GB2316991A - Double layer liner pipe - Google Patents

Abstract

The liner pipe 2 comprises a first layer 4 of a first polymeric material and a second layer 6 of a second polymeric material, wherein the second material has a more elastomeric character or has a greater plastic limit than that of the first material; the two layers 4,6 being bonded together to an extent sufficient to substantially prevent differential straining between the layers. The first layer is selected from polyolefins, polyamides, ethylene vinyl alcohol copolymer, polyesters, polyvinyl or polyvinylidene halides. The second layer is selected from low density polyethylene, ethylene copolymers, block copolymers of polyesters and polyether glycols, thermoplastic polyurethanes, thermoplastic polyesters, plasticised polyvinyl halides, nitrile rubber blends, plasticised polyamides.

Description

IMPROVEMENTS IN OR RELATING TO LINER PIPES This invention relates to a liner pipe, and in particular to a multilayer liner pipe, and to methods of lining a pipeline using the liner pipe.

There is a significant need for a reliable repair system that will prevent leakage from pipe joints and pipes that have deteriorated in, for example, pipelines conveying potable water. Polymer pipe lining systems of various types are known and these have been installed by methods which are intended to result in a close final fit of the liner pipe within the deficient host pipe so that there is not too great a reduction in the bore and hence carrying capacity of the pipeline. In order to improve ease of installation, recently such linings have often been relatively thin walled, for example 5mm at 4" nominal mains size, 7mm at 10" nominal mains size and 15mm at 24" nominal mains sizes. More recently still, the use of very thin polymeric liners having wall thicknesses as low as imm or thereabouts has been mooted.

With very thin walled liners, the costs of installation may be expected to be as low as those typically encountered with spray lining pipe rehabilitation techniques, due for example to the increased ease with which long lengths can be transported, and the general improved ease of handling and insertion, and termination at the liner extremities. However, even though such very thin liners are able to bridge, under normal pipeline operational pressure, gaps of up to typically 25mm at pipeline joints, they are not able to bridge host pipe gaps of up to 1 50mm or more at, say, repair collars. With gaps of this size, the liners need to be able to expand radially into such annular cavities, and this may entail expansion of the liners by up to 30% or more of their natural diameters, under the commissioning and/or operational pressure of the pipeline. Such expansion needs to be accommodated without significant risk of failure by splitting or perforation for example, in either the short or the long term. It is desirable that the risks of such failures are minimised over a range of ambient temperatures, and for a variety of liner surface defects that may occur during insertion or under operational conditions. In contrast to sprayed linings, where failure may result only in locally increased corrosion of the host pipe bore, failure of a thin polymer liner could result in its partial or total collapse, and this could result in lost pipeline capacity and loss of protection over a significant length of the host bore.

Considerable effort has been expended by the present applicant to identify an existing commercially available polymer, from which very thin liners could be manufactured, that would permit the very high aforementioned strains to take place in a controlled way without risk of failure. A liner made from such a polymer would need to possess the long term strength and stress crack resistance necessary to bridge without failure the normal discontinuities in the host pipe bore wherever joints are present, as mentioned above. Moreover, for use in potable water pipelines, the liner would need to be made from a material which has full Drinking Water Inspectorate (DWI) approval for such use, or for which such approval could readily be obtained.

The above requirements have been found by the present applicant to be mutually incompatible, in as much as all of the polymers investigated having DWI approval cannot be safely strained above approximately 20% without a significant risk of failure occurring, or are too elastic in nature leading to fretting and abrasion against rough edges in the host main.

Furthermore, many alternative polymers not currently possessing DWI approval, but which might be expected to be suitable for carrying potable water, would also not satisfy the aforementioned structural requirements.

Hence, it would seem from the inventors' investigations to date that, insofar as single layer polymer pipes are concerned, there is an irresolvable confiict between, on the one hand, the need for high strainability throughout the range of circumstances encountered in use, and on the other hand, the need for adequate strength to provide for bridging of normal bore discontinuities, and dimensionally stable behaviour when exposed to normal pipeline flow pressure fluctuations. Dimensionally stable behaviour is important in preventing or reducing continual partial expansion and contraction of the expanded liner which would otherwise increase the risk of the liner being damaged from fatigue and/or by fretting against sharp edges on the host pipe bore, for example.

It is an object of the present invention to provide a polymeric liner that will accommodate safe expansion up to a size at least 30% greater than its natural size, and in its enlarged state will possess similar physical characteristics to the same liner in its initial unstrained state, and in both states will have comparable strength and life characteristics to those of similar thickness liners made from conventionally accepted pipe grade polymers.

The present invention sets out to achieve this object by providing a laminar pipe comprising a first layer formed from a first polymer, to which is bonded a second layer of a second polymer having a more elastomeric character than the first polymer.

Thus, in a first aspect, the invention provides a multilayer liner pipe for lining a pipeline, the liner pipe comprising a first layer of a first polymeric material and a second layer of a second polymeric material, wherein the second material has a more elastomeric character than that of the first material; the two layers being bonded together to an extent sufficient to substantially prevent differential straining between the layers.

In a further aspect, the invention provides a method of lining an existing pipeline, which method comprises introducing into the bore of the existing pipeline a liner pipe as hereinbefore defined.

In a still further aspect, the invention provides a pipeline comprising an outer pipe having disposed within its bore a liner pipe as hereinbefore defined.

In a further aspect, the invention provides a multilayer liner pipe for lining a pipeline, the liner pipe comprising a first layer of at first polymeric material and a second layer of a second polymeric material, wherein the second material has a plastic limit which is greater than that of the first material; the term "plastic limit" as used herein being the maximum elongation achievable in the bulk material without localisation of elongation (often referred to as "necking") taking place; the first and second layers being bonded together to an extent sufficient to substantially prevent differential straining between the layers In each of the aforementioned aspects of the invention, the first layer can be disposed radially inwardly or radially outwardly of the second layer.

In one preferred embodiment, the first layer is disposed radially inwardly of the second layer.

In a particularly preferred embodiment, the second layer is the radially outermost layer of the pipe. In this particularly preferred embodiment, the first layer is typically, but not exclusively, the radially innermost layer of the pipe.

In addition to the first and second layers, the multilayer pipe can have one or more additional layers. Such layers may be employed, for example, to impart such characteristics as improved gas or petroleum barrier properties.

The first polymer, from which the first layer is formed, is typically a pipe grade polymer, and is preferably one having approval for use with potable water. The first polymer may on its own exhibit relatively low strainability of about 10% to 20% before local yielding occurs at one or more locations, but preferably possesses good strength and stiffness characteristics both before and after yielding. Conversely the second polymer, from which the second layer is formed, may have relatively low strength but preferably possesses high extendibility with even drawing characteristics.

The second (e.g. radially outer) layer may advantageously be thicker than the first (e.g. radially inner) layer. For example, the first layer may be from one and a haif times up to three times the thickness of the second layer.

The total wall thickness will typically depend on the diameter of the pipeline to be lined. For example, the wall thickness for a liner pipe intended for lining a pipeline of 24 inch nominal diameter may be as low as 1 mm and as high as 1 5mm, whereas the wall thicknesses of liners intended for 10 inch and 4 inch nominal diameter pipelines may be, for example, as low as imm and as high as 7mm and 5mm respectively.

Purely by way of example, the inner layer can be from 0.3mm to 3mm thick, preferably 0.1 to 1 .5mm thick, and more preferably 0.5mm to 1 mum thick, whereas the outer layer can be from 0.7mm to 7mm thick, preferably 1 mum to 5mm, and more preferably 1.25mm to 2mm thick, the precise thickness depending on the diameter of the pipeline to be lined.

The advantage of the laminar arrangement of the present invention is that when expansion of the multilayer pipe wall takes place, the first layer would be constrained by the second layer to adopt to a significant extent the strainability characteristics of the outer layer. Thus the even drawing characteristics of the second layer would help to promote even drawing of the first layer also, which latter layer would on its own have normally exhibited local yielding in such circumstances, as previously stated. Once expanded, the multilayer liner would be relatively stable dimensionally, irrespective of its stress state, by virtue of the restraining characteristics of the relatively strong and stiff first layer.

The liner pipe of the invention can comprise only two polymer layers, or more than two polymer layers, A pair of adjacent incompatible polymer layers may be bonded together by means of an adhesive tie layer interposed therebetween. Alternatively, if formed from compatible polymers, the first and second layers may be bonded together by fusion or adhesion generated during coextrusion.

However, it is most preferred that the first and second layers should be bonded together so as to prevent relative movement therebetween. If the layers are not bonded together, movement of the first layer and hence differential straining between the layers and localised necking may still occur despite the presence of the second layer. It is most preferred that the first and second layers are bonded together, either directly, or through the intermediacy of one or more intervening layers over substantially all of the area in which they are in contact.

By varying the number and properties of the layers it is envisaged that it should be possible to confer virtually any desired comoination of strainability andlor strength characteristics for a particular application.

Furthermore it will be understood that the thicknesses of individual layers could be tuned to assist in the provision of any particular combination of characteristics. Moreover, fibre reinforcement of any suitable type or orientation could be incorporated in one or more layers.

Examples of polymers from which the first (e.g. inner) layer can be made include any extrudable thermoplastic polymers, which may or may not be crosslinkable. Particular examples are polyolefins such as polyethylene, e.g. medium density polyethylene, polypropylene, and polybutylene; polyamides; ethylene vinyl alcohol copolymer (EVOH); polyesters such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT); and polyvinyl and polyvinylidene halides such as polyvinylidene chloride (PVDC) and polyvinylidene fluoride (PVDF).

The first layer may advantageously have gas barrier properties and examples of such polymers include EVOH, PVDC, PVDF and polyamides.

It is envisaged that the second (e.g. outer) layer may be made, for example, from a polymer with a crystallinity of less than 50%, for example less than 30%, more preferably less than 20%.

Examples of polymers from which the second (e.g. outer) layer can be made include polymers having at least some elastomeric character. Such polymers can include, for example, crosslinked elastomers and thermoplastic elastomers. The polymers can be for example homopolymers or copolymers such as block copolymers, or they can be blends of polymers having the required characteristics. Particular examples are very low density polyethylene, ethylene copolymers such as ethylene vinyl acetate (EVA); block copolymers of polyesters and polyether glycols, such as polyalkylene terephthalate/polyether glycols; thermoplastic polyurethanes; thermoplastic polyesters; plasticised polyvinyl halides such as plasticised polyvinyl chloride and polyvinyl chloride - nitrile rubber blends; and plasticised polyamides such as plasticised nylons.

In another aspect, the invention provides a multilayer liner pipe for a pipeline, and a pipeline lined with the said multilayer liner pipe, the liner pipe comprising: (a) a first layer of a first polymeric material selected from polyolefins such as polyethylene, e.g. medium density polyethylene (MOPE), polypropylene and polybutylene; polyamides; polyesters such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT); and polyvinyl and polyvinylidene halides such as polyvinylidene fluoride; and (b) a second layer of a second polymeric material selected from very low density polyethylene, ethylene copolymers such as ethylene vinyl acetate (EVA); block copolymers of polyesters and polyether glycols, such as polyalkylene terephthalate/polyether glycols; thermoplastic polyurethanes; thermoplastic polyesters; plasticised polyvinyl halides such as plasticised polyvinyl chloride and polyvinyl chloride - nitrile rubber blends; and plasticised polyamides such as plasticised nylons; wherein the second material has a more elastomeric character than that of the first material; the two layers being bonded together to an extent sufficient to substantially prevent differential straining between the layers.

In a most preferred embodiment, the polymeric liner can accommodate safe expansion up to a size at least 30% greater than its natural size, without necking or cracking taking place.

The invention will now be illustrated by reference to the accompanying drawings, in which: Figure 1 is a side sectional elevation through a pipeline containing a liner pipe Figure 2 is an enlarged view of the region marked A in Figure 1; Figure 3 is a side sectional elevation of a liner pipe according to one embodiment of the invention; Figure 4 is an enlarged view of the region marked B in Figure 3; Referring now to the drawings, Figure 1 illustrates a pipeline formed from cast iron pipes P of nominal diameter of 4 inches, one of which has corroded through with the result that a hole H of over 1 50mm in length has formed in the side wall W of the pipe P. Leakage from the pipe P has been stopped by means of repair clamp R which is clamped about the pipe P. A liner pipe L formed from a single layer of a potable water-compatible grade of MDPE has been inserted into the pipe to prevent leakage of water in the event that the outer cast iron pipe P deteriorates further. The MDPE liner pipe L has a wall thickness of approximately 2mm in an unstressed state.

Under the pressures typically encountered in water mains pipelines, the region of the liner pipe L spanning the hole H expands radially outwardly into the hole, the expanded radius of the liner pipe L being approximately 30% greater than the normal or unexpanded diameter of the liner. The effect that such expansion has on the wall of the liner pipe is shown more clearly in Figure 2 which is an enlarged view of the region of liner pipe spanning the hole H. As can be seen, the MDPE has relatively low strainability and cannot accommodate expansion of more than about 20%.

Instead of extending in a uniform manner, the liner has undergone localised extension or necking to produce a region R of considerably reduced wall thickness at which cracking is very likely to occur after a relatively short period of use. In addition, although not shown, shearing can occur around the periphery of the expanded region, particularly in the region of the sharp edge E presented by the pipe P. These problems could be overcome to a large extent by making the liner pipe wall thicker but this in turn would create its own problems of increased difficulty of installation, due to the increased bulk and stiffness of the liner, as well as increased cost as a result of the increased amounts of materials used.

Figures 3 and 4 illustrate a corroded cast iron mains pipe of 4 inch nominal diameter similar to that shown in Figures 1 and 2 except that it has been lined with a multilayer liner pipe 2 according to the invention. The liner pipe 2 is formed from inner (first) 4 and outer (second) 6 layers bonded together by an adhesive layer 5. The inner layer 4 in this embodiment is made from polypropylene pipe grade polymer and is approximately 0.5mm thick, whereas the outer layer 6 is formed from a block copolymer of polybutylene terephthalate and polyether glycols, for example of a type sold by Du Pont under the trade mark "HYTREL", which is approximately 1 .5mm thick. The adhesive layer 5 is an ethylene methylacrylate copolymer such as "Lotryl 24MA005" available from Elf Atochem.

With the multilayer liner shown in Figures 3 and 4, the localised extension or necking of the layer 4 is prevented by the fact that it is adhesively bonded to the "HYTREL" layer 6; and consequently the inner layer 6 is constrained to undergo uniform extension or plastic deformation rather than necking. As a result, severely thinned regions of the type shown in Figure 2 do not arise. Thus by means of the present invention, the liner pipe 2 can be formed from a thin polymer material yet has sufficient strength to bridge the hole in the cast iron pipeline wall without cracking.

The invention has been illustrated by means of a multi layer pipe formed from polypropylene and a block copolymer of polybutylene terephthalate and polyether glycols but it will be appreciated that other polymers may be used instead of the two specifically described can be used for the inner (first) layer 4 and outer (second) layer 6 provided that the outer layer is formed from a material of greater elastomeric character than the inner layer. Moreover, although the invention has been illustrated by reference to mains water pipes, it is equally applicable to other situations where existing mains pipes have been corroded and repaired and where inserting a liner is an appropriate solution to the problem of future leakage of the pipe. All such modifications and alterations are intended to be embraced by this application.

Claims (8)

1. A multilayer liner pipe for lining a pipeline, the liner pipe comprising a first layer of a first polymeric material and a second layer of a second polymeric material, wherein the second material has a more elastomeric character than that of the first material; the two layers being bonded together to an extent sufficient to substantially prevent differential straining between the layers.

2. A multilayer liner pipe for lining a pipeline, the liner pipe comprising a first layer of at first polymeric material and a second layer of a second polymeric material, wherein the second material has a plastic limit which is greater than that of the first material; the first and second layers being bonded together to an extent sufficient to substantially prevent differential straining between the layers

3. A multilayer liner pipe according to claim 1 or claim 2 wherein the first layer is disposed radially inwardly of the second layer.

4. A multilayer liner pipe according to claim 3 wherein the second layer is the radially outermost layer of the pipe.

5. A multilayer liner pipe according to any one of the preceding claims wherein the first layer is formed from a polymer selected from polyolefins such as polyethylene, e.g. medium density polyethylene, polypropylene, and polybutylene; polyamides; ethylene vinyl alcohol copolymer (EVOH); polyesters such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT); and polyvinyl and polyvinylidene halides such as polyvinylidene chloride (PVDC) and polyvinyiidene fluoride (PVDF).

S. A multilayer liner pipe according to any one of the preceding claims wherein the second layer is formed from a polymer selected from low density polyethylene, ethylene copolymers such as ethylene vinyl acetate (EVA); block copolymers of polyesters and polyether glycols, such as polyalkylene terephthalate/polyether glycols; thermoplastic polyurethanes; thermoplastic polyesters; plasticised polyvinyl halides such as plasticised polyvinyl chloride and polyvinyl chloride - nitrile rubber blends; and plasticised polyamides such as plasticised nylons.

7. A method of lining an existing pipeline, which method comprises introducing into the bore of the existing pipeline a liner pipe as defined in any one of the preceding claims.

8. A pipeline comprising an outer pipe having disposed within its bore a liner pipe as defined in any one of the preceding claims.