GB2272039A

GB2272039A - Lining of elongate hollow member

Info

Publication number: GB2272039A
Application number: GB9322229A
Authority: GB
Inventors: David Charles Harget; Alan John Dickinson; Trevor George Stafford
Original assignee: UPONOR ALDYL Ltd; British Gas PLC
Current assignee: UPONOR ALDYL Ltd; British Gas PLC
Priority date: 1992-10-31
Filing date: 1993-10-28
Publication date: 1994-05-04
Anticipated expiration: 2013-10-28
Also published as: GB9322229D0; GB2272039B; GB9222862D0; GB2272496A

Abstract

A method of forming a heat-recoverable liner for an elongate hollow member which comprises: bringing a tube formed from a polymeric material eg. cross-linked polyethylene to a first temperature at or above the crystalline melting point of the polymeric material, or at or above the softening point of the polymeric material in the case of an amorphous material, deforming the tube at said first temperature so as to reduce the external diameter thereof, cooling the tube to a second temperature below the crystalline melting point or softening point of the polymeric material, and further deforming the tube to further reduce the external diameter thereof. As shown, after being extruded through a die 2, the liner passes into a cooled reducing die through cooling means 5 and between rollers 6 to deform it into a V-shaped or star shape. Alternatively it may be axially twisted. <IMAGE>

Description

LINING OF ELONGATE HOLLOW MEMBERS This invention relates to a method of lining an elongate hollow member, and more particularly to a method of lining an elongate hollow member in which a deformed liner is inserted into the elongate hollow member and then expanded into contact therewith.

In many countries the relining of old pipes, in particular gas, water and sewer pipes has become a matter of great urgency. Many methods have been proposed for relining such pipes, but few have been found to be acceptable in practice and all of them are expensive and labour intensive. Of the many methods which have been proposed, there are a number which involve the introduction of a deformed liner into a pipe followed by expansion of the liner against the internal wall of the pipe.

Exemplary of the prior art is EPA 0254489 which describes a pipe relining method in which a polyolefin tube is extruded from an extruder die into a water bath to cool at least the surface of the tube and then drawn to produce a size-reduced polyolefin tube in a single operation between a pair of haul-off units.

In the pipe lining method of US 3856905, a plastic liner tube is produced by plastically deforming the tube at a temperature which lies between its glass temperature and its softening point. Other methods which involve the deformation of the liner and subsequent expansion utilising the property of elastic or plastic memory are described in: GB1580438, GB2188695, EPA065886, FR2503622, DE3519439, W088/04987, EPA0301697, US4863365, US4986951, US4998871, FP1201451, EPA0241297.

The disclosures of all the above patents are incorporated herein by reference.

In addition to the above mentioned disadvantages it has been found in practice that very few of the prior art methods of pipe relining are suitable for use with crosslinked polymeric materials, which for many applications would be the preferred materials for the liner due to their improved mechanical properties and chemical resistance. Thus, for example, many of the methods involving the use of elastic or plastic memory which have been proposed are impractical due the difficulty of obtaining the necessary temperatures inside the pipe to cause recovery of the cross-linked polymeric material.

We have now discovered a new method of lining an elongate hollow member which substantially obviates the above mentioned difficulties, by using a liner which is deformed in stages at decreasing temperatures.

In one aspect the invention provides a method of forming a heat recoverable liner for an elongate hollow member which comprises: heating a tube formed from a polymeric material to a first temperature at or above the crystalline melting point of the polymeric material, or at or above the softening point of the polymeric material in the case of an amorphous material, deforming the tube at said first temperature so as to reduce the external diameter thereof, cooling the tube to a second temperature below the crystalline melting point or softening point of the polymeric material, and further deforming the tube to further reduce the external diameter thereof.

In another aspect the invention provides a method of lining an elongate hollow member which comprises: inserting a heat-recoverable liner formed from a polymeric material and having an external diameter less than the internal diameter of the elongate hollow member into the elongate hollow member, the liner having been deformed at a first temperature at or above the crystalline melting point of the polymeric material, or at or above the softening point of the polymeric material in the case of an amorphous material, so as to reduce the external diameter thereof, and subsequently further deformed at a second temperature below the crystalline melting point or softening point of the polymeric material to further reduce the external diameter thereof, and causing recovery of the liner by heating such that it expands into contact with the elongate hollow member.

The invention also provides a heat recoverable liner produced by the method of the invention and an apparatus for the production of such a liner.

The invention is particular applicable to the lining and relining of underground pipes and conduits, where it would be extremely expensive or impractical to dig up the pipe or conduit and replace it with a new section.

The tubular liner is heat-recoverable, that is to say it possess the property of elastic or plastic memory.

A heat-recoverable article is an article the dimensional configuration of which may be made to change appreciably when subjected to heat treatment. Usually these article recover, on heating, towards an original shape from which they have previously been deformed but the term "heat-recoverable", as used herein, also includes an article which on heating adopts a new configuration even if it has not been previously deformed from that configuration but from a different original shape.

In their most common form, such articles comprise a tube made from a polymeric material exhibiting the property of elastic or plastic memory as described, for example, in US Patents Nos. 2027962, 3086242, and 3597372. As is made clear, for example, in US Patent 2027962, the original dimensionally heat-stable form may be a transient form in a continuous process in which, for example, an extruded tube is expanded, whilst hot, to a dimensionally heat-unstable form, but in other application a pre-formed dimensionally heat-stable article is deformed to a dimensionally heat-unstable form in a separate stage.

Although the invention is generally applicable to any heat-recoverable material, preferably the tubular liner is formed from a cross-linked polymeric material.

The polymeric material may be cross-linked at any stage in its production that will enhance the desired dimensional recoverability. One method of producing a heat-recoverable article comprises shaping the polymeric material into a desired heat-stable form, subsequently cross-linking the polymeric material, heating the article to a temperature above the crystalline melting point, or for amorphous materials the softening point, as the case may be, of the polymeric material, deforming the article and cooling the article whilst in the deformed state so that the deformed state of the article is retained. In use, since the deformed state of the article is heatunstable application of heat will cause the article to assume its original heat-stable shape.

In another method of producing a heat recoverable article, the article is heated, if necessary, to a temperature below the crystalline melting point, or softening point, of the polymer, but still above the temperature at which the article is able to be deformed, albeit, with the application of greater force. Such articles which have been "cold deformed" are recoverable, in general, at lower temperatures than those which have been deformed above their crystalline melting point or softening point.

In preferred embodiments the present invention makes use of both methods of producing a heat recoverable article in order to produce a unique tubular liner.

The tubular liner may be formed from any suitable polymeric material, but preferably the polymer is a thermoplastic, such as for example, a polyolefin or an olefin copolymer, and for example it may be a polymer or copolymer of ethylene, propylene, butylene, pentene, or a substituted olefin. Particularly good results have been obtained using polyethylene, and cross-linked polyethylene is the preferred polymeric material for use in the present invention. Suitable polyethylenes for use in the present invention include low, medium and high density polyethylenes of density from 0.90 to 0.98 and especially high density polyethylenes of density about 0.95 and above.

The deformation may be carried out on a pre-formed tubular liner, in which case the liner will need to be heated in the first deformation step to a temperature above the crystalline melting point or softening point of the polymeric material, or alternatively the first deformation can be carried out on an extruded tubular liner after it leaves the extruder die and whilst it is still above the crystalline melting point or softening point of the polymeric material.

Deformation of the tubular liner so as to reduce the external diameter thereof may be achieved in a variety of ways. Thus, for example, the liner may be stretched axially, thereby reducing its external diameter, or it may be pushed or pulled through a die in order to apply compressive forces thereto. Alternatively, the liner may be folded and collapsed inwards along its length. In a still further method the liner may be twisted axially as described in our co-pending application number No.

(Agents Reference P30402GB), the disclosure of which is incorporated herein by reference.

The deformation of the tubular liner at a first temperature and its subsequent further deformation at a second temperature may be of the same or different types as appropriate. Preferably the liner retains a crosssection of circular shape after the first deformation, but the further deformation can comprise deforming the liner such that its cross-section has a non-circular shape, although this is not essential. Thus, for example, the liner may be given a reduced diameter by stretching or pulling through a die at a first, higher temperature and then folded or twisted to further reduce its external diameter at a second, lower temperature.

Other combinations are also possible, and for example the tubular liner could be pulled through dies of decreasing diameter at the first and second temperatures.

Preferably the diameter reduction of the tubular liner in the first deformation step is at least 10% preferably at least 15%, and most preferably from 20 to 30%.

The first temperature is usually at least 100C above the crystalline melting point or softening point of the polymeric material, and preferably at least 300C above the crystalline melting point or softening point. The second temperature is usually at least 100C below the crystalline melting point or softening point of the polymeric material and preferably at least 300C below the crystalline melting point or softening point.

Heat recovery of the tubular liner when inserted into the elongate hollow member can be achieved by any one of a variety of methods. By way of example, after inserting the tubular liner into the elongate hollow member, by pushing or pulling it into position by the use of, for example, a pulling cable, or other suitable technique, elongate hollow member either the pipe may be heated externally, or preferably a heated fluid or a heating element may be passed along the elongate hollow member to cause heat-recover and expansion of the tubular liner.

Any suitable heating fluid or heating element may be used to apply heat to the tubular liner, for example hot air or steam may be passed down the elongate hollow member or the liner, or both, but preferable a heating device, and particularly an infra-red heating device is inserted into one end of the liner and pushed or pulled therethrough, recovering the liner as it moves along the elongate hollow member. Other techniques, such as electrical heating or the use of a heated pig, may be used in appropriate circumstances.

In another novel aspect of the invention, the liner is caused to recover and to expand into contact with the elongate hollow member by the use of a fan-assisted infra-red heater. In this technique the fan-assisted infra-red heater is passed along the interior of the tubular liner fully recovering the liner as it proceeds along the length thereof. A fan, associated with the infra-red heater, blows hot air from the heater along the liner in advance of the infra-red heater. The hot air is sufficient to cause recovery of the diameter reduction induced in the tubular liner by the further deformation below the crystalline melting point or softening point of the polymeric material.By preheating and recovering the tubular liner in this way, it is found that the infra-red heater can proceed more rapidly down the tubular liner, completing recovery of the liner within the hollow elongate member by heating the liner to a temperature at or above its crystalline melting point or softening point, as the case may be. Preferably the hot air from the fan raises the temperature of the liner to within 40 to 500C of its crystalline melting point or softening point, and the infra-red heater heats the liner to at least 10 to 300C above its crystalline melting point or softening point.

A method and apparatus according to the invention will now be described and illustrated with reference to the accompanying drawing in which: Figure 1 shows in diagrammatic side elevation an extrusion line and ancillary apparatus for the production of a first tubular liner.

Figure 2 shows a second liner being pulled through an underground pipe; and Figure 3 shows the liner of Figure 2 installed within a pipe and being expanded into contact therewith.

Referring to Figure 1, an extruder, designated generally at 1, is provided with an annular die (2). The extruder die (2) is separated from a cooled reducing die (3) by an insulating layer (4). Cooling means (5), which may be simply an air space, or a water bath, but is preferably a slightly tapering water cooled annular metal tube, is provided adjacent to the reducing die outlet.

Rollers (6) are provided to further deform the extrudate.

In operation, polyethylene granules are fed to the extruder (1) together with an appropriate quantity of a chemical cross-linking agent such as, for example, cumyl peroxide. Cross-linking of the polyethylene takes place within the extruder and the molten cross-linked polyethylene is conveyed by the extruder screw to the die (2) at a temperature of around 200 to 220 OC. The extrudate exiting the die then passes into a reducing die (3) in which its diameter is reduced.The reducing die is water cooled, in order to lower the temperature of the cross-linked tubular extrudate within the die to around 150 OC. In addition to further cooling the tubular extrudate as it leaves the reducing die, the cooling means (5) also provides a back pressure due to friction of the extrudate on the walls of the metal tube, so that the effect of the reducing die is to decrease the diameter and increase the wall thickness of the tubular extrudate, and minimise axial extension. The tubular extrudate leaves the cooling means at a temperature of from 50 to 70 CC and is passed through rollers (6) which further reduce the external diameter, for example, by deforming the cross-section of the extrudate into a Ushape, or a star-shape. In an alternative method the tubular extrudate is gripped by a twisting means which reduces the cross-section of the extrudate by axial twisting, as described and claimed in our co-pending application No. (Agents reference P30402GB). In further stages (not shown) the extrudate is cooled to room temperature and coiled onto a drum.

Referring now to Figure 2, and using as an example a tubular liner that has been axially twisted, the twisted liner (10) is fed from a reel (11) into a hole (12) which has been excavated at one end of the length of pipe (13) which is to be relined. The twisted liner is pulled through the pipe (13) by means of a pulling wire (14) which extends through a hole (15) dug at the other end of the section of pipe (13) to be relined.

Referring now to Figure 3, the liner is expanded into contact with the pipe using an infra-red heater (20) which is pushed along the pipe by a push-rod (21) activated by rollers (22). A fan (23) situated behind the infra-red heater blows air over the heater and along the liner in front of the heater. This air, warmed by the heater, heats the liner in front of the heater sufficiently to cause recovery by untwisting (usually above the deformation temperatures, for example around 800C). After this partial recovery, the heater is able to pass along the liner to complete the recovery process.

By the use of an alternating direction of twist in sections of the liner, it is possible to avoid undue friction as the liner untwists within the pipe to be relined. By combining higher temperature size reduction through a reducing die with twisting at a lower temperature, it is possible to arrange that any expansion of the liner axially due to the twisting can counterbalance any contraction of the liner due to axial stretching, so that there is substantially no change in length during recovery.

The invention provides a simple and convenient means of relining pipes and conduits with materials such as cross-linked polyethylene having improved abrasion and chemical resistance.

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

All the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps or 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.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

Claims

1 A method of forming a heat-recoverable liner for an elongate hollow member which comprises: bringing a tube formed from a polymeric material to a first temperature at or above the crystalline melting point of the polymeric material, or at or above its softening point of the polymeric material in the case of an amorphous material, deforming the tube at said first temperature so as to reduce the external diameter thereof, cooling the tube to a second temperature below the crystalline melting point or softening point of the polymeric material, and further deforming the tube to further reduce the external diameter thereof.

2 A method according to claim 1, in which the polymeric material is cross-linked.

3 A method according to claim 1 or 2, in which the polymeric material is polyethylene.

4 A method according to any of the preceding claims, in which the first temperature is at least 100C above the crystalline melting point, or softening point, of the polymeric material.

5 A method according to any of the preceding claims, in which the tube is deformed at said first temperature by passing it through a reducing die.

6 A method according to any of the preceding claims, in which the second temperature is at least 100C below the crystalline melting point or softening point of the polymeric material.

7 A method according to any of the preceding claims, in which the tube is further deformed to further reduce the external diameter thereof by deforming its crosssection into a non-circular shape.

8 A method according to claim 7, in which the crosssection of the tube is deformed into a U-shape, a starshape, and/or the tube is axially twisted.

9 A method according to any of the preceding claims substantially as hereinbefore described.

10 A method of lining an elongate hollow member which comprises: inserting a heat-recoverable liner formed from a polymeric material and having an external diameter less than the internal diameter of the elongate hollow member into the elongate hollow member, the liner having been deformed at a first temperature at or above the crystalline melting point of the polymeric material, or at or above the softening point of the polymeric material in the case of an amorphous material, so as to reduce the external diameter thereof, and subsequently further deformed at a second temperature below the crystalline melting point or softening point of the polymeric material to further reduce the external diameter thereof, and causing recovery of the liner by heating such that it expands into contact with the elongate hollow member.

11 A method according to claim 10, in which the liner is caused to recover and to expand into contact with the elongate hollow member by the use of an infra-red heater.

12 A method according to claim 11, in which a fan, associated with the infra-red heater, blows hot air along the liner in advance of the infra-red heater.

13 A method according to any of claims 10 to 12 in which the liner is heated by a heater which is inserted into the liner, and air heated by the heater is blown along the liner in advance of the heater sufficient to cause recovery of the diameter reduction induced in the tubular liner by the further deformation below the crystalline melting point or softening point of the polymeric material, thereby expanding the liner sufficiently to ease the passage of the heater along the liner to complete the expansion.

14 A method according to any of claim 10 to 13, in which there is used a liner formed by a method according to any one of claims 1 to 9.

15 A method according to any of claims 10 to 14 substantially as hereinbefore described.

16 A tubular liner produced by process according to any of claims 1 to 9.

17 A lined elongated member produced by a process according to any of claims 10 to 15.

18 An apparatus for the production of a heat recoverable polymeric tubular liner for an elongate member, which comprises: an extruder having a die outlet, a reducing die for reducing the diameter of the extrudate from the die outlet, cooling means for cooling the extrudate as it leaves the die outlet to a temperature below the crystalline melting point or softening point of the polymeric material of the extrudate, and deforming means for deforming the cooled extrudate to further reduce the external diameter thereof.

19 An apparatus substantially as hereinbefore described with reference to and as illustrated in Figure 1 of the accompanying drawings.

20 A heat recoverable liner suitable for lining an elongate hollow member, which comprises a tube formed from a polymeric material, the tube having been deformed at a first temperature at or above the crystalline melting point of the polymeric material, or at or above the softening point of the polymeric material in the case of an amorphous material, so as to reduce the external diameter thereof, and subsequently further deformed at a second temperature below the crystalline melting point or softening point of the polymeric material to further reduce the external diameter thereof.

21 A liner according to Claim 20, in which the polymeric material is cross-linked.

22 A liner according to Claim 20 or 21 substantially as hereinbefore described.