GB2561197A

GB2561197A - Liner pipe

Info

Publication number: GB2561197A
Application number: GB1705434.7A
Authority: GB
Inventors: John Muckle Derek
Original assignee: Radius Systems Ltd
Current assignee: Radius Systems Ltd
Priority date: 2017-04-04
Filing date: 2017-04-04
Publication date: 2018-10-10
Also published as: GB201705434D0

Abstract

A liner pipe for lining a host pipe comprises a core 1 and an outer layer 2 attached to the core. The outer layer includes a ultra-violet inhibitor, such as carbon black in the range 2-2.5 wt% or a hindered amine light stabiliser (HALS) which can be distributed uniformly. The core and outer layer can comprise materials derived from polyethylene, materials which can be fusion welded during extrusion, or materials with a melt flow index range of 0.2-2.0 g/10min. The core and the outer layer can be inseparable by thermal cycling of the liner pipe between -20 and 60 degrees C, and can be inseparable by tensile testing at a rate of 25mm/min and an elongation of >350%. The core can comprise a raised temperature polyethylene, PE-RT or PE100-RT, core, and the outer layer can comprise pipe pressure grade polyethylene, such as PE80 or PE100. The outer layer can be trapped in compression against the host pipe when installed such that it is not capable of contacting fluid being transported through the lined host pipe. The core and the outer layer can be co-extruded, with external formations or grooves formed by a profiled die head.

Description

(54) Title of the Invention: Liner pipe

Abstract Title: Liner pipe with ultra-violet inhibitor (57) A liner pipe for lining a host pipe comprises a core 1 and an outer layer 2 attached to the core. The outer layer includes a ultra-violet inhibitor, such as carbon black in the range 2-2.5 wt% or a hindered amine light stabiliser (HALS) which can be distributed uniformly. The core and outer layer can comprise materials derived from polyethylene, materials which can be fusion welded during extrusion, or materials with a melt flow index range of 0.2-2.0 g/10min. The core and the outer layer can be inseparable by thermal cycling of the liner pipe between -20 and 60 degrees C, and can be inseparable by tensile testing at a rate of 25mm/min and an elongation of >350%. The core can comprise a raised temperature polyethylene, PE-RT or PE100-RT, core, and the outer layer can comprise pipe pressure grade polyethylene, such as PE80 or PE100. The outer layer can be trapped in compression against the host pipe when installed such that it is not capable of contacting fluid being transported through the lined host pipe. The core and the outer layer can be co-extruded, with external formations or grooves formed by a profiled die head.

FIGURE 1

1/1

FIGURE 2

LINER PIPE [0001] This invention relates to a liner pipe for lining a host pipe, in particular but not exclusively for applications in which the liner pipe needs to operate at temperatures higher than those normally used for conventional pressure pipe grades of polyethylene.

BACKGROUND [0002] Since at least the 1980s, techniques have been known for renovating existing underground pipe networks, typically utility pipe networks of the type used to transport natural gas or water for domestic consumption, by lining the mains pipe or other existing host pipe in situ with a liner pipe. Various different lining techniques are known in the industry and are referred to as “close fit lining techniques”.

[0003] As the close fit liner techniques were developed, it was realised that the techniques could be used for applications other than renovation of existing pipe networks. For example, in mining industries, it was found that a plastics liner pipe on the inside surface of a steel host pipe could significantly extend the life of the steel pipe by reducing the effect of abrasive wear on the interior of the steel pipe caused by slurry passing therethrough. In the upstream oil and gas industries, it was found that a plastic liner on the inside surface of a steel pipe acts a corrosion resistant barrier which allows lower specification steels to be used instead of the usual corrosion resistant alloys (“CRA”).

[0004] Typically, liner pipes for renovating existing pipe networks were manufactured from so-called “pressure pipe” grades of polyethylene which are designed to have a thermal window of normal operation typically in the range -20 to +40°C. However, this conventional material is unsuitable for some of the other applications for liner pipes, where a higher operating temperature may be required. Attempting to use a material at the limit of or outside its thermal window of normal operation may result in stress cracking or accelerated oxidation of the liner pipe material.

[0005] For higher temperature applications, other materials have been considered. Pressure pipe grades of polyethylene as mentioned above may be used for temperatures up to around 65-70°C. Random copolymer polypropylenes may be used to around 95°C. Polyamides may be used to temperatures to around 110-120°C.

[0006] Close fit lining techniques usually involve temporarily reducing the diameter of the liner pipe in order to insert it into the host pipe, after which the diameter of the liner pipe can revert to or nearly to its original diameter. However, not all polymers are suitable for use in such diameter reduction techniques. Some materials, owing to their structure, simply will not undergo the cold flow strain deformation required for the diameter reduction stage.

[0007] Some materials, including certain grades of random co-polymer polypropylene, do not flow uniformly during the diameter reduction process. Rather they tend to move in unexpected directions as a result of the applied force and, in effect, ‘corkscrew’ through the reduction die which makes them impractical to insert into the host pipe.

[0008] Some materials have a low strain at yield in contrast to the level of strain occurring in the diameter reduction process and whilst they can pass through the die, they show little or no elastic recovery after being drawn through the die because the bulk of the material has substantially passed its yield point. This means such materials are difficult to revert in an elastic way against the host pipe into which they have been inserted [0009] Pressure pipe grades of polyethylene do not have these disadvantages.

However, they cannot be readily used at higher temperatures. More recently, “raised temperature” pressure pipe grades of polyethylene (designated “PE-RT”) have been considered as an alternative to random copolymer propylene materials in the manufacture of freestanding pipes, particularly in the market for hot and cold pipe systems for residential and commercial properties. PE-RT materials have improved resistance to stress crack defects and to oxidation when operating at temperatures above 60°C, as compared with the normal pressure pipe grades of polyethylene described above. This means that PE-RT can be substituted for pressure pipe grade polyethylene but with the advantage of being able to operate at a higher temperature as described above. For example, PE-RT can be used in applications at least to 95°C based on a nominal 20 year asset life.

[0010] PE-RT is not supplied with a UV inhibitor. UV inhibitors are used in situations where a pipe is likely to be stored in an environment where it may be exposed to UV (e.g. strong sunlight) which may degrade the material of the pipe. PE-RT is usually intended for use in residential and commercial property installations, for example made into relatively small diameter plumbing pipes. Such pipes are stored in warehouses or other premises so that a UV inhibitor is not required. In any case, the relatively high cost of adding a UV inhibitor is undesirable as such pipes are already relatively expensive because of the need to include diffusion barrier layers, which is essential for such residential and commercial plumbing installations.

BRIEF SUMMARY OF THE DISCLOSURE [0011] In accordance with the present invention there is provided a liner pipe for lining a host pipe, the liner pipe comprising:

a. a core;

b. an outer layer attached to said core, the outer layer including a UV inhibitor.

[0012] Preferably said core and said outer layer comprise materials within a melt flow index range of 0.2 to 2.0 g/10min (190°C/5kg). The core and the outer layer may comprise materials derived from polyethylene.

[0013] In an embodiment, said core and said outer layer comprise materials which can be fusion welded during extrusion. In an embodiment, said core and said outer cannot be separated by thermal cycling of the liner pipe between -20°C and 60°C. In another embodiment, said core and said outer layer cannot be separated by tensile testing at a rate of 25mm/min and elongation of >350%.

[0014] Preferably, said core comprises a raised temperature polyethylene (“PE-RT” or “PE100-RT”) core.

[0015] The outer layer may comprise a pipe pressure grade polyethylene and/or PE80 or PE100 polyethylene pipe grade materials.

[0016] In an embodiment, said UV inhibitor comprises carbon black, preferably in the range 2- 2.5 wt%. Alternatively, said UV inhibitor comprises a hindered amine light stabiliser (HALS) [0017] Preferably, said UV inhibitor is distributed substantially uniformly throughout said outer layer.

[0018] In an embodiment, the outer layer may be trapped in compression against the host pipe when installed such that it is not capable of contacting fluid being transported through the lined host pipe.

[0019] The outer layer may have a thickness in the range 0.5-1,5mm, in the range 0.5 - 1.0mm or a thickness of less than 0.5mm.

[0020] In an embodiment, the core and outer layer are co-extruded. The core may include one or more external formations or grooves and said outer layer may follow said formations or grooves. The formations or grooves may be formable by a profile die head.

DESCRIPTION OF THE DRAWINGS [0021] Embodiments of the invention will now be more particularly described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a cross-sectional view of a first embodiment of the invention; and Figure 2 is a cross-sectional view of a second embodiment of the invention.

DETAILED DESCRIPTION [0022] In the present disclosure, the following terms may be understood in view of the explanations below:

[0023] The term “pressure grade PE” may refer to polyethylene having a melt flow rate or melt flow index preferably in the range 0.2 to 1.0 g/10min (190°C/5kg condition) but in any case in the range 0.2 to 2.0 g/10min (190°C/5kg condition).

[0024] The term “UV inhibitor” may refer to a substance which slows down or protects against the effects of UV radiation, for example solar radiation, on the material containing the substance.

[0025] The term “thermal window of operation” may refer to a temperature range to which a pipe is typically expected to be exposed, without significant adverse effect, during manufacture of the pipe and/or during normal operation of the pipe.

[0026] Liner pipes are commonly manufactured and then stored outside, either in sticks or coils. Depending upon the local climate and the storage period, the material of the liner pipe may be substantially degraded by the effect of solar radiation. Parts of the liner pipe which are stored uppermost will degrade more quickly than those parts which are underneath or more sheltered from solar radiation, resulting in a liner pipe of uneven quality. There is thus a need to provide a liner pipe which includes a UV inhibitor which can counteract or resist the negative effect of the solar radiation on the material of the liner pipe.

[0027] PE-RT is normally supplied as a natural material of substantially white colouring.

If a UV inhibitor was to be added to this material, this would have to be created as a special order item that attracts a premium price. Carbon black is well known as a UV inhibitor but manufacturers are discouraged from adding it to PE-RT because PE-RT is conventionally used in pipes for residential or commercial applications where it is desirable to produce coloured pipes. Carbon black would interfere with the desired colouring. The manufacturer would be more likely to consider a more expensive UV inhibitor, as an alternative to carbon black and which would not interfere with the colouring of the pipe.

[0028] The applicant has realised that, for the purpose of UV protection, it is not necessary to distribute UV inhibitor throughout the material of a liner pipe. Instead, a coextruded liner pipe can be produced comprising a core of one material and an outer layer of the same or a different material. Only the outer layer need contain the UV inhibitor.

[0029] A liner pipe can be produced from a core of natural PE-RT material co-extruded with an outer layer of carbon black compounded PE100 of a standard pressure pipe grade. The core may for example typically have an initial outside diameter of 268mm, capable of being reduced using known diameter reduction techniques by around 10-12% such that it is temporarily circa 236mm outside diameter for insertion into a 10 inch [25.4 cm] nominal bore host pipe. Once installed, the liner pipe can expand back towards its original diameter and form a tight fit against the inside of the host pipe.

[0030] The core of the liner pipe thus has a starting diameter of 268mm in this example, and could have a total wall thickness of 14mm. The core is made from PE-RT in order to function as a high temperature liner pipe whose bore is resistant to cracking due to combination of the installation process affecting the material and operating conditions at a temperature greater than 65°C, typically 95°C or perhaps higher. In order to minimise cost, the market norm of a natural PE-RT material is used. To provide UV protection, a relatively thin outer layer of pressure pipe grade PE100 with carbon black stabiliser is provided on the outside of the core in such a way that it forms an integral part of the liner pipe structure. The outer layer may be co-extruded with the core. The outer layer needs to be sufficiently thick so as to absorb and protect the PE-RT core from UV degradation during storage in challenging climatic conditions, for example up to a year in Houston, Texas. A preferable thickness for the outer layer is less than 0.5mm, typically 0.1-0.2mm, but for practical purposes to provide scratch resistance for example and to allow for use of conventional extrusion equipment a more suitable thickness is 0.5-1.0mm, or 0.5 to 1,5mm. The outer layer would be this same thickness irrespective of the diameter or wall thickness of the core itself, which may vary for different liner pipe requirements.

[0031] Temporary end caps may be provided for the liner pipe to further protect it in storage from the effects of UV degradation. Without endcaps, if the liner pipe is stored in sticks or lengths with the PE-RT core exposed at the ends thereof, UV degradation can occur at these ends. The endcaps are removed when the liner pipe is being handled for welding to form it into long strings (e.g. 1000m) required as an assembly step when preparing to line steel pipes on a spool base. In these long strings, the outer layer continues to protect the liner pipe, except at the butt fusion welded joints which can have a temporary UV protective tape applied. The localised taping of a pipe joint every 18 or 24m is more practical than attempting to cover a single 1000m long pipe string with a continuous outer layer to protect it from UV solar radiation.

[0032] Once the liner pipe has had its diameter reduced and has been inserted into a host pipe, it is no longer subjected to the effects of UV solar radiation. The carbon black stabilised outer layer no longer serves a practical function other than as a thin layer of material trapped in compression between the host pipe and the PE-RT core, characterised in that it is not in fluid contact with the fluid to be transported by the pipeline.

[0033] Once the lined host pipe is back in service, the PE-RT core provides a high temperature stabilised pipe form that is resistant to degradation originating from the bore of the liner pipe in the form of a stress crack defect or premature oxidation of the material which would be the expected failure modes.

[0034] Example embodiments are illustrated in Figures 1 and 2. Figure 1 shows a crosssectional view of a liner pipe form comprising an inner core (1) and an outer layer (2). The inner core (1) is a PE-RT material and the outer core (2) is a UV stabiliser polyethylene material.

[0035] An alternative embodiment is shown in Figure 2 in which the liner pipe comprises an inner core (1’) and an outer layer (2’). The liner pipe has been extruded using a profile die that introduces a series of grooves (3), axially formed along the length of the liner pipe. One or more grooves (3) may be present; in the illustrated embodiment there are four grooves (3) disposed around the circumference of the liner pipe. The extrusion method forms grooves initially in the inner core (T) and the outer layer (2’) containing the UV inhibitor follows the inner core’s profile to maintain full protection from UV degradation in storage.

[0036] Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to”, and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0037] Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments.

The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

[0038] The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

Claims

1. A liner pipe for lining a host pipe, the liner pipe comprising:

a. a core;

2. The liner pipe of claim 1 wherein said core and said outer layer comprise materials within a melt flow index range of 0.2 to 2.0 g/10min (190°C/5kg).

3. The liner pipe of claim 1 or claim 2 wherein said core and said outer layer comprise materials derived from polyethylene.

4. The liner pipe of any of the preceding claims wherein said core and said outer layer comprise materials which can be fusion welded during extrusion.

5. The liner pipe of claim 4 wherein said core and said outer cannot be separated by thermal cycling of the liner pipe between -20°C and 60°C.

6. The liner pipe of claim 4 wherein said core and said outer layer cannot be separated by tensile testing at a rate of 25mm/min and elongation of >350%.

7. The liner pipe of any of the preceding claims wherein said core comprises a raised temperature polyethylene (“PE-RT” or “PE100-RT”) core.

8. The liner pipe of any of the preceding claims wherein said outer layer comprises a pipe pressure grade polyethylene.

9. The liner pipe of any of the preceding claims wherein said outer layer comprises PE80 or PE100 polyethylene pipe grade materials.

10. The liner pipe of any of the preceding claims wherein said UV inhibitor comprises carbon black, preferably in the range 2- 2.5 wt%.

11. The liner pipe of any of claims 1-9 wherein said UV inhibitor comprises a hindered amine light stabiliser (HALS)

12. The liner pipe of any of the preceding claims wherein said UV inhibitor is distributed substantially uniformly throughout said outer layer.

13. The liner pipe of any of the preceding claims wherein the outer layer is trapped in compression against the host pipe when installed such that it is not capable of contacting fluid being transported through the lined host pipe.

14. The liner pipe of any of the preceding claims wherein the outer layer has a thickness in the range 0.5 - 1,5mm.

15. The liner pipe of any of the preceding claims wherein the outer layer has a thickness in the range 0.5 - 1.0mm.

16. The liner pipe of any of claims 1 to 13 wherein the outer layer has a thickness of less than 0.5mm.

5

17. The liner pipe of any of the preceding claims wherein the core and outer layer are co-extruded.

18. The liner pipe of claim 17 wherein the core includes one or more external formations or grooves and wherein said outer layer follows said formations or grooves.

19. The liner pipe of claim 18 wherein said formations or grooves are formable by a 10 profile die head.

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