WO1994009970A1

WO1994009970A1 - Pipe couplings

Info

Publication number: WO1994009970A1
Application number: PCT/GB1993/002243
Authority: WO
Inventors: David John Hill
Original assignee: Victaulic Plc
Priority date: 1992-11-02
Filing date: 1993-11-01
Publication date: 1994-05-11
Also published as: GB2271958A; GB9222952D0; AU5374794A

Abstract

The invention provides a method of connecting a first polyolefin pipe element (1) to a second pipe element (3) by electrofusion, the first polyolefin pipe element (1) prior to electrofusion jointing having a substantially intact oxidised surface layer (9), which method comprises providing a surface of one of the pipe elements (3) which surface is to be fused to a surface (9) of the other pipe element (1), with a surface layer of a polymer composition containing at least 0.1 % of an adhesive polymer derived from epoxy or unsaturated acyl compounds. The invention also provides an electrofusion coupling device having a surface formed of a polymer composition containing at least 0.1 % by weight of an adhesive polymer.

Description

PIPE COUPLINGS

The invention relates to improved methods of electrofusion coupling of polyolefin pipes, and to electrofusion coupling devices for use in the said methods.

The connecting together of plastics pipes using an electrofusion coupling device is well known. A typical electrofusion device consists of a sleeve or socket having an electrically conducting heating coil placed in the bore, or the vicinity of the bore. In use, the end of a pipe is placed into the sleeve or socket and current is passed through the coil leading to melting of the abutting plastics surfaces of the sleeve or socket and the pipe and then subsequent fusion together to form a joint. Electrofusion devices can be used to couple polyolefin pipes together end to end, or can be used to enable the coupling to a pipe of a branch connector. In the latter case a saddle type fitting having a pad covering part or all of the main pipe circumference is employed.

A well known drawback of the electrofusion method of coupling together pipe elements is the need always to scrape the pipe surface in preparation for welding. This operation is critical to the weld being accomplished successfully and all manner of scraping tools have been devised to remove an even and consistent layer of material from the surface of the pipe. In scraping the pipe, not only is dirt and contamination removed, but also oxidised surface polymer is removed, ideally to give a pristine surface for welding. The precise nature of the surface layer of the pipe is the subject of current speculation, but it is generally accepted that oxidised polymer is the main constituent of the surface layer. In addition, there will also be traces of wax, low molecular weight species, reactor residues, additives etc. The nature of the surface layer and surface contamination is such that simple cleaning, even with solvents, is not always sufficient to ensure a good weld.

Experience has shown that a significant proportion of electrofusion joints are imperfect and prone to failure through incorrect jointing procedures. Failure to observe high standards of cleanliness at all stages, skin contact of prepared pipe ends of fittings, and water penetration prior to fusion are all considered prime reasons for imperfect joints. The reasons why these problems arise are easy to understand, since the installation of polyolefin pipe systems in the ground is not ideal for exclusion of dirt and dust, whether as mud in wet conditions or by static attraction in dry conditions. Furthermore, it is difficult to achieve the total exclusion of water from a joint in a water pipe that may recently have been in service, and thereby bears traces of residual water clinging to the bore of the pipe which occasionally trickle to the joint vicinity prior to fusion. Thus it can be seen that under field conditions, the scope for imperfections and failures of electrofusion joints is considerable.

It is an object of the present invention to overcome or at least alleviate the aforesaid problems and provide a method of coupling pipes by electrofusion which reduces the need for pipe scraping prior to fusion and which improves tolerance to errors in the jointing procedures.

In a first aspect, the invention provides a method of connecting a first polyolefin pipe element to a second pipe element by electrofusion, the first polyolefin pipe element prior to electrofusion jointing having a substantially intact oxidised surface layer, which method comprises providing a surface of one of the pipe elements, which surface is to be fused to a surface of the other pipe element, with a surface layer of a polymer composition containing at least 0.1% of an adhesive polymer derived from epoxy or unsaturated acyl compounds.

In another aspect of the invention, there is provided the use of an electrofusion coupling device having a fusible surface layer formed of a polymer composition containing at least 0.1% by weight of an adhesive polymer derived from epoxy or unsaturated acyl compounds, for connecting together polyolefin pipe elements having a substantially intact oxidised surface layer.

In a further aspect, the invention provides an electrofusion coupling device for connecting together pipe elements formed of polyolefinic materials; the electrofusion coupling device comprising a sleeve having a fusible surface of plastics material to which a pipe is to be fused; a heating element being located at or beneath said surface, characterised in that the surface is formed of a polymer composition containing at least 0.1% by weight of an adhesive polymer derived from epoxy or unsaturated acyl compounds.

In each of the aforesaid aspects of the invention up to 100% by weight of the surface polymer composition may be constituted by an adhesive polymer derived from epoxide or unsaturated acyl compounds. More particularly up to 60% of the surface polymer composition may be constituted by the adhesive polymer, for example, up to 50% of the surface polymer composition, eg approximately 25%. In one embodiment 1-10% (e.g. 2.5-7.5) of the surface polymer composition is an adhesive polymer derived from epoxide or unsaturated acyl compounds.

The surface polymer compositions containing the adhesive polymer can be present in a thin layer, e.g. a monolayer or a layer up to several millimetres in thickness, at the surface, or can be present as an integral part of a more substantial body of polymer. For example, an electrofusion coupling device can be formed integrally from a polymer composition containing at least 0.1% by weight of the adhesive polymers defined hereinabove. It is preferred that when the electrofusion coupling device is formed integrally from the adhesive polymer, the concentration of the adhesive polymer does not exceed 60% and more preferably does not exceed 50%. It is preferred that with surface polymer compositions in excess of 50%, the adhesive polymer is contained within a discrete surface layer.

The electrofusion coupling device can alternatively be formed as a multilayer extruded fitting in which a radially inner layer of polymer contains at least 0.1% adhesive polymer as hereinbefore defined. The surface layer containing the adhesive polymer can be formed integrally with the electrofusion coupling device or can be applied to the relevant surface of the coupling device after formation thereof. For example, a solid or liquid film containing the said adhesive polymer can be applied to the relevant surface following moulding of the electrofusion coupling device.

The term unsaturated acyl compound as used herein refers to an unsaturated carboxylic acid or a derivative thereof such as an ester, amide, imide,anhydride, etc.

Examples of adhesive polymers derived from epoxide and unsaturated acyl compounds are co-polymers containing repeating units derived from unsaturated olefins such as ethylene, and repeating units derived from unsaturated carboxylic acid compounds and derivatives thereof. Examples of such compounds are unsaturated carboxylic acids such as acrylic acid, methacrylic acid, alpha-ethyl acrylic acid and esters thereof such as glycidyl acrylate, and glycidyl methacrylate. The unsaturated acyl compound can also comprise unsaturated dicarboxylic acids and their derivatives such as maleic acid, furaaric acid, tetrahydrophthalic acid, methyl tetrahydrophthalic acid, endo-cis-bicyclo hepto-5-en-2,3-dicarboxylic acid and methyl-endo-cis-bicyclo-hepto-5-en-2,3-dicarboxylic acid and derivatives thereof such as the acyl halides, amides, imides, acid anhydrides and esters. Examples of such derivatives include maleic anhydride, maleic acid monomethyl ester and maleic acid dimethyl ester.

The repeating units derived from epoxy compounds can be, for example, unsaturated glycidyl esters having the general formula "R.CO.O.CH₂.CHOCH₂" where R is a hydrocarbon group having an ethylenically unsaturated bond capable of polymerisation. Further examples of the epoxy compounds include glycidyl ethers having the general formula R.X.CH₂.CHOCH₂ where X represents a divalent group such as methyleneoxy (-CH₂.0-) or phenyleneoxy (-C_βH_s.0-) and epoxy alkenes having the general formula R.R'.COCH₂ where R¹ is hydrogen or lower alkyl, e.g. methyl. Such epoxy compounds include those derived from glycidyl acrylate, glycidyl methacrylate, mono-and diglycidyl esters of itaconic acid, mono-, di- and triglycidyl esters of butene tricarboxylic acids, mono- and diglycidyl esters of citraconic acid, mono- and diglycidyl esters of endo- cis-bicyclo[2.2.l]-hepto-5-en-2,3-dicarboxylic acid, raono- and diglycidyl esters of endo-cis-bicyclo[2.2.l]-hepto-5- en-2-methyl-2,3-dicarboxylic acid, mono- and diglycidyl esters of allylsuccinic acid, glycidyl esters of p-styrene carboxylic acids, allyl glycidyl ether, 2-methyallyl glycidyl ether, styrene-p-glycidyl ether, 3,4-epoxy-l- butane, 3,4-epoxy-3-methyl-l-butane, 3,4,-epoxy-l-pentene, 3,4-epoxy-3-methyl-l-pentene, 5,6-epoxy-l-hexene and vinylcyclohexene monoxide.

The adhesive polymers can be prepared by random co- polymerisation or block-polymerisation of olefin monomers and unsaturated acyl monomers or epoxy monomers, or by graft co-polymerisation of polyolefins with unsaturated acyl or epoxy compounds. In the context of the present invention graft-polyolefins are preferred, and a most preferred polymer composition is a graft-copolymer formed from polyethylene and maleic anhydride.

Methods of forming copolymers by block co- polymerisation or graft polymerisation are well known and details need not be given here. It is sufficient to mention that such methods include, for example, graft co- polymerisation of a mixture consisting of a molten polyolefin and the graft monomer, and methods in which co- polymerisation is carried out on mixtures containing the polyolefin dissolved in a solvent along with the graft co- monomer. As is well known, graft co-polymerisation can be conducted in the presence of radical initiators such as organic peroxides and azo compounds. Radiation can also be used to generate such radicals.

The adhesive polymer typically can contain about 1 to about 15% repeating units derived from epoxy or unsaturated acyl compounds. Consequently, the aforesaid surface polymer compositions containing the adhesive polymer can contain, for example, 0.01 to about 15% (eg 0.01 to about 10%) repeating units derived from epoxy or unsaturated acyl compounds, e.g. more particularly 0.05-5%, such as 0.1-1%.

An embodiment of the invention will now be illustrated, but not limited, by reference to the accompanying drawings in which:

Figure 1 is a partial sectional view through an electrofusion coupler according to one embodiment of the invention; and

Figure 2 is a partial side sectional view through another embodiment of the invention.

Referring to Figure 1 it can be seen that there is illustrated a technique for coupling two polyethylene pipes 1 and 2 by means of an annular coupling sleeve 3. Annular coupling sleeve 3 is formed of a polymer composition comprising polyethylene and 2-5-7.5% (preferably about 5%) by weight of an adhesive polymer derived from polyethylene and unsaturated acyl or epoxy compounds. The polymer composition can be formed by random or block co-polymerisation or by graft co- polymerisation as described above. Pipes 1 and 2 each have a thin surface layer of oxidised polyolefin, denoted by reference numerals 9 and 10 respectively. A heating wire coil 4 is embedded in the body of the sleeve 3 just beneath the innermost surface and is provided with terminal wires 5 and 6 which can be connected to a suitable electricity supply.

In operation, the ends of pipes 1 and 2 are cleaned with a degreasing composition in order to remove grease and other contaminants from the surface of the pipe. Normally prior to electrofusion, the ends of the pipes would also be scraped to remove the layer of oxidised polyolefin 9, 10. However, by virtue of the use of a polymer composition containing 2-5% adhesive polymer comprising polyethylene and unsaturated acyl repeating units or epoxy repeating units, it has been found that a strong joint can be formed without the need first to scrape the pipe surface.

The cleaned pipe ends are inserted into the sleeve 3 so as to engage the central register 7, and then electrical current is passed through the wire 4 embedded in the sleeve 3 such that the sleeve melts at its inner surface whilst the pipes 1 and 2 are heated on their external radial surfaces. A fused joint is thus achieved in standard manner.

-A second embodiment of the invention is illustrated in Figure 2 wherein it is shown that electrofusion coupling sleeve can be formed as a co-extrusion with an outer layer 8 of polyolefin and an inner layer 11 of a polyolefin wherein up to 5% of the repeating units are derived from unsaturated acyl or epoxy compounds. The welding sleeve is used in the same manner as described in relation to the embodiment of Figure 1.

Evample 1

A commercial medium density polyethylene gas pipe grade was blended with a commercially available polyethylene/maleic anhydride graft copolymer in the following ratio using a single screw compounder:-

MDPE 95 : PE/Copolymer graft 5

The materials having the following nominal characteristics:-

MDPE PE graft

Density 0.94 0.94

Melt flow (M12) 0.2 0.45

The blended characteristics being similar to the MDPE grade.

The blended material was formed by injection moulding into 125ram electrofusion type coupler fittings, into which was introduced a conductive wire. These fittings were of identical construction and appearance to conventional 125mm MDPE electrofusion gas fittings.

Fittings from the blended polymer and standard fittings from conventional MDPE gas grade were then assembled with scraped and unscraped short pipe lengths of conventional MDPE yellow gas grade and subjected to fusion procedures in the normal way. In each case, one end of the fitting was fused to a scraped short pipe length, and the other end to an unscraped short pipe length, fusion of both ends being carried out simultaneously. For unscraped, short pipe lengths, pipe ends were carefully cleaned using propan-2-ol and then carefully inserted into the fitting up to the pipe stop. For scraped short pipe lengths, pipe ends were carefully scraped so that between 0.05 and 0.2mm of the pipe surface was removed, extending beyond the area to be covered by the fitting, and then carefully inserted into the fitting up to the pipe stop.

Testing of cooled pipe and fitting assemblies was carried out by means of a conventional peel test upon samples taken from the melt zone area. In all cases with the fittings from blended polymer, good joints with similar strength and failure mechanism were observed to scraped and unscraped pipe, it not being possible to distinguish between them, separation of the weld line did not proceed beyond the second wire. The fittings from conventional MDPE gas grade were found to always give good joints with scraped pipe but less reliably so with unscraped pipe, joint failure proceeding along the weld line and well beyond the second wire on a number of samples .

It will readily be apparent that numerous modifications and alterations can be made to the electrofusion coupling devices of the present invention and their method of use without departing from the underlying principles of the invention, and all such modifications and amendments are intended to be embraced by this application.

Claims

1. A method of connecting a first polyolefin pipe element to a second pipe element by electrofusion, the first polyolefin pipe element prior to electrofusion jointing have a substantially intact oxidised surface layer, which method comprises providing a surface of one of the pipe elements, which surface is to be fused to a surface of the other pipe element, with a surface layer of a polymer composition containing at least 0.1% of an adhesive polymer derived from epoxy or unsaturated acyl compounds.

2. A method according to Claim 1 wherein up to 100% by weight of the surface polymer composition is an adhesive polymer derived from epoxide or unsaturated acyl compounds.

3. A method according to Claim 2 wherein up to 60% by weight of the surface polymer composition is an adhesive polymer.

4. A method according to claim 3 wherein up to 50% by weight of the surface polymer composition is an adhesive polymer.

5. A method according to claim 4 wherein up to 40% by weight of the surface polymer composition is an adhesive polymer.

6. A method according to claim 5 wherein up to 30% by weight of the surface polymer composition is an adhesive polymer.

7. A method according to claim 6 wherein up to 25%, for example up to 20%,of the surface polymer composition is an adhesive polymer.

8. A method according to claim 7 wherein 1-10% by weight of the surface polymer composition is an adhesive polymer derived from epoxide or unsaturated acyl compounds.

9. A method according to any one of the preceding claims wherein the surface polymer composition containing the adhesive polymer is present in a thin layer, e.g. a monolayer or a layer up to several millimetres in thickness, at the surface.

10. A method according to any one of claims 1 to 8 wherein one of the polyolefin pipe elements is an electrofusion coupling device which is formed integrally from a polymer composition containing at least 0.1% by weight of the adhesive polymer.

11. A method according to any one of claims 1 to 8 wherein one of the polyolefin pipe elements is an electrofusion coupling device which is formed as a multi- layer extruded fitting in which a radially inner layer of polymer contains at least 0.1% adhesive polymer.

12. A method according to any one of the preceding Claims wherein the adhesive polymers are co-polymers containing repeating units derived from unsaturated olefins such as ethylene, and repeating units derived from unsaturated carboxylic acid compounds and derivatives thereof.

13. A method according to Claim 12 wherein the adhesive polymer is a polymer which can be prepared by random co- polymerisation or block-polymerisation of olefin monomers and unsaturated acyl monomers or epoxy monomers, or by graft co-polymerisation of polyolefins with unsaturated acyl or epoxy compounds.

14. A method according to Claim 13 wherein the adhesive polymer is a graft co-polymer formed from polyethylene and maleic anhydride.

15. A method of connecting a first polyolefin pipe element to a second polyolefin pipe element by electrofusion, the method being substantially as described herein with reference to the accompanying drawings.

16. The use of an electrofusion coupling device having a fusible surface layer formed of a polymer composition containing at least 0.1% by weight of an adhesive polymer derived from epoxy or unsaturated acyl compounds, for connecting together polyolefin pipe elements having a substantially intact oxidised surface layer.

17. The use according to Claim 16 wherein the surface polymer composition contains an amount of adhesive polymer as defined in any one of claims 2 to 8.

18. The use according to Claim 16 or Claim 17 wherein the surface polymer composition containing the adhesive polymer is present in a thin layer, e.g. a monolayer or a layer up to several millimetres in thickness at the surface.

19. The use according to Claim 16 or Claim 17 wherein the electrofusion coupling device is formed integrally from a polymer composition containing at least 0.1% by weight of the adhesive polymer.

20. The use according to Claim 16 or Claim 17 wherein the electrofusion coupling device which is as a multi-layer extruded fitting in which a radially inner layer of polymer contains at least 0.1% adhesive polymer.

21. The use according to any one of Claims 16 to 20 wherein the adhesive polymer is derived from epoxide and unsaturated acyl compound which are co-polymers containing repeating units derived from unsaturated olefins such as ethylene, and repeating units derived from unsaturated carboxylic acid compounds and derivatives thereof.

22. The use according to Claim 21 wherein the adhesive polymer is one that can be prepared by random co- polymerisation or block-polymerisation of olefin monomers and unsaturated acyl monomers or epoxy monomers, or by graft co-polymerisation of polyolefins with unsaturated acyl or epoxy compounds.

23. The use according to Claim 22 wherein the adhesive polymer is a graft co-polymer formed from polyethylene and maleic anhydride.

24. The use of an electrofusion coupling device substantially as described herein with reference to the accompanying drawings.

25. An electrofusion coupling device for connecting together pipe elements formed of polyolefinic materials; the electrofusion coupling device comprising a sleeve having a fusible surface of plastics material to which a pipe is to be fused; a heating element being located at or beneath said surface, characterised in that the surface is formed of a polymer composition containing at least 0.1% by weight of an adhesive polymer derived from epoxy or unsaturated acyl compounds.

26. An electrofusion coupling device according to Claim 19 wherein the surface polymer composition is as defined in any one of claims 2 to 8.

27. An electrofusion coupling device according to Claim 25 or Claim 26 wherein the surface polymer composition containing the adhesive polymer is present in a thin layer, e.g. a monolayer or a layer up to several millimetres in thickness, at the surface.

28. An electrofusion coupling device according to Claim 25 or Claim 26 which is formed integrally from a polymer composition containing at least 0.1% by weight of the adhesive polymer.

29. An electrofusion coupling device according to Claim 25 or Claim 26 which is formed as a multi-layer extruded fitting in which a radially inner layer of polymer contains at least 0.1% adhesive polymer as hereinbefore defined.

30. An electrofusion coupling device according to any one of Claims 25 to 29 wherein the adhesive polymer is derived from epoxide and an unsaturated acyl compound and is a co- polymer containing repeating units derived from an unsaturated olefin such as ethylene, and repeating units derived from an unsaturated carboxylic acid compound or a derivative thereof.

31. An electrofusion coupling device according to Claim

30 wherein the adhesive polymer is one which can be prepared by random co-polymerisation or block- polymerisation of olefin monomers and unsaturated acyl monomers or epoxy monomers, or by graft co-polymerisation of polyolefins with unsaturated acyl or epoxy compounds.

32. An electrofusion coupling device according to Claim

31 wherein the polymer composition is a graft co-polymer formed from polyethylene and maleic anhydride.

33. An electrofusion coupling device substantially as described herein with reference to the accompanying drawings.