Note: Descriptions are shown in the official language in which they were submitted.
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FILE, I~W l~ THIS AM~NDED
K3~ TRANSLATION
E 15129
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
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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
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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
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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
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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.
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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:
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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-
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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
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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
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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.
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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.
