WO2001046611A1

WO2001046611A1 - Coupling assembly for coupling a plastic pipe with another pipe

Info

Publication number: WO2001046611A1
Application number: PCT/NL2000/000848
Authority: WO
Inventors: Petrus Johannes Bus
Original assignee: Petrus Johannes Bus
Priority date: 1999-12-22
Filing date: 2000-11-20
Publication date: 2001-06-28
Also published as: AU2237401A

Abstract

Coupling assembly for coupling a plastic pipe (1) with another pipe (19), both intended to carry chemical liquids, in particular fuels, at least comprising a first coupling piece (5) which comprises at least a hose nipple (7), which hose nipple (7) is intended to be attached to the plastic pipe (1) by means of radial expansion of the hose nipple (7) with permanent deformation, a second coupling piece (13) which is intended to be attached to the other pipe (19), and coupling means (11) for coupling the first and second coupling pieces (5, 13) to one another, the coupling assembly furthermore comprising a bush (8) which is used to securely clamp the plastic pipe (1) between this bush (8) and the hose nipple (7), while the plastic pipe (1) has a double wall (2, 3) with one or more interspaces (4) extending over the length thereof, the coupling assembly furthermore comprises a connecting sleeve (9) which is intended to be arranged over the plastic pipe (1) in the vicinity of the hose nipple (7), which connecting sleeve (9) comprises a connection opening (10) which can be brought into communication with one or more of the interspaces (4), in which assembly one coupling piece has an external, circumferential, conical metal sealing surface (18), and the other coupling piece comprises an internal, circumferential, conical metal sealing surface (17), and in which assembly when one coupling piece is coupled to the other coupling piece the two conical sealing surfaces (17, 18) form a metal-metal seal.

Description

Short title: Coupling assembly for coupling a plastic pipe with another pipe

The present invention relates to a coupling assembly for coupling a plastic pipe with another pipe, both intended to carry chemical liquids, in particular fuels, at least comprising a first coupling piece which comprises at least a hose nipple, which hose nipple is intended to be attached to the plastic pipe by means of radial expansion of the hose nipple with permanent deformation, a second coupling piece which is intended to be attached to the other pipe, and coupling means for coupling the first and second coupling pieces to one another, the coupling assembly furthermore comprising a bush which is used to securely clamp the plastic pipe between this bush and the hose nipple, while the plastic pipe has a double wall with one or more interspaces extending over the length thereof, the coupling assembly furthermore comprises a connecting sleeve which is intended to be arranged over the plastic pipe in the vicinity of the hose nipple, which connecting sleeve comprises a connection opening which can be brought into communication with one or more of the interspaces. A coupling assembly of this type is known in the prior art. Coupling assemblies of this type are often referred to in practice as press couplings. In these assemblies, that section of the press coupling which has the hose nipple is positioned over the tie rod of an often hydraulic machine. Then, a conical component with a maximum diameter which is larger than the internal diameter of the hose nipple but smaller than the internal diameter of the pipe is screwed onto the tie rod. Then, an often metal bush with an internal diameter which is larger than the external diameter of the pipe is positioned over the hose nipple. Next, the pipe is placed over the hose nipple and, at the same time, into the bush. Then, the conical component is pulled in the axial direction through the hose nipple, which is to be expanded, of the coupling piece. In the process, the hose nipple is expanded with permanent deformation. The bush limits the expansion of the plastic pipe. In this way, a permanent fixed connection between the coupling piece and the pipe is brought about .

According to the prior art, the fitted coupling piece can then be coupled to other components, for example metal pipes or a connection piece of a storage system, for example by means of a union nut with a sealing ring. The coupling piece may also comprise a simple flange.

In practice, this coupling has proven reasonably satisfactory for all kinds of liquids, including chemical liquids, such as fuels.

However, in many countries authorities are specifying that leakage (permeation, sweating) of chemical substances, including hydrocarbons such as fuels, through the walls of the pipe must be minimal. In some countries, no permeation of substances through the walls of the pipe into the ground at all is permitted. However, union nuts with a sealing ring and flanges with an O-ring or gasket are not permeation proof. To eliminate these drawbacks with regard to permeation through these union nuts and flanges, couplings with clamping shells (clamping couplings) are used. These clamping couplings often comprise two clamping shells which are provided with an opening for the pipe ends and are screwed together with the aid of nuts and bolts, and an often metal part which on one side comprises a straight hose nipple and on the other side comprises a screw thread. In this way, a connection to the pipe is created which ends at a screw thread. The section bearing the screw thread is firstly coupled to other components, for example metal pipes or a connection piece of a storage system. Then, the pipe is fitted over the hose nipple. Next, the clamping shells are fitted. However, the clamping couplings used are large and heavy, and consequently are difficult to handle, particularly when weather conditions are poor, the quality of the connection is dependent on the fitter, and large amounts of insulating material are required when cathodic protection is used.

The object of the present invention is to provide a solution to the above problems, and to this end the invention is characterized in that one coupling piece comprises an external, circumferential, conical metal sealing surface, and the other coupling piece comprises an internal, circumferential, conical metal sealing surface, and in that when one coupling piece is coupled to the other coupling piece the two conical sealing surfaces form a metal-metal seal.

The coupling obtained in this way is permeation- proof, compact and therefore requires little insulating material for cathodic protection, while fitting is independent of weather conditions and can be carried out easily and quickly. The coupling is self-centring, and the quality of the connection is not dependent on the fitter. The number of components is minimal, with a small number of connections between them, therefore offering optimum reliability. US-A-3, 575,447 and US-A-3 , 532, 365 have in themselves disclosed a coupling assembly in which two coupling pieces which have circumferential conical sealing surfaces and are clamped together with the aid of coupling means are likewise used. However, these coupling assemblies are intended for brakeline systems and are not suitable for use with plastic pipes which are intended to carry fuels as in the present invention, which plastic pipes comprise a double wall with interspaces which extend along the length thereof . The design of the conical metal-metal seal is not particularly limited, but rather can be selected from various coupling systems which are known in the prior art for the purpose of coupling metal pipes, for example . For example, the vertex angle of the cone of the conical sealing surfaces and the dimensions of the sealing surfaces can be adapted to the other requirements imposed on the connection, for example with regard to the maximum use pressure .

In cathodically protected installations, the coupling, to prevent corrosion, is preferably designed in metal grades which have the same potential as standard fittings and other metal components, such as underground tanks.

The couplings are particularly intended for lines with diameters of between 0.5 inch (1.27 cm) and 6 inches (15.24 cm), more particularly ³A inch (1.91 cm),

1.5 inches (3.81 cm), 2 inches (5.08 cm), 3 inches (7.62 cm) and 4 inches (10.16 cm).

The selection of on which coupling piece the external, circumferential, conical sealing surface is arranged and on which coupling piece the internal, circumferential, conical metal sealing surface is arranged, is not restricted, but preferably an external, circumferential, conical metal sealing surface is arranged on the first coupling piece.

The coupling means can be selected from numerous means which are known in the prior art . The coupling means preferably comprise a union nut on one coupling piece and an associated screw thread on the other coupling piece. The union nut is advantageously present on the first coupling piece.

The design of the second coupling piece is in no way limited. The second coupling piece advantageously forms a unit with a metal pipe. This pipe may, for example, form a component of an (underground) storage tank. It is also possible for the second coupling piece to be a pipe stub which, for example, is directly connected to storage tank.

It is also possible for the second coupling piece to comprise an integrated bend or elbow or a threadedbush or other integrated flexible coupling part . The invention also provides a pipe system, at least comprising one or more double-walled plastic pipes for carrying chemical liquids, in particular fuels, which pipe system is characterized in that it comprises one or more coupling assemblies according to the invention.

According to the invention, it is also possible to couple two plastic pipes together. For this purpose, a first coupling piece with hose nipple is arranged at the ends which are to be coupled of each of the two pipes. One of these two first coupling pieces is provided with an external, circumferential, conical metal sealing surface, while the other is provided with an internal, conical metal sealing surface. In this way, it is advantageously possible to connect two permeation-free plastic pipes with a double-wall in a permeation-proof manner.

Furthermore, the invention provides a coupling piece, at least comprising a hose nipple and a circumferential, conical metal sealing surface, clearly intended for a coupling assembly according to the invention.

Finally, the invention provides a method for using a coupling assembly according to the invention for coupling a double-walled plastic pipe with another pipe, at least comprising the steps of: locally removing one or more layers from the outer wall of the plastic pipe in the vicinity of the end which is to be coupled, in such a manner that the interspaces are exposed; arranging the bush over the plastic pipe at the location of the exposed end; fitting the hose nipple of the first coupling piece into the pipe; - radially expanding the hose nipple; fitting the connecting sleeve, in such a manner that the connection opening is in communication with the interspace. It will be clear that the order of the steps is not essential. After the first coupling piece has been attached to the plastic pipe, the first coupling piece can be coupled to the second coupling piece with the aid of a suitable coupling design, for example a union nut or the like. The second coupling piece does not have to be a separate coupling piece, but rather may form a part of the other pipe.

In particular, the bush used has a radial thickness which is such that, after it has been secured over the exposed end of the plastic pipe, the outer wall of the bush lies substantially in one plane with the outer wall of the plastic pipe.

Advantageously, the connecting sleeve is arranged in such a manner that on one side it is situated on the bush and on the other side is situated on an unmachined section of the plastic pipe.

It will be clear that the bush according to the invention, unlike conventional bushes, is substantially completely cylindrical, with a smooth outer side.

The abovementioned preferred embodiments will be explained in more detail in the figure.

In the text which follows, the invention will be explained in more detail with reference to the appended drawing, in which the single figure shows a diagrammatic, opened-up view of an embodiment of a coupling assembly according to the invention.

In the figure, 1 denotes an end of a double-walled plastic pipe for carrying chemical liquids, for example fuels. The pipe 1 comprises an inner pipe 2 and an outer pipe 3, which together define interspaces 4. At the end of the pipe 1, the outer wall 3 has been removed locally over the entire circumference of the pipe 1, as will be explained in more detail below. The first coupling piece is denoted by reference numeral 5 and comprises a circumferential flange 6 and a hose nipple 7. The hose nipple 7 has been fitted into the end of the pipe 1 and radially expanded. A bush 8 is situated around the outside of the plastic pipe 1 at the location of the hose nipple 7. The bush 8 serves to limit the radial expansion of the hose nipple 7. Its thickness is such that its outer side lies substantially in one plane with the outer side of the outer wall 3 of the plastic pipe 1.

9 denotes a connecting sleeve which is attached with the aid of two hose clips 20, on one side over the bush 8 and on the other side over the outer wall 3 of the pipe 1. The connecting sleeve 9 comprises a connection attachment 10 inside which there is a continuous passage which is in communication with the interspaces 4 of the double-walled plastic pipe 1.

A union nut is denoted by 11 and has an internal screw thread 12.

A second coupling piece is denoted by 13, having a first external screw thread 14 and a second external screw thread 15. At the location indicated by 16, the coupling piece 13 is designed as a nut. At the end directed towards the first coupling piece 5, a circumferential, internal, conical metal sealing surface 17 is present in the coupling piece 13, which surface can be seen in the figure. A metal pipe end is denoted by 19, comprising an internal screw thread (not shown) which is able to interact with the second screw thread 15 of the second coupling piece 13.

If appropriate, the second coupling piece 13 could also form a unit with the pipe 19 or could, for example, be welded thereto. In practice, however, there is often a screw thread connection with a so-called "BSP gas thread" or "NPT" thread. The metal pipe may be a pipe stub of a storage tank, for example an (underground) fuel storage tank, or a connection piece of a pump. When attaching the coupling assembly according to the invention, firstly the outer wall 3 is removed in the vicinity of the end of the plastic pipe 1, so that the interspaces 4 are exposed. Then, the connecting sleeve 9 and the union nut 11 are pushed over the plastic pipe, after which the bush 8 is fitted. Next, the hose nipple 7 is pushed into the end of the plastic pipe 1, and the bush 8 is moved towards the end of the plastic pipe 1 until the bush surrounds the hose nipple 7.

Next, the hose nipple 7 is expanded so as to be permanently deformed, for example as a result of a conical component, which is attached to a rod and has a maximum diameter which is greater than the internal diameter of the hose nipple 7, being pushed or pulled through the hose nipple 7. During this process, the bush 8 serves to limit the expansion of the plastic pipe 1. In this way, a permanent, secure connection is obtained between the exposed end of the plastic pipe 1 and the first coupling piece 5. An example of an expansion method of this type is described in DE-A-40 03 379.

To produce a coupling between the plastic pipe 1 and the metal pipe 19, the second coupling piece with the screw thread 15 is screwed into the latter. The conical sealing surface 18 of the first coupling piece 5 is placed into the second coupling piece 13. Then the union nut 11 is screwed onto the first external screw thread 14 of the second coupling piece 13. It is thus possible, by tightening the union nut, to bring about a permeation-proof metal-metal seal between the first coupling piece 5 and the second coupling piece 13 , by means of the metal-metal seal of the conical sealing surfaces 17,18. It will be clear that the invention is in no way limited with regard to the pipes which can be coupled using the coupling assembly according to the invention.

Claims

1. Coupling assembly for coupling a plastic pipe (1) with another pipe (19) , both intended to carry chemical liquids, in particular fuels, at least comprising a first coupling piece (5) which comprises at least a hose nipple (7) , which hose nipple (7) is intended to be attached to the plastic pipe (1) by means of radial expansion of the hose nipple (7) with permanent deformation, a second coupling piece (13) which is intended to be attached to the other pipe (19) , and coupling means (11) for coupling the first and second coupling pieces (5,13) to one another, the coupling assembly furthermore comprising a bush (8) which is used to securely clamp the plastic pipe (1) between this bush (8) and the hose nipple (7) , while the plastic pipe (1) has a double wall (2,3) with one or more interspaces (4) extending over the length thereof, the coupling assembly furthermore comprises a connecting sleeve (9) which is intended to be arranged over the plastic pipe (1) in the vicinity of the hose nipple (7) , which connecting sleeve (9) comprises a connection opening (10) which can be brought into communication with one or more of the interspaces (4) , characterized in that one coupling piece has an external, circumferential, conical metal sealing surface (18) , and the other coupling piece comprises an internal, circumferential, conical metal sealing surface (17) , and in that when one coupling piece is coupled to the other coupling piece the two conical sealing surfaces (17,18) form a metal-metal seal.

2. Coupling assembly according to claim 1, characterized in that the first coupling piece (5) comprises an external, circumferential, conical metal sealing surface (18) .

3. Coupling assembly according to claim 1 or 2, characterized in that the second coupling piece (13) forms a unit with the other pipe (19) .

4. Pipe system, at least comprising one or more double-walled plastic pipes for carrying chemical liquids, in particular fuels, characterized in that it comprises one or more coupling assemblies according to one or more of the preceding claims.

5. Coupling piece, at least comprising a hose nipple and a circumferential, conical metal sealing surface, clearly intended for a coupling assembly according to one or more of claims 1 - 3.

6. Method for using a coupling assembly according to one or more of claims 1 -3 for coupling a double-walled plastic pipe with another pipe, at least comprising the steps of : locally removing one or more layers from the outer wall of the plastic pipe in the vicinity of the end which is to be coupled, in such a manner that the interspaces are exposed; arranging the bush over the plastic pipe at the location of the exposed end; - fitting the hose nipple of the first coupling piece into the pipe; radially expanding the hose nipple; fitting the connecting sleeve, in such a manner that the connection opening is in communication with the interspace.

7. Method according to claim 6, characterized in that the bush used has a radial thickness which is such that, after it has been secured over the exposed end of the plastic pipe, the outer wall of the bush lies substantially in one plane with the outer wall of the plastic pipe.

8. Method according to claim 6 or 7, characterized in that the connecting sleeve is arranged in such a manner that on one side it is situated on the bush and on the other side is situated on an unmachined section of the plastic pipe.