GB2109660A

GB2109660A - Radiographic examination apparatus

Info

Publication number: GB2109660A
Application number: GB08228533A
Authority: GB
Inventors: Stanley Beetham; John Hogg
Original assignee: Northern Engineering Industries PLC
Current assignee: Rolls Royce Power Engineering PLC
Priority date: 1981-11-07
Filing date: 1982-10-06
Publication date: 1983-06-02
Also published as: GB2109660B

Abstract

Tube examination apparatus has a head 48, actuated by fluid pressure, for centralising a radioactive source 40. Preferably, the source 40 is shielded during transport from its storage unit to the head 48. A body 12, attached to a drive-wire 20, has hollow shield-parts 28, 30, which define a radiation window therebetween, and closure shield- parts 32, 34, which have source 40 located therebetween and which are a sliding fit in the parts 28, 30. A spring 44 biases parts 32, 34 towards a first position, relative to body 12, in which the source 40 is enclosed. When the body 12 moves along a guide 10 in the head 48, the part 32 engages an abutment surface 52 which arrests the parts 32, 34. Further movement of the body 12, to engage an abutment surface 50, causes relative movement between the parts 28, 30 and 32, 34 to a second position relative to body 12 in which the source 40 is exposed at the window. Retraction of the body 12 along the guide 10 allows the spring 44 to restore the parts 28, 30, 32, 34 to the first position. <IMAGE>

Description

SPECIFICATION Radiographic examination apparatus The invention relates to radiographic examination apparatus for examining tubes.

One form of such apparatus is described and claimed in UK patent application No. 78 37515 (Publication No. 2030430 A). That apparatus comprises a pneumatically-actuated centralising head and a feed mechanism which has two coaxial tubes defining a gas space between themselves for gas supply to the head. A radioactive source within a capsule is passed from a shielded storage unit through the inner of the two tubes until it abuts an abutment surface in the head which is located at a predetermined site within a welded join between lengths of tube.

Film surrounding the welded join is then irradiated by the source.

Such apparatus suffers from the disadvantage that the shielding effect of the source containment during a tube examination is inadequate for the proper protection of personnel so that it is necessary for personnel to leave the vicinity of the tube while it is being examined.

It is an object of the invention to provide apparatus in which the radioactive source is properly shielded at least until the source is at the predetermined site at which examination is required.

According to the invention, radiographic tube examination apparatus comprises a guide leading to abutment means, a body movable within the guide, a capsule, containing a radioactive source, located within the body and shield means which are resistant to nuclear radiation and which are carried by the body, the shield means comprising parts which co-operate in first relative positions to enclose the capsule but which in second relative positions expose the capsule, the first relative positions of the parts being changed to the second relative positions when the movement of a part or parts with the body is arrested by the abutment means, another part or parts moving with the body against a spring until the body is arrested by the abutment means, retraction of the body from the abutment means allowing the spring to restore the parts to their first relative positions.

Preferably, the shield means comprises four parts, two being spaced-apart aligned hollow parts which define a radiation window therebetween and the other two being closure parts which have the capsule located therebetween and which are sliding fits within the hollow parts.

Radiographic tube examination apparatus will now be described to illustrate the invention by way of example only with reference to the accompanying drawings, in which: Figure 1 is a longitudinal section through part of radiographic examination apparatus showing a radioactive source which is exposed; and Figure 2, is a schematic longitudinal section through part of the apparatus shown in Figure 1 but showing the radioactive source completely shielded.

The apparatus includes a hollow tubular guide 10 which is part of a centralising head described more fully below. The guide 10 is preferably made of a low-friction material such as polytetraflouroethylene (PTFE) or polyurethane.

A tubular hollow body 12 of titanium alloy for example is siidable within the guide 10 and is driven along the guide by mechanism including a helically-wound drive-wire 20.

The body 12 has two cylindrical portions 14 and 1 6, the portion 14 being of smaller diameter than the portion 16. The portion 14 has a wall 1 5 intermediate its ends. The drive-wire 20 is located in the portion 14 on the side of the wall 1 5 remote from the portion 1 6. That part of the portion 14 surrounding the end of the drive-wire 20 is secured thereto by crimping.

The end of the portion 1 6 remote from the portion 14 is internally screw-threaded to receive a closure cap 22 of stainless steel. The cap 22 is screwed into the portion 1 6 and bonded to the portion 1 6. The cap 22 has a central throughpassage 26 which is countersunk at its exterior end.

Shield means of tungsten or lead, for example, are provided within the portion 1 6 of the body 1 2.

The shield means has four parts; two hollow parts 28, 30 and two closure parts in the form of solid cylinders 32, 34. The hollow parts 28, 30 have an internal sleeve 36 which has an external formation to space the parts 28, 30 apart in the body 1 6 to define an annular radiation window.

The closure parts 32, 34 are coaxial with the hollow parts 28, 30 and are close sliding fits within the sleeve 36.

A radioactive source 40 within a cylindrical capsule 42 is located between the closure parts 32, 34. The capsule 42 has a threaded tail screwed into the part 32 and has a rounded nose received in a concave seating in the part 34.

The source 40 is a pellet of the nuclide ytterbium-1 69 (or alternatively of thulium-1 70) and the capsule 42 is of stainless steel and is some 8 millimetres long and 3 millimetres in diameter. Typically, a ytterbium source has a halflife of 30.7 days. The source emits gamma radiation.

A pre-load coil compression spring 44 is trapped between the wall 1 5 in the portion 14 of the body 12 and the part 34 to bias the closure parts 32, 34 towards the stop represented by the cap 22, in which position the capsule 42 and, thus, the source 40 is completely enclosed within the hollow parts 28, 30 closed by the closure parts 32, 34 (as shown in Figure 2).

The body 12 is moved along inside a tubular feed system 46 by the drive-wire 20 in a manner similar to that described in publication No.

2030430 A, for example, until the body reaches the centralising head 48 of the examination apparatus which has already been located at a predetermined site at a welded join between and within two tubes. The centralising head includes the tubular guide 10 and two abutment surfaces 50 and 52. The surface 50 is a surface of a component 54 of the head and the position of the surface 50 determines the final position of the body 1 2 relative to the head. The surface 52 is on the end of a peg 56 which extends along the central longitudinal axis of the guide 10 from the component 54.

As the body 12 advances within the centralising head 48, the peg 56 enters the body 12 through the through-passage 26 in the cap 22 and the abutment surface 52 engages the closure part 32 so as to arrest the closure parts 32, 34 and the capsule 42. Further movement of the body 1 2 in the same direction relative to the head 48 causes further compression of the spring 44 as the hollow parts 28, 30 move relatively to the closure parts 32, 34. When the body 12 engages the abutment surface 50, further movement of the body 12 is prevented. The further movement of the body 12 has brought the closure parts 32, 34 to the position relative to the hollow parts 28, 30 which is shown in Figure 1, in which the source 40 within the capsule 42 is exposed at the radiation window.

Gamma radiation from the source 40 within the capsule 42 passes through the weld under examination and reaches a piece of photographic film arranged around the weld on the outside of the tubes, which are connected by the weld. The quality of the weld is judged by the appearance of the exposed film.

Retraction of the body 12 from the centralising head allows the spring 44 to relax to its original position to restore the position of the closure parts 32, 34 relative to the hollow parts 28, 30 to that shown in Figure 2, in which the capsule once more is fully enclosed.

The hollow part 30 of the shield means limits the escape of radiation lengthwise of the body 12 to a relatively low level. That is particularly advantageous when the externai equipment associated with the tube examination apparatus, i.e. the head locating device and the film holder, is also substantially shielded. In that instance, even when the film is being irradiated through the tube, only slight radiation escapes from the examination site and personnel can continue to work relatively closely to the examination site.

In a modification (not shown) the hollow parts may be movable relatively to the body instead of the closure parts with suitable re-arrangement of the spring.

The centralising head 48 also comprises a ring made up of two parts 58, 60 brazed together secured in sealed relationship to an elastomeric expansible tube 62. Pressurised air can reach the ring 58, 60 through passages in a ring made up of two parts 64, 66 brazed together at the end of the feed system 46 which communicate with an annular space 68 between a corrugated tube 70 and an inner tube 72 of the feed system 46.

The space 68 is connected to a source of pressurised gas (not shown), for example air. The air passes through the passages in the rings 64, 66 and 58, 60 and enters a space between the guide 10 and the expansible elastomeric tube 62.

The head 48 is passed through a tube assembly including the welded joint to be examined and is centralised in the tube by passing pressurised air into the tube 62 to expand the tube 62 to centralise the head, in a manner similar to that described in publication No.

2030430 A.

The head 48 includes an externally-radiussed annular end-member 74 of PTFE which facilitates travel of the head 48 within the tube.

A housing 76 is secured by a spring pin 78 in a ring 80 mounted within the end-member 74. The housing 76 includes a hollow spigot 82 containing a low-activity radioactive reference source (not shown) retained by a screw 84.

Claims

1. Radiographic tube examination apparatus comprising a guide leading to abutment means, a body movable within the guide, a capsule, containing a radioactive source, located within the body and shield means which are resistant to nuclear radiation and which are carried by the body, the shield means comprising parts which co-operate in first relative positions to enclose the capsule but which in second relative positions expose the capsule, the first relative positions of the parts being changed to the second relative positions when the movement of a part or parts with the body is arrested by the abutment means, another part or parts moving with the body against a spring until the body is arrested by the abutment means, retraction of the body from the abutment means allowing the spring to restore the parts to their first relative position.

2. Apparatus according to claim 1, in which the shield means comprises four parts, two being spaced-apart aligned hollow parts which define a radiation window therebetween and the other two being closure parts which have the capsule located therebetween and which are sliding fits within the hollow parts.

3. Apparatus according to claim 2, in which the hollow parts are movable with the body and the closure parts are movable relative to the body between the first and second relative positions.

4. Apparatus according to any preceding claim, in which the body is attached to an end of a drivewire.

5. Apparatus according to any preceding claim, in which the spring is a compression spring located under pre-load between a wall of the body and one of the parts.

6. Apparatus according to any preceding claim, in which the guide and the abutment means comprise parts of a centralising head for locating the source centrally within a tube.

7. Apparatus according to claim 6, in which the head has centralising means operable by fluid pressure.

8. Radiographic tube examination apparatus according to claim 1 substantially as hereinbefore described with reference to the accompanying drawings.