Login| Sign Up| Help| Contact|

Patent Searching and Data


Title:
METHOD FOR EXPANDING A TUBULAR STRUCTURE
Document Type and Number:
WIPO Patent Application WO/2018/197848
Kind Code:
A1
Abstract:
The invention provides a method for expanding a diameter of a tubular structure. The method comprises fitting a removable sizing gauge around an external surface of the tubular structure and inserting a substantially tubular metallic insert within the tubular structure. The metallic insert comprises an external diameter smaller than an unexpanded internal diameter of the tubular structure. The method comprises urging said metallic insert radially outwardly within the tubular structure to expand said metallic insert and said tubular structure. The metallic insert is arranged such that said urging results in work hardening of the metallic insert.

Inventors:
WALLACE, Gordon James (5 Eastern Avenue, Valley ParkBolsover, Chesterfield South Yorkshire S44 6SN, S44 6SN, GB)
Application Number:
GB2018/051057
Publication Date:
November 01, 2018
Filing Date:
April 23, 2018
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
RADIUS SYSTEMS LIMITED (Radius House, Berristow Lane South Normanton, Alfreton Derbyshire DE55 2JJ, DE55 2JJ, GB)
International Classes:
F16L13/14; B21D41/02; B29C57/04; F16L47/06
Domestic Patent References:
WO2012001335A12012-01-05
Foreign References:
DE1704254A11971-05-06
FR2917151A12008-12-12
Attorney, Agent or Firm:
HGF LIMITED (Fountain Precinct, Balm Green, Sheffield South Yorkshire S1 2JA, S1 2JA, GB)
Download PDF:
Claims:
CLAIMS

1. A method for expanding an internal diameter of a tubular structure comprising

fitting a removable sizing gauge around an external surface of the tubular structure; inserting a substantially tubular metallic insert within the tubular structure, wherein said metallic insert comprises an external diameter smaller than an unexpanded internal diameter of the tubular structure; and

urging said metallic insert radially outwardly within the tubular structure to expand said metallic insert and said tubular structure,

wherein said urging comprises work hardening the metallic insert.

2. A method according to claim 1 , wherein said removable sizing gauge comprises an internal diameter corresponding to a desired expanded external diameter of the tubular structure.

3. A method according to claim 1 or claim 2, wherein said removable sizing gauge comprises a sleeve having an adjustable internal diameter.

4. A method according to any preceding claim, wherein said tubular structure is a polyolefin tubular structure.

5. A method according to any preceding claim, wherein said metallic insert comprises copper. 6. A method according to any preceding claim, comprising heat treating the metallic insert so that the metallic insert is in a fully soft state, prior to said inserting.

7. A method according to claim 6, wherein said heat treating comprises heating the metallic insert to 550°C for 30 minutes.

8. A method according to claim 6 or claim 7, wherein said heat treating comprises cooling the metallic insert after said heating.

9. A method according to claim 8, wherein said cooling comprises quenching the metallic insert in water at an ambient temperature.

10. A method according to claim 9, wherein said quenching is implemented for at least 30 minutes.

1 1. A method according to any preceding claim, comprising sizing the metallic insert prior to said inserting.

12. A method according to claim 1 1 , wherein said sizing comprises drawing the metallic insert over a former. 13. A method according to claim 11 , wherein said sizing comprises milling the metallic insert to desired initial dimensions.

14. A method according to any preceding claim, wherein said urging comprises

inserting a multi segment expansion head within the metallic insert within the tubular structure; and

actuating the multi segment expansion head to urge the metallic insert and tubular structure radially outwardly.

15. A method according to claim 14, wherein said urging further comprises

rotating the multi segment expansion head within the metallic insert and tubular structure and repeating said actuating.

16. A method according to any of claims 1 to 15, wherein an external surface of the end region of the tubular structure is accessible for later, on-site, joining to a fitting or to a polyolefin pipe.

17. A method as claimed in any of claims 2 - 16 wherein said internal diameter of the removable sizing sleeve is substantially constant. 18. A method of making a joint to a polyolefin pipe, or of joining two such polyolefin pipes, the method comprising:

expanding a diameter of an end region or end regions of the pipe or pipes by a method according to any of claims 1 to 17;

installing an electrofusion fitting over an external surface or surfaces of the end region or end regions of the pipe or pipes;

activating the electrofusion fitting to fuse the end region or end regions of the pipe or pipes to the electrofusion fitting

19. A substantially tubular metallic insert for use in a method according to any of claims 1 to 18. 20. A substantially tubular metallic insert according to claim 19, wherein the insert comprises copper in a fully soft state.

Description:
METHOD FOR EXPANDING A TUBULAR STRUCTURE

TECHNICAL FIELD

The present invention relates to a method for expanding a tubular structure. Particularly, but not exclusively, the invention relates to a method for expanding an end of a pipe or a pipe liner, such as a polyolefin pipe or pipe liner.

BACKGROUND

It is known to provide polyolefin tubular structures, in the form of pipes and in the form of pipe liners. Polyolefin pipes may be manufactured having structural properties which enable them to be buried directly in the ground. Materials such as polyethylene are widely used for the manufacture of polyolefin pipes intended to convey fuel gas or drinking water for residential and industrial consumption. In many territories, such as the UK, there generally is an acceptable range of standard pipe diameters which may be used for these applications. For standard pipe diameters, there typically exists a corresponding range of fittings that are routinely manufactured and are readily available for use with pipes having standard diameters.

Whilst standard pipe diameters are generally used, in some cases, this may not be practical or even possible. For example, obstacles may occur which result in pipes of nonstandard diameters being installed instead. For example, pipelines and pipeline assets are often optimised based on a lifetime costing model. Costs through the life of the pipeline may preferably be optimised to reduce direct costs associated with consumables such as electricity, and consequential effects such as carbon dioxide release. Consequently, it is sometimes economically preferable to modify pipe geometry away from standard offerings and instead manufacture an optimised product.

Thus, in many cases, polyolefin tubular structures are manufactured having one or more non-standard dimensions, such as a non-standard external diameter. A non-standard diameter tubular structure causes difficulty in making couplings or joints to the polyolefin tubular structure and invariably leads to a requirement of specialist mechanical fittings.

In the field of tubular pipe liners, there exists a plethora of manufacturing techniques. Polyolefin liners may be first manufactured to a standard geometry or having one or more non-standard dimensions. Such liners may subsequently be subjected to a secondary process either in a factory or on a construction site to mechanically alter the geometry of the liner so that it can be inserted inside another tubular structure, such as a pipe, in a reduced size to act as a liner. Liners may be employed to provide corrosion protection, abrasion resistance or for general renovation of old pipelines.

EP0514142 describes an example of a polyolefin liner which is first formed as a tubular liner and subsequently mechanically deformed on a construction site to permit insertion into a host pipe, for example an old metallic pipe. The tubular liner is first extruded so as to have an external diameter substantially the same, or slightly smaller than an internal diameter of the host pipe. This usually means that the tubular liner has a non-standard external diameter and wall thickness. The liner is mechanically folded at a construction site and subsequently inserted inside the host pipe. After insertion, the liner will unfold and partially recover towards its original tubular form, but cannot achieve this fully until a coupling is formed to permit filling of the liner with water to expand the liner into position within the host pipe.

EP0834034 describes a further example of a polyolefin liner which is first manufactured as a tubular liner and subsequently mechanically deformed for insertion into a host pipe. A diameter of the tubular liner is temporarily reduced by passing the tubular liner through a series of rollers forming elliptical openings. In the case of a polyethylene liner, the reduction in diameter by this method might typically be 8-10% or 8-15%, depending on the grade of material used. After insertion, the liner will partially recover towards its original tubular form, but in order to achieve a full return to its original dimensions, which may be non-standard, a coupling is required to enable the liner to be filled with water and expanded.

Once a liner is inserted in a pipe, a coupling is then desired to connect the pipe and/or liner to adjacent infrastructure or to another pipe, particularly in scenarios where the liner is used as a structural renovation solution to take over the duty of supply from an aged pipe. Some fittings for making such couplings for non-standard pipe sizes and for tubular liners are available to order. Such fittings are generally mechanical fittings that are bespoke manufactured when required to suit the non-standard pipe or liner. Examples of such fittings are marketed under the trademark Viking Johnson Linergrip ® (UK trade mark number UK00002126727). The fittings are manufactured to order and are designed to form a coupling by manufacturing the parts to match the size of the particular liner. Alternative solutions for coupling polyolefin tubular structures having a non-standard diameter to adjacent infrastructure comprise expanding the diameter of the tubular structure, at least in a region of the tubular structure to which the adjacent infrastructure or pipe will be joined. Such expansion is typically limited to expansion within the elastic range of the polyolefin material, or at least is limited to expansion within a range that does not result in wall thinning, particularly localised wall thinning of the tubular structure. Using polyethylene as an example, a strain of between 5% and 8.5% might typically be applied to expand the end of a tubular structure to increase the diameter of the tubular structure.

A particularly common approach to expanding a polyolefin tubular structure, particularly comprising polyethylene, is to first use a multi segment expanding head, such as the multi segment expanding head of the type shown in Figure 1. The multi segment expanding head 100 comprises a hydraulic ram 1 and a pair of cones 2a, 2b arranged to be pulled towards each other when the hydraulic ram 1 is activated. A set of plates 3 are radially disposed about the cones 2a, 2b and are held in place by O-rings 4. The plates 3 are arranged such that when the ram 1 is activated and the cones 2a, 2b are pulled towards each other, the plates 3 move radially outwardly from a first position 5, towards a second, expanded position 6. Such multi segment expanding heads are well known in the art and are commercially available.

In use, such multi segment expanding heads must be actuated a number of times with a slight rotation of the tool between each expansion, in order to achieve a roughly circular enlargement of the end of the tubular structure. However, after each expansion step, the material will generally have been subject to elastic expansion and will attempt to return to its original size, for example by a viscoelastic response. The rate of the viscoelastic response depends on the time for which the tubular structure has been expanded and on the temperature of the material.

Once the tubular structure has been expanded with the multi segment expanding head, an insert is inserted in the expanded region of the tubular structure. The tubular structure then contracts towards the insert as part of the viscoelastic response, attempting to return to its original dimensions. This results in the tubular structure forming a tight fit onto the insert. The insert is typically metallic, but plastic inserts may also be used. The insert is sized such that after installation, an external diameter of the tubular structure is generally a standard diameter within territorial and industry specifications for pipes.

Figure 2 shows an example of a polyolefin tubular structure 7 that has been expanded using the above described prior art method. An initial external diameter 9 of the polyolefin tubular structure 7 has been expanded using the tool described and shown in Figure 1 , such that an insert 8 can be inserted. As the tubular structure 7 attempts to shrink elastically back towards its initial external diameter 9, the tubular structure 7 comes into contact with the insert 8 and is maintained at a larger external diameter 10. The larger external diameter 10 is a standard diameter found in industry standards for commercially available polyolefin pipes and is compatible with mass produced pipe couplings.

One disadvantage of this method is that the polyolefin tubular structure starts to recover to its original dimensions immediately upon removal of the multi head expanding tool. This leaves a very short window of time within which to place the insert in the tubular structure. This poses a safety risk in that a user may trap one or more of their fingers between the tubular structure and the insert as the parts shrink together. An inability to place the insert within the tubular structure and the insert becoming trapped only partially inserted in the end of the tubular structure are also well known problems. These problems may cause users to attempt to over expand the tubular structure to make it easier to fit the insert into the end of the tubular structure. However, overexpansion of the tubular structure is often at the expense of at least some plastic deformation which means that the tubular structure may be unable to shrink back fully onto the insert. This leads to further delays in fitting a coupling or the like to the tubular structure.

BRIEF SUMMARY OF THE DISCLOSURE

Aspects and embodiments of the invention provide methods and an insert. The invention is defined in the appended claims.

According to an aspect of the invention, there is provided a method for expanding an internal diameter of a tubular structure comprising

fitting a removable sizing gauge around an external surface of the tubular structure; inserting a substantially tubular metallic insert within the tubular structure, wherein said metallic insert comprises an external diameter smaller than an unexpanded internal diameter of the tubular structure; and

urging said metallic insert radially outwardly within the tubular structure to expand said metallic insert and said tubular structure,

wherein said urging comprises work hardening the metallic insert.

Advantageously, a user is not required to use quick movements to withdraw an expansion tool from an end of the tubular structure and to place an insert into the tubular structure before it shrinks back. This minimises risk of the user trapping one or more fingers between the tubular structure and the insert as the tubular structure elastically recovers, thereby improving safety for the user. The method also advantageously improves safety for users from a manual handling perspective working within an excavation site, in which may be space limited. Advantageously, the method substantially prevents over expansion of the tubular structure, thereby minimising any undesired plastic deformation or general damage of the tubular structure. The method also advantageously enables control over a final shape or geometry of an expanded region of the tubular structure, thereby enabling expansion without substantially compromising functionality or structural integrity of the tubular structure. The insert is advantageously work hardened by the process of said urging expansion and will therefore resist attempts by the tubular structure to shrink back towards its original dimensions. The insert may also advantageously be arranged to cooperate with a coupling body of a mechanical coupling.

In an embodiment, said removable sizing gauge comprises an internal diameter corresponding to a desired expanded external diameter of the tubular structure. Advantageously, this substantially prevents over expansion of the tubular structure, thereby minimising any undesired plastic deformation or general damage of the tubular structure.

In an embodiment, said removable sizing gauge comprises a sleeve having an adjustable internal diameter. Advantageously, this enables the removable sizing gauge to be used with a range of tubular structures having a range of different initial diameters.

In an embodiment, said tubular structure comprises polyolefin.

In an embodiment, said tubular structure is a polyolefin tubular structure.

In an embodiment, said metallic insert comprises copper.

In an embodiment, the method comprises heat treating the metallic insert so that the metallic insert is in a fully soft state, prior to said inserting. Advantageously, this improves workability of the insert, thereby facilitating said urging.

Optionally, said heat treating comprises heating the metallic insert to 550°C for 30 minutes. Advantageously, this removes or at least reduces any strain hardening of the insert which may have previously occurred during a previous process of forming or sizing the insert.

Optionally, said heat treating comprises cooling the metallic insert after said heating. In an embodiment, said cooling comprises quenching the metallic insert in water at an ambient temperature. Said ambient temperature may comprise room temperature. Room temperature may be a temperature of between 20°C and 25°C, inclusive. Optionally, said quenching is implemented for at least 30 minutes.

In an embodiment, the method comprises sizing the metallic insert prior to said inserting. Advantageously, this enables the insert to be provided with appropriate geometry. Optionally, said sizing comprises drawing the metallic insert over a former.

Optionally, said sizing comprises milling the metallic insert to desired initial dimensions.

In an embodiment, said urging comprises

inserting a multi segment expansion head within the metallic insert within the tubular structure; and

actuating the multi segment expansion head to urge the metallic insert and tubular structure radially outwardly. Advantageously, said multi segment expansion head may be arranged to exert a substantially equal force in all radial directions, thereby providing substantially uniform expansion of the tubular structure. This helps to maintain the tubular form of the tubular structure.

Optionally, said urging further comprises

rotating the multi segment expansion head within the metallic insert and tubular structure and repeating said actuating. Advantageously, this helps to provide substantially uniform expansion of the tubular structure. This helps to maintain the tubular form of the tubular structure.

Preferably, an external surface of the end region of the tubular structure is accessible for later, on-site, joining to a fitting or to a polyolefin pipe.

In an embodiment, said internal diameter of the removable sizing sleeve is substantially constant. According to another aspect of the invention, there is provided a method of making a joint to a polyolefin pipe, or of joining two such polyolefin pipes, the method comprising:

expanding a diameter of an end region or end regions of the pipe or pipes by a method according to any of the above description;

installing an electrofusion fitting over an external surface or surfaces of the end region or end regions of the pipe or pipes;

activating the electrofusion fitting to fuse the end region or end regions of the pipe or pipes to the electrofusion fitting. Advantageously, a joint may be made to a polyolefin pipe or two such pipes may be joined by a method conferring improved safety and reliability. By expanding a diameter of an end region or end regions as above described, a user is not required to use quick movements to withdraw an expansion tool from an end or ends of the pipe or pipes and to place an insert into the pipe or pipes before it shrinks back. This minimises risk of the user trapping one or more fingers between the pipe and the insert as the pipe elastically recovers, thereby improving safety for the user. The method also advantageously improves safety for users from a manual handling perspective working within an excavation site, in which may be space limited. Advantageously, the method substantially prevents over expansion of the end region or end regions, thereby minimising any undesired plastic deformation or general damage of the polyolefin pipe or pipes. The method also advantageously enables control over a final shape or geometry of an expanded region of the pipe or pipes, thereby enabling expansion without substantially compromising functionality or structural integrity of the pipe or pipes. According to another aspect of the invention, there is provided a substantially tubular metallic insert for use in a method according to any of the above description.

Optionally, the insert comprises copper in a fully soft state. BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 (PRIOR ART) is a prior art multi-segment expansion tool;

Figure 2 (PRIOR ART) is a sectional view of a pipe end expanded using a prior art method; Figure 3 is a sectional view showing part of a method for expanding a tubular structure according to an embodiment of the invention;

Figure 4 is a sectional view of a pipe end expanded using a method according to an embodiment of the invention and a removable sizing gauge;

Figure 5 is a perspective view of a removable sizing gauge;

Figures 6A to 6F show partial perspective views of a method for expanding a tubular structure, according to an embodiment of the invention; and

Figure 7 is a sectional view of a pipe coupled to the pipe of Figure 4 after the removable sizing gauge has been removed. DETAILED DESCRIPTION

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of the words, for example "comprising" and "comprises", means "including but not limited to", and is not intended to (and does 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.

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.

In the present disclosure, the following terms may be understood in terms of the below explanations:

The term "crystalline material" may refer to a homogenous solid body of chemical element, compound or isomorphous mixture, having a substantially regular lattice arrangement. The term "lattice arrangement" may refer to a three dimensional repeating array of points, representing a structure of a crystalline material.

The terms "grain" or "crystallite" may refer to a discrete particle or crystal forming a microstructure of a crystalline material.

The term "grain boundary" may refer to an interface at which grains or crystallites having different orientations meet. The term "heat treatment" may refer to subjecting a material to one or more changes in temperature to modify or to at least initiate a change in one or more physical and/or chemical properties of a material. The term "heat treatment" may include annealing, stress relieving and quenching. The term "annealing" may refer to a heat treatment which improves workability of a material. Improved workability may comprise any one or more of an increase in ductility, a reduction in hardness and removal or at least a reduction of internal stressed within the material. The term "annealing" may refer to a heat treatment which causes atoms migrate in a lattice arrangement of a crystalline material. The term "annealing" may include heat treatments comprising heating the material to above its recrystallization temperature, maintaining the material at a suitable temperature, and subsequently cooling the material. Said cooling may be relatively slow.

The term "recrystallization temperature" may refer to a temperature at which recrystallization of a crystalline material occurs. The recrystallization temperature may be a temperature below a melting temperature of the crystalline material.

The term "recrystallization" may refer to a process by which, in a crystalline material, new grains nucleate and grow to consume an existing grain structure. The new grains may have fewer defects, such as dislocations.

The term "dislocation" may refer to a crystallographic defect or irregularity within a crystal structure. The term "dislocation" may include The term "stress relieving" may refer to a heat treatment which promotes removal or at least reduction of internal stresses within a material. The term "fully soft state" may refer to a material which has been fully annealed. The term "fully soft state" may refer to a material which has been annealed to an extent that a resulting microstructure of the material is substantially uniform and substantially stable, which microstructure may closely resemble an equilibrium microstructure of the material's phase diagram.

The term "quenching" may refer to cooling a material at a relatively rapid rate.

The term "work hardening", also referred to in the art as "strain hardening", or "cold working" may refer to a process of strengthening a metallic material by plastic deformation of the material.

The term "plastic deformation" may refer to irreversible deformation of a material brought about by application, to the material, of a mechanical force exceeding an elastic limit of the material.

The term "metallic" may refer to a material comprising metal or a metal alloy.

The term "on-site" may refer to a construction site or other installation site remote from the factory or manufacturing site.

Embodiments of the present invention provide a method for expanding a diameter of a tubular structure, such as a pipe or a pipe liner. With reference to Figures 3 and 4, a tubular structure 7' to be expanded comprises an initial external diameter 9'. The tubular structure comprises a plastics material, such as a polyolefin material. In some embodiments of the invention, the tubular structure comprises polyethylene.

To expand a region of the tubular structure 7', a substantially tubular insert 1 1 is inserted within the tubular structure 7'. The insert 1 1 comprises an external diameter, D1 , smaller than an internal diameter D2 of the tubular structure 7' and may, in some embodiments, be relatively loosely fitted in the tubular structure 7'. The insert 11 may comprise a crystalline material. The insert 1 1 may comprise metal, such as copper or a copper alloy.

In some embodiments, prior to inserting and expanding the insert 1 1 , the insert 11 is heat treated to alter one or more physical and/or chemical properties of the material. Said altered physical property may comprise at least one of: an increase in ductility, a reduction in hardness, and an increase in workability. In some embodiments, the heat treatment comprises annealing. Annealing may comprise heating the insert 11 to a temperature above a recrystallization temperature of the material of the insert 1 1 , maintaining the insert 1 1 at said temperature and then cooling the insert 1 1. The annealing process may comprise three stages of progression. Firstly, upon heating, recovery of the material of the insert 11 occurs and results in softening of the material through removal of defects, such as dislocations, and internal stresses. Recovery may occur below the recrystallization temperature of the material of the insert. Secondly, a recrystallization stage may occur, allowing crystallites, also referred to in the art as "grains" of the crystalline material to form a new structure or arrangement of grains. This allows new, strain-free grains to nucleate and replace original grains, which original grains may have been deformed due to said internal stresses. Finally, the new grains may grow until original grains have been at least partially consumed, or preferably substantially or entirely consumed. The new grain structure may contain relatively fewer defects, such as dislocations, than the original grain structure.

In some embodiments, the heat treatment comprises fully annealing the insert 11. This is sometimes referred to in the art as annealing the material of the insert 11 to a fully soft state. Fully annealing a material typically results in the material having a substantially uniform and stable microstructure, which microstructure closely resembles an equilibrium microstructure of the material's phase diagram. This allows the material to attain relatively low levels of hardness.

Said heat treating may comprise cooling the insert 11 after heating. Cooling may comprise slowly letting the insert cool to an ambient room temperature in substantially still air. Alternatively, said cooling may comprise quenching the insert 1 1 in water at an ambient temperature, such as room temperature. In some embodiments, the insert 1 1 is quenched for at least 30 minutes. The method may also comprise sizing the insert 1 1 prior to inserting and expanding the insert 11. Said sizing may be carried out before subjecting the insert 11 to one or more heat treatments as above described. In some embodiments, sizing the insert 11 comprises drawing the insert 11 over a former to shape the insert 11 into a desired starting geometry having initial dimensions. Alternatively or additionally, said sizing may comprise machining or milling the metallic insert to a desired initial starting geometry. In embodiments wherein the insert 11 comprises copper, an exemplary heat treatment may comprise heating the insert 11 to 550°C, maintaining the insert 11 at 550°C for 30 minutes and subsequently cooling the metallic insert to an ambient room temperature in substantially still air.

In some embodiments, a removable sizing gauge 12, such as a sizing sleeve, may be placed over the tubular structure 7'. The removable sizing gauge 12 functions to limit radial expansion of the tubular structure 7'. That is, the removable sizing gauge 12 may substantially prevent the tubular structure 7' from being expanded past a maximum desired external diameter. The removable sizing gauge 12 may comprise an internal cross sectional shape corresponding to a desired cross sectional shape of the tubular structure 7' after expansion. The internal cross sectional shape may be substantially circular. The removable sizing gauge 12 may comprise an internal diameter 10' substantially equal to said maximum external diameter, which maximum external diameter may be a desired expanded external diameter 9" of the tubular structure 7'. The removable sizing gauge 12 may have an adjustable internal diameter 10' so that the removable sizing gauge 12 can be used for a variety of desired expanded external diameters. Figure 6 shows an example of a suitable removable sizing gauge 12, comprising a first part 12a and a second part 12b connected by a hinge 20. Clamping regions 22a, 22b are provided for temporarily securing the removable sizing gauge 12 over the tubular structure 7'. A handle 24 is provided for gripping by a user.

The insert 11 may then be urged radially outwardly within the tubular structure 7'. As the insert 1 1 is urged radially outwardly, the insert 1 1 and the tubular structure 7' are brought into contact with one another. Further urging of the insert functions to expand both the insert 11 and the tubular structure 7'. In this way, the insert 1 1 and the tubular structure 7' are co-expanded together. The insert 1 1 may be urged radially outwardly until the insert 11 has expanded the tubular structure 7' into contact with an internal inside surface of the removable sizing gauge 12. As illustrated by Figure 4, the expanded insert 1 1 comprises an external diameter D1' substantially equal to an internal diameter D2' of the expanded tubular structure 7'. The expanded tubular structure 7' comprises an expanded external diameter 9" substantially equal to the internal diameter 10' of the removable sizing gauge 12. An expansion tool, such as the multi segment expansion head illustrated by Figure 1 may be used for said urging the insert 11 radially outwardly within the tubular structure 7'. The multi segment expander 100 is placed into the insert within the tubular structure 7' and actuated, for example by hydraulic means such as said hydraulic ram 1 to expand the insert radially outwards. The multi segment expander may be used for a number of cycles by rotating the multi segment expander 100 slightly within the insert 11 and again actuating the expander 100 within the insert 11. In this way, the insert 11 is urged radially outwardly in such that the insert 1 1 comprises a substantially circular cross section once expanded. In some embodiments, the multi segment expander 100 comprises eight or more segment jaws.

After the insert 1 1 has been radially urged outwardly so that the tubular structure 7' is of a desired external diameter 9", the expansion tool 100 may be withdrawn and the removable sizing gauge 12 may be removed from the tubular structure 7'. The expanded form of the tubular structure 7' is held by the work hardened insert 1 1 , in a form substantially the same as that shown in Figure 2. In the expanded form, the tubular structure 7' comprises a region having an external diameter that is compatible industry standard size couplers. The couplers may comprise mechanical couplers or electrofusion couplers, or a combination thereof.

The insert 11 is arranged such that the process of expanding the insert 11 causes work hardening of the insert 1 1. That is, the diametrical expansion of the insert 11 plastically deforms the material of the insert 1 1 , resulting in work hardening of the insert. This allows the insert 1 1 to stay in its expanded state and also strengthens the insert 11 , enabling the insert 11 to resist attempts by the tubular structure 7' to shrink back towards its original diameter 9', for example by elastic recovery, at least for a period of time long enough to enable an electrofusion coupling to be welded to the expanded region of the tubular structure 7'.

Figures 6A to 6F show a method for expanding an initial diameter 9' of an end region of a tubular structure 7', such as a polyethylene liner pipe, according to an embodiment of the invention. In this embodiment, a removable, adjustable sizing gauge 12, such as the sizing gauge shown in Figure 5, is adjusted to comprise an internal diameter 10' corresponding to a desired expanded diameter 9" of the tubular structure 7'. The clamping regions 22a, 22b, which may comprise bolts 23a, 23b, are bolted closed, preferably by hand. As shown in Figure 6A, the removable sizing gauge 12 is then placed around the end region of the tubular structure 7', so that an end face of the removable sizing gauge 12 is flush with an end face of the tubular structure 7'. The substantially tubular insert 1 1 , which in some embodiments, comprises copper in a fully soft state, is inserted over plates 3' of a multi segment expansion tool, such as illustrated in Figure 6B. The multi segment expansion tool and copper insert thereon are subsequently inserted within the tubular structure 7' such as illustrated in Figure 6C, so that an end face of the insert 1 1 is sub-flush to the end face of the tubular structure 7' by no more than 10 millimetres. The plates 3' of the multi segment expansion tool may then be driven radially outwardly, for example by means of a hydraulic ram, to urge the insert 1 1 radially outwardly within the tubular structure 7', thereby radially expanding the tubular structure 7'. Radial expansion of the insert 11 and tubular structure T is continued until the tubular structure 7' is tight to, or in contact with, the removable sizing gauge 12. As described above, the multi segment expansion tool may be used for a number of cycles by rotating the multi segment expansion tool slightly within the insert 11 and again driving the plates 3' radially outwardly within the insert 11. In this way, the insert 11 is urged radially outwardly in such that the insert 1 1 comprises a substantially circular cross section once expanded. Finally, with reference to Figures 6D and 6E, the multi segment expansion tool is removed. The shape of the tubular structure T is checked and the expanded diameter 9" is measured. The removable sizing gauge 12 is removed, leaving the tubular structure 7' with a diametrically expanded end supported by the work hardened insert, as shown in Figure 6F. Once the removable sizing gauge 12 has been removed, a joint may be made to the expanded tubular structure 7'. This is possible because, after removal of the sizing gauge 12, an external surface of the expanded end region of the tubular structure is accessible for later, on-site, joining to a fitting or to a polyolefin pipe. The sizing gauge controls the quality of this external surface which can be produced to a high tolerance in terms of being both parallel to the longitudinal axis of the pipe and smooth/free of defects. Control of the material thickness of the expanded end region of the pipe is less important and need not be to such a high tolerance. Plastic pipes are usually made with the outside diameter controlled to a tolerance range and a wall thickness controlled to a tolerance range. This means the internal diameter of the pipe bore can have a relatively wide range as it has a compound tolerance formed by these two values. This variation in bore size is a problem when it is desired to use a fixed size insert to expand a pipe to a desired diameter within a target diameter range (the target diameter range being required so as to be compatible for subsequent attachment to a standard fitting). Using prior art methods, it is virtually impossible to achieve the target diameter in practice and it becomes necessary to remove some plastic from the outside diameter (beyond that needed for preparation for welding) in order to for the expanded pipe end to be properly compatible with the fitting. In the method described herein, the expanding insert removes the impact of the compound tolerance effect. The adjustable sizing gauge determines the final external diameter of the pipe as well as its surface quality/roundness. The use of an insert capable of changing its nominal diameter automatically compensates for the tolerance in wall thickness of the pipe.

Unlike the new method described herein, the known practice in this field is to use inserts that are simple metallic or plastic cylinders machined remotely from the construction site. The pipe is expanded on site and the insert quickly popped into the pipe before it shrinks back elastically onto the insert. These known methods do not provide compensation for dimensional changes experienced by the pipe due to original production tolerances, or perhaps experienced as changes by virtue of the installation process.

To make a joint to a tubular structure 7' having an expanded end region, an electrofusion fitting 15 may be installed over an external surface of the expanded end region of the tubular structure 7'. An electrofusion element 16 may be energised by connecting a power supply to terminal pins 18a, 18b to fuse the expanded region of the tubular structure 7' to the electrofusion fitting 15. Alternatively, with particular reference to Figure 7, to join the tubular structure 7', which may be a pipe, to another tubular structure 14, such as another pipe, an electrofusion fitting 15 may be installed over an external surface of the expanded region tubular structure 7' and over an end of the other tubular structure 14. The electrofusion element 16 may be energised by connecting a power supply to terminal pins 18a, 18b to fuse the expanded region of the tubular structure T to the electrofusion fitting 15 and to fuse the end of the other tubular structure 14 to the electrofusion fitting. In this way, the two tubular structures 7', 14 may be coupled together via the electrofusion fitting 15. Once an electrofusion coupling has been welded to the expanded region of the tubular structure 7', the insert is deemed to have fulfilled its structural purpose which is to hold the tubular structure 7' at a diameter suitable for enabling the weld to be formed using standard electrofusion couplings. However, in some embodiments, a mechanical coupling may be used instead of an electrofusion coupling. Standard mechanical couplings generally require an insert to cooperate with a body of the mechanical coupling and with the tubular structure 7' trapped therebetween. In some embodiments, the insert 1 1 can fulfil this role long term without the requirement for a further component to be inserted. This may be achieved by said urging comprising plastically deforming the insert 1 1 to an extent that the insert 11 is work hardened enough to maintain its expanded diameter and resist attempts by the tubular structure 7' to shrink back towards its original diameter 9', for example by elastic recovery, for a relatively long period of time. The relatively long period of time may be at least a lifetime of the tubular structure 7'.