GB2225406A - Methods and apparatus for use in pipe lining. - Google Patents

Abstract

A pipe (11) e.g. a water main is lined by moving a thermoplastic liner (10) without heat through a die (16) to reduce the cross-section of the liner, and introducing the reduced liner (10) into the pipe (11). The liner (10) subsequently moves into engagement with the inner surface of the pipe (11) by recovery in cross-section on release of axial tension. A flexible expansion device Fig. 8 may be moved through the liner to expand the liner into engagement with the pipe. The die (16) may be mounted on the pipe (11) and be in separable parts. The minimum cross-section of the die (16) may be on a part replaceable by another part defining a different cross-section. The liner material may be polyolefin, polyamide, polyvinyl chloride, ABS. <IMAGE>

Description

METHODS D APPARATUS FOR US IU PIPE LINIIIG This invention relates to pipe lining particularly but not exclusively to methods and apparatus for the lining of pipes in situ.

According to one aspect of the invention a method of lining a pipe without application of heat comprises moving a thermoplastic liner through a die to reduce the cross-section of the liner, the material of the liner comprising material from the group polyolefin, polyamide, polyvinyl chloride, acrylonitrile butadiene styrene, and introducing the reduced liner into the pipe, the liner subsequently moving into engagement with the inner surface of the pipe.

The liner may be allowed to recover in cross-section into engagement with the inner surface of the pipe or may be caused to move into said engagement by moving an expansion device through the liner. The expansion device may be flexible in cross-section and may be a plurality of parts biassed outwards by resilient means.

The die may have a minimum cross-section in substantially a single transverse plane. The die may be mounted on the pipe whilst the liner is introduced into the pipe and may be in separable parts for subsequent removal from the pipe.

According to another aspect of the invention a method of lining a pipe comprises mounting a die on a pipe to be lined, and moving a liner through the die into the pipe.

The invention also provides a die for use in pipe lining having an orifice defined by parts which are separable from each other. Further the invention provides a die for use in pipe lining comprising a first part and a second part together defining a passage, the second part being removable from the first part and defining the minimum cross-section of the pass#ge. There may be a plurality of second parts respectively defining different minimum croas-sections.

Preferably the die is of circular cross-section and the liner is of circular cross-section.

The invention may be performed in various ways and some specific embodiments with possible modifications will now be described by way of example with reference to the accompanying partly diagrammatic drawings, in which: Fig. 1 is a side view part in section of part of a pipe lining device; Fig. 2 is a graph showing changes in liner diameter; Fig. 3 shows a modification; Fig. 4 shows a pipe lining arrangement; Fig. 5 shows a modification; Figs. 6 to 8 show modifications; Figs. 9, 10 are end view and longitudinal section of a die; and Figs. 11, 12 show a modification.

Underground water pipes may become cracked leading to leakage losses and one way of responding to this is to provide the pipe with a liner. If the pipe interior is encrusted or coated with deposits these should be removed by pulling a suitable pig through the pipe to leave a substantially smooth inner surface.

In the present case a thermoplastic liner 10 e.g. of polyethylene, of initial diameter Do is inserted into a pipe 11 of inner diameter Dp. The leading end 12 of the liner 10 is gripped to a plug 13 connected to a tow line 14 which is connected to a pulling device, for example a winch 15, to pull the liner into the pipe 11 without application of heat from an external source. The liner 10 is pulled or drawn through a die 16 which has an inner surface 17 which tapers uniformly inwardly to a minimum diameter 91 at essentia1l# a single axial position 18 (substantially in a single transverse plane) bounded by a smooth surface (not sharp) and the die inner surface then widens at 19. The surface 17 is polished.

Although normally the die and winch would be mounted on the road surface (Fig. 5) the die and winch may be located in pits 20, 21 at the ends of the length 22 of pipe to be lined as shown in Fig. 4. The die may be held in the end of the pipe to be re-lined. When the pipe leaves the die it is subject to an initial recovery to a diameter 1)2 (see Figs. 2 and 3) and retains this diameter until the tension on the liner is released either by the trailing end of the liner leaving the die or by the liner being cut downstream of the die but upstream of the pipe.When tlie tension is released, the diameter of the pipe sharply increases to D3 (see Fig. 3) with a nhortenin~r of the length of the liner. The liner wil ] then continue to recover in diameter as indicated at 25 Fig. 2 until it engages the inner surface of the pipe. The liner would, in the absence of the pipe, recover to a dinmeter D4 (less than D0) and thus firmly engages the inner surface of the pipe, Successive lengths of pipe can be lined and successive lengths of liner can be joined to provide a continuous liner.

If the die had a minimum diameter extending over an axial length the time taken for recovery from D3 to Dp would be greater and the pulling forces would increase.

As showii in Fig. 5 the die and winch can be at ground level with pulley 30 or other guides for the liner in the pits.

If tlie die is positioned at ground level (Fig. 5) the tension is normally removed by pulling the trailing end of the liner through the die. In this case the die is positioned such that sufficient length of liner remains outside the pipe to accommodate subject contraction into the pipe.

Where the die is located in the pit (Fig. 4) it is normally anchored to the existing pipe. In this case the drawing operation is stopped before the trailing end of tlie liner reaches the die and the tensioii is removed by relaxing tension on the winch cable, All subsequent colltraction will then occur from the leading end of the l er. Wib}i this method the die is in two or more sclrnrabln ments 50, 51 (Fig. 9), normally held tngetijn-.r b; ; suitable meons e.g. bolts 52, in order that the die may be removed from the liner.

In more detail, the method utilises the viscoelastic properties of tliermoplastics to enable a pipe or tube to be provided with a tightly fitting liner without the npplicntion of heat.

A particular application is the use of the method to renovate pipes and mains in the Water Industry using polyethylene. The use of a polyethylene liner provides resistance to corrosion, improves flow characteristics, and eliminates leakage from joints in the original pipe or main.

The method comprises: 1. Redllcing the diameter of the thermoplastic pipe 10 initially brenter than the internal diameter of the tube or pipe to be lined without the application of heat.

2. Im#erting the thermoplastic liner into the existing pipe whilst maintaining its reduced diameter by the application of a tensile axial force.

3. Utilising the viscoelastic properties of the thermoplastic to expand the liner onto the inner diameter of the pipe on removal of the tensile force.

Tfie leading end of the thermoplastic liner 10 of constant wall thickness and diameter Do is rigidly clamped to a tapered 'nose cone' or 'pulling hend' 13.

The diameter of the nose cone is such that it is capable of passing through the reduction die 16 without contact.

The liner may be a continuously extruded length or formed by jOillillg shorter individual lengths of extruded tube, typically by the butt-fusion welding technique.

In order to transfer axial loads to the liner it may be necessary to attach the nose cone to a short length of thicker line 32 welded at 31 to the leading end of the liner. A steel winch cable is threaded through both the pipe or main to be lined and the reducing die and attached to the nose cone by a shackle and rotating eyebolt 33.

As tension is progressively applied to the cable by the winch the thermoplastic pipe is drawn into and through the rigidly held conical die, resulting in a gradual reduction in pipe outer diameter from Do to D1, accompanied by an increase in length. Cleanliness of the liner is important during the drawing or swaging operation to minimise frictional forces and to prevent the build-up of dirt within the die resulting in scoring of the liner surface.

Lubrication of the die should preferably also be used to reduce friction.

A typical die has an included angle of 15q The diametral reduction may be chosen to suit the particular application. Typical reductions vary between 5 and 15% of the initial external diameter of the liner. A generous radius 34 on the minor diameter of the die eliminates damage to the liner as it exits from the die.

The diametral and longitudinal strains introduced into the thermoplastic during the swaging operation consist of three components: a) The maJor component is elastic strain which is recovered immediately as stress is removed from the liner.

b) A viscoelastic strain recovered over an extended period of time by 'relaxation' or recovery.

c) Irrecoverable strain due to permanent rearrangement of the molecular structure within the material.

As the liner leaves the die a small elastic recovery to diameter D2 occurs as the radial restraint on the material is removed, This process takes place over a distance of approximately ten liner diameters downstream of the die. Thereafter any further recovery is prevented by the axial tensile stress applied by the winch cable. The reduced diameter D2 is therefore maintained as the liner is drawn through the pipe or main allowing for ease of insertion with minimum friction from liner /host pipe contact. In cases where the main has suffered from corrosion or contains deposits, sedimentation or tuberculations it should be cleaned, e.g. by scraping prior to insertion.

As the swaging process is completed and the end of the liner is drawn through the die, the axial stress is released resulting in an immediate elastic recovery of strain in both the diametral (increases to D3) and longitudinal direction.

Further expansion in diameter and contraction in length occurs over an extended period of time due to viscoelastic relaxation or recovery. During this stage of the process the liner comes into contact with the internal diameter Dp of the pipe. The tendency to increase further in diameter ensures a tight fit between the liner and pipe.

There are theoretically no restrictions on the size and thickness of liner although practical considerations (e.g. safe working loads) may impose limitations. In the maJority of applications standard tubular diameters and wall thicknesses will be used both to minimise liner costs and to ensure liner availability, although future developments may involve the use of large diameter thin walled, non-standard liners.

In the particular case of renovation of water pipes or mains, the lining thickness will be determined by the condition of the original pipe. Where the original material is considered 'sound', the liner and pipe may be considered as a composite structure enabling the use of thin liners supported by the pipe. In cases where the original pipe is no longer considered capable of sustaining pressure a full pressure-bearing liner will be used. The advantage of the swaging process in the latter case are in minimising the amount and cost of excavation and reinstate- ment.

The degree of pipe reduction (Do - D1) in the die is a compromise between the clearance (Dp - D2) required to draw the liner through the pipe and the recovery required to ensure an interference fit (D4 - Dp) in the pipe. As the amount of irrecoverable strain (Do - D4) increases with the degree of reduction, an absolute limitation on the die reduction is imposed by the requirement for a tight fit between the liner and pipe.In practice typical die reductions are 5 to 15% of the original outside diameter of the liner. An included die angle of 15 has been found to optimise the balance between the drawing load and frictional drag but other angles are possible, e.g. 300, say between 50 and 450, which may depend on the initial diameter.

An experimental programme can enable design criteria to be established whereby the degree of die reduction to ensure both adequate clearance and a tight fit within the pipe can be predicted. In situations where the inside diameter of the pipe to be lined is known with confidence, a single piece die can be manufactured in advance. In water pipes and main, considerable variations in the inside diameter may exist within pipes of a nominal size. For successful relining it is important that the maximum and minimum diameters are known, as variations in die reduction of as small as 1 can significantly alter both the clearance and final diameter of the liner. These dimensions are often only able to be measured immediately prior to the swaging operation, giving insufficient time to manufacture the correct sized die. One solution to this problem is to provide a basic die 40 Fig. 3 with one or more removable extension plates 41 offering slightly different final diameters. This would enable dies of the required dimensions to be assembled immediately prior to swaging.

The load on tile winch is determined by the force required to draw the liner through the die together with the frictional drag of the liner within the pipe to be lined.

It has been established by mathematical analysis confirmed by experiment that the drawing force is proportional to the cross-sectional area of the thermoplastic liner wall and to the ffi reduction imposed and that this force is essentially independent of drawing speed.

The additional frictional load increases in proportion to the length of liner within the pipe or main.

The swaging operation induces longitudinal strains in the liner resulting in an increase in length. During insertion the winch force maintains the longitudinal strain which in turn constrains the tendency to increase in diameter. It is therefore important that an axial force is maintained until the insertion operation is completed.

For a given die reduction both the initial expansion in length and subsequent contraction due to recovery or relaxation can be predicted from test data obtained. It is therefore possible to estimate accurately the initial length of thermoplastic tube required to provide the liner with provision of adequate lengths of liner for the fitting of connections.

Knowledge of the viscoelastic characteristics of the material enables the time required for the liner to provide a tight fit against the inside diameter of the pipe to be predicted. This recovery time will be a function of the initial tube reduction and the time during which the liner is under axial load. At constant drawing speed the latter is directly proportional to the distance of a liner section from the die and therefore the liner will recover at slightly different rates along its length.On release of the winch load, lateral contraction and diametral expansion will initially take place over the whole length of the liner as the instantaneous elastic recovery is followed by viscoelastic recovery or relaxation, Contact between the liner and pipe bore will normally occur first at the section adjacent to the die where the liner has been under axial load for the minimum time. Subsequent movemetlt due to contraction will proceed from the leading end of the liiier until intimate contact is achieved over the length of the pipe. Total recovery time in typical applicatioiis is less than 24 hours.

Features described include: a) A method of reducing the diameter of the thermoplastic liner by drawing through a die without the application of heat.

b) The maintenance of the reduced diameter by the application of an axial load.

c) Experimental data and theoretical calculations enabling prediction of the process parameters to be made.

d) A multi-part die enabling speedy modification of the reduction ratio to be made to suit variations in the size of pipe to be lined.

When it is appropriate to have a much shorter recovery period for ttle liner then re-expansion may be effected using a device such as that shown in Figures 6 and 7.

This device may also be used to expand the liner into intimate contact with the host pipe in situations where, after scraltillg it is found that there are numerous reduced sections (A, B in Fig. 8) which could prevent contact being made over the whole pipe length due to pinning at the sites of diameter reduction (e.g. between sections A & B in Fig. 8) The re-expansion device 80 is a cylindrical/conical shape with segments (e,g. X and Y etc. in Fig. 6) which can be expanded by means of an actuator Z (Fig. 6). The actuator may be a mechanical spring or a pneumatic or hydraulic system.

Following insertion of the liner into the main pipe to be reliiied, the expansion device is inserted into the liner and attached to a cable 61 previously placed inside the liner. The other end of the cable is attached to a winch which is used to draw the expansion device 8 o along the length of the liner.

As the expansion device enters the lined system, the liner is forced into contact with the host pipe as shown in Fig. 7. Having made contact with the host pipe the remaining liner is increased into contact, increasing its diameter and shortening in length.

Where restrictions (A, B in Fig. 8) are encountered the liner will be forced to adopt the appropriate profile by adjustment of the expansion force F (Fig. 6) provided by the actuator. Because the liner ahead of the expansion device is in reduced form there is no tendency to contact at other sections (e.g. B in Fig. 8) until the expansion device is winched to those sections.

With this equipment and technique a satisfactory lining in full contact with the host pipe may be effected with greater speed and efficiency if this is desirable.

In a modified arrangement Figs. 11, 12 the expansion device 90 has oppositely facing flexible curved parts 91 engaging the liner and pulled by line 92 connected to a winch. The parts or segments 91 are angularlg spaced so as to engage substantially the whole of the inner surface of the liner as the device 90 is pulled along the liner.

Similarly the segments in Fig. 6 engage around substantially the whole liner surface.

Other thermos plastics can be used for the liner e.g. the polyolefin family for example polypropylene; polyvinyl chloride (unplasticised or modified); polyamides; acrylonitrile butadiene styrene (ABS).

In Fig. 3 the piece 41 defines the minimum die diameter and is shaped to provide R smooth stepless junction with surface 17 of piece 40. Pieces 41 may typically be removably held by bolts 42.

The invention can be used in pipes which may be required to carry water, sewage, gas, chemicals, slurries and other flowable substances.

Use of the invention is intended to combat leakage.

Claims (1)

1. A method of lining a pipe without application of heat comprising moving a thermoplastic liner through a die to reduce the cross-section of the liner, the material of the liner comprising material from the group polyolefin, polyamide, polyvinyl chloride, acrylonitrile butadiene styrene, and introducing the reduced liner into the pipe, the liner subsequently moving into engagement with the inner surface of the pipe.

2. A method as claimed in Claim 1, in which the liner is allowed to recover in cross-section into engagement with the inner surface of the pipe.

3. A method as claimed in Claim 1, in which the liner moves into engagement with the inner surface of the pipe by recovery in cross-section and by moving an expansion device through the liner.

4. A method as claimed in Claim 1, in which an expansion device which is flexible in cross-section is moved through the liner.

5. A method as claimed in Claim 4, in which the expansion device comprises a plurality of parts biassed outwards by resilient means.

6. A method as claimed in any preceding claim, in which the die has a minimum cross-section in substantially a single transverse plane.

15. A method of lining a pipe as claimed in Claim 1 and substantially as hereinbefore described.

16. A method of lining a pipe as claimed in Claim 9 and substantially as hereinbefore described.

17. A die for use in pipe lining substantially as hereinbefore described with reference to and as shown in Figs. 9 and 10 of the accompanying drawings.

18. A die assembly for use in pipe lining substantially as hereinbefore described with reference to and as shown in Fig. 3 of the accompanying drawings.

19. A pipe when lined by a method as claimed in any of Claims 1 to 10 or Claim 15 or Claim 16.

Amendments to the claims have been filed as follows 1. A method of lining a pipe without application of heat comprising moving a thermoplastic liner through a die to reduce the cross-section of the liner, the material of the liner comprising material from the group polyolefin, polyamide, polyvinyl chloride, acrylonitrile butadiene styrene, and introducing the reduced liner into the pipe, the liner subsequently moving into engagement with the inner surface of the pipe.

2. A method as claimed in Claim 1, in which the liner is allowed to recover in cross-section into engagement with the inner surface of the pipe.

3. A method as claimed in Claim 1, in which the liner moves into engagement with the inner surface of the pipe by recovery in cross-section and by moving an expansion device through the liner.

4. A method as claimed in Claim 1, in which an expansion device which is flexible in cross-section is moved through the liner.

5. A method as claimed in Claim 4, in which the expansion device comprises a plurality of parts biassed outwards by resilient means.

6. A method as claimed in any preceding claim, in which the die has a minimum cross-section in substantially a single transverse plane.

7. A method as claimed in any preceding claim, in which the die is mounted on the pipe whilst the liner is introduced into the pipe.

8. A method as claimed in Claim 7, in which the die is in separable parts for subsequent removal from the pipe.

9. A method of lining a pipe comprising mounting a die on a pipe to be lined, and moving a liner through the die into the pipe.

10. A method as claimed in Claim 9, in which the die is in separable parts for removal from the pipe.

11. A die for use in pipe lining having an orifice defined by parts which are separable from each other.

12. A die assembly for use in pipe lining comprising a first part and a second part together defining a passage, the second part being removable from the first part and defining the minimum cross-section of the passage.

13. A die assembly as claimed in Claim 12, comprising a plurality of said second parts respectively defining different minimum cross-sections.

14. A die assembly as claimed in Claim 12 or Claim 13, in which the minimum cross-section is defined in a single transverse plane.

15. A method of lining a pipe as claimed in Claim 1 and substantially as hereinbefore described.

16. A method of lining a pipe as claimed in Claim 9 and substantially as hereinbefore described.

17. A die for use in pipe lining substantially as hereinbefore described with reference to and as shown in Figs. 9 and 10 of the accompanying drawings.

18. A die assembly for use in pipe lining substantially as hereinbefore described with reference to and as shown in Fig. 3 of the accompanying drawings.

19. A pipe when lined by a method as claimed in any of Claims 1 to 10 or Claim 15 or Claim 16.