METHOD OF JOINING PIPES AND PIPE JOINT

Abstract: A sealing system is described for joining imperfectly abutting pipes (2), particularly pressurised pipes. The system comprises a sealing member (16), typically sleeve-like and a further member (14) that is rigid and also typically sleeve-like e.g. tubular or wraparound. The rigid member (14) may be positioned either around the sealing member (16) or within it. It therefore acts to support the sealing member (16) and/or to deflect laterally any pressure exiting from the pipes.

Description: Description METHOD OF JOINING PIPES AND PIPE JOINT This invention relates to a method of sealingly joining pipes in end to end relationship, and to an end to end sealed joint between pipes. Where pipes are joined end to end, especially where the diameters of the pipes are relatively large, e.g. greater than 300 mm, especially greater than 800 mm diameter, it is sometimes difficult to achieve a perfect abutting relationship. The end surfaces are rarely completely flat and it is common for gaps of 0.5 cm or even 1cm or more to be present at the pipe ends. A typical known method for joining pipes in end to end relationship, especially large pipes, is butt welding for polymeric pipes where a hot plate is placed between the pipe ends to melt them slightly, and then the plate removed and the pipes allowed to fuse together. Another known method involves wrapping a non corrosive strap around the pipe ends, supplied on its inner surface with a sealing compound, and securing it in place by mechanical means. Disadvantages of the prior art are that they take considerable time to install (often hours e.g. in the case of butt welding) and in the case of mechanical closures they may be bulky and difficult to install. Whatever coupler is used, it must be able to withstand forces exerted on it by pressure exiting from within the pipes, through any gaps between the pipe ends. It is an object of the present invention to provide a sealing system including a sealing member and also including another member which may be sufficiently rigid to support the sealing system against any pressure exiting from within the pipes, and/or may divert any pressure exiting from gaps between the pipe ends to a smaller cross-sectional area of the sealing member than it would impact if the other member were not present. In general the larger any gaps between the pipe ends the larger the force acting on the sealing system since force is the product of pressure and area. Therefore diverting the pressure reduces the force acting on the sealing system. A first aspect of the invention provides a method of joining end to end two imperfectly abutting pipes, the method comprising (i) positioning a first tubular or wraparound member around the pipe ends to bridge any gap between the pipe ends, and (ii) positioning a flexible sealing member around the pipe ends, either (a) before positioning the first member so that it lies within the first member or (b) after positioning the said first member so that it overlies and extends beyond both ends of the first member, and is sealed to the pipe surfaces projecting on either side of the said first member, Where the sealing member lies within the first member, the first member is preferably of such rigidity that it supports the sealing member. Preferably the first member extends completely over the sealing member, or even overlaps the edges of the sealing member. The advantages of this arrangement is that, provided the first member is sufficiently rigid, it substantially prevents peel failure of the sealing member as a result of the exiting pressure. Where the sealing member is positioned around the first member, the first member preferably has such rigidity that the force exerted by pressure within the pipe onto the sealing member is decreased relative to the force that would be exerted on the sealing member in the absence of the said first member. This is because the first member diverts any exiting fluid pressure from the pipe axially along the pipe. Where the gap between the pipe ends is greater than the gap between the first member and the pipe surface then the force acting on the sealing member is reduced since it is acting on a smaller area. This reduction is force effected by diversion of pressure by the first member may also apply where the first member lies outside the sealing system. A second aspect of the invention provides an end to end joint between two imperfectly abutting pipes comprising: a) two pipes in imperfect abutting relationship, b) a first tubular or wraparound member positioned around the pipe ends to bridge any gap between the pipe ends; and c) a flexible sealing member positioned around the pipe ends, either within or around the first member, wherein when the sealing member lies within the first member it is coterminous with or smaller than the first member, and when the sealing member lies around the first member it overlies and extends beyond both ends of said first member. Regardless of the position of the said first tubular or wraparound member, any gap between the said first tubular or wraparound member and the outwardly facing pipe surfaces is preferably smaller than any gap between the imperfectly abutting pipe ends. The force exerted from within the pipe onto the sealing member is the product of pressure and the surface area of impact onto the sealing member. Therefore the first tubular or wraparound member may act to deflect any fluid exiting from a gap between the pipes into a gap between the first member and the pipe which is smaller than the gap between the pipes. Thus a smaller force is exerted onto the sealing member covering the smaller gap between the first member and the pipe which is easier to seal than would be the case in the absence of the first member. Where the said first tubular or wraparound member lies within the sealing member, it preferably substantially contacts the said outwardly facing pipe surfaces around an entire inner circumference. This means there is substantially no gap or a very very small gap between the said member and the pipe surfaces. Where the said first member surrounds the sealing member, it is preferably also arranged of appropriate diameter so that there is substantially no gap or a very small gap between the pipe surfaces and the sealing member. In this case the said first member is preferably coterminous with the sealing member. Alternatively it may be larger than, i.e. cover and extend beyond, the sealing member. The said first tubular or wraparound member is preferably rigid, preferably sufficiently rigid to deflect the exiting pressure. Preferably the first member exhibits a bend modulus of at least 200 Pa. Preferably it exhibits a tensile strength of at least 500 N/mrτ.2. Preferably the first member comprises a metal tube or wrappable sheet. Preferably it is at least 0.5 mm thick e.g. about 1 mm thick. A suitable material is steel. Another advantage of the first member's rigidity when it is positioned within the sealing member is that it can act to align the pipe ends. Where the first member lies within the sealing sleeve it is preferably at least 50 mm, preferably 80 mm, especially about 100 mm long. Where the first member surrounds the sealing sleeve it is preferably at least as long as the sealing sleeve, e.g. typically about 200 mm long. By "length" of sleeve is meant the length it extends axially along the pipeline. Advantageously the same length first member may be used to join a variety of sizes of pipes. The first member may be tubular or wraparound. If it is wraparound longitudinal edges of the sheet are overlapped in use and secured together, preferably by mechanical means, preferably rivets. The sealing sleeve may be any suitable type. In one embodiment it comprises a tubular or wraparound recoverable sleeve. It is preferred to use sleeves that are recoverable by the action of heat. In their most common form, heat-recoverable sleeves comprise polymeric material exhibiting the property of elastic or plastic memory, as described in US-2027962, US- 3086242 and US-3597372, for example. As is made clear in US- 2027962, for example, the original dimensionally heat stable form may be a transient form in a continuous process in which, for example, an extruded tube is expanded while hot to a dimensionally heat-unstable form but, in other applications, a preferred dimensionally heat unstable article is deformed to a dimensionally heat unstable form in a separate state. Heat-recoverable articles based on fabrics are also known, and are described in GB-A-2133639, GB-A-2133740, GB-A-2134334, GB-A-2135632, GB-A-2135836 and GB-A-2130142, the disclosures of these documents are incorporated herein by reference. The sealing sleeve of the present invention may comprise a fabric recoverable sleeve. Wraparound recoverable sleeves have the advantage over tubular sleeves that they can be installed around an object without having to gain access to an end of the object. Known closures for wraparound sleeves include adhesives coated patches such as that disclosed in US-4200676, and the so-called "rail and channel closure" disclosed in GB-1155470. Where sealing sleeves that are recoverable by heat are used, it may be advantageous for the first member to surround the sealing sleeve. If not, then specific care is preferred to ensure that any heat applied to recover the sealing sleeve does not cause the first member to relax. Efforts to avoid relaxation may include, for example, appropriate selection of materials for the first member, or specific heating mechanisms for the sealing sleeve. In order to bond to the pipes, the sealing sleeve is preferably coated on at least part of an inner surface with an adhesive or sealant. It may also be at least partially coated e.g. with gel for desired specific performance. Where the said first tubular or wraparound member is within the sealing sleeve it may also be coated on its inner surface with an adhesive sealant or gel etc. Especially where the pipes to be joined have a non planar outer surface, a coating on the inner member (be it the sealing sleeve or the first member) may be useful to fill any gaps between the pipes outer surfaces and the first member, as well as to form the bond the pipes. The sealing sleeve is bonded to the pipe. Preferably the tensile strength of the sealing sleeve is at least as great as the maximum thermal forces exerted on the pipe in use. Preferably the pull-out force of the sealed system is at least 1000 N per diameter inch of pipe. The sealing sleeve may be applied as a single layer or as a double or more layers. For example if the sealing sleeve is wraparound it may be multiwrapped. Multilayers may be advantageous where, for example, the system is in situations where it is likely to be subjected to high stresses and forces. The pipes to be joined may be of any construction. The invention is particularly applicable for large diameter pipes. Typical pipes include sewer, water or gas-carrying pipes. One particular type of pipe that can be connected according to the invention is one of cellular construction in longitudinal section. Such a pipe is common in, for example, the sewer industry. Viewed from the outside such pipes typically have alternating circumferential ridges and depressions extending around the pipes. With such pipes the said first member can align circumferential ridges on either side of the joint. The invention can be used to join pipes of the same shape and size or different shape and size. If they are the same shape and size, then the first tubular member or wraparound member when wrapped may typically be cylindrical in shape. Where the pipes are different in shape and size the first member is preferably profiled accordingly. An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawing, wherein: Figure 1 is a longitudinal part-sectional view through two pipes joined by a method according to a first embodiment of the invention. Figure 2 is a longitudinal part sectional view through two pipes joined by a method according to a second embodiment of the invention. Figure 1 shows two pipes 2 joined by a method according to the present invention. Each pipe 2 has a single layer hollow cellular construction in longitudinal section. Each cell 6 has opposed siightly convex surfaces 8 facing inwardly and outwardly of the pipe 2, so that the pipe structure has alternating ridges 10 and depressions 12 extending circumferentially around the pipes 2. Because of end irregularities of pipes 2 there is a gap 4 between the pipe ends. The method according to the invention comprises first positioning a first wraparound steel sleeve 14 around the pipes 2 and then installing an outer heat recoverable fabric sealing sleeve 16. The wraparound steel sleeve 14 is about 1mm thick, and 100 mm long. Longitudinal edges of the sleeve 14 are overlapped and are secured together by mechanical rivets (not shown). The rivets are installed in the field after the sleeve 14 has been wrapped around the pipes 2. The sleeve 14 is positioned tightly around the pipes (a mechanical teπsioning device can be used for tightening) and acts both to align pipes 2, and to deflect any fluid exiting from the gap 4 between the pipes through 90° i.e. to a direction longitudinally of the pipe. The sleeve 14 rests against ridges 10 of pipes 2 around an entire inner circumference of sleeve 14 so that the fluid presses against the sealing sleeve 16 through a much smaller gap than the gap 4 between the ends of pipes 2. The sealing sleeve 16 comprises a recoverable fabric comprising recoverable polyethylene fibres in the circumferential direction, heat-stabie glass fibres in the longitudinal direction, and a polymer matrix. The sleeve is lined with hot melt adhesive to seal it to pipes 2. The sleeve 16 is tubular or wraparound and is installed by heating e.g. with a gas torch, to recover it into conformity with pipes 2. The heat also activates the lining adhesive on the sleeve 16. Figure 2 shows an alternative embodiment according to the invention. In this case the wraparound steel sleeve (designated 14') is wrapped around the outside of the fabric (designated 16'). Also in this case the length of the recoverable fabric 16' and steel sleeve 14' are substantially the same length, in this case 200 mm. The steel sleeve 14' supports the fabric sleeve 16' and substantially prevents peel failure of sleeve 16' as a result of pressure acting from within. Other features of the embodiments shown in Figure 2 (e.g. the adhesive lining of the fabric sleeve 16', and the wraparound nature of the metal belt 14') are as for the embodiment of Figure 1.

Claims: Qlajm? 1. A method of joining end to end two imperfectly abutting pipes, the method comprising (i) positioning a first tubular or wraparound member around the pipe ends to bridge any gap between the pipe ends, and ( i i) positioning a flexible sealing member around the pipe ends, either (a) before positioning the first member so that it lies within the first member or (b) after positioning the said first member so that it overlies and extends beyond both ends of the first member, and is sealed to the pipe surfaces projecting on either side of the said first member. 2. A method according to claim 1 , wherein the first member surrounds the sealing member and is either coterminous therewith, or projects beyond the edges thereof. 3. A method according to claim 1 or 2, wherein any gap between (a) the innermost of the said first member and the sealing member and (b) the said outwardly facing pipe surface, is smaller than any gap between the imperfectly abutting pipe ends. 4. A method according to claim 1 , 2 or 3 wherein the said first tubular or wraparound member is within the sealing member substantially contacts the said outwardly facing pipe surfaces around an entire inner circumference. 5. A method according to any preceding claim wherein the said first tubular or wraparound member exhibits a bend modulus of at least 200 Pa, and preferably also a tensile strength of at least 500N/mm2. 6. A method according to any preceding claim wherein the said first member comprises metal, preferably steel. 7. A method according to any preceding claim wherein the said first member comprises a wrappable sheet having a thickness of at least 0.5 mm, preferably at least 0.8 mm. 8. A method according to claim 7 wherein longitudinal edges of the sheet are overlapped in use and secured together, preferably by mechanical means, preferably rivets. 9. A method according to any preceding claim, wherein the sealing sleeve comprises a tubular or wraparound heat recoverable, preferably heat shrinkable, cover. 10. A method according to claim 9 wherein the sealing sleeve comprise a heat recoverable fabric. 1 1 . A method according to preceding claim wherein the sealing sleeve is coated on at least part of its inner surface with one or more of an adhesive, a mastic and a gel. 12. An end to end joint between two imperfectly abutting pipes comprising: a) two pipes in imperfect abutting relationship, b) a first tubular or wraparound member positioned around the pipe ends to bridge any gap between the pipe ends; and c) a flexible sealing member positioned around the pipe ends, either within or around the first member, wherein when the sealing member lies within the first member it is coterminous with or smaller than the first member, and when the sealing member lies around the first member it overlies and extends beyond both ends of said first member. 13. A joint according to claim 12, wherein the walls of the pipes are cellular in longitudinal section. 14. A method or joint according to any preceding claim wherein the two pipes have substantially the same cross sectional shape and area.

Inventors: VAN BEERSEL JOZEF, VAN ESCH WILLY, VAN BEERSEL, JOZEF, VAN ESCH, WILLY
Applicants: RAYCHEM LTD, RAYCHEM SA NV, NV RAYCHEM S.A., RAYCHEM LIMITED
Application year: 1992
Main classification: F16L47
IPC codes: B29C65, B29L23, F16L47