GB2218488A

GB2218488A - A method of lining installed pipework

Info

Publication number: GB2218488A
Application number: GB8810896A
Authority: GB
Inventors: Brian Edward Mcguire
Original assignee: British Gas PLC
Current assignee: British Gas PLC
Priority date: 1988-05-09
Filing date: 1988-05-09
Publication date: 1989-11-15
Anticipated expiration: 2008-05-09
Also published as: GB2218488B; GB8810896D0

Abstract

Includes heating a length of plastics liner pipe 1 of external diameter greater than the internal diameter of the pipework 10 to be lined by means of hot fluid sprays 4, drawing the liner pipe 1 through a swaging die 7 using pulling means under tension attached to the leading end of the liner pipe 1 and threaded through the pipework 10 to reduce the external diameter of the liner pipe 1 by up to 15%, the tension applied by the pulling means being such as partially to restrain the radial expansion of the outer surface of the liner pipe 1 after its emergence from the die 7, drawing the liner pipe 1 through the installed pipework 10 with its outer diameter reduced to and/or maintained at a dimension less than that of the inner diameter of the pipework 10 and thereafter expanding the liner pipe 1 to a close fit within the pipework 10. <IMAGE>

Description

PIPELINES CASE NUMBER 5 This invention relates to a method of and apparatus for the lining of existing pipes. The invention will be described in relation to gas, oil and water supply pipes,#but it will be appreciated that the invention is applicable to pipes of all kinds.

When lining installed pipes (which pipes when ground embedded are prone to crack due to ground movement) it is known to draw a heated liner of a plastics tube through a die to reduce the diameter and then into a length of the existing pipe.

Other and novel methods of liningpipework are described in our co-pending applications designated at follows: (a) "Hot Pipe Swaging" Application No. ~~~~~~~~~~~ (b) "Cold Pipe -Swagi#g" Application No. ~~~~~~~~~~~ (c) "Die Abuttment" Application No. ~~~~~~~~~~~ (d) "Vacuum Swaging" Application No. ~~~~~~~~~~~ (e) "flie" Application No. ~~~~~~~~~~~~ The present invention relates to an improved method of lining installed pipework when using a swaging die to reduce the diameter of the line pipe prior to its being drawn into the existing pipework.By "installed" pipework is meant pipework that has already been installed in position to carry out its intended purpose, such as for example, ground embedded pipework for gas, oil, water or sewage, pipework forming part of a larger installation such as an oil or gas refinery or storage installation, or pipework resting on the ground and laid down to connect a source of supply to the recipient such as an oil pipe connecting a well to a refinery or port.

In the case of ground embedded pipework it will be appreciated that the normal arrangement when such a process is being carried cut will involve a winch adjacent to an excavation at one end of a length of pipe to be lined whence a cable or similar flexible ligament passes through the length of pipe to a second excavation beyond which it is attached to the front end of a liner pipe of plastics material. Adjacent to the second excavation is a tube heating and compressing apparatus which has a heater and a size-reduction die. At a downstream end of this apparatus there may be a reciprocatable "pusher" which can grip the pipe and draw it from the apparatus and urge it towards the pipe to be lined.

The present invention provides an improvement over the prior art known methods in that it assists in securing uniform preheating of liner pipes of large diameters before swaging, particularly where the pipe thicknesses are correspondingly large or are required to be relatively large by reason of the use to which the lined pipework is to be put.

According to the present invention, there is provided a method of lining installed pipework which includes the steps of heating a length of liner pipe made from a memory retaining plastics material of external diameter greater than the internal diameter of the pipework to be lined, by means of hot fluid sprays, drawing the liner pipe through a swaging die using pulling means under tension attached to the leading end of the liner pipe and threaded through the pipework to reduce the external diameter of the liner pipe by up to 15% the tension applied by the pulling means being such as partially to restrain the rad ;; expansion of the outer surface of the liner pipe after its emergence from the die, drawing the liner pipe through the installed pipework with its outer diameter reduced to and/or maintained at a dimension less than that of the inner diameter of the installed pipework and thereafter allowing the liner pipe to expand within the pipework by relaxation of the said tension followed by memory induced expansion at ordinary atmospheric pressure and at the ambient temperature of the pipework.

The present invention envisages in a preferred aspect of its operation the employment of a swaging die that is provided with a surface which or part of which is inclined at an angle between 6 degrees and 32 degrees, there being no part at an angle of more than 32 degrees to the die axis and which extends over an axial length that is at least 70% of the axial distance between the part where the liner pipe engages with such surface and the part where the liner pipe disengages from the die.

Dies used according to the prior art methods of pipe swaging as employed in practice have comprised two portions, the first being the inclined swaging surface reducing in diameter to a minimum value and the second being an axial continuation of the die interior having its walls parallel to the die axis and an internal diameter equal to such minimum value. We have found that in the carrying out of the present invention, it is advantageous to reduce the axial length of the said second portion relative to the axial length of the first portion, or else to dispense with the second portion altogether.In particular, by so designing the die that the first part extends over an axial distance that is at least 70%, and preferably over 80%, and advantageously over 85% of the axial distance between the part where the liner pipe engages with the inclined surface and the outlet where the pipe emerges from the die, the pulling tension required to swage the liner pipe is substantially decreased.

Another consequence of the use of such a die in the carrying out of the present invention is that, when using a liner pipe of synthetic hydrocarbon resins such as polyethylene or modified polyethylene as conventionally used in practice, the liner pipe on emerging from such orifice manifests a greater tendency towards radial expansion relative to the degree of swaging exerted by the die than in the case where, as in the prior art, the swaging die was provided with a second portion as mentioned above of substantial lengths, typically in the order of 50% of the overall die length. On release of pulling tension, such tendency will result in a greater proportional radial expansion in relation to the pulling tension employed than would have occurred using the prior art dies.

The process of the present invention relies both upon the expansion of the liner pipe within the pipework as a result of relaxation of the pulling tension and also as a result of the memory induced expansion of the swaged liner pipe. By the use of a die having a reduced axial length of its second portion relative to the axial length of its first portion as mentioned above, the proportionate expansion resulting from the relaxation of the pulling tension may be significantly increased thus resulting in improved control over the pipe lining operation.

The arrangements described above furthermore provide a significant advantage in relation to the case where a "pusher" device, as e.g. of the kind described in our co-pending Patent Application UK No. 8806926 is used. It is inherent in the operation of such a pusher that, when it grips the liner pipe and urges it towards the pipework to be lined, there is experienced a temporary reduction in the pulling tension exerted by the pulling device (such as a winch) at the far end of the pipework. Upon the pusher releasing its grip the tension resorts back to its original value. In practice, this results in a continuous fluctuation in the tension. It is also desirable that the changeover between maximum and minimum tensions in the course of the fluctuations be effected as smoothly as possible and with the minimum amount of sharp transitions or jerks.

We have found that as a result of the use of the prefered dies of the present invention which require substantially lower pulling tensions to effect a comparable degree of swaging as compared with prior art dies and which furthermore bring about a greater "springback" tendency on the part of the pipe emerging from the die orifice, the amplitudes of the fluctuations are reduced and the fluctuations themselves become smoother. Having regard to the very high forces involved in exerting the pulling tension, this again constitutes a significant improvement in both the safety and the efficiency of the operations.

The length of the pipework which may be lined in a single operation by the method of this invention may typically be from 10 metres upwards. The limiting length of pipework which may be lined in any particular case will depend upon a combination of #actors including the friction resistance to the movement of the liner within the pipework, the extent to which the liner pipe with reduced diameter after insertion into the pipework becomes subject to deformation (a problem encountered with larger diameter liner pipes of relatively large SDR ratio), the limiting tension on the leading end of the liner pipe beyond which it may suffer permanent damage or elongation, the capacity of the mechanism (such as a winch) operating the pulling means and the uniformity of diameter and/or direction or otherwise of the pipework interior.The most suitable practicable length to be lined in any particular case can readily be ascertained by trial and error. By the method of the present invention it becomes possible to line lengths of pipework up to 450 metres or more. The surface finish of the die may be provided by means known in the art. It is preferred that such surface finish should be at least down to N7 typically down to N6 preferably down to N5 and ideally in the order of N4 or lower. It has been found advantageous to employ a die having a relatively shallow angle of inclination of the inclined surface of the die to the die axis and within the range of 12 degrees to 20 degrees and preferably from 20 degrees to 25 degrees.

Reduction of the angle assists in reducing the pulling load required to effect compression of the liner pipe, but at the same time increases the area of the swaging surface for any given degree of compression. The optimum angle will be that which, in any particular case, minimises the overall disadvantages of a high load to bring about compression on the one hand and a large friction inducing die surface area on the other hand. The die surface may be frusto conical in shape. Alternatively, it may have been a variable angle of inclination to the die axis within the above stated limits.

It is a significant and advantageous feature of the present invention that when using a liner pipe made of a deformable memory retaining material in accordance with the method of the invention the liner pipe may be left to expand radially within the lined pipework and under the influence of the memory of the material constituting it. By suitable choice of initial diameter of the liner pipe, degree of compression during the swaging operation and die outlet orifice diameter in relation to the internal diameter of the pipework to be lined, the present invention can bring about the provision of a close fitting lining to the pipework resulting following relaxation of tension from the memory induced expansion of the pipelining at the ambient temperatures and pressure within the pipework.It is unnecessary to have recourse to the means provided by the prior art for expanding the pipelining within the pipework such as the application of internal super atmospheric pressure or the application of heat to the pipelining from within or the initial application of very high stretching forces to the pipelining to bring about an initial reduction in its diameter prior to insertion into the pipework. The precise operating conditions employed in order to carry out the method of the present invention will depend upon the several factors referred to above in any particular case and will vary according to the pipework internal diameter and the purpose for which it is put to use (for example whether for water or gas) the material of the pipelining and the SDR of the pipelining. (By SDR is meant the ratio of the diameter of the pipelining before swaging to its wall thickness).

According to another aspect of the present invention there is provided apparatus for lining an existing pipe comprising a support structure, a swaging die disposed in the structure for reducing the diameter of a liner pipe pulled through it, fixing means enabling the structure to be fixed to the pipe to be lined and heater means comprising hot fluid sprays associated with the swaging die to enable the die to be heated to heat liner pipe being pulled therethrough.

A preferred material for the liner pipe is polyethylene, but other materials having the necessary memory retaining characteristics, such as a co-polymer of polyethylene and at least one alphaolefin of up to ten carbon atoms may equally well be used. Although the reduction in diameter of the liner pipe during passage through the swaging die may be up to 15% reductions in the range 5.0% to 9.8% are preferred.

The reduction should be such as to allow drawing of the liner pipe through the existing pipe. This somewhat simple requirement is complicated by the fact that existing pipes are often not accurately sized internally, that the internal diameter may vary along the length of the pipe and that the rate of recovery of the liner pipe may vary with ambient conditions and with the material from which the pipe is made. The wall thickness of the liner pipe should be as thin as possible consistant with the use to which the pipe is to be put and the requirement to provide adequate internal sealing of the existing pipe. A ratio of wall thickness to diameter of the liner pipe in the range 10 to 46 is preferred.

The maximum tension chosen for pulling the liner pipe through the existing pipe should advantageously be in the range 45% to 55% of the yield strength of the liner pipe in question, and in particular about 50%. The ratio of the throat diameter of the die to the diameter of the existing pipe should advantageously be in the range 1.05:1 to 1.15:1. A reciprocatable pusher may be employed to augment the tension exerted by the said pulling means to draw the liner pipe through the swaging die.

In order that the invention may be more clearly understood, one embodiment of the invention will now be described by way of example, with reference to the accompanying drawing which is a side elevational diagramatic view in section of one form of apparatus whereby the method of the present invention may be carried out. In the said drawing, the broken line 1 represents the outer surface of the liner pipe which is drawn through aperture 2 into a heating chamber 3 which is furnished with a plurality of spray means 4 disposed so as to project hot water sprays which impinge upon the liner pipe 1 as it is pulled through the heating chamber from left to right as shown on the drawing and so increase its temperature to within the range of from 35 C to 95 C and preferably to about 50 C.It is advantageous to have the hot water sprays so arranged and the supply of hot water to the several sprays so controlled as to ensure that the liner pipe 1 is heated uniformly around the whole of its circumference by the time it reaches the die 7.

At point 5, the outer surface of the line pipe 1 engages with the inclined surface 6 of the swaging die 7 from which swaging die the liner pipe emerges with a reduced diameter at the die orifice 8. In the embodiment shown, the die outlet orifice 8 is located at the point where the diameter of the inclined swaging surface 6 of the die 7 attains its minimum value.

On emerging from the orifice 8 of die 7, the line pipe 1 which is under the influence of the pulling tension drawing it through the die manifests a radial expansion (not shown in the drawing) so that as it, proceeds forwardly, its outer diameter will exceed the diameter of the orifice 8. Such radial expansion will be limited by the continued tension exerted upon the liner pipe 1 as it continues on its way towards and into the pipework 10 that is to be lined.

It may be advantageous to attach the swaging die 7 either directly or indirectly to the pipework 10 as indicated in our co-pending application no. . Alternatively, the heating chamber 3 with its associated die 7 may be located away from and anchored separately from the pipework 10.

The method of the present invention has been found to be particularly useful where the pipework to be lined is of large diameter and is such as to call for correspondingly large diameter liner piping, for example in cases where the outer diameter of the liner pipe exceeds 450mm and, in particular, 600mm and especially 800mm; and further in the case where a liner pipe in the lower range of outer diameters such as from 290mm to 550mm has an SDR below 16. Hitherto, it has proved difficult to heat satisfactorily under operating conditions such large and/or thick liner pipes prior to swaging using the methods hitherto known and used in this art. The die 7 itself may optionally be provided with heating means, such as an internal electrical heating coil or hot fluid channels so as to maintain surface 6 at a temperature equal to or above the temperature of liner 1 as it passes through the swaging die. Furthermore, cooling means of a kind known per se, in the art may be provided to cool the liner pipe immediately after its emergence from the die orifice 8.

Claims

1. A method of lining installed pipework which includes the steps of taking a length of liner pipe made from a memory retaining plastics material of external diameter greater than the internal diameter of the pipework to be lined, drawing the liner pipe through a swaging die which is attached directly or indirectly to the pipe to be lined using pulling means under tension attached to the leading end of the liner pipe and threaded through the pipework to reduce the external diameter of the liner pipe by up to 15%, the tension applied by the pulling means being such as partially to restrain the radial expansion of the outer surface of the liner pipe after its emergence from the die, drawing the liner pipe through the installed pipework with its outer diameter reduced to and/or maintained at a dimension less than that of the inner diameter of the pipework and thereafter allowing the liner pipe to expand within the pipework by relaxation of the said tension followed by memory induced expansion at ordinary atmospheric pressure and at the ambient termperature of the pipework.

2. A method as claimed in Claim 1 in which the liner pipe is pre-heated before the swaging step to a temperature between 35 degrees C and 90 degrees C.

3. A method as claimed in Claim 2 in which the liner pipe is pre-heated to a temperature of from 30 degrees C to 65 degrees C.

4. A method as claimed in Claim 3 in which the liner pipe is pre-heated to a temperature of from 45 degrees C to 55 degrees C.

5. A method as claimed in any preceding Claim in which the liner pipe is pre-heated, at least in part, within the die structure prior to swaging.

6. A method as claimed in Claim 1 in which the liner pipe is drawn into the die structure at ambient temperature and no heat is supplied to or generated within the swaging die structure save such heat as may be generated by friction between the liner pipe and the swaging die internal surfaces during passage of the liner pipe through the swaging die.

7. Apparatus for lining installed pipework comprising a support structure, a swaging die disposed within the structure for reducing the diameter of a liner pipe passed through it, and fixing means for enabling the structure to be fixed to the pipe to be lined in which the swaging die is provided with a swaging surface which, or part of which is inclined at an angle between 6 degrees and 32 degrees and no part at an angle of more than 32 degrees to the die axis.

8. Apparatus as claimed in Claim 7 in which the angle of inclination the swaging surface is between 12 degrees and 29 degrees.

9. Apparatus as claimed in Claim 8 in which the angle of the swaging surface is between 20 degrees and 25 degrees.

10. Apparatus as claimed in any of Claims 7 to 9 in which the inclined surface extends over an axial length that represents a proportion r at least 70% of the overall axial distance between that part of the swaging surface that has the maximum diameter and the die outlet.

11. Apparatus as claimed in Claim 10 in which the proportion is at least 80%.

12. Apparatus as claimed in Claim 11 in which the proportion is at least 85%.

13. Apparatus as claimed in any of claims 10 to 12 in which the walls of that part of the die interior that extends between the said swaging surgace and the outlet are paralled to the die axis.

14. Apparatus as claimed in any of Claims 7 to 13 which comprises heater means disposed within the swaging die structure whereby heat may be applied to the liner pipe during passage through the die.

15. Apparatus as claimed in any of Claims 7 to 14 which comprises a pusher device adapted to grip the liner pipe after its emergence from the die and urge it towards the pipework.

16. A method as claimed in any of Claims 1 to 6 in which use is made of apparatus as claimed in any of Claims 7 to 15.

17. A method as claimed in any of Claims 1 to 6 or 16 in which the liner pipe is reduced in diameter during passage through the die by an extent within the range from 1.05:1 to 1.15:1.

18. A method of lining installed pipework substantially as herein described.

19. Apparatus for lining installed pipework substantially as herein described.