GB2038976A - Sleeves for joints in ducts - Google Patents

Abstract

A lining for pipe joints is provided by a sleeve (1) having end portions (2, 3) adapted to be sealed to the pipes and an axially extensible central portion (8), which is preferably corrugated and made of rubber. The sleeve (1) can be used to provide an inner lining to a prior art sealing sleeve (10) joining two pipes, with the sleeve extending radially within but axially beyond the outer sealing sleeve and forming a fail-safe sealing system if the pipes are displaced relative to one another by, for example, earthquake movement. The sleeve may be provided with means (9) for providing controlled leakage, and the outer sleeve may be modified by the provision of a rupturable line (11) of weakening so that if used in a gas main, leakage at a joint is slow but detectable. <IMAGE>

Description

SPECIFICATION Sleeve for joints in ducts This invention relates to a sleeve which is intended to be used in conjunction with a sleeve joint as described in United Kingdom Patent 1200225. In that patent there is disclosed a sleeve which is to be fitted internally within a duct so as to span a joint between two pipes forming the duct. Ring projections are provided on the outer periphery of the sleeve towards the ends of the sleeve and these are going to be forced into contact with the internal periphery of the respective pipes one at each side of the joint. This is done by expanding rings fitted radially inside the sleeve. The effect is to form a complete seal at the junction between the pipes. This system is of value for rendering leak-proof main ducts such as gas mains where the existing packing between the pipe joints may be inadequate.

The system as described in United Kingdom Patent 1200225 is not however completely adequate for situations where there is a reasonable probability of relative movement of the pipe being joined. This might arise through soil instability or, more seriously, through earth tremors or earthquakes. If the sleeve as described in 1200225 was to be used as there instructed in the situation where an earthquake or land subsidence caused the pipes to be drawn apart in their axial direction, one or other of the sets of ring projections would slip on its pipe and, where the pipes had been drawn apart a length of the sleeve would be left unsupported.The sleeve might withstand the pressure of the gas within it and maintain its seal, more likely, especially when there were surges in pressure, it would blow out and there would be a catastrophic loss of gas or other material from within the duct (remembering that in the circumstances envisaged the original packing between the joints would have been rendered completely ineffective).

The object of the present proposal is to modify and add to the seal disclosed in U.K. 1200225 in such a way that it can be used effectively and safely in situations where there is a serious risk of earth subsidence of earthquake.

In this invention we propose to add to the seal seen in U.K. 1200225 by providing a modified sleeve which is to span the pipe joint. The modified sleeve may span over not only the pipe joint but also over a prior art sleeve. It too has ring projections on its radially outer surface which are adapted to be forced into contact with the radially inner surface of the respective pipes to form a seal with them. Between these ring portions ofxthe sleeve of the invention, that sleeve is corrugated so as to allow for axial expansion of its length and therefore to allow the pipes which the ring seals are in contact to be moved apart to a certain extent without rupture of the material of the sleeve or of loss of the seal between the ring seals and the pipes.

This provision of expansibility while the seal is retained represents a first line of defence against dislocation of the joint as a result of earth movements, and such capacity is not provided by the simple sleeve of United Kingdom Patent 1200225.

However, we strongly prefer a more complex arrangement using the sleve of the present invention which arrangement continues to use a prior art sleeve such as that of United Kingdom Patent 1200225 in a manner exactly as there diclosed (with a possible deliberate weakening of that sleeve as will be described below) but uses also the sleeve of the invention as an additional sleeve for the joint. In this arrangement the seal provided by the prior art sleeve is allowed or even encouraged to fail and sealing is then provided by the sleeve of the invention. This arrangement has a double safety-factor and is versatile in that it can be adapted to use where there is a pre-existing prior art sleeve seal without dismantling the latter.

Furthermore it allows the possiblity of'permitting a controlled, minor, leak through the additional sleeve which will serve as an indicator of the failure of the seal afforded by the prior art sleeve.

For this purpose, within the material of the sleeve of the invention and in the concertinaed portion there is preferably provided at least one controlled leak path for gas preferably by means of a window of sintered material formed by a disc of that material moulded into the material of the sleeve during the process of forming the sleeve.

To ensure operation of the controlled leak when pipes have been drawn apart, and when the sleeve of the present invention is being used as an additional sleeve, we prefer to modify the sleeve previously seen in 1200225 so as to provide it with at least one line of weakening in its axial length between the respective sets of ring projections so that when those ring projections are drawn apart that modified prior art sleeve will break at the or a line of weakening.

The purpose of providing a controlled leakage in the second sleeve is to enable, after the subsidence or earthquake, location where disclocation of the joint has occurred so that a permanent and secure resealing may be effected: then the second sleeve according to the invention is not intended to provide a permanent and perfect seal after serious joint dislocation has occurred.

On the other hand if in those circumstances destruction of the joint does occur then in the presence of the second sleeve of the invention there will be no catastrophic loss of gas and the main can remain in service while detection is carried out at the surface to discover the site of dislocated joints.

A particular embodiment of the invention will now be described with reference to the accompanying drawings wherein:~ Fig. 1 is an enlarged section on one radius through the sleeve embodying the present invention, and Fig. 2 is a cross section showing the sleeve of the invention in position within a duct also equipped with a sealing sleeve according to United Kingdom Patent 1200225.

Referring to Fig. 1 a generally cylindrical sleeve 1 embodying the invention is seen in cross section on one radius. The sleeve is formed of a resilient elastomeric material of which the characteristics will be selected in accordance with the intended utilisation of the sleeve i.e. according to the material which will be passing through the duct which it will be sealing.

At each end of the sleeve there is provided on its radially outer periphery a plurality of ridges 2, 3 respectively which are destined to form sealing contact with the radially inner periphery of the pipes being sealed. At each extreme end of the sleeve there is a radially outwardly projecting tapering angled portion 4, 5 forming a sealing lip and which also offers a tapered and comparatively aerodynamically smooth transition between the pipe walls and the sleeve. The radially inner periphery of the sleeve has, opposite where radially outwardly projecting ridges are provided, a groove 6, 7 which is for the reception of an expansible hoop or ring which will be expanded to force the projection 2. 3 radially outwardly against the inner surface of the pipes.

Between its end portions the sleeve 1 has at least one region where it is corrugated or concertinaed. In the embodiment being particularly described there is one region of such corrugations 8 of which the amplitude is such as to allow an extension of 150 mm and of which the wave length is approximately equal to twice their amplitude (by "amplitude" and "wavelength" we mean the properties of the wave seen in a single radial cross-section to the corrugations).

Within at least one of the corrugations 8 and preferably at a portion which is radially innermost there is moulded into the sleeve during its formation a window 9 in the form of disc or plaque of a porous sintered material such as bronze or copper. The material, total numbers and total areas of these windows 9 will be chosen with reference to the chemical properties and viscosity material to pass through the duct with which it is to be used, and the pressure at which it will be conducted.

The sleeve according to the invention is installed at the same time as or as a later addition to a sleeve according to U.K. 1200225 and it is strongly preferred that the sleeve of United Kingdom Patent 1200225 should be modified by the provision of one or more lines of weakening in its central portion between its two sets of radially outwardly projecting ridges. This is to ensure if there is an axial parting of the pipes joined this sleeve will break rather than having one of its sets of ridges being displaced along a pipe: this will ensure that a leak is set up and that a joint which is in unsafe condition shall be detected.

As seen in Fig. 2 within a sleeve 10 according to United Kingdom Patent 1200225, preferably modified by the addition of a line of weakening 11 there is fitted a sleeve 1 embodying the invention.

This lies radially within and extends axially beyond the sleeve 10 and is fitted in exactly the same way as the sleeve 10, by the expansion into the grooves 6 and 7 of split or spring rings 12, 13 so that it is forced into engagement with the respective pipes 14, 15 at each side of a joint 16.

It can be seen that if the pipes 14, 15 move axially apart, the sleeve 10 will either break or develop a leak but the additional sleeve 1, having capacity in its corrugation for axial expansion. will employ that capacity and will not break. However, as soon as a leak path to the outside pipe develops controlled leakage is permitted through the window(s) 9 of the sleeve 1. This will enabledetection of the medium, such as gas, from the duct at the surface above the joint and allow remedial action to be taken in due time. However since this is a controlled leak the duct can remain in service and finding and curing the leak should not be a matter requiring emergency attention.

Instead of being moulded or bonded into the sleeve the discs or plaques 9 can be secured in apertures in it by a mechanical coupling such as a gland.

Claims (12)

CLAIMS:

1. A sleeve for forming a lining between two pipes at a joint between those pipes by being sealed to the respective pipes at its respective end portions, the end portions having on their outer periphery means for sealing them to the respective pipes, the sleeve being axially expansible between its end portions where they are adapted to be held sealed to the respective pipes.

2. A sleeve according to Claim 1 , the sleeve being corrugated to give it axial expansion capacity.

3. A sleeve according to Claim 1 or Claim 2 wherein each end portion is provided on its inner periphery with a groove for reception of an expanding ring for forcing it into engagement with its pipe.

4. A sleeve according to any preceding claim which is provided between its end portions with at least one controlled leak path.

5. A sleeve according to Claim 5 wherein the controlled leak path is a sintered insert in the sleeve.

6. A sleeve for forming an inner lining between two pipes at a joint between those pipes and being sealed at its end to those pipes respectively while being radially within and extending axially beyond an outer lining sealing sleeve, the inner lining sleeve having capacity for axial expansion between its ends.

7. A sleeve according to Claim 4 which is corrugated between its end portions.

8. A sleeve according to Claim 6 or Claim 7 which is provided between its end portions with at least one slow leak path.

9. A pipe joint lined by a sleeve as claimed in any one of claims 6 to 8 as well as by an outer lining sleeve radially outside and axially within the inner lining sleeve.

10. A pipe joint according to Claim 9 wherein the outer sleeve has a rupturable line of weakening between its end portions.

11. A sleeve for forming a lining substantially as herein described with reference to the accompanying drawings.

12. A pipe joint substantially as hereinbefore described with reference to the accompanying drawings.