GB2042860A - Radiographic examination of pipes - Google Patents

Abstract

In a method and apparatus of radiographing pipes in order to reduce the dangers inherent in the use of high intensity radiation sources while enabling such sources to be used, the provision of a frame (1) which can be fastened around a pipe (4) and which supports an inner frame (20) which is movable circumferentially around the pipe on the main frame. A radiation source holding means (27) is located at one point on the inner frame (20) and a film carrier (41) is located diametrically opposite to that point and is movable axially of the movable frame and the pipe. Suitable control means, including a timer, are provided for sequentially positioning the inner frame at a chosen circumferential location, exposing the radiation source, and moving the film carrier (preferably under mechanical interrelation with the movement of the inner frame). <IMAGE>

Description

SPECIFICATION Radiographic examination of pipes This invention relates to the radiographic examination of pipes or cylindrical tubes.

in cases where it is not possible to have access to the inside wall of a pipe which includes a cylindrical weld it is possible to obtain a radiographic examination of the weld by locating a source of radiation on the outside of the pipe adjacent to the weld and to place a radiation sensitive film on the outside of the pipe opposite to the source of radiation. Three or more exposures are required to achieve complete coverage of the weld. Accordingly, the radiographer is required to move and reposition the various parts of the apparatus after each exposure. In order to reduce the labour costs involved it is desirable therefore to use high intensity radiation sources so as to reduce the length of time of the exposure and therefore the idle time of the radiographer. However the use of high intensity radiation sources brings with it its own particular problems and dangers.

In accordance with the present invention there is provided a method of radiographing a pipe comprising mounting a radiation source on the pipe so that the source is locatable about the external surface of the pipe, holding said source in a first position with respect to the pipe, exposing a first portion of radiation sensitive film located on the outside of the pipe opposite to the radiation source to radiation therefrom, moving said source about the pipe to a second position circumferentially spaced from said first position, and exposing a second portion of radiation sensitive film again located on the outside of the pipe opposite said radiation source to radiation therefrom.

Preferably a single piece of film is moved parallel to the axis of the pipe in order to locate successive portions of the piece of film opposite to said source in the successive said positions thereof, and preferably also, the movement of the film is related to the movement of the radiation source about the pipe between said first and second positions. Preferably the method includes making at least three exposures in relation to the entire circumferential distance of the pipe.

In a preferred embodiment of the invention the exposure time is determined automatically and the radiation source is moved by a motive power means which is triggered by the terminatiqn of the exposure period.

In accordance with the invention also there is provided apparatus for radiographing pipes including means for holding a radiation source and means for mounting said holding means on a pipe for movement of the source about the outer surface of the pipe.

Preferably the apparatus includes a film carrier arranged to be movable with the holding means and located opposite thereto when the holding means is mounted on a pipe. Preferably the film carrier is arranged to be movable parallel to the axis of the pipe upon movement of the holding means around the outer surface of the pipe.

Preferably the movement of the holding means is mechanically inter-related with the movement of the film carrier.

In preferred embodiment of the present invention the radiography apparatus includes a timer for determining the exposure and control means which operate motive power means for moving the holding means after expiry of the exposure period and for determining the movement of the holding means after a required rotation about the pipe and for initiating a new exposure of radiation sensitive film.

In accordance with a further aspect of the present invention there is provided a method of radiographing a pipe comprising, mounting a support frame on the pipe, mounting a radiation source on the frame so that the source is movable thereon so as to be locatable about the external surface of the pipe, holding said source in a first position with respect to the pipe, exposing a first portion of radiation sensitive film located on the outside of the pipe opposite to the radiation source to radiation therefrom, moving said source about the frame and pipe to a second position circumferentially spaced from said first position, and exposing a second portion of radiation sensitive film again located on the outside of the pipe opposite said radiation source to radiation therefrom.

In accordance with a still further aspect of the present invention there is provided apparatus for radiographing a pipe, comprising a support frame mountable about a pipe holding means for a radiation source movably mountable on the frame so that the source is locatable about the external surface of the pipe, and carrier means for radiation sensitive film locatable on the frame opposite to the radiation source holding means and movable therewith about the frame.

The invention will now be further described and illustrated by way of example only with reference to one embodiment of apparatus thereof which is illustrated in the accompanying drawings in which Fig. 1 is a schematic longitudinal side view of the embodiment of apparatus of this invention mounted on a pipe; Fig. 2 is a cross section on the line A-A of Fig.

1; and Fig. 3 is a cross section on the line B-B of Fig.

1.

The figures of the drawing are illustrative only and some parts have been omitted from the various figures for clarity.

A main frame 1 comprises a pair of annular members 2 and 3 which are split along a diameter and have axially aligned adjacent edges of the two halves thereof hinged together and clamping means (not shown) are provided for clamping the other edges of the halves of each of the annular member together when the apparatus is to be secured to a pipe 4. The two annular members 2 and 3 are held in axially aligned spaced relation by a plurality of rods 5 which are connected by brackets 6 to the annular members 2 and 3.

Each annular member 2 or 3 includes a respective axially inwardly directed annular projection 7, 8 which provides radial and axial running tracks 9 and 10 for the wheels respectively 11 and 12 of an inner movable frame 20.

The brackets 6 and the rods 5 are so arranged and positioned that the frame 20 and the various parts thereof and secured thereto are free to move within the frame 1 and coaxially with respect thereto when it is clamped to a pipe 4. Bracing members 1 3 extend between certain of the rods 5.

The inner frame 20 includes two almost semicylindrical sleeve members 21 and 22 which have radially outwardly extending wheel carrying members 23 secured thereto. The members 23 carry the radial positioning wheels 12 and the axial positioning wheels 11 when the apparatus is assembled about a pipe 4. Means 25 are provided for securing the two semi-cylindrical sleeves 21 and 22 together when the apparatus is assembled about a pipe.

The semi-cylindrical sleeve 21 has a central aperture 26 and holding means 27 for a radiation source 28 are located in the aperture 26 by support members 29 for rotation with the sleeve about the pipe. The holding means 27 comprise an outer block 30 of a dense metal which has a cylindrical hole bored therein on a centre line extending parallel to the axis of the pipe 4 and in a position such that the wall of the bore is adjacent to the surface of the block 30 which lies adjacent to the pipe.A substantially solid cylindrical element 31 of dense metal is rotatably mounted in the bore and carries the radioactive source 28 located near the surface of the cylinder 31 so that in one position of the cylinder 31 the source lies substantially in the middle of the block 30 but in a position 180 therefrom the source lies adjacent to the surface of the block 30 which is adjacent to the pipe 4 and aligned with an aperture 32 in the said surface which serves as an accurate coilimating aperture for radiation. A toothed wheel 34 is secured to the end of the cylinder 31 and is rotatable by means of a pneumatically operated piston and cylinder mechanism 35 whose piston carries a toothed segment 36 and cylinder is secured to the block 30.The other semi-cylindrical sleeve 22 has a longitudinal slit 40 therein which is located diametrically opposite the aperture 26 in the sleeve 21 in the assembled condition of the apparatus. Afilm carrier 41 is located radially inwardly of the sleeve 22 and has a boss 42 extending radially outwardly through the slit 40.

The film carrier 41 has a length such that it can be moved longitudinally of the sleeve 22 from a position in which one end of the film carrier 41 lies opposite the aperture 26 in the other sleeve to a position in which the other end of the film carrier lies diametrically opposite the aperture 26, the boss 42 sliding longitudinally along the slit 40 meanwhile.

The boss 42 is formed as a nut and a screw 44 is rotatably engaged in the boss 42 and is mounted in brackets (not shown) which form part of the main frame 20 and are secured to the sleeve 22. Pinions 45 and 46 are secured to the screw 44 at the ends thereof and engage spur gear tracks 1 7 and 18 on the annular members 2 and 3. The screw 44 and the pinions 45 and 46 can be rotated by means of a drive motor 47 whose casing is fixed relative to the inner frame 20.

The film carrier 41 incorporates an air sac (not shown) which can be inflated to press a radiation sensitive film and any lead screens included therewith in a light proof envelope against the outer surface of the pipe in order to ensure good contact between the film and the portion of the pipe, e.g. weld, which is to be examined radiographically. Suitable lead shielding is also included in the inner frame 20 but not shown in the drawings.

Suitable supply lines and control lines for the radiation holding means 27, the motor 47, and the air sack, are included in the apparatus but not illustrated as is a control panel which includes among other things suitable relays and a timer in order that the method of the invention described hereafter can be carried out.

Prior to carrying out the preferred embodiment of the method of the invention which will now be described the apparatus described above is assembled about a pipe 4 in the manner illustrated in the accompanying drawings so that the inner frame 20 is axially guided on and rotatable about the main frame 1 by the wheels 11 and 12 of the frame 20 running on the guide surfaces 9 and 10 of the main frame, the pinions 45 and 46 being in engagement with the gear tracks 1 7 and 1 8 on the main frame. A piece of radiation sensitive film is located in the film carrier 41 and the frame 20 rotated within the frame 1 until the film carrier has adopted the position shown in Fig. 1, namely with one end portion of the film located opposite to the radiation source 28.

The piston and cylinder mechanism 35 is now operated to cause the cylinder 31 to be rotated in the block 30 so that the radiation source 28 is adjacent tote aperture 31 so that radiation is directed towards the end portion of the film carried in the film carrier 41 and located diametrically opposite the aperture 32. At the same time a timer in the control panel is started and at the end of the desired exposure period the piston and cylinder mechanism is reactivated to rotate the cylinder 31 to place source 28 in its entirely shielded position in the centre of the block 30. At the same time the motor 47 is activated to cause the frame 20 to rotate with respect to the frame 1 by relative engagement of the pinions 45 and 46 with the gear tracks 1 7 and 18 and to cause the film carrier 41 to move parallel to the axis of the pipe 4 by relative engagement of the screw 44 in the threaded bore in the boss 42 of the film carrier. The operation of the motor 47 is terminated when the frame 20 and film carrier 41 have respectively rotated through approximately 1 200 and arrived at a position in which the central portion of the film carried by the film carrier lies opposite the aperture 32. The deactivation of the motor can occur by use of reed switches or alternative limit switches suitably positioned.The piston and cylinder mechanism 35 is now activated again to expose the central portion of the film carried by the film carrier 41 to radiation and the entire procedure described above is repeated both for this position of the film carrier and for a further position of the source 28 at a further rotation of the frame 20 through an angle of 1200 and a further longitudinal movement of the film carrier 41 to place the other end portion of the film opposite the aperture 32. At the end of each movement of the frame 20 and film carrier 41 the air sac in the film carrier 41 is inflated to press the film against the pipe.

It will be apparent that the entire radiographing of the tube can be conducted automatically by the control apparatus and that it is not necessary for the operator to concern himself with the operation of the described embodiment of the apparatus once it has been set up on a particular section of pipe. The control apparatus can have alarm systems to indicate when an exposure is about to start and during the course of an exposure when there may be a risk of radiation contamination.

In fact the apparatus and method of the invention as described above have the advantages of allowing precise relative positioning of the source, the weld or other portion of the pipe to be examined and the radiation sensitive film during exposure, the automatic movement of the film and source container between the exposures, a particularly safe operation in that sense that there is no need for the presence of radiographer during the operation and a substantial saving in labour costs. Because the actual operation of photographing the cylindrical portion of the pipe in .its entirety is automatic it is possible to have a single operator who is positioning and setting up a series of these devices in succession and leaving each device to operate automatically as described.

Thus, the operator can be usefully employed for much longer periods. There is the further advantage that the time of the operator being fully occupied there is less emphasis on the need to use high radiation sources to reduce exposure time.

Accordingly, there is a cost reduction since the radiation sources do not need to be replaced as frequently and this is a significant reduction because the radiation intensity is related logarithmically to the half-life of the source material. Furthermore, the use of low intensity radiation sources reduces the risk of radiation contamination.

Claims (14)

1. A method of radiographing a pipe comprising mounting a radiation source on the pipe so that the source is locatable about the external surface of the pipe, holding said source in a first position with respect to the pipe, exposing a first portion of radiation sensitive film located on the outside of the pipe opposite to the radiation source to radiation therefrom, moving said source about the pipe to a second position circumferentially spaced from said first position, and exposing a second portion of radiation sensitive film again located on the outside of the pipe opposite said radiation source to radiation therefrom.

2. A method according to claim 1, wherein a single piece of film is moved parallel to the axis of the pipe in order to locate successive portions of the piece of film opposite to said source in the successive said positions thereof.

3. A method according to claim 2, wherein the movement of the film is determined by the movement of the radiation source about the pipe between said first and second positions.

4. A method according to any of claims 1 to 3, including making at least three exposures in relation to the entire circumferential distance of the pipe.

5. A method according to any preceding claim, wherein the exposure time is determined automatically and the radiation source is moved by a motive power means which is triggered by the termination of the exposure period.

6. Apparatus for radiographing pipes including means for holding a radiation source and means for mounting said holding means on a pipe for movement of the source about the outer surface of the pipe.

7. Apparatus according to claim 6, further including a film carrier arranged to be movable with the holding means and located opposite thereto when the holding means is mounted on a pipe.

8. Apparatus according to claim 7, wherein the film carrier is arranged to be movable parallel to the axis of the pipe upon movement of the holding means around the outer surface of the pipe.

9. Apparatus according to claim 8, wherein the movement of the holding means is mechanically inter-related with the movement of the film carrier.

1 0. Apparatus according to any one of claims 6 to 9, further including a timer for determining the exposure and control means which operates motive power means for moving the holding means after expiry of the exposure period, determines the movement of the holding means after a required rotation about the pipe and initiates a new exposure of radiation sensitive film.

11. A method of radiographing a pipe comprising mounting a support frame on the pipe, mounting a radiation source on the frame so that the source is movable thereon so as to be locatable about the external surface of the pipe, holding said source in a first position with respect to the pipe, exposing a first portion of radiation sensitive film located on the outside of the pipe opposite to the radiation source to radiation therefrom, moving said source about the frame and pipe to a second position circumferentially spaced from said first position, and exposing a second portion of radiation sensitive film again located on the outside of the pipe opposite said radiation source to radiation therefrom.

12. Apparatus for radiographing a pipe, comprising a support frame mountable about a pipe, holding means for a radiation source movably mountable on the frame so that the source is locatable about the external surface of the pipe, and carrier means for radiation sensitive film locatable on the frame opposite to the radiation source holding means and movable therewith about the frame.

13. A method of radiographing a pipe substantially as hereinbefore described with reference to the accompanying drawings.

14. Apparatus for radiographing a pipe substantially as hereinbefore described with reference to the accompanying drawings.