GB2459831A

GB2459831A - A coupling for connecting a plastic pipe to a metal pipe

Info

Publication number: GB2459831A
Application number: GB0804232A
Authority: GB
Inventors: Robert William Jardine; Paul Maurice Thompson
Original assignee: Crane Ltd
Current assignee: Crane Ltd
Priority date: 2008-03-07
Filing date: 2008-03-07
Publication date: 2009-11-11
Anticipated expiration: 2028-03-07
Also published as: GB2459831B; GB0804232D0

Abstract

A coupling for connecting a pipe such as a polyethylene gas pipe 1 to a metal pipe fitting such as a steel riser 3 in a service head connection. The pipe 1 extends within a protective tube 5. The coupling comprises a transition tube 9 which has a first end adapted for connection to the pipe 1 and a second end 13 adapted for welding to the metal pipe fitting 3. An annular connection skirt structure 12 extends radially from the transition tube and is adapted to sealingly connect 12a to the open end of the protective tube. The skirt may have screw plugs 14 which seal apertures in the skirt 12. The apertures facilitate the filling of cavity 15 with grout. The skirt may be attached to the transition tube 9 by welding or a screwed union (22, 23 figure 3 not shown). The transition from the transition tube 9 and the polyethylene pipe 1 may be via a crimp joint.

Description

PIPE COUPLING

The present invention relates to a transition coupling for connecting a plastics pipe to a metal pipe or fitting. More particularly, the present invention provides a coupling method and a pipe coupling for connecting a plastics gas supply pipe to a metal riser.

Gas supply pipes for transmitting gas to buildings are generally fabricated from a plastics material, usually a thermoplastic such as polyethylene (PE). PE and other plastic gas pipes are not generally used inside buildings, however, because the relatively low melting point of the pipe material presents a risk of gas leakage in the event of a fire or similar incident. Accordingly, many building regulations stipulate that internal pipe work must be metal, typically steel. It is therefore necessary to provide a transition coupling to couple a plastics supply pipe to the internal metal pipe A common approach for supplying gas to a building is by below ground entry.

A PE or similar gas supply pipe enters a building beneath ground level and is connected to metal pipe work within the building. It is generally preferable to make the connection between the PE pipe and the metal pipe work above ground level so that it is less susceptible to corrosion. In many installations the PB supply pipe enters the building from below ground and is connected to a generally vertical metal pipe known as a riser'.

Given that the join between the PE pipe and the metal riser is made above ground, there will generally be a length of PE pipe extending into the building. Many building regulations stipulate that the PE pipe must not be exposed at all in the building, and therefore must be protected within a metal conduit, sometimes referred to as a carrier pipe. Typically, the carrier pipe surrounds the PE pipe and extends from the termination region of the PE pipe to a location outside of the building. The internal end of the carrier pipe at the PB termination must be sealed and the external end is left open so that any gas that may leak from the PE pipe into the carrier pipe (for instance in the event of an accident) is vented outside of the building.

The transition coupling provided between a PE gas supply pipe and an internal metal riser is commonly known as a service head adapter. Known service head adapters comprise threaded connections between the adapter and the carrier pipe and between the adapter and the metal pipe work. However, some building regulations stipulate that where such threaded connections are used the service head adapter and riser must be enclosed within a dedicated ventilated duct so that any gas leaking from the adapter via the screw threaded connections will not enter the building. This is a disadvantage of such known service head adapters.

It is an object of the present invention to obviate or mitigate the above disadvantage.

According to a first aspect of the present invention there is provided a coupling for fluidly connecting an end of a portion of a first pipe to a metal pipe fitting, said portion of the first pipe extending within a protective tube which has an open end, the coupling comprising a transition tube having a first end adapted for connection to the end of the portion of the first pipe and a second end adapted for welding to the metal pipe fitting, and an annular connection structure extending radially from the transition tube and adapted to be sealingly connected to the open end of the protective tube.

The present invention also provides a method of fluidly connecting an end portion of a first pipe to a metal pipe fitting, said portion of the first pipe extending within a protective tube which has an open end, the method comprising connecting a coupling according to the first aspect of the present invention to the end of the first pipe, the metal pipe fitting, and the open end of the protective tube.

The invention may for instance be embodied as a service head adapter for connecting a plastics (e.g. PE) gas supply pipe to a metal fitting such as a metal riser pipe.

The annular connection structure may be welded to the open end of the protective tube or may be coupled to the open end of the protective tube using a known fitting such as a union coupling.

The present invention thus provides a coupling and a method for connecting a gas service pipe to a riser which provides a welded join to the riser and a gas tight (e.g. welded) join to the protective tube (or carrier pipe).

Other features of the invention will become apparent from the following

description.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a schematic illustration showing general features of the installation of a gas supply pipe; Figure 2 illustrates a first embodiment of the present invention; and Figure 3 illustrates a second embodiment of the present invention.

Referring first to Figure 1, this schematically illustrates entry of a gas supply pipe, such as PE supply pipe 1, into a building 2 from below ground level. The gas supply pipe 1 enters the building through the building foundation 2a and is connected to metal pipe work including a steel riser 3. Also shown is a connection to a gas meter 4. The length of PE pipe 1 that extends into the building is protected within a steel carrier pipe 5 which is sealed at its internal end 6 where the PE pipe terminates. The exernal end 7 of the carrier pipe 5 is open to allow gas to vent in the event that any gas leaks from the PE pipe within the carrier pipe 5. The PE pipe 1 is connected to the riser 3 by a service head adapter 8.

Referring now to Figure 2, this illustrates a first embodiment of a service head adapter in accordance with the present invention. Where appropriate the same reference numbers used in Figure 1 will be used in Fig 2. The service head adapter comprises a metal (e.g. steel) transition tube 9 a first end of which 10 is swaged to a reduced diameter to form a spigot and a second end 11 of which has a diameter corresponding to that of a metal (e.g. steel) riser pipe 3. An annular skirt 12 is welded around the transition tube 9 at a weld location between the ends 10 and 11. In the illustrated embodiment this location is approximately one third along the length of the transition tube 9 from the end 11. The skirt 12 has a depending annular rim 13 which has a diameter corresponding to that of the internal end of the carrier pipe 5. The skirt is provided with two screw plugs 14 (only one of which is shown) which seal respective apertures in the skirt 12.

The spigot end 10 of the transition tube 9 is adapted for connection to the end of the PE pipe 1; the end 11 of the transition tube 9 is adapted to be welded to the riser pipe 3; and the depending rim 13 of the skirt 12 is adapted to be welded to the carrier pipe 5. One method of connection of the service head adapter to the gas supply pipe 1 and carrier pipe 5 in accordance with the present invention will now be described.

The steel carrier pipe 5 is typically first installed from below groimd and the PE supply pipe 1 subsequently inserted through the carrier pipe 5 from outside of the building until it protrudes beyond the internal end of the carrier pipe 5 (the external end of the PE supply pipe will generally not be connected to the supply pipe at this stage -certainly the PE pipe will not be carrying gas until the service head adapter has been fitted).

The spigot end 10 of the transition tube 9 is then inserted into the open end of the PE pipe 1 and the two are secured together by crimping a sleeve 15 (which may for instance be made of copper) around the end of the pipe 1 to form a gas tight connection. The spigot end 10 of the transition tube and the end of the PE pipe 1 are then pushed back into the carrier pipe 5 until the lower rim 13 of the skirt 12 abuts the external end of the carrier pipe 5. The skirt 13 and carrier pipe 5 are then butt-welded together as indicated by reference 16. A backing ring 17, as illustrated, is preferably first friction fitted within the open internal end of the pipe 5 both to facilitate easy location of the skirt 13 for the subsequent welding operation, and to prevent sparks from the welding operation from entering the annular cavity 18 defined between the transition tube 9 and the carrier pipe 5.

The end 11 of the transition tube 9 is then butt-welded to the end of the steel riser 3 as indicated by reference 19 Finally, the cavity 15 may be filled with grout via the apertures in the skirt which are subsequently sealed by the screw plugs 14.

It will therefore be appreciated that the connection between the service head adapter and the carrier pipe and also the connection between the service head adapter and the riser are welded connections. The use of screw threaded connections at these important joints is thereby avoided and improved gas seal is obtained.

A second embodiment of the invention is illustrated in Figure 3. This embodiment has many features in common with the first embodiment and thus the same reference numerals will be used where appropriate. The second embodiment differs from the first embodiment in the configuration of the skirt 20 and the manner of its connection to the carrier pipe 5. Specifically, the skirt 20 which is again welded to the transition tube 9 at weld location 21, is configured for coupling to the carrier pipe 5 using a union connector comprising a union socket 22 which is screw threaded onto the end of carrier pipe 5, (which is similarly threaded) and a union nut 23 which screws onto the socket 22. The union socket 22 has a radially inwardly extending annular rim 24 (having regard to the longitudinal axis of the transition tube 9) which bears against an annular shoulder 25 defined by the skirt 20 so that as the union nut 18 is tightened onto the union socket 17 the lower rim 19 of the skirt 16 is clamped against the union socket 22. The socket 23 is formed from malleable iron and forms a gas tight seal around the skirt rim 26. In particular tightening of the union nut 24 will not rotate the transition tube 9 which might otherwise compromise its connection to the PE pipe. Union couplings of this general type will be well known to the skilled person and provide good gas tight seals.

Thus, according to the second embodiment of the invention the service head adapter provides a welded connection with the riser 3 and a welded connection with the skirt 4 which may be coupled to the carrier pipe 1 using an industry standard gas tight union coupling. Although not shown in Fig 3, the skirt 20 can again be provided with apertures sealed with screw plugs to enable grout to be introduced into the cavity between the transition tube 9 and the carrier pipe 5.

It will be appreciated that modifications may be made to the embodiments of the invention described above. For instance, the nature of the connection between the transition tube 9 and PE pipe 1 may vary from that illustrated. That is, the particular crimp' joint illustrated is only one example of a number of possible means of connection which would be apparent to the appropriate skilled person.

Similarly, the detailed configuration of the skirt may vary from that illustrated, as may be the particular configuration of the union coupling used in the second enthodiment of the invention. The transition tube 9 may not have the same diameter of the riser 3 along its length, although it is preferable that the end of the transition tube 9 has the same diameter as the end of the riser 3 (or other fitting to which the transition tube 11 to be welded) for the weld between the two. Similarly, the depending rim of the skirt 12 of the first embodiment of the invention need not have the same diameter as the end of the carrier pipe 5, but could for instance overlap the end of the carrier pipe 5, or be received within the open end of the carrier pipe 5, provided the two can be welded together. In some embodiments the skirt could be replaced by an alternative connecting structure such as a simple annular flange.

The length of the transition tube 9 relative to the other components of the assembly may vary from that illustrated. It is however preferable that the length is selected to minimise transmission of heat from the welding operation to the PE pipe.

In many applications a 250mm length will be sufficient to avoid conduction of significant heat to the PE pipe using gas or arc welding, and if arc welding is used a smaller length would be sufficient.

The screw plugs provided in the skirt may be replaced by other closure means, such as welded stoppers or caps or omitted entirely.

The material of the transition tube is selected to be appropriate for welding to the riser (or other pipe fitting) and need not necessarily be steel.

Other possible modifications will be readily apparent to the appropriately skilled person.

It will be appreciated that the invention is not limited to connection between a gas supply pipe and a vertical riser, the connection may have any orientation including installation on a generally horizontal axis and may be made between the PE pipe and any appropriate metal fitting. It will also be appreciated that the plastics pipe need not be fabricated from PE and may transmit a fluid other than gas.

Claims

CLAIMS1. A coupling for fluidly connecting an end of a portion of a first pipe to a metal pipe fitting, said portion of the first pipe extending within a protective tube which has an open end, the coupling comprising: a transition tube having a first end adapted for connection to the end of the portion of the first pipe and a second end adapted for welding to the metal pipe fitting, and an annular connection structure extending radially from the transition tube and adapted to be sealingly connected to the open end of the protective tube.
2. A coupling according to claim 1, wherein the first pipe is a plastics pipe.
3. A coupling according to claim 1 or claim 2, wherein the metal pipe fitting is a metal pipe.
4. A coupling according to any preceding claim, wherein the transition tube is metal.
5. A coupling accordingly any preceding claim, wherein the first end of the transition tube is formed as a spigot for insertion into the end of the first pipe, and the second end of the transition tube has a diameter corresponding to the diameter of the pipe fitting.
6. A coupling according to any preceding claim, wherein said connecting structure extends from the transition tube at a location intermediate its ends.
7. A coupling according to any preceding claim, wherein the connecting structure is welded to the transition tube.
8. A coupling according to any preceding claim, wherein the connecting structure is adapted to be welded to the open end of the protective tube.
9. A coupling according to any one of claims 1 to 7, wherein the connecting structure is adapted for connection to the end of the protective tube by a union coupling comprising a socket connected to the end of the protective tube, and a nut screwed onto the socket which clamps the connection structure there between.
10. A coupling according to any preceding claim wherein said connection structure includes a depending annular skirt defining an annular rim.
11. A coupling according to claim 10, wherein said annular rim has a diameter corresponding to the diameter of the open end of the protective tube.
12. A coupling according to any preceding claim, wherein the coupling is a service head adaptor for connecting a plastics gas supply pipe to a metal pipe.
13. A method of fluidly connecting an end portion of a first pipe to a metal pipe fitting, said portion of the first pipe extending within a protective tube which has an open end, the method comprising connecting a coupling according to any preceding claim to the end of the first pipe, the metal pipe fitting, and the open end of the protective tube.
14. A method according to claim 13, wherein the first pipe is a plastics gas supply pipe and the metal pipe fitting is a metal pipe such as a gas riser or the like.
15. A method according to claim 12 or claim 13, wherein: i. The first end of the transition tube is first connected to the end of the first pipe; ii. The second end of the transition tube is then welded to the pipe fitting; iii. The connecting structure is then coupled to the open end of the carrier pipe.
16. A method according to claim 15, where the connecting structure is welded to the open end of the protective tube.