GB2218489A

GB2218489A - A method of lining installed pipework

Info

Publication number: GB2218489A
Application number: GB8810897A
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: GB8810897D0; GB2218489B

Abstract

Comprises of drawing a liner pipe of plastics material of external diameter greater than the internal diameter of the pipework to be lined through a swaging die to reduce its diameter sufficiently to enable the liner pipe to be drawn through the pipework using pulling means under sustained tension attached to the leading end of the liner pipe and threaded through the pipework wherein the swaging die is provided with an internal swaging surface which, or part of which is inclined at an angle of between 6 degrees and 32 degrees and no part at an angle or more than 32 degrees to the die axis and which extends over an axial length that is at least 70% of the overall axial distance between the part where the liner pipe engages with such surface and the part where the liner pipe disengages from the die.

Description

PIPELINE LINER PIPES AND LINER PIPE WAGING DIES This invention relates to a method for reducing the diameter of a liner pipe intended for use as a liner to existing pipework such as ground embedded gas, oil or water pipes.

When lining existing ground embedded pipework, it is known to draw a hot liner pipe of plastics tube through a die to reduce the diameter and then into a length of the existing pipework. The swaged liner pipe is subsequently caused to expand within the embedded pipework so as to provide a close fitting liner within the pipework. Such expansion may according to the prior art be effected by the application of internal heat or elevated internal pressure.It is also known to subject the liner pipe to extremely high tension so as to stretch it and thereby reduce its diameter sufficiently to enable it to be introduced into the existing pipework, and then to bring about expansion of the liner pipe within the existing pipework by release of the tension whereby the liner pipe reverts forthwith to or almost to its original length and external diameter, thus providing a close fit within the existing pipework.

Other and novel methods of lining pipework are described in our co-pending applications designated as follows: (a) "Hot Pipe Swaging" Application No.

(b) "Cold Pipe Swaging" Application No.

(c) "Die Abuttment" Application No.

(d) "Vacuum Swaging" Application No.

(e) "Hot Spray" 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 liner pipe prior to it 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.

The present invention also relates to improved swaging dies for use in pipelining operations. Dies used according to the prior art methods of liner pipe swaging in the course of lining operations for installed, typically ground embedded pipes 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 carrying out the liner pipe swaging step in the course of pipelining operations, there are substantial advantages to be gained by reducing the axial length of the said second portion relative to the axial length of the first portion. Furthermore, the second portion may be dispensed with altogether.

According to the present invention, there is provided a method of lining installed pipework which comprises drawing a liner pipe of plastics material of external diameter greater than the internal diameter of the pipework to be lined through a swaging die to reduce its diameter sufficiently to enable the liner pipe to be drawn through the pipework using pulling means under sustained tension attached to the leading end of the liner pipe and threaded through the pipework wherein the swaging die is provided with an internal 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 and which extends over an axial length that is at least 70% of the overall axial distance between the part where the liner pipe engages with such surface and the part where the liner pipe disengages from the die.

Preferably, such inclined surface will extend over an axial length that is at least 80% of the axial distance between the part where the liner pipe engages with such surface and the part where the pipe disengages from the die, and advantageously over an axial length that is advantageously 85% of such axial distance.

The present invention results in a significant advantage in that the pulling tensions required to swage the liner pipe using the dies of the present invention have been found to be substantially less than the pulling tensions required to swage the liner pipe using the dies of the prior art. Such dies were provided with second portions as referred to above which were axial continuations of the die interiors having walls parallel to the die axis and internal diameters equal to the minimum die interior diameter. Typically, such second portions extended over a distance of 50% of the overall axial distance between the part where the liner pipe engaged with the inclined surface of the die and the outlet orifice from which the pipe emerged and disengaged from the die after the swaging operation.The reduction in the tension required to effect the swaging operation using the method of the present invention has been found to be up to one third as compared with the tension required for operation using the dies of the prior art.

Since in practice the pulling tension required to carry out pipelining operations using swaging dies are commonly to be measured in terms of several tonnes, it will be appreciated that reduction in the required tension results not only in greatly increased ease of operation, but also in a substantial increase in the safety of the operation.

We have also found that as a consequence of the carrying out of swaging operations in accordance with the method of the present invention, and when using liner pipe of synthetic hydrocarbon resins such as polyethylene or modified polyethylene as conventionally used in practice, the liner pipe on emerging from the die outlet orifice manifests a greater tendency towards radial expansion relative to the pulling tension exerted on the liner pipe to pull it through 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 length, typically in the order of 50% of the overall die length. On release of pulling tension such tendency wil result in greater radial expansion in relation to the pulling tension employed.

This provides significant advantages in the overall pipe lining operation. Firstly, there is provided improved control over the pipe lining operation. Secondly, by providing in accordance with the method of the present invention for an increased tendency towards radial expansion of the liner pipe on its emergence from the die orifice, a significant advantage is secured in relation to the case where a "pusher" device, as for example, of the kind described in our co-pending Patent Application UK No. 8806926 is used. It is inherent in the operation of such as a pusher device that, when it grips the liner pipe and urges it towards the pipework, 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 reverts 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 with the minimum amount of sharp transitions or jerks.

We have found that as a result of the use of the 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 outlet 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 present invention furthermore relates to a die for use in reducing the diameter of plastics liner pipe prior to its insertion into installed pipework which 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 and which extends over an axial length that is at least 70% of the overall axial distance from that part of the swaging surface that has the maximum diameter to the die orifice of smaller diameter, and preferably over 80% and advantageously over 85% of such axial distance.

Any sharp edge surrounding the outlet orifice of the dies of the present invention may advantageously be bevelled, radiused or rounded off so as to prevent the edge from cutting into the pipe as it emerges from the die.

We have further found in practice that it is advantageous to employ dies in accordance with the present invention having a relatively shallow angle of inclination of the inclined swaging surface of the die to the die axis and within the range of 12 degrees to 29 degrees, and preferably from 20 degrees to 25 degrees. Reduction of the angle assists in reducing the pulling load required to effect the 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 found to 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 on the other hand.Thus the optimum angle will vary according to the dimensions of the liner pipe to be swaged, the material from which such liner pipe is made and the SDR of the liner pipe in question. (By SDR is meant the ratio of the diameter of the liner pipe to its wall thickness before swaging).

The surface finish of the die is preferably down to N7, or beyond, advantageously to N6 and ideally to N5 or N4.

The die swaging surface may be frusto conical in shape.

Alternatively, it may have a variable angle of inclination to the die axis within the above stated limits.

For pipe lining operations, it has been found advantageous to use swaging dies according to the present invention wherein the ratio of the maximum internal diameter to minimum internal diameter ranges from 1.05:1 to 1.15:1.

Furthermore, the pipe lining operation in accordance with the present invention whereby the liner pipe is drawn first through the swaging die of the present invention and subsequently into the pipework to be lined is best carried out using a pulling tension in the range of from 45% to 55% of the yield strength of the liner pipe in question, and in particular, a tension in the region of about 50%. It will thus be appreciated that the present invention, be reducing the amount of tension required to draw the liner pipe through the die, will provide a greater margin of "available tension" to draw the liner pipe through the existing pipework. Such additional tension is required to overcome the frictional resistance of the existing pipework to the passage of the liner pipe into and through it.It will thus be appreciated that by the use of the method of the present invention and/or the dies or the present invention, it becomes possible to line substantially longer lengths of existing pipework in the course of any single pipelining operation using the same equipment than was practicable using the dies of the prior art.

Another substantial advantage resulting from the use of dies in accordance with the present invention is secured in the case where, as described in our co-pending patent application number the liner pipe is drawn into the swaging die at ambient temperatures ("cold swaging"). In such a case the use of a heater for the liner pipe before swaging is dispensed with. Because of the reduced resistance to the passage of the liner pipe through the dies of the present invention, it becomes possible to employ the "cold swaging" operation making use of liner pipes of greater diameter, or else of lower S.D.R., or both, than would otherwise be practicable.

The dies of the present invention may be independently heated. In practice, it is found that the friction resulting from the pulling of the liner pipe through the die will generate heat and cause a significant increase in the temperature of the swaging die surface.

In carrying out the method of the present invention, it has been found to be advantageous to vary within the above stated limits the axial length of the second portion of the die interior having walls parallel to the die axis, relatively to the axial length of the first portion of the die interior having inclined converging walls, according to the nature of the swaging operation, the conditions under which the operation is carried out and the nature of the material of the pipelining. As already indicated, such second portion may be done away with altogether so that the inclined swaging walls of the first portion extend all the way to the die outlet orifice (which in such a case is preferably provided with a radiused or bevelled circumferential configuration so as to avoid the disadvantage of the presence of a sharp edge which would tend to cut into the material of the liner pipe).

On the other hand, by varying the relative axial length of the second portion of the die in relation to the axial length of the first portion, the extent of the springback or tendency towards expansion of the liner pipe under tension after emergence from the die may be controlled. A longer relative second portion tends to diminish such springback or tendency towards expansion, and vice versa.

Depending on the circumstances of the operation being carried out, this may have an influence on the choice of die to be used for a particular operation. Where it is intended to line a substantial length of pipework in one pull, it may well be desirable to select a die having a relatively long second portion within the limits set out above. In such a case, the length of the pipework together with the duration of the period of time required to complete the pulling operation can call for the use of a die that will ensure maintenance of a particular liner pipe diameter within predetermined limits for the whole of the swaging operation. Likewise if the ambient temperature be high, the tendancy of the liner pipe to expand will be increased; and an operation carried out under such circumstances may call for the use of a die where the axial length of the first portion extends to no more than, say, 80% to 75% of the overall die length.

Conversely, in lining short lengths of pipework and/or when carrying out operations in cold weather, the relative length of the second portion may be reduced so as to enhance the advantage of a relatively lower tension or pull to effect the swaging operation whilst at the same time benefitting from the improved smoothing effect upon and the diminution of the amplitudes of the fluctuations in tension already referred to.

In practice, using the prior art dies, such fluctuations during the course of a single pull were generally in excess of 10% and frequently in the order of 15% of the "swaging tension" ie. the pulling tension required to swage the liner pipe. Using dies made in accordance with the present invention, on the other hand, such fluctuations have been reduced to the order of 7% of the swaging tension.

As already indicated, the swaging tension required using the dies of the present invention is itself in turn substantially less than the swaging tension required when using the dies of the prior art. It will thus be seen that there will be a two-fold reduction in the fluctuations in tension at the winch. Thus where, as has been found in practice, the swaging tension required when using the dies of the invention is in the order of 67% of the swaging tension required using a comparable prior art die, the overall reduction in the fluctuations of tension will be in the order of from about 47% to 70%. Bearing in mind the very high tensions employed in carrying out operations of the kind referred to, it will be seen that such a reduction results in substantial advantages both as regards the operation of the equipment used and also the safety of the operators.The smaller and less abrupt the amplitudes of the fluctuations, the lesser the danger of a cable break under high tension, or the dislodging of the pulling equipment from its anchorage, both of which events are notoriously condusive to extreme hazard to all in the vicinity.

The following example illustrates the manner in which a die made in accordance with the present invention operates.

Example A. Two identical lengths of 315mm diameter polyethylene pipe known commercially as S & L ('Stewart & Lloyds') "PEX" pipe ("PIPE.A") were drawn by a cable attached to a mitred end portion through two respective dies, the first being a die as used in accordance with the prior art and the second a die in accordance with the present invention.The relevant dimensions of the dies were as follows: First die Second Die Overall length 202mm 50mm Axial length of swaging surface 100mm 42mm Axial length of continuation of interior of minimum diameter beyond inclined swaging surface 102mm 6mm Axial length of radiused outlet orifice - 2mm Diameter of inlet aperture 312mm 320mm Diameter of outlet orifice (D) 285m 285m Circumference of outlet orifice (II D) 895.4m 895.4m Both liner pipes were drawn into the respective dies at the ambient temperature of 13 degrees c. In each case, the die surface temperature increased as a result of friction against the liner pipe to from 80 degrees c.

to 83 degrees c.

On emerging from the die outlet orifice, each liner pipe forthwith increased in diameter and circumference whilst still under tension. Such increased circumference was measured along pre-determined points along the respective pipes. A succession of pulls were made, each over a distance of one metre, and the pulling tension released after each pull. The respective circumferences were increased at the same points in each case within one minute of the release of tension. In each case, there was manifested a further increase in circumference.

B. Using the same dies and under the same ambient temperature of 13 degrees C, the same procedure was followed in the case of two identical lengths of 315mm diameter polyethylene pipe known commercially as "Dupont PEA" ("PIPE B"). Similar internal die temperatures resulting from friction of the die surface against the liner pipe were recorded.

The following average results were obtained: PIPE CIRCUMFERENCE AT AFTER 1 MINUTE INCREASE LOAD INCREASE OUTLET EMERGENCE AFTER (MM) (tonnes) PER UNDER TENSION TONNE TENSION RELEASE (mm/Tonne) PIPE A 1ST DIE 895.4 935.4 959.2 24.5 7.21 3.40 2ND DIE 895.4 934.0 954.5 20.5 4.75 4.32 PIPE B 1ST DIE 895.4 938.0 964.8 26.8 6.34 4.23 2ND DIE 895.4 936.6 961.0 24.4 4.58 5.33 The figures in the penultimate column illustrate the manner in which swaging tension may be reduced using the dies of the present invention.

The figures in the last column provide an indication of the degree of reduction in fluctuations in swaging tension per unit tonne which in practice has been found to result from the use of the dies of the present invention.

Claims

1. A method of lining installed pipework which comprises of drawing a liner pipe of plastics material of external diameter greater than the internal diameter of the pipework to be lined through a swaging die to reduce its diameter sufficiently to enable the liner pipe to be drawn through the pipework using pulling means under sustained tension attached to the leading end of the liner pipe and threaded through the pipework wherein the swaging die is provided with an internal swaging surface which, or part of which is inclined at an angle of between 6 degrees and 32 degrees and 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 overall axial distance between the part where the liner pipe engages with such surface and the part where the liner pipe disengages from the die.

2. A method as claimed in Claim 1 in which the internal swaging surface extends over an axial length that is at least 80% of the said overall axial distance.

3. A method as claimed in Claim 2 in which the internal swaging surface extends over an axial length that is at least 85% of the said overall axial distance.

4. A method as claimed in any preceding claim in which the walls of that part of the die interior that extends between the said swaging surface and the outlet orifice where the liner pipe emerges from the die are parallel to the die axis.

5. A method as claimed in any preceding claim in which the internal swaging surface is inclined to the die axis at an angle of from 12 degrees to 29 degrees.

6. A method as claimed in Claim 4 in which the inclined swaging surface is inclined to the die axis at any angle from 20 degrees to 25 degrees.

7. A method as claimed in any preceding claim in which the reduction in the diameter of the liner pipe within the die during the swaging operation is within the range of from 1.05:1 to 1.15:1.

8. A method as claimed in any preceding claim in which the die outlet orifice is radiused or bevelled around its circumference.

9. A method as claimed in any preceding Claim in which there is employed a pusher device whereby the liner pipe after emerging from the die is repeatedly gripped and urged towards the pipework.

10. A die for use in reducing the diameter of plastics liner pipe prior to its insertion into installed pipework which is provided with a swaging surface which, or part of which is inclined at an angle of between 6 degrees and 32 degrees to the die axis and 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 overall axial distance from that part of the inclined swaging surface of the die that has the maximum diameter to the die outlet orifice.

11. A die as claimed in Claim 10 in which the inclined swaging surface extends over at least 80% of the said overall axial distance.

12. A die as claimed in Claim 10 in which the inclined swaging surface extends over at least 85% of the said overall axial distance.

13. A die as claimed in any of claims 10 to 13 in which the walls of that part of the die interior that extends between the said swaging surface and the outlet orifice, are parallel to the die axis.

14. A die as claimed in any of Claims 9 to 13 in which the swaging surface is inclined to the die axis at an angle of from 12 degrees to 29 degrees.

15. A die as claimed in Claim 14 in which the swaging surface is inclined to the die axis at an angle of from 20 degrees to 25 degrees.

16. A die as claimed in any of claims 9 to 15 in which the diameter of the swaging surface is reduced from the die inlet to the part having a minimum diameter by a ratio of from 1.05:1 to 1.15:1.

17. A die as claimed in any of claims 9 to 16 in which the outlet orifice is radiused or bevelled around its circumference.

18. A die as claimed in any of claims 9 to 17 in which the internal surface is reduced down to N7, and preferably N6 and advantageously N5 or beyond.

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

20. Swaging dies of the invention substantially as described herein.