WO1993010330A1

WO1993010330A1 - Fracturing device

Info

Publication number: WO1993010330A1
Application number: PCT/SE1992/000723
Authority: WO
Inventors: Ulf STÅLKLINT
Original assignee: WESTBOENERGI AB
Current assignee: WESTBOENERGI AB
Priority date: 1991-11-22
Filing date: 1992-10-16
Publication date: 1993-05-27
Anticipated expiration: 1994-05-22
Also published as: ZA928292B; SE500317C2; AU2958792A; SE9103462L; SE9103462D0

Abstract

A fracturing device which is intended, by insertion into a bore in a material and expansion therein, to fracture or crack the material, comprises two end pieces (4, 5) which are disposed at the opposing ends of the fracturing device and are interconnected via a longitudinally directed drawbar (1). An elastic expander sleeve (8) surrounds the drawbar (1) and seals against the end pieces (4, 5), and may be subjected to inner excess pressure. In order to avoid rupture at the anchorage of the expander sleeve (8) in the end pieces (4, 5), the expander sleeve (8) is provided with a radially expanding, thick-walled central portion (23). At each end thereof, there is disposed interiorly in each end piece (4, 5), an axially extendible thin-walled strain portion (26). The expander sleeve (8) has, at its opposite ends outside the strain portions (26), thick, bead-shaped end portions (38) which are accommodated in corresponding interior, annular grooves (12) in the end pieces (4, 5).

Description

FRACTURING DEVICE

TECHNICAL FIELD

The present invention relates to a fracturing device of the type which, by insertion and expansion in a bore in a material, is intended to fracture the material and which includes end seals disposed at the ends of the fracturing device and interconnected via a drawbar, there extending about the drawbar and sealingly between the end seals an expander sleeve produced from elastic or resiliently yieldable material, and the space interiorly in the expander sleeve being pressurizable.

BACKGROUND ART

European Patent Application No. 85905247.4 describes a device of the type mentioned by way of introduction. In one embodiment which is described in this patent application and which has been commercially tested, the end seals have conical regions where the diameter merges from the hole diameter through which the drawbar extends to that hole diameter which corresponds to the outer diameter of the expander sleeve. The expander sleeve has a corresponding, conical end termination and is vulcanized in place at the conical inner surface of the bushing.

A design of this type functions well in practice for its intended purpose, but has a relatively short service life since the expander sleeve, which is made of natural rubber, often breaks or ruptures in the transitional region adjacent the end seal despite the extremely high degree of extensibility in the material.

Furthermore, in the prior art device, the expander sleeve has, in its position of rest, i.e. when it is not subjected to inner excess pressure, substantially the same outer diameter as the end seals. When an elevated inner excess pressure, up to the order of 1 500 bar, is subsequently applied interiorly in the expander sleeve, this is forced out into abutment against the wall of the bore in which the fracturing device is inserted. For self-explanatory reasons, the bore cannot be of any high degree of precision but, as a rule, is of one or more millimeters' excess dimension in relation to the unloaded outer diameter of the fracturing device. As a result, the expander sleeve will naturally expand radially, but also a certain proportion of the material of the expander sleeve is forced out into those gaps which are created between the surrounding bore and the end seals. When the pressure is subsequently relieved and the expander sleeve contracts, this material will be jammed between the end seal and the bore wall, for which reason it may be impossible or at least difficult to draw out the fracturing device from the bore after use.

PROBLEM STRUCTURE

The present invention has for its object to realise a fracturing device of the type mentioned by way of introduction, the fracturing device being designed in such a manner as to obviate the problems inherent in prior art designs and constructions. In particular, the present invention has for its object to design the fracturing device so that it may be employed several times without the risk of crack formation or fracture in the elastic expander sleeve, in particular in its anchorage regions in the end seals. The present invention also has for its object to realise the fracturing device such that, after use, it may readily be removed from a bore. Furthermore, the present invention has for its object to realise a fracturing device which is simple and economical to manufacture and which permits ready replacement of possibly worn or destroyed parts.

SOLUTION

The objects formfng the basis of the present invention will be attained if the fracturing device mentioned by way of introduction is also characterized in that the expander sleeve, with surrounding, bead-shaped end portions, extends Into correspondingly shaped, annular inner grooves in the end seals, that the expander sleeve is provided, in the longitudinal direction inside the end portions, with strain portions which are surrounded by correspondingly shaped portions of the end seals, and that the expander sleeve is provided, inside the strain portions, with an expander portion of considerably greater material thickness than the strain portions.

As a result of this design of the anchorage of the expander sleeve in the end seals, the major proportion of the deformation caused by the inner excess pressure in the end portions of the expander sleeve will be taken up and distributed along the movable strain portions.

In a first embodiment, the end seals are produced from a rigid material.

In a second embodiment, it further applies according to the present invention that at least the portions of the end seals located about the strain portions of the expander sleeve are expandable in a radial direction.

As a result of these characterizing features, the advantage will be afforded that the portions of the end seals located most proximal the expander sleeve expand into abutment against the surrounding cavity wall. This measure seals off the gap in which the material of the expander sleeve would otherwise risk being forced and jammed, with greatly impeded removal of the fracturing device after use as a result.

Further advantages will be attained according to the present invention if the invention is also given one or more of the characterizing features as set forth in appended Claims 3-5 and 7-15.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The present invention will now be described in greater detail hereinbelow, with particular reference to the accompanying Drawings. In t h e accompanying Drawings:

Fig. 1 shows an axial diameter section through a fracturing device according to the present invention;

Fig. 2 is a detail magnification in axial section through an anchorage region between the expander sleeve and an end seal in a first embodiment of the present invention; and

Fig. 3 is a view corresponding to that of Fig. 2 of a second embodiment of the present invention. DESCRIPTION OF FIRST EMBODIMENT

The fracturing device illustrated in Fig. 1 has a centrally disposed drawbar 1 with tensile force absorbing nuts 2 and 3 at each end. inside the two nuts 2 and 3 there are located end seals or end bushings 4 and 5 whose design and construction will be described in greater detail below. The end bushings 4 and 5 are, in this embodiment, made of a rigid material such as steel and have through bores with relatively good fit to the drawbar 1 , and sealing washers 6 and 7 are disposed in these bores for sealing against inner excess pressure in the fracturing device.

An expander sleeve 8 which is manufactured from a resiliently yieldable, preferably elastic material such as natural rubber, is secured in both of the end bushings 4 and 5. The expander sleeve is tubular or hose shaped and surround the drawbar 1 and has substantially the same inner diameter as the outer diameter of the drawbar. The outer diameter of the expander sleeve 8 is, in the unloaded state of the expander sleeve, slightly less than the outer diameter of the two end bushings 4 and 5.

For expanding the expander sleeve 8, the drawbar 1 has a longitudinal channel 9 which, via a short cross channel, discharges in the circumferential surface of the drawbar, for example 20-30 mm inside the end bushing 5, so that a pressure medium can be forced this way in between the drawbar and the inner defining wall of the expander sleeve. The channel 9 discharges in a projecting portion 10 of the drawbar which extends past the nut 3 and serves as connection for pressure medium.

According to the invention, both ends of the drawbar 1 can be provided with longitudinal channels 9 and corresponding connections, whereby a plurality of fracturing devices can be connected in series. When only one fracturing device is to be employed, the one connection is kept sealed.

The pressure medium employed is, as mentioned above, fed to the channel 9 from a pump which is not specified in any detail but which may deliver a very high pressure, at least of the order of magnitude of 1 ,000 to 1 ,500 bar.

The end bushings 4 and 5 can be of identical design and have an end wall 11 of sufficient thickness to withstand the axial force to which the fracturing device is subjected under the action of the inner excess pressure. Inside the end wall (the term inside should here be interpreted as axially inside the ends of the fracturing device), the end bushings are provided with a circumferential groove 12 which, in the axial direction towards the central portion of the fracturing device, is defined by a conical or axially inwardly inclined wall 13 or sealing surface. The radial inner edge of this conical or inclined wall is located a slight distance from the outer periphery of the drawbar 1 and merges there by the intermediary of a rounded transitional region into a substantially cylindrical wall surface 14. An arched flaring wall portion 15 connects axially inside this wall surface and merges in an approximately radial end wall 16 to the end bushings.

Preferably, all transitions between the inner defining surfaces of the end bushings are gently arched and have radii which will be described more closely below.

In the circumferential groove 12 of the end bushings 4 and 5, there is accommodated a circumferential bead-shaped and preferably complementary portion 38 (Fig. 2), located at opposite ends of the expander sleeve 8. This bead-shaped, external portion 38 serves for sealing against the walls of the groove 12, essentially against its obliquely inclined sealing surface 13.

In Fig. 2, a ghosted line is shown at reference numeral 17, this line constituting the centre line of the fracturing device and its drawbar 1. In the Figure, the peripheral surfacer of the drawbar has reference numeral 18, while the outer peripheral surface of the expander sleeve 8 which, in the unloaded state, is assumed to be approximately cylindrical, has reference numeral 19.

As has been mentioned above, the end bushing 5 has a relatively thick end wall 11 which has an outer surface 20 and an inner surface 21 which substantially lie in the radial plane and are, therefore parallel with one another.

The inner surface 21 forms a defining surface to the interior, circumferential and annular groove 12 in the end bushing. This groove has a radially outer defining surface 22 which forms a bottom surface in the above-mentioned groove and which may be substantially cylindrical and thereby parallel to the centre line 17, or alternatively be gently arched and convex outwardly. Inside this bottom surface 22, the above-mentioned conical or inwardly inclined wall 13 connects, the wall optionally having a cone angle of the order of magnitude of 45° with the centre line 17. Possibly, this tapering wall may also, at least along its radial inner portion, be gently arched and convex in a radial outward direction so that thereby the groove tapers in a radial direction outwardly.

In association with the inclined wall 13, the end bushing 5 has a substantially cylindrical wall 14 which is substantially parallel with the centre line 17. The width of this wall, i.e. its axial extent, is of approximately the same order of magnitude as the material thickness in the expander portion 23 of the expander sleeve 8 in fracturing devices of normal length. In general, the width of the cylindrical portion 14 may amount to 1 %-3% of the total length of the fracturing device.

At the axial inner edge of the cylindrical wall 14, the inner defining wall of the end sleeve has a radially outwardly flaring wall portion 15 which is preferably gently arched. This wall portion 15 subsequently merges radially outwardly into a substantially radially directed end wall 16 of the end bushing, the outer edge portion of this end wall merging, via a rounded transitional region 24, into the outer circumferential surface 25 of the end bushing. This circumferential surface is substantially cylindrical and is of slightly larger outer diameter than the expander portion 23 of the expander sleeve 8. With an outer diameter of 32 mm of the end bushing, the outer diameter of the expander sleeve can be of the order of magnitude of between 28 and 30 mm, which approximately corresponds to the situation that the expander sleeve has an outer diameter which amounts to the order of magnitude of between 85 and 95% of the outer diameter of the end bushing, preferably approx. 93%.

As was mentioned above, all transitional regions between the different surfaces interiorly in the end bushing are preferably gently rounded and may, for example at the transitional regions between the surfaces 21 and 22, between the surfaces 22 and 13 and between the surfaces 13 and 14 and finally also between the surfaces 16 and 25, have radii of curvature of the order of magnitude of 1 mm on condition that the diameter of the end bushings is approx. 32 mm. On the other hand, the radius of curvature at the transitional region 15 is ideally somewhat larger, for example 2 mm. Correspondingly, the transitional region between the end surface 20 and the circumferential surface 25 can have a radius of curvature of the order of magnitude of 1 mm.

On manufacture of the expander sleeve, two end bushings 4 and 5 are placed on a mandrel in an injection moulding tool in which non-vulcanized rubber material is injected for forming the expander sleeve 8. This implies that the defining surfaces of the expander sleeve in the region of the end bushings will be complementary to the inner defining surface of the end bushings with extremely good fit.

According to the present invention, the expander sleeve 8 and the end bushings 4 and 5 may also each be manufactured separately and then assembled together in that the expander sleeve 8 is forced into the end sleeves. In such instance, a binder or adhesive may possibly be applied to the walls of the groove 12, but in the majority of cases this is not necessary.

In a first alternative, the entire contact surface between the expander sleeve 8 and the inner defining surfaces of the surrounding end bushings 4 and 5 is left uncoated with primer in order that thereby no surface adhesion will be achieved during the vulcanisation. This thus implies that the vulcanised rubber material can ready be separated from the surfaces of the end bushings 4 and 5 throughout their entire contact surface. In particular, a certain axial movement may occur between the material in the expander sleeve 8 which abuts against the surface 14 and this surface.

On the other hand, in a second alternative the surfaces 21 , 22 and 13, i.e. those surfaces which define the groove 12 of the end bushings 4 and 5 are coated with primer so that the expander sleeve 8 receives a permanently vulcanised annular bead 38 which is secured in the surrounding surfaces on the end sleeve. On the other hand, the substantially cylindrical wall 14 should not be coated with primer, nor should the arched transitional surface 15 and the radial end wall 16 be provided with primer, so that hereby the rubber material in the expander sleeve 8 and the metallic material in the end bushing will be free to move mutually along these surfaces. As a result of the above-described manufacturing methodology, and the design of the expander sleeve 8, the sleeve will have strain portion 26 which is movable and free in relation to the surrounding surfaces of the end bushings 4 and 5 so that substantially all of the strain which is generated in the axial direction and to some degree in the radial direction outwardly around the arched wall 15 and the radial end wall 16 of the end bushing will be accommodated by and distributed along this strain portion 26.

The material selected for manufacture of the expander sleeve 8 may be of any optional type of elastic, non-compressible, yieldable or deformable material such as natural rubber, which is capable of undergoing an elongation or extension of approx. 500% before rupture occurs. As an alternative to natural rubber, synthetic materials such as polyurethane materials, silicon materials etc. may also be employed. In. order to ensure that the majority of the relevant strains in the anchorage regions of the expander sleeve 8 in the end bushings 4 and 5 actually occur in the intended manner in the strain portions 26, it is essential that these are of considerably lesser material thickness than applies to the expander portion 23 of the expander sleeve 8. Suitably, the strain portion may have a material thickness which amounts to the order of magnitude of between 25 and 45 % of the material thickness in the expander portion 23, preferably approx. 36 %.

The radial extent of the groove 12 is not critical, but may lie in the range of between 60 and 80 % of the material thickness of the expander portion 23 of the expander sleeve 8, preferably approx. 65 % or approximately double the material thickness in the strain portion 26.

SECOND EMBODIMENT

In the first embodiment, the end seals were manufactured in one piece of rigid material, preferably steel. In the second embodiment, the end seals consist of a rigid end piece 27 against whose outside the two nuts 2 and 3 abut at opposite ends of the drawbar 1. In its periphery, this end piece has a collar 28 whose purpose will be described in greater detail below.

In the second embodiment, the end seal consists of an end bushing 29 which has surfaces cooperating with both end portions of the expander sleeve 8, approximately in the manner described above, but which is produced from a slightly yieldable, possibly elastic material. Thus, also in this embodiment, the end bushing has an internal, circumferential groove 12 in which the bead-shaped end portions 38 of the expander sleeve 8 extend out and seal. Inside this circumferential groove 12, the end bushing 29 has a conical sealing surface 13 with approximately the same inclination and design as described above. Furthermore, the end bushing has a wall 14 which is substantially cylindrical in the unloaded state and which connects to the strain portion 26 of the expander sleeve 8. Also in this embodiment, the inwardly facing end surface 16 of the end bushing 29 is substantially radially directed and planar. On the other hand, the transitional region between the end surface 16 and the cylindrical wall 14 need not be arched in the same manner as that described above, but instead the arching or radius of curvature between these surfaces may be render considerably smaller without any risk of material breakage or rupture in the material of the expander sleeve 8. The reason for this is that the end bushing has an expander portion 30, and so the material of the expander sleeve 8 will not be displaced to the same extent around the corner between the cylindrical surface 14 and the end surface 16 o n pressurization, as mentioned above.

As has been mentioned above, the end bushing 29 was produced from an expandable material. This implies that at least that portion 30 of the end bushing which is located about the sealing portion 26 of the expander sleeve 8 will form an expandable portion which, on pressurization of the fracturing device, expands outwardly into abutment against the surrounding cavity wall 36. Possibly, a further portion of the end bushing (i.e. the portion located outside the groove 12) may also undergo a certain expansion in the same manner. At its end facing towards the expander sleeve 8, the end bushing 29 is exteriorly provided with a conical or arched portion 37 whose diameter corresponds to the diameter of the expander sleeve 8 most proximal thereto, but whose diameter increases in a direction away from the expander sleeve, i.e. in a direction out towards both of the nuts 2 and 3.

In that the axial inner portion 30 of the end bushing 29 expands when the fracturing device is placed under pressure, the end bushing will abut against the cavity wall 36 and thereby seal off that gap in which the material in the expander sleeve 8 in earlier embodiments risked being forced and jammed so that as a result removal of the fracturing device was seriously impeded or even made impossible.

In order to prevent an excessively exaggerated deformation of the end bushing 29, in particular in its outer region, the end bushing is provided at its outer end with an externally circumferential groove 31 which accommodates the collar 28 of the end piece 27. Hereby, the axially outer end portion of the end bushing can be considered as rigid at least in the radial direction.

In the above-described embodiment, the end bushing had, in its surface facing towards the drawbar 1, an interior, circumferential groove 7 for accommodating a sealing O ring or washer. In the embodiment according to Fig. 2, sealing against the drawbar 1 is achieved in a different manner in that the end bushing 29 has a tubular or sleeve-shaped, preferably externally conical sealing portion 32 with a central bore for accommodating the drawbar 1. This sealing portion extends from the outer end of the end bushing 29 axially inwardly and surrounds the drawbar along a certain distance. On manufacture of the end bushing 29, this can be given a slightly conical bore where the diameter at the minor end of the cone which is turned to face axially inwardly is insignificantly smaller than the outer diameter of the drawbar so that the sealing portion 32 is expanded on insertion of the drawbar. Hereby, the sealing portion 32 will be pretensioned so that a good seal is obtained even at low inner excess pressure. The sealing portion is outwardly defined by a surface 34 which inwardly tapers in the axial direction or is conical and which, hence, has its minor end facing towards the central region of the fracturing device and, at its major end merges via an arched transitional portion into the surfaces defining the groove 12. The axial length of the sealing portion should lie in the region of between 25 and 60 % of the diameter of the drawbar 1. The conicity of this surface 34 may lie in the region of between 15° and 30°, preferably approx. 20°, while the conicity of the inner bore of the sealing portion 32 may lie in the region of between 0° and 5°.

Interiorly in the axially inner end of the sealing portion 32, there may suitably be provided one or more circumferential and bead-shaped or more or less sharp edge-shaped or cross-sectionally triangular sealing members 35 which further improve the seal against the drawbar 1. In order to achieve an amplified urging of the sealing portion 32 against the drawbar 1, it is important that the excess pressure prevailing interiorly in the expander sleeve 8 can act radially outwardly towards the sealing portion. In order to ensure this, either the inner end of the sealing portion 32 or the expander sleeve 8 is provided with a recess 33 which, in the circumferential direction, distributes pressure medium to the gap-shaped space which is formed between the outer defining surface 34 of the sealing portion 32 and the surface of the expander sleeve 8 cooperating therewith, this being located in the axial direction in register with the groove 12. Penetration of pressure medium into this gap-shaped space also amplifies the urging force of the bead-shaped portion of the expander sleeve 8 against the defining surfaces of the groove 12 and primarily against the obliquely inclined sealing surface 13 of the end bushing 29.

In this embodiment, where the strain portion 26 undergoes a smaller axial extension and does not slide to the same extent around the arched transitional region 15, the strain portion 26 may be of greater radial thickness than disclosed previously. Thus, the strain portion may be of a radial thickness which amounts to approximately 45-65 %, preferably approx. 50 % of the thickness of the expander portion 23 of the expander sleeve 8.

On manufacture of this embodiment, the end bushing 29 is produced separately by injection moulding, casting, or milling processing of plastic, rubber or other elastic material of greater hardness than the expander sleeve 8. Correspondingly, the expander sleeve 8 is produced in a suitable tool. Assembly then takes place quite simply in that the end bushings 29 are axially pressed onto the end portions of the expander sleeve 8. No binder or adhesive or the like is needed between cooperating surfaces of the expander sleeve 8 and the end bushings 29, for which reason these surfaces are free to move in relation to one another on pressurization.

Two different embodiments according to the present invention have been described with reference to Figs. 2 and 3. However, various alternative embodiments ranging between these two are also conceivable. Thus, for instance one variation may be designed as is apparent from Fig. 2 but with the difference that the material, at least in the portion of the end bushing 5 located outside the surface 14 may be more or less elastic, deformable or yieldable as described with reference to Fig. 3.

Another alternative would entail that the design and construction described with particular reference to Fig. 3 is modified, as intimated above, so that it has an arched transitional region 15 (according to Fig. 2) between the surfaces 14 and 16.

Other combinations of characterizing features taken from the different embodiments of the present invention are also possible.

DESCRIPTION OF ALTERNATIVE EMBODIMENTS

According to the present invention, the interior groove 12 of the end seals 4 and 5 may have a different design from that described above. Thus, the cross-sectional configuration of the groove may be limited by circular arcs so that, for instance, the portion of the groove located radially outside the cylindrical wall 14 may consist of an approximate semi-circle, which merges via a gently arched region into the cylindrical wall and, at the opposite side, merges into a more or less radial wall which corresponds to the inner surface 21.

Furthermore, embodiments are conceivable in which the defining wall 14 of the end bushings against the strain portion 26 is not completely cylindrical but gently conical in one direction or the other.

The end wall 16 has been described above as substantially radial, but this can, of course, also be given conical shape or generally arched shape.

The present invention should not be considered as restricted to that described above and shown on the Drawings, many modifications being conceivable without departing from the spirit and scope of the appended Claims.

Claims

1. A fracturing device of the type which, by insertion and expansion in a bore in a material, is intended to fracture the material and which includes end seals (4, 5) disposed at the ends of the fracturing device and interconnected via a drawbar (1), there extending about the drawbar (1) and sealingly between the end seals, an expander sleeve (8) produced from elastic or resiliently yieldable material, and the space interiorly in the expander sleeve being pressurizable, characterized in that the expander sleeve (8), with surrounding, bead-shaped end portions (38), extends out into correspondingly shaped, annular and interior grooves (12) in the end seals (4, 5); that the expander sleeve (8) has, in the longitudina. direction inside the end portions, strain portions (26) which are surrounded by correspondingly shaped portions (14) of the end seals (4, 5); and that the expander sleeve (8) is provided, inside the strain portions (26) with an expander portion (23) of considerably greater material thickness than the strain portions.

2. The fracturing device as claimed in Claim 1, characterized in that at least the portions (30) of the end seals (4, 5) located about the strain portions (26) of the expander sleeve (8) are expandable in the radial direction.

3. The fracturing device as claimed in Claim 1 or 2, characterized in that the end seals (4, 5) are provided, about the drawbar (1) with an annuJar sealing portion (32) with a radially outer surface (34) which is actuable by the pressure prevailing interiorly in the expander sleeve (8), whereby the sealing portion (32) is forcible against the drawbar (1).

4. The fracturing device as claimed in any one of Claims 1 to 3, characterized in that the end seals (4, 5) are provided, at their ends facing towards the expander seal (8), with an outer, circumferential surface (37) of a diameter which increases in a direction away from the expander sleeve (8).

5 The fracturing device as claimed in any one of Claims 1 to 4, characterized in that the surfaces of the expander sleeve (8) cooperating with the end seals (4, 5) are free in relation to one another.

6. The fracturing device as claimed in Claim 1, characterized in that the end seals (4, 5) are produced from a rigid material.

5 7. The fracturing device as claimed in Claim 1 or 6, characterized in that the surfaces of the expander sleeve (8) cooperating with the end seals (4, 5) are free in relation to one another.

8. The fracturing device as claimed in Claim 1 or 6, characterized in that l 0 the bead-shaped end portions (38) are secured in adjacent surfaces (13,

21 _r 22) of the annular grooves (12), while the strain portions (26) are free from adjacent surfaces (14) on the end seals or bushings (4, 5).

9. The fracturing device as claimed in any one of Claims 1, 6 to 8, 5 characterized in that the expander sleeve (8) is provided, between the strain portions (26) and the expander portion (23), with an exteriorly gently arched transitional portion between the relatively slight material thickness of the strain portion (26) and the relatively large material thickness of the expander portion (23); and that this transitional portion is free from the 0 correspondingly shaped surfaces (15, 16) of the end bushings (4, 5).

10. The fracturing device as claimed in any one of Claims 8 or 9, characterized in that both the strain portions (26) and the transitional portions are free and movable in relation to adjacent, complementarily 5 designed surfaces (14, 15, 16) on the end bushings (4, 5).

11. The fracturing device as claimed in any one of Claims 1 to 10, characterized in that the expander sleeve (8) is of smaller outer diameter than the end bushings (4, 5). 0

12. The fracturing device as claimed in Claim 11, characterized in that the outer diameter of the expander sleeve (8) constitutes approximately 85 - 95 % of the outer diameter of the end bushings (4, 5).

13. The fracturing device as claimed in any one of Claims 1 to 12, characterized in that the bead-shaped end portions (38) are of a material thickness in the radial direction of the order of magnitude of between 60 and 80 % of the material thickness in the expander portion (23).

14. The fracturing device as claimed in any one of Claims 1 to 13, characterized in that the strain portions (26) have a material thickness of the order of magnitude of 25 - 60 %, preferably approximately 50 %, of the material thickness in the expander portion (23).

15. The fracturing device as claimed in any one of Claims 1 to 14, characterized in that the strain portions (26) are of a width in the axial direction which approximately amounts to between 1 and 3 % of the length of the fracturing device.