GB2349928A

GB2349928A - A coupling device with a sleeve having an impermeable inner barrier layer

Info

Publication number: GB2349928A
Application number: GB9906182A
Authority: GB
Inventors: Wayne Clifton Augustus Wright; Stephen Colin Ruffle
Original assignee: Petrotechnik Ltd
Current assignee: Petrotechnik Ltd
Priority date: 1999-03-17
Filing date: 1999-03-17
Publication date: 2000-11-15
Anticipated expiration: 2019-03-17
Also published as: GB2349928B; GB9906182D0

Abstract

A coupling device for forming a joint in a pipeline system, comprises a sleeve 22 with at least one socket or hollow spigot for receiving or extending within an end of one of the pipes. The sleeve incorporates an inner barrier layer 21, being substantially impermeable to the fluid being conveyed in the pipeline system. A method of making the coupling device may include the steps of injection moulding an internal sleeve from a polymeric plastics material, wrapping electrical resistance heating wires around the internal sleeve, and inserting pins into the sleeve which are connected to the wires. An external part of the fitting is injection moulded around the inner component, and an inner barrier layer is applied using either fluourination, co-extrusion, or chemical vapour deposition. The device may be used for pipework in petroleum installations such as on garage forecourts.

Description

2349928 IMPROVED PIPE COUPLINGS

Field of the Invention

The present invention relates to pipe couplings with improved impermeability to fluids. It is particularly applicable, but in no way limited, to couplings for pipework systems designed to carry hydrocarbons.

Backqround to the Invention Pipes made of plastics material are used extensively in industry and in construction. Many applications now use pipes made from plastics materials such as polyethylene and polypropylene rather than metal. One such application is the pipe work used in petroleum installations such as garage forecourts.

In the design of petroleum forecourt installations for example, it is regarded as increasingly important to contain and detect any leaks of petrol or diesel fuel from sub-terrainian pipes which connect one or more storage tanks to dispensing pumps in the installation, To that end, many current designs of forecourt installation utilise secondary containment. This involves containing each supply pipeline in a respective secondary containment pipeline which is optionally sealed at its ends to the fuel supply pipelines. The secondary containment pipeline prevents leaks from the fuel supply pipeline from being discharged into the environment, and also can convey leaked petrol to a remote sensing device.

Whilst every effort is made to avoid having joints in an underground supply pipeline, otheir than inside manhole chambers, these joints sometimes cannot be avoided. Such joints are con\7bntionally made using special fittings and the connections are made using a chemical-based jointing compound or by electrofusion welding. The latter technique is preferred in many applications.

1 Traditionally the pipes used as the supply pipe is forecourt installations contain an inner, barrier layer which is substantially impervious to hydrocarbon fuels.

Examples of such barriers are Nylon 612, or other polyamides, polyvinylidene chloride or fluoride, or polyethylene terphthalate.

These barrier layers, although relatively thin, are significantly less permeable than the material used to construct the body of the pipe, which is typically polyethylene or polypropylene.

There are a wide variety of known couplings designed to form an end to end connection between two pieces of pipe. Typical examples are electrofusion weld fittings supplied by PetroTechnik Limited. However, these fittings suffer from the disadvantage that the inner surface of the fitting does not include any barrier-type layer. Thus the pipework run has increased permeability in the region of any joint.

It is the object of the present invention to overcome or mitigate the problem outlined above.

Summary of the Invention

According to a first aspect of the present invention there is provided a coupling device for forming a joint in a pipeline system comprising a plurality of pipes in end to end alignment, said coupling device comprising a sleeve with at least one socket or hollow spigot for receiving or extending within an end of one of the pipes characterised in that the sleeve incorporates an inner barrier layer.

The present invention covers both the coupling devices themselves, methods of manufacturing the coupling devices and a method of joining pipes using such couplings.

2 Brief DescriPtion of the Drawinqs

The invention will now be described, by way of example only, with reference to the accompanying drawings wherein:- Figures 1 and 2 illustrate side elevations including hidden detail and end views of part-formed couplings according to the present invention.

Description of the Preferred Embodiments

The present embodiments represent the best ways know to the applicant of putting the invention into practice, but they are not the only ways in which this could be achieved. They are illustrated, and they will now be described, by way of example only.

These coupling devices traditionally comprise two parts, an inner portion which incorporates electrical resistance heating windings around which an outer portion is formed. Traditionally this is achieved by machine injection moulding an internal sleeve which is the portion visible on the internal bore of a traditional fitting. Electrofusion wires are then wrapped around this fitting and the metal pins for contact to a welder, are inserted in the top face of the sleeve. This inner, internal sleeve is then taken to the next process where the sleeve is inserted into an injection moulding machine and the external part of the fitting moulded around it to form a complete fitting of the type which is currently available.

Figure 1 illustrates a typical inner portion 11 of a fitting as described above. In this example the inner portion comprises a polyethylene sleeve 12 with a substantially smooth inner surface 15 with the exception of pipe stops 16 which project into the bore of the sleeve. These stops prevent the pipes to be joined passing too far into the fitting and effectively centralise the fitting over the ends of two adjacent pipes.

3 The outer surface of sleeve 12 has two sets of spirally wound grooves 17, 18 into which electrical resistance heating wire 13, 14 is wound. Electrofusion wires A are effectively wrapped around this sleeve and metal pins that connect the surface of the fitting for contact to a welder are inserted onto the top face of the sleeve 5 shown as B in Figure 1 - The internal sleeve is then taken to the next process where the sleeve is inserted into an injection moulding machine and the rest of the body of the electrofusion fitting is moulded around the sleeve to form a fitting in its final form.

A first aspect of the present invention relates to methods of forming an additional impermeable barrier into the region of the inner sleeve portion between the two sets of windings. This region is inevitably in constant contact with the fluid within the pipe and yet is significantly more permeable than the pipe itself.

In a first method the inner sleeve portion is subjected to a fluorination process, preferably in a fluorination chamber, prior to carrying out the second stage of the moulding process. Fluorination is an excellent way of improving the impermeability characteristics of a polymer, Fluorinating a surface also decreases the surface energy of a plastic substrate, resulting in excellent non-stick properties.

However, it is advisable not to fluorinate the entire inner sleeve because this would cause welding problems when welding a pipe to the internal surface of the fitting. There are several ways in which partial fluorination of the fitting can be carried out.

1. Firstly, it is advisable only to expose the surface area D to the fluorination process by covering up all other areas.

2. In a second method it is possible to only expose the surfaces D and E to the fluorination process by covering up all other areas.

4 3. In a third alternative it is possible to fluodnate the outside of the sleeve 15 only by covering up all the internal surface areas. This effectively provides an impermeable barrier between two polyethylene layers of the fitting.

Once fluorinated the sleeve is placed into an injection moulding machine and the remainder of the fitting moulded over the top of the sleeve to produce the finished fitting in the normal way.

It may be preferable to carry out the fluorination process prior to introducing the heating wires so that there is no possibility that the wires could be affected. In any event, the fluorination of polyethylene is a known process as is the protection of certain areas of plastic where fluorination is not required. The details of this process are known to the materials specialists and to fluorination chemists.

It will be appreciate that, in the examples where area E is fluorinated, while the pipes to be joined extend over this area, electrofusion welding only takes place outside of this area. The strength of the resulting weld is therefore unimpaired.

In a second manufacturing procedure a co-extrusion process is used to introduce an inner barrier layer of nylon, polyvinylidene fluoride or chloride, Teflon@ or other highly impermeable material onto the inner polyethylene sleeve illustrated in Figure 1. One version of this coextruded product is illustrated in Figure 2. This shows an inner barrier layer of some substantially impermeable plastics material 21 formed within with polyethylene sleeve 22. This multi-component sleeve is then subjected to the remainder of the construction process described above to form the finished fitting.

In its central region this fitting contains, in effect, three discrete layers; an inner, barrier layer, an inner polyethylene layer incorporating heating wires and an outer polyethylene body.

It will be appreciated that the barrier layer could equally well have been formed around the outside of the inner polyethylene sleeve 22. This version is not illustrated. The net result is still the same in that an impermeable barrier layer is inserted between the inside, fluid carrying region of the pipe fitting and the outside of the fitting. Placing the impermeable layer on the outside of the sleeve has the advantage that it cannot, by definition, interfere with the welding process.

In a third method of manufacture, a thin barrier coating is applied to the sleeve 12, 22 by Chemical Vapour Deposition. The main feature of this technique is that small sub-micron metallic films can be applied onto a substrate giving the outer portion of the inner sleeve greatly improved permeability characteristics.

Any suitable material which can be deposited using Chemical Vapour Deposition and which provides a substantially fluid-impermeable barrier can be used. It is generally easier to apply this technique to the outer portion of the inner sleeve rather than using a complex masking system which would be required if the Vapour Deposition was to take place on the inner portion of the inner sleeve.

It will be appreciated that this invention relates to methods of manufacturing the improved fittings described above, to the fittings themselves which are novel in their own right and to methods of joining pieces of pipe using such fittings, The optimum materials for use in the present fittings will be determined by the materials specialist. The barrier layer should be substantially impervious to the fluid to be carried within the pipe and generally comprises a polymeric plastics material selected from the group consisting:

nylon 612 polyamides polyamides 6, 11 or 12 polyethylene terphthalate polyvinyl chloride polyvinyl fluoride polyvinylidene chloride or fluoride polypropylene ethylenelvinyl alcohol copolymers or mixtures thereof, the selection being based on the nature of the fluid being conveyed.

This selection is not intended to be limiting but rather demonstrates the flexibility and breadth of the invention. The plastics material with the lowest permeability to the fluid in question will usually be chosen. Furthermore, it is known to use blends of two or more polymers and this invention extends to cover known and yet to be developed blends of plastics material. Preferably the body of the sleeve comprises a plastics material selected form the group comprising:polyethylene polypropylene polyvinyl chloride polyvinyl fluoride or variations and combinations of plastics material specified for the inner layer. In a particularly preferred embodiment the inner layer comprises Nylon 612 or polyvinylidene fluoride and the body of the sleeve comprises linear low density polyethylene.

7

Claims

1. A coupling device for forming a joint in a pipeline system comprising a plurality of pipes in end to end alignment, said coupling device comprising a sleeve with at least one socket or hollow spigot for receiving or extending within an end of one of the pipes, characterised in that the sleeve incorporates an inner barrier layer, said inner barrier layer being substantially impermeable to the fluid being conveyed in the pipeline system.

2. A coupling device as claimed in Claim 1 wherein the inner barrier layer comprises a fluorinated region on the inner surface of the sleeve.

3. A coupling device as claimed in Claim 1 wherein the inner barrier layer comprises a fluorinated layer within the body of the coupling device.

4. A coupling device as claimed in Claim 1 wherein the inner barrier layer comprises a polymeric plastics material selected from the group consisting:

nylon 612 polyamides polyamides 6, 11 or 12 polyethylene terephthalate polyvinyl chloride polyvinyl fluoride polyvinylidene chloride polyvinylidene fluoride polypropylene Teflono 8 ethylene/vinyl alcohol copolymers or mixtures thereof, the selection being based on the nature of the fluid being conveyed.

5. A coupling device as claimed in any preceding claim wherein the body of the sleeve comprises a plastics material selected from the group comprising:

polyethylene polypropylene polyvinyl chloride polyvinyl fluoride or variations and combinations of plastics materials specified for the inner layer.

6. A coupling device as claimed in any preceding claim wherein the device further incorporates electrical resistance heating wires.

7. A coupling device as claimed in Claim 1 in which the sleeve is made of linear low density polyethylene and the inner barrier layer is made of a material selected from the group comprising nylon 612 and polyvinylidene fluoride.

8. A coupling device for forming a joint in a pipeline system substantially as hereinbefore described with reference to and as illustrated in any combination of the accompanying drawings.

9. A pipeline system incorporating a coupling or couplings as claimed in any preceding claim.

9

10. A method of manufacturing a coupling device as claimed in any of Claims 1 to 8 inclusive, said method comprising the steps of: (a) injection moulding an internal sleeve from a polymeric plastics material; (b) wrapping electrical resistance heating wires around the internal sleeve; (c) inserting metal pins into the sleeve, connected to the wires of step (b), for subsequent contact to a welder; (d) injection moulding the external part of the fitting around the inner component; (e) applying an inner barrier layer to the inner sleeve of the coupling device at an appropriate stage in the sequence using a method selected from the group 10 comprising:- (i) fluorination of selected region(s) of the inner sleeve; (ii) co- extrusion of a second polymeric plastics material selected from those given in Claim 4; (iii) chemical vapour deposition of a thin metallic film. 15

11. A method of manufacturing a coupling device substantially as herein described with reference to and as illustrated in any combination of the accompanying drawings.