EP0133384B1 - Shell production method, especially for a cryogenic fluid storage vessel, and shell thus obtained - Google Patents

Description

The invention relates to a method of manufacturing an assembly consisting of a sheet metal ferrule and a coil, in particular for a container for storing a cryogenic fluid formed by a reservoir housed in said ferrule and separated from the latter. by an interwall maintained under vacuum, and at least one heating coil placed in said interwall against the ferrule.

Cryogenic fluid storage containers generally consist of an internal tank and an external envelope, both metallic separated by a sealed volume maintained under vacuum and called "interwall".

The outer envelopes of these containers are generally formed of a cylindrical sheet metal body closed at each of its ends by a bottom and must be provided to withstand atmospheric pressure as well as mechanical stresses. This is achieved either by giving the sheet a sufficient uniform thickness, or by providing the envelope with uniformly distributed stiffening members.

For some containers, storage is done in a liquid state; the fluid is maintained in pressure by means of a heating coil known as "pressurizing" and is vaporized, before use, by means of a heating coil known as "of use", these two coils being placed in the aforementioned interwall, against the outer wall. This arrangement has the advantage of using the external surface of the container as a heat exchange element and therefore makes it possible to produce a very compact assembly.

Current containers, because they are provided, to resist atmospheric pressure and vertical forces resulting from the weight of the internal tank, with thick-walled envelopes or reinforced by stiffening members, have the disadvantage of having a prohibitive weight. It has been proposed to use the coil or coils to contribute to the stiffening of the envelope, but experience has shown that this use made with the currently known assembly methods does not bring a substantial gain.

The present invention aims to overcome the aforementioned drawbacks and, therefore, to economically and reliably produce a ferrule capable of withstanding significant stresses, whether due to atmospheric pressure or mechanical requirements, and much more light than those obtained by prior techniques.

To this end, the invention provides a manufacturing process as defined in claim 1.

According to another aspect, the invention relates to a manufacturing process as defined in claim 2.

The invention achieves the deformation, therefore the stiffening of the cylinder, by means of the coil, and simultaneously incorporates the latter. This has the advantage of adding the inertias of the deformed cylinder and the coil while taking advantage of the stiffening provided by the work hardening of the metal. As a result, it is possible to use a sheet which is thinner than those which have been used until now.

If it is desired to ensure good thermal contact between the tube and the cylinder, it is preferable to fix them to each other after said injection. In cases, advantageously, they are provided, on their facing walls, with a layer of a tinning product, and the aforementioned fixing is carried out by brazing.

This also gives a ferrule ensuring the best buckling resistance conditions.

DE-A-2 441 664 shows the use of an inflatable coil. However, it is a question of carrying out between two ferrules a helical path for the circulation of a heating or cooling fluid, by compensating for the variable ovalizations of the theoretically circular sections of the two ferrules. We therefore limit ourselves to the support of the coil on the two ferrules, without any deformation of these being envisaged.

Furthermore, in a different context, the fRA1 429 875 teaches the use of an extensible mandrel to fix a helical element in a cylinder. The mandrel does not serve as a support for an inflatable tube, and this document does not in any way provide for the use of the helical element to deform the wall of the cylinder.

Other characteristics and advantages of the invention will emerge during the description which follows.

• -la figure 1 montre, de façon schématique, en coupe et avec arrachement partiel, une virole en cours de fabrication;
• -la figure 2 est une vue identique de la figure 1 mais montrant une phase ultérieure de la fabrication;
• -la figure 3 est une vue schématique d'une virole achevée selon un premier mode de réalisation;
• -la figure 4 est une vue également schématique d'une virole selon un second mode de réalisation de l'invention en cours de fabrication;
• -la figure 5 montre la virole de la figure 4 après achèvement.

In the accompanying drawings given solely by way of nonlimiting example:

• FIG. 1 shows, schematically, in section and with partial cutaway, a ferrule during manufacture;
• FIG. 2 is an identical view to FIG. 1 but showing a later phase of manufacture;
• FIG. 3 is a schematic view of a ferrule completed according to a first embodiment;
• FIG. 4 is also a schematic view of a ferrule according to a second embodiment of the invention during manufacture;
• FIG. 5 shows the ferrule of FIG. 4 after completion.

The object of the invention is to obtain a significant stiffening of the shell by using only the metal which constitutes it and by deforming this metal to give it the desired stiffening function, a solution which has the advantage of eliminating the addition of reported stiffeners and allow the use of a thinner sheet than for previously known ferrules. In addition, this deformation results in work hardening of the metal which substantially increases the stiffening.

The aforementioned deformation is carried out using the heating coil (s) and incorporating them into the shell, which makes it possible to add the inertias of the deformed and hardened shell and of the coil (s).

There are shown in Figures 1 and 2 two of the main phases of manufacture of the shell which consists essentially of the tube 1 and the cylinder 2. The tube 1 is made of a sufficiently malleable material, generally copper, and has a cross section Si of flattened shape, that is to say that its facing walls are almost contiguous, leaving only a very small space between them just sufficient for the admission of a hydraulic fluid under high pressure. This tube can be obtained from an ordinary tube of circular cross section which is flattened by stretching. One such tube of circular cross section having a wall thickness e _cu thus leads, after drawing, to a flattened tube having a thickness 2e _cu . The tinning of the outer wall of the tube 1 is then carried out, while it is in flattened form, by passing it through an appropriate bath. The tube 1, thus covered with a layer of tinning product, is wound on an extensible mandrel schematically indicated in M, so as to constitute a helix of pitch p and of external diameter D _H.

Furthermore, the cylinder 2 is formed from a sheet of thickness e _T made of a metal with high mechanical resistance and high resistance to corrosion, generally made of stainless steel. Is deposited on this sheet, while it is flat, a tinning product disposed in strips 3 corresponding to the developed of the propeller of pitch p above. The sheet metal thus pre-tinned is then rolled to obtain a cylinder of circular cross section, the two edges of which are welded according to a generatrix. The internal and external diameters of cylinder 2 thus obtained have been designated by D _ci and D _cE . The internal diameter D _c is very slightly greater than the diameter D _H of the propeller formed by the flattened tube 1 (D _cl = D _H + ε).

We then thread the cylinder 2 on the mandrel and the propeller, this threading is done without difficulty due to the slight difference in dimension mentioned above. The cylinder is positioned so that the strips of tinning product 3 on its internal wall coincide with the flattened wound tube 1.

The mandrel M is then put in radial extension, which has the effect of pressing the flattened tube 1 against the internal wall of the cylinder 2, so as to eliminate any play, therefore preventing any relative movement between the tube and the cylinder during subsequent operations.

The two ends 1a a and 1 of the tube 1 are then connected to a hydraulic pressurizing device (not shown), delivering a pressure P capable of producing an expansion of the tube 1 which takes or takes up a circular cross section s ₂ of diameter external D and constitutes a coil of external diameter D _SH . This expansion of the tube causes that of the cylinder 2 which then takes the form indicated in 4, that is to say of a ferrule whose wall 5 has a helical imprint 6 of pitch p, equal to the pitch of the helical tube 1 before or after expansion.

The assembly constituted by the tube and the ferrule 4 is then separated from the mandrel M after having made them provisionally integral with one another (for example by brazing the two ends 1g and _1b to said ferrule 4) and we pass said assembly in an oven at about 220 ° C to cause the tinning material to melt and thus ensure brazing. Then the rinsing of the shell thus obtained is rinsed.

A certain number of assays have been made to determine, in the case where the ferrule must be obtained from a copper tube and a stainless steel sheet, the most appropriate values for the thickness and the diameter of the tube and for the thickness of the sheet.

avec K=45 cette valeur de K étant imposée par les propriétés mécaniques des matériaux et

h étant la hauteur de l'empreinte en saillie sur la paroi de la virole, c'est-à-dire la flèche que présente l'empreinte hélicoïdale 6 par rapport au diamètre extérieur initial D_CE du cylindre 2.By adopting, for the cylinder, an external diameter of 508 mm, a current value for the usual containers for storing cryogenic fluids, and a sheet thickness between 1 and 1.5 mm capable of having sufficient resistance to buckling as well as the punctual shocks which can be imposed on this type of device, the following relationships have been determined experimentally:

with K = 45 this value of K being imposed by the mechanical properties of the materials and

h being the height of the imprint projecting from the wall of the ferrule, that is to say the deflection which the helical imprint 6 has with respect to the initial outside diameter D _CE of the cylinder 2.

d'autre par la résolutions des deux équations (1) et (2) a donné:

The buckling resistance calculations of the shell gave:

on the other hand by the resolution of the two equations (1) and (2) gave:

There are shown in Figures 3 to 5, in which the same reference numerals designate the same elements as in Figures 1 and 2, two different embodiments of a ferrule according to the invention.

The ferrule of Figure 3, made from a stainless steel cylinder, comprises two helical copper coils 7 and 8, the two ends are designated 7a, _7b and 8a, _8b and constitute an aspect of use or and a pressurizing element respectively. These two coils were obtained from two separate tubes which were wound on the same mandrel, simultaneously or separately, but with the same pitch. In the finished shell, they are arranged following one of the other and are housed in the interwall 9 which separates the shell itself from the internal reservoir 10.

The ferrule of Figures 4 and 5 is made from a single copper tube 12 are ends are designated by 12a and _12b which, after brazing was sectioned at two points Si and S ₂ of one of its turns . Two straight elements 13 and 14 are then connected to the two points Si and S ₂ , the ends of which are designated by 13a and 14a respectively. There is thus obtained a coil 12-13 for use and a coil 12-14 for pressurizing, as in FIG. 3. This embodiment has the advantage of simplifying the various manufacturing operations, in particular the winding. It should be noted that the sectioning of the coil at points S ₁ and S ₂ preferably carried out after the expansion operation.

By way of example, a ferrule according to the invention has been produced in the following manner:

The cylinder consists of a sheet of stainless steel Z5 CN 18.09 NFA 36209 with a thickness of 1.5 mm. It is internally tinned according to the development of an 80 mm pitch propeller over a width of 20 mm using a mixture of lead, tin, antimony and flux. It is then rolled to give a cylinder of circular cross section with an outside diameter D _CE = 508 mm.

The coil (or coils) is made from a copper tube Cu state 0 NFA SI 124 of circular cross section, having an outside diameter D = ₁₂ mm and _had a thickness e = _1, 6 mm. After flattening, the tube is coated, on its external wall, with a layer of tinning product by passage through a bath comprising a mixture of 60% lead and 40% tin. Wind the tube on the mandrel according to a helix with a pitch of 80 mm which corresponds, of course, to that of the tinning of the cylinder. After extension of the mandrel, the tube is expanded by connecting it to a hydraulic pressurization device which makes a liquid penetrate into it under a pressure of 500 bars. After expansion, the two ends of the coils are fixed to the sheet, preferably by silver brazing, and the entire mandrel is removed. It is then possible, in the case where it is desired to obtain a ferrule of the type shown in FIG. 5, proceed to the connection of the rectilinear elements necessary for this purpose. The ferrule is then placed in a brazing oven to bring it to a temperature of approximately 220 ° C. Finally, the ferrule is rinsed to remove foreign bodies, soldering residues or the like.

Buckling tests carried out on ferrules thus produced showed that the buckling pressure was greater than 3b.

By way of comparison, it has also been observed that an unreinforced shell having substantially the same dimensional characteristics, that is to say the same diameter (508 mm) and the same length (for example 1 m) must, for have equivalent buckling resistance and equivalent impact resistance, be made from a stainless steel sheet of the same type as above but having a thickness of 2.5 mm.

Many variants could be made to the embodiments described and shown without departing from the scope of the invention. Thus, for example, the brazing material could be deposited on the cylinder and on the tube after the pressurized expansion operation. One could also use a fixing method other than soldering, for example welding. In addition, it is understood that the process can be very simply adapted to the manufacture of any mini ferrule from an internal coil, and even from an external coil. In the latter case, it suffices to wind the copper tube or tubes in a radially contractible hollow mandrel.

Claims (8)

1. Process for the production of an assembly comprising a sleeve of sheet metal and a coil, for a container for storage of a cryogenic fluid formed by a tank housed in the said sleeve and separated from this latter by means of an interwall space kept under vacuum, and at least one heating coil situated in the said interwall space, against the sleeve, comprising the following stages:

-a metal tube (1) having a flattened shape in right-angled cross-section is wound onto a radially extensible mandrel (M), in such a way as to obtain a helix of pitch p and of external diameter D_H;

-a sheet metal cylinder (2) of circular cross-section and having an internal diameter very slightly greater than D_H is drawn over the mandrel and the tube;

the tube is applied against the wall of the cylinder by expansion of the mandrel;

-a fluid, in particular a hydraulic fluid, is injected into the aforesaid flattened tube under a sufficient pressure to cause it to assume by expansion the shape of a coil of circular cross-section and locally to deform the cylinder wall to a helical impression, in such a way as to form the sleeve (4) of the vessel; and

-the assembly formed by the tube (1) and the sleeve (4) is separated from the mandrel (M).

2. Process for the production of an assembly comprising a sleeve of sheet metal and a coil, for a container for storage of a cryogenic fluid, formed by a tank housed in the said sleeve and separated from this latter by an interwall space kept under vacuum, and at least one heating coil placed against the sleeve, comprising the following stages:

-at least one tube having a flattened form in cross-section is wound within a radially contractible mandrel, in such a way as to obtain a helix of pitch p and of internal diameter D_H;

-a sheet metal cylinder having a circular cross-section and an external diameter very little smaller than D_H is drawn into the mandrel and the tube;

-the tube is applied against the wall of the cylinder by contraction of the mandrel; and

-a fluid, in particular a hydraulic fluid, is injected into the aforesaid flattened tube, under a sufficient pressure to cause the same to assume by expansion the shape of a coil of circular cross-section and locally to deform the cylinder wall to a helical impression, in such a way as to form the sleeve of the tank; and

-the assembly formed by the tube and the sleeve is separated from the mandrel.

3. Process according to one of claims 1 and 2, characterised in that the coil is secured to the sleeve after the said injection.

4. Process according to claim 3, characterised in that the tube and the cylinder are provided, on their confronted walls, with a layer of a tinning product, and in that the aforesaid securing is by brazing.

5. Process according to claim 4, characterised in that the tinning product is applied on a plane metal sheet which, after rolling-is intended to form the aforesaid cylinder, along the development of the aforesaid helix of pitch p.

6. Process according to any one of the claims 1 to 5, for the production of a sleeve provided with two coils (7, 8), characterised in that two tubes of flattened cross-section are coiled separately.

7. Process according to any one of the claims 1 to 5, characterised in that after the said injection, the tube (12) is severed in such a way as to form two coils (12-13, 12-14).

8. The process according to any one of the claims 1 to 7, characterised in that, the sleeve being formed by a cylinder (2) of stainless steel sheet and an internal helical coil formed from a copper tube (1) having a circular cross-section after expansion-the following relationships apply:

in which:

e_cu=gauge of the copper tube

D=external diameter of the copper tube

e_T=gauge of the sheet metal

D_CE=external diameter of the cylinder

K=45 (for 1 mm<e_T<1.5 mm)

h=deflection of the impression in the wall of the sleeve.

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