GB2406889A - Method for making and installing a pipe liner - Google Patents

Abstract

A method is described for shaping a polymeric tube by controlled vacuum collapse into a multi-lobed form with at least fo<WC 1>ur lobes <WC 1>so as to confer a reduced overall diameter that facilitates insertion as a liner into another pipe, elongate hollow member or elongate underground cavity. A short length of said tube <B>1</B> contained between fluid containment plug seals <B>2</B> and <B>4</B> is evacuated. A third plug seal <B>3,</B> open at its axis, is provided for cylindrical stability. Plug <B>4</B> also acts as a sliding piston being connected externally via an anchored rod <B>8</B> so that when tension is applied to said polymeric tube, for instance by a towing sock <B>7,</B> the evacuated volume can be progressively extended. The multi-lobe collapse of the tube between seals <B>3</B> and <B>4</B> is thus extended in a controlled and stable manner over the entire length of said tube. The tube 1 can be inflated back to its original <WC 1>cross-section by releasing the vacuum after it has been placed, <WC 1>eg towed, into the required location.

Description

1 2406889 TITLE: Materials and Method for Making and Installing a Pipe

Liner

DESCRIPTION

Area of Application A method is described for shaping a polymeric tube by controlled vacuum collapse into a multi-lobed form so as to confer a reduced overall diameter that facilitates insertion as a liner into another pipe, elongate hollow member or elongate underground cavity. The invention is particularly applicable to the refurbishment of aged pipelines, protection of new metallic pipes from internal corrosion and conferring better fluid containment properties to pipelines susceptible to earthquake or landslip. Maintaining the collapse vacuum permits the tube to be efficiently packaged or coiled for use on site. If the tube is manufactured from polymer of high elastic memory, releasing the vacuum initiates a self-inflation leading to significant recovery of the original dimensions of the tube.

A variety of technologies are currently available for providing a subsidiary lining (usually of polymeric material) within an existing pipe that is made usually, but not exclusively, of metallic material. One reason for lining existing pipes is to refurbish an old or defective pipeline that may be leaking at corroded areas, joints or sites of external damage. A second reason for lining pipes, applicable to newer systems, is to prevent corrosion or other chemical attack by aggressive fluid carried by the pipe. A third reason, which has become recognised as important in regions of the world subject to earthquake is to obtain improved tolerance of the very high strains placed upon underground services by ground shear occurring in land-slip or earthquakes.

The recorded responses of pipeline infrastructures to earthquakes that have occurred in California and Japan show that iron and steel pipes are damaged and allow leakage but that plastic pipelines remain intact. Lining of existing metal pipelines retains the strength and resistance to penetrative damage of the original installation but confers leaktightness due to the superior ductility and the ability to survive severe strain that is provided by a tough polymer.

All the currently available methods for lining existing pipe systems have disadvantages that limit their application. Our invention aims to overcome these limitations to provide a more efficient and more widely applicable technology. The method utilises a combination of material properties, product geometry, deformation processing and installation technique that represents significant improvement over earlier ways of lining pipes. A list illustrating typical existing technologies for lining utility pipework is given in Tabl - 1. This also records the disadvantages of each method.

Tablet

Existing Liner Pipe Insertion Techniques

Name, Description Limitations

Vlip-lning A smaller diameter pipe is loosely filled Results in loss of carrying capacity into an existing pipe. because new diameter is smaller than ongnal.

Not close fit.

Break-out Holing An expansion/breaking tool is driven High capital cost, residual supporting through the existing pipe route, pulling strength of host pipe is lost.

in a new plastic pipe behind it. Not close fit.

Difficult to remove.

Potential damage from broken pipe fragments.

Swagelning A new plastic pipe is "die-drawn" to a High capital cost, confined to smaller diameter prior to insertion in the relatively straight pipe applications.

old pipe. On release of the haul-in load, Axial contraction on release of it expands into place. towing loads - requires large access holes.

Locked-in, difficult to remove.

Roll-down A new plastic pipe is subjected lo a High capital cost, confined to "rolling-mill" to reduce its diameter relatively straight pipe applications.

prior to insertion. It is then expanded Locked-in, difficult to remove.

into place by hydraulic pressure. Some diameter shrinkage if operated ater at low presswes.

Limited insertion length, as the whole pipe length has to be completed before roll down.

Thermal A cross-linked polyethylene "memory" Limited size, high capital costs, high Expansion/ plastic tube is reduced in diameter in the material cost, jointing limitations, Recovery of PE-X factory end then revertedinside the host possible overheating risk from the pipe main by internal healing. high intensity heating source.

Not recyclable.

Pressure A mechanically constrained pipe, or one High capital costs, expansion only Expansions of lower diameter, is subjected to high maintained if fluid pressure is high.

Recovery internal pressure to bring it into contact Would shrink back in low-pressure with host pipe. applications.

Locked-in difficult to remove.

U-lne The pipe is flattened then curled up into Banding the pipe is relatively a U shape. The shape is nntained by a expensive. Limited insertion length, series of straps along the pipeline. After as the whole pipe length has to be insertion into the host pipe, high formed into the U shape before pressure is required to burst the straps insertion.

and force the pipe into a circular shape. Locked-in, difficult to remove.

Set against these methods our invention has the following advantages: Low installation cost - no large capital costs.

Speed, simplicity and reliability of installation - no high operator skills or time constraints.

Practicality for real pipelines - i.e. those with bends and offset joints.

Any insertion problems may be overcome by re-applying vacuum collapse to facilitate removal and re-insertion.

Compatibility with conventional PE for fusion jointing into an existing system.

Applicable to a very wide range of pipe sizes. Environmental advantage of ease of recovery for recycling at end of useful life.

It is also possible to utilise the lobed shape and the self-inflation feature of our invention to assist in the distribution of an inner layer of polymeric material intended as a coating or adhesive layer on the outer tube.

Nature of the Invention Essentially we claim to have devised a method for obtaining the temporary reduction in overall diameter of a polymeric liner tube by causing initial buckling and collapse, using internal vacuum, into a four or more lobed cross section and then progressively extending the region of controlled collapse along the tube length by the relative displacement of the tube and a combination of internal piston seals that maintain the internal vacuum and then by subsequently releasing the said vacuum, a self inflation of the deformed tube is initiated that contributes to the recovery of the original dimensions of the tube. If the said tube has an outer diameter similar to the internal diameter of an intended host pipe then the said multi-lobe form can be inserted easily into the host pipe and then be re-inflated to form a closely fitting lining. The process of controlled collapse under vacuum also provides a means of controlling the time and place of "self- inflation" and shape recovery within the host pipe because release of the vacuum is at an operator's discretion.

To be effective as a liner the precursor tube should be made of a tough polymeric material, preferably, but not exclusively, using a grade of polyethylene showing high elastic recovery. The advantage of using such grades of polyethylene is not only in their tolerance of high mechanical distortion but also in their fusion jointing compatibility with conventional, widely used polyethylene pipe materials. The preferred materials also exhibit very high ductility, toughness, and crack resistance which makes them suitable for resisting damage by ground movements even when the host pipe has fractured. Alternatively and where necessary, we believe our method of making the lining could also be utilised with many other types of plastic linings made for instance from the plastic materials that are typically used for pipe production.

The concept of reducing the overall diameter of a liner tube by collapsing it into four or more lobes has been established by prior art but none of the previously disclosed techniques give a method of controlling and stabilising the shape in a practically achievable manner. In one known example of prior art EP0065886 Al (Laurent), a tube formed of rigid plastic material (ultra high molecular weight polyethylene) is proposed to be distorted into a variety of shapes, including a multi- lobed example that would permit easy insertion for lining purposes. However, the recovery of cylindrical shape depends on heating the material beyond its crystallinity temperature in order to recover its elastic memory. In patent specification GB1580438 (Trio Engineering), it is proposed that a thin wall polymeric liner be formed into four-lobes (with vacuum assistance) around a profiled mould or former prior to insertion. The former is then removed and the liner returns to circular shape by releasing the vacuum and increasing internal pressure. US Patent 6,299,803 (Ledoux) teaches the use of vacuum collapse and maintenance of collapsed shape of a tube by internal vacuum prior to insertion as an in- situ pipe liner. The Ledoux product however utilises only the fundamental two-lobe collapse mode, which flattens the tube in an uncontrolled manner and requires additional folding in the axial direction in order to reduce overall diameter am - rmit insertion. There is no anticipation ofthe control Pipe buckling to achieve a controlled collapse into four or more lobes that give a reduced diameter without any additional folding process.

In selecting a preferred material for our process and in applying the concept of circular shape recovery to pipe lining applications, we recognise the prior art revealed by WO 00/63605 A1 (Connor). The techniques revealed by that patent have been applied to lining small pipes using an extruded star shaped tube, which may be formed with vacuum assistance but is not dependent on vacuum to facilitate insertion recovery being essentially by internal pressure increase to remove the original star shape. Our invention represents a significant step beyond WO 00/63605 A1 and the other prior art in that it provides a technique for controlling and stabilising the evacuated, collapsed state of the potential liner tube allowing it to remain evacuated and collapsed until ready to re-inflate as a lining inside a pipe or other elongate cavity.

By extensive research and theoretical analysis of the interaction of material properties, collapse geometries, physical constraints and conditions of external temperature and pressure, we have now found it possible to design a controlled form of pipe collapse which then lends itself to transport, insertion and recovery of the liner in the required shape. We have identified the possibilities for utilising collapse into a shape consisting of four or more lobes, which gives a substantial reduction of overall diameter without the requirement for additional folding of the natural "flat" collapse to create a "U" shape liner. Figure 1 illustrates the typical scale of reduction achieved by multiplelobe collapse and the extent of overall diameter reduction.

Figure la represents a three-lobe collapse, Figure lb a four-lobe collapse, Figure lc a six-lobe collapse and Figure Id an eight-lobe collapse. Each of the figures is drawn to scale and the collapsed shapes have the same peripheral length as the circles they are contained within. It may be concluded that the three-lobe collapse would give no benefit as an insertable tube since its overall diameter is not much less than its equivalent cylinder diameter. The four-lobe collapse shows a considerable advantage because its overall diameter is reduced by about 80% from the equivalent cylinder size. The higher orders of lobe collapse show diminishing advantages and for these reasons our preferred collapse geometry is the four-lobe shape.

A Practical Example

A theoretical analysis has indicated that a vacuum of 0.9bar obtained within a tube made from a material with a ring stiffness of approximately 300Pa will, with appropriate initiation and constraint, form a stable four-lobe hollow section as shown in Figure lb. Theoretically, the means of initiation assumed an inward acting force from four equally spaced radial positions. However, we found by experimentation that maintaining a stable four-lobe geometry before complete four-lobe collapse was very difficult because the tube inherently prefers to form the lower energy state of a two-lobe (flat or U-shape) collapse. We then made the important observation that the two-lobe fundamental collapse shape could be suppressed by initiating collapse within a short length of tube. At a critical tube length, it was found possible to create a stable four lobe collapsed shape when air was pumped from the internal volume of the tube.

Moreover, this four-lobed shape could be maintained with full stability when the evacuated length was steadily increased.

In our specific example, the selected tube material was DuPont-Dow type Engage 8540 polyethylene thermoplastic elastomer. was extruded as a tube of outside diameter 97mm and wall thickness 2.4mm (standard dimension ratio - SDR 41). It was discovered that the tube collapsed naturally under vacuum to a 4-lobe shape if the evacuated length was in the range 50160mm. At longer lengths 175-250mm, the collapse was into a three-lobe shape and above 250mm it formed the normal two-lobe shape. The process was reversible and repeatable.

Long lengths of four-lobe tube were subsequently obtained by starting the collapse with a tube length of less than 160mm then increasing the length by gradually withdrawing the internal plug whilst the vacuum was maintained. Lengths of up to lm were produced and these distances were only limited by the available tube lengths.

The four-lobe collapsed shape proved to be very stable provided the collapse was complete i.e. the sides of the lobes touched each other. The tip-to-tip diameter of the collapsed tube was then approximately 70mm with the collapse shape completely symmetric. The reduction in tube diameter from 97mm to 70mm (28% reduction) would allow it to be inserted easily through old metal mains of 4inch (lOOmm) nominal diameter.

Our experimental details are illustrated as a general arrangement in Figure 2.

Referring to Figure 2, the component parts of our experimental rig were: I - the 97mm diameter polymeric tube; 2 - the first twin plug (dumbbell) vacuum seals; 3 - the fixed position twin plug forming one end of the collapse section (axial duct left open to vacuum both sides); 4 - the third twin plug that acted as a moving piston to extend the collapse section; S - the rigid metal vacuum tube forming an axle to the first twin seal; 6 - a flexible hose connecting the metal vacuum tube to a vacuum pump (not shown); 7 - the metal mesh towing sock that compresses and grips the polymer tube when tensioned; 8 - the rigid metal rod connected to a fixing eyelet and with the third twin seal forming a piston that moves relative to the polymer tube during extension of the collapse length.

The twin seal plugs were made from widely available 3/inch (9Omm) "pipe stoppers" or "drain plugs". A first pair was inserted at one end of the tube, with its central hole connected via an outlet pipe to a vacuum pump. The plug diameters were adjustable by tightening a wing nut, which compresses a peripheral rubber seal. (It was found that a single plug could easily twist inside the tube so losing its seal, therefore this was replaced by a double (dumbbell) seal formed from two plugs connected together). A commercially available wire mesh "towing-sock" was pulled over the tube end and the first twin plug so that tension could be applied to the tube later. The sock automatically tightens as the tension increases and grips the tube. The external compression assists in preserving the vacuum seal at the first plug. Some slippage of the mesh over the smooth tube, when tension was applied, was solved by attaching self-adhesive emery/sand paper to the tube to increase friction. The vacuum connection was ducted as a metal tube through the mesh wall to avoid crushing before changing to a plastic hose. On the vacuum side of the first plug seal, another twin plug was inserted at a distance approximately equal to one tube diameter. This twin plug became necessary, after some experimentation, in order to maintain the normal circular shape of the tube away from the distortion caused by the towing sock, which normally covered the end plug. This second twin plug was left open at the centre so that vacuum was maintained on both sides and it remained in a fixed position. At the other end of the tube, another twin plug system was introduced, which was attached to the end of a steel rod, with a connecting eye on the other end. This twin plug could be moved in the manner of a piston by sliding up and down the tube bore. This plug functioned as a movable vacuum seal. All the rubber plugs were lubricated to ease insertion, initially using a silicone oil, but because it was absorbed into the rubber and softened it, the oil lubricant was replaced by water and a little detergent that had no swelling action on the tube or the seals.

Initially the test section distance between the central plug, 3, and the moveable plug attached to the rod, 4, was set at 50mm. This was measured as the distance between the metal plates of the neared plugs and approximated to the length of tube under vacuum. Tension was applied to the tube using the towing sock at one end and the rod attached to the moveable plug at the other. The load was just sufficient to slide the moveable plug into the correct position. If the load were not applied, the vacuum would later cause the plugs to be sucked towards each other.

It is possible to either hold the towing sock and tube and then slide the piston plug out of the tube or fix the piston and move the towing sock and tube. The latter method was adopted because this could be used during tube production, where the tube is the moving entity and the piston seal could be fixed in relation to the production line. By winching from the towing sock end, the tube was slowly drawn over the piston plug.

Due to the vacuum, the tube maintained the four-lobe shape throughout the increasing length. Although the vacuum pump was operated continuously in the tests, in principle, it is not necessary, as the vacuum is automatically created because the piston action prevents air entering the increasing internal volume between the seals.

At an evacuated section length of 140mm, some twist of the collapsed section became evident. This twist increased to about 45 as the length increased to 1 50mm. It seems that at this length, the full collapse in the centre of the test section is produced as the sides of the lobes begin to get close together. The buckling strength is then reduced and a twist develops as the atmospheric pressure acts on the end seals. The four-lobe shape was maintained up to Im - the full length of the available tube. It is very probable that the shape could have been maintained indefinitely even if the section length increased further. It seems that the four-lobe shape becomes very stable once the sides touch to form the tight lobe, as it would then require the sides to slide over each other to lose the shape. Moreover, once the tension on the tube was released, nothing happened provided the vacuum was maintained; the four- lobe shape didn't alter. The average tip-to-tip width of the four-lobe collapsed section was measured at 70mm. Once the vacuum was totally released, the tube rapidly went to a near circular form though there were some ridges remaining from the tips of the lobes, which dictated a slightly square shape. The process of initiation and extension of the controlled collapse is illustrated by Figure 3, which is a schematic representation of the general arrangement shown in Figure 2.

Figure 3a represents the condition prior to evacuation of the tube between the seals.

Figure 3b illustrates the initiation condition when vacuum is created and a four-lobe collapse occurs with suppression of the two and three lobe conditions. Figure 3c shows the extended condition when tube had been pulled by tensioning the towing sock and the third seal is now near the other end of the tube. The central section of the tube remains under vacuum with a stable four-lobe collapse condition persisting.

Although the above details are specific to one material, one pipe size and one condition of ambient temperature and pressure, it is our belief that this leads to a production method that could induce and control a stable four-lobe collapse in a far wider range of materials and pipe geometries. It is believed that the critical length for suppression of two-lobe collapse and initiation of four-lobe collapse is a function of the ring stiffness and the elastic foundation resistance provided by the tube. This critical length, in turn, is dependent on the combination of Young's elastic modulus of the material and the ratio of tube diameter to wall thickness (often referred to by engineers as the "Standard Dimension Ratio" of a pipe and abbreviated SDR). For those polymeric materials likely to be suitable as pipe linings, Young's modulus is temperature dependent. Therefore, for a material that has a higher modulus than our example or is stiffer by virtue of a lower SDR, it would be necessary to find a critical four-lobe collapse condition by increasing the temperature of the tube and/or using a shorter critical length. This might conveniently and efficiently be the case at some point in conventional thermoplastic pipe production by extrusion before the product had been completely cooled.

Once collapse is initiated, it becomes stable under the external air pressure with internal vacuum but without external physical constraints. Thus, it would be possible to achieve continuous production downstream of an extruder, if necessary whilst the tube remains at an elevated temperature. Alternatively, it could be achieved as a separate batch process in which a tube is drawn, at an appropriate temperature, through a constraint whilst under internal vacuum.

There is likely to be a variety of conditions that can be adopted to obtain suitable products depending on selection of the right combination of material properties, geometry and external conditions. It is also likely that some advantage may be gained by applying supplementary external constraint. In the course of our experiments we also applied some additional shaping and control by drawing the tube through an octagonal array of rollers set so as to further constrain the initial four-lobe shape but without excessively increasing the hauling load and causing unwanted stretching of the liner tube. Such techniques may be advantageous for achievement of controlled progressive vacuum collapse, especially in thicker walled tube or stiffer material types.

The vacuum requirement can be provided by a simple, low performance vacuum pump since high vacuum is not required. Alternatively, we have established the concept of a self-sustaining vacuum condition, which is achieved by preventing airflow into the tube as it passes over a sealed plug just prior to the collapsing constraint. Since no air can enter either end of the tube as it passes over the plug and through the constraints, an internal vacuum is generated. This would be a considerable advantage in larger scale manufacture.

Practical Application Aspects The stability of the lobed shape under vacuum after its formation allows it to be subjected to additional distortions to facilitate packaging, storage and transport to the site of application. Whilst, in principle, the lobe shape could be formed just prior to insertion into a host pipe, we envisage that in practice it will be more convenient to produce it in a factory and transport it in coiled or drum form. To achieve an efficient form of packing it is possible to temporarily flatten the four-lobed version of our invention. By drawing the four-lobed collapsed tube through a set of rollers and winding immediately on to a coil, the lobes could be flattened into a horizontal H- shape as shown in Figure 4. Figure 4a represents the appearance of a four- lobe collapse tube and Figure 4b represents the same section flattened to the "Horizontal H" shape that would prove easier to wrap on a drum for storage and transport. Using the four-lobed tube formed in our experimental example, we found it possible to further compress the collapsed tube by hand to the "H shape" and then wrap it straight on to a carrier drum of approximately lm diameter without additional mechanical assistance. We expect that the horizontal H shape would be maintained by the successive overlaps of coil winding and form a compact package with minimal volume wastage. Moreover, the vacuum could be released or partially released and the shape maintained simply by the tension in the coil.

Because the chosen material is likely to be one of high elastic recovery, the recovery from the H-shape is no more demanding than the recovery from the four-lobe shape itself, although some assisted recovery from the Hshape may be necessary to speed the operation.

For practical purposes the ends of the tube need to be sealed to create and maintain the vacuum during production and aftenvards until the lining needs to be expanded in place. A suitable method is to compress the tube ends by heating between two hydraulically clamped platens so that the tube is melted, squeezed and fused together to form a solid spade end. On cooling, the end will form a very effective, long-term seal to preserve the vacuum. The spade end can be drilled to make a towing eye so that it can be pulled through the rest of the production line. Moreover, it can be used to tow the tube though the old metal main as it is unwound from the storage drum. If short lengths are required from the drum, then similar heated platens can be used in the same way to fuse a section of the flattened tube into a solid flat shape. This can then be cut into two and the vacuum in either section is maintained.

The process to insert the liner in a host pipe is simple and can utilise the well- established methods adopted for slip lining insertion. The leading pipe end requires the specially fused end to seal and maintain vacuum and to allow attachment of the means of haul-in. Once the collapsed tube has been drawn into position inside the metal main, the vacuum can be released by cutting off the fused end. The tube will then spring back to a near circular shape immediately fitting the liner close to the host pipe internal wall. The degree of re-rounding will depend upon: temperature and degree of localised bending of the tube when it was initially collapsed to the lobed shape; temperature and degree of compression (drum tension) as the lobed shape is flattened, storage time and ambient temperature. The time-temperature effect can be interchanged in terms of tube recovery. A short time at high temperature will be equivalent to a longer time at lower temperature.

Studies of the preferred polymer type and grade, (DuPont Dow Engage E8540) , have shown that the tube reverts rapidly to a near circular shape after a few minutes even if the vacuum has been applied for some time and the sides of the lobes have touched.

The initial shape is likely to be slightly square, the corners coming from the remaining memory of the tips of the star shape. If there is any significant pressure introduced into the tube, then the true circular shape can be restored. If other grades of polymer are used there may be some permanent deformation caused by viscous creep during the period of time that the four-lobe shape was held. Most of this could be removed immediately if required by pressurising the tube with hot water Alternatively, for pipe that is likely to transport fluid at a pressure of lbar or greater, the internal pressure will probably force the liner tube to gradually form a close fit with no significant residual stresses.

If for any reason there is a requirement to remove a liner that has beeninstalled by this method, - for instance because of any installation snags - or for re-cycling at the end of a useful life, then it is possible to extract the tube by a reverse process of evacuation in a multi-lobe form. This could be achieved by collapsing the tube by an internal seal drawn through and away from a sealed end, possibly with the assistance of an internal shaped former. This might become an important advantage in future when materials recovery for re-cycling is necessary.

Another variation of simple insertion and vacuum release to create the pipe lining would be to introduce a liquid or gel between the unrecovered tube and the host pipe.

Such a fluid medium could, for instance, be conveniently contained in thin, burstable sachets that are placed between the lobes during insertion. Release of vacuum and recovery of the tube to its cylindrical form would then disperse and maintain the fluid around the inner surface of the host pipe. If the fluid was a solidifying resin, then it could act as an adhesive agent between the liner and the host pipe inner wall and would also act to prevent gas or liquid leaking from a liner failure from tracking between the liner and the main pipe wall. Other fluids may be used to block holes in the host pipe or possibly solidify the surrounding ground so that the tube, now supported, could span greater holes than would have been previously possible.

The coilability of the collapsed four-lobed tube offers the opportunity to install very long lengths into underground pipes through tight bends using small access holes in the ground and yet spring back by self- inflation to the round shape once the vacuum is released to form a continuous lining. The liner can then become the external layer of a multi-layer composite tube obtained by spraying or coating one or more materials (for example fast curing polymeric resins) on the inside of the inserted tube.

Although the invention in its inserted form has not yet been subjected to real earthquake or landslip conditions, we have conducted 3-point bend tests where the tube was pressurized up to 2 bar inside a 4 inch iron pipe. Bending displacements of 5-lOmm were imposed, at which point the iron pipe ruptured, but bending was continued until the displacement was about 150mm where it was possible to observe, through the fracture, that the tube was still undamaged and the pressure had been maintained. This exceeds many earthquake effects known to cause problems for iron or steel pipes.

Claims (11)

1. A method for obtaining the temporary reduction in overall diameter of a polymeric liner tube by causing initial buckling and collapse, using internal vacuum, into a four or more lobed cross section and then progressively extending the region of controlled collapse along the tube length by the relative displacement of the tube and a combination of internal piston seals that maintain the internal vacuum and then by subsequently releasing the said vacuum, a self inflation of the deformed tube is initiated that contributes to the recovery of the original dimensions of the tube.

2. A method of lining tubular cavities such as an existing pipe or insitu pipeline by inserting a polymeric product in the form of a tube whose overall diameter has been reduced and maintained at a reduced level by controlled vacuum collapse, as described in Claim 1, to a four, or more, lobed shape, and by subsequently releasing the said vacuum to initiate an inflation which will assist the lining to recover its original dimension and become a closer fit to the host pipe wall.

3. A further development of Claim 1 whereby the action of the external ambient pressure is supplemented by additional force provided by external fluid pressure, a profiled die or an array of rollers arranged appropriately to the desired collapse shape or any combination of such techniques.

4. An additional process of flattening of the collapsed shape of the tube obtained by the method of Claim 1 so that it may have a minimum resistance to bending for it to be wound conveniently and efficiently on a drum for storage and transport prior to installation and with preservation of the internal vacuum.

5. A further development of Claim 4, where the vacuum is released during storage yet the collapsed shape is retained by the tension in the coil on the drum.

6. Application of the methods that are the subject of Claims I to 5 to tube made from polymers showing high elastic recovery that combine the processability of thermoplastics with the high recovery properties of elastomers and thereby result in production of liner tubes that can progressively self-recover their tubular shape when the internal vacuum is released to air.

7. Application of the methods that are the subject of Claims I to 5 to conventional plastic pipe materials such as polyethylene, crosslinked polyethylene, polypropylene, polybutylene, and polyvinyl chloride when the process is conducted using an appropriate combination of diameter, wall thickness, external forces and elevated temperature so as to permit controlled vacuum collapse.

8 Application of any combination of Claims 1 to 7 where the lobed tube of reduced overall diameter obtained by controlled collapse is utilised to improve the operating characteristics of another, typically metallic, pipe by inhibiting it fluid release due to degradation by corrosion, chemical attack, physical impact or damage caused by land slip or earthquake.

9. Application of any combination of Claims 1 to 7 where the lobed tube of reduced overall diameter obtained by controlled collapse is utilised in combination with an external fluid that can be dispersed by the expansion of the liner to form a coating on the internal surface of the host pipe and thereby improve the performance of the lined pipe by resisting the tracking of other fluids between the liner and the host pipe or by acting as an adhesive agent between the liner and the host pipe or stabilising the ground to improve tube support at defects in the host pipe.

10. Application of any combination of claims I to 7 where the tube obtained by controlled collapse and inflation is used as a preform for the construction of a composite pipe inoortcratting an inner layer(s) of polymeric material such as polyurethane Mat is formed for instance by spray coating.

11. Any abdication 0t the process of progressive and controlled vacuum collapse Described by CIaim I to assist in the removal of an existing polymeric tube Born its precook installed place of service.