GB2030430A - Radiographic examination of small diameter tubing - Google Patents

Abstract

Panoramic radiographs of small diameter tubing 112 can be obtained by apparatus comprising a radioactive isotope capsule exposure head 110, pneumatically-actuated centring means 160 and a capsule feed mechanism (114) for the head 110. The mechanism (114) has two tubes 130, 132 one within the other defining a gas space (134) therebetween. The centring means 160 is supplied with gas through space (134) and a capsule 84 is positionable in the head 110 by being passed through the inner tube 130. The head 110 is positioned by detecting a reference source 156 incorporated in the head 110. The centring means can include resilient tubular means shown inflated at 160b or spring members (362, Fig. 7) which can be bowed outwardly. <IMAGE>

Description

SPECIFICATION Radiographic tube examination apparatus The invention relates to radiographic tube examination apparatus.

Radiographic examination of tubes, i.e. for defects in welds etc., is preferably performed by positioning a suitable source centrally within the tube at the required location, positioning a radiographic film around the tube at that location and exposing the film to obtain a single "panoramic" view of the location. For large diameter tubes, for example in pipelines, this is relatively easily done. There are apparatuses known as X-ray crawlers which are remote controlled and carry X-ray generating equipment along the pipeline to the require location. The crawlers can be equiped with Geiger-Muller tubes so that their position in the pipeline can be controlled relative to the radioactive reference sources.

However, these crawlers are clearly unsuitable for small diameter tubes, i.e. down to 12 millimetres (mm) in diameter. For such smaller diameter tubes, an apparatus is known in which a head, which is centred by radially-directed springmounted wheels is attached to a rigid guide tube along which a radioactive isotope capsule is passed to a stop in the head. Positioning of the head is achieved by measuring the distance of, for example, the weld from the end of the tube and then inserting the head and rigid guide tube the required distance. This apparatus is limited in that it can only be used to examine welds positioned relatively closely to tube ends and it cannot negotiate bends.

Where this type of apparatus cannot be used, for example a relatively long way down a tube or around a bend in a tube, then the gamma radiographic examination has to be performed externally of the tube. An apparatus by which this can be done has a flexible P.V.C. coated steel tubular member alcng which a radioactive isotope capsule is passed to a stop at the end of the tubular member. With the tubular member in position externally of a welds a radiographic film is positioned on the opposite side of the tube and the capsule is passed along the tubular member to the stop to expose the film. To obtain an overall picture of the weld, at least several exposures have to be made at different positions around the weld. The technique also suffers since the exposures are being made through two wall thicknesses.

It is an object of the invention to provide an apparatus with which a panoramic radiograph of a relatively small diameter tube can be obtained a relatively long way down the tube or around bends in the tube.

Generally, the radiographic tube examination apparatus has a radioactive isotope capsule centralising head incorporating a pneumaticallyactuated centring means and feed mechanism for the head which has two tubes one within the other to define a gas space between them. Gas is fed to the centring means through the gas space and a capsule is positioned in the head by being passed through the inner tube. At least the inner tube is preferably made of low-friction material.

First ends of the tubes are provided with first and second connectors, the first connector being connectable to a supply of pressurised gas and the second connector being connectable to a capsule storage unit. Preferably,the two connectors are combined in a single adaptor member secured to the first ends of the tubes.

The head has a nose member, a low activity radioactive isotope source and an abutment surface located a predetermined distance from the reference source and against which the capsule can abut. Preferably, the source is incorporated in the nose member.

The feed mechanism may have a third reinforcing tube which may be positioned over at least a part of the length of the first and second tubes either internally or externally of the second tube to prevent kinking or other damage to that part of the tubes lying, for example, on the factory floor during use of the apparatus. The second tube is preferably also of low-friction material.

Alternatively, the second tube acts as a reinforcing tube. A third tube of low-friction material may be positioned externally of the second tube.

Preferably, the low-friction material is polytetrafluoroethylene (P.T.F.E.).

Preferably, the reinforcing tube is spiraliy ccrrugated steel tubing.

In one form of the invention, the second ends of the tubes are attached to the nose member, the portions of the tubes immediately adjacent to said second ends forming part of the centralising head.

In a second form of the invention, the second ends terminate in a first adaptor which cooperates with a second mating adaptor on the centralising head, the cooperating adaptors having cooperating gas passages whereby said gas space is in communication with a second gas space difined within said head.

In this second form of the invention, there is also included apparatus which comprises said tubes and also comprises at least two heads having said adaptors, said heads being suitable for different size ranges of tubes to be examined and being interchangeable one with the other.

In one form of the centralising head, a flexible expansible tubular member is located around, and is in sealing engagement at its ends with, the second tube adjacent the second end thereof, or is located around said second form of head and is in sealing engagement with an external wall of the head, the first or the second gas space respectively, being in communication with the interior of said tubular member.

In a second form of the centralising head, flexible spring members are anchored by first ends to an annular anchoring means and by second ends to the cylinder of a piston and cylinder mechanism, the working space of the cylinder being in communication with said first or second gas space whereby pressurisation of said respective space results in the first and second ends of the spring members moving together to effect radially outward bowing of the spring members.

The invention will now be described by way of example only with reference to the accompanying drawings, in which: Fiqure 1 is a schematic perspective view of an apparatus in use; Figure 2 is an enlarged sectional view of the part circled A in Figure 1; Figure 3 is a view similar to Figure 2 but with the centralising head of the apparatus energised; Figure 4 is an enlarged view, partially in section, of a modified form of the feed mechanism; and Figures 5, 6 and 7 are all sectional views similar to Figure 2 but of modified forms of the centralising head of the apparatus.

In Figures 1 to 3, there is shown a centralising head 10 for a radioactive. isotope capsule, a tube 12 in which the head 10 is positioned, a feed mechanism 14 by which the head 1 0 has been fed along the tube 12, a head positioning unit 16, a capsule storage unit 1 8 and a capsule propelling unit 20.

The capsule propelling unit 20 has a motor (not shown) which drives a sprocket wheel (not shown) mounted in casing 22. A handle 24 is provided so that the sprocket wheel can be turned manually in the event of a power failure. The casing 22 has two tubular limbs 26 to which are secured flexible tubes 28. The tubes are secured at their opposite ends to the storage unit 1 8.

Located within the tubes 28 is a spirally-wound steel drive wire (such as shown at 88 in Figure 5).

The drive wire passes through the casing 22 and engages, and is driven by, the sprocket wheel. One end of the drive wire can pass through the storage unit 1 8 and has attached thereto a radioactive isotope source capsule (such as shown at 84 in Figure 5) which contains a radioactive material capable of exposing a radiographic film through the wall of the tube 12 under consideration.

The propelling unit 20 has an indicator (not shown) for indicating how far the drive wire has been paid out and, therefore, gives a guide as to how far along the tube 1 2 the capsule has gone.

The capsule storage unit 1 8 consists of a steel housing containing depleted uranium shielding material. The unit 1 8 has a passage (not shown) passing through it which, when viewed in plan, has two parallel portions forming the passage exits and an angled portion joining the inner ends of the parallel portions. The angle subtended by the angled portion with the parallel portions is such that when the capsule is stored in the angled portion there is no direct radiation path from that portion along the parallel portions to the outside of the unit 1 8.

The feed mechanism 14 has first and second tubes 30 and 32, respectively. The first tube 30 is located within, and has a smaller outer diameter than the inner diameter of, the second tube 32.

Thus, the outer surface of tube 30 and the inner surface of tube 32 define a gas space 34. Both of the tubes are of low-friction flexible material such as P.T.F.E. The low-friction material of the tube 30 allows the capsule to pass through it with the minimum of frictional resistance. The low-friction material of the tube 32 ensures that frictional resistance due to the tube 32 on the tube 12 is kept to a minimum.

First ends, indicated as 36, 38 in Figure 1 , of the tubes 30, 32, respectively, are sealed to an adaptor member 40. The adaptor member 40 has first and second connectors 42 and 44, respectively, which are respectively attached to a pressurised gas supply, for example a compressed air supply, and to the exit from the storage unit 18.

One form of adaptor member is shown in more detail in Figure 4.

The second ends 46, 48 of the tubes 30,32, respectively form part of the centralising head 10.

The second ends 46, 48 are sealed to a nose member 50 of the head. The nose member 50 is preferably of low-friction material such as P.T.F.E.

and has a stem 52, an intermediate stem 54 of increased diameter to which the end 46 of the tube 30 is sealed and a bulbous head portion 55 to which the end 48 of the tube 32 is sealed. A low activity, i.e. a few microcuries of activity, radioactive isotope reference source 56 is incorporated in the bulbous head portion 55 of the nose member 50. The reference source 56 can be typically Cesium 137. The end 58 of the stem 52 of the nose member 50 acts as an abutment surface to stop the capsule a predetermined distance from the reference source.

A flexible expansibel tube 60 of, for example, neoprene rubber is bonded by its ends to the second tube 32 to form a pneumatically-actuated centring means. An aperture (not shown) in the tube 32 interconnects the gas space 34 with the interior of the tube 60. Bonded to the outer surface of the expansible tube 60 are a plurality of image quality indicator (I.Q.I.) wires 62, the use of which per sue are well-known in the art.

Positioned outside the tube 12 is the head positioning unit 1 6. This unit 1 6 consists of a split housing for at least one Geiger-Muller (G.-M.) tube 64 and a collimator 66. The G.-M. tube 64 is provided to position the centralising head 10 by detecting the presence of the reference source 56 in the nose member 50 of the head 10. The G.-M. tube 64 gives a signal to a positive/negative position indicator device 68 shown here for convenience as being mounted on the capsule transport unit 20. Located by the lower wall (as shown) of the unit 1 6 is a piece 70 of radiographic film which is wrapped around the tube 12 so that on exposure a panoramic view of a weld 72 will be obtained.

In use of the apparatus, the following procedure can generally be adopted.

The head positioning unit 1 6 is positioned around the tube sufficiently away from the weld 72 to allow the film 70 to be wrapped around the tube 12 which is then so wrapped. The centralising head 10 is then introduced into the tube 12 and manually pushed along it by the feed mechanism 14 until a reading shows on the indicator device 68. The head 10 is then slowly moved until the device 68 gives a central zero reading.

The operator then introduces air into the gas space 34 and, therefore, to the interior of the expansible tube 60 to expand the tube 60 to locate the head 10 within the tube 12. The operator can then retire to a safe distance as is allowed by the tubes 28 of the capsule propelling unit 20. Operation of the unit 20 causes the capsule to pass along the first tube 30 of the feed mechanism 14. When the capsule hits the abutment surface 58 of the nose member 50, the unit 20 senses an increase in the drive torque and cuts the drive current. The capsule is left in position for a predetermined time to expose the film 70. The exposure period can either be checked by the operator or the de-energisation of the drive current can actuate an automatic timing device.At the end of the exposure period, the drive is reversed to retract the capsule and the apparatus then removed from the tube and the film developed.

The radioactive isotope in the capsule can be typically Thulium 1 70 for wall thicknesses up to 5 mm, Ytterbium 1 69 for wall thicknesses in the range 5 to 10 mm or Iridium 192 also for wall thicknesses up to 10 mm. These isotopes are all high activity sources but range between relatively low to relatively high energy sources over the three examples given.

The feed mechanism 14 can be reinforced to prevent it being kinked or otherwise damaged. The reinforcement can be a third tube made of spirallycorrugated steel tubing (not shown) located either in the gas space 34 or externally over the tube 32 to reinforce the tube 32 over that portion of it which remains outside of the tube 12.

in a modification (not shown), where the diameter of the centralising head 10 or of the tube 12 is such that friction losses on the feed mechanism 14 are not important, an outer tube of low-friction material may not be necessary. For example, the tube 32 may be polyvinyl chloride (P.V.C.) or may be steel as is shown in Figure 4, although in that case a third tube of P.T.F.E. is provided since that feed machanism is intended to be used with different sized heads as is more fully described below.

In a further modification (not shown), a second housing containing at least one G.-M. tube may be positioned around the pipe in an approach position to give an indication of when the source is close to the weld area. This would be in addition to any indication given by the propelling unit 20 which may be inaccurate due to snaking of the feed mechanism 14.

Figure 4 shows a feed mechanism 11 4 attached to a capsule storage unit 118 similar to that described with reference to Figures 1 to 3.

The mechanism 114 has an adaptor 140 which has a first connector 142 attached to a pressurised gas supply line 1 42a and a second connector 144 by which the adaptor member 140 is attached to the unit 1 18. The second connector 144 is formed by an annular flange 144a and an inwardly flanged nut 1 44b, the flange of which engages the annular flange 1 44a and pulls that flange 144a into contact with a bolt member 118a. The bolt member 1 8a has a bore 1 1 8b through which a radioactive isotope capsule can pass.

The adaptor member 140 has a stepped bore 1 40a. A first end 136 of a first tube 130 of the mechanism 114 is sealed in the smallest diameter of the bore 1 40a. A first end 1 38 of a second tube 132 of the mechanism 114 is sealed in the largest diameter of the bore 1 40a. The intermediate diameter portion 1 40b forms the start of a gas space 134 between the tubes 130, 1 32, the connector 142 communicating with the space 134.

The tube 130 is made of P.T.F.E. and the second tube 1 32 is made of spirally-corrugated steel tubing.

A third tube 1 32a made of P.T.F.E. and sorrounding the second tube 1 32 is also provided.

As explained previously, such an outer low-friction material tube may not be necessary. However, in this instance, since the mechanism 114 is intended to be used with different sizes of centralising heads, it is preferred that such a tube is provided.

The second ends 146, 148 of the tubes 130, 132, respectively, are sealed to a internally screwthreaded female adaptor 176. The female adaptor 1 76 is provided with a gas passage 178 and a threaded aperture 180 for receiving a locking screw. The female adaptor 1 76 is enagageable with a cooperating screw-threaded male adaptor 182, 282, 382 on a centralising head as is shown in Figures 5, 6 and 7, respectively. By using cooperating adaptors 180 and 182, the mechanism 114 can be used with a variety of centralising heads, for examples those shown in Figures 5, 6 and 7 and described below.

As shown in Figure 5, the centralising head 110 has a screw-threaded male adaptor 1 82 which has a cylindrical extension 1 82a and a gas passage (not shown) communicating with the gas passage 178 in the female adaptor 176; an inner, P.T.F.E.

tube 131 and a flexible outer, e.g. P.V.C., tube 133 both sealed at one of their ends to the cylindrical extension 1 82a of the adaptor 182; a nose member 1 50 having a reference source 1 56 similar to the nose member 50 and source 56 described with reference to Figures 1 to 3 and to which the tubes 131 and 133 are sealed at their other ends; and a flexible expansible tube 1 60 to which are bonded l.Q.I. wires 162.

The tubes 131 and 133 together define a second gas space 1 34a which is in communication with the gas space 134 in the feed mechanism 114 through the communicating gas passages in the adaptors 1 76 and 182. The tube 133 has an aperture 1 33a which interconnects the second gas space 1 34a and the interior of the expansible tube 1 60.

The expansible tube 1 60 is provided with protective metal end caps 160a.

The expanded shape of the expansible tube 1 60 is shown in ghost outline at 1 60b.

A radioactive isotope capsule 84 having the isotope indicated at 86 is secured to the end of a spirally-wound steel drive wire 88 is shown abutting the abutment surface 158 of the stem 152 of the nose member 150.

The expansible tube 1 60 is typically neoprene rubber and in this embodiment may be 20 mm outside diameter, 80 mm long and a wall thickness of 3.2 mm at its ends and 1.6 mm at its centre. A test expansible tube 1 60 made to these measurements gave consistent centralising of a head within the tube 12. This size of expansibie tube is typically suitable for tubes 12 of inside diameters in the range 22 to 30 mm. Also the head was passed around bends of radius 62.5 mm with a 33 mm inside diameter tube 12 and of radius 120 mm with a 22 mm inside diameter tube 12. The head was passed along tubing which was substantially U-shaped i.e. had two 900 bends spaced apart from one another.

The head 210 shown in Figure 6 is basically the same as that shown in Figure 5 except that it is larger adn has a slightly differently constructed expansible tube shown unexpanded at 260 in ghost outline and expanded at 260b in full outline.

Those parts which are basically the same have been given the same reference number but with a "2"prefix instead of a "1" prefix.

To support the part of the outer tube 233 to which the expansible tube 260 is sealed, a cylindrical plastics member 233b is located internally of the outer tube 233. The member 233b has an air passage 233c.

The head 210 is useful with tubes of a diameter larger than specified in relation to the head 110, for example up to 60 mm.

The expansible tubes 160 and 260 shown in Figures 5 and 6, respectively, have relatively stiff end portions 1 60c and 260c respectively, to resist movement in the direction of the longitudinal axis of the head 210 when it is in its expanded condition. The end portions of the tubes may be stiffened by being thicker, in which case they preferably taper; or by being provided with rubber "fingers", extending in the direction of the longitudinal axis of the tube, the rubber of the fingers being harder than that of the remainder of the tube; or by being otherwise reinforced.

The head 310 shown in Figure 7 has a modified pneumatically-actuated centralising means.

Otherwise it is basically the same as shown in Figures 5 and 6 and similar reference numerals have been used but with a "3" prefix.

In this embodiment, the nose member 350 forms part of the pneumatically-actuated centralising means. The intermediate stem 354 of the nose member 350 is formed by two parts of different diameters the larger of which ends in a grooved annular member 354a which forms the fixed piston of a piston and cylinder assembly in which the cylinder is floating. The annular member 354a has an O-ring seal 354b in its groove.

Extending from the intermediate stem 354 is a locating member 354c for the bulbous head portion 355 of the nose member 350. A gas passage 354d passes through the intermediate stem 354 to interconnect the second gas space 334a with the cylinder working space 334b.

The reference source 356 is also located in the larger diameter portion of the intermediate stem 354 instead of in the bulbous head portion 355 as in the other embodiments.

The bulbous head portion 355 of the nose member 350 is slidable on the locating member 354c. A cylindrical member 3 55a is secured to the bulbous head portion 355 and it has an inwardlyextending flange 355b which slides on the intermediate stem 354 and thereby forms the floating cylinderofthe assembly. The flange 355b has an O-ring seal 355c.

Around the periphery of the flanged end of the cylindrical member 355a are a plurality of slots 3 55d in which are pivotally secured first ends of the l.Q.I. wires 362. The second ends of the l.Q.I.

wires 362 are similarly pivotally fixed in slots 382c provided in the flange 382b of the male adaptor 382.

The supply of gas pressure to the gas spaces 134, 334a and 334b, during use of the apparatus, causes the floating cylinder of the bulbous head portion 355 to move from the position indicated at 355e in ghost outline to the position shown in full.

This movement causes the l.Q.I. wires 362 to bow out from the relaxed position shown in ghost outline at 362a to the position shown in full whereby the head 310 is centralised.

The head 310 is suitable for use with tubes 312 of sizes similar to the head 210 described with reference to Figure 6.

In modifications (not shown), the constructions of the pneumatically-actuated centralising means described with reference to Figures 5, 6 and 7 could be used with the apparatus described with reference to Figures 1, 2 and 3.

Claims (24)

1. Radiographic tube examination apparatus comprising a radioactive isotope capsule centralising head and a feed mechanism therefor, the feed mechanism having first and second tubes of flexible material, the first tube being within, and having an outer diameter smaller than the inner diameter of, the second tube whereby a gas space is defined by the outer and inner surfaces, respectively, of the first and second tubes, first connector means located at or adjacent first ends of the tubes by which said space can be connected to a pressurised gas source, second connector means attached to the first end of the first tube by which that end can be connected to a radioactive isotope capsule storage unit from which the capsule is transportable through the first tube, second ends of the tubes forming part of or being attached to the head, the head comprising a nose member, a low activity radioactive isotope reference source, an abutment surface, against which a radioactive isotope capsule can abut having been transported through the first tube, located a predetermined distance from said reference source and a pneumaticallyactuated centring means.

2. Apparatus according to claim 1, in which the first tube is made of low-friction material.

3. Apparatus according to claim 1 or claim 2, in which the second tube is made of low-friction material.

4. Apparatus according to any preceding claim, in which a third reinforcing tube is positioned over at least a part of the length of the first and second tubes either internally or externally of the second tube.

5. Apparatus according to claim 1 or claim 2, in which the second tube acts as a reinforcing tube.

6. Apparatus according to claim 5, in which a third tube made of low-friction material, is positioned externally of the second tube.

7. Apparatus according to any claim of claims 2, 3 or 6, in which the low-friction material is polyetrafluoroethylene.

8. Apparatus according to claim 4 or claim 5, in which the reinforcing tube is spirally-corrugated steel tubing.

9. Apparatus according to any preceding claim, in which said reference source is incorporated in the nose member.

1 0. Apparatus according to any preceding claim, in which the second ends of the first and second tubes are attached to the nose member, the portions of the tubes immediately adjacent to said second ends forming part of the centralising head.

11. Apparatus according to any claim of claims 1 to 9, in which the second ends terminate in a first adaptor which cooperates with a second mating adaptor on the centralising head, the cooperating adaptors having cooperating gas passages whereby said gas space is in communication with a second gas space defined within said head.

12. Apparatus according to claim 11, in which at least two heads having said adaptors are provided, said heads being suitable for different size ranges of tubes to be examined and being interchangeable one with the other.

1 3. Apparatus according to any preceding claim, in which the pneumatically-actuated centring means comprises a flexible expansible tubular member either located around, and in sealing engagement at its ends with, the second tube immediately adjacent the second end thereof or located around, and in sealing engagement at its ends with, an external wall of the head intermediate the nose member and the adaptor, the first or the second gas space, respectively, being in communication with the interior of said tubular member.

14. Apparatus according to claim 13, in which the expansible tubular member has end portions which are relatively stiffer than the central portion intermediate said end portions whereby said end portions provide resistance to movement in the direction of the longitudinal axis of the head when the expansible tubular member is in its expanded condition.

15. Apparatus according to claim 1 3 or claim 14, in which a plurality of image quality indicator wires are secured to the expansible tubular member substantially parallel to the longitudinal axis of the head.

16. Apparatus according to any claim of claims 1 to 12, in which the pneumatically-actuated centring means comprises flexible spring members and a piston and cylinder mechanism, the spring members being anchored by first ends to an annular anchoring means secured to the head and by second ends to said mechanism, the working space of the cylinder being in communication with said first or second gas space whereby pressurisation of said respective space results in the first and second ends of the spring members moving together to effect radially outward bowing of the spring members.

17. Apparatus according to claim 16, in which the second ends of the spring members are secured to the cylinder of said mechanism.

1 8. Apparatus according to claim 17, in which the nose member forms said mechanism and comprises a stem having an annular member at one end and a locating member extending from that end, a bulbous head portion slidable on said locating member, a cylindrical member secured to the bulbous head portion and slidably on the annular member, the cylindrical member having an annular inwardly extending flange in sliding engagement with the stem and a gas passage extending through the stem to connect the working space of the cylinder to the first or second gas space, the working space of the cylinder being defined by the stem, the annular member, the cylindrical member and the annular flange.

19. Apparatus according to any claim of claims 1 6 to 18, in which the spring members are image quality indicator wires.

20. Apparatus according to any preceding claims, in which the abutment surface comprises an end surface of a stem forming part of the nose member.

21. Apparatus according ta claim 1 substantially as hereinbefore described with reference to Figures 1 to 3 of the accompanying drawings.

22. Apparatus according to claim 1, substantially as hereinbefore described with reference to Figures 1 to 3 of the accompanying drawing as modified by any one of the Figures 5 to 7 of the accompanying drawings.

23. Apparatus according to claim 1, substantially as hereinbefore described with reference to Figure 4 and to any one of Figures 5 to 7 of the accompanying drawings.

24. Apparatus according to claim 1, substantially as hereinbefore described with reference to Figure 4 and to Figures 5 and 6 of and to Figures 5 and 7 of the accompanying drawings.