GB2349927A

GB2349927A - Electrofusion couplings with inner and outer fittings

Info

Publication number: GB2349927A
Application number: GB9906181A
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: GB9906181D0; GB2349927B

Abstract

An electrofusion coupling device for use in forming joints in secondarily contained pipeline systems comprises an inner 11 and an outer electrofusion fitting 10, which are adapted to receive or extend within an end of a primary and a secondary pipe respectively. The electrofusion fittings incorporate electrical heating windings 15, where the inner and outer fittings are slidably mounted one within the other, for instance they may incorporate a rib 20 and channel 19 arrangement, where the rib is slidable within the channel. The rib and channel may include electrodes, which make mutual contact when the inner and outer fittings are mounted one inside the other. The electrofusion device may be used for pipework in petroleum installations such as on garage forecourts.

Description

2349927 Improved Electrofusion Couplings

Field of the Invention

The present invention relates to a method and apparatus for joining together lengths of pipe. It is particularly applicable, but in no way limited, to a method and apparatus for joining together lengths of secondarily contained plastic pipe.

Backoround 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-terranean 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, other than inside manhole chambers, these joints sometimes cannot be avoided. Such joints are conventionally 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 In conventional single containment plastic piping systems, successive lengths of plastic pipe are joined end to end using so-called electrofusion couplings or welding muffs, which typically comprise short plastic sleeves providing sockets at either end having internal diameters of a size to receive the ends of the respective pipes as a close fit and incorporating electrical resistance heating windings. Thus two adjoining pipe lengths can be connected end to end by inserting the adjoining pipe ends into such an electrofusion coupler from opposite ends thereafter passing electric current through the heating windings in order to fuse the internal surfaces of the electrofusion coupling and the adjoining the external surfaces of the inserted pipe ends, thereby welding the pipe ends to the electrofusion coupling to form a fluid tight joint.

Hitherto, in constructing secondary containment pipeline systems utilising plastic pipes, the pipe lengths forming the inner plastic pipe have been connected end to end by a first series of electrofusion couplings, whilst the pipe lengths forming the outer pipe have been connected end to end by a second series of electrofusion couplings distinct from and separate from those connecting the lengths of inner pipe. This procedure inevitably involves threading the outer pipe and the electrofusion couplings for the outer pipes over the inner pipes and/or the longitudinal displacement of the outer pipes and the associated electrofusion couplings relative to the inner pipes. This involves substantially more labour than the construction of a comparable single containment pipe system by similar techniques. In addition, where separate electrofusion couplings are used for the inner and outer pipes, the number of electrofusion operations required is doubled as compared with a comparable single containment piping system.

2 Attempts have been made to fabricate a coupling device for connecting endto-end to adjacent runs of a double pipe in a secondary containment system. One such device is described in GB2318543A (Glynwed Pipe Systems Limited) and consists of a thermoplastic moulding provided at either end with an inner and an outer cylindrical sleeve for engagement respectively with the end part of an inner and outer pipe. The sleeves maybe provided with electrical resistance heater windings whereby, after assembly of the pipe joint, the respective windings can be energised to weld together the plastics of each sleeve and the adjacent thermoplastic pipe, thereby effecting a strong and leak-tight connection. The form of these electrofusion couplings is effectively that of a combination of two conventional electrofusion couplers, arranged concentrically one within the other. The inner portion is of a size appropriate to the inner pipe and the outer coupling is of a size appropriate to the outer pipe, with the two electrofusion couplings being connected by a bridge piece or pieces extending between the two.

Such fittings are complex to manufacture and requires intricate and expensive apparatus. Such apparatus is described in GB2318543A. As a result, these fittings costs significantly more than two separate electrofusion couplings as used in the previous prior art.

It is an object of the present invention to overcome or mitigate some or all of the problems outlined above.

Sum[13ary of the Invention According to a first aspect of the present invention there is provided an electrofusion coupling device for use in forming joints in a secondarily contained pipeline system said device compring an inner and an outer elctro-fusion fitting, said fittings being adapted to receive or extend within an end of a primary and a 3 secondary pipe respectively, said electrofusion fittings incorporating electrical resistance heating windings and wherein the inner and outer fittings are slidably mounted one within the other.

Forming the inner and outer electrofusion fiffings as separate components which are a slidable engagement fit one within another significantly simplifies the construction and manufacture of such fittings.

Preferably the inner and outer fittings incorporate a rib and channel arrangement, the rib being slidable within the channel.

Ribs and channels extending longitudinally along the fitting are particularly easy to manufacture and provide a positive sliding fit arrangement.

Prefereably the rib(s) and channel(s) incorporate electrodes. These electrodes provide a means of providing electrical power to the electrical resistance heater windings in the inner fitting in a simple and elegant fashion.

Brief description of the drawinqs

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

Figure 1 shows a perspective view of a coupling according to the present invention; Figure 2 shows a second view of the fitting in Figure 1.

Description of the preferred embodiments

The present embodiments represent the best ways known 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.

4 Referring to Figure I this illustrates the essential components of a fitting according to the present invention. This consists of an outer, electrofusion fitting 10 and a separate inner electrofusion fitting 11. The two fittings are designed to nest one within the other in a special fashion which is described in more detail below.

Externally, the outer electrofusion fitting resembles a conventional electrofusion fitting for a single pipe fun. That is to say, it comprises a plastic collar or muff whose internal surface 13 is a snug fit with the external surface of the secondary pipe (not shown). A step or stop 14 limits the distance that the outer secondary pipe may be inserted into the fitting. A similar stop is provided at the other end of the fitting.

The inner surface 13 of this fitting accommodates windings 15 of electrical heating wire which lie close to, or at, the internal surface of sleeve 10. These windings are electrically connected to terminal pins 16 projecting from the outer sleeve and shrouded by hollow cylindrical plastic terminal shrouds 17 projecting from and integral with sleeve 10.

The inner electrofusion I I comprises a straight-sided tube with an internal diameter adapted such that an inner supply pipe can fit internally into this fitting. This inner electrofusion fitting 11 incorporates windings 18 of electrical heating wire which lie close to, or at, the internal surface of this sleeve. These electrical windings are connected to metallic strips B which, in this example, are set into channels 19 which run along the length of the inner sleeve in a longitudinal direction. The channels 19 are adapted to engage with longitudinal ribs 20 set in the internal wall of the outer fitting. The ribs 20 also accommodate metallic strip electrodes on their surface. When the inner fitting is threaded into the outer fitting the two sets of ribs, and hence the two sets of electrodes, on the inner and outer components engage to form an electrical connection. That is to say the ribs 20 and channels 19 cooperatively engage with each both to locate the inner fitting and to make electrical contact between the two. Application of electric current to the electrodes 16 causes the windings on both the outer and inner fiffings to heat up, the connection between the inner windings and the electrode 16 being made through the strips B and C.

The channels and corresponding ribs may be any suitable size and shape within reason and need not be uniform along their entire length. In fact, there is positive advantage in making them non-uniform because this feature can be used to ensure that the inner fitting engages with the outer fitting in one direction only.

For example, the ribs and the channels may be trapezium-shaped in cross section for part of their length. The remainder of the rib/channel can be some other shape, such as rectangular in cross-section. Fittings will then only slide together in a pre-determined way. In addition, the inner fitting will only slide so far within the outer fitting before coming to a stop. This can ensure that the inner fitting is always centered within the outer fitting.

The two components of this fitting can be manufactured using existing techniques and require no special apparatus. The outer fitting also has the advantage that it can be used as a conventional electrofusion fitting for a single pipe and no modifications are required.

In a further important feature of the invention, the inner surface of the inner electrofusion fiffing 11 can be covered with a banier material substantially impermeable to hydrocarbons or to the intended contents of the supply pipe generally in the region between the electrofusion welds. That is to say, because the inner fitting is simply a straight-sided tube it can be constructed in the same way as the pdmary fuel supply pipe, with an impervious nylon or other barder film layer where necessary.

By way of example, the invention involves an inner sleeve which contains windings and is dimensioned such that a 63mm pipe can fit internally. The windings 6 1 in the inner sleeve are connected to a metallic strip B. The whole sleeve is inserted into a larger fitting which contains the pins for connection to a welding machine. Once locked in place the metal strip B connects to another metal strip C in the outer part of the fitting to form an electrical contact. This then enables a welding machine to weld both a 75mm pipe which fits between the inner sleeve of the 63mrn fitting and the inner surface of the outer 75mm fitting and a 63mm pipe which fits over the 63mm inner sleeve.

It is quite possible that the 75mm fitting can be used to create an electrowelded joint between two lengths of 75mm pipe without the need for the 63mm pipe 10 insert.

The present invention also encompasses a method of joining pipes using the fittings described above and a method of manufacturing such fittings.

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Claims

1. An electrofusion coupling device for use in forming joints in a secondarily contained pipeline system said device comprising an inner and an outer electrofusion fitting, said fittings being adapted to receive or extend within an end of a primary and a secondary pipe respectively, said electrofusion fittings incorporating electrical resistance heating windings and wherein the inner and outer fittings are slidably mounted one within the other.

2. An electrofusion coupling device as claimed in Claim 1 whereas the inner and outer fittings incorporate a rib and channel arrangement, the rib being slidable within the channel.

3. An electrofusion coupling device as claimed in Claim 2 wherein the rib(s) and 15 channel(s) incorporate electrodes.

4. An electrofusion coupling device as claimed in Claim 3 wherein the electrodes contained within the ribs and channels of the inner and outer fittings make mutual contact when the inner and outer fittings are mounted one inside the other.

5. An electrofusion coupling device as claimed in Claim 2, Claim 3 or Claim 4 wherein the cross-sections of the ribs and channels are shaped so as to enable the ribs and channels to interlock at least part way along their length.

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6. An electrofusion coupling device as claimed in any of Claims 2 to 5 inclusive wherein the ribs and channels are trapezium shaped in crosssection for part of their length.

7. An electrofusion coupling device as claimed in any preceding claim, wherein the inner surface of the inner fitting incorporates a barrier material substantially impervious to the intended contents of the pipeline system.

8. An electrofusion coupling device for use in forming joints in a secondarily contained pipeline system substantially as hereinbefore described with reference to and as illustrated in any combination of the accompanying drawings.

9. A method of forming a joint in a secondarily contained pipeline system using an electrofusion coupling device as claimed in any preceding claims substantially as herein described with reference to and as illustrated in any combination of the accompanying drawings.

10. A pipeline system incorporating a coupling or couplings as claimed in any of Claims 1 to 8 inclusive.

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