GB2084681A - Electrically insulating pipe fitting - Google Patents

Abstract

An electrically insulating pipe fitting has first and second cylindrical members 10 and 20. First member 10 has pipe receiving portion 11, outwardly extending radial wall 12 and axially extending circumferential flange 13. Second member 20 has pipe receiving portion 21 and outwardly extending radial wall 22 to fit radially within flange 13. Annular locking collar 30 locks together members 10, 20 with their pipe receiving portions 11, 21 and radial walls 12, 22 aligned. Resilient sealing means 40 is interposed between portions 14, 24 of walls 12, 22. First barrier 51 of electrically insulating material is arranged between directly adjacent surface portions 15, 25 of walls 12, 22. Second barrier 52 of electrically insulating material is arranged between the collar 30 and surface 26 of wall 22. A cavity 61, 62, 63 defined by member 20, collar 30 and flange 13 is filled with thermosetting plastics material. <IMAGE>

Description

SPECIFICATION An electrically insulating pipe fitting This invention relates to an electrically insulating pipe fitting.

When a utility service is piped into a building, such as a gas supply, a connection is made between a pipe from the utility supply to a pipe taking the supply into the building. Because the pipe within the building may carry a net voltage, due to earthing of electrical circuits within the building, known as cross bonding, in the absence of adequate electrical insulation at the pipe fitting connecting the utility supply pipe to the building supply pipe a residual voltage will appear on the utility supply pipe. Such a residual voltage may lead to electrolytic erosion of the utility supply pipes. For this reason it is known to employ a pipe fitting which electrically insulates the building supply pipe from the utility or mains supply pipe. Hitherto problems have been experienced in obtaining electrical insulation which is adequate in the field.Problems which have arisen concern (a) mechanical failure of the insulation material in the pipe fitting due to stress arising when the union between the pipes is made, (b) electrical failure of the insulation material, (c) destruction of the sealing capacity of the pipe fitting in the event of fire at the user building leading to excessive gas leakage from the fitting.

The present invention therefore seeks to provide an embodiment of an electrically insulating pipe fitting which avoids the above disadvantages and in particular has the advantages of: (a) electrical insulation material housed in the fitting in such a manner that mechanical forces applied to the pipes and fitting during assembly do not result in mechanical stress sufficient to impair the insulation properties of the insulation material; (b) the insulation material has adequate electrical insulation charateristicsto meet the standards required; (c) the pipe fitting is designed to prevent excessive gas leakage after the event of fire.

According to the present invention there is provided an electrically insulating pipe fitting comprising a first member having a pipe receiving portion, an outwardly extending radial wall and an axially extending circumferential flange extending from the radial wall away from the pipe receiving portion, a second member having a pipe receiving portion and an outwardly extending radial wall adapted to be received radially within the circumferential flange of the first member, an annular locking collar for locking together the first and second members with their pipe receiving portions axially aligned and their radial walls aligned, a first barrier of electrically insulating material arranged between the radial walls of the first and second members, a second barrier of electrically insulating material between the annular locking collar and the radial wall of the second member, and wherein a cavity defined by the second member, annular locking collar and first member flange is filled with a plastics material.

Preferably non-conductive resilient sealing means are interposed between radially inward contiguous surface portions of the radial walls of the first and second members.

In the preferred embodiment the first barrier extends between parallel surface portions of the radial walls of the first and second members, the surfaces of the first and second members contiguous with the first barrier and radially inward thereof are configured to receive the resilient sealing means, said resilient sealing means extending an air gap between the first and second members.

The pipe receiving portions of the first and second members may be adapted for threaded engagement with their respective pipes. In the preferred embodiment the first and second members are adapted on radially inward surfaces for engagement with the pipes, i.e. they provide so called female connections.

One or both may be adapted on a radially outward surface for engagement with its pipe, i.e. to provide a so called male connection.

The plastics material is preferably a plastics material selected for its mechanical strength and electrically insulating and adhesive properties.

Preferably such a plastics material fills a further cavity defined by oppositely directed surface portions of the first and second members, said further cavity being radially inward of the sealing means.

The provision of plastics material eliminates the possibility of a tracking path for electrical conduction through a moisture layer bridging the interior surfaces of the first and second members across the sealing means.

In such an embodiment the sealing means is provided with a smooth surface contiguous to the plastics material so as to avoid the creation of stress points in the plastics material.

In a preferred embodiment the first and second barrier each comprise an annular disc of electrically insulating material such as mica.

In the preferred embodiment the annular locking collar and circumferential flange of the first member are threadedly connected by mating circumferential threaded surfaces thereon. When torque is applied to the annular locking collar, if the collar came into direct contact with a second barrier formed of a material such as mica damage to the mica could result from direct contact of the rotating collar and the mica. For this reason this embodiment is provided with an annular plate interposed between the annular locking collar and the radial wall of the second member, the second barrier being interposed between the annular plate and the radial wall of the second member. The annular plate then protects the second barrier from mechanical wear during assembly. The preferred material of the annular plate is steel.

In an alternative embodiment the barrier between the annular locking collar and the radial wall of the second flange may be formed by a coating on one or both of their adjacent surfaces, the coating having suitable electrically insulating characteristics, high temperature mechanical stability, and being suffi ciently abrasion resistant to avoid significant impairment of its insulating function after assembly of the pipe fitting. Such a coating would avoid the requirement for an annular protective plate.

In a further alternative the annular plate may itself be formed of an electrically insulating material with high temperature mechanical stability or the plate may have at least one side coated with an electrically insulating layer of high temperature mechanical stability.

An alternative to the filling of the further cavity with a plastics material is the provision of a dressing of electrically insulating material across the cavity, said dressing being capable of eliminating tracking.

The plastics material may be reinforced with glass fibre to manufacturer's instructions.

An embodiment of the invention will now be described with reference to the accompanying drawing, in which there is shown a partial elevational section of an electrically insulating pipe fitting according to the present invention.

In the drawing there is shown an electrically insulating pipe fitting having a first member 10 and a second member 20. Although the Figure shows the pipe fitting in partial section, it will be clear that members 10,20,30,40,51,52 and 70 are cylindrical when viewed axially of the pipe fitting and also that, whilst in the partial elevation only the upper half of the fitting is shown, the lower half is similar since the fitting is rotationally symmetrical about its longitudinal axis.

First member 10 has a pipe receiving portion 11, an outwardly extending radial wall 12 and an axially extending circumferential flange 13. Flange 13 extends from the radial wall 12 away from the pipe receiving portion 11. Second member 20 has a pipe receiving portion 21 and an outwardly extending radial wall 22 adapted to be received radially within the circumferential flange 13 of the first member 10.

An annular locking collar 30 locks together the first and second members 10,20 with their pipe receiving portions 11, 21 axially aligned and their radial walls 12, 22 aligned. Resilient sealing means 40 is interposed between radially inward contiguous surface portions 14,24 of the radial walls 12,22 of the first and second members 10,20. A first barrier 51 of electrically insulating material is arranged between directly adjacent surface portions 15,25 of the radial walls 12,22 of the first and second members 10,20.

A A second barrier 52 of electrically insulating material is arranged between the annular locking collar 30 and the surface 26 of the radial wall 22 of the second member 20 adjacent thereto. A cavity 61,62,63 is defined by the second member 20, annular locking collar 30 and first member flange 13. This cavity 61, 62,63 is filled with a thermosetting plastics material selected for its mechanical strength and electrically insulating properties. In this embodiment the thermosetting plastics material is sold under the trade name PERMABOND E15.

The first barrier 51 extends between the parallel surface portions 15,25 of the radial walls 12,22 of the first and second members 10, 20 which after casting are prepared for parallel alignment. The surfaces 14,24 of the first and second members 10, 20 contiguous with the first barrier 51 and radially inward thereof are configured to receive the resilient sealing means 40. The provision of the resilient sealing means 40 ensures an air gap 64 between the first and second members 10, 20. After assembly of the pipe fitting of this embodiment, the gap has an axial dimension of at least 3 mm to ensure adequate insulating space between surfaces 14, 24.

The pipe receiving portions 11,21 of the first and second members 10, 20 are adapted at 17, 27 for threaded engagement with their respective pipes.

One member receives the utility or main supply pipe and second member receives the building supply pipe: these supply pipes in this embodiment are of 51.0 mm (2 inch) diameter. As one skilled in the art will readily recognise, receiving portions 11 and 21 are suited to one form of pipe connection. The fitting may be made to suit any recognised form of mechanical connection.

In this embodiment a further cavity 65, which is defined by oppositely directed surface portions 18, 28 of the first and second members 10, 20, is filled with the plastics material PERMABOND E15. The further cavity 65 is radially inward of the sealing means 40. The provision of plastics material in cavity 65 and at 29 partly along the interior surface of member 20 eliminates the possibility of a tracking path for electrical conduction through a moisture layer bridging the interior surface 18, 28 of the first and second members 10, 20 across the sealing means 40. Sealing means 40 is provided with a smooth surface 41 contiguous to the plastics material in cavity 65 so as to avoid the creation of stress points in the plastics material.Likewise surfaces 18, 28 are of curvilinear configuration in order that stress points do not occur in the plasticp material along the boundary thereof with these surfaces 18, 28.

As illustrated the first and second barriers 51, 52 are each provided by an annular disc of mica available under the trade name "MUSCOVITE" and each has a minimum thickness of 0.3 mm. Also as illustrated, the annular locking collar 30 and circumferential flange 13 of the first member 10 are threadedly connected by mating circumferential threaded surfaces 31, 19 thereon. When torque is applied to the annular locking collar 30, if the collar 30 came into direct contact with the second mica barrier 52, damage to the mica could result from their direct, rotational contact. For avoidance of such damage, an annular plate 70 is interposed between the annular locking collar 30 and the radial wall 22 of the second membwer 20. The second barrier is interposed between the annular plate 70 and the radial wall 22 of the second member 20. The annular plate 70 then protects the second barrier 52 from mechanical wear during assembly. As shown annular plate 70 is dimensioned to fit radially inward of the flange 13 and radially outwardly of the pipe receiving portion 21 of member 20.

The sealing means 40, as well as defining an air gap, may also (as illustrated) provide abutment surfaces 42, 43 for the radially inner end 53 of the first barrier member 51 which facilitates the assembly of the pipe fitting. In addition, sealing means 40 has several axial protrusions 44 for abutment with surface 24 of second member 20 and flat surface 45 for compression by surface 14 of first member 10.

The sealing means 40 is formed of resilient nonconductive plastics material. The illustrated configuration of sealing means 40 is one of many suitable. As an alternative an O-ring sealing ring may be employed. The presence of the sealing ring 40 further ensures that the end 53 of first barrier 51 does not contact the plastics material in the cavity 65. Locaiised contact between the radially inner end 53 of barrier 51 could result in a local stress point in the plastics material in cavity 65. During connection of the supply pipes to the pipe fitting, such a stress point in the absence of sealing means might give rise to fracture in the plastics material as a result of the forces applied between the pipes and pipe fitting.

As mentioned earlier the cavity 61, 62, 63 is defined by the collar 30, second member 20 and flange 13. More particularly, cavity portion 61 extends circumferentially of the second member por tidn 23 and radially between portion 23 and collar 30.

The plastics material in cavity portion 61 extends axially from the radial plane defining the radial end face 113 of flange 13 to the surface 26 of the radial wall 22. Cavity portion 62, as illustrated, extends as a passage through the collar 30. There are four such passages in collar 30. These passages enable the plastics material to enter cavity portion 63 and are provided for engagement by a tool (not shown) for rotating the collar 30 during assembly of the pipe fitting to advance the collar 30 axially along the thread 19 of flange 13 into its locking position shown in the Figure. Cavity portion 62 extends circumferentially round the radially outer faces 71, of the annular plate 70 and radial wall 22 and axially from the collar 30 to radial wall 12. It is also defined by the contiguous inner surface 119 of flange 13.

The assembly of the pipe fitting requires sealing means 40 to be inserted axially into first member 10 and then barrier 51 to be inserted. Member 20 is brought axially into alignment with member 10 and its radial wall 22 into contact with barrier 51. Barrier 52 and annular plate 70 are then radially positioned.

Collar 30 is then secured. The cavity 61, 62, 63 is then filled with the PERMABOND E15 material and allowed to set according to the manufacturer's instructions. Likewise PERMABOND El 5 material is placed in cavity 65 and along the location 29.

The pipe fitting of this embodiment has been tested and found to meet the requirements of the following design parameters: (a) the insulation formed by the thermosetting plastics material in cavity 61, 62, 63 and mica barriers 51,52 had a resistance in excess of 100 Kilo ohms when a voltage of 500 volts d.c. is applied across the fitting; (b) this insulation withstood an alternating voltage of 2500 volts applied across the fitting; (c) the pipe fitting with the collar 30 and the cavity 61,62, 63 filled with set PERMABOND El 5 is capable of withstanding torsional loading of 480 Newton metres and a bending moment across the fitting of 1200 Newton metres; (d) the leakage of gas flowing through the fitting is less than 0.1416 cubic metres per hour in the event of fire; ; (e) the plastics material in the cavity 65 and the surface layer between surfaces 23 and 113 prevented surface tracking 6f residual voltage on the pipe connected at member 20 to the pipe connected at member 10.

Modifications have already been indicated in the generalised statements preceding the description of the Figure.

Claims (8)

1. An electrically insulating pipe fitting comprising a first member having a pipe receiving portion, an outwardly extending radial wall and an axially extending circumferential flange extending from the radial wall away from the pipe receiving portion, a second member having a pipe receiving portion and an outwardly extending radial wall adapted to be received radially within the circumferential flange of the first member, an annular locking collar for locking together the first and second members with their pipe receiving portions axially aligned and their radial walls aligned, a first barrier of electrically insulating material arranged between the radial walls of the first and second members, a second barrier of electrically insulating material between the annular locking collar and the radial wall of the second member, and wherein a cavity defined by the second member, annular locking collar and first member flange is filled with a plastics materal.

2. A pipe fitting as claimed in Claim 1,wherein non-conductive resilient sealing means are interposed between radially inward contiguous surface portions of the radial walls of the first and second members.

3. A pipe fitting as claimed in Claim 2, wherein the first barrier extends between parallel surface portions of the radial walls of the first and second members, the surfaces of the first and second members contiguous with the first barrier and radially inward thereof are configured to receive the resilient sealing means, said resilient sealing means extending an air gap between the first and second members.

4. A pipe fitting as claimed in Claim 3, wherein said plastics material fills a further cavity defined by oppositely directed surface portions of the first and second members, said further cavity being radially inward of the sealing means.

5. A pipe fitting as claimed in any one of Claims 1 to 4, wherein the first and second barrier each comprise an annular disc of electrically insulating material.

6. A pipe fitting as claimed in any one of Claims 1 to 5, wherein the annular locking collar and circumferential flange of the first member are threadedly connected by mating circumferential threaded surfaces thereon.

7. A pipe fitting as claimed in any one of Claims 1 to 6, comprising an annular plate interposed between the annular locking collar and the radial wall of the second member, the second barrier being interposed between the annular plate and the radial wall of the second member.

8. An electrically insulating pipe fitting arranged, constructed and adapted to operate substantially as hereinbefore described with reference to the accompanying drawing.