Note: Descriptions are shown in the official language in which they were submitted.
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METHOD OF JOINING TOGETHER METAL PIPES BY EXPLOSION
AND DEVICE FOR CARRYING OUT SAID METHOD
The present invention relates to a method of
joining toyether metal pipes by explosion, according
to which the facing ends of the pipes are inserted
between an outer metal ring and an inner metal ring,
of which the latter has an outer profile with inclined
edges, so that a wedge-shaped gap is formed between
-the inner ring and the interior lateral surface ûf each
pipe end, whereafter an explosive charge is caused to
detonate inside the inner ring.
Various methods of explosive joining of pipes are
previously known. For example, Britisn Patent Sperif;-
cation 766 741 reveals a method in which the pipe ends
are inserted between an outer ring and an inner ring,
and an explosive in the form of a cylinder is caused to
detonate inside the latter. The pipe ends and the outer
ring are thereby deformed so as to establish a shape-
dependent join-t be~r~een the pipes. The inner ring,
which consists of soft material such as lead, is
pressed into the gap between the end surfaces ox the
pipes to protect these end surfaces against corrosion.
In using this method, there is a substantial rlsk that
the joint will not be tight for media under high
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pressure and high temperature. the mechanical strength
of the joint is practically entirely dependent on the
deformation of the outer ring and the pipe ends, since
the inner ring consists o soft material which does not
increase the strength appreciably.
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IJnited States Patent ',pecification 3 290 771 reveals a
method of explosive joining of thin-walled pipes provided with
corrosion-protective coating. The pipe ends are inserted into
annular grooves or depressions in the ends of a plastic sleeve,
which surrounds the explosive charge and is in turn surrounded by
a separable outer ring with a pair of annular grooves. Upon
detonation, the grooves give rise to alternating valleys and ridges
in the pipe ends and the sleeve, which lock the pipe ends to the
plastic sleeve. After the detonation, the outer ring is split and
removed. It is only possible to use this method when joining thin
pipes and not for joining heavy iron pipes, e.g. in pipelines for
oil or gas, and especially not for district heating pipes, which
must withstand pressures up to 20 bar and temperatures up to 120C.
Generally, the present invention is intended to provide
a method of achieving, by explosion, a tight high-strength between,
in the first place, heavy metal pipes such as pipes for pipelines
and district heating lines. Up to now, such pipes have been welded
together, which is an expensive method requiring high levels of
professional skill, especially since the welding work must often
be performed in inaccessible locations such as inside conduits.
In many cases the welding joints must be X-rayed, which increases
costs even further. Thus the invention also intends to provide a
simpler, less time-consuming method requiring less equipment, for
joining pipes, especially pipes located in positions which are
difficult to get at.
The invention provides method of joining together metal
pipes by explosion, according to which the facing ends of the pipes
are inserted between an outer metal ring and an inner metal ring,
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of which the la-tter has an outer pro:Eile wi-th inclined edyes, 50
that a wedge-shaped gap is formed be-tween -the inner ring and the
interior lateral surface of each pipe end, whereafter an explosive
charge is caused to detonate inside the inner ring, characterized
in that an annular explosive charge is used, which has an axia]
leng-th substantially grea-ter than its radial thickness and is
caused to detonate wi-th -the aid oE detonator means which produce a
detonation evenly distributed over the circum-ference of the charge,
said detonation commencing only in the axially central portion of
the charge, to produce oppositely directed detonation waves
diverging from said central portion of the charge, the explosive
force of the charge being adapted so that the collision pressure
between the pipe ends and the inner ring as the latter expands
produces a weld between the ma-terial in the inner ring and the
material in the pipe ends.
The invention also provides device for joining together
metal pipes by explosion, comprising firstly, an outer metal ring
and an inner me-tal ring, between which the facing ends of the pipes
can be inserted, the inner metal ring having an outer profile with
inclined edges, and secondly, an explosive charge insertable into
the inner ring, characterized in that the explosive charge is
annular and has an axial length substantially greater than its
radial thickness and has detonating means arranged to produce a
detonation evenly distributed over the circumference of the charge,
said detonating means being disposed only in the axially central
portion of the charge, thereby to produce oppositely directed
detonation waves diverging from said central portion of the charge,
and that the explosive force o:E the charge is adapted so that the
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collision pressure between -the pipe ends and the inner r:ing as the
la-tter expands produces a welcl be-tween -the material in the inner
ring and the material in the pipe ends.
The invention is based on the idea of crea-ting conditions
similar to -those in explosive welding two sheets for example, in
which one sheet, after a short acceleration distance, is made to
strike the other sheet, wi-th -the detonation being initiated at one
end, so that the collision takes place successively towards the
other end. By using, according to -the invention, an inner ring
with inclined edges and starting the detonation in the center, -the
collision zones proceed from the center in opposite directions
towards the ends of the inner ring.
The joining of pipes in inaccessible spaces is particu-
larly simple ifl in a preferred application of the method according
to the invention, the inner ring is first fixed to -the ou-ter ring
with the aid of spacer means placed cen-trally between the edges of
the rings. The outer ring with the attached inner ring can then be
slipped over one pipe end until the pipe end edge abu-ts agains-t the
spacer means in the gap between the rings. After fixing the
annular explosive charge in place on the inside of -the inner ring,
the other pipe end is inserted in-to the gap between the rings until
its end edge abuts against the spacer means. This process requires
no access at all to the joint itself; rather it is sufficien-t that
the outer end of one of the pipes be accessible, so that a force
can be applied to -this end to push the pipes together. The spacer
means assures that the rings will be centered precisely in relation
to the pipe ends, which is essen-tial for achieving uniform deforma-
tion and welding of the pipe ends.
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The inven-tion will be descri.bed in more detail below
with reference to the embodirnen-ts shown in the accompanyiny draw-
ings.
Figure 1 shows a longitudinal section through one embodi-
ment of a coupling device for carrying out the
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process according to the invention, applied to a pair
of piC~e ends.
E`ig. 2 shows a mocli~ied ernbodiment of the inne-~
ring in E'ig. 1.
Figs. 3 and A shcw longltuclinal sectiO;Is through
additional embodiments of the outer ring and the inner
riny prior to and after detona-tion.
FigO 5 shows a side view of an em~Dodiment oE a
spacer element.
In Fig. 1/ 1 and 2 designate the end portions o f a
pair of standard iron pipes 32 cm in diameter, on which
a coupling device according to the invention is mounted.
It comprises an outer iron ring 3 of greater thickness
than the thickness of the pipes and consequently greater
streng-h in the radial direction than the pipes. The
ring 3 is made with an inner peripheral groove 4 which
is essentially V--shaped with edges 5, 6 inclined to-
wards each other on either side of a narrow flat bo-ttom
surface 7~ As can be seen from the figure, the ends of
the pipes 1, 2 extend as far as the edges of the bo-t-tom
surface 7.
Inside the pipe in the center oE the groove 7,
there is an inner iron ring 8, the width of which is
approximately equal to the width of the groove 4. Its
top side is made with inclined surfaces 9, 10 with
the same incline as the edges 5, 6 of the groove. The
surfaces 9, 10 are separated by a shallow groove 11
with a flat bottom, the width o which is equal to the
width of the bottom ~urEace 7.
The ring 3 and the ring 8 are fixed to each other
with the aid of a spacer means, which can be formed
of a wave-shaped s-teel band 12, which is shown in more
detail in Fig. 5. The Rand 12 has alternating portions
13 and I4, which in the position of the rings shown in
Fig 2 are spot-welded to -the bot-tom of the groove
and are snapped into the groove 11 of the ring 8. The
band 12 thus has an elasticity which permits a spring
movement corresponding -to the depth of the groove 11.
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In Fig. 5, 15 indicates the wel.dirlg po.ints to the
grove 4. Alternati~,~ly, the bancl 12 can b- divided
int.o evenly dijtrlbuted short segrllents, as indicated
betwt-erl the dash-dot lines in Eig. 5. By using a
resilient bar-d, which snaps into the groove in the
inner ring, the assembly will be simple because the
existing inclined surfaces 9, 10 are used to press
the band out of the way. An addi-tional advantage of
using a spacer means of the -type described is that
after the deformation it takes up very little space,
as will be described below.
In Fig. 1 the upper half shows the position and
shape of the component parts prior to detonation of
an explosive charge lh (shown schematically) fixed
to the inner ring 8. Tne explosive charge, which can
consist of an annular dynami-te charge enclosed in a
paper jacket, is caused to detonate by means of a
number of detonators 17 distributed evenly around
the circumference of tile charge and connected to
electric wires 18 exiting through one of the pipes
After the detonation with the accornp~lny;ng e~.pansi.or
of the ring 8, a joint is obtai.ned with the appear--
ance shown in the lower half of Fig. 1. The pipe ends
are coned outwards and clamped between the rings,
which results in a joint w;th a tensile strength
fully comparable to tha-t of the pipe itself. Su-it-
able proportioni.ng of -the explosive chaLge together
with careful. cle~nincJ of the join-t areas will also
provide welding betweerl the material. in -the inner
ring and thy ma-terial in the pipes in -the area
between the arrows in Fig. 1, so as to provide a
tight joint. The band 12 is easily folded together
into the space between -the pipe ends and thus does
not disrupt the deformation process. As can be seen
in Fig. 1 r the inner ring 8 provides a practically
smoo-th transition between the pipe endsr so that -the
joint wiil not produce any apprec:i.ab]e turbulence in
the flowing medi Ulll .
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In the elrlbocl:imerl showll in E'ig. 1, the greatest
length oF the momerlt m is obtai.rled at the initial.
deformat.ion oF the wipes, slnce the inner ring 8
abuts against the pipe ends near their outer edyes.
Since the size of the charge is firs-tly dependen-t on
the deformation work to be carried out, this arrange-
ment minimizes the aize o:E -the charge required, Via
ventilation ducts 19, which are evenly distributed
around the outer ring 3 and connect the groove 4 with
the surrounding atmosphere, -the medium enclosed in
the groove can be quickly evacuated, wnich further
contributes to keepir~.J- the optimum size of the charye
small.
The optimum shape of the groove 4 of the outer
ring and the inner ring 8 can vary depending on
various factors such as pipe dimension, material
characteristi.cs; welding requirements e-tc. Fi.gs. 2, 3
and 4 show several modified embodiments of the outer
ring and the inner ring in which the same reference
numerals as in Fig. 1 are used Eor corresponding
parts.
