WO2001016520A1

WO2001016520A1 - Swage lining

Info

Publication number: WO2001016520A1
Application number: PCT/GB2000/003258
Authority: WO
Inventors: Derek Muckle; David Charles Hargett
Original assignee: Uponor Limited
Priority date: 1999-08-27
Filing date: 2000-08-24
Publication date: 2001-03-08
Also published as: AU6853300A; GB2353581A; GB2353581B; GB9920294D0

Abstract

A method of lining a service pipe comprising the steps of: a) providing a cross-linked polyethylene ('PEX') liner pipe of outside diameter substantially equal to or greater than the internal diameter of the service pipe; b) drawing the liner through a swage diet to reduce its diameter and increase its length; c) maintaining the swaged pipe under tension to maintain its reduced diameter; d) passing the reduced diameter swaged pipe along the service pipe; e) relieving the tension to permit the liner to elastically recover at least a proportion of its original dimensions; f) heating the liner to permit recovery of a further proportion of said original dimensions. This permits the advantages and benefits of PEX pipe to be employed in appropriate situations, e.g. where greater resistance to temperature or mechanical damage is required. More importantly, it enables lining of smaller pipes because larger relative diameter reductions are feasible with PEX.

Description

Swage Lining

The present invention relates to the rehabilitation of pipelines and particularly to the process of swage lining of service pipes. Pipelines are operated by oil companies for the extraction and transportation of oil and gas, by water and gas utility companies m their distribution systems, and by district heating schemes for the distribution of hot water.

GB-A-2186340, GB-A-2218487 and GB-A-2218488 , and also EP- A-0581348 and EP-A-0344940 all relate to this process. A plastics pipe of polyethylene is made with dimensions approximately the same as a service pipe (usually steel or cast iron) which is cracked or leaks or otherwise needs repair, or which perhaps merely requires lining for corrosion or other protection against chemical attack. A swage die is located at the mouth of the service pipe (le the steel or cast iron pipe) . A draw line is fed up the service pipe for some distance, which may be anything up to 600 metres, although more usually up to about 100 metres. The draw line is attached to one end of the liner pipe (le the plastics pipe) . The liner pipe is then drawn through the swage die so that its diameter is reduced. As its diameter reduces, its length increases and while sufficient tension is retained on the swaged liner it maintains its reduced diameter. In this reduced diameter the liner pipe has a smaller external diameter than the internal diameter of the service pipe. Consequently it can be drawn through the service pipe until it extends beyond the other end of the service pipe. At that point the tension can be released and, as long as the swaging is within certain limits, the elasticity of the polyethylene draws the liner pipe back into the service pipe while it simultaneously expands radially outwardly to press against the bore of the service pipe. Complete recovery of the plastics pipe seldom happens and some yielding occurs, particularly near the internal surface of the liner pipe, and at least when diameter reductions of between 12 and 15% are employed. Such reductions generally result in a permanent deformation of the order of 3%. In fact, to eliminate permanent deformation completely, swaging is typically limited to 5.5 to 8.5%. In larger pipes these limits are not usually a problem. For example, on a 300mm diameter service pipe, a liner diameter reduction of 7.5% represents about 23mm which is plenty to accommodate the occasional intrusions into the service pipe which might occur at service branches etc. However, on smaller diameter service pipes, 7.5% liner diameter reduction might not be enough to clear intrusions. Indeed, it is a fact that there are nearly always more intrusions on the smaller diameter pipes (ie about 100mm diameter) , given that it is these pipes which are employed in residential areas where numerous service take-offs would normally be found. Consequently, greater diameter reductions are needed. However, this in turn means that diameter recovery may not be complete and so there may be significant loss of internal pipe volume.

Because the tension is released over the entire length of the pipe simultaneously, it might occur that as the diameter increases there may be "lock-ups" at different points along the liner where it contacts intrusions in the service pipe. These may then prevent further expansion between lock-ups or perhaps even result in ripping of the liner if it gets hung-up on sharp intrusions.

Another limitation of this method of lining is that polyethylene has a relatively low service temperature and m some applications it would be desirable to go above the normal temperature limits of about 40°C (or 60°C for pipe liners supported by steel service pipes) .

It has been proposed to employ cross-linked polyethylene ("PEX") for liner pipes by utilising its property of heat recoverability . Numerous patents describe such processes wherein a PEX lmer pipe is heated to a temperature above its crystalline melting point, the pipe is deformed to a smaller diameter, cooled so that it freezes at the smaller diameter and subsequently, after the pipe has been inserted into a service pipe, it is reheated by any convenient means above its crystalline melting point whereupon it reverts to its original dimensions.

Examples of such a method are described m GB-A-2300457 , GB-A-2272038 and GB-A-2272039. However, re-linmg using the heat recoverability of PEX has proved to be difficult m practice. The recovery temperature of heat recoverable cross-linked polyethylene is well m excess of 125°C, and this temperature is difficult to reach inside a service pipe whilst ensuring uniform recovery. In addition, heat recovered cross-linked polyethylene tends to shrink back from the cold internal surface of the service pipe, leaving voids which can be a source of weakness and reduce the useable internal cross-section of the lined pipe.

Finally, heat recoverability of PEX liners has generally involved the use of combustion heaters drawn along the liner to raise its temperature. Such heaters have not been well received m water systems because of the fear of contamination of water flowing through the pipe m due course, either by soot deposits or more likely by charring of the pipe surface.

Thus, whilst the swaging of uncross-linked polyethylene liner pipes has been exploited commercially, the use of heat recoverable PEX liner pipe to reline existing service pipes has not met with commercial acceptance in some industries .

Notwithstanding the many hundreds of patents which have been published on methods of pipe relining, there is still a need for a versatile system for relining existing service pipes which can overcome the disadvantages set out above .

It is therefore an object of the present invention to provide a method of lining service pipes which improves or at least is comparable with existing methods.

According to the present invention a swage lining method is provided wherein the liner pipe is formed from a cross- linked polyolefin.

In a first aspect, the invention provides a method of lining a service pipe comprising the steps of : -

a) providing a cross-linked polyethylene ("PEX") liner pipe of outside diameter substantially equal to or greater than the internal diameter of the service pipe;

b) drawing the liner through a swage die to reduce its diameter and increase its length;

c) maintaining the swaged pipe under tension to maintain its reduced diameter; d) passing the reduced diameter swaged pipe along the service pipe;

e) relieving the tension to permit the liner to elastically recover at least a proportion of its original dimensions.

f) heating the liner to permit recovery of a further proportion of said original dimensions.

Wherein, said heating step is effected progressively so that partially recovered liner pipe is drawn into the service pipe by further recovery of the liner pipe during said progressive heating.

It has been found that the elastic properties of PEX are substantially better than uncross -linked polyethylene resulting in much greater diameter reductions being possible for the same permanent deformation. Alternatively, for the same diameter reductions, much less permanent deformation results.

It has also been discovered that while PEX exhibits rapid elastic recovery within certain strains (subject to any permanent yielding) it also exhibits time dependent viscous recovery which can be significantly accelerated by heat .

In accordance with the invention, progressive heating and resultant progressive recovery inhibits the tendency for lock-up of the liner and helps to ensure as complete recovery of the liner as is feasible.

Said heating is preferably up to a maximum of 100°C and may be in the region of 60 to 80°C. Said progressive heating may be effected by a number of methods. For example, a bag of heated oil may be drawn along the pipe. An electrical heating element may be in the oil by means of which the temperature of the oil is kept constant .

Alternatively, a pig having sealing fms and between which is disposed a slug of heated water may be drawn along the pipe. Again, an electrical heating element may maintain water temperature.

Finally, a steam pig employing an external steam boiler may be run along the pipe .

By employing the combination of substantially instantaneous elastic recovery and heat assisted viscous recovery, diameter reductions of the order of 25% can be achieved with less than 5% residual strain. Two advantages follow. The first is simply that PEX offers numerous structural advantages over polyethylene which are well appreciated. These relate to such issues as operating temperature range, as well as rupture and puncture resistance and resistance to stress crack failure. The second and more significant result is that the use of PEX widens substantially the operating envelope of the swage lining process. Because such large recoveries are possible, the system can be employed on smaller diameter pipes without the risk of fouling intrusions. For example, the 23mm clearance mentioned above can now be achieved with 100mm internal diameter pipes rather than just the 300mm mentioned above.

Indeed, the resistance to damage during the installation process is another distinct advantage of using PEX, because the outer surface of the liner can become heavily scored during the insertion process, and, once installed, there can be point loads on the liner. In these instances, PEX offers superior benefits to polyethylene, because of its better resistance to stress crack failure modes and which would, in these circumstances, be the failure mode.

It is an aspect of the present invention that, because of the increased structural benefits of using PEX, and because of the two modes of diameter recovery (with the second, heat activated, mode being controllable from one end of the service pipe) , very long lengths of PEX liner can be inserted at any given time, particularly if lengths are joined together by butt fusion before passing through the swage die.

In other words, preferably, said method includes, between step a) and b) above,

a joining lengths of said PEX l er pipe by butt fusion thereof.

Such fusion may be effected by heating adjacent ends of two pipes and disposing therebetween a thin (about 0.1mm) film of polyethylene, which is also heated, and pressing said ends together with the film trapped between to effect fusion-jointing of the ends. A suitable method is disclosed in WO-A-9706205. In this way, 150 metre coils of 180mm outside diameter pipe can be joined to make lengths of perhaps 600 metres for insertion in an old pipeline in a single stage.

Alternatively, or in addition, it is feasible with PEX, and employing its elastic properties, to coil it flat, so that long lengths are even more manageable. The swaging die is then employed to re-round the liner pipe, although it is also possible, and perhaps preferable, to have a re-rounding die ahead of the swage die.

The invention is not limited by the method employed to cross-link the polyethylene, other than that it is a pre- insertion operation. That is to say, the liner is cross- linked before passing through the swaging die. Thus, any of the conventional methods can be employed, including peroxide (PEX-a) , which is preferred, silane (PEX-b) , radiation (PEX-c) and diazo (PEX-d) .

A lower limit of cross-linking is about 30%, but is preferably in the normally accepted range of 60-90% for PEX pipes .

The invention is further described hereinafter, by way of example, with reference to the following Example.

EXAMPLE

Two PEX-a pipes of sizes 90SDR17.6 and 160SDR26 made by Wirsbo Bruks AB in Sweden were evaluated. The pipes are of the type presently sold under the brand Wirsbo- inPEX. The degree of cross- linking is typically in the range 60 to 90%. The density of the pipe material is about 938 kg/m³. Five trials were undertaken, two with the 90mm pipe and three with the 160mm pipe. The 90mm pipe was subjected to a pull through a 78mm die (15% diameter reduction) and a 72mm die (20% reduction) . The 160mm pipe was subjected to a pull through a 144mm die (14% reduction), a 136mm die (17.5% reduction) and a 120mm (25% reduction) die. Prior to undertaking the trials, the pipes were marked up into half-metre lengths and the diameter measured at each point. During testing the distance between the points was measured, to determine the extension of the pipe, as well as the reduction of diameter at each point, and hence permitting calculation of the strains imposed. These measurements were taken while the pipe was under tensile load, but were also taken after removal of the load to note recovery of the pipe. Tables 1 and 2 below present the results achieved.

In Table 1, it is apparent that despite substantial strains imposed, residual strains are well within acceptable limits. Indeed, m the case of pipe E, samples were removed after 120 minutes to hot water tanks for three minutes immersion at 60C and 80C respectively. They showed residual strains of about 6-7% (based on diameter comparisons with pipe D) .

In Table 2, the results are summarised, showing the original strain under load and the final strains after two hours and twelve hours respectively. Also shown is the percentage recovery of the strain, and while these obviously reduce with increasing initial strain/ deformation, nevertheless, even with the 25% diameter reduction there is 76% strain recovery. Moreover, the the viscous heat recovery aspect of the present invention is clearly demonstrated m that 76% strain recovery, because at 12 hours such a figure would seem unlikely (a figure something less than the 71% of pipe D would be expected) . Whereas, by using some mild heating as described above, the recovery is m line with strain recovery achieved with the 14% diameter reduction employed with pipe C or the 20% diameter reduction employed with pipe B.

Also shown in Table 2 are the average pulling loads imposed during each test. In the last test, the average was higher for the initial stages (average about 1.4 tonnes) . However, water lubrication was employed after a period of time which both reduced the load and increased the speed of swaging. These pull loads are not different significantly to comparable pull loads with ordinary polyethylene pipes.

Similarly, the rates of recovery of the PEX-a pipes were also comparable to ordinary polyethylene.

Finally, tensile tests were performed on samples of the material of the tested pipes both before and after the diameter reduction/recovery tests.

For dumbell samples of PEX-a, prior to any swaging, stresses m excess of 15Mpa were required to achieve elongations of the sample m excess of 350%. In fact, stresses of about 20Mpa and about 510% elongation were achieved.

For dumbell samples from PEX-a pipe previously subjected to 25% diameter reduction, stresses m excess of 15Mpa were still required and elongations of the sample m excess of 350% were still achieved. In fact, substantially similar stresses were required, although elongations of only about 460% on average were achieved.

Thus for both unswaged and the swaged/recovered material, the PEX is likely to pass relevant standards required m many pipe-line applications. The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

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

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

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

π: m m

73 m

Table 1

n c

CD CO

m

CO

I m m -H 3 c m en

Table 2

Claims

1. A method of lining a service pipe comprising the steps of : -

c) maintaining the swaged pipe under tension to maintain its reduced diameter;

d) passing the reduced diameter swaged pipe along the service pipe;

e) relieving the tension to permit the liner to elastically recover at least a proportion of its original dimensions;

f) heating the liner to permit recovery of a further proportion of said original dimensions,

wherein said heating step is effected progressively so that partially recovered liner pipe is drawn into the service pipe by further recovery of the liner pipe during said progressive heating.

2. A method as claimed in claim 1, in which said heating is up to a maximum of 100°C and, preferably, in the region of 60 to 80°C.

3. A method as claimed in claim 1 or 2 , in which said progressive heating is effected by a bag of oil drawn along the pipe .

4. A method as claimed in claim 1 or 2 , in which said progressive heating is effected by a pig having sealing fins and between which is disposed a slug of water drawn along the pipe .

5. A method as claimed in claim 3 or 4 , in which an electrical heating element maintains the temperature of the oil or water as the case may be.

6. A method as claimed in claim 3 or 4 , in which said progressive heating is effected by a steam pig, employing an external steam boiler, which is run along the pipe.

7. A method as claimed in any preceding claim, in which said method includes, between step a) and b) above, the following step : -

a_x) joining lengths of said PEX liner pipe by butt fusion thereof.

8. A method as claimed in claim 7, in which such fusion is effected by heating adjacent ends of two pipes and disposing therebetween a thin (about 0.1mm) film of polyethylene, which is also heated, and pressing said ends together with the film trapped between to effect fusion-jointing of the ends.

9. A method as claimed in any preceding claim, in which the liner pipe is coiled flat.

10. A method as claimed in claim 11, in which the swage die is employed to re-round the liner pipe or in which a re-rounding die is employed to re-round the liner pipe ahead of the swage die.

11. A service pipe lined with a cross-linked polyolefin liner pipe by a method as claimed in any preceding claim.

12. A method of lining a service pipe substantially as described in the Example.

13. A method of lining a service pipe with a liner pipe substantially as hereinbefore described.