GB2166514A

GB2166514A - Pipe connector or end piece

Info

Publication number: GB2166514A
Application number: GB08526821A
Authority: GB
Inventors: Klaus Schippl; Gunther Blumenberg
Original assignee: Kabelmetal Electro GmbH
Current assignee: Kabelmetal Electro GmbH
Priority date: 1984-11-02
Filing date: 1985-10-31
Publication date: 1986-05-08
Also published as: GB8526821D0; FR2574524A1; JPS61165089A; DE8432062U1

Abstract

The invention provides means for connecting together pipes for the transport of low-temperature media, or for attaching an endpiece to a pipe, the parts to be connected being inserted one into the other in the manner of a male-and-female connection, wherein these parts comprise an inner part composed of a metal having a subnormal or low coefficient of expansion e.g. bush 13, and an outer part composed of a metal having a normal coefficient of expansion e.g. bush 5. The said inner and outer parts may for example be composed of Invar (RTM) and of brass, copper or stainless steel, respectively. Differential contraction of the said inner and outer parts produces a shrink fit when the assembly concerned is cooled to the temperature of the low-temperature medium to be transported. <IMAGE>

Description

SPECIFICATION Pipe end connection means This invention relates to means for connecting together pipes for the transport of low-temperature media, or for attaching an endpiece or other fitting to such a pipe, the parts to be connected being inserted one into the other in the manner of a male-and-female connection.

German Published Specification (Offenlegungsschrift) 3,142,702 has described a plugin connection system for the inner pipes of a vacuum-insulated pipeline, in which the inner pipes are joined together in the manner of a male-and-female connection. In this type of connection, liquid can escape at the connection between the end faces of the pipes, and can penetrate into the annular gap between the pipes of the plug-in connection, and evaporate there. Since this annular gap is sealed off at its far end, a "pressure cushion" builds up and prevents a further escape of liquid from the inner pipe. However, this pressure cushion builds up only when the pipe is disposed vertically, and then only when the male end is introduced into the female end from above.

According to German Published Specification (Offenlegungsschrift) 3,310,034, the sealingoff problem is solved by covering the ends of the inner pipes with a thermoplastic sleeve which, when a low-termperature medium is transported, contracts to a substantially greater extent than the metal pipe ends, and thus adheres, with lasting firm adhesion, to the ends of the inner pipes. When the sleeve is shrunk on to the ends of the inner pipes, this ensures a liquid-tight sealing-off effect.

However, the disadvantage of this plug-in connection system is that it cannot be used where there is radioactivity, inasmuch as the plastics material employed is liable to decompose as a result of being irradiated. A further disadvantage of the known connection system is that the plastics sleeve can become very brittle during cooling, and can consequently become mechanically unreliable.

It is an object of the present invention, therefore, to improve the known male-and-female connection system in such a way that it can be used where there is radioactivity, and also in such a way that it will possess greater mechanical strength.

According to the present invention, we provide means for connecting together pipes for the transpiort of low-temperature media, or for attaching an endpiece or other fitting to such a pipe, the parts to be connected being inserted one into the other in the manner of a male-and-female connection, wherein these parts comprise an inner part composed of a metal having a subnormal coefficient of expansion, and an outer part composed of a metal having a normal coefficient of expansion.

Thus, in connecting pipes together utilising the means provided by the invention, one can rely upon the said outer part shrinking on to the said inner part when a low-temperature medium is transported through the connected piping. It is especially advantageous for the said inner part to be composed of a steel containing over 30% nickel. This material is characterised in that is has an amount of shirnkage of less than 0.05% over the temperature range from room temperature down to 5 K. Moreover, this material can be machined very easily. The said outer part may appropriately be composed of brass, copper or stainless steel, for instance. Over the temperature range mentioned above, the amount of shrinkage of these materials is approximately 0.35 to 0.4%.When the materials for the said outer and inner parts are selected, it should be remembered that they should be reasonably easy to machine and that it is desirable to be able to solder or weld them to stainless steel. Conveniently the said outer and inner parts are of a tubular configuration, one being insertable into the other. They are normally welded or soldered to the ends of respective inner pipes of a pipeline. To ensure that the shrink connection which seals off the low-temperature medium effectively is obtained, it is advisable to arrange for the difference between the inside diameter of the said outer part and the outside diameter of the said inner part to be less than 0.5% at room temperature. Those surfaces of the said outer and inner parts which are to be in contact with one another are advantageously polished.

By "surfaces" are meant here more particularly the inner surface of the said outer part and the outer surface of the said inner part.

The invention is explained in more detail below with reference to the accompanying diagrammatic drawing, in which: Figure 1 is a fragmentary view in axial section showing two pipes connected together by the utilisation of the means provided by the present invention, and Figure 2 is a similar fragmentary view of an enlarged scale, showing only a central portion of the assembly of Fig. 1.

In Fig. 1, two pipes which are to be connected to one another are shown at 1a and 1 b. These each comprise a corrugated inner tube 2a or 2b, an outer corrugated tube 3a and 3b, and a polyethylene outer casing 4a or 4b. The annular spaces between the tubes 2a and 3a, and 2b and 3b, are vacuum-insulated.

Pipelines of this type are preferably used for transporting low-temperature media, e.g. liquid oxygen, nitrogen, hydrogen or helium. If appropriate, the outer tube 3a or 3b can also be surrounded by further corrugated tubes insulated from one another. To make a connection between such pipe ends, the outer tube 3a or 3b is first stepped over an appropriate length, a bush 5 is screwed on to the inner corru gated tube 2a, and the end of the corrugated tube is welded to the end face of the bush 5.

A screw 6 is screwed on to the outer tube 3a and welded to the corrugated tube 3a in the same way. A tubular piece 7 is welded to the outer periphery of the screw bush 6, and, together with a further tubular piece 8 welded to the outer periphery of the bush 5, forms an annular space 9. This annular space 9 is closed off by means of a ring 10, which is welded both to the tubular piece 7 and to the tubular piece 8. As is evident, the annular space 9 communicates with the annular space between the tubes 2a and 3a, that is to say the annular space 9 is likewise evacuated. A flange 11 is welded to the ring 10.

A smooth tubular piece 12 is welded to the end of the inner tube 2b, and a bush 13 is welded to the free end of this smooth tubular piece 12. A bush 14 is screwed on to the outer tube 3b and welded to the end of the tube 3b. A flange 16 is welded via an intermediate connector 17 to the free end of a tubular piece 15 welded on the outer periphery of the bush 14. A tube 18 is welded to the inside of the intermediate connector 17 and to the outer periphery of the bush 13.

The annular space located between the smooth tubular piece 12 and the tube 18 communicates directly with the annular space between the tubes 2b and 3b, that is to say is likewise evacuated.

To make a connection, the end of the tube 1b is now introduced into the end of the tube la in the way illustrated in Fig. 1. It is essential, here, that the outside diameter of the tube 18 be only sufficiently less than the inside diameter of the tubular piece 8 to alloy the two parts to be pushed easily one into the other. The bushes 5 and 13 each have a cylindrical part, 5a and 13a respectively, and the latter are guided concentrically one into the other. Both the inner surface of the cylindrical part 5a and the outer surface of he cylindrical part 13a are polished. In accordance with the present invention, the bush 13, or at least the cylindrical part 13a, is composed of a steel with at least 30% nickel, viz. Invar (RTM). This material has a very low coefficient of thermal expansion.The bush 5 and its cylindrical part 5a appropriately consist of a brass, which can easily be cut by machining. The inside diameter of the cylindrical part 5a and the outside diameter of the cylindrical part 13a are so related that, at room temperature, they can be pushed one into the other easily. It is recommended that the difference in diameter should be less than 0.5%.

When a low-temperature medium flows through the inner tube la or 1b, the bushes 5 and 13 cool immediately to the temperature of the low-temperature medium, and, as indicated above, the bush 5 and consequently the cylindrical part 5a contract to a substantially greater extent than the bush 13 and the cylindrical part 13a. This produces a shrink fit which almost completely prevents the passage of a medium in the liquid or vapour state.

The present invention thus enables an arrangement for connecting "cryogenic" lines which is permanently leak-proof, even in the presence of radioactivity, to be provided in a particularly simple manner.

It will of course be understood that the present invention has been described above purely by way of example, and that various modifications of detail can be made within the ambit of the invention.

Claims

1. Means for connecting together pipes for the transport or low-temperature media, or for attaching an endpiece or other fitting to such a pipe, the parts to be connected being inserted one into the other in the manner of a male-and-female connection, wherein these parts comprise an inner part composed of a metal having a subnormal coefficient of expansion, and an outer part composed of a metal having a normal coefficient of expansion.

2. Means as claimed in claim 1, wherein the said inner part is composed of a steel containing over 30% nickel.

3. Means as claimed in claim 1 or 2, wherein the said outer part is composed of brass, copper or stainless steel.

4. Means as claimed in claim 1, 2 or 3 wherein the said inner and outer parts are of a tubular configuration.

5. Means as claimed in claim 1, 2, 3 or 4, wherein the said inner and outer parts are each welded or soldered to the ends of a pipe.

6. Means as claimed in any of claims 1 to 5, wherein the difference between the inside diameter of the said outer part and the outside diameter of the said inner part at room temperature is less than 0.5%.

7. Means as claimed in any of claims 1 to 6, wherein the surfaces of the said inner and outer parts which are in contact with one another are polished.

8. Means as claimed in claim 1, substantially as described with reference to the accompanying drawing.

9. An assembly comprising a pipe for the transport of low-temperature media which has been connected to a similar pipe, or attached to an endpiece or other fitting, by the utilisation of means as claimed in any of claims 1 to 8.