CA2105987A1

CA2105987A1 - Double-walled pressure vessel and process for manufacturing it

Info

Publication number: CA2105987A1
Application number: CA002105987A
Authority: CA
Inventors: Theodor Cyron
Original assignee: Individual
Current assignee: Individual
Priority date: 1991-03-12
Filing date: 1992-03-09
Publication date: 1992-09-13
Also published as: ATE125924T1; DE9102936U1; EP0575395B1; JPH06506046A; EP0575395A1; DE4139739A1; WO1992016787A1; DE59203120D1; ES2076755T3

Abstract

(57) Abstract A double-walled pressure vessel comprises a thin-walled inner vessel (5, 6, 7, 8) mode or a dense, corrosion-resistant material, in particular special steel, and a pressure-tight outer vessel (1) which has a shell (11), a transition part (12), a neck part (13) and a base part (12). The base part (2) and/or the transition part (12) with the neck part (13) are/is arranged inside a cylindrical or slightly conical end region of the shell (11) The base part (2) or the transition part (12) has an outer collar (4) which runs, at least in sec-tions, approximately parallel to the end region of the shell (11), to which it Is collected by a structural connection (9). It is particularly advantageous if the structural connec-tion is a welded (9) or hard-soldered joint and the joint is located at a distance (a) from the inner base (5) considerably greater than the wall thickness (d) of the shell (1), prefer-ably greater than twice the wall thickness (d). The outer vessel (1) can be made of highly tempered steel, e g, 34CrMo4, without sustaining damage. The invention makes it pos-sible to manufacture comparatively light pressure vessels, e g, for high-purity gases

Description

2~0~9~7 FILE, I~W l~ THIS AM~NDED
K3~ TRANSLATION

s DOUBLE-WALLED PRESSURE VESSEL AND METHOD FOR
ITS MANUFACT'URE

The present invention relates to a double-walled pressure vessel with a thin-walled inner container of corrosion-resistant, dense material, particu-o larly special steel, and a pressure-proof outer container, particularly of a highly tempered steel.

Such pressure vessels are used particularly as pressurized gas bottles for gases of high purity or particular aggressiveness, which are needed for instànce in the semiconductor industry or in the testing industry. Single-walled special stee] containers are very costly both to manufacture and from the standpoint of material and are also very heavy, because on account of the low strength of the material of typical special steels they have to be made with thicker walls than bottles of the same strength made from tempered steels.

German Patent 38 15 347 describes several different pressurized gas bottles comprising a thin-walled special steel inner container and a multiple-part pressureproof sheath surroundin~ it, as well as several 2s methods for manufacturing such pressurized gas bottles. The essential characteristic common to all these pressurized gas bottles is that the various parts of the outer sheath are screwed together after the inner container has been inserted. Mamlfacturing a thread suitable for this purpose is very complicated. In the region of the thread, the outer diameter is increased relative to the actual sheath, which leads to high weight. After installation, the inner container is made to rest against the inner wall of the sheath - by being plastically expanded. An outer container made up of two parts welded together is expressly stated to be known. The welding construction shown has an encompassing weld seam on the jacket, the welding root of which is located in the immediate 5 vicinity of the thin-walled inner container. This weld seam can damage the inner container, which cannot be properly tested later. For an outer container of tempered steel, such a weld seam is impractical in the region under heavy strain, because the high temperature during welding can alter the microscopic structure. Nor can the we]ding zone be tempe-o red afterward by heat treatment, because then the thin-walled inner container would suffer.

The object of the present invention is to create a double-walled pressure vessel with a reduced weight and/or lower manufacturing costs compared s with the prior art. Another object is to disclose a suitable manufactu-ring means.

This object is attained by a double-walJed pressure vessel with a thin-walled inner container of a corrosion-proof, tight material, in particular 20 special steel, and having a pres.sureproof outer container, which has a jacket, a transitional part, a neck part, and a bottom part, wherein the bottom part and/or the transitional part is disposed with the neclc part on the inside in a cylindrical or slightly conical end region of the jacket, and wherein the bottom part or the transitiona] part has an outer collar, 2s which at least in segments extends ~pproximately parallel to the end region of the jacket and is joined to it by a joined connection.

The pressure vessel has a pressureproof outer container that closely surrounds an inner container whose thin-walled neck is extended out of 30 the outer container and flanged over, for instance. The thin-walled 210~87 inner container is first thrust into the outer container, which is open on one end, and only then is the outer container closed, with an inserted bottom part and/or neck part. If the inner container is of metal, particularly special steel, then since it is normally made up of several s parts it can first be welded together, and then cleaned and tested by conventional methods. It is practical to give the inner container an outer shape that matches the later internal shape of the outer container.
The inner container may be hydraulically or pneumatically expanded after the bottom part and/or neck part inserted into the outer jacket have o been joined, so that it will press against the outer container without gaps, with little plastic deformation. This method avoids possible gaps that might arise from inaccuracies in production. Suitably, the inner container intentional]y has a few slight longitudinal corrugations in the cylindrical part. This makes it easier to insert into the outer container.
15 These corrugations are made to rest on the outer container by the ensuing expansion process. Suitab]y, the gap between the inner container and the outer container is evacuated before the expansion process, so that substantial quantities of gas or air cannot remain behind. To that end, and also to test for tightness, an opening is provided in the outer 20 container.

The inner container may also be of plastic.

The joined connection, particularly by welding or hard soldering, of the 2s pressure-bearing outer container to the inserted bottom part and/or neck part may, because of the special shaping of the bottom part, be done with an outer collar in a locally only lightly stressed zone. The outer container according to the invention can therefore be made of conventio-nal, commercially available tempered steels and can be joined in the 30 tempered state without subsequent thermal tempering. This is made 4 210~87 possible because tangential strains dictated by internal pressure do not at the joining zone in the outer jacket, because of the pressureproof inner container. The reduced-strength zone, resulting from the thermal strain during joining, of the tempered, quenched steel has to absorb only the s axial force resulting for the internal pressure, and as a result the stress occurring in the joining zone and hence the requisite strength of the tempered steel are reduced by approximately half, Also, the joining point, if suitably located, is not subject to tensile strain but only to a shear strain, which because of the special shaping of the bottom part 10 and/or neck part is distributed over a joining surface area that is m~
tiple times (for instance two to four times) larger than the jacket cross--sectional area. To keep the thermal strain of the steel in the joining zone as low as possible, a beam welding process, such as electron beam welding, is especially favorable, or an alternative is hard soldering resp, 15 brazing that is done at lower temperature. Moreover, the joining point should be farther away from the inner surface of the pressure vessel in the bottom and/or neck part than the thickness of the jacket.

One essential advantage of the double-walled pressure vessel according 20 to the invention, when the inner containers are of special steel, is a smooth, clean, particle- and tarnish-free inside surface of the inner container, because after being introduced into the outer container, the inner container is no longer changed by high temperatures With inner containers of plastic, damage from high temperatures is likewise avoided.

In a further feature of the invention, the bottom part and/or neck part is formed by a supporting bottom curved outward and a formed-on cylindrical or slightly conical outer collar, whose outer shape corresponds to the inner shape of the jacket. This bottom part and/or neck part 30 may be pressed in one piece into a mold. If it has a slightly conical - 5 210~.87 outer shape, it can be mounted without any special problems in the suitably shaped jacket. With a cylindrical outer shape, it can be shrunk into the jacket with slight cooling.

s In a further feature of the invention, it is provided that the outer container includes at least one opening to the interstice between the outer container and the inner container. With this opening, the inter-stice can be evacuated after installation and prior to welding. Moreover, with this opening the tightness of the inner container can be checked, o for instance by a helium leakage test. It is also suitable to evacuate the inner container prior to the initial filling, .so that no substantial quanti-ties of air will remain that would contaminate the gas to be introduced later. ~n that case, that is, if the inner container is under a vacuum, then the interstice should also be under a vacuum so that it will not S become compressed by the outer pressure.

In a further feature of the invention, this opening may be provided with a plug, which is pressed outward if there is overpressure in the inter-stice. This plug provides proof that the inner container is still tight.
20 By way of example, such a p]ug could be of rubber or other elastomers or of a curing-type plastic.

The bottom part andlor neck part may also rest for instance with a shoulder disposed approximately vertically to the welding beam direction, 2s on a suitably shaped shoulder of the jacket. With these shoulders it is assured that the welding beam will not reach as far as the inner contai-ner and possibly damage it. Moreover, such a shoulder provides a clearly defined bearing surface for installing the bottom part and/or neck part in the jacket.

To bring about the joined connection and the bottom part, a hard soldering resp. brazing process has proved particularly favorable, since the temperature can remain below the critical temperature, for altera-tions caused by joining, in highly tempered steels, such as 34CrMo4. In 5 particular, a solder resp. brazing material that can be used at temperatu-res in the range of approximately 730C can be used. To fasten the supporting bottom in the jacket of a pressure vessel, both the outside and the inside are first machined to size. The supporting bottom is then inserted by its face end into the jacket, so that the outer collar of o the supporting bottom and the jacket rest approximately concentrically with respect to one another, leaving a solder gap. The solder gap can be used to deposit the solder resp. brazing material, which is in wire, foil or powdered form.

5 Next, the col]ar and the end of Ihe jacket are inductively heated to the soldering resp. brazing temperature, or dipped in liquid solder resp.
brazing material up to the upper line of the connecting face. After only a brief action of heat upon the pRssure-bearing parts of the jacketand supporting bottom, the soldering resp brazing process is terminated, so 20 that no changes in microstructure occur in the pressure-bearing parts. An example of a suitable soldering resp. brazing device is an annular solder resp, brazing material container which is heated by induction coils and into which the pressure bottom can be lowered 2s Figs, 1-6 shows exemplary embodiments of the invention, each being a vertical longitudinal section through a pressure vessel, or part of it, according to the invention.

Shown are:
~o - 21 0~7 Fig. 1, a pressure vessel before completion on the right and after com-pletion on the left;

Fig. 2, an alternative embodiment;
s Fig. 3, a further alternative;

Fig. 4, another alternative;
. . .
o Fig. 5, an embodiment with a lateral weld seam; and Fig. 6, a form and device for hard-soldered resp. brazed connections.

The right ha]f of Fig. I shows the pressure vessel prior to completion 15 and the left half shows it after completion. The outer container 1 comprises a jacket 11, open on one side and produced from a tube, for instance by a compression process, with a transitional part 12 to a formed-on neck 13 and with an inserted bottom part 2. The inner container in this case comprises a spherical inner bottom 5, a cylinder 20 inner jacket 6, and an inner transitional piece 7 with an inner neck 8;
parts 5-7 are joined together by weld seams, which can be cleaned and tested properly bèfore the parts are built in. After the insertion of the inner container, comprising parts 5-8, a suitably shaped bottom part 2 is inserted into the jacket 11. It is appropriate for the inner container, 25 which after all can be deformed substantially more easily, to be given an outer form from the very outset that matches the inner form of the outer container 1. After the insertion of the bottom part 2, or also of a neck part of suitable shape, not shown, the outer container is joined to the bottom part 2 or neck part with a joined connection 9, preferably 30 by means of an electron beam process or by hard soldering resp. bra-~ 0~ ~87 zing, because there is less heat sIrain. The bottom part 2 has an actualsupporting bottom 3 and an outer collar 4; the joined connection 9 is always on the outer collar 4, especially at a distance a from the inner bottom 5 that is greater than the wall thickness d of the outer container s 1.

For the sake of clarity in the drawing, parts 5-8 have been drawn thicker than necessary. A wall thickness of 0.5 to 0.8 mm is adequate and can be produced properly by welding techniques. The outer contai-ner 1 in this case has an outer diameter of approximately 200 mm and an internal volume 10 of from 50 to 60 I. It is suitable for an opera-ting pressure of 200 bar and has a wall thickness d of approximately 4 to 8 mm.

l5 In the left half, Fig. l shows the final state of the pressure vessel; the neck 13 is provided with a first outer thread 14 for conventional connec-ting fixtures. A second outer thread 15, for attaching the guard hood pressurized gas bottles typically have, is provided in a known manner by shrinking a suitable threaded ring 16 onto it. The joined connection 9, 20 as a connection of the jacket ll and the bottom 2, can be protected against damage by a protecting ring 17 of U-shaped longitudinal section.
This protecting ring 17 can be shrunk on or may be fastened to the jacket by several spot welds. In the inner container comprising parts 5-8 can be made to rest, after installation and after joining, on the inner 2s wall of the outer container 1 comprising the parts 11, 12, 13, 3 by plastic expansion.

Fig. 2 shows an alternative to Fig. 1, with a bottom part 22 that rests on a shoulder 20 in the jacket 21 and is secured with a conventional 9 ~105~8~

weld seam 29. In the region of the bottom part 22, the jacket 21 is hollowed out, so that any desired fit can be attained here.

Fig. 3 shows another alternative with a bottom part 32 that rests in an s expanded region of the jacket 31. The encompassing groove 30 produ-ced between 32 and 31 is filled up when the inner container 35, 36 is plastically expanded. The bottom part 32 includes an opening 37, with which the gap between the jacket 31 and the inner container 35, 36 can be evacuated prior to the joining and can be tested for leaks after the o joining. This opening 37 can be closed with a plug 38, on the one hand to avoid contamination of the interstice and on the other to provide proof of tightness of the inner container.

Fig. 4 shows another alternative, in which the outer collar 44 of the s bottom part 42 rests with a shoulder 40 on the jacket 41 and is welded to the jacket 41 by a beam process. Here it is clearly apparent that an axially parallel welding beam, even under unfavorable conditions, cannot pass through the necessarily existing gap between the bottom part 42 and the jacket 41 far enough to reach the inner container 45, 46. Once 20 again, an opening 47 is shown.

Fig. 5 shows an another alternative in which the outer colla~ 54 of the bottom part 52 has a step 50 on the outside, with which the jacket 51 is connected by means of an encompassing radial weld seam S9. This 25 version has the following distinctions from the versions above: The weld seam S9 is more readily accessible for production purposes, yet the load-bearing cross section of the weld seam is limited to the wall thick-ness of the pressure-bearing jacket Sl. Once again, an opening 57 is provided, which in this case is disposed in the jacket 51 and therefore - ~la~qs7 is more readily accessible when the bottle is upright. The inner contai-ner 55, 56 is unchanged.

Fig. 6 shows a form of jacket 61 and supporting bottom 63 or outer s collar 64 that are especially suitable for a hard-soldered (brazed~ connec-tion 69. The connecting point 69 is once again located far away from the inner bottom 65. Here as well, an encompassing groove 60 and a relief opening 67 are also provided. As a soldering resp. brazing device, an annular solder container 70 with solder resp. brazing material 71 is ~o schematically shown; it can be heated by means of an inner induction coil 72 and an outer induction coil 73.

The concentric solder gap 74 with a dimensionally constant gap width, produced by the slightly conical shaping of the jacket end 61 and the s supporting bottom collar 64, is suitable both as a place to deposit solder resp. brazing material in solid form, for instance as a foil, wire or powder and as a capillary-action gap for solder resp. brazing material rising out of the solder bath.

~o Although the previous paragraphs refer to a relief opening 37, 47, 57 or 67, this is not intended to preclude the possibility that a plurality of openings may be disposed over the circumference. Moreover, it may be practical to dispose grooves, not shown in detail, corresponding to the grooves 60 in Fig. 6 in the corresponding bottom parts in order to degas 2s the interstice, and these grooves would then lead to the aforementioned opening.

This pressure vessel according to the invention may be constructed of high-strength materials, and therefore with slight wall thicknesses and 30 correspondingly low weight and low manufacturing costs.

Advantages are demonstrated not only with the aforementioned tempered steels but also with other materials for the outer container, whose heavy-duty zones are not intended to be altered undesirably by the heating that occurs in the joint connection zone upon welding or hard s soldering resp. brazing.

In Figs. I-S, the gap between the bottom part and the jacket is shown às cy]indrical. It may also have a very slightly conical shape at the jacket end, for example with a conical angle of 2 to 5 and preferably o 3. This makes the installation of the bottom part in the jacket easier.

Claims

CLAIMS:
1. A double-walled pressure vessel with a thin-walled inner container (5, 6, 7, 8: 25, 26; 35, 36; 45, 46; 55, 56) of a corrosion-proof, tight material, in particular special steel, and having a pressureproof outer container (1), which has a jacket (11; 21; 31; 41; 51; 61), a transitional part (12), a neck part (13), and a bottom part (2; 22; 32; 42: 52) wherein the bottom part (2; 22; 32; 42; 52) and/or the transitional part (12) is disposed with the neck part (13) on the inside in a cylindrical or slightly conical end region of the jacket (11;
21; 31; 41; 51; 61), and wherein the bottom part (2; 22; 32; 42;
52) or the transitional part (12) has an outer collar (4; 24;
34; 44; 54; 64), which at least in segments extends approximately parallel to the end region of the jacket (11; 21;
31; 41; 51; 61) and is joined to it by a joined connection (9;
29; 39; 49; 59; 69), brazing temperature below the critical temperature for microstructural changes in the highly tempered steel, for instance at 730°C.

4. The pressure vessel of claim 1 or 2, in which the joined connection (9; 29; 39; 49; 59) is produced by a beam process, in particular by electron beam welding.

5. The pressure vessel of one of the foregoing claims, wherein the bottom part (2; 22; 32; 42; 52) comprises an outwardly curved supporting bottom (3; 23; 33; 43, 53; 63) and a cylindrical or slightly conical outer collar (4; 24; 34; 44; 54; 64), whose outer shape corresponds to the inner shape of the jacket (11; 21; 31; 41; 51; 61).

6, The pressure vessel of one of the foregoing claims, wherein at least in some regions an interstice is present between the outer container (1) and the inner container (5, 6, 7, 8; 25, 26; 35, 36; 45, 46; 55, 56), and the outer container (1) has at least one relief opening (37; 47; 57; 67), which communicates (30; 60) with the interstice.

7. The pressure vessel of claim 6, wherein each relief opening (37; 47;
57; 47), is closed with a plug (38), which can be pressed outward if there is overpressure in the interstice.

8. The pressure vessel of one of the foregoing claims, wherein the jacket (21; 31; 41; 51? 51) and/or the outer collar (24; 34; 44; 54; 64) is provided with steps (50) and/or grooves (30; 60) in order to simplify the assembly and/or to provide pressure relief if the inner container (5, 6, 7, 8; 25, 26; 35, 36; 45, 46; 55, 56) begins to leak.

9. A method for securing the supporting bottom (63) of a pressure vessel as defined by claim 3, having the following steps:

a. the jacket (61) and outer collar (64) of the supporting bottom (63) are machined to size on the inside and outside, respectively;

b. the supporting bottom (63) is intended by its face end into the jacket (61), so that the outer collar (64) and the jacket (61) are located approximately concentrically relative to one another, leaving a solder resp. brazing gap (69), which can preferably contain a solder resp.
brazing material deposit (74);

c. the collar (64) and jacket (61) are soldered resp. brazed to one another, but only far enough that the solder resp. brazing material does not reach the inner bottom (65);

d. after only a brief influence of heat on the pressure-bearing part of the jacket (61) and on the supporting bottom (63), the soldering resp.
brazing process is terminated, so that no microstructural changes occur in the pressure-bearing parts.

10. The method of claim 9, wherein the solder resp. brazing material (71) is contained in an annular container (70) which is heated by induc-tion coils (72, 73).