GB2143936A - Apparatus for freezing a medium flowing through a pipe in a nuclear installation - Google Patents

Abstract

Apparatus for freezing a medium flowing through a pipe in a nuclear installation comprises a tongs-like head with two jaws (22,23) which can be clamped round the pipe and which are joined together by a hinge (24). A chamber is formed in each of the jaws (22,23) and can be supplied, through connections (29), with a liquid refrigerant which flows out through a plurality of radial holes (27) onto the surface of the pipe to be frozen and evaporates thereby cooling the pipe and freezing the medium flowing through the pipe. The free ends of the jaws (22,23) preferably taper to assist engagement of the pipe. A motor may be provided to close the jaws (22,23). <IMAGE>

Description

SPECIFICATION Apparatus for freezing a medium flowing through a pipe in a nuclear installation The invention relates to apparatus for freezing a medium flowing through a pipe in a nuclear installation.

In maintenance work within a nuclear installation it may be necessary, to repair a pipeline, to exchange a piece of the pipe of the pipeline. Before the pipe can be severed, the medium flowing in the pipeline has to be frozen into a frost plug adjacent the cutting position. The pipeline can then be sawn through adjacent the frost plug. The frost plug acts as a sealing element.

As a means for releasing joins in radioactive pipelines, it is known from German Patent Specification No. 12 37 707 to fill a pipe with a casting material at the junction. The casting material cools into a sealing plug which bonds the residual radioactive particles and which is cut through at the junction to sever the pipe.

Various kinds of apparatus for freezing pipes with medium flowing through them are known. They are sometimes described as 'frost tongs'. One apparatus of this kind is known from German Patent Specification No.

23 30 807. It comprises a handle with an annular portion in which an annular chamber is constructed. The chamber can be supplied with a refrigerant from a gas-forming pressurized liquid source via an inlet and an outlet.

The outer wall and side walls of the annular chamber are made integrally of a material with the elasticity of rubber. They contain a slot extending parallel with the pipe, through which the pipe can be inserted into the rubber member forming the annular chamber, by stretching the walls. The whole annular portion containing the chamber is constructed as a self-supporting rubber unit for tightly enclosing the pipe to be frozen. The outlet from the annular chamber communicates with the atmosphere.

This apparatus has the disadvantage that the annular chamber made of rubber can easily become brittle. Nor can the known apparatus conveniently meet a requirement for two frost plugs to be made quickly at a distance away from one another since the rubber clings to the pipe at the freezing temperatures utilized, approximately minus 1 96'C.

A further disadvantage of the apparatus disclosed in German Patent Specification No.

23 30 807 is that it is not suitable to place on pipes in a nuclear installation by remote operation. However, remote operation is an essential prerequisite in radioactive rooms or cells of nuclear installations.

According to the invention there is provided apparatus for freezing a medium flowing through a pipe in a nuclear installation, comprising a tongslike head with a pair of jaws which are joined together by a hinge and can be engaged around the pipe, each of which jaws has a chamber therein which can be supplied with a liquid refrigerant wherein the jaws are made of metallic material, are curved to correspond to the diameter of the pipe to be frozen and are provided on their inner faces with a plurality of radial outlet holes through which refrigerant supplied to the chambers can pass to atmosphere.

Such apparatus can be suitable for use in nuclear installations and can enable a pipe with a medium flowing through it to be frozen quickly and reliably at two frost points.

When the apparatus has been engaged on a pipe to be frozen, the chambers of the two jaws are supplied with liquid refrigerant. The refrigerant is passed through the radial holes in the two jaws onto the surface of the pipe, where it evaporates. A high freezing speed can be attained, enabling two frost plugs, which between them define a length of pipe to be exchanged, to be made rapidly one after the other.

Advantageously the radial holes are arranged in a plurality of rows parallel to the axis of the pipe, and are connected in each row by a groove extending in an axial direction. In this way optimum contact can be established between the refrigerant and the surface of the pipe.

Preferably each of the jaws of the tongs tapers away in thickness towards it free end.

Such a construction can facilitate engagement of the tongs on the pipe to be frozen.

An outer end portion of each jaw can be fitted with a metal which conducts heat well, preferably up to the position at which the shaping of the jaw to fit round the pipe begins. The casting of material into the tips of the jaws prevents the cavities therein from filling accidentally with the liquid refrigerant.

The invention is diagrammatically illustrated by way of example in the accompanying drawings, in which: Figure 1 is a perspective view of a first embodiment of mechanically actuated freezing apparatus according to the invention; Figure 2 is a detail, showing a tip of a jaw of the apparatus of Fig. 1 in cross section; Figure 3 is a perspective view of a second embodiment of freezing apparatus according to the invention; Figure 4 is a perspective view of a third embodiment of freezing apparatus according to the invention, appropriate for crane manipulation; Figure 5 shows the open position of the jaws of the apparatus shown in Figs. 3 and 4; and Figure 6 shows the freezing apparatus illustrated in Fig. 5, in a position in which it is clamped round a pipe by the closed jaws.

Freezing apparatus shown in Fig. 1 has a manipulating block 7 whereby the apparatus can be engaged by a remotely operated, powered manipulator. Two connecting plates 8 are secured to opposite sides of the block 7.

The two plates 8 are joined together by stabilising cross struts 9. The free ends of the connecting brackets 8 form a support and a fulcrum 11 for two pairs of levers 12 and 13 and a connecting bolt 14. Each free end of the pairs of levers 12 and 13 forms a fulcrum 15 and 16 respectively for two further pairs of levers 17 and 18. Connecting bolts 19 and 20 are disposed at the fulcrums 15 and 16.

The ends of the pairs of levers 17 and 18 are welded rigidly to tong-like jaws 22 and 23 and the two jaws 22 and 23 are linked by a hinge 24.

As a result of this construction, a set-down pressure exerted on the open jaws 22 and 23 seated on a pipe, via the manipulating block 7 and the connecting brackets 8, in the direction of the arrow B, will cause the jaws 22 and 23 to close. If the set-down pressure in the direction of the arrow B is maintained the pairs of levers 12 and 13 at the fulcrums 15 and 16 of the stationary pairs of levers 17 and 18 will be moved beyond an imaginary horizontal line of the coupling point 11, far enough towards the hinge 24 to produce a self-clamping effect. The self-clamping effect brings the two jaws 22 and 23 into optimum contact with the surface of the pipe to be frozen.

The jaws 22 and 23 are hollow and thus each form an annular chamber 25 of semicircular shape. The chambers 25 comunicate with the atmosphere through radial holes 27 formed in the inner surfaces 26 of the jaws 22 and 23. A liquid refrigerant, preferably N2, flows to and evaporates at the surface of the pipe, via the holes 27 and passages 28 which are cut into the two inner surfaces 26 of the jaws in an axial direction; the refrigerant having been supplied to the jaws 22 and 23 from a source via connections 29.

When a frost plug has been formed in the pipe to be frozen, the jaws 22 and 23 are opened by increasing the application pressure in the direction of the arrow B, which terminates the self-clamping effect. The freezing apparatus can be set down again on the pipe immediately at a further position to be frozen.

Free end portions 31 of the jaws 22 and 23 which taper away in thickness are filled with metal 32, preferably lead (Figure 2), up to the level of the inner surface 26 containing the radial holes 27, which represents the diameter of the pipe to be frozen up. This is to prevent the cavities, which are formed by moulding in the tips of the jaws 22 and 23, from being accidentally filled with N2.

In the freezing apparatus shown in Fig. 3, two jaws 41, 42 are movably connected by a hinge 43. They ca be opened and closed by means of an electric motor 44 and a threaded spindle 45, through an appropriate lever arrangement 46 designed to be self-clamping.

The frost tongs have a manipulating block 47 which can be coupled to the grab (not shown) of a remotely controlled powered manipulator. The block 47 is linked to lateral brackets 49 by two connecting brackets 48.

The lever construction 46 comprises four pairs of levers 51, 52, 53, 54 which are mounted in movable bearings 43, 55, 56, 57 (Fig. 5).

The lower ends of the lateral brackets 49 mount the hinge 43 of the two jaws 41, 42.

The electric motor 44 is fixed between the lateral brackets 49 below the manipulating block 47. By means of the threaded spindle 45, which is coupled to the motor shaft and mounted in a bearing member 58, the motor moves the two jaws 41, 42 by way of the lever arrangement 46. The frost tongs can be moved from the 'open' position to the 'closed' position by a change in the rotary direction of the electric motor 44. Connecting cables 59 are provided for the motor 44.

The size of the jaws and the leverage are designed according to the diameter of the pipe to be frozen, so that optimum clamping contact is obtained on the surface of the pipe.

The jaws 41, 42 have connections 60 through which the liquid refrigerant, N2, is supplied. The chambers formed in the jaws 41, 42 communicate with atmosphere through radial holes 61 in the inner surfaces 62 of the jaws.

The modified embodiment of frost tongs operated by an electric motor shown in Fig. 4 in equipped for manipulation by a remotely operated crane. A carrying cowl 72 is engaged on lateral brackets 71 and has a carrying loop 73 mounted on its upper surface. In the lower region of the lateral brackets 71 a four-part, plate-like cross strut arrangement 74 is mounted around the brackets, and a further carrying loop 75 for manipulation by a remotely operated crane is arranged on one side surface thereof.

In Fig. 5 the frost tongs are shown in the extreme open position. Fig. 6 shows the tongs moved by the electric motor to the closed position. The necessary movements of the lever arrangement can be seen diagrammatically from these two views.

The mode of operation of the embodiment of the invention operated by an electric motor will now be explained in detail.

The frost tongs are either taken hold of at the manipulating block 47 (Fig. 3) by the grab tools of a powered manipulator, or suspended from the carrying loops 73, 75 (Fig.

4) by means of a remotely operated crane.

The tongs are assumed to be in the extreme 'open' position (Fig. 5). They are placed on a pipe 81 to be frozen by means of the powered manipulator or the crane. The electric motor 44 turns the threaded spindle 45 coupled to it, and thereby lowers the end piece 45 of the spindle provided with the central bearing 55. The lever arrangement 46 is thereby moved, in such a way that the two upper pairs of levers 51 and 52 extend horizontally and, acting through the bearings 56, 57, push out the lower pairs of levers 53, 54 fixed to the jaws 41, 42. In the end position of Fig. 6, the tongs are fully closed and clamped fast on the pipe 81 to be frozen.

When the jaws 41, 42 have closed around the pipe to be frozen, the chambers in the two jaws 41, 42 are supplied with the liquid refrigerant, N2, via the two connections 60.

The liquid refigerant N2 flows through the radial holes 61 in the inner surfaces 62 of the two jaws and onto the enclosed surface of the pipe, where it evaporates. A temperature of minus 196 C can be reached in an extremely short time. Monitoring of the temperature of the pipe and disconnection of the supply of refrigerant can be effected in known manner by means of a magnetic view (not shown).

When a frost plug of the desired size has been formed in the pipe, the jaws 41, 42 of the tongs are opened by energising the electric motor 44 to rotate with the reverse direction and to move the threaded spindle 45 upwards. The central fulcrum of the movable bearing 55 is thereby moved upwards and pulls the upper pair of levers 51, 52 upwards out of the horizontal position. A pivoting movement about the fulcrum formed by the hinge 43 is exerted on the lower pair of levers 53, 54 via the coupling points of the movable bearings 56, 57, leading to an opening of the two jaws 41, 42. An abutment member 82 is arranged between the lower pair of levers 53, 54 to define the extreme 'open' position. The frost tongs are thus opened and can be set down on the pipe at the next place to be frozen.

Claims (9)

1. Apparatus for freezing a medium flowing through a pipe in a nuclear installation, comprising a tongs-like head with a pair of jaws which are joined together by a hinge and can be engaged around the pipe, each of which jaws has a chamber therein which can be supplied with a liquid refrigerant wherein the jaws are made of metallic material, are curved to correspond to the diameter of the pipe to be frozen and are provided on their inner faces with a plurality of radial outlet holes through which refrigerant supplied to the chambers can pass to atmosphere.

2. Apparatus according to claim 1, in which the radial holes are arranged in a plurality of rows parallel to the axis of the pipe, and are connected in each row by a groove extending in an axial direction.

3. Apparatus according to claim 1, in which each of the jaws of the tongs tapers away in thickness towards its free end.

4. Apparatus according to claim 1 or claim 2, in which each of the jaws of the tongs tapers away in thickness towards its free end and an outer end portion of each jaw is filled with a metal which conducts heat well.

5. Apparatus according to claim 1, in which the jaws can be pivoted apart and together by means of a lever arrangement, and the lever arrangement can be acted on, via a common coupling position over the hinge by a force acting in the common plane of the hinge and the coupling point.

6. Apparatus according to claim 5, in which the coupling position is connected by a pair of connecting brackets to a manipulating block appropriate for grasping by a remote handling machine.

7. Apparatus according to claim 5 or claim 6, in which the tongs include a threaded spindle, which is coupled to an electric motor and arranged to act on the lever arrangement.

8. Apparatus according to claim 6, in which the connecting brackets are equipped with carrying loops for manipulation by a crane.

9. Apparatus for freezing a medium flowing through a pipe in a nuclear installation substantially as hereinbefore described and illustrated with reference to the accompanying drawings.