Note: Descriptions are shown in the official language in which they were submitted.
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1 PROCEDURE AND APPARATUS FOR CObD JOxNING
OF METALT.IC PIPES
3 FielB of the Invention
Method and apparatus xor cold joi.riing metallic pipes with
the use of magnetic force.
6E~ aack~rflund of the Invention
7 This invention comprises a method and implementing appaz~atus
B to permit joining of metallic tubes, such as oil or gas
pipelines, and oil well casings, without flame or arc welding.
The invention is teased upon use of the magnetic "pinch effect",
I1 ( sometimes called "magnetic pulse forming", to squeeze a joining
121 tube of conductive metal around the ends of similarly
131 electrically conductive or less electrically conductive pipes to
14f be joined. With care in use, the method alsa can be used to join
pipes of the same conductive material as the joining tube, or
16 even tubes of non--conductive materials, such as ceramic ("tile")
17 utilixin~ a conductive connection. Thr= method also can be
18 applied to produce neck-down or flare--up points between tubes of
19 different sizes.
In addition to being a flame hazard, the use of arc welding
21 on steel pipes can produce serious stress micro-cracks that can
22 form the basis for splits and ruptures when the metal is vibrated
23 ' or stressed in the future. Some examples of disasters from this
24 cause were experienced during the 1940's wher' arc welders used to
"strike an arc" against the deck plates pf a "Victory Ship" being
26 constructed. The micro-cracks being later worked by the motion
27 of the shi at sea a I
p P pparently caused several instances of
28 tearing that neaxly or Completely destroyed the ships, This
29 phenomenon apparently is worse when the arc welding~is done in
I
' very cold weather, when the arc appears to instantly, in effect,
31 anneal smaller width lines along the steel (versus the same
32 situation in warm weather}. In addition, arc welding tends to be
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=~' 1 ~ non-uniform, and requires greater operator skill and complicated
2~I post welding inspections,
3 In the oil drilling environment, it would be particularly
4 advantageous to have a means for cold joininr~ the sections of
well casing pipes as they were successively sunk into the hole,
6 without heat and without the need for accurately threaded
7 fittings. Threaded fittings require some turning of the pipe
8 sections in advance, or even on site. Although Blame brazing and
9 arc welding have_been used to join pipes in the drilling field
environment, there is often the risk of igniting a flan;e which is
11 difficult to extinguish, because hydrocarbon gases tend to escape
12 from the hole before any oil is found.
I3 ~~ Similarly, large pipeline segments can be joined in the
lA field without. requiring the tedious and time-consuming efforts
required by any class of welding, and this can be done in any
16 kind of weather.
17 Long Before the so called "heavy press " program or the
18 explosive forming program for forming large objects,~'~nd a Still
lg older method involved beating the soft metal against a sand bag,
zp and repetitively trying its fit over the pattern. Although the
21 results were acceptable, there also was a non-uniform
22 distribution of work hardening stresses In the metal as the
23 result of many, versus few. hammer blows on the various areas.
24 The magnetic pinch effect or "magnetic pulse forming" has
for several decades been used to cause conductive metals, such as
26 duraluminum to very rapidly (almost instantly) conform to a male
27 pattern in order to produce deep draw forms, such as aircraft
28 engine nacelles, This reduced the labor that formerly was
29 ~ involved in the repetitive hand forming and fitting of sections
of sheet aluminum to a wooden, ceramic, plastic ar plaster
31 pattern,
32
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1 Magnetic pulse forming, while requiring rather heavy and
2 expensive equipment, is able to rapidly produce nearly
identical
3 draws to the same pattern with very little hand labor
involved,
4 and with the elimination of much of the human error thst
beset
the earlier methods when used for certain classes of materials.
6 snd certainly with less expense and with greater
convenience''
than
(.'Vi''''n
the heavy presses or explosions which was
reviousl
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,
~-' 8 Whenever a rapidly changing magnetic flux cuts across a
9 conductive material, a current is induced within the
material.
'This current as proportional to the initial intensity and
time
11 rate of change of the magnetic flux. The higher the rata
of
12 change, the greater the induced current.
13 Then, whenever there is an induced currene. there is an
14 associated magnetic field of such polarity as to 0 ose the
.
magnetic field producing the current. Thie reactive force
16 between the rapidly changing magnet and a metallic material
17 within its field can produce very significant forces of
18 repulsion. The effect sometimes is called "Gem 's haw
19 Repulsion". One rather large-scale illustrative use of the
effect i9 in the levitation of magnetically suspended railroad
_.. . ._._ 21 trains above the conductive tracks. In that case large
22 alternating currents can be used in the coils to produce
larger,
23 repetitive changes in magnetic flux.
24 Zn magnetic pulse forming, a rapidly changing,
unidirectional current is applied to the work coil from
an energy
26 storage capacitor. The required high rate of change of flux
is
27 produced by rapidly discharging a large electric charge
from an
28 energy storage capacitor through a very low resistance call
of a
29 few turns. The initial discharge current can be extremely
heavy
'and will rapidly decrease in the early part of i,ts exponentjal-
31 decay curve. This heavy current, rapidly decaying, causes
y
a
32 ~ ////
2154638
rapidly decaying flux that induces a heavy, similarly decaying
current within the metal of the work piece.
Because the flux is concentrated within the core of
the work coil, the reaction flux from the induced current is
directed radially outward against t-he flux of the work coil.
This causes extreme forces of repulsion to "pinch" the work
piece radially inward. (Of course, the work coil also,
alternatively, can be placed within the work piece to produce
a force that tends to swell the work piece radially outward
toward an external form.)
The basic principle of magnetic pulse forming is
well known to the industry, but with the advent of heavy deep-
draw presses, magnetic pulse forming tended to be less used in
practice. However, as with any natural phenomenon, there are
niches where it can become the method of choice in trade-offs
versus the advantages and disadvantages of other methods of
forming. The method herein described is such an application
niche.
Summary of the Invention
The invention provides a method for joining two
large-diameter steel pipe segments together, each pipe segment
having a central axis, an inner wall with an inner diameter,
an outer wall with an outer diameter, said diameters of said
two segments being equal to one another, an axial passage
defined by the inner wall, a wall thickness between said
walls, said wall thickness of said two segments being equal to
one another and an end face extending between said walls, said
method comprising: placing the pipe segments in axial
alignment with said end faces in close proximity to one
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62599-175
2154638
another; placing a metal tubular joining sleeve bridging
between two pipe segments, closely fitting to their outer
walls adjacent to their end faces and overlapping them for a
substantial distance; surrounding said tubular sleeve adjacent
to both of said end faces with an electrically conductive
coil; and applying to said coil a brief electrical pulse to
produce a magnetic field to shrink the sleeve onto said pipe
segments, said coil being formed in two separate coil segments
which are separately joined together to surround said sleeve
l0 when said coil segments are fitted around said pipe segments
where they abut, and overlapping a substantial portion of said
sleeve on each side of the adjacency of said pipe segments.
The outer diameter of the pipe segments is preferably at least
as large as 12 inches.
From another aspect, the invention provides
apparatus for joining two steel pipe segments together, each
pipe segment having a central axis, an inner wall with an
inner diameter, an outer wall with an outer diameter, an axial
passage defined by the inner wall, a wall thickness between
20 said walls, an end face extending between said walls, the pipe
segments being in axial alignment, with said end faces in
close proximity to one another and with a metal tubular
joining sleeve bridging between the two pipe segments, closely
fitting to their outer walls adjacent to their end faces, said
apparatus comprising: a ring-shaped segmented electrically
conductive coil for surrounding said tubular sleeve adjacent
to said end faces, said tubular coil being formed in two semi-
circular segments hinged together to open and receive said
sleeve and pipe segments, connector means to join the coil
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62599-175
2154 638
segments together when the coil encircles the pipe segments,
to form a complete coil circuit, and a source of pulsed
electrical current for said coil circuit to provide a brief,
intrusive magnetic field.
Accordingly to a preferred but optional feature of
the invention, external grooves are formed in both of the
pipes, into which the sleeve is pressed, in order to provide
additional structural strength to resist axial separation of
the pipe segments.
The above and other features of this invention will
be fully understood from the following detailed description
and the accompanying drawings in which:
Brief Description of the Drawings
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62599-175
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1 Fige. la-ld are fragmentary views of four sequential
2 conditions of the workpieces;
3 Fig. 2 ie a semi-schematic view at the coil assembly; ,
4 Fig. 3 is a block diagram of the .invention; and
5' Fig. 4 shows a cutter for making grooves in the pipe
segments.
Detailed Description of the Inyention
8, Figure 1 shows a joining tube 10 made of a conductive metal.
.9 such as copper, brass, silver, beryllium coppar, aluminum etc.
that is sized for a smooth, loose fit over the ends 11, 12 of
11 pipe segments 13, 14 which are to be joined. In each of the pipe
12 segments to be joined, a multiplicity of annular grooves 15. 16
I3 are cut by use of a cutting, tool. These grooves are cut to a
14 depth of about one third of the wall thickness of the pipes and
are useful to provide s positive mechanical interlocking of the
16 two joined ends. xhe ends of the pipes are roughly cut to meet
17 each other, although the method allows for considerable mismatch,
18 or "slop" in this, and they need not abut in full surface--to-
19 surface contact although they may. Also, it is not necessary to
have exactly accurate cuts in the grooves. The mechanical
21 strength :f the segments lost in cutting the groove~a, is later
22 compensated for by the strength of the joining tube,.
23 Additionally, a small quantity of microencapstzlated pressure
24 sensitive adhesive (1?) may be dusted into the grooves or coated
on the interior of the joining tube, prior to placing the joining
26 tube over the pipes. The joining tube is fitted over the gap
27 between the pipe segments arid over the grooves.
28 A hinged magnetic work coil 20 Fig. 2 then is closed aver
29 the joint area in the condition shown in Fig, 1c, and the
i necessary heavy pulse of current is applied. This shrinks the
31 more conductive outer joining tube more than the less conductive
32 ,or partially shielded pipe segments, thus causing the metal of
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1 ~the joining tube to conform closely into the grooves and around
the roughness of the somewhat irregular pipe segments.
3 Because the pipe segments are not likely to have a perfectly
' 4 smooth finish, and because the joining tube is not completely
plastic during the short pulse of contraction, there may be tiny
E roughness spaces between the joining tube and the work pipes.
Thus, the microencapsulated, pressure sensitive adhesive fills
these micro-spaces to provide a pressure tight seal, as well as
9 , to provide an additional bonding,. The extreme pressure between
the pipe segments and the joining tube causes rupture of the tiny
11 capsule., of adhesiv~, which permits the adhesive to flow out into
12 the roughness of the pipe surfaces and i»to the grooves. The
13 joined pipe segments have effectively been put together with a
14 strong pressure--tight splice which required no significant amount
I5 of heat and no precision machining of the metal. Typically, the
16 duration of the forming pulse is less than 1/ip,00~ of a second
17 ~>o.oaoi,sec.~
18 THE APPARATUS: '
19 The working coil 20 is shown in Figure 2. The coil is
contained within a pair of jaws 22, 22 which are supported by a
21 positioning arm 23. Axm 23 grasps the pipe sagments firmly.
22 while permitting hand closure of the jaws over the working area,
23 in a somewhat loose fit between the jaws and the pipe segments,
24 The turns 25 of the coil are completed through connector pans 26
and sockets 2T to provide a completed coil circuit around the
26 work area, when tha jaws are closed.
27 In practical field applications the Work pieces will be
28 quite large, often on the order of 12 to 36 inches in diameter.
29 The work head with its coil will accordingly be quite'heavy, so
.that some means of support will be provided by a'work vehicle
31 which will uaritain the power supply and controls ss well as the
32 manipulating arm to position the coil jaws over the work pieces.
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1 The heavy conductive leads 28 and 29 to the two ends of the coil
2 ~ are carried down the positioning arm of the vehicle to the
3 power/control unit.
Figure 3 is a functicnal block diagram showing the various
' S required modules in the system to supply the necessary pulse of
_ _--'
6 decaying current to the work coil with its connectors closed.
7 The coil is not connected to the energy storage capacitor 30
8 until the firing switch 31 closes. Switch 31 must remain open
9 until the desired energy level of the capacitor has been achieved ,
by charging from the power supply 32 through the charging switch
11 33. This charging switch must remain closed until the capacitor
12 has been charged for a preset time as Limited by the timer
13 control module 34 set by the energy set level module 35. The
1~1 charging switch 33 must open when the preset time has expired,
and this event delivers a "ready" signal to the timer control
16 module.
17 The charging action is l.ndicated by a charging indicator
18 light 36 which goes out when the charging switch opens. The
19 readiness condition 3s indicated by the ready light 3? which
remains on until the manual. firing switch 31 is closed, when the
21 firing switch is closed, it signals to the timer control unit 34
22 to close the firing discharge switch 38 if, and only if, the
23 charging path switch module 33 is in an open condition. This
24 last action permits the energy storage capacitor to suddenly
discharge through the firing discharge switch module and the work
26 coil, The preferred emboditnerit of the firing discharge switch
27 (not known) is a closed tube containing a few drops of mercury -
28 metal and having heavy contacts at one end. The tube is rotated
29 by a solenoid to produce closure as the mercury metal.falls to
.the contact end of the tube and flows against th,e contents. This
31 keeps the heavy arc of contact closure confined in ords?r to
32 reduce any flame hazard, The charging switch, on the other hand
9
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1 can be a battery of silicon controlled rectifiers, since its
2 current is smaller and is applied wee a longer time. The
3 ~ reverse resistance of such rectifiers must be adequate to resist
4 any significantleakage of the capacitor back the
through
charging power supply circuitb. xher~e rectifiersplaced in
are
6 an "off" condition in order to prevent the closingth4
of
7 discharge path Prom overloading the power supply.e energy
Th to
8 perform all these operations may be provided engine
~ of by an
9 driven generator vehicle.
or "alternator"
mounted on
the work
The annular grooves in the pipe segments, when used, may be
11 produced by the groove cutter 40 shown in Figure 4, A drive
12 motor 41 turns a multiplicity of milling cutters (or grinding
13 wheels) 42 against the outside of the pipe with a pressure and
14 depth of cut roughly controlled by sn inside guide 43 which is
slipped into position by means of telescoping lock screw knob 44.
16 The assembly is maneuvered around the circumference of the pipe
17 segment by use of a pistol grip handle 45 that holds the assembly
18 together. A chip shield 46 protects the operator from flying
19 debris as the grooves are bEing cut. The preferred embodiment of
the cutters is high speed steed coated with a cathodic arc hard
21 coating (as taught in tl,s, Patent No, x,625,848 by Alvin A.
22 ,Snaper) to greatly increase the usoful life of the cutters in the
23 field envircnment.
2a Alternately, the grooves may be applied during the pipe
fabrication process or in some cases, depending upon service
26 application of the pipe, eliminated entirely.
27 The method and apparatus provide the following advantages
28 among others:
29 i. A relatively noiseless, rapid, economical and flameless
-system Por joining pipes in a fie2d environment.!
31
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214838 ~ 4509
1 2. A pipe joining method that does not require precision ,
2 machining of the Work pieces.
3 3. A systemized group of equipment that permits rapid
4 application of the pipe joining system at almost any location.
4. A pipe 3aining method that precludes leaks or undue
pressure drops.
7 S. A system for producing pipe joints that can introduce
8 almost zero frictional discontinuity for the fluids solids or
9 gases being conveyed in the pipe.
6. A pipe joining system that can so rapidly repair breaks
11 and leaks in a limited number of pipe sizes as to greatly
12 minimize the costly "down time" in such applications as repair of
13 gasoline, oil, natural ryas, water etc, pipes. Such repetitive
14 repair needs may be encountered in such large papa systems as oil
wells, oil transport lines, city water systems or "aqueducts",
l6 natural gas supply lines, mine pump systems and chemical
17 processing plants, eCc.
18 7. A repair system that requires stocking of only $
19 limited number of stat'~dard repair sleeve sizes.
B. A pipe joining system that will permit joining pipes of
21 different diameters.
22 9. An effective pipe joining and repair system far such
23 pipe intensive operations as central steam heating systems and
24 chemical ~,:ocesoing plants.
This invention is not to bf= limited by the embodiments shown
26 in the drawings and described in the description, which are given
27 by way of example and not of limitation, but only in accordance
28 with the scope ef the acco;npanyfng claims. ,
29 f~~~ ,'
. '
31
32 i
