GB2388639A - Method of lining pipes - Google Patents

Abstract

A method of lining a pipe comprising the steps of folding a liner 101 into a small diameter form, inserting the liner 101 into a protective sleeve 102 and then both liner 101 and sleeve 102 into the bore of a pipe, applying heat to the folded liner 101 and effecting reversion of the folded liner 101 wherein the application of heat to the folded liner 101 is confined to one or more regions susceptible to creep relaxation. The heating may be provided by conductive tapes or wires (302, 303, 304 of fig 3 and 401 of fig 4) which supply heat to the one or more regions susceptible to creep relaxation.

Description

MF,THOD 01INING PIPE,

The present invention relates to an improved method of lining pipes. In particular to a method of relining low pressure gas pipes with a thermoplastic liner.

s Background

In the rehabilitation or renewal of pipe systems it i s a great advantage i f the existing pipeline can be relined rather than be replaced. A number of processes have been commercially developed to satisfy the need for 'no-dig' renovation such as SubcoilTM available from Subterra Limited 10 and Compatt Pipe_ available from Wavin GmbH. One ofthe most successful ofthese processes involves the use of a thermoplastic liner which is folded and retained in the folded shape to reduce its overall dimensions so that it can easily be inserted through the existing pipeline needing to be renovated.

15 Cylindrical liners, folded into a U. C, G or spiral shape, can have very low cross sectional areas which enables them to be inserted into host pipes using smaller loads than would be needed for cylindrical liners that are circularly reduced by rollers or dies prior to insertion. When folded liners are made from materials having generally thermoplastic characteristics, creep relaxation of the material comprising the liner can take place at the folds during storage and before 20 insertion. Subsequent temporary reversion pressurization after insertion, even at relatively high pressures, typically results in a distorted non-circular shape obtaining in subsequent service if the operational pressure in the host pipe is low and the liner external diameter is less than the host pipe internal diameter.

25 EP 0 787 940 discloses a folded liner located within a thin outer sleeve which holds the liner in the desired folded shape during storage and insertion into a host pipe, an example of which is shown in Figure 1. Reversion of the liner within the host pipe is accomplished by the application of pressure from and/or heat from within the liner.

30 During manufacture a liner 101 is folded into a U-shape and then covered by a tight fining

sleeve 1()2 The liner 1()1 then comprises an inner lobe 1()3 and twit outer 1'hcs 1()4 1()S typically the inner lobe 1()3 1cing bent more scvcrcly than the two outer lathes 1()4, 1)5 In fact, the sense o! curvature ot the top ol the liner is completely reversed imposing high strains at the inner and outer surfaces of the liner at this region. When the installed liner 101 is reverted, this 5 region of maximum strain again lies at the top of the liner, if no rotation has occurred from its typical insertion orientation, and due to the high peak strain when folded there is a significant risk of a residual crease which may not be completely removed by the operational pressure in the liner 101 after the renovated pipeline has been re-commissioned. If a residual crease remains in the liner 101 after reversion, it is likely that the crease is located at or near the top of the liner.

10 The liner is typically supplied already folded within the sleeve in long lengths wound onto a drum. The sleeved folded liner offers many advantages over other folded liner technologies, including protection of the liner from cuts and abrasion during insertion, the provision of a smooth 15 external surface which aids insertion and gives low pulling forces and protection during storage.

After insertion into the host pipe the application of pressure causes the liner 101 to expand and burst open the sleeve 102. Rupture of the sleeve 102 is readily achieved with pressures of 2-3 bar at ambient temperatures.

90 In the renovation of water pipelines, hydrostatic pressure levels of up to 10 bar or more can easily be applied to effect the reversion of the liner. The operational pressure of water pipes is typically sufficiently high to ensure continued roundness and a close fit of the liner within the host pipe.

25 There is also a need to renovate low pressure gas distribution pipes. However, in the case of such pipes there are several important operational differences that can impact on the practicality of using folded liners for their renovation. Firstly, it is customary for gas pipelines to operate with significantly higher safety factors than water pipelines thus requiring a greater wall thickness for liners used in gas pipelines. The increased thickness results in higher peak strains 30 being generated at the folds in the liner and consequently greater difficulty in re-rounding and

removing any residual creasing resulting from the folds. tSccondly, low pressure L;as distribution pipes operate at very much lower pres.surcs than water pipes such that the operational pressure may lee nsut'lcient to keep the hoer fully circular and/or maintain the liner in close contact with the host pipe, even over long periods of operation. Thirdly, the use of clectrofusion self-tapping 5 saddles for service connections to gas pipes is widespread. 'I'he reliability of any joints made to the creased area of the liner is of great concern.

The use of air for reversion is much preferred by the gas industry. The reversion pressure will be constant over the whole length of the liner irrespective of elevation changes. Air is a far 10 better medium to cause the sleeve to burst along its entire length than water as it applies nearly constant reverting effort, even if slight expansion or partial reversion has occurred, thus resulting in significant burst momentum. However for health and safety reasons the air pressure is restricted to a maximum of 2-3 bar which is insufficient pressure to completely re-round a liner and produce a close fit between the reverted liner and the host pipe when liners of thickness 15 appropriate for gas use are used at substantially ambient temperatures GB 2 327 997 discloses a liner, for lining pipelines, folded into a G shape comprising a polyolefin homopolymer or copolymer or a blend of polyoleGm and one or more other polymers wherein the ratio of the diameter over wall thickness of the reverted liner is in the range 55-145, 20 the wall thickness being in the range 100-10000 lam. The liner is optionally inserted into a sleeve. The reversion process requires the liner to be subject to pressure and/or heat.

US 5 487 411 discloses a foldable liner for lining pipelines comprising an inner rigid thermoplastic layer and an outer flexible thermoplastic layer, the inner rigid thermoplastic layer 25 being heat softened by, preferably, steam passed through the liner after insertion into a host pipe.

The later application of, in preference, pressurised steam reverts the liner.

In US 5 205 886, a deformable liner is disclosed comprising a plurality of concentric flexible thermoplastic tubes enveloped by a sleeve. The liner and sleeve is inserted into a host pipe and 30 inflated and heated to fuse the tubes to each other preferably by passing steam through the liner.

In low-pressure pipelines, such as those used for conveying gas to consumers in distribution systems typically operating; at tallow 1 l:,ar, there is little or no liner rc-rounding effect front operational pressure and the distorted shape of the reverted liner does nest necessarily improve with the passage of time. It is widely known that deformation and relaxation of stresses within 5 thermoplastic products is enhanced by the application of moderate heat and heat has been used, l for example In the form of steam as disclosed in US 5 487 411. to help revert folded thermoplastic liners and provide a close fit within the host pipe. However the use of heat for liner reversion has several drawbacks, namely: the hire of equipment to generate hot heat l transfer fluid such as water or steam; the cost of fuel to heat the heat transfer fluid; the time 10 taken to effect reversion; the cost of heat transfer fluid required to pressure revert liner; the disposal of the heat transfer fluid after reversion; and the removal of residual heat transfer fluid from inside liners prior to re-commissioning the pipeline.

The present invention reduces or eliminates the aforementioned disadvantages by reducing the 15 amount of heat required by concentrating the heat to where it is needed most and in a preferred embodiment, by not exposing the bore of the liner to any heat transfer fluid.

: Summary of the Invention

An aspect of the present invention is provision of a method of lining a pipe comprising the steps 20 of: a. folding a liner into a form comprising an overall diameter less than the diameter of the liner prior to the folding step; b. inserting the folded liner into a protective sleeve; c. inserting the protective sleeve into a bore of a pipe; 25 d. applying heat to the folded liner; and e. effecting reversion of the folded liner, wherein the application of heat to the folded liner is confined to one or more regions susceptible to creep relaxation Optionally steps (b) and (c) may be reversed in order.

30 The liner can be folded into a form selected from a U-shape, C-shape, G-shape or spiral shape.

The protective sleeve typically comprises a hurstable or longitudinally slit protcctve sleeve. In larder to rcndcr tle protective sleeve easy to burst, the protective sleeve oltcn comprises intermittent slitting, holing or piecing.

5 The method can additionally comprise the step of removing the protective sleeve following reversion of the folded liner. Optionally the interacting surfaces between the pipe, protective sleeve and liner are lubricated.

In one embodiment the step of applying heat comprises the provision of conductive tapes or 10 wires to the one or more regions susceptible to creep relaxation and the conduction of heat through the conductive tapes or wires. Alternatively one or more reactants can be applied to the one or more regions susceptible to creep relaxation and the one or more reactants contacted with one or more co-reactants thereby initiating an exotherrnic reaction. Preferably the one or more reactants is selected from lithium, potassium, sodium, magnesium, and calcium oxide and the 15 one or more co-reactants is water. The one or more reactants may be applied in the form of a tape or wire.

In another embodiment, the step of applying heat comprises applying hot water or steam to the one or more regions susceptible to creep relaxation. The hot water or steam can optionally be 20 recirculated to the one or more regions susceptible to creep relaxation. A removable feed pipe can be located adjacent at least part of one of the one or more regions susceptible to creep relaxation and the hot water or steam passed through the removable feed pipe.

The one or more regions susceptible to creep relaxation can comprise one or more regions of the 25 liner folded back on themselves. In particular the one or more regions susceptible to creep relaxation can comprise an exterior surface of the one or more regions of the liner folded back on themselves. When the liner is formed into a C-shape comprising two outer folds and an inner fold, the one or more regions of the liner folded back on themselves consists of the inner fold.

30 Reversion can be effected with a pressurised gas such as air or nitrogen or through mechanical

() mc.lns Brief Description of the Figures

5 F.mbodiments of the present invention will now be described with reference to the figures in which: I igure I shows a cross-sectional view of a liner within a sleeve; 10 Figure 2 shows a cross-sectional view of a liner within a sleeve indicating the locus of heating of a liner according to the method of the invention,] Figure 3 shows a crosssectional view of a liner within a sleeve indicating a first embodiment I of the method of the invention; Figure 4 SilOWS a cross- sectional view of a liner within a sleeve indicating a second embodiment of the method of the invention; Figure 5 shows a cross-sectional view of a liner within a sleeve indicating a third embodiment 20 of the method of the invention; and Figure 6 shows a cross-sectional view of a liner within a sleeve indicating a fourth embodiment of the method of the invention.

25 Detailed Description of the Invention

Figure I shows a cross-sectional view of a liner 101 within a sleeve 102, the liner 101 folded into a U shape. As can be seen in Figure 2, the optimal locus of heating is the conduit 201 at the inner fold 202 between the two outer lobes 104, 105. This has the advantage that the heat can l be applied predominantly to the region of the inner fold 202 where the maximum strains exist 30 and where the maximum recovery is needed. A further advantage arises from the use of

1ocalscd heating of the folded liner 101 as the heat is directed to the inner fold 2()1 of the liner lip t<' two the outer circumEcrence remains relatively cold by comparison. Phe 'utcr.scction 2()5 of the fielded liner is under bending tension due to its reduced radius of curvature as compared

to that of the unfolded liner and as long as it is not heated substantially this stored energy is 5 available during the reversion. During the reversion process, the stored energy beneficially acts to tension the heated and therefore softened inner fold 202 and thereby helps to re-establish liner circularity. The liner is folded in the factory relatively slowly and at room temperature or above. In contrast, 10 the reversion process carried out in the field is relatively fast and at times carried out at

temperatures as low as 0 C. Under these field conditions, the liner may suffer damage in the

form of reduced fast running fracture resistance (rapid crack propagation resistance) and/or local voiding. In the extreme case of polyethylene pipes squeezed off to stop flows, reversion to circularity after squeeze off has to be carried out at a relatively low rate in the field in order to

15 minimize damage risks or similar reasons, squeeze off (and thus also reversion to circularity) is not allowed in the case of thick-walled polyethylene pipes since in such cases the surface . strain rates are higher for a given rate of reversion. Thus a further advantage of prior heating of the inner fold 202 is the significantly reduced likelihood of damage caused to the liner 10] during the reversion process when carried out in the field at low temperatures.

Lao When hot fluid, in particular heated water or steam, has been used in the past to aid the reversion of folded or otherwise deformed liners, this fluid has generally passed up the interior of such liners. The site equipment that generates such hot fluid often suffers from various malaises, such as furring up, unless the fluid is chemically treated in some way. l hese treatment chemicals can 25 sometimes leave deposits on the bore of the liner that can taint or otherwise affect the fluid that the lined pipeline will convey aDer commissioning. An advantage of the present invention is that such deposition does not occur in the present invention as only the exterior of the liner 101 is exposed to the treated fluid during the reversion process.

30 If the inner fold conduit 201 is flooded with hot water, or another suitable fluid, this takes out

( the set from approximately half of the two outer folds 203 904 as well as from the entire inner loUc 11)3. Another advantage of the present nvcnt'n Is the rclatvely low heat energy input s required as the rcvcrsc side of the liner wall at the inner idol 202 is not in contact with the typically metal host pipe but insulated by the outer section 205 of the folded liner.

s When the inner fold 202 has been heated, the liner 101 can be reverted to a substantially circular shape by application of only low air pressure (up to 3 bar) Whilst under pressure the heated section of the liner may come into contact with the outer pipe and this will serve to accelerate natural cooling, causing the new circular shape to set into the liner such that the shape is 10 substantially retained even when the pressure is removed. Any slight sleeve punctures during insertion are unlikely to matter, even if heating is by flowing water for example, because this damage would occur where the sleeve 102 is stretched over the body form of the liner 101 and therefore the resulting water leakage would be negligible at the pressures of interest. Such water loss through points of minor sleeve damage could be eliminated by introducing a thin-walled I 5 lay flat tubing into the inner fold 202 of the liner during the folding process. This tubing would then form a heated water conduit and would heat the adjacent folded liner areas via conduction through its thin walls.

. "; Heat may be applied by several different means such as flowing hot fluid, electrical heating 20 wires or tapes, or by chemical reaction of materials that generate heat when mixed. Heating by electrical wires or tapes can be achieved in different ways. Heating wires 302, 303, 304 or tape 301 can be applied to the exterior surface of the inner fold 305 during the folding process and may be bonded in place as shown in Figure 3. Once installed the heating, wires 302, 303, 304 or tape 301 are energised by applying a voltage determined by the length of the liner 101 such 25 that a designated electrical current flows to provide uniform heating along the length of the liner 101. When sufficient heat has been applied to the liner 101 the current is switched off and the wires 302, 303, 304 or tape 301 either removed or left in situ as the liner 101 is reveded using air pressure Alternatively, the heating wires 302, 303, 304 or tape 301 may be inserted to lie along the exterior surface of the inner fold 305 once the folded liner 101 has been installed in 30 the host pipe. After energising, the heating wires 302, 303, 304 or tape 301 are removed and

() rcLancd lor reu.sc before the liner 1()1 Is reverted with air pressure lleating by means of cxothcrmc chemical reaction is also possible. For example, reactions between water and certain metals, such as lithium and potassium, and compounds, such as 5 calcium oxide, are highly exothermic. Once the folded liner 101 Is inserted into the host pipe, an alkal i metal tape 4()1 is inserted to lie along the exterior surface of the inner fold 305 and the conduit 201 at least partly filled with water as shown in Figure 4. The water reacts with the alkali metal tape 401 and heat is generated. The relative quantities of water and metal determine the amount of heat generated and the quantities are determined such that the metal becomes 10 completely consumed in the reaction. Following heating, any by-products of the reaction are released into a storage container before or during the time the liner 101 is reverted using air pressure. This type of heating can be advantageously used where an adequate electricity supply is not available.

15 Prcssurised hot water or steam has historically been used to fill liners in order to revert or assist reverting them. In the present application the use of hot water heating between the sleeve 102 and the inner fold 202 of the liner is provided as this greatly reduces the volume of water required and the water is isolated from the air used to revert the liner. For example a 147.6mm (6") diameter host pipe would require a liner with an internal bore of approximately 140mm 20 (5.69"). Conventional heating of the inside of the liner 101 with hot water requires a water volume of about 4.51/m of liner. Utilising the localised external heating of the inner lobe 103 requires about 11/m of cheer, a reduction of around 75%.

Water or steam heating may be applied in various ways. In one example, a small diameter feed 25 pipe 501 can be introduced within the conduit as shown in Figure 5. The feed pipe 501 can be attached to, for example, a hot water or steam generator in open or closed 1Oop nnode. Hot water circulated through the feed pipe 501 heats the inner fold 202. Once sufficient heating had taken place the feed pipe 501 is retracted and the liner 101 reverted using air pressure. In another example, both the sleeve 102 and liner 101 are seal together at the same ends and an open- ended 30 feed pipe placed the full length of the inner fold 202. Hot water is pumped into an inlet end of

the feed pipe' escaping back down the conduit 201 to the inlet cod calf the feed ppc, aver passing tllrough the fUIt length of the feed pipe I his method has the advantage that the inlet anti outlet of the hot water are In the same proximity arid allow for easy re-circulanon Additionally the opposed flow and return directions optimist heat recovery and provide for a more even heating S along the liner 1()1 thereby facilitating more rabid and even reversion of the liner 101.

The feed pipe can be arranged to terminate at a midpoint along the length of the liner. Hot water can then discharge from the end of the heating pipe into the space between the inner fold 202 and the sleeve 102. The water can then flow in both directions discharging from the two ends I O of the liner. This method has the advantage that the heating is more uniform along the length of the liner and gives a shorter heating time. The disadvantage is that the method becomes more difficult to operate in a closed loop.

In a further example, hot water heating is introduced into the conduit as shown in figure 6.13y 15 forming a seal between the liner 101 and the sleeve 102, water can be introduced to one end of the sleeve 102 and recovered from the other end. This can be achieved through the use of special end fittings that seal the gap between the sleeve 102 and outer surface of the liner. T he contact of the hot water directly with the outer surface of the inner fold 202 greatly increases heat transfer and reduces heating times compared the other above mentioned methods. The only 20 additional costs are those for the end fittings. Raising the inlet end of the sleeved liner 101, 102 above ground level allows hot water introduced at the end of the sleeve to flow through the conduit 201 under the head of pressure provided. The water discharged at the other end can be re-circulated. 25 All the above mentioned methods using hot water as a heating medium require relatively little water. Furthermore there is no need to dry out the reverted liner bore prior to return to service by, for example, the time-consuming use of foam pigs since the water does not enter a bore of the liner at any time.

30 The sleeve may be inserted into the host pipe separately of the liner, with the liner then being

1 1 inserted into the sleeve, the liner being held in a folded form by straps, ties, adhesive, spot welds or seam wcki.s Dependent on the means for heating the inner lokl 2()2, the sleeve may he withdrawn from the host pipe leaving the folded liner for reversion therein, alternatively, the sleeve may be left within the host pipe becoming trapped between the host pipe and liner when S the liner is subsequently reverted.

Whether the sleeve is to be left within or removed from the host pipe, the sleeve can be rendered burstable by the provision of intermittent slitting or some other form of weakening such as intermittent holing or piecing. Alternatively the sleeve can be a longitudinal slit sleeve of the 10 type as set out in GB 2 327 997, the contents of which are incorporated by reference.

In order to reduce friction between the host pipe, sleeve and liner during insertion or removal, the interacting surfaces may be lubricated.

15 The liner may also comprise more than one layer.

It will be appreciated that various modifications and changes may be made to the above described preferred embodiments of the invention without departing from the invention as set out in the following claims.;

Claims (1)

1. ['[aims I method of lining a pipe comprising the steps of a. folding a

   liner into a form comprising an overall diameter less than the diameter 5 of the liner prior to the folding step; b. inserting the folded liner into a protective sleeve; c. inserting the protective sleeve into a bore of a pipe; d. applying heat to the folded liner; and e effecting reversion of the folded liner, 10 wherein the application of heat to the folded liner is confined to one or more regions susceptible to creep relaxation.

   2. A method according to claim I wherein the liner is folded into a form selected from a U-shape, C-shape, G-shape or spiral shape 3. method according to claim I or claim 2 wherein the folded liner is inserted into a protective sleeve comprising a burstable or longitudinally slit protective sleeve ,, ', ' 4. A method according to any one of the preceding claims wherein the protective sleeve 20 comprises intermittent slitting, holing or piecing thereby rendering the protective sleeve easy to burst.

   5. A method according to any one of the preceding claims comprising the additional step of removing the protective sleeve following reversion of the folded liner.

   6. A method according to any one of the preceding claims wherein interacting surfaces between the pipe, protective sleeve and liner are lubricated.

   7 method according to any one of the preceding claims wherein the step of applying heat 30 comprises the provision of conductive tapes or wires to the one or more regions

   susceptible to creep rciaxatQn and the conduction of heat through the condrctivc tapers or wires 8 A method according to any one of claims I to 6 wherein the step of applying heat 5 comprises applying one or more reactants to the one or more regions susceptible to creep relaxation and contacting the one or more reactants with one or more co-reactants thereby initiating an exothermic reaction.

   9. A method according to claim wherein the one or more reactants is selected from 10 lithium, potassium, sodium, magnesium, and calcium oxide.

   10. A method according to claim wherein the one or more co-reactants is water.

   I I. A method according to any one of claims 8 to 10 wherein the one or more reactants is 15 applied in the form of a tape or wire.

   12. A method according to any one of claims I to 6 wherein the step of applying heat comprises applying hot water or steam to the one or more regions susceptible to creep relaxation.! 1 3. A method according to claim 12 wherein the hot water or steam is recirculated to the one or more regions susceptible to creep relaxation.

   14. A method according to claim 12 or claim 13 comprising the step of locating a removable 25 feed pipe adjacent at least part of one of the one or more regions susceptible to creep I relaxation and passing the hot water or steam through the removable feed pipe.

   15. A method according to any one of the preceding claims wherein the one or more regions susceptible to creep relaxation comprise one or more regions of the liner folded back on 30 themselves.

   ( 1(. method according to any one of claims I to 14 wherein the one or more regions iusccptiblc to creep rclaxatrn comprise an exterior surface of the one or more regions of the liner folded back on themselves.

   s 1 7. A method according to any one of claim 1 5 wherein the one or more regions of the liner folded back on themselves consists of an inner fold of a liner formed into a C-shape i comprising two outer folds and an inner fold.

   10 18. A method according to any one of the preceding claims wherein reversion is effected with a pressurised gas such as air or nitrogen.

   19. A method according to any one of claims I to 17 wherein reversion is effected mechanically. 20. A method of lining a pipe substantially as described hereinbefore with reference to Figures 2 to 6. 1