GB2504261A

GB2504261A - Polymer lined pipe

Info

Publication number: GB2504261A
Application number: GB201209793A
Authority: GB
Inventors: Stuart Ian Mcintyre
Original assignee: MCINTYRE ASSOCIATES Ltd
Current assignee: MCINTYRE ASSOCIATES Ltd
Priority date: 2012-06-01
Filing date: 2012-06-01
Publication date: 2014-01-29
Also published as: GB201209793D0

Abstract

A method by which a polymer liner 1 is inserted into a host pipe 2. That method comprising the steps of forming of a polymer liner pipe of external diameter somewhat less than the internal diameter of the host pipe, inserting the liner pipe into the host pipe, securing the liner pipe in place within the host pipe, and introducing a pressurising fluid into the bore 12 of the liner pipe so that the liner pipe expandably contacts the host pipe. Apparatus for use in the method are also claimed. The annular void 3 between host pipe and liner pipe may be utilised and fluid communication can take place into and within that void. A means may be provided comprising a collar for securing the liner within the host pipe which allows communication with the annular space through the collar (see figure 4). Signal or communications cables may be present in the annular void.

Description

Method of Installing a Polymer Liner in a Pipe The present invention provides a method for lining a pipe with a polymer liner pipe comprising the steps of: inserting the liner pipe, securing it in place, and then expanding it using a pressurising fluid to form a close fit with the host pipe.

The liner may be inserted for corrosion prevention purposes, but other beneficial features can be provided by the liner including flow enhancing benefits, thermal insulation, or the preservation of the purity of the pipeline contents from contamination by the host pipe.

The liner may be inserted into the host pipe prior to it entering into service, or it may be inserted at some later date, for example, as part of a refurbishment programme of an existing pipeline or piping system.

It will be understood that the term liner' signifies that the polymer barrier would itself be incapable of containing the fluid of the intended service without support from the host pipe.

The host pipe provides the function of structural support, whilst the liner serves the alternative purposes described previously.

It will further be understood that whilst the polymer liner is sealed to the host pipe to form an effective barrier between host pipe and process fluid, many polymer materials are to a degree permeable, so that over a period of time, fluids may permeate from the process fluid through the liner and into the annulus between the liner and its host. This permeation process does not limit the application of the present invention, but where the permeated fluids are toxic or harmful in some way, then a means of collecting these fluids will also need to be provided.

The present invention takes as its example an application where the liner is inserted into a subsea pipeline used to convey high pressure sea water, and where the liner is inserted some years after the pipeline was first brought into service; but it will be appreciated that the methods described can also be applied to a pipe at any stage prior to it being brought into operation. Furthermore, the invention may be applied to pipes conveying alternative fluids, including oil and gas products and corrosive fluids and it may be located on land, as well as subsea.

The benefits of polymer liners are widely recognised, and several methods have been developed by which they may be inserted into host pipes. The various methods may be distinguished by the way they achieve a practical clearance gap between liner and host to facilitate insertion without excessive snagging or dragging, and at the same time maximise the cross sectional area available for flow.

The insertion methods may be grouped into four families distinguished by their structural form prior to insertion.

The first approach is to spray-on the liner. Spray applied liners such as cement mortars, epoxy, polyurethane or other coatings solve the problem of insertion by delivering the liner in an initially liquid state.

The second approach is to install a deflated fabric bag, inflate, and cure it in place. Cure-in-place liners solve the insertion problem using a fabric construction soaked in a resin that is initially uncured and pliable. This allows the liner to be folded into a compact package for insertion. Once inserted the liner is inflated against the pipe until the resin cures and the liner takes its final rigid form.

The third method comprises the construction of a liner within the host pipe by forming a liner pipe of interlocking profiles. These profiles may be delivered as rolls or strip and the liner pipe is held in place by a grout injected between the liner and host.

The fourth method employs liners that are self-supporting pipes in their own right prior to insertion, and it is to this family that the present invention belongs.

In the present invention, rigid' means that the liner pipe is able to support its own weight whilst lying on a hard, flat surface at ambient temperature and pressure, with a diametral reduction of less than 10%.

There are a number of advantages to using rigid liners as defined above, but perhaps the most important are that a wide range of thermoplastic and elastomeric liner materials are available and that the quality of the fully formed liner can be assured prior to insertion.

The problem of insertion is particularly acute for rigid types of liner, and several methods are known that address this challenge by temporarily reducing their diameter as part of the insertion process.

One method is disclosed in EP0341941A1, where the liner is temporarily reduced in diameter by pulling it through a swaging die.

Another method is described in EP0266951A2, where the liner diameter is reduced by squeezing it through a succession of rollers.

Yet another method is described in GB1437273A, where the liner pipe is deformed by creasing it along its length into a U' shape. The U' shape is restrained by various means until the liner is inserted, whereupon pressure is applied to burst the securing means and the liner reverts to its original dimension.

In the prior art, the liner pipe has initially the same or slightly greater outside diameter than the internal diameter of the host pipe, whereas in the present invention, the liner pipe initially has a smaller outside diameter than the internal diameter of its host. It is therefore not necessary to undertake the complex diametral reduction processes, as described in the

prior art.

The degree of initial looseness described in the present invention is determined by reference to the diametral variations within the host pipe, and the properties of the liner material.

Diametral variations may include restrictions at pipeline fittings, bends, thick-walled pipe, weld penetrations, dents and debris, and the effects of corrosion.

Corrosion features such as pits and grooves are particularly demanding locations for liner conformance, as the liner must deform significantly in attempting to comply with their surfaces.

The selection of the liner diameter in the present invention is thus based on an analysis of the features described above, and critically, on the tensile strain capacity of the liner material.

The magnitude of the strain imposed on the liner as it conforms with the host pipe is an important criterion in the selection of the liner material, as the magnitude of the material's rupture strain must be well above the strain requirement from the expansion and conformance process that are imposed whilst the liner expands to make a tight fit with its host.

It will be recognised that many polymer materials exhibit properties that are strongly influenced by temperature, stress history and strain rate. Consequently, there are various ways of describing the strain response of the polymer. In some cases, such as with elastomers and cross-linked materials, the response will be mainly elastic, but other responses are also suitable for the present invention. For example, the liner response may be elastic-plastic, where the material initially stretches to a degree that is recoverable upon removal of the load, but when strained beyond its proportional limit, some permanent deformation occurs.

Polyethylene is a particularly attractive material in the present invention, because of its competitive cost and suitable engineering properties, including large rupture stain. This material may be described as visco-elastic, where creep and stress relaxation occurs, although these properties are very sensitive to temperature and rate of loading. An allowance also needs to be made in the design process, for gouges or other discontinuities on the liner, as these can cause strain localisations that lead to excessive thinning or premature rupture.

It will be recognised that a number of polymers and elastomers are suitable for the method described in the present invention, including the aforementioned polyethylene, polypropylene, polyamide, polyesters, ABS. PVC and other polymeric materials, and that where the liner has visco-elastic properties, stresses and strains within the liner will change over time as it conforms more closely with the host pipe. A time dimension will therefore form an important element of the liner selection process.

The liner is anchored to its host following insertion, so that a suitable coverage of the internal surface of the host pipe can be assured. And once it is anchored, it is expanded using a pressurising fluid introduced into the bore of the lined pipe assembly.

Expansion is necessary for two reasons. First, it allows the cross sectional area available for flow to be maximised, but secondly, the host is engaged to provide continuous restraint to the liner so that thermal expansion loads, for example from a warm production fluid does not cause it, through a peristaltic action, to walk' down the pipeline until it either ruptures at one end, or buckles axially at the other.

During the expansion process it may be necessary for fluids trapped within the annulus between liner and host to be evacuated so that the liner can expand to achieve the desired dimension.

Where the trapped fluid is a compressible gas, the liner may expand sufficiently without venting, but where the fluid is relatively incompressible, such as water, the trapped fluid will prevent the liner from fully expanding and venting will be required.

Means of venting can conveniently be provided within the liner anchoring devices. In this instance, vent paths pass from the annulus, through the anchor end fitting, and exit to the external environment. Flow control devices such as valves or check valves may be fitted to the vent path.

The expansion process preferably forms part of the pipeline quality control process known as hydrotesting', where a pipeline is pressure tested with a benign fluid prior to bringing it into service, or it may occur when the pipeline is brought into operation, using the pressure of the production fluid itself.

If the liner is to be expanded by the production fluid, then special procedures may be required to ensure that pressure is applied first (before heating), so that the liner conforms with its host and is therefore restrained before being heated. Similarly, on shutdown it may be necessary to maintain pressure within the lined pipe so that the liner remains secured until ambient conditions are achieved.

The advantage of expanding the liner as part of a hydrotest is that water at ambient temperature is used, so thermal stresses are minimised.

After the liner is expanded, the vent ports may be closed, so that when the expansion pressure is removed, the annulus cannot return to its original loose fit because fluids cannot flow back into the annulus. It is recognised however, that despite these efforts, the liner will tend to retract from the host due to residual elastic strain and a partial vacuum may form in the annulus. The liner will however remain sufficiently close fitting that it will contact the host pipe immediately upon the pipeline entering into operation.

The objectives have therefore been achieved. The host pipe has the benefits of a liner as described previously, the cross sectional area available for flow is maximised, and the liner is supported by the host so that pressure and thermal loads cannot cause it damage.

The invention is now described with reference to drawings and an example in which: Figure 1 shows a cross-section of pipe with a liner prior to expansion.

Figure 2 shows a cross-section of pipe with a second liner embodiment, but following liner expansion.

Figure 3 shows a third liner embodiment, prior to insertion in the host pipe.

Figure 4 shows an example of a device for anchoring the ends of the liner within the host pipe.

As shown in the figures, a polymer material selected for its compatibility with a fluid to be conveyed, and having a large tensile strain capacity is formed into a liner pipe (1) and inserted into a host pipe (2). The liner pipe (1) provides desirable properties in relation to the fluid to be conveyed (12) that cannot be achieved by the host pipe (2) alone, whilst the host pipe provides for other functions of the composite system, such as additional structural support.

It will be appreciated that the term pipe' does not necessarily imply a simple circular shape.

For example, it may be advantageous for the liner pipe to have an irregular shape, or to features grooves or fins so that some utility can be achieved within the annulus (3) between liner and host. It will also be recognised that the host pipe (2) may be irregularly shaped, for example being oval in shape, or suffering from the effects of corrosion, such as a groove (4) in the bottom of the host pipe.

In one embodiment of the invention, sea water is to be conveyed at a pressure of 2SObar and 20°C. In this embodiment, the liner has been selected for its corrosion resistance and hydraulic smoothness, and it has been found that grades of Polyethylene with a rupture tensile strain of 300% to 600% are suitable.

The liner (1) initially has an outside diameter somewhat less than the internal diameter of the pipe (2) in which it is to be inserted, so that there is initially a clearance gap or annulus (3). The annulus dimension is selected to suit the diametral variations of the host pipe, the strain capacity of the liner, and the dimension of apparatus to be installed within the annulus such as ribbon anodes (5), or instrumentation and cables as illustrated in Figure 3 where they have been gathered together into the form of a keel (6).

The annulus (3) created by this method of insertion permits several things: First, it allows the liner to be inserted with reduced friction and risk of snagging. Second, it allows fluids such as corrosion inhibitors, bactericides, pH buffers or other treatment chemicals to be introduced through the vent ports (9), to contact the inner surface of the host pipe. Thirdly, it allows for the evacuation of trapped fluids through the vent ports (9) when the liner is expanded and in operation. Fourthly, the method permits the simultaneous introduction of additional apparatus such as communication cables, instrumentation and sensors pre-assembled, tested and attached to the liner prior to insertion.

The additional services to be inserted in the annulus may be retained within grooves cut or extruded in the liner, or simply attached to it, for example by an adhesive. They may be pre-assembled into a sub-assembly which is fixed to the liner pipe at some convenient time prior to insertion. Such sub-assembly may be made from a component specifically extruded for the purpose and need not be made from the same material as the liner. The weight of these additional components may be distributed around the circumference or they may be grouped together to act as a keel (6).

The keel (6) may be used to trim the liner pipe buoyancy, and in conjunction with a buoyant component, act as a turning couple such that the liner adopts a particular attitude during insertion. This feature prevents the liner (1) from rolling, so that wear or rubbing strips may be accurately placed, and the exit location of cables and any of the other services provided can be correctly located at the end fittings (8).

The additional services inserted within the annulus create passageways that allow fluids to migrate to the vent ports (9).

In one embodiment, Illustrated in Figure 1, a ribbon anode (5) is inserted within the annulus, in order to arrest corrosion on the inner surface of the host pipe.

In the example sea water application, the pipe to be lined (2) has an internal diameter of 232mm, with a variable groove in its bottom (4) caused by corrosion. In this instance the corrosion groove (4) is up to 100mm wide and 10mm deep. A polyethylene liner pipe (1) with an outside diameter of 200mm is selected, thus providing a nominal radial gap of 16mm on installation, which is equivalent to a uniform hoop strain of approximately 16%.

For polyethylene materials, the liner thickness may be chosen to achieve an SDR (standard dimensional ratio) of outside diameter to wall thickness in the range 20 to 30, and in the example embodiment, the initial liner thickness is 8mm.

It will be appreciated that the strains and dimensions calculated are representative only, as significantly higher strains occur at local discontinuities such as the corrosion groove (4), weld penetrations, corrosion features on the inner wall of the host pipe and at other pipeline features.

In the example application, the host pipeline is located on the seabed at a water depth of 120m. The cost of carrying out work in this subsea environment is very high, so it is desirable to carry out the lining operation as quickly as possible. The liner is therefore delivered to the worksite location in lengths of 500m.

The delivery operation takes advantage of several other advantageous material properties of polyethylene. These include its low density; such that it can be floated on the sea even when filled with seawater; and its flexibility, which allows the floating pipe to comply with waves without suffering fatigue or other damage. It can therefore simply be towed on the surface of the sea from an onshore facility where the liner pipe was fabricated, to the The liner may also be coiled on a reel, as best suits the circumstances, but straight lengths are preferred so that residual curvature is minimised and installation forces are thus also minimise d.

The host pipe has previously been removed from operation and cleaned of debris using pigs and other means, and its ends have been opened to allow the liner to be inserted. A pull wire may preferably be inserted and attached to the front of the liner for installation, but a mechanical device such as a crawler may also be fitted to the front of the liner to provide traction effort if the circumstances dictate this to be more efficient than installing a pull wire.

A sensor package is preferably carried at the front of the liner so that various parameters may be measured within the pipeline as the liner insertion progresses. For example, pull load and cameras or ultrasonic measurement sensors to inspect the condition of the pipeline. Preferably, a tracking device is also fitted to the front of the liner. There are a number of devices that can perform this function including radio-active sources, acoustic pingers', or extra-low frequency EMF transmitters. The location of the end of the liner within the host can thereby be tracked continuously.

The effectiveness of the sensor package may be enhanced by providing a flush of fresh seawater through the liner pipe, thus clearing debris mobilised by the insertion process.

Power and communications may be provided by a cable inserted in the liner pipe, but this cable is removed once the liner is inserted. Alternatively, the crawler may be driven by a turbine driven by water pumped through the liner itself.

Bends within the host pipeline increase installation forces significantly, and limit the length that may be inserted in one operation. In this instance it may be necessary to cut access windows into the pipeline at intermediate locations so that the liner insertion may be assisted from that access point. The access windows are repaired once the liner is inserted.

The repairs themselves need not be fluid-tight, but they must support the liner so that it provides the necessary fluid-tight function.

In the example embodiment, where the subsea pipeline is substantially straight, the liner may be inserted in lengths of many kilometres at one time because the liner is lubricated by the surrounding water and its submerged weight has been adjusted to make it close to neutrally buoyant so that friction forces are reduced to a minimum.

The liner's submerged weight can be further adjusted by filling it with a fluid of appropriate density. For example, if more buoyancy is required, flesh water may be used instead of sea water, or if more weight is required, dense brine may be used to fill the liner.

In the example application, the submerged weight of the liner has been adjusted by attaching a keel in the form of a ribbon anode (5). The ribbon anode is preferably made from a metallic alloy of composition selected to provide a specific electrochemical potential between itself and the host pipe, such that the keel is anodic relative to the host and acts to prevent corrosion that may be caused by residual contaminants within the pipe. The selection of the anode material and its galvanic potential must also take into account scales that may exist on the host pipe wall, such as iron sulphides, as these are known to assist with the corrosion of pipe steels. The keel also provides a drainage channel between the liner and host along the edges of which, water trapped during liner insertion may be ejected when the liner is expanded, and in operation.

A guiding device is fitted to the entry to the host pipe so that the liner is not gouged on sharp edges of the pipe. It also allows marine currents and wave actions to move the distant end of the liner pipe to some degree without misaligning it and thus disrupting the installation operation.

The first length of liner is pulled to the seabed and into the host pipe, and when the hindmost end is about to submerge, it is captured by a surface support vessel, and the second liner section is connected to it. The connection process is preferably by butt-fusion, but where the liner material is not joinable in this way, low-profile mechanical connectors, or adhesive systems may be used. The installation continues in this way until the liner protrudes from both ends of the host pipe section being lined.

The liner is then trimmed to length and the anchorage devices inserted. An example of an anchoring device is illustrated in Figure 4.

The anchorage device comprises a collar (8) which extends over the outside of the liner (1).

It is fitted prior to expansion. A locking ring (7) is inserted to force the liner (1) into intimate contact with serrations (10) provided for the purpose of achieving a seal and secure grip.

The collar(s) may then be secured to the host pipe (2) by some means including pipe flanges (11) attached to the host pipe (2).

The anchorage device secures the ends of the liner within the host pipe, and provides vent ports (9) for the escape of water or other fluids trapped in the annulus (3) between liner and host. The anchorage devices may also provide a means of effecting the connection of the cables, sensors or other apparatus installed in the annulus, with the outside world.

The annulus (3) may now be flushed with a corrosion inhibiting or other fluid by injecting it through the vent ports (9). The objective of this flush is to leave some residue in contact with the host pipe following completion of the lining operation. The residue may have some conditioning or stabilising effect on the host pipe such as may be provided by biocide or corrosion inhibitor.

It will be recognised that the flushing process may be continued at anytime, including with the pipeline in operation, subject to the flow rates achievable through the annulus and associated venting means, and that as the treatment fluid is separated from the process fluid by the liner, the treatment fluid need not be compatible with the process fluid. In this way, the annulus may be continuously treated, of required.

Once the liner anchorage devices are secured, the liner may be expanded by introducing a pressurising fluid into the bore (12) of the lined pipe assembly. The pressurising fluid may be any fluid compatible with the liner pipe.

Where suitable conditions exist (for example where the pipeline is located at great depth subsea), the liner may be expanded by connecting a suction pump to the vent port (9) SO that the annular fluid is sucked out. This causes the liner to expand using the pressure already present in the bore (12). The differential pressure necessary to expand the liner may therefore be created by either pressurising the bore (12), or evacuating the annulus (3).

The liner is preferably expanded during a pipeline hydrotest.

During the expansion process, water will be ejected from the annular space (3) through the vent ports (9).

The speed at which the liner is expanded is controlled so as not to drive debris along the annular gap and to ensure a suitable strain rate for the liner material under the applicable environmental conditions. In the example application where a polyethylene liner pipe is being expanded subsea at an ambient temperature of 6°C, an expansion rate of 0.25% strain per minute is selected.

The liner will have some residual elastic strain following expansion, so it will tend to shrink away from the host pipe when the expansion pressure is removed, but with the passage of time in operation, a more intimate fit develops.

The vent ports (9) may be closed once the liner (1) is inflated, to restrict the liner's ability to loosen when pressure is removed, or they may be left open so that permeation products can escape when the pipeline is in operation. This can be achieved by fitting an automatic check valve or non-return valve or some other flow control device to the vent ports (9).

The method of venting will depend on the degree of tightness required between liner and host, the type of fluid being conveyed, the stress-strain characteristics of the liner material and the permeation rate of fluids through the liner.

Where the permeating fluids may not be discharged directly to the environment, then some means of collection should be incorporated with the vent holes (9). Such collection means may comprise a tank or piping system, and the efficiency of collection may be enhanced by pumping or suction means.

A pressure monitoring device may be fitted to the vent port (9) to inform when venting is required.

When the pipeline operates at high temperature it is particularly desirable that the liner be tight fitting against the host pipe, so venting is particularly important in this instance.

Although the method of lining has been illustrated by reference to a pipeline lying on the seabed, the method is also well suited to the refurbishment of risers.

Risers are sections of the pipeline that rise from the seabed to a topsides process facility above sea level. They usually have many bends, and have vertical as well as horizontal sections. The present invention is beneficial over the prior art in relation to lining risers, as a large clearance gap can be achieved, the liner can be pushed as well as pulled, and intermediate windows can be cut to assist insertion without compromising liner integrity.

It will be understood that the generality of the method is not limited to the specifics of the

example provided.

Claims

Claims 1. A method of lining a pipe comprising the steps of; forming a liner pipe of polymeric material of external diameter less than the internal diameter of a host pipe into which it is to be inserted; inserting the liner pipe into the host pipe; sealably securing the liner pipe to the host pipe; and introducing a pressurising fluid into the bore of the liner pipe so that it expandably contacts the host pipe.
2. Apparatus for use in the method according to claim 1 comprising means by which fluids may communicate with the annular void between the liner and host pipe.
3. Apparatus according to claim 2 wherein the liner pipe includes on its external surface means for facilitating the communication of fluids along the annulus through the formation of voids between liner and host pipe.
4. Apparatus according to claim 3 wherein the means for forming voids for communication of fluids along the annulus is a ribbon anode.
5. Apparatus according to claim 3 wherein the means of forming voids for communication of fluids along the annulus is an extruded linear component attached to the liner.
6. Apparatus according to claim 3 wherein the means of forming voids for communication of fluids along the annulus is a groove formed in the external surface of the liner pipe.
7. Apparatus according to claim 5 wherein the extruded linear component includes signal and communications cable.
8. Apparatus for use in the method according to claim 1 wherein the means of securing the liner pipe within its host comprises a sealable attachment means and means to allow fluids to communicate through the sealable attachment means to the annular space.
9. Apparatus according to claim 8 wherein the means of securing the liner pipe within its host pipe comprises a collar sealably secured to the liner pipe within the annular space between liner pipe and host pipe; a locking ring inserted within the liner pipe to force engagement between liner pipe and collar, the collar including means to allow fluids to communicate with the annular space through the collar.
10. Apparatus according to claim 8 wherein the securing means is adapted to fit flange fittings present on the host pipe.
11. Apparatus according to claim 8 wherein the securing means is welded to the host pipe.
12. Apparatus according to claim 8 wherein the securing means is adhesively bonded to the host pipe.
13. Apparatus according to claim 8 wherein the securing means is a mechanically energised to grip the internal surface of the host pipe.
14. Apparatus according to any of the preceding claims 8,9, 10, 11, 12 and 13 whereby the apparatus of claim 7 is provided with a suitable connection means such that the apparatus of claim 7 may be continued between the securing means of lined pipe sections.
15. Apparatus according to any of the preceding claims 8,9, 10, 11, 12 and 13 whereby the apparatus of claim 7 is provided with a suitable external connection means such that the apparatus of claim 7 may be continued externally to the host pipe.
16. Apparatus according to claim 2 wherein the means by which fluids may communicate with the annular void between the liner pipe and host pipe comprises a hole in the host pipe.
17. Apparatus according to claim 2 wherein a flow control means is provided to the means by which fluids communicate with the annular void between the liner pipe and host pipe, so that the communication of fluids with the annulus may be regulated.
18. A method of treating the internal surface of the host pipe following the insertion of the liner by the introduction of treatment fluids through the communication means of claim 2.