GB2300684A

GB2300684A - Axially flexible plastics pipe, e.g. for lining a pipeline

Info

Publication number: GB2300684A
Application number: GB9609289A
Authority: GB
Inventors: Steven Robert Wood; Jyri Jaakko Jarvenkyla
Original assignee: Uponor Ltd UK
Current assignee: Uponor Ltd UK
Priority date: 1995-05-06
Filing date: 1996-05-03
Publication date: 1996-11-13
Anticipated expiration: 2016-05-03
Also published as: GB9509283D0; GB2300683B; GB2300683A; GB2300684B; GB9609289D0

Description

1 4 2300684 IMPROVEMENTS IN OR RELATING TO FLEXIBLE PIPES This invention

relates to flexible pipes and is more particularly concerned with a novel flexible plastics pipe and its use in a method f or relining or replacing service pipes.

Relining or replacement of corroded, damaged, or fractured service pipes is a major problem for many utility companies. In view of the high cost of renewing service pipes, which frequently involves digging up the entire length of the original pipe in order to lay a new section, various methods for relining or replacing the existing service pipe have been proposed.

In UK published patent applications nos. 2227071A, 2236158A, and 2275981A, there are described methods for replacing or relining pipes, particularly domestic gas service pipes, by inserting a replacement pipe into the existing pipe. Af ter the insertion of the replacement pipe, any clearance between the pipes is sealed with a sealant of a flowable, settable type, for example a grout or an anaerobic sealant.

The liner or replacement pipe is normally provided with a nose-cone which is connected to the leading end thereof in order to assist the liner or replacement pipe to negotiate any curves or bends in the original pipe 6 2 work. The nose-cone is provided with a tubular body having a down- stream portion which is inserted in the leading end of the liner or replacement pipe, and sealing means comprising a series of flanges which form an interference fit with the internal wall of the existing pipe. The flanges stop gas entering the clearance between the pipes and also prevent the sealant from flowing beyond the leading end of the liner or replacement pipe. The nose-cone also has a frangible means to seal the bore of the tubular nose-cone body temporarily, in order to prevent the ingress of gas into the replacement pipe until the repair has been completed. The entire disclosures of the above mentioned patents are incorporated herein by reference for all purposes.

The length of service pipe being replaced may be several metres, and there may be several 90' bends over that length. Typically the service pipe to be replaced has an internal diameter of around 25mm, and extends from a service main in the road to a subscriber's premises.

A major obstacle to the widespread introduction of the above relining and replacement systems is the flexibility of the liner or replacement pipe, which, even with the assistance of the nose-cone, can be extremely difficult to insert fully into an existing pipe having a plurality of 90 bends. The liner or replacement pipe must be highly flexible to circumnavigate the bends in

0 00 3 the pipe, and yet be resistant to surf ace scratches, radial distortion and'axial compression. The properties of liner pipes or replacement pipes which have been used hitherto have been a compromise between these conflicting 5 requirements.

The present invention provides a flexible plastics pipe, suitable for relining or replacing an existing service pipe having at least one 900 bend, the flexible pipe having a smooth inner wall and a convoluted outer wall.

In a f irst aspect, the invention provides an axially flexible plastics pipe having a smooth inner wall and a convoluted outer wall, wherein the ratio of the axial length of a peak of a convolution to the axial length of a trough between adjacent convolutions is 1. 5 or greater, and wherein the nominal radius of a peak of a convolution is greater than twice the nominal radius of a trough between adjacent convolutions.

In a second aspect, the invention provides a method of relining or replacing a service pipe in which there is inserted into the service pipe an axially flexible plastics pipe having a smooth inner wall and a convoluted outer wall, wherein the ratio of the axial length of a peak of a convolution to the axial length of a trough between adjacent convolutions is 1.5 or greater, and a 0.

4 wherein the nominal radius of a peak of a convolution is greater than twice the nominal radius of a trough between adjacent convolutions.

In a third aspect, the invention provides a method of relining or replacing a service pipe which comprises inserting into the service pipe an axially flexible dual layer plastics pipe, the flexible plastics pipe having a smooth inner wall and a convoluted outer wall, and introducing a sealant into the clearance between the outer wall of the flexible plastics pipe and the service pipe.

The flexible plastics pipe can be of integral construction, but preferably comprises two or more coaxial layers which can be co-extruded, or formed by any other suitable means. The pipe can, for example, comprise a smooth-walled inner tube and a convoluted outer tube. In such a construction, the flexibility of the dual layer pipe depends in part upon the connection, if any, between the inner and outer tubes. Normally each of the troughs of the outer convoluted tube will be fused, welded, adhered, or otherwise anchored to the outer wall of the inner tube, but for increased flexibility it is also possible to arrange that only some of the troughs are anchored to the inner tube. For example, only alternate troughs of the convoluted tube could be so anchored to the inner tube, in order to give b 0 0.

enhanced flexibility. Preferably the troughs of the outer convoluted tube and the outer wall of the inner tube are fused together, and preferably the total thickness of the fused region is f rom 0. 5 to 1. 0, more preferably around 0.8, x the combined nominal wall thickness.

In this specification, the axial length of a peak of a convolution is measured between the points of greatest slope on each side thereof, or, if the sides are straight, the mid-points of the straight sections thereof. The axial length of a trough between adjacent convolutions is measured in a similar f ashion between the same points.

Preferably the ratio of the axial length of a peak of a convolution to the axial length of a trough between adjacent convolutions is from 2 to 4, for example about 3.

The nominal radius of a peak of a convolution is taken as the average radius of the curved section thereof and a nominal radius of a trough between adjacent convolutions is measured similarly.

Preferably the nominal radius of a peak of a convolution is from 2 to 4 times the nominal radius of a trough between adjacent convolutions.

b 0 04 6 The shape of the convolutions is preferably such that in profile the peaks and troughs are curved, for example, in a generally sinusoidal shape, although this is not always essential and in the method of the invention it may sometimes be possible to use convolutions having a substantially triangular (sawtooth), rectangular, or other shaped profile.

The outer diameter of the flexible plastics pipe is preferably such as to be a relatively close f it in the service pipe within which it is to be inserted. Typically, where the service pipe has a bore of 25mm, the flexible plastics pipe will have an outer diameter of around 20mm. In general, the flexible plastics pipe can have any suitable outer diameter, depending on the application, although usually the pipe will have an outer diameter of from 10 to 10Omm, for example, from 15 to 50mm.

Preferably the height (amplitude) of the convolutions of the outer wall of the flexible pipe is f rom 0. 08 to 0. 12 x OD, f or example about 0. 10 x OD, where OD is the outer diameter of the pipe. Preferably the axial length of a peak of a convolution is from 0.12 to 0.15 x OD, for example about 0.125 x OD.

The pitch of the convolutions (peak-to-peak) can be chosen to suit the particular application, but is 0 7 preferably f rom 0. 12 to 0. 20 x OD. Lengthening the pitch allows more room for the convolutions to compress on the inner radius of a bend, reducing the strain on the outer radius, conversely, shortening the pitch reduces the amount that the inner wall will encroach into the bore of the pipe as if flexes on the inner radius of the bend and hence reduces pressure loss of any fluid in the pipe.

It is important that the flexible plastics pipe 10 should have a smooth inner wall in order to avoid a pressure drop along the pipe when, for example, gas is flowing therethrough. Preferably the depth of any undulation in the inner wall of the pipe is less than 5 of the height of a convolution, when measured on the straight (undeformed) pipe. The variation in bore diameter of the inner wall of the pipe across one pitch of the convolution is preferably no greater than 2.5%, more preferably no greater than 1.5t, of the nominal bore diameter.

The flexible plastics pipe is preferably so constructed that it can relatively easily negotiate the 900 bend in a pipe of only slightly greater diameter than the greatest diameter of the convoluted outer wall. This must of course be achieved without substantial radial deformation of the flexible plastics pipe and preferably without substantial axial compression thereof. Preferably the flexibility of the plastics pipe is such 0 8 that when bent to a nominal radius to the centre line of the bend of 1.35 x OD, the ovality at the bend is less than 15% and preferably less than 10.

Where the flexible plastics pipe is of dual layer construction, the inner layer is preferably formed from a plastics material of substantial flexibility, preferably having an elongation at break of greater than 100%, and an elastic modulus of less than 0.5MPa. A preferred material for the inner layer can have, for example, an elongation at break of from 350 to 600%, and an elastic modulus of from 0. 2 to 0.7MPa.

The inner layer preferably has a thickness of from 0.01 to 0.02 x OD, more preferably about 0.015 x OD. An inner layer wall thickness of from 0.275 to 0.325 mm has been found to be particularly useful.

The outer convoluted layer is preferably also formed from a highly flexible plastics material, and preferably has a flexural modulus of at least 0AMPa, more preferably from 0.8 to 1.1MPa.

The outer convoluted layer is preferably formed from a 25 plastics material having a thickness of from 0.015 to 0. 03 x OD, more preferably about 0. 02 x OD. An outer layer wall thickness of from 0.375 to 0.425 mm has been found to be particularly useful.

9 Both inner and outer layers are preferably f ormed from plastics materials having substantial stress crack resistance.

Both inner and outer layers are preferably of uniform thickness and for example, the thickness of either layer should not vary by more than about 5%.

Where the pipe is of dual layer construction, the annular spaces between the convolutions and the inner tube can be voids, or can be f illed with a suitable flexible material, for example, a gel or a rubbery polymeric material.

Suitable plastics materials for use in the production of a flexible pipe in accordance with the invention include, for example, polyolefins such as polyethylene and polypropylene, and ethylene copolymers, for example with propylene, butene, hexene, octene, vinyl acetate or other vinyl esters, methyl, ethyl or butyl acrylate; polyamides; polyurethanes; polyvinyl chloride; polyvinylidene fluoride, or other fluorinated polymers or copolymers; and elastomers such as EPM The inner and outer walls are normally sealed theretogether so that the volume therebetween is enclosed and the quantity of air or gas situated between the walls is constant. This may be problematical, particularly when the external pressure surrounding the walls varies with respect to the internal pressure between the inner and outer walls. The inner wall may buckle or be otherwise distorted so that the inner most surface of the internal wall is not smooth and flat. This is undesirable in a pipe for use as a service pipe to deliver gas in which a low pressure drop, which is provided by a smooth bore, is preferred.

In addition, the regularity and/or shape of the undulations of the outer wall may also be affected by variations in pressure between the pressure in the enclosed volume and the surrounding atmospheric pressure and/or the pressure within the central volume. For example, over pressure in the enclosed volume between the walls may cause a decrease in flexibility. or indeed it may place a strain on the anchoring means between the inner and outer walls. Temperature variations, for example, during production, may also be problematical.

In addition, these may produce pressure variations. The outer undulating wall is normally arranged so that the contents of the pipe are isolated from the atmosphere.

In a further aspect of the invention there is 25 provided an axially flexible plastics pipe having a smooth inner wall and a convoluted outer wall, wherein the enclosure between the inner and outer walls is in fluid connection with the central volume of the pipe.

11 Preferably, the inner wall is provided with one or more apertures.

It will be understood from the above that where one or more apertures are provided, the volume enclosed between the inner and outer layers is in f luid connection with the central volume of the pipe. The central volume of the pipe may be connected to the atmosphere or may form part of, for example, a gas delivery network. In either case, the pressure is balanced between the volume enclosed between the inner and outer layers and the volume enclosed within the inner layer in the central bore of the pipe. The inner layer therefore remains substantially flat and smooth. A plurality of perforations may be provided as, for example, one or more lines of holes extending longitudinally along the pipe. Alternatively, or in addition, the aperture may comprise one or more continuous axially extending slots in the inner layers. Preferably, the holes or slots are sufficiently small with respect to the circumference of the pipe that the flow of gas or other fluids through the pipe is not significantly affected. The outer corrugated layer is arranged such that the pressure of the fluid flow is contained.

The flexible plastics pipe of the invention can be made by any of those methods currently available for the manufacture of convoluted plastics pipes and dual wall 12 plastics pipes. In manufacturing the convoluted outer wall, an extruded plastics pipe can be heated to its softening point and moulded, for example, by vacuum moulding or blow moulding, or a combination of both, to produce the corrugations. In a further aspect of the invention, a convoluted flexible plastics pipe is manufactured by a method comprising:

(i) (ii) (iii) (iv) heating the pipe to its softening point; surrounding the pipe with one or more mould blocks shaped to produce convolutions; creating a differential pressure between the inside and outside of the pipe such that the pipe is forced into the mould block or blocks to produce the corrugations; and adjusting the pressure within the pipe to provide convolutions of the required depth.

Preferably the mould blocks are vacuum mould blocks.

In a preferred method in accordance with this aspect of the invention, the pipe is vacuum formed into a convoluted shape, and, af ter the pipe leaves the mould 13 cavity, the hot gas, usually air, inside the pipe is allowed to cool such that, as its volume contracts, the differential pressure between the inside and the outside of the pipe serves to stabilise, and/or deepen the 5 convolutions.

At least the outer wall or layer of the pipe can, if desired, be crosslinked to give improved abrasion resistance. Cross-linking can be, for example, by irradiation by means of an electron beam, or by a chemical cross-linking method, for example silane crosslinking. A preferred cross-linking method, however, involves incorporating cross-linking initiators into the plastics material and cross-linking by irradiation with ultra-violet light.

In a method according to a further aspect of the invention, a flexible dual layer plastics pipe is inserted into a service pipe as a lining or replacement therefor, and a sealant is introduced into the clearance between the flexible pipe and the service pipe. For details of the sealant and procedure used, the reader is referred to the disclosures of UK published patent application nos. 2227071A, 2236158A and 2275981A mentioned heretofore.

a 14 An embodiment of a flexible plastics pipe according to the invention will now be described with reference to the accompanying Drawings, in which:

Figure 1 shows an axial section through a wall of a dual layer pipe according to the invention in an undeformed condition; and Figure 2 shows a section through the same pipe when fully compressed by axial bending as would occur on the inner radius when the pipe is inserted into a 900 bend in a service pipe.

Figure 3 shows a cross-sectional perspective view of a pipe in accordance with a further aspect of the invention.

Referring first to Figure 1, the dual layer pipe illustrated generally at 1 comprises an inner smooth bore flexible tube 2 and an outer convoluted tube 3. The pipe 1 has an outer diameter of 20mm and an inner diameter of 15mm and is intended to be capable of bending in a 90' sharp bend inside a pipe bore of 25mm. The inner tube 2 has a wall thickness of 0.3mm and the convoluted outer tube 3 has a wall thickness of 0.40mm.

00 0 01 The trough 4 of the convoluted outer tube is anchored at 5 to the outer wall 6 of the inner tube 2 for example by welding.

AS illustrated, the axial length of the peak of the convolution 7 is 2. 25mm measured from the midpoint 8 and the axial length of the trough 4 is 1. 15mm, giving a ratio of 2. 0. The nominal radius of the peak of the convolution 7 is 1.15mm measured from the outer wall and the nominal radius of the trough 4 is 0.3mm, measured from the inner wall, giving a ratio of 3.8 to 1.

The pitch of the convolutions of the flexible pipe is 3Amm, on an OD of 20mm.

Referring now to Figure 2, there is shown the configuration of the flexible pipe 1 when subjected to compression by axial bending, as would occur, for example, on the inside radius of the bend. It can be observed that the effect of compression is to force the f lexible inner tube 2 to f lex into the pipe bore thus allowing more compression on the inner bend radius, reducing the strain on the outer radius of the bend and hence reducing any effect on ovality.

Plastics pipes in accordance with the invention may find a wide variety of applications in relining service 0 00 0 0 16 pipes of all types. The pipes of the invention can be particularly useful in the relining and replacement of pipes carrying a fluid under pressure, and especially domestic gas service pipes.

Referring now to Figure 3, there is shown a flexible pipe la having an outer convoluted tube 3 and an inner flexible tube 2a. Tube 2a is provided with a series of apertures 9 which extend axially in two lines, in this particular embodiment, along tube 2a. Alternatively, or in addition, tube 2a is provided with one or more slots 10 extending axially along tube 2a. Where perforations 9 are provided these are substantially opposite the peaks of convoluted tube 3. Apertures 9 and slots 10 may be of any suitable cross-section. Typically, holes 9 are cylindrical in crosssection and slots 10 are rectangular in cross-section.

When gas flows along the pipe, the provision of apertures 9 or one or more slots 10 enables the pressure of the volume between the inner and outer layers to equalise with the pressure within the central bore of tube 2a, no matter what shape pipe la is required to adopt. Thus, the inner surface of tube 2a is not subjected to distorting or deforming forces.

Alternative embodiments of the invention can be envisaged by those skilled in the art from the 00 0 0 1 0 17 information contained herein, all such alternative embodiments are intended to lie within the scope of this application.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

18 The invention is not restricted to the details of the foregoing embodiment(s). This invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

6 19

Claims

1. An axially flexible plastics pipe having a smooth inner wall and a convoluted outer wall, wherein the ratio of the axial length of a peak of a convolution to the axial length of a trough between adjacent convolutions is 1.5 or greater, and wherein the nominal radius of a peak of a convolution is greater than twice the nominal radius of a trough between adjacent convolutions.

2. A pipe according to Claim 1, which comprises two or more coaxial layers.

3. A pipe according to Claim 1 or 2, which comprises a smooth-walled inner tube and a convoluted outer tube.

4. A pipe according to Claim 3, in which the troughs of the outer convoluted tube are fused, welded, adhered, or otherwise anchored to the outer wall of the inner tube.

5. A pipe according to Claim 4, in which only some of the troughs of the outer convoluted tube are anchored to the inner tube.

6. A pipe according to any of the preceding claims, in which the ratio of the axial length of a peak of a convolution to the axial length of a trough between adjacent convolutions is from 2 to 4.

7. A pipe according to any of the preceding claims, in which the nominal radius of a peak of a convolution is from 2 to 4 times the nominal radius of a trough between adjacent convolutions.

8. A pipe according to any of the preceding claims, in which. in profile, the peaks and troughs are curved in a generally sinusoidal shape.

9. A pipe according to any of the preceding claims, in which the height (amplitude) of the convolutions of the outer wall is from 0.08 to 0.12 x OD, where OD is the outer diameter of the pipe.

10. A pipe according to any of the preceding claims, in which the axial length of a peak of a convolution is from 0.12 to 0.15 x OD.

11. A pipe according to any of the preceding claims, in which the pitch of the convolutions (peak-to-peak) is preferably from 0.

12 to 0.20 x OD.

0. 0 21 12. A pipe according to any of the preceding claims, in which the depth of any undulation in the inner wall is less than 5% of the height of a convolution, when measured on the undeformed pipe.

13. A pipe according to any of the preceding claims, having a flexibility such that when bent to a nominal radius to the centre line of the bend of 1.35 x OD, the ovality at the bend is less than 15.

14. A pipe according to any of the preceding claims, which is of dual layer construction and has an inner layer formed from a plastics material having an elongation at break of greater than 100%, and an 15 elastic modulus of less than 0.5 MPa.

15. A pipe according to Claim 14, in which the material of the inner layer has an elongation at break of from 350 to 600% and an elastic modulus of from 0.2 20 to 0.7 MPa.

16. A pipe according to any of the preceding claims, that is of dual layer construction and has an inner layer having a thickness of from 0.01 to 0.02 x OD.

17. A pipe according to any of the preceding claims, that is of dual layer construction, and has an outer 00 a 4 4 22 convoluted layer having a flexural modulus of from 0.8 to 1.1 MPa.

18. ' A pipe according to any of the preceding claims, 5 that is of dual layer construction and has an outer convoluted layer formed from a plastics material having a thickness of from 0.015 to 0.03 x OD.

19. A pipe according to any of the preceding claims, 10 that is of dual layer construction, and wherein the annular spaces between the convolutions and the inner tube are filled with a gel or a rubbery polymeric material.

20. A pipe according to any of the preceding claims, that is of dual layer construction, and wherein at least one of the inner and outer layers comprises polyethylene.

21. A pipe according to any of the preceding claims, wherein at least the outer wall or layer thereof has been cross-linked.

22. A pipe according to any of the preceding claims, 25 wherein an enclosure between the inner and outer walls is in fluid connection with the central volume of the pipe.

0 0 0 0

23 23. An axially flexible plastics pipe having a smooth inner wall and a convoluted outer wall, wherein an enclosure between the inner and outer wall is in f luid connection with the central volume of the pipe.

24. A pipe according to claim 22 or 23, in which one or more apertures are provided in the inner wall.

25. A pipe according to claim 24, wherein a plurality of perforations are provided, which perforations are axially spaced along the pipe.

26. A pipe according to claim 25, in which each perforation is substantially opposite a peak of the convoluted outer wall.

27. A pipe according to any of claims 24 to 26 in which an aperture is provided in the inner wall 20 corresponding to each peak in the outer wall.

28. A pipe according to claim 24 wherein the aperture comprises one or more axially extending slots in the inner wall.

29. A pipe according to any of claims 25 to 28, wherein two or more series of perforations and/or slots are provided, which series of perforations and/or slots Q 1 24 are substantially equispaced radially about the circumference of the inner wall.

30. A pipe according to any of claims 23 to 29, wherein 5 the aperture or apertures are sufficiently small with respect to the circumference of the pipe such that the f low of gas, and/or other f luid, through the pipe is not significantly affected.

31. A pipe according to any of the preceding claims, substantially as hereinbefore described with reference to and as illustrated in the accompanying Figures 1, 2, and/or 3.

32. A flexible convoluted plastics pipe having a smooth inner wall substantially as hereinbefore described.

33. A method of relining or replacing a service pipe in which there is inserted into the service pipe an axially flexible plastics pipe having a smooth inner wall and a convoluted outer wall, wherein the ratio of the axial length of a peak of a convolution to the axial length of a trough between adjacent convolutions is 1.5 or greater and wherein the nominal radius of a peak of a convolution is greater than twice the nominal radius of a trough between adjacent convolutions.

.0

34. A method according to Claim 33 in which there is used a pipe according to any of Claims 1 to 32.

35. A method according to Claim 33 or 34 substantially as hereinbefore described.

36. A method of relining or replacing a service pipe which comprises inserting into the service pipe an axially flexible dual layer plastics pipe, the flexible plastics pipe having a smooth inner wall and a convoluted outer wall, and introducing a sealant into the clearance between the outer wall of the flexible plastics pipe and the service pipe.

37. A method according to Claim 36 in which there is used a pipe according to any of Claims 1 to 32.

38. A method according to Claim 36 or 37 substantially as hereinbefore described.

39. A method of producing convoluted flexible plastics pipe a method comprising:

(i) (ii) heating the pipe to its softening point; surrounding the pipe with one or more mould blocks shaped to produce convolutions; (iii) (iv) 26 creating a differential pressure between the inside and outside of the pipe such that the pipe is forced into the mould block or blocks to produce the corrugations; and adjusting the pressure within the pipe to provide convolutions of the required depth.

40. A method according to Claim 39 in which the mould blocks are vacuum mould blocks.

41. A method according to Claim 39 or 40, in which the pipe is vacuum formed into a convoluted shape, and, after the pipe leaves the mould cavity, the hot gas inside the pipe is allowed to cool such that, as its volume contracts, the differential pressure between the inside and the outside of the pipe serves to stabilise, and/or deepen the convolutions.

42. A method according to any of Claims 39 to 41 substantially as hereinbefore described.

43. A flexible plastics pipe, suitable for relining or replacing an existing service pipe having at least one 90 bend, the flexible pipe having a smooth inner wall and a convoluted outer wall.