the subjacent insulating barrier. The primary insulating barrier consists of boxes filled with heat insulating material and the primary fluid-tight barrier is made like the secondary fluid-tight barrier, with the plates of the primary barrier being connected to each other by welding their inwardly bent edges against the two surfaces of a rectangular hooked plate engaging through a sliding joint one of the sides of each of the boxes, and characterized by the fact that a metallic strip to which the metallic plates of the secondary fluid-tight barrier are welded is inserted in the horizontal joint between the heat insulating boxes of the secondary insulating barrier and retained with respect to these boxes by a sliding assembly. The attaching brackets are located from point to point along the metallic strips and are attached to these strips, each bracket being also attached by an elastically deformable means perpendicularly to the secondary fluid-tight barrier by means assuring the connection of the boxes of heat insulating material of the primary insulating barrier to the metallic strips.

In a first embodiment the metallic strip used to which the edges of the metallic plates of the secondary fluid-tight barrier are welded is the central member of a composite beam, said strip being gripped along one edge between two battens made of wood for example, the sliding assembly being due to the fact that the said composite beam is inserted between two adjacent heat insulating boxes of the secondary insulation barrier so that the battens of the composite beam are retained in the direction of the interior of the tank by a member fixed to the boxes of the secondary insulating barrier.

In a second embodiment, the sliding connection to the metallic strip to which the metallic plates of the secondary fluid-tight barrier are welded edge to edge consists of a sliding joint formed by the bent back edge of the said metallic strip and the edge of a metallic strip attached at the edge of one of the horizontal faces of each box of the secondary insulating barrier. One horizontal batten which acts as a spacer for the interfitted edges of the joint being interposed between the sliding joint and those of the boxes of heat insulating material which do not carry the said metallic strip.

The sliding joint and the batten forming a spacer are positioned in a longitudinal recess in the edge of the horizontal surface of each box of secondary insulating material. For these two embodiments the metallic strip to the opposite sides of which the metallic plates of the secondary fluid-tight barrier are welded consists preferably of a strip of sheet material made of steel having a high percentage of nickel, and advantageously Invar.

In a preferred form of the first embodiment, the battens which grip the central strip of each beam are wooden battens cut into sections of the same length, the upper and lower segments of these battens being exactly superposed and two successive sections being separated by a space inside which the composite beam is reduced to the thickness of its central strip. The members attached to the boxes of the secondary insulating barrier which engage the batten of each composite beam are tenons extending the length of an edge of each parallelopipedic heat insulating box. The battens of the composite beam are nailed to the central strip of the beam.

In a preferred embodiment of the second variation the boxes of heat insulating material in the secondary insulating barrier carry, along the horizontal edge to which the bent strip constituting a part of the sliding attaching joint is attached, a reinforcing tenon which may consist of several members distributed side by side along the length of the box. The folded strip constituting one part of the sliding joint of the secondary barrier is attached to the heat insulating material boxes by means of a screw passing through the wall of the box of heat insulating material and penetrating into the reinforcing tenon positioned inside the box. Each box of heat insulating material of the secondary insulating barrier comprises prolonged horizontal faces extending beyond the box above their vertical surfaces perpendicular to the double hull or double partition of the ship. Each of these extensions carries near the hull or partition of the ship an attaching tenon fixed to said extension, for example by means of fasteners or adhesively. The four tenons of four adjacent boxes of heating material in the insulating secondary barrier are attached to the double hull or double partition of the ship by means consisting of two corner tabs, one flange of each tab being attached by a threaded stud and nut to the hull or partition of the ship. The two other flanges are connected to each other by bolts. The edges of each square tab which are parallel to the corner of the square are folded perpendicularly to each face of the square.

For the second embodiment of the invention the following supplemental arrangements may advantageously be adopted. The mounting brackets comprise two strips which grip therebetween the metallic strip to the opposite sides of which the two bent-back edges of the metallic plates of the secondary fluid-tight barrier are attached. The bracket is fastened to this metallic strip by welding or riveting. The fastening means connected to each bracket consists of a threaded rod, a nut, and a locking tab, each tab bearing on at least one box of heat insulating material in the primary insulating barrier. The locking tab of the attaching means associated with each bracket bears on a depressed zone positioned at the corner of a box of heat insulating material, with said locking tab bearing simultaneously on the corners of four adjacent boxes of heat insulating material of the primary insulating barrier.

The elastic connector which connects the mounting bracket to the attaching means cooperating with the boxes of insulating material in the primary insulating barrier may be made in two different ways. In one construction the elastic connecting means consists of an elastically deformable metallic ring connected at one side to the said bracket and at the opposite side to the threaded rod of the corresponding attaching means. In this case, the elastically deformable ring is mounted in the plane of the mounted metallic strip to which it is attached, or in a plane perpendicular thereto.

In a second construction, the elastic connecting means between the mounting bracket and the attaching means which cooperates with the insulating boxes of the primary insulating barrier consists of two metallic leaves welded together by their ends, one of the leaves being welded to the central part of the mounting bracket and the other leaf to the corresponding threaded rod, the plane of contact of these two metallic leaves being parallel to the planes of the primary and secondary fluid-tight barriers.

In a third embodiment, the device permitting elastic deformation consists of a U-shaped leaf spring, one of its branches being connected to the aforesaid bracket and the other branch carrying a threaded stud to which the boxes of insulating material of the primary insulating barrier are attached. In this case the U-shaped spring is attached to the associated brackets of the secondary fluid-tight barrier preferably either by means of rivet or by means of pins passing through said brackets and one end of the U-shaped spring, said pins being held in place by a steel wire in the form of a pin. It will be seen that the tank according to the invention has considerable advantages as compared with the previously described prior arrangement. In effect, the attaching means has been simplified so as to insure a mechanical connection between the supporting double hull, the heat insulating barriers, and the primary and secondary fluid-tight barriers. It is no longer necessary to provide the assemblies of horizontal planks and vertical bars which were heretofore indispensable. It follows from these simplifications that there is a considerable reduction in the time and labor necessary to mount the various components of an integral tank designed to transport liquefied gas. Moreover, it has been found that the method of mechanical connection used in the arrangement according to the present invention leads to a very substantial reduction in the thremal bridges created by the mechanical connecting means attaching the components of the tank to the supporting double hull of the ship. Finally, the elimination of the horizontal plank and the vertical bars results in a substantial decrease in the weight of the attaching means per square meter of the inner surface of the tank. These arrangements assure, moreover, like those described in French Pat. No. 1,438,330, both sliding connections between the fluid-tight barriers and the subjacent insulating barrier on the one hand, and on the other hand a permeability to the gas by the heat insulating boxes, and finally, free spaces between the boxes permitting free circulation of these gases.

It should be noted that the second embodiment hereinbefore described for the tank according to the invention has three advantages over the first embodiment. In effect, in the first place, the section of the connecting zones positioned at each end of the boxes of the secondary insulating barrier is increased, which makes it possible to increase the forces on the attaching means. In the second place the seating inside the longitudinal recesses of the sliding joint holding the metallic strip at the level of the planes of the joints between the boxes of the secondary insulating barrier makes it possible to avoid any horizontal space between the heat insulating boxes, thus avoiding the need to insert a complimentary insulating material. Finally, in the third place, the attachment which comprises two square tabs at each connection of four adjacent boxes of the secondary insulating barrier is made by means of two studs attached to the hull of the wall of the ship, which constitutes a safety factor in case of breakage of one of the studs and makes it possible, moreover, to take up the play during mounting.

Finally, it is an object of the present invention to produce as a new article of manufacture a ship adapted to transport liquefied gas, and particularly liquefied natural gases having a high methane content, characterized by the fact that it comprises at least one integral tank of a type hereinbefore described.

In order that the invention may be better understood several embodiments thereof will now be described, purely by way of illustration and example, with reference to the accompanying drawings, on which:

FIG. 1 is a perspective view, with portions broken away, showing a tank according to the first embodiment of the invention, including the assembly comprising the primary and secondary fluid-tight barriers, the primary and secondary insulating barriers, and the double hull of the ship;

FIG. 2 is a perspective view showing in detail the mounting of a bracket on the assembly comprising the central strip of a composite beam and by the two flanges of the metallic plates which are fastened to this central strip, the corresponding elastic connecting means being a ring lying in a plane perpendicular to the plane of the said central strip;

FIG. 3 is a sectional detail view showing the attachment of the heat insulating boxes of the secondary barrier of FIG. 1 to the supporting hull of the ship, one composite beam being inserted between two superposed adjacent boxes of said secondary barrier;

FIG.4 is a detail view showing in section a detail from FIG. 1, to wit, the riveting of the mounting bracket to the assembly formed by the central strip of the composite beam and the two flanges which are welded to said strip;

FIG. 5 is a perspective view showing another embodiment of the means for mounting a bracket on the composite beam of FIG. 1, the elastic connecting means being an elastically deformable ring positioned in the plane of the central strip of the said composite beam;

FIG. 6 is a perspective view showing a variation of the elastic connecting means consisting of two metallic strips welded together at their ends;

FIG. 7 is a cross-sectional view showing in detail the means connecting the flanges of the plates of the primary fluid-tight barrier by soldering them to the opposite sides of a central metallic strip hooked over a strip attached to the boxes of the primary fluid-tight barrier to form a sliding joint, said arrangement being the same for both the first embodiment illustrated in FIG. 1 and the second embodiment illustrated in FIG. 8;

FIG. 8 is a perspective view with portions broken away showing a second embodiment of a tank according to the invention, including the assembly of the primary and secondary fluid-tight barriers, the primary and secondary insulating barriers, and the double hull of the ship;

FIG. 9 is a perspective view showing in detail the attachment of the metalic strip associated with the secondary insulating barrier of FIG. 8, the heat insulating boxes of the secondary barrier being shown broken away and empty;

FIG. 10 is a perspective view showing in detail the attachment of a heat insulating box of the secondary insulating barrier of FIG. 8 to the supporting double hull of the ship;

FIG. 11 is a sectional view of the sliding joint of FIG. 9;

FIG. 12 is a sectional view of the attaching means of FIG. 10;

FIG. 13 is a sectional view showing in section the U-shaped spring which, in the embodiment of FIG. 8, connects the metallic strip associated with the secondary barrier to the boxes of heat insulating material in the first insulating barrier; and

FIG. 14 is a sectional view taken along the line 14--14 of FIG. 13.

Turning now to the drawings, and more particularly to FIGS. 1-5 and 7, it will be seen that, in this first embodiment of the invention, reference numeral 1 indicates the double supporting hull of the ship, while 2 indicates the threaded studs welded to the hull 1 and perpendicular thereto. The studs 2 are mounted in vertical rows and their spacing within a row corresponds to the height of one of the parallelopipedic boxes 3 which form the secondary insulating barrier. The spacing of two adjacent rows of studs 2 determines the length of the boxes 3, which boxes are so disposed that there is a stud 2 at each of their corners. The boxes 3 are made, for example, of wood. They contain a heat insulating product, preferably the one sold under the trademark PERLITE.

Reference numeral 3a indicates the surfaces of the boxes 3 which abut the hull 1 and reference 3b indicates the opposite surfaces. Each box 3 carries vertically at each side of the surface 3a a tenon 4 which extends vertically along each lateral vertical surface of each box 3. In the area in which the corners of four adjacent boxes 3 meet, a space is provided between the boxes 3 which permits the passage of the corresponding stud 2. The end of the stud 2 is threaded and cooperates with the nut 2a which bears on the square tab 5. Each tab 5 fastens one corner of each of four adjacent boxes. Reference numerals 3c and 3d indicate the horizontal surfaces of the boxes 3. The surfaces 3c and 3d carry, where they meet the surface 3b, tenons 6 extending along the length of the boxes 3. The boxes 3 are piled one above the other along the length of the hull 1 between the rows of studs 2 and are attached to the hull 1 by the tabs 5 which bear on the tenons 4 of the four adjacent boxes 3. The spaces between the boxes are filled with rock wool to perfect the thermal insulation.

Between each two horizontal rows of boxes 3 is a composite beam 7. This composite beam consists of a central strip 8 seated between two wooden battens 9. Each batten 9 extends along one of the edges of the strip 8. The battens 9 are divided into sections, each two successive sections being separated by about 20 centimeters. Each section is about 1 meter long. The sections of the upper batten and the lower batten of each beam are exactly superposed so that the composite beam 7 comprises a zone having no batten 9. The central strip 8 consists of a thin strip of Invar. This arrangement makes it possible to store the composite beams 7 by rolling them up, since the zones having no batten 9 make it possible to bend them sufficiently to permit such rolling. The composite beams 7 are positioned between the surfaces 3c and 3d of two boxes 3 positioned one above the other, the battens 9 being placed on the same side of the tenon 6 as the hull 1. The strip 8 is thus positioned between the two tenons 6 of two superposed boxes 3 so that the tenons 6 urge the composite beam 7 toward the interior of the ship.

When a wall constituting the secondary insulating barrier has been formed by superposing the boxes 3, smooth metallic plates 10 having flanges 11 are positioned on the faces 3b of the boxes 3 with the distance separating the two flanges 11 of the same metallic plate 10 being equal to the distance separating two consecutive central strips 8 in the secondary heat insulating barrier.

The flanges 11 of the two plates 10 positioned one above the other are automatically welded together so that the two flanges 11 grip therebetween the strip 8 of the composite beam 7 and the welding solidarizes the three thicknesses of metal in the welding zone 11a. Between two vertical rows of studs 2 is a substantially trapezoidal recess 12 in the edge of the central strip 8 which projects toward the inside of the tank. This recess extends to the zone in which the flanges 11 of the metallic plates 10 are located.

In alignment with each recess 12, and perpendicular to the hull 1 and the secondary fluid-tight barrier 10, in the median part of the boxes 3, are brackets 13, between the two arms of which the assembly formed by the strip 8 and the two flanges 11 is inserted. The bracket 13 is attached to this assembly either by welding or riveting, the latter solution being shown on FIG. 4, in which reference numeral 14 indicates the rivet.

Each bracket 13 is connected by elastic means, which will be hereinafter described, to a rod 15 which is threaded at one end. A nut 15a cooperates with this threading and bears on a locking plate 16. Between the assemblies formed by each bracket 13, rod 15, and plate 16 are wooden boxes 17, each box being so positioned that one of the assemblies 13, 15, 16 is positioned at each of its corners. The boxes 17 are similar to the boxes 3 which constitute the secondary insulating barrier, and constitute the primary insulating barrier. They rest one upon the other, have walls of self-supporting wood, and are filled with an insulating material sold under the trademark PERLITE. The boxes 17 have at each corner a recess adapted to receive one of the assemblies 13, 15, 16, and provide bearing surface which cooperates with one-fourth of the locking plate 16. Each locking plate 16 thus attaches four adjacent corners belonging to four boxes 17 of the primary heat insulating barrier to a composite beam.

Reference 17a indicates the surface of a box 17 which faces the secondary fluid-tight barrier comprising the plates 10, and 17b indicates its opposite surface. The boxes 17 have an upper horizontal face 17c and lower face 17d. In the face 17d of each box 17 along the zone in which it meets the surface 17b are recesses 18 adapted to receive a hooking strip 19 folded back over itself on the surface 17c of the box 17 located therebelow. The strips 19 are fixed to the surface 17c by nails 20. The hooking strip 19 cooperates with a hooking strip 21 the rear edge of which engages the channel in the strip 19 as is shown in FIG. 7. The strip 21 projects toward the interior of the tank all along the horizontal planes passing between the boxes 17.

A primary fluid-tight barrier consisting of metal plates 22 having bent back flanges 23 is positioned on the surfaces 17b of the boxes 17. The width of the plates 22 is substantially equal to the height of the boxes 17 so that the bent back flanges 23 of the plates 22 are positioned on opposite sides of the strip 21. If the bent back flanges 23 and the central strip 21 are automatically welded together, this produces a primary continuous fluid-tight barrier attached to the surfaces 17b of the primary heat insulating barrier. The primary fluid-tight barrier is slidably attached to the primary heat insulating barrier by the strips 21 and 19 and the nails 20. The metallic plates 22 consist of sheets of Invar.

It will be seen that it is thus possible to provide an integral tank positioned inside a ship, with all the components of this tank hooked to the smooth inner wall of the ship's hull, it being understood that the frame of the ship is positioned between the outer hull and the inner or double hull 1. The boxes 3 are mechanically fastened to the hull 1 by the studs 2 provided with their plates 5 and their nuts 2a, with the plates 5 bearing on the tenons 4. The secondary fluid-tight barrier is hooked to the secondary heat-insulating barrier by the central strips 8 of the composite beams 7 which strips are welded to the bent back flanges 11 of the plates 10. The boxes 17 which constitute the primary heat insulating barrier are attached to the components of the secondary barriers by the battens 9 engaged by the tenons 6, by the strips 8 attached to the battens 9, by the brackets 13 attached to the strips 8 and the plates 16 fastened to the brackets 13. The plates 22 which constitute the primary fluid tight barrier barrier are slidably attached to the primary heat insulating barrier by the strips 21 and 19 and the nails 20. The assembly of the components constituting the integrated tank is thus firmly attached to the double hull 1 of the ship. It should, however, be remarked that, because of the high temperature gradient which must exist in the components of the tank during the cooling because of the temperature reductions during the filling of the tanks, it is absolutely necessary to permit a certain amount of movement between the components of the primary and secondary barriers while maintaining a cohesion between these two barriers. For this purpose elastic connecting means is interposed between the brackets 13 and the rods 15. FIGS. 2, 5 and 6 show three different types of elastic connecting means suitable for such use.

In FIG. 2 the bracket 13 is pierced, where it is connected to the flanges 11 of the plates 10, by a hole 24 through which passes a ring 25 lying in a vertical plane, the ring 25 being welded to the rod 15. FIG. 5 shows that the bracket 13 is made of a folded strip of metal, with the bottom of the fold indicated by reference 13a and is shaped to receive a horizontal ring 26 which passes through a hole 27 in the end 15b of the rod 15. In these two embodiments it will be seen that, during the cooling and filling of the tank, deformation of the rings 25 or 26 may take place without any destruction of the attachment between the components of the primary and secondary barriers.

FIG. 6 shows a third embodiment of the elastic connecting means. In this embodiment, the bracket 13 is welded to a vertical metallic plate 28 which is connected to a second metallic plate 29 welded to the end of the rod 15. The two strips 28 and 29 are welded together at their ends, the weld being indicated by reference 30. When a tractive force is exerted on the rod 15, for example, as the tank cools, the two strips 28 and 29 curve with opposite convexities and form a spring. The advantages of this arrangement are the same as those previously indicated for the rings 25 and 26. It should be noted that, in the device according to this first embodiment of the invention, all the spaces between the boxes 17 or between boxes 3 are filled with a porous insulating material such as rock wool, for example, to insure free circulation of gas. Referring now to FIG. 8-13 illustrating the second embodiment of the invention, it will be seen that reference numeral 31 indicates the double supporting hull of the ship and 32 the threaded stud welded to the hull 31 and perpendicular thereto. The studs 32 are welded in vertical rows and are arranged in groups of two, the spacing between the center points of two successive groups in any given row being equal to the height of one of the parallelopipedic boxes 33 constituting the secondary insulating barrier. The spacing between two adjacent rows of studs 32 determines the length of the boxes 33, which are so positioned as to provide at each corner a group of two studs 32. The boxes 33 are made, for example, of wood. They contain a heat insulating product, preferably the product sold under the trademark PERLITE.

Reference numeral 33a indicates the face of the boxes which rests on the hull 31 and reference numeral 33b indicates the opposite surface. 33c and 33d indicate the horizontal surfaces of the boxes 33. The faces 33c and 33d of the boxes 33 project beyond the vertical faces of the boxes which are perpendicular to the hull 31. Reference numeral 34 indicates these extensions. Near the hull 31, and in the direction of the median zone of each box, each extension 34 carries a projection 35 which is attached to the extension 34 and is of substantially the same thickness.

The boxes 33 are stacked one above the other along the side of the hull 31 between the rows of studs 32 and are fastened to the hull 31 by attaching means consisting of two square tabs 36. Each tab 36 has two relatively perpendicular sections, one (36a) positioned parallel to the hull 31, and the other (36b) positioned perpendicularly thereto. The edges of the sections 36a and 36b which are remote from the corner 36c of the square tab 36 are bent perpendicularly to the sections 36a, 36b, and the bent edges of the sections 36a and 36b are indicated by reference numerals 37a and 37b respectively. The length of the section 36b is slightly less than that of the projection 35. Each tab 36 is attached to the hull 31 of the ship by means of a stud 32 and a nut cooperating with said stud. The two tabs 36 of the same attaching means are fastened by the two studs 32 of the same group of the same vertical row. The two tabs 36 are attached to each other by means of a bolt 38 perpendicular thereto. The bent edges 37b of two tabs 36 of the same attaching means simultaneously fasten the edges of four projections 35 attached to four adjacent insulating boxes of the secondary insulating barrier. The surfaces 33c and 33d of two boxes of heat insulation are superposed with practically no play therebetween, and rest one upon the other. On the contrary, the vertical faces perpendicular to the hull 31 are spaced by a distance slightly more than twice the thickness of an extension 34. A longitudinal recess 38a is formed in the surfaces 33c and 33d of each box of heat insulating material and in the secondary insulating barrier, near the surface 33b. In alignment with the recess 38a, inside the box 33, is a reinforcing tenon 39 extending the full length of the box, but divided into several pieces in order to permit the passage of the transverse member 40 inside the box 33. The reinforcing tenons 39 are attached to the boxes 33 by fasteners or adhesively. The two longitudinal recesses 38a of two adjacent heat insulating boxes 33 are positioned opposite each other and define a space which receives, on the one hand, a sliding joint consisting of a hooked strip 41 and a metallic strip 42, and, on the other hand, a spacing strip 43. The strip 41 is attached to the box 33 by screws 44 which pass through the surface 33d of a box and enter the reinforcing tenon 39 positioned above the recess 38a. The edge of the strip 41 which is on the outside of the box 33 is bent back at 180.degree.. The metallic strip 42 has a bent back edge which hooks into the channel in the strip 41. The assembly comprising these two interfitted channel members constitutes the sliding joint which insures the attachment of the metallic strip 42 to the boxes of heat insulating material 33 forming the secondary insulating barrier. In order to make it possible to subject the metallic strip to substantial traction perpendicular to the hull 31, the channel members of the sliding joint must be prevented from opening. For this purpose the spacing batten 43 is mounted between the sliding joint and the bottom of the recess 38a in the box 33 adjacent to which the strip 41 is mounted. It will thus be seen that it has been possible to attach the metallic strip to the boxes of the secondary insulating barrier 42 without it being necessary to provide any open space between the facing surfaces 33c and 33d.

When a wall forming a secondary heat insulating barrier has been produced by superposition of the boxes 33, smooth metallic plates 45 having bent back flanges 46 are positioned on the surfaces 33b of the boxes 33. The distance separating the two bent back flanges 46 of the same metallic plate 45 is equal to the distance separating two successive metallic strips 42 of the secondary heat insulating barrier.

The bent back flanges 46 of the two plates 45 which are welded together are positioned one above the other, with the two flanges 46 gripping therebetween the strip 42 so that the weld attaches together three thicknesses of metal in the welding zone 46a.

Between two consecutive vertical rows of studs 32 a yoke 47 is mounted on the metallic strip 42 and attached to the strip 42 by welding them together along the welding zone 47a. The yoke 47 may be made of two sheets positioned on opposite sides of the strip 42 and welded to each other not only in the welding zone 47a but also in a parallel welding zone 47b positioned along the longitudinal edge of the sheets opposite of the welding zone 47a. Each yoke is connected by a U-shappd inverted spring 48 to a rod 49 which is threaded at one end. A nut 49a cooperates with these threads and rests on a locking plate 50. Between the assembly formed by a yoke 47, its rod 49 and its plate 50 are mounted the wooden boxes 51, each box being so positioned that one of the assemblies 47, 49, 50 is at each corner. The boxes 51 are entirely analogous to the boxes 33 which constitute the secondary insulating barrier, and constitute the primary insulating barrier. However, on the one hand, they do not comprise lateral extensions analogous to the extensions 34, and, on the other hand, the longitudinal recess which in the secondary barrier, are provided on the upper and lower faces of each box, are here only provided on the lower faces. The latter difference is apparent on FIG. 8 which shows in section the zone connecting two boxes 51. The boxes 51 are identical to the boxes 17 of the first embodiment of the invention and are assembled as shown on FIG. 7, the component parts being the same, only the reference numerals corresponding to each of these components being changed. As has been described in the case of the first embodiment, the sliding joint utilizing interfitting channel strips makes it possible to attach in the planes of the joints a metallic strip 55, on opposite sides of which metallic plates 56 having bent back flanges 57 are welded. The metallic plates 56, like the metallic plates 45, consist of sheets of Invar. For further details it suffices to refer to the construction described for the primary insulating barrier and the primary fluid-tight barrier of the first embodiment. The U-shaped spring 48 consists of a strip of cryogenic metal having a high elastic limit curved into the shape of a U. One of the ends of this strip is fastened to a plate 48a which bears on both the flanges 46 and the yoke 47. The plate 48a is attached to the yoke 47 by means of screws 48b which pass through the plate 48a and the yoke 47 and are held in position by a stainless steel wire 48c in the form of a pin. The spring 48 is adapted to deform elastically in a direction perpendicular to the hull 31, which permits separation of the primary barrier with respect to the secondary barrier in this direction. The construction and mounting of this elastic deformable device is particularly simple and inexpensive.

It will be seen that it is thus possible to provide an integral tank inside a ship with all the components of this tank being attached to the smooth inner wall of the ship, it being understood that the framework of the ship is between the outer hull and the inner or double hull 31. The boxes 33 are attached to the hull 31 by studs 32 and attaching plates 36 bearing on the attaching yokes 35. This arrangement makes it possible by elastic deformation of the square plates 36 to provide the clearances which are required during mounting when the boxes 33 are put in place.

Moreover, it insures sufficient mechanical strength in case one of the bolts 32 breaks, thus providing a supplemental safety feature.

The secondary fluid-tight barrier is attached to the secondary heat insulating barrier by metallic strips 42 and this type of attachment has two essential advantages. In the first place, there is no open space between the horizontal superposed surfaces of two boxes 33. In the second place, the sliding joint 41, 42 may be subjected to important forces transmitted by the metallic strip 42 due to the presence of the spacing batten 43, which limits to a millimeter at the most the opening of the sliding joint. The boxes 51, which constitute the primary heat-insulating barrier, are attached to the components of the secondary barrier by the metallic strip 42, the yokes 47 of the spring 48, studs 49, and the locking plates 50. The interposition of the spring 48 makes it possible, as in the first embodiment hereinbefore described, to permit limited movement between the components of the primary and secondary barriers.

It will of course be appreciated that the embodiments hereinbefore described have been given purely by way of illustration and example, and may be modified as to detail without thereby departing from the basic principles of the invention.

Claims

What is claimed is:

1. In a fluid-tight heat-insulated tank integrated with the hull of a ship, which tank comprises

a secondary heat insulating barrier formed from a plurality of boxes of heat insulating material fastened to said hull,

a primary heat insulating barrier formed from a plurality of boxes of heat insulating material and positioned inside said secondary heat insulating barrier,

a secondary fluid-tight barrier positioned between said heat insulating barriers, and

a primary fluid-tight barrier positioned inside said primary heat insulating barrier,

the improvement according to which each fluid-tight barrier is made of a plurality of metallic plates of substantially the same height as said boxes and having bent back upper and lower edges, said tank comprising:

horizontal metallic strips to which said bent back edges are welded, each strip having first catch means extending longitudinally along one edge thereof, which edge projects between the superposed boxes of the heat insulating barrier on the outer side of said strip,

second catch means attached to the boxes of said heat insulating barriers and cooperating with the first catch means on said strips to form sliding joints which permit each fluid-tight barrier to slide longitudinally with respect to the heat insulating barrier immediately outside it, but prevent relative inward and outward movement therebetween,

and resilient means connecting the strips welded to said secondary fluid-tight barrier to said primary heat insulating barrier.

2. Tank as claimed in claim 1 in which each metallic strip to which metallic plates of the secondary fluid-tight barrier are welded is secured for a portion of its width between two elongated battens which are inserted between two superposed heat insulating boxes of the secondary insulating barrier, which superposed boxes carry tenons positioned between said battens and secondary fluid-tight barrier to hold said battens and metallic strip against movement toward the interior of the tank.

3. Tank as claimed in claim 1 in which those metallic strips to which the edges of the metallic plates of the secondary fluid-tight barrier are attached have an edge bent back on itself to form a hook which engages the hook formed by similar metallic strip means attached to one of the adjacent horizontal surfaces of each pair of superposed boxes in the secondary insulating barrier, and comprising a horizontal batten acting as a wedge for the interfitting sliding joint formed by said hooks interposed between said sliding joint and the other of said adjacent horizontal surfaces.

4. Tank as claimed in claim 1 in which the metallic strip to which the metallic plates of the fluid-tight secondary barrier are welded is made of a steel having a high percentage of nickel.

5. Tank as claimed in claim 2 characterized by the fact that the battens secured to said metallic strips are wooden battens divided into sections of the same length, the sections of the upper and lower battens being exactly superposed.

6. Tank as claimed in claim 2 in which the tenons attached to the boxes of the secondary insulating barrier which retain said battens extend the length of one edge of each heat insulating box.

7. Tank as claimed in claim 2 in which said battens are attached to said metallic strips by nailing them thereto.

8. Tank as claimed in claim 3 in which the boxes of heat insulating material of the secondary insulating barrier comprise a reinforcing tenon therein along the horizontal edge to which the sliding joint is attached.

9. Tank as claimed in claim 8 in which each of said similar strips constituting one part of the sliding joints of the secondary insulating barrier is attached to a box of insulating material by means of metallic fasteners passing through the wall of the box of heat insulating material and penetrating into the reinforcing tenons positioned inside the box.

10. Tank as claimed in claim 3 in which each box of heat insulating material in the secondary insulating barrier comprises horizontal side walls which project beyond the ends of the box above the vertical faces thereof which are perpendicular to the double hull or the double partition of the ship to form extensions, each of said extensions carrying a supporting tenon near the hull of the ship.

11. Tank as claimed in claim 10 in which the four adjacent supporting tenons of each four adjacent boxes of heat insulating material in the secondary heat insulating barrier are attached to the hull of the ship by a pair of tabs, each tab comprising two flanges at right angles to each other, one flange of each tab being attached to the hull of the ship and the other two flanges being connected to each other by a bolt and gripping said tenons therebetween.

12. Tank as claimed in claim 11 in which a free edge of each flange is bent back perpendicularly to the flange from which it extends.

13. Tank as claimed in claim 1 in which said resilient means are attached to said metallic strips by yokes, each of which comprises two arms which grip the metallic strip therebetween.

14. Tank as claimed in claim 13 in which each yoke is attached to a threaded rod, carrying a nut and a locking plate, said locking plate bearing on at least one box of heat insulating material in the primary insulating barrier.

15. Tank as claimed in claim 14 in which the locking plate associated with each yoke bears simultaneously on the four recessed corners of four adjacent boxes of heat insulating material in the primary heat insulating barrier.

16. Tank as claimed in claim 1 in which said resilient means comprises a metallic ring which is elastically deformable and connected by one part to said metallic strip and the opposite part to said primary heat insulating barrier.

17. Tank as claimed in claim 16 in which each elastically deformable ring is connected to said metallic strip by yoke means and is positioned in the plane of the metallic strip to which it is attached.

18. Tank as claimed in claim 1 in which said resilient means comprises two metallic strips welded together at their ends, one of said strips being welded in its central part to a yoke connected to said secondary insulating barrier and the other strip to a threaded rod forming part of means connecting said resilient means to said primary heat insulating barrier, the plane of contact of said two metallic strips being parallel to the planes of the fluid-tight barriers.

19. Tank as claimed in claim 1 in which said resilient means comprises a U-shaped leaf spring one arm of which is connected to said secondary fluid-tight barrier and the other arm of which carries a threaded stud to which the boxes of heat insulating material of the primary insulating barrier are attached.

20. Tank as claimed in claim 19, in which the U-shaped spring is attached to yokes connected to the secondary fluid-tight barrier by means of rods passing through said yokes and one end of the U-shaped spring, said rods being locked in place by a steel pin.

21. Tank as claimed in claim 19, in which the U-shaped spring is attached to a yoke connected to the secondary fluid-tight barrier by means of rivets.

22. Tank as claimed in claim 1 which is integrally mounted in a ship.