GB2218370A - A method of lining installed pipework - Google Patents

Abstract

Comprises drawing a liner of plastics material having an outer diameter greater than the internal diameter of the pipework 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 reducing in diameter to a minimum value and 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, a die interior having its walls parallel to the die axis and an internal diameter equal to such minimum value which extends over an axial length of from zero to 42% of the axial distance between where the liner pipe engages the swaging surface and that part of the swaging surface that has a minimum diameter, and extending from such intermediate part a diverging axial continuation of the die interior with its walls inclined to the die axis and its diameter progressively increasing in the direction of the die outlet. <IMAGE>

Description

PIPELINING AND LINER PIPE SWAGING DIES This invention relates to improvements in methods and apparatus for reducing the diameter of a liner pipe intended for use as a liner to existing pipework such as a ground embedded gas, oil or water pipe.

When lining existing ground embedded pipework, it is known to draw a hot liner pipe of plastics tube through a die to reduce its diameter and then into a length of the existing pipework. The swaged liner pipe is subsequently caused to expand within 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 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 provides 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 installed 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 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. In our co-pending Application No. it is disclosed that in carrying out the liner pipe swaging step in the course of pipelining operations, there are substantial advantages to be gained over and above the practice of the prior art by reducing the axial length of the first portion in accordance with the invention the subject of that Application.

Furthermore, the second portion may be dispensed with altogether.

Such advantages may also be secured or, in appropriate cases, enhanced in the case where at the outlet end of the die, and extending towards the outlet from that part of the interior surface of the die which has a minimum diameter, there is provided a diverging interior surface which increases in diameter in the direction of the die outlet.

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 bed 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 reducing in diameter to a minimum value and 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, a die interior intermediate part 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 and which extends over a proportionate axial length of from zero to 42% of the axial distance between where the liner pipe engages the swaging surface and that part of the swaging surface that has a minimum diameter, and extending from such intermediate part a diverging axial continuation of the die interior with its walls inclined to the die axis and its diameter progressively increasing in the direction of the die outlet.

It will be appreciated that where the said die interior intermediate part is of zero axial length, there will be an immediate transition between the "converging" die swaging surface and the said diverging axial continuation of the die interior.

Such a case is included within the scope of the present invention.

Preferably, such interior intermediate part will extend over a proportionate axial length of less than 30% of the said axial distance and, advantageously, less than 21% of such axial distance.

As in the case of the invention of our said co-pending Application, 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 are substantially less than the pulling tensions required to swage the liner pipes 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 orifice from which the pipe emerged 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 can 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 tensions 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.

When using lining pipes of synthetic hydro-carbon resins such as polyethylene or modified polyethylene as conventionally used in practice, one consequence of having a relatively short or no die interior part with parallel walls extending from the die orifice manifests a greater tendancy 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 with parallel walls of substantial length, typically in the order of 50% of the overall die length. On release of pulling tension, such tendency will result in greater radial expansion in relation to the pulling tension employed.

The method of the present invention provides means for greater control of the radial expansion or "spring back" tendency of the liner pipe under tension after emergence from the die interior part having parallel walls or, where the length of such part is reduced to zero, from the narrowest part of the swaging portion of the die.

In the preferred method of carrying out the present invention, the angle of inclination of the divergent surface of the die interior is so selected that the liner pipe after passing through the said die interior intermediate part bears against such surface for at least part of the distance from such intermediate part and the die outlet.

The divergent part may be frusto conical in shape.

Alternatively, it may have a variable angle of inclination to the die axis.

The optimum angle of inclination of the surface walls of the divergent part will depend upon the circumstances of the carrying out of the swaging operation. The range of angles for at least part of the divergent surface may conveniently be from 2 degrees to 15 degrees. In ascertaining the optimum angle in any particular case, consideration should be given inter alia, to the inherent properties including the "spring back" tendency of the material of the liner pipe, the temperature of the operation, the pulling tension and the frictional resistance encountered within the swaging part of the die during the swaging operation. In general, a higher temperature results in a relatively greater tendency towards "spring back".Conversely, increased resistance by the swaging surface to the passage of the liner pipe resulting from increased friction or the choice of a swaging angle that offers more resistance to the passage of the liner pipe through the die will result in a relatively higher pulling tension on the liner pipe after its emergence from the die interior intermediate part and, in consequence, a lesser degree of axial radial expansion or spring back.

In one embodiment of the present invention, the angle of inclination of the divergent surface to the die axis decreases from the point adjacent to the die interior.

intermediate part as one proceeds towards the die outlet.

By providing a relatively sharp decrease adjacent such intermediate part, the contour of the surface (taken in cross section) may be caused to emulate approximately the contour that would be adopted by the liner pipe surface if it emerged from such intermediate part and where allowed to expand unrestrained save for the pulling tension exerted on the liner pipe. In this way, the variation in frictional resistance between the liner pipe and the divergent surface as the liner pipe proceeds towards the outlet may be reduced; and this can provide an advantage in relation to the smooth operation of the overall swaging process.

By adjustment of the angle and length of the divergent portion of the die, the extend of the tendency towards radial expansion or "kick back" of the swaged liner pipe may be controlled. Furthermore, and as compared with the prior art, by providing in accordance with the method of the present invention for an increased tendency towards radial expansion or "springback" of the liner pipe after swaging, 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 and with the minimum amount of sharp transitions or jerks.

The dies of the present invention require substantially lower pulling tensions to effect a comparable degree of swaging as compared with prior art dies. They furthermore bring about a greater "springback" tendency on the part of the pipe emerging from the die outlet orifice. In consequence, 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 a plastics liner pipe to its insertion into installed pipework which is provided with an internal swaging surface extending from its inlet and reducing in diameter to a minimum value and 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, a die interior intermediate part 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 and which extends over a proportionate axial length of from 0 to 42% of the axial distance between that part of the swaging surface that has the maximum diameter and that part of the swaging surface that has the minimum diameter, and, extending from such intermediate part a diverging axial continuation of the die interior with its walls inclined to the die axis and its diameter progressively increasing in the direction of the die outlet.

Preferably, the said intermediate part extends over a proportionate axial length of less than 30% of the said axial distance, and advantageously less than 21%.

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 in the case where it is intended that the liner pipe should remain in contact with the divergent surface all the way to the outlet.

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 using swaging dies according to the present invention, the ratio of the maximum internal diameter to minimum internal diameter is optimally from 1.05:1 to 1.15:1.

The pipe lining operation in accordance with the present invention 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, by 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 thus becomes possible to line substantially longer lengths of existing pipework in the course of any single pipelining operating 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 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 SDR, 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.

The circumstances of the operation being carried out 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 intermediate part within the limits set out above or else a shallow angled divergent surface, or both.

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 maintainance of a particular liner pipe diameter within pre-determined limits for the whole of the swaging operation. Likewise, if the ambient temperature be high, the tendency 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 aforesaid intermediate part extends to say, 21% to 30% of the axial length of the swaging surface, or else again a relatively shallow angled divergent part, or both.

Conversely, in lining short lengths of pipework and/or when carrying out operations in cold weather, the relative length of the intermediate part may be reduced and/or the angle of the divergent part increased 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" i.e. the pulling tension required to swage the liner pipe. Using dies made in accordance with the present invention, on the other hand, such fluctuations may be 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 in itself 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 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 of the dislodging of the pulling equipment from its anchorage, both of which events are notoriously conductive to extreme hazard to all in the vicinity.

The invention may be illustrated by reference to the accompanying drawings in which Figure 1, Figure 2 and Figure 3 represent respectively in section three embodiments of dies made in accordance with the present invention, and Figures 1A, 2A and 3A are enlarged representations of the respective die interior ("upper") walls where transition occurs from a converging surface to a divergent surface.

In Figure 1, the swaging surface a converges from the inlet to the point of minimum diameter, whence the die interior intermediate part k having its walls parallel to the die axis extends as far as the divergent surface c.

The divergent surface in turn leads to the die outlet.

The broken line represents the outer surface of the liner pipe before entering and after emergence from the die. In this particular case, the diameter of the liner pipe emerging from the die is governed by the outlet diameter of the die, so that within the divergent part of the die itself, the liner pipe remains in contact with the divergent surface along the whole of its length.

In Figure 2, the interior intermediate part having walls parallel to the die axis has been dispensed with and the divergent surface g starts at the point of minimum diameter of the swaging surface p. Here again, the liner pipe remains in contact with the whole of the divergent surface q as far as the die outlet.

In Figure 3, there is again a sharp transition from the convergent swaging surface x to the divergent surface y z. In this case, however, the divergent surface is shown as having an angle of inclination to the die axis which decreases sharply from a maximum at Z adjacent the transition point. The divergent surface then continue to diverge at a shallower angle (as at z) up to the outlet.

In this particular case, the liner pipe is shown to be in contact with part only of the divergent surface and disengages from such surface before it reaches the outlet.

Claims (22)

1. A method of lining installed pipework which comprises drawing a liner pipe of plastics material having an outer 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 reducing in diameter to a minimum value and 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, a die interior having its walls parallel to the die axis and an internal diameter equal to such minimum value which extends over a proportionate axial length of from zero to 42% of the axial distance between the liner pipe engages the swaging surface and that part of the swaging surface that has a minimum diameter, and extending from such intermediate part a diverging axial continuation of the die interior with its walls inclined to the die axis and its diameter progressively increasing in the direction of the die outlet.

2. A method as claimed in Claim 1 in which the angle of the divergent surface of the die interior is so selected that the liner pipe after passing through the said intermediate part bears against such surface for at least part of the distance from such intermediate part to the die outlet.

3. A method as claimed in any preceding Claim in which the angle of inclination of the divergent surface to the die axis decreases from the point adjacent to the said intermediate part as one proceeds towards the die outlet.

4. A method as claimed in any preceding Claim in which the intermediate part extends over a proportionate axial length of less than 30% of the said axial distance.

5. A method as claimed in Claim 4 in which intermediate part extends over a proportionate axial length of less than 21% of the said axial distance.

6. A method as claimed in any preceding Claim in which the angle of inclination of at least part of the divergent surface is from 2 degrees to 15 degrees.

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

8. A method as claimed in Claim 7 in which the swaging surface is inclined to the die axis at an angle of from 20 degrees to 25 degrees.

9. A method as claimed in any preceding Claim in which the reduction of 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.

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

11. 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.

12. A die for use in reducing the diameter of plastics liner pipe prior to its insertion into installed pipework which is provided with an internal swaging surface reducing in diameter to a minimum value and which, or part of which is inclined at an angle between 6 degrees and 32 degrees and no part at an angle of greater than 32 degrees to the die axis, a die interior intermediate part 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 and which extends over a proportionate axial length of from zero to 42% of the axial distance between that part of the swaging surface that has the maximum diameter and that part of the swaging surface that has the minimum diameter, and extending from such intermediate part a diverging axial continuation of the die interior with its walls inclined to the die axis and its diameter progressively increasing in the direction of the die outlet.

13. A die as claimed in Claim 12 in which the angle of inclination of at least part of the divergent surface to the die axis is from 2 degrees to 15 degrees.

14. A die as claimed in either of Claims 12 or 13 in which the angle of the inclination of the ivergent surface to the die axis decreases from the part adjacent to the said intermediate part as one proceeds towards the die outlet.

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

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

17. A die as claimed in any of Claims 12 to 16 in which the said intermediate part extends over a proportionate axial length of less than 30% of the said axial distance.

18. A die as claimed in Claim 17 in which the intermediate part extends over a proportionate axial length of less than 21% of the said axial distance.

19. A die as claimed in any of Claims 12 to 18 in which the diameter of the swaging surface is reduced from the part having a maximum diameter to the part having a minimum diameter by a ratio of from 1.05:1 to 1.15:1.

20. A die as claimed in any of Claims 12 to 19 in which the internal surface is reduced down to N7, and preferably N6 and advantageously N5 or beyond.

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

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