GB1579047A

GB1579047A - Method and apparatus for examining objects by means of radiation in particular of weld connections

Info

Publication number: GB1579047A
Application number: GB46906/77A
Authority: GB
Original assignee: Neratoom BV
Current assignee: Neratoom BV
Priority date: 1976-11-11
Filing date: 1977-11-10
Publication date: 1980-11-12
Also published as: IT1087884B; DE2749879A1; NL171200C; FR2370975A1; NL171200B; NL7612537A

Description

(54) IMPROVEMENTS IN OR RELATING TO A METHOD AND AN APPARATUS FOR EXAMINING OBJECTS BY MEANS OF RADIATION, IN PARTICULAR OF WELD CONNECTIONS (71) We, B. V. NERATOOM, a Dutch body corporate of Laan van Nieuw Oost India 129-135, The Hague, the Netherlands, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement::- The present invention relates to a method of examining objects by means of radiation, in particular weld connections, in which an object to be examined is located between a source of radiation and a film responsive to radiation from the source, after which the object, and via the object the film, is irradiated with radiation from the source while the film, after exposure, is developed, as well as to an apparatus for use in this method.

In conventional methods of radiographic examination of weld connections and in general of objects to be examined, a source of radiation is commonly disposed in a stationary and spaced apart relationship from the object and a film disposed at the other side of the object is exposed to radiation from the source. An optimal investigation of objects is not quite possible in this manner, since in particular faults in the material of the objects which are at least substantially parallel to the incident radiation, are very difficult to detect. In the examination of weld connections considerable weld defects, such as cracks and bonding errors may thus be missed as a result of their location relative to the radiation direction.Another drawback of the prior techniques is that upon application of a stationary source of radiation, various parts of an object to be examined are impinged by the radiation at different angles, as a result of which the material thickness to be irradiated differs from place to place, even with objects having an identical overall thickness. Usually a difference in material thickness to be irradiated of maximum 10% is allowable. With special techniques this tolerance however is not more than 6%, as a result of which several exposures will have to be made of an object in order to achieve a proper examination resultl It is the object of the present invention to provide a method in which the above drawbacks are not or practically not encountered.

Also the invention has the object to provide an apparatus suitable for application in the method according to the invention.

According to the invention there is provided a method of inspecting objects, in particular weld connections, by means of radiation in which the object to be examined is positioned between a source of radiation and a film responsive to radiation from the source with a slotted collimator being arranged between the source of radiation and the object after which the object and via the object the film is irradiated by radiation from the source, and the film, after exposure, is developed, the source of radiation and the slot, during exposure, being moved in synchronism with each other in a direction substantially perpendicular to the slot, while simultaneously the path of radiation from the source is reciprocated back and forth in a direction parallel to the slot.Preferably a second slotted collimator is disposed between object and film and during the examination is moved synchronously with the first slotted collimator.

Upon application of the method according to the present invention the radiation by means of which the object is examined may be radiation from a radio-active source or X-rays from an X-ray tube. Which type of radiation is employed is only of minor importance for the principle of the method according to the present invention. Upon use of a radio-active isotope as radiation source, it is slowly moved in longitudinal direction over the object to be examined, e.g.

a weld. The radiation beam is restricted by means of a narrow slotted collimator.

Simultaneously the radiation source is reciprocated transversely to the direction of the slow movement. When X-ray tube is used a special tube may be employed comprising deflection coils for reciprocating the electron beam in the tube across the anode so that a reciprocating beam of X-rays emerges from the tube.

One embodiment of an apparatus for using the method according to the present invention comprises a container with a radio-active source of radiation arranged in a housing which is adapted to permit the emission of radiation from the source along a predetermined path, a slotted screen arranged spaced apart from the housing for transmitting radiation from the source therethrough, means for moving the housing and the screen in a direction perpendicular to the extent of the slot, and means for reciprocating the container with the source of radiation in a direction parallel with the slot and substantially perpendicular to the direction of movement of the housing and screen.

The housing for the radiation source may comprise in a known manner an envelope of plate steel wherein there is disposed a protective coating of lead or of used uranium.

In the protective material there is accommodated a space for the isotope container, which space is so arranged that the isotope container, driven by an electric motor, attached to the housing, can perform a reciprocating or rotating movement. The electric motor, if desired, may also serve for moving the housing. Naturally it is also possible to provide a construction wherein the isotope container is fixedly attached in the housing and wherein the entire housing performs a reciprocating or rotating movement.

As radiation source may serve any suitable isotope, the choice of isotope will depend upon the thickness and the material of the object to be irradiated. Suitable isotopes are e.g. Ir 192 and Co 60. The slotted collimators used in the apparatus may comprise lead, tantalum, used uranium or another suitable material. A first collimator is so spaced apart from the housing that an object to be examined is arranged during the examination at the collimator side facing away from the housing. The radiation impinging upon the object is collimated by the collimator to a comparatively narrow beam, in order to also limit scattered radiation from the object.

Preferably a second collimator is employed which is so arranged that it is disposed between the object to be examined and the film to be exposed. Said second collimator also prevents scattered radiation from reaching the film.

The collimators may be mounted directly to the housing of the radio-active source or they may be attached together with the housing to a supporting member.The construction at any rate is such that housing and colli mator or collimators may be noved synchron ously with each other.

Another embodiment of an apparatus for using the method according to the present invention comprises an X-ray tube with a filament or cathode, an anode positioned spaced apart from the cathode, means for focussing in operation an electron beam being emitted from the cathode, means for deflecting the focussed electron beam, as well as means for energizing the deflection means such that the electron beam strikes the anode in a reciprocating movement, at least one slotted screen spaced from the X-ray tube, said slot extending parallel to the path of electrons along the anode so that the reciprocating X-ray beam emitted from the anode can pass therethrough and means for moving the X-ray tube and screen in a direction substantially perpendicular to the longitudinal direction of the slot in the screen simultaneously with operation of the beam deflecting means.

The X-ray tube used in the above apparatus is of a special type having an anode or a target structure having an elongated target surface. In the X-ray tube there is conventionally formed an electron beam which is subsequently formed by means of an electronic lens or focussing coil to a substantially point beam. Said point electron beam is moved across the target structure by means of the deflection coils, thus producing a reciprocating X-ray beam. In the embodiment of the apparatus with X-ray tube at least one slotted collimator is used in a manner analogous to the embodiment with radio-active source.

The invention will now be explained, by way of example, with reference to the accompanying drawings, wherein: Fig. 1 is a diagrammatic side view of an embodiment of an apparatus for application of the method according to the invention; Fig. 2 shows in cross-section a part of the apparatus according to Fig. 1; Fig. 3a diagrammatically shows the examination of a weld connection by means of a stationary source: Fig. 3b shows analogously the examination with a moving source according to the invention; Fig. 4a is a diagrammatic side view of the major parts of an X-ray apparatus for application of the method according to the invention; Fig. 4b is a diagrammatic top view of the same parts as shown in Fig. 4a; and Fig. 5 shows a part of an object to be examined, indicating how the object is scanned through application of the method according to the invention.

Fig. 1 diagrammatically shows an apparatus for X-ray examination of an object. The apparatus comprises a base 1 which may, as shown, be in the form of a plate. On the base 1 there is fixed a table 2 on which table 2 there is to be disposed film to be exposed.

On the base 1 there is furthermore arranged a motor 3 serving for moving a system 4 accommodating a source providing radiation for exposing the film to be positioned on table 2. The system 4 comprises a housing 5 accommodating the source as will be explained in Fig. 2. Housing 5 is secured by means of a rod 8 to a side plate 9. To the side plate 9 there is furthermore attached a screen 6 having a slot, the screen 6 being spaced a slight distance from housing 5 such that the slot is present in a suitable place underneath housing 5, Slightly spaced from the screen 6 and underneath the screen 6 relative to the housing 5, there is disposed a screen 7, likewise provided with a slot and likewise mounted on the side plate 9.The entire system 4 may be moved by means of the motor 3, e.g. in that in the manner diagrammatically shown in the Figure a toothed rod 10 extends from side plate 9 with the teeth on the rod engaging the teeth of a gear 11 attached to the motor 3. It will be clear that for a proper operation of the apparatus the system 4 and/or the rod 10 should be supported or bearing-mounted in some way or other. Such a support or bearing is not shown in the drawings for the sake of simplicity.

Fig. 2 shows a part of the apparatus according to Fig. 1 in cross-section. In particular it is shown how in housing 5 to which rod 8 is attached, there is disposed a radioactive source container 12, which container 12 is connected by a rod 13 to an electric motor 14. The electric motor 14 in operation imparts to the source container 12 a reciprocating movement perpendicular to the plane of the Figure. The supply of the electric motor is not shown but it will be clear that this may be effected in any suitable manner by means of a voltage source to be arranged adjacent the system 4. In housing 5 there is furthermore accommodated a slot 15 through which the radiation from the source in source container 12 can be emitted. The slot 15 is in registry with the slots in screens 6, 7 respectively.It is shown in Fig. 2 how an object 16 may be disposed in the space between screens 6 and 7, while underneath screen 7 there is arranged a film 17 responsive to radiation from the source in the source container 12, the film 17 being disposed on the table 2.

In operation the object 16 to be examined and the film 17 are maintained in a stationary position relative to each other. Movement of the system 4 produces movement of the source and synchronously therewith the screen 6 and the screen 7 relative to the object 16 and the film 17 so that radiation emitting from the source impinges successive parts of film 17 via successive parts of the object 16. Simultaneously the source makes a reciprocating movement in the direction perpendicular to the direction of movement of the system 4, but substantially parallel to the film 17, as a result of which the object and in particular a weld to be inspected in the object is irradiated from different points and the film 17 is exposed in a zig-zag pattern.

Fig. 3a shows how an object 16 has been examined up till now by means of a conventional technique with radiation from a single point. In the object 16 there is shown a weld connection 18 while it is assumed that 19 indicates a welding defect in the weld connection 18. Such a welding defect can usually be detected only if the examining radiation extends substantially parallel along the edge of the weld connection 18 through the object 16. If, as shown, the radiation source 20 is disposed in a stationary position above the weld connection 18, the welding defect 19 will, at the very least, be difficult to detect, since the quantity of material that is irradiated by the radiation prior to impinging upon the film 17 depends very little upon and is barely influenced by the presence of the welding defect 19.

Fig. 3b shows how an object 16 is examined by means of the method according to the present invention. In the object 16 there is present again a weld connection 18, while it is again assumed that a welding defect 19 is present in the weld connection 18. Slightly spaced above the object 16 there is disposed source container 12 from where radiation impinges upon the object through the slot 15 in the housing 5, not shown in Fig. 3b and through the slot in screen 6, which is not shown either. The source container 12 is reciprocated and occupies successively the positions shown in Fig. 3b. It appears therefrom that the radiation impinges in particular upon the weld connection 18 at different points of time and at different angles.From the rightmost position of the source container 12 the radiation impinges upon the weld connection 18 in such a way that the radiation travels along the edge comprising the welding defect 19. The quantity of material that is irradiated at said moment by the radiation, through the presence of the welding defect 19, is less than the quantity of material that is irradiated if the container occupies the leftmost position shown in Fig. 3b. This results in a modified exposure of the film 17 underneath the object 16, which may be detected after development of film 17.

Fig. 4 diagrammatically shows how an X-ray tube may be arranged for application of the method according to the present invention. Fig. 4a is a side view in cross-section of the most essential parts, while Fig. 4b depicts a corresponding top view. The embodiment shown of the X-ray tube comprises an envelope or housing, not shown, accommodating a filament or cathode 21.

Around the end of cathode 21 from which in operation the electron beam 26 is emitted, there is disposed in a conventional manner a static focussing cap 22, which cap already effects a focussing of the electron beam 26. Slightly spaced from the static focussing cap 22 there is present an electronic lens or focussing coil 23 in the X-ray tube. This part effects a subsequent focussing of the electron beam 26. Beam 26 subsequently travels through the system of deflection plates or coils 24 and finally impinges upon anode 25. The electron beam 26 releases a quantity of X-rays from anode 25, which X-rays are emitted as X-ray beam 27 from the X-ray tube. Fig. 4a shows how the X-ray beam 27 impinges upon an object 16 to be examined via a slotted screen 6 and how the radiation traversing the object 16 can impinge upon film 17.If desired, here too, a slotted screen may be disposed underneath the object 16, analogously to what is shown in Fig. 2. The entire X-ray tube shown in Fig. 4 may naturally form part of an apparatus as shown in Fig. 1, instead of housing 5 comprising the source of radioactive radiation.

The deflection plates 24 are so energized that they ensure such a deflection of the electron beam 26 that it reciprocates between the position shown in Fig. 4b by 26a and the position indicated by 26b. The electron beam consequently effects a reciprocating movement in a horizontal plane. The X-ray beam 27 released from anode 25 by the electron beam 26 also effects thereby a reciprocating movement in a substantially vertical plane wherein there is likewise present the slot in the screen 6. When the system 4 (Fig. 1) accommodating the X-ray tube instead of the housing 5, is moved in the above described manner, the object 16 and via the object the film 17 is irradiated according to a zig-zag pattern, which will be further explained in Fig. 5.It is observed that the means for energizing the X-ray tube and for energizing the various parts in the X-ray tube, such as the focussing coil 23 and the deflection plates or coils 24, may be of a conventional type.

Fig. 5 shows a top view of a part of an object 16 comprising a weld connection 18.

On the object is shown the zig-zag pattern traversed by the radio-active or X-radiation.

It will be clear that this pattern in actual fact is not visible on the object 16, but a similar pattern will be realized on film 17 though.

The double arrow 28 indicates the reciprocating movement of the X-ray beam 27 or the beam of radiation from the source container 12. The arrow 29 shows the direction of movement of the entire system 4 (Fig. 1) relative to the object 16. Together these movements result in the zig-zag movement 30. It is clearly shown in Fig. 5 that the weld connection 18 is entirely scanned and is irradiated from different angles, so that all defects in the weld connection are expressed in the exposure of the film disposed underneath the object 16.

WHAT WE CLAIM IS:- 1. A method of inspecting objects, in particular weld connections, by means of radiation in which the object to be examined is positioned between a source of radiation and a film responsive to radiation from the source with a slotted collimator being arranged between the source of radiation and the object after which the object and via the object the film is irradiated by radiation from the source, and the film, after exposure, is developed, the source of radiation and the slot, during exposure, being moved in synchronism with each other in a direction substantially perpendicular to the slot, while simultaneously the path of radiation from the source is reciprocated back and forth in a direction parallel to the slot.

2. A method according to claim 1, wherein a second slotted collimator is disposed between object and film and during the examination is moved synchronously with the first slotted collimator.

3. An apparatus for use in the method according to claim 1 or claim 2, comprising a container with a radio-active source of radiation arranged in a housing which is adapted to permit the emission of radiation from the source along a predetermined path, a slotted screen arranged spaced apart from the housing for transmitting radiation from the source therethrough, means for moving the housing and the screen in a direction per pendicular to the extent of the slot, and means for reciprocating the container with the source of radiation in a direction parallel with the slot and substantially perpendicular to the direction of movement of the housing and screen.

4. An apparatus for use in the method according to claim 1 or claim 2, comprising an X-ray tube with a filament or cathode, an anode positioned spaced apart from the cathode, means for focussing in operation an electron beam being emitted from the cathode, means for deflecting the focussed electron beam, as well as means for energizing the deflection means such that the electron beam strikes the anode in a reciprocating movement, at least one slotted screen spaced from the X-ray tube, said slot extending parallel to the path of electrons along the anode so that the reciprocating X-ray beam emitted from the anode can pass therethrough and means for moving the X-ray tube and screen in a direction substantially perpendicular to the longitudinal direction of the slot in the screen simultaneously with operation of the beam deflecting means.

5. An apparatus according to claims 3 or 4, wherein a second screen is provided spaced apart and parallel to the first screen and has a

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. is disposed in a conventional manner a static focussing cap 22, which cap already effects a focussing of the electron beam 26. Slightly spaced from the static focussing cap 22 there is present an electronic lens or focussing coil 23 in the X-ray tube. This part effects a subsequent focussing of the electron beam 26. Beam 26 subsequently travels through the system of deflection plates or coils 24 and finally impinges upon anode 25. The electron beam 26 releases a quantity of X-rays from anode 25, which X-rays are emitted as X-ray beam 27 from the X-ray tube. Fig. 4a shows how the X-ray beam 27 impinges upon an object 16 to be examined via a slotted screen 6 and how the radiation traversing the object 16 can impinge upon film 17.If desired, here too, a slotted screen may be disposed underneath the object 16, analogously to what is shown in Fig. 2. The entire X-ray tube shown in Fig. 4 may naturally form part of an apparatus as shown in Fig. 1, instead of housing 5 comprising the source of radioactive radiation. The deflection plates 24 are so energized that they ensure such a deflection of the electron beam 26 that it reciprocates between the position shown in Fig. 4b by 26a and the position indicated by 26b. The electron beam consequently effects a reciprocating movement in a horizontal plane. The X-ray beam 27 released from anode 25 by the electron beam 26 also effects thereby a reciprocating movement in a substantially vertical plane wherein there is likewise present the slot in the screen 6. When the system 4 (Fig. 1) accommodating the X-ray tube instead of the housing 5, is moved in the above described manner, the object 16 and via the object the film 17 is irradiated according to a zig-zag pattern, which will be further explained in Fig. 5.It is observed that the means for energizing the X-ray tube and for energizing the various parts in the X-ray tube, such as the focussing coil 23 and the deflection plates or coils 24, may be of a conventional type. Fig. 5 shows a top view of a part of an object 16 comprising a weld connection 18. On the object is shown the zig-zag pattern traversed by the radio-active or X-radiation. It will be clear that this pattern in actual fact is not visible on the object 16, but a similar pattern will be realized on film 17 though. The double arrow 28 indicates the reciprocating movement of the X-ray beam 27 or the beam of radiation from the source container 12. The arrow 29 shows the direction of movement of the entire system 4 (Fig. 1) relative to the object 16. Together these movements result in the zig-zag movement 30. It is clearly shown in Fig. 5 that the weld connection 18 is entirely scanned and is irradiated from different angles, so that all defects in the weld connection are expressed in the exposure of the film disposed underneath the object 16. WHAT WE CLAIM IS:-

1. A method of inspecting objects, in particular weld connections, by means of radiation in which the object to be examined is positioned between a source of radiation and a film responsive to radiation from the source with a slotted collimator being arranged between the source of radiation and the object after which the object and via the object the film is irradiated by radiation from the source, and the film, after exposure, is developed, the source of radiation and the slot, during exposure, being moved in synchronism with each other in a direction substantially perpendicular to the slot, while simultaneously the path of radiation from the source is reciprocated back and forth in a direction parallel to the slot.

slot parallel to the slot in the first screen and in registry therewith whereby in use of the apparatus radiation can pass through the slot in the second screen after having passed through an object being examined from the slot in the first screen.

6. An apparatus according to any one of claims 3 to 5, which comprises means for containing or retaining a film to be exposed at a fixed location for movement relative thereto of the housing or the tube and of the or each screen.

7. A method of examining objects by means of radiation substantially as herein described with reference to the accompanying drawings.

8. Apparatus for examining objects by means of radiation constructed and arranged to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.