CA1317985C

CA1317985C - Pipe connection

Info

Publication number: CA1317985C
Application number: CA000589517A
Authority: CA
Inventors: Lothar Elsner
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-02-01
Filing date: 1989-01-30
Publication date: 1993-05-18
Anticipated expiration: 2010-05-18
Also published as: IL89131A0; MX172184B; CN1037385A; AU3051889A; EP0327080B1; WO1989007221A1; EP0327080A1; PT89588B; EP0473572A1; CN1019682B; DE58907628D1; IL89131A; YU21989A; PT89588A

Abstract

ABSTRACT

A connection for connecting lengths of pipe in end-to-end relation includes a cylindrical coupling element, threaded at each end to receive a threaded coupling member. Internally, the coupling element has a frustoconical surface engageable by a corresponding surface on an annular coupling ring. Internally the coupling ring has a plurality of sharp-edged annular ribs for gripping the external surface of a pipe The clamping ring has a central helical slot extending therethrough, for about four turns, and a flat end surface facing a flat locating surface on the coupling member. The slot winds in the opposite direction to that of the threads between the coupling element and the coupling member. As the coupling member is tightened into the coupling element it will engage the coupling ring to force it into sealing engagement, via the mating conical surfaces, with the pipe, and also to twist the body of the coupling ring, due to the helical slot, to improve sealing and to improve the resistance of the connection to separation.

LCM:HWR

Description

~31L~98~

Pipeline systems generally consist of individual pipes of different lengths, and also of different diameters, which are joined together at their ends with pipe couplings. Located at various points along the systems are fittings of various kinds, for example cocks, valves or shut-off gates which are connected to adjoining pipes in the same way. All of these joints must be as strong and leakproof as the individual lengths of pipe. This applies to both metal pipes and plastic pipes. The latter may be made entirely of plastic, to wit a thermoplastic synthetic material, but they must also be made of a composite material, with reinforcements and reinforcing elements, more particularly in the form of glass fibres embedded in a duroplastic material. These are known as GFR
pipes. Since they are, in any case, made in layers, it is possible to make different layers out of different plastics which are particularly well suited to particular purposes.
In the case of high-strength metal pipes, it is normal to use coupling elements made oE metal, so-called "fittings", the ends of the pipes and the coupling parts being provided with cut threads so that they can be screwed directly together.
There are also cutting ring joints i.n which the end cutting edge of a cutting ring is forced into an internal cone, so that the end cutting edge contracts and cuts into the pipe surrounding it. This kind of pipe joint may also be used for low-strength metal pipes but not for plastic pipes.

~k MLS:HWR

131 7 9 $ ;, For plastic pipes there are permanent joints in which pip2 sections are joined together by welding or gluing, or by means of coupling elements. When the ends of two pipes are welded together, an internal burr is often produced at the weld. This may substantially restrict the internal diame-ter of the pipe and cause turbulence in a fluid passing therethrough. Glued joints require considerable care in their execution which must be carried out by skilled tradesman. Even then, glued joints cannot always be produced on site with lo sufficient reliability. Moreover, glued joints may be attacked by certain fluids and/or by the content of the fluid and, for this reason alone, they cannot always be used. One great disadvantage is that susceptibility to a fluid, or to the content thereof, may be discovered, ovex the course of time, after the joint has been made, in which case the whole system may have to be replaced. Another major disadvantage of both welded and glued joints is that the joints can never be disconnected again when changes are needed in the system and when additional connections are required.
For pipeline systems using plastic pipes there are also detachable joints in the form of clamped connections of different designs. Common to all of these is a clamping part which can be deformed, a clamping ring, between which two conical locating surfaces, adapted to move in relation to each other, are clamped axially. As a result of the resilient change in shape produced, the clamping ring bears tightly, on the one hand against the pipe and, on the other had, against MLS:HWR 2 :

-.~ .~"

. .

~3~73~5 another part of the pipe coupling, thus uniting khe two ends of the pipe firmly together.
In many of the clamped pipe connections, a supporting sleeve is frequently required. This may either be a loose part which is inserted into the end of the pipe, or it may be moulded to the ccupling element, being pushed into the pipe with the coupling part when the pipe is joined.
These supporting sleeves, which are of many kinds, have the major disadvantage of bringing about a considerable cross sectional constriction in the pipeline. This always results in a corresponding pressure drop and is often associated with a considerable amount of noise. In the case of pipeline systems comprising a large number of fittings, pressure drops at successive joints may add up to a very high value. The use of supporting sleeves also has another major disadvantage, namely that the end of the pipe must be heated before the supporting sleeve is pushed into it or before the pipe is pushed into the coupling element with the moulded-on sleeve.
Unskilled heating may damage the pipe. There are also clamped pipe connections without supporting sleeves, in which the clamping rings are always slotted continuously at a peripheral location because, in the absence of the supporting sleeve, resilient deformation of the pipe is relatively major, especially in the vicinity of the conical surfaces between the supporting ring and the coupling screw. ~n additlon to this, and especially in the case of pipes made of a thermoplastic synthetic material, it is known that dimensional tolerances are very larqe and a large change in diameter and/or diametrical MLS:HWR 3 ~3~.7~

tolerance, must be bridged. This longitudinal slotting makes it impossible for the clamping rings to ensure a seal, making it necessary to use an O-ring as the actual sealing element.
A recess is provided in the coupling element.
In one type of clamped pipe connection, the O-ring is inserted into a groove having two shoulders on the inside of the coupling element. It is pressed by the fluid itself against the shoulder lying outside in the direction of pressure, and this provides the sealing action. In ano-ther type of clamped connection, the 0-ring is inserted into an axial recess in the coupling element, where it bears against one side of the O-ring and this is pressed against the 0-ring by the pipe joint coupling screw. It is thus deformed resiliently in the remaining cavity and bears tightly, in the radial direction, on the one hand against the coupling element and, on the other hand, against the outside of the pipe.
In the first of these clamped pipe connections, the pipe is held by a clamping ring which is seated upon the pipe externally of the O-ring and is pressed against the coupling element by a coupling nut. The latter comprises an internal conical surface which co-operates with an external conical surface on the clamping ring and, when the coupling nut is tightened, ensures that the sharp inner edges of the peripheral annular ribs, located on the inside of the clamping ring, cut into the outside of the pipe. In the second of these clamped pipe connections, the clamping ring is located between the thrust-ring for the O-ring and the internal conical surfaces, remote therefrom, of a coupling screw. This clamping ring, MLS:HWR 4 ~7.3~9 when the coupling screw is tightened, is also dePormed radially, inwardly and resiliently so that, here again, the internal annular ribs cut into the outside of the pipe. At the same time, the head of the coupling screw presses the thrust-ring against the O-ring.
In these two types of clamped pipe connection, the 0-ring ensures sealing at the joint, whereas the annular ribs on the inside of the clamping ring provide the necessary holding force between the pipe and the coupling. This force cannot be provided by the O-ring alone but is necessary to prevent the pipe system from being pulled apart by the pressure of the fluid. These clamped pipe connections having O-rings have the disadvantage that the O-rings do not have a very long life and that they undergo changes in the course of time when used with fluids at varying pressures and, especially, at varying temperatures, as a result of which the sealing action declines or disappears completely. In this connection, the increasing creep in the material of the O-rings is a disadvantage.
These clamped pipe connections also have the disadvantage that the clamping ring is clamped between the pipe and an internal ronical surface of the coupliny nut or coupling screw, so that as these are tightened, considered torque is applied to the pipe through the adjacent conical surfaces. If fittings are already connected to the pipeline, twisting of the pipe must be prevented. If the pipe is held by existing fittings, the clamped connections thereof may be loosened again. If the pipe itself is held, it may be damaged since this re~uires the use of grips.

MLS:HWR 5 r~ . ~ '2 In these clamped pipe connections, the clamping force of the clamping ring is produced by co-operation between the conical surfaces and the clamping ring, on the one hand, and the coupling nut or screw on the other hand. Since the flank-angle is relatively steep in relation to the longitudinal axis of the pipe coupling, the conical surfaces have only a very short axial extension and the radial force applied to the pipe by the clamping ring is concentrated in a very short longitudinal section of the pipe. This means that the pipe is subjected to very high local stresses, leading to relatively sharp resilient constriction at this location. There is also the danger of the annular ribs on the cutting ring cutting very deeply into the outside of the pipe over this short longitudinal section. This causes a considerable notch-effect in the pipe, concentrated over a very short length, leading to a very considerable reduction in the fatigue strength of the pipe.
It is the purpose of the invention to provide a clamped pipe connection which has greater fatigue strength than existing clamped connections.
When the coupling screw or coupling nut, as the actuating member of the clamped connection, is tightened, the clamping ring is first of all pressed axially into the very slender internal cone of the coupling element which is thus constricted resiliently. As the resistance to displacement in the unslotted longitudinal section at the front end of the clamping ring increases, so does the axial locating force at the rear end of the clamping ring, and the also flat locating MLS:HWR 6 ~7~
surface on the actuating member increases. This increases the frictional force between these two surfaces in the peripheral direction. The spiral slot then causes the adjacent turns of the clamping riny to constrict, so that its external conical surface bears less heavily against the internal conical surface of the coupling element, while the cylindrical inner side bears increasingly heavily upon the pipe. In this way, the unslotted longitudinal section at the front end of the clamping ring is pushed over further into the internal cone of the coupling element which, because of its resilient, inward, radial deformation, bears fully upon the pipe. If the pipe is smaller in relation to the nominal diameter of the clamping ring, and/or if the radial elasticity of the pipe i5 greater, the unslotted longitudinal section may also be deformed plastically, i.e. it may be permanently constricted. When the unslotted longitudinal section is constricted, the annular ribs thereon dig into the outside of the pipe and ensure a satisfactory seal between it and the clamping ring. On the outside, the very slender conical surfaces of the unslotted longitudinal section of the clamping ring and of the coupling element, ensure very good sealing between them as they bear against each other, with no need for additional sealing elements in the form of O-rings.
During this procedure, the turns of the clamping ring adjacent the unslotted longitudinal section gradually enter an axial area of the coupling ring where they not only bear firmly upon the pipe with theix internal surfaces, but where their external conical surfaces bear firmly upon the internal conical MLS:HWR 7 rl/ 9 ~ ~

surface of the coupling element. The annular ribs on the insides of the turns of the clamping ring dig into the outside of the pipe. In the case of the turns adjacent the unslotted longitudinal section of the clamping ring the wall thickness increases constantly towards the rear end, and in these turns the moment of resistance to bending also increases constantly and progressively. The result of this is that, under the action of the peripheral force arising when the coupling screw or coupling nut on the rear side of the clamping ring is tightened, the turns of the slotted longitudinal section bear with decreasing intensity upon the pipe, and the annular ribs thereon accordingly dig, with decreasing intensity, into the wall of the pipe. The pipe is thus clamped and held over the entire length of the clamping ring. However, there is no local mechanical overstressing of the pipe at any point in the axial area of the clamping ring. Since the depth to which the annular rings dig in decreases towards the rear end of the clamping ring, the ribs cause no unwanted notch-effect at the transition to the free section of pipe outside the clamping ring. As a result of the large number of annular ring, or annular-rib sections, digging more or less deeply into the outside of the pipe, the pipe is prevented from being pulled out o~ the coupling by the pressure exerted by the fluids in the pipeline system.
Since there are no sealing elements made of elastomeric materials, no ageing of the seals can occur. Since a greater length of pipe end is clamped, with correspondingly improve distribution of radial and axial clamping and retaining forces, MLS:HWR 8 .

~317~
local overstressing of the pipe n~ed no-t be ~eared. A clamped pipe connection of this kind thus acquires a fatigue strength at least approaching that o~ the pipe outside the joint, if not equalling it. This is far greater than the fatigue strength to be expected with conventional clamped pipe connections.
Another advantage of this clamped pipe connection is that the unslotted longitudinal section of the clamping ring has the least wall-thickness and is therefore easily deformed, even with a closed ring. Because of this, and of the great elasticity of the turns in the slotted area of the clamping ring, the thread for the coupling screw or coupling nut may be relatively coarse. It is even possible to use the thread normally used with metal fittings for the relevant pipe diameter. If necessary it is possible to screw a normal drain plug into the coupling element, or to screw a fitting having a normal pipe thread thereto. This eliminates the need for adapters with different types of thread.
In one configuration of the clamped pipe connection according to this invention, the production of spiral slots is ~0 facilitated by making it possible to clamp the clamping ring at both ends. The unslotted longitudinal section also prevents the final turn from running out to a pointed end which, because of the decreasing moment of resistance to bending, would be more exposed to the constricting action of frictional contact with the coupling screw or coupling nut. This also prevents sharp points at the rear ends of the clamping rings which could cause injury when handled, especially if the points have been inadvertently bent. The cylindrical external surface of the MLS:HWR g -~3~ 7~
unslotted longitudinal section prevents the latter from becoming jammed in the external cone o the coupling element, before the remaining parts of the clamping ring have been pushed far enough into the internal cone of the coupling element.
One form of the clamped pipe connection makes it possible to achieve a balanced relationship between axial displacement and axial displacement force, on the one hand, and adequate radial and axial clamping force, on the other hand.
This applies more particularly to GFR pipe which can be produced with relatively small dimensional tolerances. In the case of pipes made entirely from one thermoplastic synthetic material, which usually have larger dimensional tolerances, it may be desirable to make the angle of inclination of the internal conical surface on the coupling ring larger, up to about 10. Reducing the angle of inclination of the external conical surface of the clamping ring ensures that the increase in the angle of inclination of a surface enclosing the clamping ring, such as occurs when the turns of the slotted longitudinal section are pushed together, is again compensated for and is adjusted to the constant angle of inclination of the internal conical surface of the coupling element.
Another configuration of the clamped pipe connection of this invention ensures that, when the coupling screw or coupling nut is tightened, the annular ribs on the clamping ring dig sufficiently far into the outside of the pipe, not only sealing it well to the outside but also holding it mechanically. On the other hand, and especially in the case MLS:HWR 10 :.

:

:-~ 3 1~

of GFR pipes, the glass-fibre reinforcing is not cut through, at least not detrimentally. The vertical front sides of the annular ribs ensure very great resistance by the clamped pipe to being pulled out. The rounding of the rear sides ensures that the material on the outside of the pipe is not displaced too much to the side and is not thereby detached from the underlying layers of material.
The configuration of the clamped pipe connection also ensures satisfactory clamping of the slots of the central longitudinal section and ade~uate stabilizing of the turns with central guidance.
The configuration of the clamped pipe connection further ensures a balanced relationship between secure clamping and retention of the pipe and restriction of the overall length of the connection.
The clamped pipe connection according to this invention ensures that the annular ribs are strong enough to penetrate into the outside of the pipe and have adequate resistance to bending in order to withstand forces seeking to pull the pipe out.
Furthermore the clamped pipe connection of this invention makes it possible for a corrosion protection agent to protect the clamping ring, specifically or generally prophylactically, at the ends and at the stepped section, against corrosive attack by fluids or by the contents thereof.
This makes it possible to protect a brass clamping ring from dezincificati~n, so that there is no need to use a special material for the clamping ring in the presence of either very MLS:HWR 11 3L 3 ~ rJ ~ ~ ~

pure fluids or very aggressive fluids. The stepped part of the exkernal conical surface on the unslotted longitudinal section of the clamping ring serves to take up the corrosion protection agent with a layer thickness preferably of o.l mm and, when the clamping ring is slid, and above all pressed, into the external cone of the coupling housing, the coating of corrosion protection agent is not shaved off. The groove at the end of the stepped section serves to take up the amounts of corrosion protection agent which project from the geometrical boundary of the external conical surface and are therefore pushed away by the pressure of the clamping ring. The sharp edged transition between the rear wall of the groove and the unstepped external conical surface ensures that any corrosion protection agent adhering -to the internal conica~ surface of the coupling element is shaved off when the clamping ring is pressed in, so that the agent cannot impair the uniformly close fit of the unstepped section of the unslotted longitudinal section of the clamping ring. Since the end of the spiral slot is secured at a certain distance from the groove, this ensures 2~ an adequately wide supporting surfacs for the unslotted longitudinal surface of the clamping ring upon the inkernal conical surface of the coupling element which provides external sealing of the clamping ring. In the developm~nt of the clamped pipe c~nnection the corrosion protection agent may be applied relatively easily and reliably. ~he choice of the corrosion protection agent depends upon circumstances at the point o~ use.

MLS:HWR 12 ,' : :
-. : - ~

:~3~J3g ~

When glass-fibre reinforced plastic is used for the clamping ring and the coupling element, these parts have the same, or at least similar, properties as regards resilient deformation and/or changes in shape and dimensions. In this way, the behaviour of the clamped pipe connection, and that of the pipe coupled thereto, are approximated. It is also possible to ensure that the annular ribs on the inside of -the clamping ring have relatively high dimensional stability, permitting reliable penetration and digging into t~e outside of the pipe to be secured, the outer layer of which usually has relatively little strength.
The clamped pipe connection may be configured to ensure that the pipes may be pushed into the connection easily and without damaging either the clamping ring or the pipe itself, if the connection is already preassembled and the clamping ring is seated loosely in the internal cone of the coupling element and is held and covered by the partly screwed-in coupling screw or the partly screwed-on coupling nut.
The clamped pipe connection according to this invention makes it easier to insert the coupling ring into the coupling element, especially since, because of the spiral slot, the clamping ring has less dimensional stability than an unslotted ring and is therefore more readily subjected to slight changes in shape during storage and handling.
In another configuration of the clamped pipe connection, when the coupling screw or coupling nut is tightened, the locking ring placed between it and the clamping ring is deformed in such a manner that its outer edge digs into the MLS:HWR 13 . . .

l~7~

matching cylindrical surface of the coupling element and the locking ring is locked to some extent to the coup]ing element, so that the clamping ring, which clamps and seals the pipe~ is held in its clamping and sealing position if the coupling screw or coupling nut, for any reason whatsoever, becomes loose or yields in some other way. This conEiguration may therefore be considered for pipe connections which either need never be released or which require greater safety against becoming disconnected and/or leaking~ This applies above all to covered pipelines which are not easily accessible at a later date.
In the case of yet another configuration of the clamped pipe connection of this invention, the radial depth of the recesses between the annular ribs follows the depth of penetration of the annular ribs into the outside of the pipe, which decreases from the front to the rear end of the clamping ring. Thus in the central and rear part of the clamping ring, the peripheral surface of the recesses guiding and retaining the clamped pipe is also made use of, so that the pipe is not hollow in this area between the annular ribs. This prevents a possible notch effect by the annular ribs, especially in the rear part of the clamping ring when the clamped pipe is subjected to bending. This applies in particular to designs of the clamping ring in which there is an unslotted longitudinal section at the end which has a smooth internal surface.
Using a coupling nut instead of a coupling screw makes it possible for the coupling element to be considerably shorter because the thread for it can be located on the outside of the LCM:HWR 14 `` ~ 3~7~

coupling element in approximately the same longitudinal section as that upon the inside of which the internal conical surface for the clamping ring is located. In addition to this, i-t is usually possible also to reduce the outside diameter of the coupling element, since the internal thread for the coupling screw has a larger inside diameter than the internal conical surface must have with its large diameter. The configuration of such a connection, with the collar-like extension of the coupling nut, permits longer axial travel of the rear end of the clamping ring since, in case of need, the extension may be moved into the coupling element. This reduces the dependency upon close production tolerances in thesè connections, above all in the case of the pipe.
In another configuration of the clamped pipe connection a shoulder ensures that a pipe, inserted into the connection, is inserted as ~ar as is necessary to achieve reliable clamping and sealing. This also prevents the pipe from being inadvertently pushed beyond the correct position and into the area of the adjoining clamped pipe connection, in which case the pipe to be inserted can no lon~er reach its correct position. Since a cylindrical surface adjoins the shoulder, and matches the outside diameter of the pipe, the pipe inserted into the connection is centred accurately in the coupling element itself, i.e. independently of the random axial and radial position of the clamping ring in the coupling element.
The internal conical surface adjoining the cylindrical surface facilitates insertion of the pipe into the longitudinal section with the cylindrical surface and, at the same time, prevents LCM:HWR 15 ~ 3 ~ r~ ~ 8 ~

the pipe from belng halted before it reaches the cylindrical surface. This configuration is always used in preference to the basic design when the resulting extension of the basic element does not prevent its use.
Plastic pipes having greater resiliency, e.g. pipes made of a thermoplastic synthetic material, may be joined reliably together or connected to a fitting. In this case the axial extension of the coupling element acts as a supporting collar for the end of the pipe which supports itself radially, with the matching recess on its inside, upon the supporting collar.
This ensures that, when the coupling screw or coupling nut is tightened, the wall of the pipe cannot yield inwardly under the action of radial force, that the annular ribs in the unslotted longitudinal section of the clamping ring can diy into the wall of the pipe, and that the pipe is reliably sealed. This also holds the pipe securely.
The invention is described in greater detail hereinafter, in conjunction with a plurality of embodiments illustrated in the drawing attached hereto, wherein:
Fig. 1 shows a longitudinal section through a pipe coupling having two clamped pipe connections, each with a clamping ring;
Fig. 2 shows a longitudinal section through one of the clamping rings;
Fig. 3 shows a detail of the clamping ring according to Fig. 2, on an enlarged scale;
~ig. 4 shows part of a longitudinal section through another embodiment of the clamped pipe connection;

LCM:HWR 16 ~3~7'~ j Flg. 5 shows a part of a longitudinal section through a modified embodiment of the clamping ring, to an enlarged scale;
Fig. 6 shows a part of a longitudinal section through a further embodiment of the clamped pipe connection, in the preassembled condition:
Fig. 7 shows part of a longitudinal section through the embodiment accordin~ to Fig. 6, in the assembled condition;
Fig. 8 is in part a longitudinal section through, and in part a side elevation of, an embodiment of the clamped pipe connection comprising a coupling nut;
Fig. 9 is in part a longitudinal section through, and in part a side elevation of, an embodiment of the clamped pipe connection comprising a supporting collar.
Pipe coupling 10, shown in Fig. 1 unites two pipes ll and 12. These two pipes are made of a composite material, to wit glass-fibre reinforced plastic, for which reason they will be referred to hereinafter as GFR pipes.
Pipe coupling 10 comprises, for each pipe 11,12 a clamped pipe connection 13,14 each connection being arranged at one end of the pipe coupling in mirror-image of the other.
The following comments regarding clamped pipe connections 13,14 also apply accordingly to other types of pipe couplings, such as a T-shaped design, or to a wide variety of fittings equipped with at least one clamped pipe connection corresponding to connections 13 and 14.
Each of the two connections 13 and 14 comprises a coupling housing 15,16 of the same design, each forming part LCM:HWR 11 of a one-piece basic element 17 which is made of metal, more particularly of brass. However, consideration may also be given to other materials normally used in pipeline systems.
Basic element 17 is an elongated hollow body of approximately cylindrical configuration. An internal shoulder 18 is located longitudinally centrally of basic element 17, i.e. at the inner end of each coupling element 15,16. The internal, cylindrical, peripheral surface thereof has an inside diameter which is preferably no smaller than that of GFR pipes 11,12 to be united. Internal shoulder 18 constitutes, with its two flat end surfaces which are at right angles to the longitudinal axis of basic element 17, a stop for the ends of GFR pipes 11,12, thus ensuring that the two pipes can be inserted only as far as the middle of basic element 17 and cannot be pushed on into the area of the other connection.
In view of the fact that connections 13,14 are mirror-images of each other, the following explanation is limited to right hand connection 14 in Fig. 1, although it also applies to connection 13.
In additional to coupling housing 16, clamped pipe connection 14 comprises a coupling screw 19 and a clamping ring 20.
Coupling element 16 comprises two longitudinal sections 21,22. The internal surface of longitudinal section 21 adjoining internal shoulder 18 is formed by a very slender internal conical surface 23 running at an angle of at least 4.5 to the longitudinal axis of coupling element 16. Second longitudinal section 22 of coupling element 16 has a LCM:HWR 18 ~ L 7 ~

cylindrical internal surface equipped with an internal thread 24 matching thread 25 of coupliny screw 19. These threads are generally cylindrical pipe threads such as are common in pipe line systems consisting of metal pipes.
The outer end of coupling screw 19 has an external hexagon. The inner end of the screw has a thread-free cylindrical neck 26, the free end of which forms a flat supporting surface 27, running at right angles to the longitudinal axis of coupling element 16, for engaginy clamping ring 20. At least in the vicinity of its end surface, the outside diameter of neck 26 is designed in such a manner that, in the operating condition, i.e. when coupling screw 19 is tightened, it does not touch internal conical surface 23 of coupling element 16. The length of neck 26 is governed mainly ~y the dimensional tolerances and by the deformability of pipes 11,12 which are to be united by pipe coupling 10.
Like coupling element 16, coupling screw 19 is made of metal, again more particularly of brass. The same applies to clamping rings 20.
Clamping ring 20 has a cylindrical inside 28. The outside thereof is in the form of a very slender 2xtsrnal conical surface 29. The angle of inclination thereof, in relation to the longitudinal axis of clamping ring 20, is somewhat smaller, up to 1 smaller, than the angle of inclination of internal conical surface 23 of coupling element 16.
The end surface having the larger conical diameter, at the rear end of clamping ring 20, serves as a locating surface LCM:HWR 19 1.3~793~

31 for coupling screw 19, i.e. for locating surface 27 thereof.
For this reason, surface 31 on clamping ring 20 is also flat and at least approximately at right angles to the longitudinal axis of the ring. At the front end of clamping ring 20, the end having the smaller conical diameter end surface 32 is also flat and at least approximately at right angles to the longitudinal axis of the said clamping ring.
The inside diameter of clamping ring 20 is at least approximately equal to the outside diameter o pipes 11,12 to be wlited. This inside diameter ~ill be referred to hereinafter as the nominal width of pipe coupling 10.
The axial length of clamping ring 20 is preferably at least approximately 0.5 times its nominal width.
As may be gathered from Fig. 2, the central part of clamping ring 20 carries a helical, radially continuous slot referred to hereinafter as spiral slot 33. The direction of the turns in spiral slot 33 is opposite to that of the turns of internal thread 24 in coupling element 16 and to that in thread 25 in coupling screw 19. Spiral slot 33 preferably has four full turns, so that the slotted longitudinal section of clamping ring 20 is divided approximately into three adjacent full turns 34. Spiral slot 33 terminates, in the axial direction, both at the rear and at the front end of clamping ring 20, at a certain distance from the end surface of the clamping ring, so that a longitudinal section 35 at the rear end, and a longitudinal section 36 at the front end, remain unslotted. The axial extension of these unslotted longitudinal sections 35,36 amounts, at least approximately, to 0.1 times LCM:HWR 20 ~3 lL7~3~
the nominal width sf clamping ring 20. The pitch of spiral slot 33 thus amounts, at least approximately, to o.l~ times the nominal width of clamping ring 20.
Unslotted longitudinal section 35, at the rear end of clamping ring 20, as distinct from the remainder of the clamping ring, has a cylindrical outer surface which extends axially at least as ar as the beginning of spiral slot 33, but which may also extend therebeyond.
The illustration in Fig. 3, to an enlarged scale includes a modification to the normal clamping ring according to Fig. 2 in that, in the vicinity of the unslotted front longitudinal section 36, in a section 38 adjoining front end surface 32, the outer surface is stepped inwardly by an amount at least approximately 0.1 mm in diameter. The axial extension of this stepped section 38 preferably amounts to 2.0 mm. ~s another part of this modification, located at the end of stepped section 38 is a peripheral groove 39 which is, at least approximately, 0.1 mm in depth in relation to stepped section 38 and is at least approximately 0.5 mm in width. The rear wall of groove 39, farthest away from front end surface 32, adjoins with a sharp edge, external conical surface 2~ of the clamping ring.
~ f, in the case of clamping riny 20, the modified design comprising stepped section 38 is selected, care must be taken to ensure that spiral slot 33 terminates in the axial direction at least approximately 0.5 mm in front of groove 39, in order to leave, at front unslotted longitudinal section 36 of clamping ring 20, an unstepped section of external conical LCM:HWR 21 ~ 3 ~

surface 29 0.5 mm in length and extending over the entire periphery of the clamping ring between spiral ~lot 33 and groove 39.
In the modified embodiment of clamping ring 20, stepped section 38 serves to take up a corrosion protection agent which is applied beyond steppPd section 38 to the whole of end surface 32. When a clamping ring of this kind is slid into coupling element 13, even when coupling screw 19 is tightened, at least some of the corrosion protection agent remains, in the vicinity of stepped section 38, adhering to the outer surface, it being possible for the corrosion protection agent displaced therefrom to collect in groove 39. Examples of corrosion protection agent are polyethylene, polytetrafluoroethylene, polyamide and also other thermoplastic synthetic materials, the choice of which depends upon the fluid, ox the contents of the fluid, against which the front end of clamping ring 20 is to be protected. The protection agents are preferably applied to the areas to be protected, in the original powder form, by the vortex-sintering prosess.
As already indicated in Fig. 2, and shown still more clearly in Fig. 3, the cylindrical inside of clamping ring 20 comprises a series of peripheral annular ribs 41, closed per se, each arranged in a plane at right angles to its longitudinal axis. The radial height of annular ribs 41 is at least approximately 0.4 mm~ The axial spacing (or division) between them is preferably between 1.2 and 1.4 mm, the small spacing being used with shorter rings and smaller nominal width and the larger spacing with longer clamping ribs and larger LCM:HWR 22 ~L 3 ~ 3 nominal width. Front flanks 42 of annular rigs 41, facing end surface 32, are at lQast approximately at right angles to the longitudinal axis of clamping ring 20. From the sharp annular cutting edge, to the kase of the front flank of next annular rib 41, rear flanks 43 are rounded at least approximately constantly. This applies above all to the smaller longitudinal spacing of annular ribs 41. With wider spacing, and above all with greater nominal width, it may be desirable to allow the curvature of rear flank 43 to run out before the next front flank into a cylindrical surface.
The inside of longitudinal section 35 is chamfered conically at the rear end of clamping rin~ 20. The angle of inclination of chamfer 44, in relation to the longitudinal axis of clamping ring 20, amounts to about 30. The axial extension of chamfer 44 amounts to about 1.0 mm. The cham~er makes it easier to push the pipe to be coupled into the clamping ring.
It is preferable for pipe coupling 10 to be delivered in a pre-assembled condition. To this end, a clamping ring is inserted loosely into each coupling element 15,16 and coupling screw 19 is screwed so far into coupling element 16 that its locating surface 27 bears against locatiny surface 31 of clamping ring 20. In this connection, turns 34 of clamping ring 20 must not bear against each other - in other words spiral slot 33 must still be at least partly open. Pipes 11,12 to be united are pushed into relevant coupling element 15,16 until their end surfaces bear lightly against internal shoulder 18. As soon as coupling screw 19 is screwed into coupling element 16, turns 3~ of clamping ring 20 come together, LCM:HWR 23 ~ 31~8.~

whereupon front unslotted longitudinal section 34 of clamping ring 20 is displaced axially along internal conical surface 23 of coupling element 16. Because of its slight wall thickness, it now constricts, initially resiliently, but subsequently also plastically. In accordance with this constriction, annular ribs 41, on the inside oE longitudinal section 36, cut into pipe 12 and into the outer layer of the GFR pipe. As the axial resistance increases when front unslotted longitudinal section 36 is pressed in, so does the frictional force between locating surface 31 on the clamping ring and locating surface 27 on coupling screw 19. As a result of this, turns 34 of clamping ring 20, adjoining rear unslotted longitudinal section 35, are carried along from front to rear to an increasing degree, so that the turns constrict and annular ribs 41, located on the inside thereof, also dig into the outside of the GFR pipe to an increasing degree. As soon as this procedure has been completed, the end section of pipe 12 is secured and sealed to pipe coupling 10.
Up to now, the explanations have covered the uniting of GFR pipes which can be produced to relatively small dimensional tolerances and which have relatively slight resilient elongation. Pipes made exclusively from a thermoplastic synthetic material, i.e. which lack glass-fibre reinforcement, have not only larger dimensional tolerances but also greater elongation.
In order to unite such pipes, it may be desirable to use a modified design of the clamped pipe connection in which the angle of inclination of the internal conical surface at the LCM:HWR 24 ~3~7~
coupling housing is up to 10 larger, so that the internal conical surface, and the internal thread, need not be excessively long. Because of the larger angle of inclination of the two conical surfaces, it may al50 be desirable to use a fine thread, instead of the normal pipe thread, between the coupling element and the coupling screw so that, in the case of the coupling screw, the ratio between the peripheral force applied to the external hexagon and the advancing force is increased in order to equalize the higher radial force when the front unslotted longitudinal section oE the clamping ring is constricted.
According to another modification of the clamped pipe connection, both the coupling element and the clamping ring are made of glass-fibre reinforced plastic. This may be desirable, even necessary, if the fluid flowing through the pipeline system does not permit the use of metal or suggests a change to plastic parts. In the case of composite GFR materials, the innermost wall layer exposed to the fluid may be adapted, within wide limits, to the requirements of the fluid, with no need for any substantial change to the remaining layers of the composite material.
The transition to a GFR material may also be indicated if, especially when there are large numbers of joints and/or fittings in the pipeline system, the overall weight of the system, or even only the "weight of metall' will be very high, or if, for other reasons, it is desirable or necessary to reduce the proportion o~ metal in thè pipe syskem.

LCM:HWR 25 ~ 7~
In the case of a clamped pipe connection made of GFR
material it is a great advantage for the glass-fibre reinforcement in the clamping ring, in the vicinity of the ànnular ribs, to be at least thicker or, better still, to be aligned completely in the peripheral direction. It is also desirable to use larger amounts of glass-fibre in the material of the annular ribs than in the material of the remaining parts of the clamping ring. This imparts to the annular ribs increased dimensional stability which, in spite of the use of GFR, allows them to dig far enough into the outside, i.e. the outer layer, of the pipe to be coupled, thus sealing it and holding it reliably.
Fig. 4 shows another embodiment of a clamped pipe connection 45 in which the coupling housing 46 is modified to some extent in relation to coupling housing 16 in the basic version.
Adjoining shoulder 47 or, to be more precise, adjoining end surface 48 thereof, is a cylindrical surface 49 and then an internal conical surface 50. The axial extension of surface 49 is preferably not less than 2 mm. The inside diameter thereof is at least approximately equal to, or slightly greater than, the nominal width of clamped pipe connection 45 or of the outside diameter of pipe 1~. Cylindrical surface 49 acts as a guide for the front end of pipe 12, especially if it is inserted into preassembled connection 45~ This ensures that the front end of pipe 12 is guided centrally of the longitudinal axis of coupling housing 46. Internal conical surface 50 serves as a lead-in for the front end of pipe 12.

LCM:HWR 26 ~3~7 ~
The angle of inclination of the internal conical surface 50 is therefore preferably between 30 and 45. Adjoining this lead-in cone, in the case of pipe connection 45, is internal conical surface 51 for clamping ring 20 which is of the same design ~s corresponding internal conical surface 23 in coupling housiny 16 (Fig. 1). The remaining parts of coupling housing 46, like coupling screw 19, are the same as the corresponding parts in the design according to Fig. 1.
Fig. 5 shows a clamping ring 52 which is a modification of clamping ring 20. In central longitudinal section 54 of clamping ring 52, slotted by spiral slot 53, the radial depth of annular recesses 55, between each two annular ribs 56, decreases from the front end of longitudinal section 54, towards its rear end, from a maximum value to zero. The maximum value of the depth of recesses 55 is at least approximately equal to the radial depth of corresponding recesses 57 in front unslotted longitudinal section 58 of clamping ring 52. Since the radial depth of recesses 55, at the rear end of slotted longitudinal section 54, has reached the value of zero, there are no internal recesses in rear unslotted longitudinal section 59 of clamping ring 52, and therefore also no annular ribs. This interior is therefore a smooth cylindrical surface 60.
FigsO 6 and 7 show another embodiment of a clamped pipe connection 61. In this case, a cylindrical surface 64 adjoins the inside of coupling element 62 at the outer end of internal conical surface 63 for clamping ring 20, the inside diameter of the cylindrical surface 64 being larger than the outside LCM:HWR 27 '' '~ :

13~79~
diameter of the rear end of the clamping ring, and ,ls thus larger than the outside diameter of the unslotted rear longitudinal section 35 of the clamping ringO The inside diameter of cylindrical surface 64 is matched to internal conical surface 63 in such a manner that transition 65, between internal conical surface 63 and cylindrical surface 64 is located within the longitudinal section of coupling element 62 which takes in clamping ring 20 after coupling screw 19 has been tightened (Fig. 7). The axial extension of cylindrical surface 64, starting from transition 65, is such that/ when clamping ring 20 is inserted in the tightened condition, the cylindrical surface extends beyond the rear end of clamping ring 20 (Fig. 6).
A locking ring 66 is inserted or interposed between rear end surface 31 of clamping ring 20 and front end surface 27 of coupling screw 19. The inside diameter of locking ring 66 is no smaller than the nominal width of clamping ring 20 or, even better, is no smaller than the inside diameter of coupling screw 19. Locking ring 66 has two end surfaces 67,68 running parallel with each other. Locking ring 66 is made conical so that its two end surfaces 67l68 are in the form of the surface of a truncated cone. The angle between truncated conical end surfaces 67l68 is between 60 and 75l preferably about 68.
With locking ring 66 in its unbraced condition of rest (Fig.
6), peripheral surface 69 thereof is a cylindrical surface in relation to the centreline of the locking ring. Above all, peripheral edge 70, between peripheral surface 6~ and inner end surface 68, has a sharp edge.

LCM:HWR 28 - .

When clamped pipe connection 61 is tightened, lockin~
ring 66 is first pressed by coupling screw 19 against clamping ring 20 and is pushed, therewith, for a certain distance, into coupling element 62 (Fig. 7). As soon as the front end of clamping ring 20 has contracted to such an extent that it clamps pipe 12 and seals it, and the resistance to displacement at the rear end of the ring has therefore risen to a higher value, locking ring 66 is pressed flat between rear end surface 31 of clamping ring 20 and front end face ~7 of coupling screw 19 (Fig. 7). Peripheral surface 69 is thus pressed outwardly and peripheral edge 70 thereof digs into cylindrical surface 64 of coupling element 52. Locking ring 66 is thus to a certain extent locked to coupling element 32. Even if coupling screw lg were to become loose, locking ring 66 would ensure that clamping ring 20 cannot expand axially since the axial force exerted by it would cause the locking ring to dig more deeply into cylindrical sur~ace 64 of coupling element 62.
Clamped pipe connection 61 may be considered for pipe connections which will not be disconnected again once they have been united, or even when there i5 a requirement for prevention of inadvertent release of the connection for any reason whatsoever.
Fig. 8 shows a pipe coupling 71 which is a modification of previously explained pipe coupling such as those of Figs.
1 and 4 in that the two connections 72,73 are e~uipped, not with coupling screws, but with two coupling nuts 74. Thus the longitudinal sections, which in the case of coupling housing 46 comprise the intarnal threads for the coupling screws, are LCM:HWR 29 ~317~
missing from coupling housing 75. Apart from this, the interior of coupling housing 75, in the vicinity oE clamping ring 20, is of the same design as coupling housing 46 ~Fig. 4).
Reference is therefore made to the explanation covering the latter housing.
In coupling housing 75, internal conical surface 76 for clamping ring 20 has an axial length which is shorter than internal conical surface 51 on coupling housing 46. Internal conical surface 76 is so short that when clamping ring 20 (Fig.
8) is in its operating or clamping position, its rear unslotted longitudinal section 35 projects partly from coupling housing 75.
External thread 77 for coupling nut 74 is arranged approximately in the same longitudinal section as internal conical surface 76 but on the outside of coupling housing 75.
Between the two longitudinal sections with external thread 77 for the two coupling screws 74, coupling housing 75 comprises a longitudinal section 78 which is provided with wrench flats 79 in tha form of a hexagon or an octagon.
Coupling nut 74 carries a circular shoulder 81, the inside diameter of which is no smaller than the nominal diameter of pipe 12 to be coupled and is preferably even slightly larger. Adjoining the intexnal end surface of shoulder 81r in the axial direction, is a collar-like extension 82, the inside diameter of which is the same as that of shoulder 81. .The outside diameter of extension 82 is no larger than the outside diameter of rear unslotted longitudinal section 35 of clamping ring 20. The axial length of extension LCkI:HWR 30 ~ 3 ~L r~ ~ ~ r~

82 is generally between 0.5 and 2.0 mm. The end surface of collar-like extension 82 forms locating surface 83 for clamping ring 20. Collar-like extension 82 provides longer axial actuating travel for cou~ling nut 74 since, in case of need, extension 82 may be moved into coupling housing 75. This enables coupling nut 74 to apply an axial force to the rear locating surface of clamping ring 20 when rear longitudinal section 35 of clamping ring 20 is already completely submerged in coupling hose 75. This condition could occur if the production tolerances of all co-operating parts, especially those relating to the diameters of internal conical surface 76, clamping ring 20 and pipe 12, were to combine adversely.
Fig. 9 shows another modification of the clamped pipe connection. Externally, pipe coupling 85 is similar to pipe-coupling 71 (Fig. 8). Each clamping connection also comprises a coupling nut 88 similar to coupling nuts 74. However, coupling housiny ~9 has a modified central longitudinal section, as compared with coupling housing 75. The reason for this is that pipe coupling 85 is intended for plastic pipes 91,92 which are made of a thermoplastic synthetic material.
Because of the low strength of this material, such pipes have much thicker walls than GFR pipes 11,12.
The inside of central longitudinal section 93 of coupling housing 98 carries a shoulder 94, the inside diameter of which is no smaller than the inside diameter of pipes 91,92.
On each end surface of shoulder 94, an external annular area has an at least approximately flat end surface 95 which is at right angles to the longitudinal axis of coupling housing 89.

LCM:HWR 31 Moulded to each side of the inwardly adjoining inner annular area is an axial extension 96. Inner peripheral surface 97 of extension 96 is an at least approximately cylindrical surface, the inside diameter of which is equal to the inside diameter of shoulder 94. External peripheral surface 98 is in the form of a truncated cone, the surfaces of which are at an angle of between 20 and 45~ to the longitudinal axis of coupling housing 89. In Fig. 9, this angle is 30.
Each of the two pipes 91,92 is provided, on the inside, at the end co-operating with pipe coupling 85, with a recess 99 matching axial extension 96 and thus appearing as the surface of a hollow truncated cone.
As may be gathered from Fig. 9, the outside diameter of extension 96, at the transition to shoulder 94, i.e. at its thickest point, has an outside diameter smaller than that of pipes 91,92. This leaves a flat circular end surface loo at the ends of pipes 91,92 externally of truncated conical recess 99 .
In order to allow recess 99 in pipe 91 or 92 to co-operate correctly with extension 96 on coupling housing 89, andto allow extension 96 to act as a supporting collar for the relevant pipe, it is desirable, when producing recess 99, probably with a conical counterboring tool, to machine end surface 100 at the same time. This ensures that end surface 100 is smooth and flat an that the sawing of the pipe has not left any irregularities which may prevent the end of the pipe from being pushed in until recess 99 bears against extension 96 to shoulder 94. The simplest way of accomplishing this is LCM:HWR 32 13~7 ~ ~3 ~
to combine the conical counterboring tool with a flat counterbore, so that recess 99 is produced and end surface 100 is machined simultaneously. In this connection, care must be taken to ensure that the depth of recess 39 is no greater than the length of extension 96 so that, when the pipe is inserted, recess 99 seats upon extension 96 before end surface 100 comes up against shoulder g4.
In the example of embodiment of clamped pipe connections according to Fig. 9, the end of the pipe is centered internally by conical extension 96. This makes it possible to dispense with the external guiding surface which is formed, in the example according to Fig. 4, by cylindrical surface 49 in front of internal conical surface 50. In khis respect the example according to Fig. 9 corresponds to the example according to Fig. 1.
Instead of a truncated conical peripheral surface 98, the axial extension to shoulder 94 may also have a cylindrical peripheral surface, but it is desirable for the outer edge of the free side of the extension to be chamfered, thus providing a kind of lead-in cone. The recess on the inside of the pipe must also be made cylindrical in order to match the cylindrical shape of the extension. However, the cylindrical shape of these two surfaces is more sensitive to production tolerances in diameter dimensions.

LCM:H~R 33 1 317~38~

lo pipe-coupling 55 recesses 11 GFR pipe 5S annular ribs 12 GFR pipe 57 recesses 13 clamped pipe connection 58 longitudinal section 14 clamped pipe connection 59 longitudinal section 15 coupling element 60 cylindrical surface 16 coupling element 6~ clamped pipe connection 17 basic element 62 coupling element 18 internal shoulder 63 internal conical surface 19 coupling screw 64 cylindrical surface 20 clamping ring 65 transition 21 longitudinal section 66 locking ring 22 longitudinal section 67 end surface 23 internal conical surface 68 end surface 24 internal thread 69 peripheral su:rface 25 screw thread 70 peripheral surface 26 neck 71 pipe coupling 27 locating surface 72 clamped pipe connection 28 inside surface 73 clamped pipe connection 29 external conical surface 74 coupling nut 31 locating surface 75 coupling housing 32 end surface 76 internal conical surface ~3 spiral slot 77 external thread 34 turns 7~ longitudinal section 35 longitudinal section 79 wrench surfaces 36 longitudinal section ~1 shoulder 37 outer surface 82 extension 38 stepped section 83 locating surface 39 groove 85 pipe coupling 41 annular ribs 86 clamped pipe connectlon 42 front flank 87 clamped pipe ~onnection 43 rear flank 88 coupling nut 44 chamfer 89 coupling housing 45 clamped pipe connection 91 plastic pipe 46 coupling housing 92 plastic pipe 47 shoulder 93 longitudinal section 48 end surface 94 shoulder 49 cylindrical surface 95 end surface 50 internal conical surface ~6 extension 51 internal conical surface 97 internal peripheral surface 52 clamping ring 98 external peripheral surface 53 spiral slot g9 recess 54 longitudinal section ~00 end surface LCM:HWR 34

Claims

1. A clamped pipe connection having the following characteristics:
a hollow coupling element comprises, for the support of a clamping ring, and internal conical surface, the major diameter of which faces a free end surface of the coupling element at the mouth of its cavity;
the coupling element comprises, adjoining its free end surface, an internal thread, arranged centrally of the internal conical surface, for a coupling screw, or an external thread for a coupling nut;
the coupling screw or coupling nut comprises an end supporting surface for the clamping ring;
the clamping ring carries, on its internal cylindrical surface, a number of closed annular peripheral ribs, each of which is arranged in a plane at right angles to its longitudinal axis;
the internal edge of each annular rib has a sharp edge;
the outside of the clamping ring has an external conical surface which matches approximately the internal conical surface of the coupling element;
characterized by the following characteristics:
the internal conical surface (23) on the coupling element (16), and the external conical surface (29) on the clamping ring (20), are at a very small angle to the longitudinal axis;

on the clamping ring (20), the locating surface (21) for the coupling screw (19) or the coupling nut, and on the coupling screw (19) or coupling nut, the locating surface (27) for the clamping ring (20), is made approximately flat and runs approximately at right angles to the longitudinal axis of the clamping ring (20);
the clamping ring (20) carries a helical, radially continuous slot (a spiral slot) which ends in the axial direction at the front end of the clamping ring (20) with the smaller conical diameter at a certain distance from the end face (22) of the clamping ring; and the winding direction of the spiral slot is opposite to that of the thread between the coupling element (16) and the coupling screw (19) or coupling nut.

2. A clamped pipe connection according to Claim 1, characterized by the following characteristics:
the clamping ring (20) also carries at its rear end, having the larger conical diameter a longitudinal section (35) of a certain length which is unslotted; and this unslotted rear longitudinal section (35) of the clamping ring (20) has a cylindrical external surface (37).

3. A clamped pipe connection according to Claim 1 or Claim 2, characterized by the following characteristics:
the internal conical surface (23) of the coupling element (16) is at an angle of approximately 4.5° to its longitudinal axis; and the external conical surface (29) of the clamping ring (20) is at an angle to its longitudinal axis up to 1° smaller than that of the internal conical surface (23) of the coupling element (16).

4. A clamped pipe connection according to Claim 1, characterized by the following characteristics:
the unslotted longitudinal section (36) at the front end o of the clamping ring (20) has an axial extension which is at least equal to the axial distance between two adjacent annular ribs on the inside of the clamping ring (20); and the axial extension of the unslotted longitudinal section (36) at the front end of the clamping ring (20) is preferably at least approximately ).1 times the inside diameter (nominal width) of the clamping ring (20) and also the outside diameter of the pipe (12).

5. A clamped pipe connection according to Claim 1, characterized by the following characteristics:
the annular ribs (41) have a radial height of at least approximately 0.4 mm;
the axial spacing between the annular ribs (41) is preferably between 1.2 and 1.4 mm; and the front edge (42), facing the front end surface (32), of the annular ribs (41), runs at right angles to the longitudinal axis of the clamping ring (20), while the rear edge (43) of the sharp edge of the annular rib (41) is rounded, at least approximately concavely, as far as the base of the front edge (42) of the following annular rib (41) in cross section.

6. A clamped pipe connection according to Claim 2, characterized by the following characteristics:
the unslotted longitudinal section (35), at the rear end of the clamping ring (20), has an axial extension which is at least 0.1 times the nominal width of the clamping ring (20).

7. A clamped pipe connection according to Claim. 1, characterized by the following characteristics:
the spiral slot (33) has at least four full turns; and the pitch of the spiral slot (33) preferably amounts to 0.1 times the nominal width.

8. A clamped pipe connection according to Claim 1, characterized by the following characteristics:
the coupling element (16) and the clamping ring (20) are made of a metal which is stronger than the material of the outside of the pipe (12) to be coupled, or at least than the outside thereof.

9. A clamped pipe connection according to Claim 7, characterized by the following characteristics:
in the vicinity of the unslotted front longitudinal section (36), and in a section of this external conical surface (29) adjoining the front end surface (32), the clamping ring (20) is stepped inwardly to a certain extent, parallel with the said external conical surface;
the radius of this stepped section (38) is preferably 0.1 mm less than that of the remaining external conical surface (29);
the axial extension of the stepped section (38) preferably amounts to 2 mm;
located preferably adjoining the stepped section (38) is a peripheral groove (39) which is preferably 0.1 mm in depth as compared with said stepped section and preferably 0.1 mm in width;
the rear wall of the groove (39) adjoins, with a sharp edge, the external conical surface (29) of the clamping ring (20);
the front end surface (32) of the clamping ring (20) is complete, and the stepped surface (38) is coated with a corrosion protection agent almost as far as the groove (39); and the spiral slot (33) ends at the front end of the clamping ring (20), at least approximately 0.5 mm in front of the groove (39).

10. A clamped pipe connection according to Claim 8, characterized by the following characteristics:
the corrosion protection agent consists of polyethylene, polytetrafluoroethylene, polyamide or of some other thermoplastic synthetic material; and the corrosion protection agent is preferably placed initially upon the clamping ring (20), byhe vortex-sintering process, in the form a powder.

11. A clamped pipe connection according to Claim. 1, characterized by the following characteristic:
the clamping ring, and preferably the coupling element also, are made of plastic, preferably of a glass-fibre-reinforced plastic GFR.

12. A clamped pipe connection, according to Claim 11, made of GFR, characterized by the following characteristics:
in the vicinity of the annular ribs on the clamping ring, the glass-fibre reinforcement is directed peripherally; and there is preferably a larger amount of glass fibre in the material of the annular ribs than in the material of the remainder of the clamping ring.

13. A clamped pipe connection according to Claim .2, characterized by the following characteristics:
the inside of the rear end of the clamping ring (20) is chamfered; and the angle of the chamfer (44), to the longitudinal axis of the clamping ring (20), is preferably 30°, while its axial length is preferably 1.0 mm.

14. A clamped pipe connection according to Claim 2, characterized by the following characteristics:
the outside of the front end of the clamping rings (20 is chamfered; and ` 41 the chamfer (45) is preferably at an angle of 30° to the longitudinal axis of the clamping ring (20), while its axial length is preferably 0.5 mm.

15. A clamped pipe connection according to Claim 1, characterized by the following characteristics:
at the coupling element (62), adjoining the internal conical surface (63) for the clamping ring (20), is a cylindrical surface (64), the inside diameter of which is greater than the outside diameter of the rear end of the said clamping ring;
a transition (65), between the internal conical surface (63) and the cylindrical surface (64), is located within the longitudinal section of the coupling element (62), which the clamping ring (20) includes after the coupling screw (19), or the coupling nut, has been tightened;
inserted between a rear end surface (31) of the clamping ring (20) and the front locating surface (27) of the coupling screw (19), or the coupling nut, is a locking ring (66), the inside diameter of which is no smaller than the nominal width of the clamping ring, while the outside diameter thereof, in the unbraced state of rest, is at least approximately equal to the inside diameter of the cylindrical surface (64) on the coupling element (62);
the two end surfaces (67,68) of the locking ring (66) run in parallel with each other and have the shape of the casing of a truncated cone;
the angle of the casings of the two truncated-conical end-surfaces (67,68) of the locking ring (66), in relation to the central axis of the locking ring (66), is preferably between 60 and 75°; and in the unbraced state of rest, the peripheral surface (69) of the locking ring (66) is a cylindrical surface, and at least the peripheral edge (70), at the transition to the internal end surface (68) of the locking ring (66), has a sharp edge.

16. A clamped pipe connection according to Claim 1, characterized by the following characteristic:
in the slotted longitudinal section (54) of the clamping ring (52), the radial depth of the recesses (55) between the annular ribs (56) decreases, from a maximum dimension at the front end of the slotted longitudinal section (54), to zero at the rear end of said slotted longitudinal section.

17. A clamped pipe connection according to Claim 1 , having a coupling nut, characterized by the following characteristics:
the locating surface (83) of the clamping ring is formed, on the coupling nut (74) by the end surface of a collar shaped extension (82) which adjoins the circular shoulder (81) of the coupling nut (74) in the axial direction, and which extends towards the internal thread (77) of the coupling nut (74);
the circular extension has:
an inside diameter no smaller than that of the rear end of the clamping ring; and an outside diameter no larger than that of the rear end of the clamping ring (20).

18. A clamped pipe connection according to Claim 1, characterized by the following characteristics:
the inside of the coupling element has a shoulder (47), the inside diameter of which is no smaller than the inside diameter of the pipe (12);
the end surface, facing the pipe (12), of the shoulder (47) is at least approximately flat and runs at right angles to the longitudinal axis of the coupling element (46);
adjoining the inside of shoulder (47), the inside of coupling element (46) is a preferably cylindrical surface (49) which has a certain axial extension and whose inside diameter is at least approximately equal to, or slightly larger than, the outside diameter of the pipe (12);
adjoining the cylindrical surface (49) is an internal conical surface (50) which is preferably at an angle of 30 - 45°
to the longitudinal axis of the coupling element (46); and the internal conical surface (51) for the clamping rings (20) adjoins the internal conical surface (51).

19, A clamped pipe connection according to Claim 1, characterized by the following characteristics:
the inside of the coupling housing (89) carries a shoulder (94), the inside diameter of which is no smaller than the inside diameter of the pipe (91,92);

Claim 19 cont'd...

from the end surface, facing the pipe(91,92) of the shoulder (94), an external annular area has at least approximately the shape of a flat end surface (95) running at right angles to the longitudinal axis of the coupling housing;
an axial extension (96) is arranged on, or moulded to, the inwardly adjoining internal annular area of the shoulder (94);
the inner peripheral surface (97) thereof being an at least approximately cylindrical surface, the inside diameter of which is no smaller than that of the pipe (91,92);
the outer peripheral surface (98) thereof being either a cylindrical surface or, preferably, a truncated cone, the casings of which are at angle of between 20 and 45° to the longitudinal axis of the coupling housing (89); and the end of the pipe (91,92), co-operating with the coupling housing (89), is provided on this inside with a recess (99) matching the axial extension (96) oP the coupling housing (89).