US3806020A

US3806020A - Apparatus for welding of pipe by use of explosives

Info

Publication number: US3806020A
Application number: US00252821A
Authority: US
Inventors: R Wittman; W Howell; T Espinoza
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1972-05-12
Filing date: 1972-05-12
Publication date: 1974-04-23
Anticipated expiration: 1991-04-23

Abstract

A high explosive ring is detonated by placing in contact with the ring a sectioned, connected, planar mounting member having a circular opening for receiving the ring of explosive and contacting the outer surface of the ring. Arranged on the mounting member, which may be formed of material destroyed on detonation of the explosive, are sets of strips of high explosive formed in a perpendicular pattern to contact the center of the ring of explosive at a multiplicity of peripherally spacedapart points. Each set of strips, such as four, is provided with a detonator connected to an electrical source such that on energization of the detonators the strips explode and initiate simultaneously explosion of the ring at each point of contact. The strips are formed into a pattern which is suitably arcuateradial or chords perpendicular to each other which in turn may connect to other arcuate-radial strips or perpendicularly arranged strip chords and then to the ring of high explosive. The strips may also be separated from the ring of high explosive by inert material at spaced apart points.

Description

United States Patent 1191 Howell et al.

[ Apr. 23, 1974 APPARATUS FOR WELDING OF PIPE BY USE OF EXPLOSIVES [75] Inventors: William G. Howell, Lakewood; Theodore A. Espinoza, Denver; Robert H. Wittman, Littleton, all of C010.

[73] Assignee: Esso Research and Engineering Company, Linden, NJ.

22 Filed: May 12, 1972 21 Appl. No.: 252,821

Primary Examiner--.l. Spencer Overholser Assistant ExaminerRobert J. Craig [5 7 ABSTRACT A high explosive ring is detonated by placing in contact with the ring a sectioned, connected, planar mounting member having a circular opening for receiving the ring of explosive and contacting the outer surface of the ring. Arranged on the mounting member, which may be formed of material destroyed on detonation of the explosive, are sets of strips of high explosive formed in a perpendicular pattern to contact the center of the ring of explosive at a multiplicity of peripherally spacedapart points. Each set of strips, such as four, is provided with a detonator connected to an electrical source such that on energization of the detonators the strips explode and initiate simultaneously explosion of the ring at each point of contact. The strips are formed into a pattern which is suitably arcuate-radial or chords perpendicular to each other which in turn may connect to other arcuate-radial strips or perpendicularly arranged strip chords and then to the ring of highexplosive. The strips may also be separated from the ring of high explosive by inert material at spaced apart points.

17 Claims, 15 Drawing Figures APPARATUS FOR WELDING OF PIPE BY USE OF EXPLOSIVES CROSS REFERENCE TO COPENDING APPLICATIONS This application is related to and commonly assigned with the following applications:

1. Ser. No. 252,820, filed May 15, 1972, in the name of William G. Howell and entitled EXPLOSIVE WELDING OF PIPE.

2. Ser. No. 252,641, filed May 12, 1972, in the names of William G. Howell and Robert H. Wittman and entitled WELDING F HOLLOW CYLINDERS SUCH AS PIPE.

3. Ser. No. 252,678, filed May 12, 1972, in the names of William G. Howell, Steve H. Carpenter, and Henry E. Otto, and entitled EXPLOSIVE WELDING 0F PIPE WITH EXPLOSIVE MEANS.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is directed to explosive welding of pipe. More particularly the invention is concerned with explosive welding of pipe wherein a particular pattern of high explosive strips are employed. In its more specific aspects, the invention is directed to explosive pipe welding in which buffered or spaced strips of high explosive on a planar surface is employed to detonate a ring of high explosive on a pipe collarand the like.

2. Description of the Prior Art Welding of sections of pipe together by the action of explosives is well known. It has also been taught to use interiorly arranged mandrels in welding of pipe to prevent collapse thereof. The prior art also teaches the use of pipe collars for welding pipe by explosive action. Such collars have been formed to provide an angle with the exterior of the pipe but the collars are usually of the same thickness throughout and so is the explosive employed. Likewise high explosives have been arranged on the exterior of the collar as a cord which is detonated. None of the prior art, however, teaches or makes obvious the, present invention wherein an expandable and compressible mandrel is employed which is easily movable through the pipe after weldment of one section to another.

The prior art does not teach or make obvious a planar surface on which buffered or spaced strips of high explosive are arranged in a pattern which may be radial-arcuate or chords perpendicular to each other to contact a particular shaped ring of high explosive on a pipe collar or a hollow cylinder. Nor does the art teach buffered connected strips which are both chords and arcuate in shape.

Moreover, the prior art does not teach the .use of such a mandrel with a particular type of collar and arrangement of explosive or use of the mandrel, collar, and a particular form of explosive.

Of the prior art considered with respect to this invention, the following patents were considered: US. Pat. Nos. 2,367,206 (Davis), 3,263,323 (Maher et al.), 3,563,713 (Rudd), 3,455,017 (Zondag), and Belgian Pat. No. 655,943. While a number of these references including Rudd, Davis (206) and Zondag, contemplate explosive joining of abutting pipe ends to a metal collar, none concern themselves with the multiple-point initiation of an explosive substantially in the plane of SUMMARY OF THE INVENTION The present invention may be briefly described and summarized as involving a high explosive perendicular pattern of high explosive mounted on a suitable planar surface which may be and preferably is destructive by the explosive, which is arranged in explosive contact with a ring or mass of high explosive on a pipe collar, and is contacted at a plurality of points on the periphery of the explosive mass by separated or buffered strips of high explosive arranged on the planar surface leading to detonation means connected to a source of electrical energy such that on detonation of the ring or mass of high explosive the collar is substantially instantaneously driven at a sufficient force against the abutting ends of the pipe sections to weld the inner surface of the collar thereto and weld the sections together.

A hollow expandable mandrel is useful in explosive welding of pipe sections together. In the present invention, the hollow mandrel is placed within abutting pipe sections having the collar circumferentially embracing the abutting ends of the pipe at least adjacent to the center of the collar. The ends of the pipe may be buffed to clean metal. The collar is interiorally formed to have a tapered shape such that the ends thereof are of a lesser thickness than the center. The outer surface of the collar may be substantially cylindrical and on it is placed a formed mass of high explosive which covers the collar and which is layered, stepped, molded, mounded, cast, or formed in any shape such that the thickness of the high explosive mass is greater at the center thereof than at its outer periphery. The force of the explosive causes the hollow mandrel segments to move from an expanded position such that it is of a lesser diameter and may be moved in the pipe to the next section to be welded onto the ever-increasing length of pipe line being formed.

VARIABLES OF THE INVENTION The mandrel is suitably formed of at least two pairs of opposing tapered pipe sections. While four sections are preferred and most desirable for 10-14 inch pipe and the like, a greater number of opposing pairs of segments may be used for larger pipe. Likewise, a plate on each end may be used with four segments; a greater even number of pairs of segments may require a greater number of plates to cause the tapered segments to be compressed into a cylindrical shape and expand against the inner surface of the pipe sections to be welded together. Four, six, eight, or a greater number of segments may be used with a plate on one end for each pair of segments. The plates are suitably angularly disposed relative to each other and for two pairs of segments may be arranged with respect to each other. The angles for a greater number of pairs will depend on the number of pairs and generally will be less than 90 relative to each other.

The high explosive used in the mass on the collar and in the pattern may be any one of a number of high explosives such as, but not limited to, Detasheet C which is 63 percent by weight PETN, 7 percent by weight nitrocellulose and 30 percent polymeric materials and has a specific gravity of 1.48, a detonation velocity of about 23,000 feet per second, and is currently supplied on the market in rubbery sheet form, pentaerythritol tetranitate (PETN) with red lead and a binder composed of a mixture of butyl rubber and polymers of B-pinene, TNT, cyclomethylene (RDX), Pentolite which is a 50:50 mixture of TNT and PETN, amatol, a 50:50 mixture of ammonium nitrate and TNT, and other well known high explosives and mixtures thereof which may be shaped or formed on the collar as will be described more fully hereinafter.

Explosives should be selected having detonation velocities within the range from about 15,000 to about 30,000 feet per second. Generally, explosives having detonation velocities within the range from about 23,000 to about 30,000 feet per second may be used in the pattern and explosives having detonation velocities within the rangefrom about 15,000 to 23,000 feet per second in the mass or ring. However, explosives having detonation velocities within the range of about 15,000 to about 30,000 feet per second may be used in both.

The high explosive shaped or formed or otherwise placed on the collar such as by casting may have a thickness at least adjacent its center about 200 to about 100 percent of the thickness of the sleeve or collar at least adjacent its center and a thickness adjacent its ends about 200 to about 100 percent of the collar at least adjacent the ends of the collar. The high explosive may be shaped, formed, cast, or molded, layered, stepped, triangular, conical, truncated conical, or mounded in cross-section.

The planar surface may be formed of plywood and the like, or of a suitable plastic material, or other destructible material of light weight. The surface may be circular with a concentric circular opening therethrough conforming to the outer circumference of the high explosive on the pipe collar and may be made of two or more sections which are easily connectible together with a fastener means which simply may be adhesive tape or latches, and the like, and is placed perpendicular to and around the pipe collar with explosive on it.

In the practice of the present invention in explosive welding of pipe essentially instantaneous initiation around'the periphery of the explosive charge or mass (ring) over the apex of the angle formed by the sleeve or collar and pipe is necessary such that the detonation waves proceed substantially perpendicular to the pipe axis and the resulting explosive shock wave proceeds substantially parallel to the pipe axis in a symmetrical fashion. Symmetry of forces is necessary so that the pipe collar or sleeve will not be propelled from its initially stationary position by unequally applied forces.

In the present invention a minimum of a plurality of initiators is required.

' If the prior art conventional line wave generators were used, they would be highly unsatisfactory because the initiator system must be positioned perpendicular to the explosive charge but parallel thereto and a line wave generator would have to be placed parallel to the explosive. The detonation wave of a line wave generator would thus interfere with the formation of the explosive mass in the present invention as it would have to lie parallel thereto.

The size of the pipe which may be welded may vary from about 2 to 48 inches in diameter with collars corresponding in size to weld the ends of the pipe together, but larger diameters of pipe may be used.

The amount of high explosive to be employed will vary, of course, with the size of the pipe collar and the detonation velocity of the explosive. However, the high explosive ring on the collar may have a thickness at the center of the collar sufficient to provide from about 4 to about 32 grams per square inch down to a thickness of from about 2 to about 16 grams per square inch at the ends or edges of the collar. For example, in welding nominal 12 inch pipe and employing Detasheet C explosive, the explosive would have a thickness at the center of the collar of about 10 to about 12 grams per square inch and at the ends or edges of the collar from about 4 to about 6 grams per square inch.

The collar may have a thickness at the center substantially the same as or slightly larger than the wall thickness of the pipe sections tapering on its inner surface to about one-half the pipe sections wall thickness.

The center inner surface of the collar or sleeve may be from about l/l6 to about 1 inch in width, while the inner tapered surfaces may each be from about 45 to about 48 percent of the'len'gth of the collar. For example, a 12-inch pipe may require a collar about 4 inches length while a 48 inch collar may require a collar of about 4 to about 6 inches length. A nominal 2 inch pipe may require a collar of about 2 inches length, whereas pipe of nominal 20 inches diameter may require a nominal 4 inches length collar.

BRIEF DESCRIPTION OF THE DRAWING The present invention will be further described and illustrated by reference to the drawing in which:

FIG. 1 is a sectional view of the mandrel taken along the line 1- l of FIG. 3;

FIG. 2 is a side elevation view of the mandrel;

FIG. 3 is a front view of the mandrel taken along the lines 3-3 of FIG. 1;

FIG. 4 is a view of the mandrel taken along the lines 44 of FIG. 1;

FIG. 5 is a view of the mandrel taken along the lines 55 of FIG. 1;

FIG. 6 is a view showing the arrangement taken along the lines 66 of FIG. 1 of the tension members not shown in FIG. 1;

FIG. 7 illustrates the mandrel in non-compressed position apart from other appurtenances;

FIG. 8 is a view showing positioning of the mandrel in pipe sections to be welded;

FIG. 9 is a view illustrating the pipe sections of FIG. 8 inposition to be welded;

FIG. 10 is a view taken along lines 10-10 of FIG. 9;

FIGS. 10A and 10B illustrate a modification of another form of means for detonating and exploding the high explosive of FIGS. 9, 10, and 13;

FIG. 11 shows the welded pipe sections of FIGS. 8 and 9;

FIG. 12 illustrates the pipe collar of FIGS. 9, 10, and 11 before explosive welding; and

FIG. 13 illustrates an enlarged view of the pipe collar and explosive of FIGS. 9 and 10.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawing and particularly to FIGS. 1 to 7, numeral 11 designates the pipe mandrel formed of tapered

hollow segments

12, 13, 14, and 15. The taper of the segments may be at an angle from about 1 to 30 but preferably is at an angle of about 7 to 8 with the longitudinal axis. Connected to each end of segments 12, l3, l4, and 15 are

longitudinal members

16, 16', 17, 17, 18, 18', 19 and 19', each provided with an eye means 16a, 16b, 17a, 17b, 18a, 18b, 19a, and 19b, respectively. Rod members 16 and-16 connect to opposite ends of segment 12 and, likewise,

members

18 and 18 connect to segment 14. Rod members 17 and 17' connect to opposite ends of segment 13 and, likewise,

rod members

19 and 19 connect to segment 15.

Rod members

16 and 18 extend through

openings

20 and 21 in plate 22 and rod members 17' and 19' extend through

openings

23 and 24 in plate 25. The

other rod members

17, 19, 16' and 18' are provided for use as will be described.

Passing through central openings in

plates

22 and 25 is a threaded longitudinally axially extending rotatable rod member 26 which threadedly engages a nut 27 welded to plate 22. Positioned on rod 26 on opposite sides of plate 25 are nuts 28 and 29, locked in place by lock nuts 28a and 29a, whereby the nuts will rotate with rod 26 and cause longitudinal movement of plate 25. The nuts 28 and 29 also allow adjustment of th plates relative to each other.

The

plates

22 and 25 are spaced from their respective segments and this space is provided with resilient pad means 30 and 31 and 32 and 33, the latter of which is shown in dotted lines in FIG. 4. The resilient means may be rubber, springs or other compressible means.

It will be seen that plate 22 with

pads

30 and 31 operably engage one end of each of the segments l2'and 14, while plate 25 with

pads

32 and 33 operably engage one end of each of the

segments

13 and 15. The

plates

22 and 25 are positioned on rod 26.

Connected to each

plate

22 and 25 are

members

34 and 35, respectively, on each end of which are yoke members 36 and 37 (FIGS. 1, 2, and 5) in the shapeof a cross and formed to carry on their ends rollers or wheels 39 for movement of the mandrel 11 through a pipe section such as 40 shown in dotted line in FIG. 5.

Referring to FIGS. 1 and 4,

telescoping members

41 and 42 are connected respectively to

plates

22 and 25 and serve to provide stability for the

segments

12, 13, 14 and 15, especially when large mandrels are used with large sizes of pipe. It will be noted that the

members

41 and 42 are square shaped in cross section and member 42 telescopes within member 41. This provides a spline assembly which extends through the central opening formed by the segments and allows longitudinal movement of the members 34 and relative to each other. It will also be noted that the end of all the rod members 16-19 are provided with enlarged heads to prevent excess longitudinal retraction of the segments relative to each other.

In FIG. 6, tension means 42, not shown heretofore for reasons of clarity are connected to eye means 160, 17a, 18a, and 19a and, of course, while not shown in this view similar tension means 43 are connected to

eyes

16b, 17b, 18b, and 19b. These tension means 43 are provided to maintain and hold the

segments

12, 13, 14, and 15 together, especially in their retracted position. The spring members 43 tend to bias the segments toward the center axis of the assembly whereby they do not drag or contact the inside wall of the pipe when retracted.

FIG. 7 shows the mandrel 11 in its retracted or nonexpanded position with the

segments

13 and 15 moved relative to

segments

12 and 14. FIGS. 1 to 4 and 6 show the segments 1215 in their expanded and locked position.

Referring now to FIGS. 813 inclusive, the mandrel 11 is in the pipe section and a collar 45 (FIG. 12) with a layered stack 46 of high explosive such as Detasheet C arranged thereon. It will be noted that the collar 45 is tapered interiorly its ends while the layered stack 46 has its greatest thickness corresponding to the greater thickness of the collar 45. The collar 45 defines angles of about 1 to 30 with the exterior of the

pipe sections

40 and 40a with a preferred angle of 8 with a detonation velocity of the explosive of approximately 23,000 feet per second, as a general rule, the greater the detonation velocity of the high explosive, the greater should be the angles. However, the angles, amount of high explosive, and detonation velocity are all important. A suitable angle is about 5 to about 15.

inches from each of the ends and the ends butted together as shown in FIG. 9. The mandrel 11 is then centrally located thereunder with the segments thereof in their retracted position. When it is determined that the pipe sections are accurately aligned and the ends thereof in full abutment, the rod member 26 is rotated by crank rod 26a in one direction to draw the

plates

22 and 25 toward each other, thereby expanding the tapered segments 12-15 against the inner wall of each of the pipe sections. At this time the collar 45 with explosive ring 46 is moved on the pipe to the position shown in FIG. 9. After the collar is properly positioned, the rod 26 is rotated in the opposite direction to move the

plates

22 and 25 away from the segments a prescribed distance as shown in FIG. 9. The segments will maintain their expanded position against the inner wall of the pipes by means of the locking effect of the taper of the segments, and are in full 360 contact with the pipe wall. This complete contact prevents occurrences of deformities during the explosive welding process.

. Thereafter the planar surface member 47 with the arrangement of Detasheet C strips 48 on planar surface 47 and detonators 49 are connected to a source of electrical energy not shown by leads 50 and strips 48 are perpendicularly placed in explosive contact with the layered mass 46, as shown in FIGS. 9 and 10, at equally spaced apart points, the two

sections

47a and 47b being held together by connecting means 470. The detonators 49 are simultaneously electrically energized and the high explosive mass 46 detonates and causes the collar 45 to be forced against

pipe sections

40 and 40a with sufficient impact to cause the

sections

40 and 40a to be welded together as shown in FIG. 11 by welding the collar 45 to the

sections

40 and 40a.

The strips 48 of high explosive are suitably arranged as shown in FIG. 10 with a plurality of strips 48 arranged in a pattern 51 such that there is a buffered zone or

spaces

52, 53, 54, 55 in the pattern 51 as the strips 48 extend inwardly separating in one or more pairs of strips toward the stepped or layered ring 46 of high explosive on the collar 45 and are arranged such that the strips 48 are in a radial-arcuate pattern 51; stating this otherwise, some of the strips 48 are arcuate and connect to radial strips to form the pattern 51. While arcuate and radial strips are described and illustrated other patterns where there is a buffer or space between the strips may be used. Forexample, rather than arcuate strips being employed, the arcuate strips may be in the form of at least portions of chords connecting to at least portions of other chords arranged perpendicular to or angularly with the other strips such that the ring of high explosive is contacted at a plurality of points for substantially simultaneous explosion of the strips and ring of high explosive to cause impact of the sleeve 45.

While the patterns are shown only on one side of the planar surface member 47, the patterns may be arranged partially on one side and partially on the other or complete patterns may be arranged on both sides. It will be noted from FIG. 11 that the force of the impact of the collar 45 against the

pipe sections

40 and 40a and mandrel 11 causes the

segments

13 and 15 to move relative to

segments

12 and 14 diminishing the circumference of the mandrel 11 (FIG. 6 and l l) and allowing it to be moved to the open end of pipe section 40a for explosive weldment of another pipe section thereon.

' Referring to FIGS. 10A and 10B, the planar surface 47 is composed of quarter section units 47 '47, and is in direct contact with explosive ring 46. The sections 47-47"" are formed of an explosively inert material such as a suitable polymer which may be styrofoam. As shown more'clearly in FIG. 103, the explosive strip pattern 48 isrecessed in a grooved template pattern 48a formed in each section of the planar surface. The strip pattern is placed in the recessed pattern 48a by adhesive means such that the strip pattern is below the surface of the sections. This arrangement provides buffering or separating means for the strip pattern 48. From an initial ignition point 48b the step wise pattern provides a plurality of contact points 480 which engage the explosive ring 46.

On simultaneous electrical energization through leads 50, detonators 49 which connect to strip pattern ignition points 48b, the ring 46 is exploded and by the force exerted, the collar 45 is forced against the pipe sections 40 and 40a.to weld same together by welding the collar to the sections.

Thus, the present invention is quite important and useful. Pipe sections may be welded together with a minimum expenditure of equipment, effort and time. Pipe sections of 12-14 inches in diameter and of greater or lesser diameter are easily welded together. The invention is, therefore, new, useful and unobvious since hereto manpower and/or machines were necessary to weld pipe together.

The nature and objects of the present invention having been clearly described and illustrated and the best mode and embodiment contemplated set forth what I wish to claim as new and useful and secure by Letters Patent is:

1. Apparatus for use in explosive welding abutting ends of hollow cylindrical members which comprises:

an upstanding planar mounting member formed in at least two connectible sections and forming when connected a circular opening adapted to be mounted in spaced relation about said cylindrical members in substantial alignment with said abutting ends;

means for connecting said sections together for mounting about said cylindrical members;

an angular pattern of buffered high explosive strips arranged on each of said sections and extending to the periphery of the connected sections forming said opening at a plurality of equally spaced-apart points;

said explosive strips being adapted to be connected to an annular band of high explosive located between said planar member and said cylindrical members;

detonation means connected to said explosive strips for initiating detonation of said explosive strips substantially simultaneously at each of said points; and

means for detonating said detonation means and said annular band of high explosive to produce a detonation wave which travels in a plane perpendicular to the axis of said cylindrical members.

2. Apparatus in accordance with claim 1 in which the pattern of explosive strips is formed by arcuate and radial interconnected strips.

3. Apparatus in accordance with claim 1 in which said explosive strips are formed into an arcuate-chord pattern wherein said spaced-apart points contact said high explosive band uniformly about its periphery.

4. Apparatus in accordance with claim 1 in which the explosive strips are buffered by providing recesses in said planar member for receiving said explosive strips.

5. Apparatus in accordance with claim 1 in which the planar mounting member is an inert polymer.

6. Apparatus in accordance with claim 1 in which said'explosive strips are formed in a pattern of at least a portion of chords angularly connected to each other.

7. Apparatus in accordance with claim 6 in which the chords are perpendicularly arranged relative to each other in each pattern.

8. Apparatus in accordance with claim 1 in which the explosive strips are adhesively attached to the planar mounting member.

9. Apparatus in accordance with claim 1 in which the high explosive comprises PETN.

10. Apparatus in accordance with claim 1 in which the high explosive is Detasheet C.

11. Apparatus in accordance with claim 1 wherein there is provided an annular metal collar between said annular band of high explosive and the abutting ends of said cylindrical members, whereby upon detonation of said explosive the collar is substantially instantaneously driven at a sufficient force against the abutting ends of said members to weld the inner surface of said collar thereto and consequently weld said members together.

12. Apparatus in accordance with claim 11 wherein said collar is interiorly formed with a tapered shape such that the ends thereof are of a lesser thickness than the center thereof.

13. Apparatus in accordance with claim 11 wherein said collar has a thickness at the center substantially 16. Apparatus according to claim 11 wherein said explosive is arranged so that upon its initiation a substantially symmetrical force is applied to said collar for welding it to said members at the abutting ends thereof.

17. Apparatus according to claim 1 wherein the length of the path of travel between said detonation means and each of said spaced-apart points are equal.

Claims

1. Apparatus for use in explosive welding abutting ends of hollow cylindrical members which comprises: an upstanding planar mounting member formed in at least two connectible sections and forming when connected a circular opening adapted to be mounted in spaced relation about said cylindrical members in substantial alignment with said abutting ends; means for connecting said sections together for mounting about said cylindrical members; an angular pattern of buffered high explosive strips arranged on each of said sections and extending to the periphery of the connected sections forming said opening at a plurality of equally spaced-apart points; said explosive strips being adapted to be connected to an annular band of high explosive located between said planar member and said cylindrical members; detonation means connected to said explosive strips for initiating detonation of said explosive strips substantially simultaneously at each of said points; and means for detonating said detonation means and said annular band of high explosive to produce a detonation wave which travels in a plane perpendicular to the axis of said cylindrical members.

6. Apparatus in accordance with claim 1 in which said explosive strips are formed in a pattern of at least a portion of chords angularly connected to each other.

13. Apparatus in accordance with claim 11 wherein said collar has a thickness at the center substantially equal to the thickness of said cylindrical members and tapering along its inner surface to about one half the thickness of the cylindrical member wall at its ends.

14. Apparatus in accordance with claim 11 wherein said explosive overlies said collar and comprises a shape having a thickness which is greater at the center thereof than at its extremities.

15. Apparatus in accordance with claim 1 wherein said upstanding planar member comprises a light-weight destructible material.

16. Apparatus according to claim 11 wherein said explosive is arranged so that upon its initiation a substantially symmetrical force is applied to said collar for welding it to said members at the abutting ends thereof.