The present invention relates to a system for estab¬ lishing a sealing connection between two axially impacting members in a pipe conduit via an intermediate, elastically yielding metal sealing ring, which is arranged in a groove between the members, where the pipe conduit is adapted to be ensured sealing under relatively low as well as under exceptionally high medium pressures, and including par¬ ticularly high, intermittently occurring medium pressures which cause axial extending of the members and which have a tendency to open a joint between the members where the metal sealing ring is arranged and where the metal sealing ring is wedge truncated and is provided with two mutually opposite sealing surfaces facing towards their respective sealing surfaces in the joint between the two members and with one, largest edge end surface of the sealing ring faced towards the interior of the pipe conduit, the sealing ring being adapted to be subjected to an axial prestressing force between the two members by means of radially moveable tension means.

The solution according to the invention shall be used first and foremost in the boring of gas and oil wells. It finds particular application in the coupling of various equipment to a well head, for example coupling of a by-pass or exhaust safeguard in connection with the well head, but can also find application in the coupling to¬ gether of other types of pipe-shaped or pipe-forming mem¬ bers in a pipe conduit.

It is of particular interest to use the present invention in connection with rapid couplings, for example rapid couplings of a corresponding type as disclosed in Norwegian Patent Application No. 861655, where a number (for example 9 peripheral mutually separated) of hydraulic or pneumatic cylinders with their respective associated locking bolt fix a socket member via locking grooves in an insert member. In the known construction nine locking bolts are proposed to be used, but in practice there can be employed a larger or smaller number of bolts than pro¬ posed. It is also possible instead of locking bolts to use segments for example segments which are each controlled by one or two hydraulic or pneumatic cylinders. The purpose of the segments is to increase the abutment surface for transferring the prestressing force and distributing the forces as uniformly as possible over the whole periphery. In this connection the present invention can be considered as a further development of the solution in said patent application. However the solution according to the present invention can also be used with advantage in other types of couplings, such as so-called "hub" couplings, where a head portion on two axially impacting members are coupled together by means of a pair of semi-circular, collar-like clamping means which are clamped together in the periphe¬ ral direction by means of transverse bolts. A second example of an alternative coupling includes API flanges or clamp flanges, which are clamped together by means of a number of 20-24 axially extending bolts.

In connection with boring of oil wells a significant static weight loading occurs on the pipe conduit and its couplings, partly as a consequence of the weight of the pipe conduit itself and partly as a consequence of the medium pressure from linear material which is received in the pipe conduit between the pipe conduit itself and the drill stem. From time to time sudden changes occur in the medium pressure in the pipe conduit, produced by back fire or so-called "kick", which occurs due to the bore intru-

ding into a gas pocket and being exposed to a momentary pressure build up. These back pressures can be relieved in the by-pass and/or the exhaust safeguard, but before this can occur there is produced a considerable axial tension loading in the members of the two different couplings. The tension loadings can in certain instances produce signifi¬ cant problems, for example in the occurrence of intermit¬ tent opening of the joint between the two axially impac¬ ting members in the coupling and from this follows momen¬ tary leakage under particularly high pressure.

With the present invention the aim is to control such occasionally occurring, momentary pressure build ups by way of simple means. For one thing the aim is to be able to achieve effective compensation for possible ope¬ ning of the joint between two axially impacting members in the coupling by means of a special mode of sealing between the members.

From U.S. Patent 4,200,312 a solution is known corresponding to that which is disclosed by way of intro¬ duction in the specification. In the known solution one is dependent upon different sealing arrangements in order to ensure sealing under different operative conditions. According to the known solution one can certainly not employ a single sealing ring, as is the aim according to the invention. There is not illustrated either a sealing ring of corresponding design and with a corresponding mode of action for that which is the aim according to the invention. There is not proposed either a material for the sealing ring which is useable for the object according to the invention.

The system according to the invention is characte¬ rised in that the sealing ring is made of highly elastic rust-free steel, that the sealing surfaces of the sealing ring and the sealing surfaces of the members converge to¬ wards each other in a direction radially outwards in the pipe conduit at an angle of from 30 to 50°, that the sealing ring-receiving groove of the members is provided

radially innermost at the largest wedge truncated end sur¬ face with combined control and stop means for the sealing ring so as to prevent displacement of the sealing ring radially inwards into the pipe conduit from a pressure relieved starting position, that the groove is provided radially outermost at the smallest wedge truncated end surface of the sealing ring with a radially outer expan¬ sion chamber designed for the reception of a radially expanded sealing ring, that the sealing surfaces of the members, which have a somewhat longer longitudinal dimen¬ sion than the sealing surfaces of the sealing ring, are extended inwardly into the expansion chamber, and that the prestressing force is substantially limited to a set, con¬ trolled clamping force which is exerted via the sealing ring exclusively via its sealing surfaces.

The present invention further relates to a process for establishing a sealing connection between two axially impacting members in a pipe conduit which operates with a medium which is subjected to high medium pressures and which intermittently can be subjected to occasionally occuring, particularly high medium pressures which cause axial extending of the members and from this follows the axial opening of a joint between the members, where a clamping arrangement effects endwise clamping together of the members after an elastically yielding metal sealing ring is inserted in the joint between the members, the sealing ring, which is wedge truncated, being inserted with two mutually opposite sealing surfaces facing towards their respective sealing surface in the joint between the two members and with one end surface of the sealing ring facing towards the interior of the pipe conduit.

The process according to the invention is characte¬ rised in that the sealing ring is placed in the joint be¬ tween the members, concentrically to them, with its one, radially inner end surface in precise alignment with the inner surface of the pipe conduit and with its other radi¬ ally outer end surface at a certain radial distance from

an end wall in an extension chamber radially outside the sealing ring, after which the sealing ring is fixed be¬ tween the members with a prestressing force which is sufficient to establish a sealing abutment between the sealing surfaces of the sealing ring and the sealing sur¬ faces of the members, when conventional medium pressures prevail in the pipe conduit, but which is substantially lower than the tension loading which can occur in the members, when particularly high medium pressures prevail in the pipe conduit, the sealing ring, which via said one end surface is subjected to the medium pressure which pre¬ vails in the pipe conduit, being elastically deformably moved with the occasional occurrence of particularly high medium pressures, radially along the sealing surfaces of the members, during compensation for an intermittent opening of the joint between the members.

By placing according to the invention the highly elastic, wedge-truncated sealing ring in connection with an extension chamber in the joint between the members, the sealing ring is given a possibility, under specific condi¬ tions with particularly high medium pressures, to expand itself radially in said expansion chamber. This is of interest under conditions where the medium pressure causes such a strong extending of the members that the joint be¬ tween these is opened axially, the wedge-truncated sealing ring thereby being able to wedge itself radially outwards and compensate for the mutual axial displacement of the sealing surfaces of the joint.

According to the invention by prestressing the coup¬ ling with a significant force during mounting, one can en¬ sure that an effective sealing abutment is maintained be¬ tween the sealing ring and members of the pipe conduit in a lower pressure zone where the pressure tops are mode¬ rate, that is to say where the prestressing force between the members exceeds occurring tension force which are momentarily supplied between the members as a consequence of momentary pressure medium increases. In an upper pres-

sure zone, where said tension forces exceed the prestres¬ sing force, one has simultaneously ensured by means of the prestressing force that the medium pressure becomes imme¬ diately effective facing the elasticity effect in the sealing ring when the force from the medium pressure exceeds the prestressing force. Thereby the medium pres¬ sure can momentarily give the desired radial expansion of the sealing ring immediately there occurs a need for this.

According to the invention the sealing ring is pre- stressed with a clamping force which constitutes from 15 to 30% and preferably about 20% of the force which determines the yield point of the material of the sealing ring.

According to the invention it is of great signifi¬ cance that the prestressing force is of an established magnitude, that is to say sufficiently large so as to be able to ensure sealing between the members before the members begin to move relative to each other, but at the same time not larger than practically necessary. In other words the aim is that the sealing ring can be actuated in different ways in different pressure mediun zones.

In this way one obtains a first, lower pressure medium zone with moderate pressures, where the prestres¬ sing force ensures sealing via the sealing ring without substantial elastic deformation of the sealing ring. Furthermore one obtains a subsequent, second, upper pres¬ sure medium zone with significant pressure, where the pre¬ stressing force is overcome and where the elasticity movements of the sealing ring get free flow after a prior pressure build up. At the top of this second, upper pres¬ sure zone the occurrence of exceptionally high pressures will produce loads on the sealing ring which can exceed the yield point of the material of the sealing ring.

In U.S. Patent Specification 1,821,863 (from 1931) there is shown an elastic metal sealing ring which is meant to give sealing by the high elasticity. Specific types of metal and metallic properties are not disclosed.

So as to be employable for the object according to the invention it is of considerable significance that a metal is employed of a specific degree of hardness which has a high yield point and simultaneously a particularly high elasticity.

According to the invention the most favourable effects are achieved by making the sealing ring of ASSI 410 rust-free steel. But other types of highly elastic, rust-free steel can also be of interest.

It is preferred according to the invention that the sealing ring is made of ASSI 410 rust-free steel, which initially has a degree of hardness of 24 Rockwell and which is heat treated at temperatures of between about 1000°C (960°C) and about 500°C (600°C) during maintenance of the original yield point of the material at the same time as the degree of hardness of the material is changed to between 18 and 20 Rockwell.

By this one can ensure that high elasticity and high yield point are obtained and simultaneously a desired de¬ gree of hardness which is suited for the purpose. In this way a sealing ring is obtained having a relatively large inherent rigidity. Such a sealing ring will be particu¬ larly suited to momentarily occurring, radially acting, elastic expansion movements, where the sealing ring has the ability to position back to the starting position, even with occasionally occurring, particularly high medium pressures, which otherwise could have caused the yield point of the material to be exceeded. In cases the pres¬ sures which occur in the pipe conduit result in the yield point of the material being exceeded, the sealing ring is unusable for further sealing, when the high pressures de¬ cline again to a more normal operative pressure.

Further features of the present invention will be evident from the following description having regard to the accompanying drawings, in which:

Fig. 1 shows a sealing connection according to the invention shown in vertical section and shown with a locking means in an active locking position.

Fig. 2 shows the same as in Fig. 1 with the locking means in an inactive position.

Fig. 3 shows schematically a vertical section of a sealing ring according to the invention under normal use conditions.

Fig. 4 shows in a corresponding section to Fig. 3 the sealing ring under conditions with the occurrence of particularly high medium pressures.

Fig. 5 and 6 show in two different vertical sections part of the sealing connection according to Fig. 1, where Fig. 5 shows a first detail of the sealing connection and Fig. 6 shows a second detail of the sealing connection.

In Fig. 1 there is shown a rapid coupling connection between two pipe-forming members 10 and 11, which form a part of their respective pipe conduit section, pipe valve or similar pipe-forming equipment in the pipe conduit for use in well boring operations in connection with gas or oil deposits.

The members 10 and 11 are provided at mutually oppo¬ site ends with coupling portions 12 and 13 of the "hub" type connection, which cooperate with equivalent coupling portions 14 and 15 (shown in broken lines) in their res¬ pective adjacent pipe conduit section. Between the coup¬ ling portions 12,14 and between the coupling portions 13, 15 there are shown a distance radially inside the inner surface 16 of the pipe conduit opposed cavities 17,18 for the reception of their respective sealing ring 19 of known construction per se. By means of two collar-forming, annu¬ lar half member-formed tension means (shown by broken lines) the coupling portions 12,14 and 13,15 can be locked together in more or less permanent connections by means of transverse bolts (not shown further) .

Alternatively there can be employed for said more or less permanent connection a second type of coupling con¬ nection, for example a clamp flange coupling with an associated series of axially extending fastening bolts.

In contrast to the said more or less permanent con¬ nections, the members 10 and 11 shall form a part of a rapid coupling connection, that is to say a connection which is adapted to be closed and opened far more often than the said, more or less permanent connections. The one member 10 in the rapid coupling connection is provided with a socket portion 20 which cooperates with an insert portion 21 on the second member 11 in the rapid coupling connection.

The socket portion 20 is provided with an internal cavity 20a which axially outermost is provided with a conically tapered first, internal guide surface 22. The guide surface 22 extends directly over into a cylindrical, axially extending, internal support surface 23, which con¬ tinues into a conically tapered, second, internal guide surface 24. Axially innermost the guide surface 24 extends over into a radially extending, internal support surface 25 which forms a vital inner joint surface for the member 20.

The insert portion 21 is provided with equivalent external guide surfaces 22a and 24a together with equiva¬ lent external support surfaces 23a and 25a, so that the members 10,11 in a fully pushed together condition close relatively tightly together, radially as well as axially.

In the following description there shall be descri¬ bed a particular rapid coupling for the members 10 and 11.

In the socket portion 20 there are installed at suitable peripheral distances a number (for example nine pieces) of locking means 26 in their respective radially extending bores 27. The locking means 26 is provided with relative to the pipe conduit a radially inner, cylindrical stem portion 28, having a radially innermost bolt portion 29. The bolt portion 29 is provided with relative to the

cylindrical peripheral surface of the stem potion 28 a locally offset, transverse locking surface 30, which extends somewhat obliquely inwards relative to a radial plane through the centre axis 28a of the stem portion 28. The locking surface 30 is localised to the upper (shown in Fig. 1 and 2) section of the bolt portion 29, the lower section of the bolt portion 29 being designed with a cylindrically shaped periphery correspondingly as the locking means 26 remaining. The locking means 26 is pro¬ vided at the opposite end with relative to the pipe con¬ duit a radially outer piston 31 which is moveable in a bore 32. A cover 33, which is received in an outermost bore 34 in the socket portion 20, defines together with the piston 31 a first working chamber 35 in the bore 32, there being formed an opposite second working chamber 36 in the bore 32 between the piston 31 and the inner wall 37 of the bore 32. There is shown a first packing 38 in the piston and a second packing 39 in the bore 27 for sealing off of the said second working chamber. Through the cover 33 and through the working chamber 35 and inwardly into a bore 40 in the locking means there extends a control bar 41 which is surrounded by a helical spring 42. As shown in Fig. 2 the control bar 41 indicates in a pushed out condi¬ tion that the locking means occupies its drawn back inac¬ tive position. The control bar is provided at its free end with a fastening pin 43 which is received in a fastening 44 in the locking means 26. In Fig. 1 the locking means is shown in an active locking position. In order to adjust the locking means in the active locking position compres¬ sed air (or pressure oil) is supplied to the working chamber 35 via a first control duct 45, while pressure is discharged in the working chamber 36 via a second control duct 46. The ducts 45 and 46 communicate with their res¬ pective ducts 47 and 48 in a connecting piece 49 which is secured to socket portion 20 of the member 10 by means of fastening screws 50 (only one is shown in the drawing). The ducts 47 and 48 communicate with respective ducts 45

and 46 for each of the locking means 26, so that these can be moved in step with each other from and to the locking position (shown in Fig. 1) to and from the inactive, drawn back position (shown in Fig. 2) by means of a single pres¬ sure activating means or by reversing the pressure in the ducts 47 and 48. The cover 33 is fastened with a number of fastening screws (not shown) directly to the socket por¬ tion 20 of the member 10 and by means of an eccentrically arranged control pin 51 is connected to an eccentrically arranged bore 52 in the piston 31. By means of the helical spring 42 one can ensure that the locking means 26 is held in place in the locking engagement position, even if the pressure should be discharged for one reason or another from the piston 31 of the locking means 26. Correspond¬ ingly the helical spring 42 will be compressed and charged by a pneumatic or hydraulic readjustment of the locking means from the active locking position to the inactive rest position.

The insert portion 21 is provided With an annular groove 53 which is adapted to receive bolt portion 29 of the locking means 26 at arbitrary locations along the groove 53. The groove 53 is provided as shown in Fig. 1 and 2 with a radially extending first side surface 54, an axially extending bottom surface 55 and a second side sur¬ face 56 which extends parallel to the locking surface 30 on the bolt portion 29 of the locking means 26. Oblique surface 20 of the locking means 26 has an angle which lies within the self-locking principle that is to say which has an angle w of up to 8° and preferably of an order of mag¬ nitude of 3-6°. The aim is an abutment between the bolt portion 29 and the groove 53 only occuring via the mutu¬ ally parallel surfaces 30 and 56, the remaining surfaces of the bolt portion and the groove 53 being without con¬ tact with each other. By this one can transfer the pre¬ stressing force in a controlled manner from surface 30 of the bolt portion 29 to surface 56 of the groove 53. It will be evident from Fig. 1 and 2 that the bolt portion 29

can be led into position in a self-controlling manner by guiding the locking surface 30 along side surface 56 of the groove 53 until the cylindrical surface of the locking means impacts against opposite side surface 54 of the groove. In the position illustrated in Fig. 1 the locking means 26 are pushed into place in the groove 53 with a precisely adapted pressure loading which presses the members 10 and 11 mutually axially together with a pres¬ sure force of for example 94 ton across an intermediate sealing ring 59.

In the joint between the socket portion 20 and the insert portion 21 there are designed opposite cavities 57 and 58, which in a common, triangular hollow space receive the intermediate sealing ring in the form of a wedge-trun¬ cated sealing ring 59. There is employed according to the invention a highly elastic sealing ring of rust-free steel, more specifically of a material of the type ASSI 410. The sealing ring is certified for DIN 50049.3.1G. Initially the forged sealing ring has a degree of hardness of 24 Rockwell, but by subjecting it to a special heat treatment the sealing ring is provided with a degree of hardness of 18 minimum and 20 maximum Rockwell, in order to guarantee the ring suitable sealing properties and suitable rigidity for the purpose. The special heat treat¬ ment ensures that at the same time as one preserves a de¬ sired high yield point and desired high elastic properties a desired degree of hardness is also provided. For example as regards a sealing ring with an inner diameter of 18" (45,7 cm) one has heat treated the forged sealing ring at a specific temperature over the course of a specific time period and thereafter effected cooling over a specific time period (such as recommended by the supplier Firth Rixson pic, Woodhouse & Rixson Works, Bessemer Road,

Sheffield S93Xs, Great Britain). More specifically one has effected a heat treatment of the sealing ring at a tempe¬ rature of 960°C with cooling (quenching) in an oil bath over 3 hours. Thereafter the sealing ring is air cooled at

a temperature of 700°C over 8 hours in order thereafter to be air cooled at a temperature of 660°C over 6 hours. As regards heat treatment and subsequent cooling of the sealing rings of greater or smaller diameter corresponding temperatures are employed, but different times all accor¬ ding to the quantity of material of the sealing ring in the individual instance. In practice however other types of highly elastic sealing ring of rust-free steel can also be used (without specific embodiments of this being dis¬ closed), even if the afore-mentioned type, which has par¬ ticularly high elasticity and which can be worked extra for totally special physical properties, will be prefer¬ red.

The cavities 57 and 58 are designed just by the inner surface of the pipe conduit, so that one largest end surface 60 of the sealing ring 59 is in alignment with the inner surface 16 of the pipe conduit under normal opera¬ tive conditions.

In Fig. 3 and 4 there is schematically illustrated a principle for the mode of action of the sealing ring 59. The sealing ring 59 is shown with a largest surface in the form of said one end surface 60 and a smallest surface in the form of an oppositely lying end surface 61. Between the surfaces 60 and 61 extend two sealing surfaces 62 and 63 converging towards each other, which in the illustrated embodiment extend at an angle v of about 20° relative to the radial joint surface between the members 10 and 11. Alternatively the angle can be of the order of magnitude of 15-25°. The height of the end surface 61 corresponds substantially to the distance b between the surfaces 60 and 61. By this there is obtained by means of an approxi¬ mately square cross-sectional area (defined within the broken lines 62a,62a) relatively large form stability and minimal local deformation of the sealing ring under vari¬ ous, occurring medium pressures in the pipe conduit. The sealing surfaces 64 and 65 of the cavities 57 and 58, which run parallel to sealing surfaces 62,63 of the

sealing ring 59 have somewhat larger dimension (for example 3-4 mm greater length) , reckoned relative to the radial dimension of the joint, than the sealing surfaces 62 and 63. Consequently there is formed radially outside the sealing ring an outer expansion chamber 66, in which the sealing ring can be received by an elastic deformation of the sealing ring.

In Fig. 3 there is illustrated the placing of the sealing ring 59 in the joint between the members 10 and 11 when normal medium pressure conditions prevail in the pipe conduit. The members 10,11 form a part in the illustrated embodiment of a pipe conduit with an internal diameter of 77 cm (30,5 inches). Conventional pipe diameters of inte¬ rest for the present purposes usually lie in the order of magnitude of 6 to 78 cm (2" to 31"), but it can also be of interest with smaller as well as larger pipe diameters where there must be a need for this.

There are indicated in Fig. 3 with vector arrows 67 moderate medium pressures of for example up to 14 kp/cm ² (200 psi) under normal operative conditions for a pipe conduit with 77 cm internal diameter. There is employed a prestressing force as indicated by vector arrows 68 be¬ tween the members 10 and 11 across the sealing ring 59 of for example 42 kp/cm ² (600 psi) and correspondingly a com¬ bined pressure between the members of about 30 ton for a pipe conduit with an internal diameter of 77 cm. Under normal operative conditions with medium pressures of close to 14 kp/cm ² , and even with relatively high medium pres¬ sures of close to 42 kp/cm ² the prestressing force will, as shown by the vector arrows 69, be able to maintain an effective sealing pressure between the members 10,11 and the sealing ring 59 without elastic deformation of the sealing ring being produced.

At particularly high, intermittently occurring medium pressures in the pipe conduit, that is to say at medium pressures which exceed the prestressing loading (about 30 ton) between the members 10,11, but which fall

short of the elasticity limit for the material of the sealing ring, the pipe conduit will be subjected to momen¬ tary, axial tension loadings within the elasticity limits of the sealing material. The particularly high medium pressures are shown in Fig. 4 with vector arrows 70 towards the radially inner end surface 60 of the sealing ring 59, while the accompanying axial tension forces are indicated by vector arrows 71 and for example are of an order of magnitude of 470 ton. The result is that the members can be intermittently drawn from each other - reckoned across the joint between radial support surfaces of the members - a distance of for example 1,4 mm. According to the invention there is obtained, by means of the highly elastic material in the sealing ring, that the sealing ring as a consequence of the high medium pressure which occurs in the pipe conduit, can be extended for axample 2 mm in the radial direction. The said radial extending follows from the occuring medium pressures which act against the radially inner surface 60 of the sealing ring. The radial extending of the sealing ring occurs at the same time as the sealing surfaces 62,63 of the sealing ring slide a corresponding distance along the sealing surfaces 64,65 of the members 10,11 to the position which is shown in Fig. 4. By this the sealing surfaces 62,63 extend wedge-shaped inwardly between equivalent, mutually converging sealing surfaces 64,65 of the members 10,11 and fill out the intermediate space between the sealing surfaces 62,64 and 63,65 gradually as the sealing surfaces 64,65 are drawn axially away from each other.

As a consequence of the inherent elasticity of the sealing ring the sealing ring 59 will be placed back from the position shown in Fig. 4 to the position shown in Fig. 3, immediately the medium pressure in the pipe conduit falls back to the normal operative pressure. This means that the members 10,11 are relieved of the occuring large axial pressures and again impact along mutually adjacent joint surfaces, while the sealing ring is placed back to

the starting position in a full operatively ready condi¬ tion and then with the original prestressing force intact between the members 10,11.

If the intermittently occurring top loading substan¬ tially exceeds in an exceptional case the afore-mentioned top loading of 450 tons, for example rises to a top load¬ ing of 600 ton or higher, one enters into a zone where the loading of the sealing ring reaches up to the yield point of the material. In such a case the sealing ring can be extended to the maximum outwardly into the cavities 57 and 58 and completely fills out the hollow space 66 radially outside the sealing ring 59. Instead of achieving an elas¬ tic back positioning of the sealing material to the star¬ ting position, when the medium pressure again falls back to the normal medium pressure, the elastic properties of the material will then disappear to a greater or smaller degree, so that the sealing ring in the continuation becomes unusable for the purpose and therefore must be replaced. In such a case there is an advantage that the connection between the members 10 and 11 is formed by a rapid coupling.

Even if there is only shown herein the solution in connection with rapid coupling, it must be understood that the solution can also be employed in connection with other couplings, for example in connection with the illustrated "hub" couplings or in connection with other couplings such as normal flange couplings with associated series of fastening bolts. In other words it will also be possible to employ the same sealing principle as shown in the rapid coupling for the more or less permanent couplings illu¬ strated also. It will also be possible to design such alternative couplings with prestressing forces correspond¬ ingly as mentioned above. In such cases a wedge-truncated sealing ring of highly elastically yielding, rust-free steel is employed in the joint between the axially impac¬ ting members and then with a possibility of movement of the sealing ring radially inwards into an extension

chamber loacated radially just outside the sealing ring. If necessary in such instances provision can also be made for the radially innermost surface of the sealing ring to then extend in alignment with the equivalent inner surface of the pipe conduit before prestressing is effected be¬ tween the members correspondingly as described above.

In order to ensure that the radially innermost sur¬ face of the sealing ring is automatically in alignment with the inner surface of the pipe conduit in each case, one can provide the sealing ring as shown in Fig. 5 with an annular, stopper-forming cavity 75 at one, internal edge portion of the sealing ring and provide the member 11 with an equivalent annular stop flange 76 at the equivalent, internal upper edge portion of the member 11.

In order to ensure that the sealing ring 59 is held securely in position on the member 11 during mounting and dismounting of the member 10 in engagement with the member 11, there are fixed for example with a 120° mutual inter¬ mediate spacing three locking members 77 (only the one is shown in Fig. 6) to the member 11 for securing the sealing ring 59 in the intended precise position on the member 11. The locking member 77 is received in a cavity 78 in the member 11 radially just outside the hollow space 66 and projects with a locking stem 79 radially inwards into an annular groove 80 along the periphery of the sealing member 59. The annular groove 80, which projects radially inwards into the sealing member 59, has sufficient depth to be able to secure the sealing ring axially on the member 11 at the same time as the sealing ring is permit¬ ted to be moved radially between the positions as illu¬ strated in Fig. 3 and 4.