CA2154638C - Procedure and apparatus for cold joining metallic pipes - Google Patents

Abstract

A method for joining together two metal pipe segments comprises placing the pipe segments in axial alignment with their end faces in close proximity to one another; bridging between the two pipe segments a metal tubular joining sleeve closely fitting to their outer walls adjacent to their end faces; surrounding the tubular sleeve adjacent to both of the end faces with an electrically conductive coil; and applying to the coil a brief electrical pulse to produce a magnetic field to shrink the sleeve onto said pipe segments. An external peripheral groove is formed in the outer wall of each of the pipe segments, and the sleeve overlaps said grooves so as to be pressed into them to increase resistance of the joined pipe segments to axial separation.

Description

. ~ '"- 214638 ~ '"' 4507 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 "fxproaf ftan"~~uo Dal or oapoalL
I hafAGy CWtity IhP.I Ihlf p8[1a! fag 1 bJln~ OQ~ 51tf0 Wlln a tea United &tstea n~.aai Gw~.rce "kaPlaaa f.tay Pcal C.~!:~.a to Addraaaau" Asrvfeo anger 17 CFR 1.511 on I56 datA If~U~tel:! at~,.vs a~:d 1 .r4dreas~d (c tna Comntlafionar of Yalenu end trademarks.
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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, .,/VL LY 7J aun i4:4y DClNHLD D. tlOtJ 818 T93 969lf P.96 . . ~ ,~, 225638 ~ ,-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 i l d p y nvo ve , ~-' 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 ~ ////

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 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 - 4a -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 - 4b -A

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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 ~u~ ~4 ya sUN 14:51 DOhlfaLD D. MO~I gig 7g~ g~~0 ~ ', z2~4s3~
a5o9 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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a 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 1~1.1t1 , 818 793 569F~ P. i2 '' 21~4638~
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.!

32 /~//

,TUL 24 95 SUN _4:54 DONfaI_D I~, fl0fv 8i8 793 9590 P. 13 ~ww ~~~w -P
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~~~ ,' . ' 32 i

Claims (7)

1. 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 at least as large as 12 inches, said diameter 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 another;
placing a metal tubular joining sleeve bridging between the 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 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.

2. A method according to claim 1 in which an external peripheral groove is formed in the outer wall of each of the pipe segments, and said sleeve overlaps said grooves so as to be pressed into said grooves to increase resistance of the joined pipe segments to axial separation.

3. A method according to claim 1 in which an adhesive is placed between said outer walls and said sleeve.

4. 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 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 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.

5. 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 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 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.

6. A method according to claim 5 in which an external peripheral groove is formed in the outer wall of each of the pipe segments, and said sleeve overlaps said grooves so as to be pressed into said grooves to increase resistance of the joined pipe segments to axial separation.

7. A method according to claim 5 or claim 6 in which an adhesive is placed between said outer walls and said sleeve.