GB2082278A

GB2082278A - Pipeline Portion With a Socket Joint

Info

Publication number: GB2082278A
Application number: GB8028362A
Authority: GB
Original assignee: Thyssen Industrie AG
Current assignee: ThyssenKrupp Technologies AG
Priority date: 1977-06-10
Filing date: 1978-06-08
Publication date: 1982-03-03
Also published as: CH637459A5; GB2000240B; FR2394007B1; GB2000240A; SE7806743L; GB2082278B; FR2394007A1

Abstract

Pipes are joined by the insertion of an end section 41 of one into a socket 37 of the other. The socket 37 holds a sealing ring 39 behind an annular collar 40. The collar 40 bears (e.g. four) evenly distributed longitudinal centring ribs 47. These limit the decentring of the pipe section 41 while allowing relative longitudinal and angular movements of the pipes. The outer surface of the section 41 has a coating 42 e.g. of PTFE enabling it to slide with low friction and wear relative to the sealing ring 39. The ring 39 may be of ethylene-propylene- rubber, harder than conventional seals, and immune to corrosive media carried by the pipes, which may carry, e.g. hot water for district heating. <IMAGE>

Description

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GB 2 082 278 A 1

SPECIFICATION

Pipeline Portion with a Socket Joint

- A very large number of proposals deal with the making of joints for so-called socket pressure 5 pipes in pipelines in which the pipes are subject to altering longitudinal movements. It is known that underground pipes for transporting in particular liquid and gaseous media are frequently built with cast-iron pipes having socket joints which permit 10 simple and rapid assembly at the site, particularly when a socket and spigot connection is used. An essential advantage of such socket and spigot connections is that the individual pipes of the line can be angled in relation to one another and are 15 movable in their longitudinal and transverse directions, so that they can undergo changes of position resulting from earth movements, traffic loads, and temperature fluctuations.

In one arrangement, which is preferred in 20 practice, an elastic sealing ring bears against a retaining collar provided on the end face of the socket and embracing with clearance the pointed end of the inserted pipe, and engages in an annular groove adjoining the retaining collar. 25 Socket connections of this kind are designed for the use of sealing elements having very good permanent elastic properties, particularly appropriately low residual compressive deformation and with the best possible resistance 30 to ageing. The sealing ring is therefore usually made of natural rubber which has proved successful and has been widely used throughout the world as a sealing material in by far the largest field of application of cast-iron pipes, 35 namely as drinking water pipes.

In addition, a movable socket joint is known in which an elastic sealing ring is disposed with a wide sliding surface in a sealing chamber which is provided in the socket and which lies between a 40 fixed flange ring, which is integrally joined to the material of the socket, and a loose pressure ring adapted to be screwed to the said flange ring, the two rings, which bound the sealing chamber, surrounding the pointed end with adequate 45 clearance permitting a certain angular deflection in the socket, whose width is correspondingly great. The inner end portion of the pointed end is slightly machined and coated with a metallic anticorrosion medium, for example zinc, which is 50 covered by a top coating of cold-setting synthetic resin lacquer of a thickness such that a completely smooth sliding surface withstanding shock, impact, and friction is obtained which is approximately flush with the non-machined 55 surface of the remainder of the end portion of the ~ pointed pipe. The cold-setting synthetic resin composition should absorb not only the frictional forces but also the compressive forces which result from transverse movements and angular "60 deflections in such a manner that no excessively high specific surface pressures can be applied to the metal body of the inserted pipe. The zinc coating should prevent sub-surface rusting of the inserted pipe. A disadvantage of this known construction is that it permits practically no or no noteworthy internal pressures inside the pipeline, since such pressures would make the seal ineffective. A movable socket joint of this kind is in particular not suitable for use for heat transmission pipes in which the seals are subjected not only to mechanical loads but also to considerable thermal loads.

The prior art also includes a movable socket joint for plastic pipelines subjected to chemical and thermal stressing and composed of thermosetting and/or thermoplastic material, which comprise an outer socket pipe provided with tangential grooves to receive rings of circular cross-section and composed of natural rubber, modified natural rubber, grades of synthetic rubber, or plastics materials, such as for example fluorine-coating polymers as sealing material for sliding, wherein it was attempted to achieve an improvement by means of an inner sliding pipe having a coating of a thermosetting material, for example of phenol, formaldehyde resin, epoxy resin, or polyester, with graphite filling as lubricant. The outer socket tube and the so-called sliding tube should be made of the same material as the thermosetting plastics coating with graphite filling on the sliding tube or else of other materials, such as for example hard PVC. The proposed graphite lubrication is intended to permit easier sliding and to reduce wear on the sealing rings. A socket joint of this kind is also not suitable for use in heat transmission pipes.

A socket joint is also ready known which is completely lined with a layer of corrosion-resistant material. Socket joints of this kind may be suitable for special uses in the chemical industry, but cannot be used for underground pipes and in particular are not suitable for use in heat transmission pipes.

The prior art also includes a socket joint which within predetermined limits can absorb expansions and contractions of a piping system which are caused by temperature fluctuations, in this known socket joint a piece of thick-walled piping lying within the elastic limit and having rounded ends and a higher temperature coefficient than that of the piping system is inserted between two pipe ends in a labyrinth-like arrangement, in such a manner that the piece of piping is axially displaceable to a slight extent with play. This socket joint is intended to be used for exhaust gas pipes, but is not suitable for joining pressure pipes because it uses no seals and is therefore not pressure tight. Accordingly a socket joint of this kind is not suitable for using cold or hot water pipes, and even less in heat transmission pipes. The rounded ends of the piece of piping moreover entail relatively high cost for production, because the piece of pipe has a complicated cross-section and is very heavy. If a socket joint of this kind were laid in the ground, even small pieces gf dirt, for example a grain, would be sufficient to make the socket joint untight at its rounded ends. Since the rounded ends are secured by retaining collars provided on

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the pipes and gripping over them, the piece of pipe can moreover adapt itself only to a very slight extent to axial movement, which would in no way be sufficient to compensate for example 5 for the alternating longitudinal and transverse movements which occur in heat transmission pipes. Since the rounded ends of such pieces of pipe are attacked by rust after a relatively short time, even relatively high grade surface treatment 10 of the rounded ends of the piece of pipe will enable the rounded ends lo lie relatively tightly against the associated walls of the socket surrounding them only for a short period of time.

In heat transmission pipes particularly 15 stringent demands are made in respect of alternating longitudinal movability in consequence of axial expansion and contraction. Hitherto these pipelines have been made of steel pipes welded together, thus entailing more 20 complicated assembly and more expensive construction of the pipeline. Apart from the need to do the welding work in the pipeline trench, pipe loops are for example necessary as length compensators and are often disposed in building-25 like walled enclosures which are made of concrete and which may mount to about one-third of the total cost of a heat transmission pipeline.

According to the invention there is provided a 30 portion of a pipeline suitable for use in transporting a medium underpressure, the portion including two pipe sections connected by a socket joint, wherein one of said sections provides the socket of said joint, there being a 35 plurality of longitudinally extending centring ribs circumferentially distributed around and projecting radially into an axial region of said socket, and an elastic sealing ring in said socket axially behind said ribs, an end portion of the 40 other pipe section penetrating into said socket so that its outer peripheral surface sealingly and slidingly contacts the sealing ring so as to maintain sealing contact therewith on relative longitudinal or angular movement of the pipe 45 sections, the ribs being dimensioned and arranged so as to allow substantial relative angular movement of the pipe sections and to limit radial decentring; at least that part of said outer peripheral surface of the pipe section which 50 is contactable with said sealing ring having a low-friction coating.

Suitable embodiments of the invention enable the provision of a portion of a pipeline which consists of at least two pipes and in which the 55 pipes may be subject to alternating longitudinal movements, wherein successive pipes are in each case connected together by a socket joint so as to be movable or capable of angular deflection not only in the longitudinal direction of the pipe but 60 also transversely thereto and also in necessary if such a manner as to be capable of considerable thermal stressing. The portion of pipeline may also be able to withstand a considerable internal pressure and if necessary withstand considerable 65 thermal stressing, such as occurs for example in heat transmission pipelines in which the ;

alternating longitudinal movements of the individual pipes, particularly those resulting from " axiai expansion and contraction are caused by the frequent changes of temperature of the medium transported. The use of pipelines embodying the invention is however not stricted to heat transmission pipelines; they can for example also be used advantageously for pressure gas pipes or the like. All in all, great reliability of the pipe joint and of its tightness may be obtained with the object of saving the cost of expensive compensators and the components which they necessitate, without giving up the advantages of a rubber-sealed joint, such as rapid dismantling and angular movability of the pipes.

It is possible to select for the sealing ring and the coating of the inserted pipe section pairs of materials which comply in optimum manner with requirements in respect of permanent elastic properties of the sealing ring, the resistance of the latter to the medium which is to be transported, and in respect of sliding properties. In this way it is possible to use for the seal an elastomer which is harder than known seals. A pipeline embodying the invention may be constructed with each sealing ring supported against a retaining flange or collar in its socket, the collar embracing with clearance the respective outer surface of an inserted end of a pipe section, the sealing ring engaging in an annular groove adjoining the collar. The invention makes it possible for this tried and tested construction to be used for example for cast-iron pipes for pipelines for transporting hot corrosive media, particularly heat transmission pipelines, particularly if the retaining collar on the respective socket of each double-socket pressure pipe is provided with the axially extending centring ribs which are distributed over its internal periphery. The radial height of the ribs may be adapted to the tolerances of the elements of the joint, so as to ensure adequate clearances. This measure makes it possible to select for the sealing ring and the coating of the pipe piece pairs of material which comply in optimum manner with requirements in respect of the permanent elastic properties of the sealing ring, the resistance of the latter to the medium which is to be transported, and in respect of sliding properties. The radial height of the centring ribs is expediently adapted to the permissible minimum dimension of the inside width of the retaining collar and/or the permissible maximum value of the outside diameter of the inserted pipe. The transverse movability of neighbouring pipes (angling, decentring as the result of earth movements) is thus achieved to such an extent as to permit the most favourable sealing ring material to be used having regard to its permanent elastic properties in each particular case (residual compressive deformation, "

compressive relaxation) without impairing the seal. In suitable embodiments of the invention it is possible to use for the sealing ring an elastomer having greater, optimum hardness than rings

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» usable in the prior art. Such materials are for example elastomers based on ethylene-propylene-rubber (EPDM), which can for example s be used for all constructions which are within the 5 scope of the principle of the invention, for example for the construction of hot water and steam transport pipelines.

In conjunction with a coating of for example PTFE, sealing rings of this kind ensure sliding with 10 very low wear and with slight tendency for the sealing parts lying against one another to adhere to one another, thus providing, in particular for heat transmission pipelines, an excellently suitable socket joint.

15 For the inserted pipe ends a coating of polytetrafluoroethylene of a thickness of 40 microns has been found particularly effective, especially when the elastic seals consist of ethylene-propylene-rubber. With this pairing of 20 material surfaces of the pointed end of the inserted pipe and of the respective sealing ring unexpectedly favourable conditions may be achieved not only in respect of wear-free adhesive and sliding friction but also in respect of the 25 resistance of the sealing ring itself to corrosive hot water, particularly in heat transmission pipelines.

Coatings of metallic materials (in particular a layer of chromium approximately 200 /urn thick) 30 have also been found useful.

A preferred embodiment of the invention will now be described with reference to the accompanying partly schematic drawings in which:

35 Figure 1 is a partial longitudinal section through a socket joint; and

Figure 2 is a cross-section on the line VII—VII in Figure 1.

In the drawing an embodiment of the invention 40 is shown applied to a heat transmission pipeline.

The figures show a joint between two pipes, the end section 41 of one being cylindrical (with a bevelled or chamfered edge), while the illustrated end section of the other pipe is formed as a socket 45 37 with a cavity 38. The socket 37 has four centring ribs 47 on the inner periphery of a sealing ring retaining collar 40. The ribs 47 extend over the width of the collar 40, coaxially to the pipe.

50 The inside width "D" of the retaining collar 40 (including the radial height of the centring ribs 47) and the outside diameter "d" of the push-in pipe section 41 provide the limits for the possible radial decentring of two pipes of a joint, for 55 example as the result of earth movements, the width "D" and the outside diameter "d" are accordingly adjusted to one another, expediently taking into account the tolerance values ; permissible for the required movability. 60 The socket 37 can be produced in a simple manner by producing the centring ribs 47—which are welded or cast on the retaining collar—with radial oversize and machining them down to their required radial height. In one form of construction 65 of the joint connection of this kind, which is intended for particularly stringent requirements, the radial height of the centring ribs 47 is adjusted to the permissible maximum value dmax of the outside diameter of the push-in pipe 41 in 70 such a manner that it is formed by the permissible minimum size of the inside width of the retaining collar and a predetermined fraction of the d tolerance range of the outside diameter of the push-in pipe 41. The value of this fraction which 75 is expendient in each particular case is dependent on the manufacturing plant used; experience has shown that it is usually from one-sixth to one quarter. With a fraction amounting to one quarter of the d tolerance range the height of the centring 80 rib is a maximum of 2.5 millimetres for a nominal width of 300 and a maximum of 2.9 millimetres for a nominal width of 600; the maximum rib height is always obtained when the actual inside width of the smooth portion of the retaining collar 85 4Q is at its maximum permissible value. In this arrangement an elastic sealing material having a residual compressive deformation of about 55% can be used. This permits the use of sealing rings 39 of synthetic elastomers which are highly 90 resistant to corrosive media and high temperatures, particularly ethylene-propylene-rubber for hot water and steam pipelines. In conjuction with a coating 42 of polytetrafluoroethylene, which may have a 95 thickness of about 40 fi, such a sealing ring ensures sliding with particularly low wear and with low tendency towards adhesion between the sealing parts 39, 42 lying one on the other and provides a socket joint which is excellently suited 100 for this application.

Claims

1. A portion of a pipeline suitable for use in transporting a medium under pressure, the portion includincptwo pipe sections connected by a socket

105 joint, wherein one of said sections provides the socket of said joint, there being a plurality of longitudinally extending centring ribs circumferentially distributed around and projecting radially into an axial region of the said 110 socket, and an elastic sealing ring in said socket axially behind said ribs, and end portion of the other pipe section penetrating into said socket so that its outer peripheral surface sealingly and slidingly contacts the sealing ring so as to 115 maintain sealing contact therewith on relative longitudinal or angular movement of the pipe sections, the ribs being dimensioned and arranged so as to allow substantial relative angular movement of the pipe sections and to 120 limit radial decentring; at least that part of said outer peripheral surface of the pipe sections which is contactable with said sealing ring having a low friction coating.

2. A portion of a pipeline according to Claim 1 125 wherein said socket has a flange or collar behind which said sealing ring is retained, and on which said ribs are provided.

3. A portion of a pipeline according to Claim 2 wherein said ribs extend over the whole axial

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lengths of the radially inner face of said flange or collar.

4. A portion of a pipeline according to any one of the preceding claims wherein said coating

5 comprises a layer of polytetrafluoroethylene approximately 40 /urn thick.

5. A portion of a pipeline according to any one of Claims 1 to 3 wherein said coating comprises a metallic material.

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6. A portion of a pipeline according to Claim 5 wherein said metallic material is chromium and is approximately 200 /zm thick.

7. A portion of a pipeline according to any one of the proceding claims wherein the sealing ring

15 comprises ethylene-propylene rubber.

8. A portion of a pipeline according to any one of the preceding claims wherein the radial height of the centring ribs is adapted to the permissible minimum dimension internal diameter of the

20 socket and/or to the permissible maximum diameter of said end portion of the other pipe section.

9. A portion of a pipeline according to Claim 8 wherein the radial height of the ribs is such that

25 the diameter of the cylinder defined by this radially inner portions of the ribs is substantially equal to the permissible maximum diameter of said end portion of the other pipe section.

10. A pipeline suitable for use in transporting a medium under pressure including at least one 95 portion according to any one of the preceding claims.

Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1982. Published by the Patent Office, 25 Southampton Buildings, London, WC2A 1 AY, from which copies may be obtained.

10. A portion of a pipeline substantially as

30 described herein with reference to and as illustrated in the accompanying drawings.

11. A pipeline suitable for use in transporting a medium under pressure including at least one portion according to any one of the preceding

35 claims.

New Claims or Amendments to Claims filed on 7 August 1981

Superseded Claims 1—11.

New or Amended Claims:—

40 1 • A portion of a pipeline suitable for use in transporting a medium under pressure, the portion including two pipe sections connected by a socket joint, wherein one of said sections provides the socket of said joint, there being a

45 plurality of longitudinally extending centring ribs circumferentially distributed around and projecting radially into an axial region of said socket, and an elastic sealing ring in said socket * axially behind said ribs, an end portion of the 50 other pipe section penetrating into said socket so* that its outer peripheral surface sealingly and * slidingly contacts the sealing ring so as to maintain sealing contact therewith on relative longitudinal or angular movement of the pipe 55 sections, the ribs being dimensioned and arranged so as to allow substantial relative angular movement of the pipe sections and to limit radial decentring; at least that part of said outer peripheral surface of the end portion of said 60 other pipe section which is contactable with said sealing ring having a low-friction coating.

2. A portion of a pipeline according to Claim 1 wherein said socket has a flange or collar behind which said sealing ring is retained, and on which

65 said ribs are provided.

3. A portion of a pipeline according to Claim 2 wherein said ribs extend over the whole axial length of the radially inner face of said flange or collar.

70 4. A portion of a pipeline according to any one of the preceding claims wherein said coating comprises a layer of polytetrafluoroethylene approximately 40 ^m thick.

5. A portion of a pipeline according to any one 75 of Claims 1 to 3 wherein said coating comprises a metallic material.

6. A portion of a pipeline according to Claim 5 wherein said metallic material is chromium and is approximately 20 thick.

80 7. A portion of a pipeline according to any one of the preceding claims wherein the sealing ring comprises ethylenepropylene rubber.

8. A portion of a pipeline according to any one of the preceding claims wherein the radial extent 85 of the centring ribs has been selected in dependence on the minimum permissible internal diameter of the socket (excluding the ribs) and/or the maximum permissible diameter of said end portion of the other pipe section. 90 9. A portion of a pipeline substantially as described herein with reference to and as illustrated in the accompanying drawings.