Line pipe for the transport of deep-frozen media

A line pipe for the transport of deep-frozen media, consisting of at least two corrugated metal pipes (2, 4) arranged concentrically and at a distance from one another, an insulation layer (3) being arranged in the annular gap between the two metal pipes (2, 4), the annular gap being evacuated, and a closing valve (10) provided in the outer metal pipe (4) being connectable to a vacuum pump, the closing valve being welded, vacuum-tight, into a smooth-walled metal pipe (9) welded, vacuum-tight, to the exterior of the metal pipes (4). The valve body (10) of the closing valve projects into the interior of the smooth-walled metal pipe (9) and is flush with the outer surface area of the smooth-walled metal pipe (9).

RELATED APPLICATION

This application is related to and claims the benefit of priority from European Patent Application No. 05292659.9, filed on Dec. 9, 2005, the entirety of which is incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to a line pipe for the transport of deep-frozen media.

BACKGROUND

EP 1 363 062 A1 discloses a line pipe for the transport of deep-frozen media, which consists of at least two metal pipes arranged concentrically and at a distance from one another, an insulating layer being arranged in the annular gap between the metal pipes, and the annular gap being evacuated. According to an advantageous embodiment, the metal pipes are longitudinally welded and corrugated high-grade steel pipes. On account of the corrugation, line pipes of the type described can be produced in great lengths. The insulating layer consists of plies arranged alternately one above the other and composed of insulating material and of a material having a reflecting surface. Glass fibre fleece and aluminium foils are preferred. An insulation composed of these materials in combination with a high vacuum is designated in cryotechnics as superinsulation. The known line pipes are used preferably as transfer lines for condensed gases, but also as cryostats for superconductor cables.

The known line pipes are distinguished by high economic efficiency, since, because of the great length which can be produced, a multiplicity of junction connections are unnecessary, as compared with lines consisting of smooth pipes. Owing to the flexibility, the lines can also be laid in narrow radii.

One disadvantage of the known lines is that, because of the great length, evacuation from the ends is highly time-consuming.

EP 1 363 062 therefore proposes to separate the exterior of the metal pipes at predetermined intervals and to weld, vacuum-tight, a pumping connection piece to the outer metal pipe at each orifice. For this purpose, metal-ring halves are placed onto the two ends of the outer metal pipe in the region of the orifice and are welded to the ends of the outer metal pipe. Half-shells consisting of a smooth-walled metal pipe are then placed onto the metal-ring halves and welded to the metal-ring halves and in their longitudinal directions. One of the half-shells has a connection piece for a vacuum pump. This design has the disadvantage that the metal-ring halves and the connection piece project out of the circumferential surface of the outer metal pipe. It is consequently not possible to draw the line pipe into narrow ducts.

OBJECT AND SUMMARY

The object on which the present invention is based is to provide a line pipe of the type mentioned in the introduction, which can be laid, even in great lengths, in narrow cable ducts and can be reevacuated quickly and simply, should the vacuum have been impaired due to possible leakages.

The essential advantage of the invention is to be seen in that, in the line pipe according to the teaching of the invention, there are no projecting parts which cause an obstruction when the line pipe is drawn into a cable duct. The pumping connection piece provided in the prior art and projecting outwards is replaced by an adapter which is attached only in the situation where repumping has to be carried out. The adapter is then screwed, vacuum-tight, to the valve body, and a gas lock known per se releases a screw plug screwed into the valve body and thus affords access to the annular space.

DETAILED DESCRIPTION

The invention is explained in more detail by means of the exemplary embodiments of a superconductor cable which are illustrated diagrammatically inFIGS. 1 to 5.

FIG. 1shows a section through a lateral view of a superconductor cable which consists of a superconducting cable core1and of a cryogenic envelope surrounding the superconducting cable core1. The cryogenic envelope is designed as a line pipe consisting of an inner pipe2, of a superinsulation3and of an outer pipe4. The inner pipe2is a longitudinally welded corrugated pipe composed of austenitic steel. A spacer5is wound helically onto the inner pipe2. Arranged on the inner pipe2and the spacer5is the superinsulation layer3which consists of alternately applied plies composed of reflecting metal foils, for example aluminium-coated plastic foils, and foils consisting of material having no heat conductivity, for example of glass fibre fleece.

The outer pipe4is likewise a longitudinally welded corrugated metal pipe composed of austenitic steel, which may be surrounded by a plastic casing6. The superconductor cable illustrated may be produced in great lengths continuously at the factory in a way customary in cable technology, the maximum length being limited by the capacity of the means of transport, for example by the size of the cable drum.

In order to accelerate or make possible at all the evacuation process both directly after manufacture and after laying, the plastic casing6and the outer pipe4are removed over a limited length at predetermined intervals of, for example, 100 m.

Two half-shells7a,7band8a,8bare placed in each case onto the ends of the outer pipe4and are welded, vacuum-tight, at their parting planes and on their mutually confronting end faces to the ends of the outer pipe4. The half-shells7a,7band8a,8blikewise consist of austenitic steel. As can be seen fromFIG. 1, the half-shells7a,7band8a,8bhave, on their surfaces confronting the outer pipe4, a profiling which is adapted to the shape of the corrugation of the outer pipe4and which connects the half-shells or the rings welded from the half-shells7a,7band8a,8bto the outer pipe4with a form fit and thus relieve the weld seam. Two half-shells9aand9b, which are produced from sheet-metal sections composed of austenitic steel, are laid around over the rings formed from the half-shells7a,7band8a,8band welded, vacuum-tight, on the end faces to the half-shells7a,7band8a,8band at their parting plane. The half-shell9ahas a valve body10, to which a vacuum pump can be connected.

Instead of the half-shells7a,7b,8aand8bplaced onto the outer pipe4, half-shells may also be used which are screwed into the outer pipe4after the longitudinal seams have been welded together.

A protective sleeve11may also be laid around over the half-shells9a,9band the plastic casing6.

The annular gap which is located between the inner pipe2and the outer pipe4and is partially filled with the superinsulation layer is partitioned off outwards, vacuum-tight, at both ends of a cable length.

After this preparatory work has been completed, vacuum pumps, not illustrated, which evacuate the annular gap, are connected to the valve bodies10.

In the case of a cable length of approximately 500 m, four valve bodies10are provided in each case at an interval of 100 m. In order to intercept residual gases which are released in the annular gap after evacuation, a getter material may be introduced into the annular gap, preferably during the production of the pumping connections.

FIGS. 2 and 3show a section through the region in which the outer pipe4of the line pipe is removed. A valve body10is welded into a bore in a smooth-walled metal pipe9which is welded at its ends to the ends of the outer pipe4. The valve body10projects into the interior of the smooth-walled metal pipe9and is adapted on its outwardly pointing surface to the rounding of the metal pipe9, so that the outwardly pointing surface of the valve body10is flush with the surface area of the metal pipe9.

The valve body10has a threaded bore10a, into which a screw plug10bis screwed, vacuum-tight. A sealing ring10censures the required sealing-off.

The version illustrated inFIG. 2is suitable for attachment to the end of the line pipe.

FIG. 3illustrates the same version, but, here, the smooth-walled metal pipe9is formed from the two half-shells9aand9bwhich are welded to one another at their longitudinal seams9c. This version is used between the two ends of the line pipe.

The version illustrated inFIGS. 1 to 3shows the state of the line pipe after evacuation. Since there is no appreciable increase in outside diameter, the line pipe can be drawn in great lengths into existing cable ducts. It is particularly advantageous if the regions where the outer pipe4is removed are accessible from outside, that is to say if a manhole, as it is known, or a cable shaft is provided there.

The operation of evacuation or reevacuation will be described in more detail below with reference toFIGS. 4 and 5.

First, an adapter12is placed onto the valve body10and connected, vacuum-tight, to the valve body10by means of screw bolts, not illustrated, which are screwed into corresponding threaded bores, not illustrated, in the valve body10. A sealing ring12aensures the required leak-tightness. A gas lock13known per se is then connected, vacuum-tight, to the adapter12by means of a tension ring14. A sealing ring13ais located at the seam between the adapter12and gas lock13.

The bolt13b, mounted rotatably in the housing of the gas lock13, is lowered and penetrates with its end confronting the valve body10into an orifice, not designated in any more detail, in the screw plug10band releases the latter as a result of rotation.

As illustrated inFIG. 5, after the release of the screw plug10b, the bolt13bis raised together with the latter, with the result that access to the annular gap between the inner pipe2and the outer pipe4or smooth pipe9is freed. A vacuum pump, not illustrated, which is connected to the flange13cof the gas lock13, can then set the evacuation operation in motion.

After the required vacuum has been generated, the bolt13b, together with the screw plug10b, moves downwards and screws the latter into the threaded bore10aof the valve body10again.

Where reevacuation is concerned, it is necessary to evacuate the interior of the gas lock13before the screw plug10bis unscrewed.

There may be no need to remove the adapter12if the evacuation process has been carried out on an already laid line pipe.