AU488317B2

AU488317B2 - Improvements in or relating to explosive welding

Info

Publication number: AU488317B2
Application number: AU70366/74A
Authority: AU
Inventors: PETER WOODALL JACKSON DEREK JAMES BROWN and JOHN ANDREW SCOTT GUTHRIE MICHAEL DICKENSON CHADWICK
Original assignee: Northern Engineering Industries PLC
Current assignee: Rolls Royce Power Engineering PLC
Priority date: 1974-06-21
Filing date: 1974-06-21
Publication date: 1976-06-08
Also published as: AU7036674A

Description

70 36674

The present invention relates to the use of explosive jointing on pipes which are submerged in a liquid, for examp. for underwater pipelines. The invention is applicablejto thf joining of two pipes directly where the-end of one pipe is formed to receive the end of the other and to the attachment of a coupling sleeve or flange to the end of a pipe to facilitate its attachment to another pipe or to an underwater device or installation. For example, the-invention may be used for the repair of an underwater pipeline by removing a damaged section and inserting a new section. One way of achieving this is to employ the invention to attach coupling flanges to the ends left free after removal of the damaged section and then secure the replacement section to the coupli flanges by conventional pipe-coupling techniques. In accordance with :the present invention there is provided a method of explosively forming a joint between ends of first and second tubular members submerged in a liquid wherein the end of the first member is arranged inside the end of the second member with a space between, the ends of the two members, with an explosive charge disposed within the end of the first member, with shock- absorbing elements disposed in the bores of the two members ad displacing liquid from at least part of the length of each bore, and with internal and external seals arranged to form an enclosure sealed against entry of the liquid, the said space forming at least part of the enclosure, the liquid present in the enclosure is removed by displacing it by a gaseous medium, and the explosive charge is then detonated to effect jointing of the ends of the tubular members.

48 8,3 17

70.3667

It is already known that explosively-formed Joints may be of two kinds, a-simple expansion joint or an explosive weld, depending upon the nature and magnitude of the explosive charge and the arrangement of the parts prior to the explosion. When an explosive weld is required it is usual to use a high-

velocity explosive and to leave a stand-off distance between the parts to be joined. Thus in the method of the invention the relative diameters of the ends of the two members would be chosen to leave an Annular space between them and the liquid mould, in accordance with the'invention, be displaced from this space by a gaseous medium prior to detonation of the explosive charge. In the case when only an expansion joint is required no stand-off distance need be provided but manu- facturing tolerances which ensure easy insertion of the end of the first member into the end of the second member and departures from roundness of the two ends result in a space between the two ends (possibly divided into a number of separate parts) which has to be cleared of liquid and of any associated dirt in order to ensure a satisfactory joint. In the case of an expansion joint the provision of an annular groove in the end of the second member strengthens the joint against axial forces. The second (outer) member should preferably have a higher yield stress than the first member in order to give a leak-tight joint. Whether an expansion joint or an explosive weld is to be formed the internal seal may be disposed within the bore of the second tubular member whereby the said enclosure includes

48 8,3 17

70.366174

a space within the bore of the second member in addition to the said space between the ends of the two members. Alternatively, the internal seal is formed between the end of the first member and the inner surface of the second member. In a preferred method the internal seal is mounted on a carrier ring which also carries the explosive charge. The carrier ring can be held in position axially by biassinE srprings acting between the carrier ring and a clamp ring clam~ped within the second member. The shock-absorbing elements are preferably inflatable bags. It is also possible to use foam material especially i the case when the second member is relatively short and consists for example merely of a coupling flange with a sleeve which fits over and is welded to the end of the first member. The explosive charge itself is preferably carried by an inflatable body which ensures close contact of the charge with the inner surface of the first member. The second memb( is preferably supported externally by a segmented clamp whicl is positioned around the region in which the explosive jointing takes place. The invention will now be described in more detail with the aid of examples illustrated in the accompanying drawings, in which Figure 1 is a schematic cross-section of an assembly for welding together two pipes by the use of a method in accordance with the invention,

4 88.3 171

70.366/74

Figure 2 is a similar cross-section of an assembly for

welding together two-pipes by the use of a second method in

accordance with the invention, and

Figure 3 is a perspective view, partly in section, of an

assembly for welding a coupling flange to the end of a pipe

by the use of a third method in accordance with the invention. Referring first to Figure 1, this shows two metal pipes

and 11 which are to be joined together. A metal sleeve

member 12 has at one end a portion 12a of reduced internal

diameter which V4 pe fits closely over the pipe 11 and is

welded thereto with a weld fillet 13. The welding of the

sleeve portion 12a to the pipe 11 is effected in air before

the pipe line is laid on the sea-bed. Fusion welding may be

employed, as shown, or alternatively, explosive welding may

be used.

At the opposite end of the sleeve member 12 there is a

portion 12b, of reduced internal diameter, which fits closely

over the pipe 10. The end of the pipe 10 extends into the

larger-diameter central portion of the sleeve member 12, an

annular space 14 being formed between the end of the pipe and

the central portion of the sleeve. The internal surface of

the sleeve 12 and the outer surface of the pipe 10 are

abraded in the region where they overlap. The bore of the pipe 11 contains an inflatable water dis-

placement bag 15 and an inflatable sealing bag 16, both of

which are inserted and inflated before the pipe 10 is inserted

in the sleeve 12. A similar inflatable water displacement

488,3 17

366/74

bag .17 is inserted in the end of the pipe 10 together with an inflatable body 18 which carries an explosive charge and which serves to seal the end of the pipe 10. The insertion and inflation of the bag 17 and body 18 can be effected in air before the pipe 10 is inserted into the sleeve 12 on the sea-bed. The body 18 carrying the explosive charge is positioned in the end of the pipe 10 in the region surrounded by the space 14 but is set back from the extreme end of the pipe to minimise entry of the products of the explosion into the space 14. The inflatable body.18 which carries the explosive charge is of the type described in British Patent Specification No. 1,297,708 which consists of a container made of a shock- wave-transmitting medium, such as rubber, the walls of which contain an explosive charge, together with a detonator and priming charge. The body is inserted in the bore of the pipe and then inflated into contact with the internal surface of the pipe. The leads for the detonator may pass through a plug in the wall of the sleeve 12 which is sealed upon detonation of the explosive or else they may be brought out through the bore of the pipe 10. Alternatively, the leads may be connected through a remotely-operable switching device to a battery which will supply sufficient current for opera- tion of the detonator. The switching device can be operated from outside the pipes 10 and 11 and sleeve member 12 by means of a magnetic field generated by an electrical winding or by means of a sonar generator.

48 8,3 17

3667 4

On the outside of the pipe 10 is a hard rubber sealing

ring 19 having a more flexible flap portion 20. The ring 19

is initially placed on the pipe 10 with the flap portion

rolled back. When the pipe 10 is inserted in the sleeve 12,

the flap is unrolled over the end of the sleeve portion 12b_

to form an external seal preventing the entry of water to the space 14 and to the space 21 within the sleeve 12 which

is closed at one end by the sealing bag 16 in the pipe 11 and

at the other end by the inflated body 18 in the pipe Inlet and outlet ducts 22 and 23, respectively, pass

through the sleeve 12 into the space 14 immediately adjacent

the end portion 12b of the sleeve. The inlet and outlet ducts

22 and 23 are connected by flexible hoses (not shown) to

valve and pumping apparatus located above the body of water

in which the pipes are submerged. To remove water from the

spaces 14 and 21, clean air or nitrogen is supplied to the

inlet duct 22 at a pressure slightly greater than the hydro-

static pressure prevailing within the sleeve 12. The water in

the sleeve 12 is thus displaced and forced out through the outlet duct 23. To avoid the deposit of dissolved salts which,

especially in the case of sea water, would occur if the

interior of the sleeve 12 were dried directly, the spaces 14

and 21 are then flushed with fresh water. The fresh water is

displaced by air or nitrogen followed by a solvent such as

methylated spirits which removes all residual water. The

spaces 14 and 21 are finally again flushed with air or nitrogen

which is dried to reduce the concentration of water vapour to

488.3 17

366/74

as low a level as is desired, using apparatus such as a Draeger tube to measure the residual concentration. A segmented clamp 24 is placed around the sleeve 12, in the region of the body 18 carrying the explosive charge, in order to support the sleeve against the force of the explosion. The clamp 24 consists essentially of a number of metal segments-held around the sleeve 12 by a clamping band or the like which is releasable after completion of the weld. After the removal of water from the spaces 14 and 21, as described above, the explosive charge is detonated to expand the end of the pipe 10 into engagement with the sleeve 12 to form a weld between them. During welding the part of the pipe projecting beyond the body 18 carrying the charge shields the weld region from the products of the explosion and thus prevents contamination. The formation of the weld separates the inlet and outlet ducts 22 and 23 from the space 21 within the sleeve 12 and thus ensures a watertight connection between the pipes 10 and 11. In the embodiment of Figure 2 parts corresponding to those of Figure 1 are given the same reference numerals and will not be further described. In the place of the sleeve 12 the pipe 11 is itself formed with a larger-diameter end portion which surrounds the end of the pipe 10, forming the annular space 14 which is closed as before by an external seal 19 with a flap 20. The inner end of the pipe 10 is, however, advanced to engage a step 26 in the pipe 11 and an inflatable seal 2? is located between the end of the pipe 10 and the inner

488,3 .17

366/74

surface of the end portion 25 of the pipe 11. The seal 27 forms an internal seal which closes the space 14.- The removal of water, flushing and drying by way of ducts 22 and 23 now only affects the space 14 which is in the immediate region of the weld and the necessity of treating the large space 21 within the sleeve is avoided. Higher gas pressures and flushing rates can be used in treating the space 14. An inflatable body 28 carrying the explosive charge is located in the end of the tube 10. The drawing shows a detonator 29) carried by the body 28. The inflatable bags 15 and 17 are placed as close as possible to the body 28 to displace water from the region of the explosion. With the arrangement of Figure 2 it is convenient if the end of the submerged pipeline is the pipe 10. The inflatable bag 17 and charge-carrying body 28 have then to be inserted in the end of the pipe and the other parts of the assembly fitted round it. The water-displacement bags 15 and 17 serve as before to absorb the shock wave when the explosive is detonated and thus prevent any bulging of the pipe walls. On completion of the weld the bags 15 and 17 and the remains of the explosive charge can be flushed out of the pipe by known means. It will be appreciated that in each of the embodiments described it is possible to use alternative forms of seal. For example, the external seal may be of the inflatable type. The explosive charge need not be carried by an inflatable body provided that it is positioned close to the inner surface of the pipe in which it is located.

9- 488,3 17,

366 /74

The method described may be applied to the welding of a number of joints in sequence. It may be used to attach a sleeve member carrying a flange to a pipe. For replacement of a damaged section of pipe, a flange may be welded to each of the free ends left after removal of the damaged section and a new section can then be mounted between the flanges by conventional pipe-coupling methods. Figure 3 shows an arrangement of equipment for underwater repair of a metal pipe 30 by the-attachxment to it of a sleeve 31 having an annular flange 32. The pipe 30 may be the free end of a pipe line from which a damaged section has been removed and the attachment or the sleeve 31 will then enable a new section to be coupled to the flange 32. A conical flared skirt 53 has a lip portion 54 welded to the end of the sleeve 31 and serves as a guide for introducing the end of the pipe 30 into the sleeve 51. An external inflatable seal 55 is located at the end of the sleeve 31 within the lip portion 34 to engage the outer surface of the pipe 30. An inflation tube 56 passing through the lip portion 54 allows the seal to be inflated. An internal inflatable seal 57 is located at the end of the pipe 30 to seal the gap between the pipe 50 and the inner surface of the sleeve 31. The seal 57 is supported by a carrier ring 38. The carrier ring 38 also supports an inflatable annular explosive charge 39 which lies within the pipe A clamp ring 40 with an expanding clamp 41 can be clamped within the sleeve 31 and provides an abutment against which

4883.1 7

366/74

compression springs 42 react to press the carrier ring 38 axially towards the pipe 30 and thereby hold the seal 37 against the end of the pipe. The carrier ring 38 is of stepped formation with a lip 43 retaining the seal 37 and a further recess 414 accommodating the charge 39. The charge 39 is retained by an end cover-plate 45 which contains a radial initiating charge connecting the charge 39 with a detonator 46. An inflation tube 47 for the charge 39 is led through one of a series of apertures 48 in the cover- plate 45 and out through the sleeve 31 and leads 49 for the detonator 46 are brought out through the sleeve 31. Within the pipe 30 is located an inflatable water dis- placement bag 50, the inflation tube for which is not shown in the drawing but is brought out through the open end of the pipe 30 and through the welding assembly. A spacing member

51,bears against the bag A segmented clamp member 52 is positioned around the outside of the sleeve 31 in the region of the charge 39 to support the sleeve 31 against the force of the explosion. A number of tubes 53 are provided on the sleeve 31 to enable water to be removed from the space 54 between the end of the pipe 30 and the inner surface of the sleeve 31 after inflation of the seals 35 and 37. The removal of water followed by flushing, cleaning and drying can be carried out as described in connection with Figure 1. The procedure for effecting a weld using the apparatus as described above involves locating sleeve 71 around pipe

_11- 4 88.3 -11- 17

70.366/74

whic h contains the Uninflated water displacement bag positioning the clamping ring '40 rigidly within the bore of the sleeve 31 by means of the clamp 41, rele asing the actuating springs 42 to spring-bias the annular carrier member 38 to the-right and inflating the seals 35 and 3? and the water displacement bag 50. The space 54 between the seals 35 and 37 is then flushed, cleaned and dried. Finally., the open bore of the clamping ring 40 and carrier ring 38 is foam-filled or air-bagged to absorb the explosive shock wave and the explosive charge 39 is exploded, by means of the detonator 46 and the radial initiating charge contained in the cover-plate 4~5, to expand the pipe 30 and weld it to the sleeve 31. On completion of the weld the segmented clamp 52 may be removed and may be re-used for further explosive welds. The materials used in the construction of the clamping ring 40, carrier ring 38 and other internal structure members may be of a plastic or similar material which will break up under the explosive impact. On completion of the weld these expendable items may then be readily removed from the bore of the pipe by standard procedures used for the removal of internal debris from pipes. Further embodiments in addition to that described will be obvious, for example, the sleeve may be formed on one end of another pipe by belling out, so that a pipeline may be formed by a series of welding operations joining a pipe with a belled end to the previously formed pipeline.

-12- 48 8,3 -12- 17

Claims

366/74

The claims defining the invention are as follows:

1. A method of explosively forming a joint between ends of

first and second tubular members submerged in a liquid

wherein the end of the first member is arranged inside the end

of the second member with a space between the ends of the two

members, with an explosive charge disposed within the end of

the first.member, with shock-absorbing elements disposed in

the bores of the two members and displacing liquid from at

least part of the length of each bore, and with internal

and external seals arranged to form an enclosure sealed

against entry of the liquid, the said space forming at least

part of the enclosure, the liquid present in the enclosure

is removed by displacing it by a gaseous medium, and the

explosive charge is then detonated to effect jointing of the

ends of the tubular members.

2. A method as claimed in claim 1 in which the internal

seal is disposed within the bore of the second tubular

member whereby the said enclosure includes a space within the

bore of the second member in addition to the said space

between the ends of the two members.

3. A method as claimed in claim 1 wherein the internal seal

is formed between the end of the first member and the internal

surface of the second member.

4. A method as claimed in claim 3 wherein the internal seal

is supported by a carrier ring secured within the second

member. 13 488,317

366/74

A method as claimed in claim 4 in which the-carrier ring is freely slidable within the second member and'is bias towards the end of the first member by springs reacting agaii a clamp ring fixed in position within the second member.

6. A method as claimed in claim 4 or 5 in which the carrier ring also supports the explosive charge.

method as claimed in any/of the preceding claims in which the displacement of the liquid by the gaseous medium is effected by way of vents in the end of the second member positioned such that the joint formed by detonation of the explosive charge lies between the vents and the]bed7.of the second member.

8. A method as claimed in any,/of the preceding claims in which the shock-absorbing elements are inflatable bags which fill the cross section of the bore in which they are located.

9. A method as claimed in any/of the preceding claims in which the explosive charge is carried by an inflatable body. ;efA method of explosively forming a joint between two tubular members substantially as described with reference to Figure 1 of the accompanying drawings. ;L.A method of explosively forming a joint between two tubular members substantially as described with reference to Figure 2 of the accompanying drawings. A method of explosively forming a joint between ends of first and second tubular members, substantially as

-14- 488317

70.366/74

described with reference to Figure 3 of the accompanying

drawings.

D A T E D this lst day of September, 1977. INTERNATIONAL RESEARCH DEVELJOPMENT COM~PAN~Y LIMITED

C By its Patent Attorneys

CALIJINAN ANDl ASSOCIATES

488.3 17

-70.366 /74

(0

cZ

488.3 17

366 /74

48 8,3 17 cn, N 0Z ey k

488.317