The invention relates to a method in accordance with the preamble of claim 1.

Known in the connecting together of interior coated pipe lengths is the use as clamping means of a clamping tool, comprising a ring of rollers which are forced by a hydraulic tensioning mechanism with considerable force against the wall of the one pipe length while the ring of rollers is made to rotate. This tool is heavy and bulky and awkward to use, especially in places that are difficult to reach, partly due to the powerful hydraulic power supply source required. As a result this known method is not very suitable for connecting pipe lengths together underwater. The known method moreover leads to cracks in the connected pipe lengths. Welding together of pipe lengths which have an anti-corrosive coating is problematic because this coating is adversely affected by welding.

Connecting pipe lengths with flanges requires the presence of these flanges at the pipe length ends and lying precisely within the scope of the objective of the current invention is the attachment, for example, of a pipe length provided with a flange to a flangeless pipe length, following which the previously flangeless pipe length with the flange fitted onto it can be coupled to a flange of an existing pipeline. The invention has for its purpose to provide a method of the type referred to in the preamble which can be performed with tooling that is small in bulk and weight in places difficult of access and of which the manufactured join, if required, permits a considerable axial tensile force between the pipe lengths and which does not lead to fatigue cracks in one or both of the connected pipe lengths and/or to damaging of the coatings.

To this end at least an explosive charge is used as clamping means, this being detonated, and the coatings of

both pipe lengths being joined to each other, when the explosion takes place, by means of a bridging ring. The join according to the invention thus has an unbroken coating, so that the coated material cannot be corroded by the aggressive substances to be transported. The operation and effect of the method according to the invention can best be elucidated on the basis of diagrams, so it suffices here to refer to the figure description hereafter following. Thereby elucidated will be the preferred steps for better control of the deformations of the pipe lengths as well as preferred steps for realizing an effective sealing ring between the pipe lengths, these steps being denoted as characteristics in the claims 2-9.

The invention also relates to and provides a join ; and pipe lengths manufactured as in the method according to the invention which are constructed for application in the method according to the invention.

It is noted that it is per se known to connect pipe lengths together by welding, them to each other under the influence of a detonation of an explosive charge, the dimensioning of which is so great that the metal is melted or that a molecular bonding results.

Use is made however in the method according to the invention of an explosive charge of a considerably smaller order of magnitude, for example one tenth, than the explosive charge required for welding. The current invention does not exclude the plastic deformation of a first (thick) wall part by an explosion in accordance with the essential insight of the current invention, nor does it exclude the melting of a second (thin) wall part by explosion of a charge of the same order of magnitude for welding onto another pipe length. In this case the charge used for the welding with respect to the small wall thickness is of another order of magnitude than the charge * used for the plastic deformation with respect to the large wall thickness.

In the drawings in diagrammatic form:

fig. la, lb and lc and 2a, 2b and 2c show three successive situations in the application of the two different methods according to the invention, fig. 3a, 4 and 6 each show a variant of fig. la, fig. 3b is a section corresponding with fig. 3a in the situation after performing the method according to the invention, and fig. 5 shows on a larger scale a variant of a longitudinal section through a fraction of a join according to the invention.

In the most primitive method according to the invention as in fig. la, lb and lc, two pipe lengths 1 and 2 coated with an anti-corrosive layer 51 are inserted coaxially into each other with clearance 3 between them. A cartridge with explosive material 4 is further arranged in the one pipe length 1 and, in fig. lb, ignited. The stages of fig. la, lb and lc can thereby be distinguished from one another. In fig. la, before the explosion, the starting dimension, that is the outer diameter d . of pipe* length 1, is slightly smaller than the inner diameter e of pipe length 2.

During the explosion as according to fig. lb the outer diameter of pipe length 1 is the same as the inner diameter of pipe length 2 which amounts to e 2 _> this value e 2 being essentially greater than the diameter e _j _, since the wall 12 of pipe length 2 is elastically deformed through the pressure applied to it by the wall 11 of pipe length 1. Under the influence of the explosion the- wall 11 is however deformed (expanded) not only over a diameter increase of e 2 -e 1 but also over the diameter increase e _j -d ^ , this deformation being too great for an elastic deformation so that due to excessive deforming the state of plastic deformation of the wall 11 in fig. lb results.

After the explosion treatment the state of fig. lc arises, whereby the wall 12 of pipe length 2, which has the tendency to spring back, applies its so-called elastic deformation tension t to the pipe length 1, which can no longer spring back, or at least not so strongly. Thereby

results an inner diameter e3 which is perhaps slightly smaller than the inner diameter e 2 _> hut which is significantly greater than its original diameter e _. This deformation tension t supplies a considerable holding 5 force.

The coating layer 51 of pipe length 1 has on its inner side a thin walled, axially extending bridging ring of the same coating material. When the explosion takes place this bridging ring 5, because it is thin walled, is

10. struck with force against both coating layers 51 of pipe Lengths 1 and 2, so that a liquid tight sealing results. -Lit unbroken coating is thus formed at the point of the join.. The bridging ring 5 adheres as a weld connection to the coa.ting layers 51.

15 In the method according to fig. 2a-2c a cylindrical cartridge 24 with explosive material built up of for example three segments is arranged inside a robust housing 25 around a pipe length 21 which is placed around a pipe leng-th 22 with a clearance g i~f i. '

20 During the explosion of fig. 2b the wall 31 of pipe length 21 is plastically deformed (compressed) and the wall 32 of pipe length 22 is deformed elastically (also compressed) in the same direction, until an outer diameter f2 results that is smaller than the original outer diameter

25 f _j and appreciably smaller than the original inner diameter gl.

After the explosion arises the situation of fig. 2c, in which the outer diameter f 3 is perhaps slightly greater than the diameter f2 but which is still essentially smaller

30 than the original outer diameter f 1, so that the elastically deformed pipe length 22 applies its outwardly directed deforming tension q to the wall 31 of the pipe length 21 and thus applies a holding force to it on the interior.

35 The pipe lengths 21 and 22 each have an interior coating layer 51. The end of the pipe length 22 is moreover provided inside and outside with a vapour deposited layer which forms a bridging ring 23.

In the following embodiments only the method of

40 plastic deformation of the inner pipe length as according

to fig. la-lc will be explained, although the reverse method of fig. 2a-2c is as equally applicable.

The practical embodiment variant of fig. 3a shows a first pipe length 41, which is for example the end of a long underwater pipe, and which has to be provided with a flange 10. To this end a pre-processed pipe length 42 according to the invention is provided with the required flange 10 for coupling to for example another pipe (not drawn). This pipe length 42 is placed onto the pipe length 41 whereby interior ribs 45 having little clearance grip round the outer diameter of pipe length 41. Accommodated in a groove 46 is an elastic sealing ring 47 and between the head end 52 of the pipe length 41 and a bulge 48 of pipe length 41 is accommodated a radial bridging ring 54 of easily deformable metal, for example copper. Both pipe lengths 41 and 42 have an anti-corrosive layer 51, for example copper.

After the explosion of the cartridge 4 with explosive material the situation of fig. 3b arises, in which material from the wall 49 is forced into the space 50 present between pipe lengths 41 and 42 and between the ribs 45. This gives a substantial axial holding rigidity. The pipe length 42 grips in fig. 3b like a sleeve around the straight pipe length 41. Such a sleeve-like pipe length can be the end of another pipe or piping element.

The pipe lengths 41 and 42 are each provided with an anti-corrosive layer 51 which is vapour deposited for example or applied in another way. It is interesting to note here that the bridging ring 54, because of the plastic deformation of pipe length 41, which as a result is also extended axially, is gripped rigidly and close fitting. In fig. 4 is shown that the cartridge 4 with explosive material can consist of a cord 4 of explosive material wound round a core 13 of plastic, around which cord is arranged a supporting bush 15 of plastic. A detonator 16 is located at the left-hand end as shown In fig. 4, so that the direction of detonation 17 is aimed from a partition 18 arranged for protection of piping elements present, if required, in or on pipe length 41, to an

expansion tank 19 which is attached to flange 10. Arranged in fig. 3 and 4 around pipe length 42 is a heavy ring 20 built up of three segments which serves as anvil. When the explosion takes place the mass of this anvil 20 supplies a reaction force which prevents with certainty the plastic deformation of pipe length 42.

It is also conceivable not to use the anvil 20. In that case a wall thickness is preferably chosen for the pipe length 42 which is markedly greater, for example 50%, than that of pipe length 41, so that this extra wall thi-ckness serves as extra mass and also as reinforcement of the pipe length 42.

Shown in fig. 5 is a fraction of a pipe length 61 that is. plastically deformed according to the Invention, whereby the material of the wall 71 is forced into the spaces 50 between the ribs 45. In addition the ribs 45 and/or the space surfaces 74 have annular grooves 75 which improve the sealing and gripping between the pipe lengths 61 and 62. Further present between pipe lengths 61 and 62 is an elastic sealing ring 76.

FinalLy, a thin walled, axially extending bridging ring 77 of pipe length 61 is welded to the pipe length 62 in- one and the same explosion process in which the plastic deformation of pipe length 61 is realized. If required a vacuum is created between the pipe lengths 61 and 62 by suction before the explosion in order to reduce the charge needed.

Bridging ring 77 is a protruding piece of a coating 83 which is welded to coating 84 of pipe length 62. In fig. 5 the material of bridging ring 77 has melted together with the adjoining coating material 84 of pipe length 62.

Fig. 6 shows a pipe length 82 in the form of a sleeve, which connects together two pipe lengths 81 after application of the method according to the invention with use of a radial bridging ring 54.

The method according to the invention, particularly the method according to fig. 4, can be performed underwater. The method according to the invention can be particularly applied underwater in a space filled with air and bounded by a habitat.