US3835323A

US3835323A - Radiation inspection apparatus with adjustable shutter for inspecting different sizes of tubular goods

Info

Publication number: US3835323A
Application number: US00278311A
Authority: US
Inventors: J Kahil
Original assignee: Individual
Current assignee: Individual
Priority date: 1972-08-07
Filing date: 1972-08-07
Publication date: 1974-09-10
Anticipated expiration: 1991-09-10
Also published as: CA991320A; GB1395852A

Abstract

In the new and improved radiation apparatus disclosed herein for inspecting tubular goods, a radiation detector is arranged on a selected inspection axis for receiving radiation from a uniquelyarranged radiation emitter facing the detector and rotating about the exterior of the tubular member as it is translated along the axis around the detector. In the preferred embodiment disclosed herein, this unique radiation emitter includes an array of sideby-side radioactive sources aligned with laterally-spaced focussing passages for producing a composite radiation pattern formed by a number of individual sharply-defined radiation patterns on opposite sides of the inspection axis as well as intersecting the axis. The emitter further includes a selectively-positionable radiation controller which is arranged for movement between one position for emitting only a single radiation beam of selected intensity to produce a radiation pattern of reduced size and another position for emitting radiation beams from all of the sources to produce the composite pattern across the inspection axis.

Description

United States Patent Kahil RADIATION INSPECTION APPARATUS TUBULAR GOODS [76] Inventor: John E. Kahil, 9607 windswept,

Houston, Tex. 77042 [22] Filed: Aug. 7, 1972 [21] Appl. No.: 278,311

[52] US. Cl 250/360, 250/366, 250/494, 250/513 [51] Int. Cl. G01t 1/18 [58] Field of Search 250/833 D, 336, 360, 494, 250/513 [56] References Cited UNITED STATES PATENTS 2,425,512 8/1947 Crumrine 250/833 D 2,486,845 11/1949 Herzog i 250/833 D 2,999,935 9/1961" Foster 250/833 D 3,628,029 12/1971 Tompkins 250/833 D 3,683,186 8/1972 Tompkins 250/833 D Sept. 10, 1974 Primary ExaminerJames W. Lawrence Assistant Examinerl-larold A. Dixon [57] ABSTRACT In the new and improved radiation apparatus disclosed herein for inspecting tubular goods, a radiation detec-.

individual sharply-defined radiation patterns on opposite sides of the inspection axis as well as intersecting the axis. The emitter further includes a selectivelypositionable radiation controller which is arranged for movement between one position for emitting only a single radiation beam of selected intensity to produce a radiation pattern of reduced size and another position for emitting radiation beams from all of the sources to produce the composite pattern across the inspection axis.

22 Claims, 9 Drawing Figures PAIENIED SEP 1 0 m4 SHEEI 2 0F 4 PATENIEI] SEP 1 0 I974 FIGS .L. v LATERAL DISTANCE FROM AX/S PAH-INTEDSEH 0:924

saw u or 4 722 FOLLOWER. ADDER RECORDER LATERAL D/STANCE FROM AXIS AVERAGER RM RADIATION INSPECTION APPARATUS WITH ADJUSTABLE SHUTTER FOR INSPECTING DIFFERENT SIZES OF TUBULAR GOODS Elongated tubular goods, such as oil-field piping or tubing and the like, are frequently inspected for hidden flaws and other latent defects that might cause failure of such tubular members while in service. As one aspect of these inspections, it is often desired to also obtain representative measurements of wall thickness of such tubular members at spaced points along their length. It will be recognized, of course, that such thickness measurements must be obtained at several points around the circumference of a pipe as well as along its entire length to be certain of reliably detecting imperfections.

Various thickness-measuring devices have, of course, been devised heretofore for inspecting long lengths of pipe and tubing. For instance, one typical device of this nature employs a rigidly-interconnected radiation detector and a radioactive source which are simultaneously rotated around an axially-moving pipe, with the resulting variations in measured radiation intensity being used to derive corresponding wall-thickness measurements along a generally-helical path around the tubular member. Although the ideal situation would be to move the pipe being inspected slowly and rotate the radiation devices at high speed, practical considerations necessarily restrict these units to low rotative speeds which correspondingly further limit the axial speed of the pipe joints and, therefore, result in inefficient inspection rates.

Alternatively, the new and improved inspection device disclosed in US. Pat. No. 3,628,029 has been found to provide accurate thickness measurements of various tubular goods at efficient inspection rates. As described in that patent, a radiation detector is mounted on the free end of a fixed, but relatively flexible, elongated lance that is aligned along a selected inspection axis and adapted to receive a tubular member being moved axially along the axis. A single radiation source is suitably mounted within an annular rotatable member adapted for rotation at high speeds around the exterior of a tubular member moving along the inspection axis. By means of a unique arrangement of converging focussing slots, a sharply-defined radiation pattern substantially smaller in area than the active portion of the radiation detector is imposed thereon. In this manner, limited lateral or vertical movements of the radiation detector confined within the moving tubular member being inspected will produce only a negligible effect on the measurements provided by the radiation detector.

Although this new and improved inspection apparatus has proven to be successful in certain situations, it has been found that the relatively-large size of the detector as well as the extreme narrowness of the single radiation pattern produced thereby restricts the use of a given unit to the inspection of tubular members only within a limited range of diameters. Moreover, it has been found that tubular members being inspected with this apparatus have to be retained as nearly as possible in coincidental alignment with the inspection axis of the apparatus to assure maximum accuracy. Accordingly, in view of these two limiting factors of these prior units, the inspection of elongated tubular members which are slightly bent or the inspection of groups of such members of widely-varying diameters require special operating and handling techniques which correspondingly reduce the efficiency of the inspection operation.

To overcome these limiting factors, another inspection device as described in Patent No. 3,683,186 employs a radiation emitter having an array of three sideby-side radioactive sources of selected intensity which are cooperatively mounted for rotation about an axially-moving pipe being inspected. By arranging the radiation patterns of the two flanking sources to complement the radiation pattern of the intermediate source, the combined patterns will enable the radiation detector to move randomly within the pipe and still produce accurate thickness measurements of the intervening pipe wall.

Still another inspection device of similar nature as disclosed in a copending patent application Ser. No. 189,306 filed Oct. 14. 1971, and also assigned to the assignee of the present application involves a single source which is rotated about a pipe being inspected. A scintillation detector of unique design is cooperatively arranged to provide a substantially uniform output as the detector moves laterally across the radiation beam. This particular unit is, however, substantially limited to inspection of relatively-small pipes.

Although the three inspection devices disclosed in the aforementioned patents and application have each been highly successful, each of these devices are respectively limited for operation in a given range of sizes of oil-field tubular members. Thus, if a particular inspection operation requires that a number of tubular members having a wide variety of diameters be tested, it has heretofore been necessary to provide completely separate inspection units respectively equipped to handle particular size ranges of these tubular members. The inefficiency of this arrangement is, of course, obvious.

Accordingly, it is an object of the present invention to provide new and improved radiation apparatus for accurately and quickly measuring the wall thickness of elongated tubular members, such as oil-field tubular goods, of widely-different diameters.

This and other objects of the present invention are attained by mounting radiation-detecting means on the free end of an elongated support that is generally aligned along a selected inspection axis and adapted for reception in a tubular member moving axially along the inspection axis. Radiation-emitting means including a plurality of radiation sources cooperatively associated with inwardly-directed focussing passages formed within radiation-shielding means are cooperatively arranged to produce a corresponding number of narrow radiation patterns which are distributed transversely across the inspection axis and together form a composite pattern of selected size and intensity. A radiation control mask is cooperatively arranged for movement across the focussing passages between one position where all radiation beams pass through the mask and another position where less than all of the radiation beams are allowed to pass the mask. In this manner, with the mask in its one position, the resulting composite pattern will allow tubular members of given range of relatively-large diameters to be accurately inspected irrespective of even significant variations in either the spacing or alignment between the radiation-emitting means and the radiation-detecting means. Alternatively, with the mask in its other position, the resulting reduced radiation pattern will be employed for obtaining thickness measurements of tubular members of relatively smaller diameters.

The novel features of the present invention are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may be best understood by way of the following description of exemplary apparatus employing the principles of the invention as illustrated in the accompanying drawings, in which:

FIG. 1 schematically illustrates thickness-measuring apparatus employing the radiation means of the present invention as it may be arranged for cooperation with typical flaw-inspection apparatus;

FIG. 2 is an elevational view, partially in crosssection, of a preferred arrangement of the thicknessmeasuring apparatus depicted in FIG. 1;

FIG. 3 is an enlarged cross-sectional view in elevation taken along the lines 33 in FIG. 2 and depicts a preferred embodiment of radiation-emitting means arranged in accordance with the principles of the present invention;

FIG. 4 is a cross-sectional plan view taken along the lines 4-4 in FIG. 3;

FIG. 5 depicts the radiation-emitting means of the present invention inone operating position for inspecting tubular members of a relatively large size;

FIG. 6 is a graphical representation illustrating the performance of the new and improved radiation means of the present invention when the radiation-emitting means are positioned as shown in FIG. 5;

FIG. 7 is similar to FIG. 5 but illustrates the radiation-emitting means in another operating position for inspecting tubular members of a smaller diameter;

FIG. 8 illustrates the performance of the radiation means of the present invention when positioned as shown in FIG. 7; and

FIG. 9 is a schematic block diagram of a preferred arrangement of electronic circuitry for use with the thickness-measuring apparatus of the present invention.

Turning now to FIG. 1, a schematic plan view is shown of thickness-measuring apparatus 10 arranged in accordance with the present invention and operatively mounted within a vehicle 11. To illustrate atypical situation in which the new and improved apparatus 10 can be advantageously used, the thickness-measuring apparatus is depicted as being axially aligned with other pipe-inspection apparatus 12 such as the flawinspection apparatus disclosed in Reissue Pat. No. 26,537. As is typical, the thickness-measuring apparatus 10 includes pipe-translating means, such as a selectively-powered conveyor 13 (which may be the conveyor shown in Pat. No. 3,565,310) mounted within the vehicle 11 and a pair of portable conveyors 14 and 15 (such as those disclosed in Pat. No. 3,250,404) arranged at the opposite ends of the vehicle, for selectively moving pipe sections as at 16 back and forth through the vehicle along a generally-horizontal inspection axis 17.

Reference should be made, of course, to the aforementioned reissue patent for elaboration of the details of the flaw-inspection apparatus 12 and the particulars of its operation. However, the general arrangement of the flaw-inspection apparatus 12 and a typical inspection operation therewith should be understood to better appreciate its cooperation with the new and improved thickness-measuring apparatus 10. In general, therefore, the flaw-inspection apparatus 12 is arranged to first progressively induce a longitudinally-oriented magnetic flux in a horizontal pipe, as at 16, being advanced axially in a first direction along the conveyor 13 so that transversely-oriented flaws in the pipe can be concurrently detected. Residual magnetism remaining in the pipe 16 is at least partially reduced by progressively subjecting the advancing pipe to a demagnetizing flux after it has been inspected for transverselyoriented flaws. When the pipe 16 is also to be inspected for longitudinally-oriented flaws, the pipe is moved onto the conveyor 14 and, after being halted, subjected to a circumferentially-oriented magnetic field. Thereafter, as the pipe 16 is returned in the opposite direction along the inspection axis 17, it is progressively inspected for longitudinally-oriented flaws. On the other hand, when this latter inspection is not performed, the pipe 16 is merely returned back through the vehicle 11 to the conveyor 15. In either situation, however, it is preferred that the new and improved thicknessmeasuring apparatus 10 be arranged for operation upon the return movement of the pipe 16 whether or not the latter flaw inspection is conducted.

To perform these inspections for transverse flaws, the inspection apparatus 10 preferably includes an annular magnetizing coil 18 having spaced sections concentrically arranged around the inspection axis 17 with a plurality of flux-detecting heads 19 arranged therebetween. A second annular coil 20 is also concentrically arranged around the inspection axis 17 to the rear of g the flux-inducing coil 18 and connected to a suitable AC or pulsating DC source (not shown) for progressively demagnetizing the pipe 16 as it leaves the fluxinducing coil.

The flaw-inspection apparatus 12 further includes an electrically-conductive, cantilevered elongated probe or lance 21 that is supported at its remote end and maintained in substantially-coincidental alignment along the inspection axis 17. When the pipe 16 is to be inspected for longitudinal flaws, it is advanced onto the lance 21 and halted when the lance has passed completely through the pipe and its free end projects out of the rearward end of the pipe. To subject the pipe 16 to a circumferentially-oriented magnetic field, a DC source 22 is connected between the remote supported end of the lance 21 and one or more laterally-movable electrical contacts 23 that are selectively engageable with the free end of the lance. Thereafter, as the pipe 16 is being returned, a plurality of flux-detecting heads 24 are selectively moved into contact with and coaxially rotated about the moving pipe for detecting generally-longitudinal flaws therein. As previously mentioned, it is preferred to operate the new and improved thickness-measuring apparatus 10 as the pipe 16 is withdrawn from over the lance 21 whether or not the pipe is to be inspected for longitudinal flaws.

In general, as depicted in FIG. '1, the new and improved thickness-measuring apparatus 10 is comprised of radiation-detecting means including one of two types of radiation detectors, as at 25 (or 25' which is operatively positioned along the axis 17 and new and improved radiation means 26 mounted on a body 27 adapted for rotation about the inspection axis. As will be subsequently explained, the radiation means 26 of the present invention are operatively arranged for alternatively producing either a single beam of radiation or a plurality of inwardly-directed beams of radiation of predetermined intensities which are respectively distributed across a selected transverse plane to pass through the wall of the pipe 16 for interception by the radiation detector.

As illustrated in FIG. 2, the radiation detector is comprised of one or the other of two types of detectors (or 25) which are respectively mounted in a suitable enclosed protective housing, as at 28, that is adapted to be alternatively coupled to the free end of the elongated probe 21 depending upon the size of the pipe sections 16 that are to be inspected. The selection of the particular radiation detector, as at 25, will be subsequently discussed with reference to FIGS. 5 and 7. To adapt the detector 25 (or 25) for movement relative to the lower internal wall of the pipe 16 as the pipe is axially advanced or returned along the inspection axis 17, the protective housing 28 includes a central tubular portion 29 of nylon or other solid material that will not significantly attenuate incident radiation. In the embodiment illustrated in FIG. 2, a plurality of removable centralizing members, as at 30 and 31, are spaced circumferentially about the end portions of the detector housing 28 for retaining the detector 25 (or 25') in general coincidental alignment with the inspection axis 17. As a matter of convenience, the

centralizers

30 and 31 are adapted to be readily exchanged with other members (not shown) of greater or lesser heights so that the new and improved inspection apparatus 10 will be effective for inspecting a wide range of sizes of tubular members. As will be subsequently explained, by arranging the radiation means 26 to alternatively produce either a single radiation beam for impinging on the detector 25' or a plurality of discrete beams of radiation that are each of a reduced transverse width somewhat less than that of the effective portion of the detector 25 and distributing these beams at predetermined intervals across the plane of rotation, the radiation detector 25 or 25' will produce a uniform output signal even when it is eccentrically disposed in relation to the inspection axis 17.

Accordingly, in the preferred embodiment of the thickness-measuring apparatus 10 shown in FIG. 2, the radiation detector 25 (or 25') is mounted on the free end of the lance 21 and coaxially positioned within the rotating body 27 which includes a horizontal, generally-tubular member 32 having one end portion rotatably journalled within an enlarged, annular stationary housing 33 and adapted for high-speed rotation around the longitudinal inspection axis 17. The radiation means 26 are eccentrically located between two longitudinallyspaced annular plates or

flanges

34 and 35 secured to the unsupported or other end portion of the rotatable member 32. To dynamically balance the rotating body 27, a target 36 of sufficient mass is mounted between the spaced

flanges

34 and 35 diametrically opposite of the radiation means 26.

As best seen in FIG. 2, the rotating body 27 is concentrically arranged about the horizontal inspection axis 17 and journalled within the housing 33 by a pair of longitudinally-spaced bearings 37 and 38 carrying the supported end portion of the tubular member 32. In one manner of driving the rotating body 27 at high speeds about its rotational axis 17, the supported end of the tubular member 32 is extended beyond the outboard bearing 37 and coupled to driving means, such as a motor 39 mounted outside of the housing 33, by a suitable power transmission such as a typical chain or belt 40 operatively interconnecting a pulley 41 mounted on the tubular member and a pulley 42 mounted on the shaft of the motor.

Turning now to FIG. 3, in the preferred embodiment of the present invention, the radiation means 26 include an array of three isotropic radiation sources 43-45 (such as Cobalt 60, Cesium 137, or other acceptable sources of gamma radiation) which are respectively encased in typical source cups, as at 46, each having either an opening in its lower end or a reduced wall thickness through which radiation can readily pass. The encapsulated radiation sources 43-45 are respectively disposed within one of three chambers, as at 47, formed side-by-side in the upper portion of a block 48 of a suitable radiation-attenuating or shielding material. To fully enclose the sources 43-45, a removable closure member, as at 49, is fitted into the open end of each of the source chambers 47 and a suitable cover plate 50 is secured to the shielding block 48 over the several closure members.

The radiation means 26 of the present invention further include particularly-arranged radiation focussing means 51 as well as selectively-operable radiationblocking or radiation-regulating shutter means 52 operatively disposed between the focussing means and the radioactive sources 43-45. As best seen in FIG. 3, the focussing means 51 are comprised of a second block 53 formed of steel, tungsten, lead or some other suitable radiation-attenuating or shielding material that is mounted between the

annular flanges

34 and 35 and spaced radially inwardly from the shielding block 48 and diametrically opposite from the target shield 36 (FIG. 2). The shutter means 52 are comprised of a third block 54 of radiation-shielding material mounted between the shielding block 48 and the focussing block 53. Three generally-parallel radially-directed radiation passages, as at'55-57, which are respectively aligned with the three radiation sources 43-45 are respectively formed in each of the

blocks

48, 53 and 54. As will subsequently be explained in greater detail, the shutter means 52 are uniquely arranged for selectively controlling the passage of radiation from the sources 4345 through the radiation passages 55-57 to the detector 25.

Of paramount significance to the present invention, it will be noted from FIG. 3 that the radiation means 26 also include a selectively-positionable masking member such as an elongated bar 58 of steel or some similar material which, in the preferred embodiment of the present invention, is slidably mounted between the

blocks

48 and 54 for selective longitudinal movement transversely across the three radiation passages 55-57. As best seen in FIG. 4, in the preferred embodiment of the masking bar 58, six openings 59-64 are provided at equally-spaced intervals along the length of the bar. with the spacing between each adjacent set of openings being equal to one half of the transverse spacing between the radiation passages 55-57. Thus, by placing the masking bar 58 in the position shown in FIG. 3, the separate, generally-parallel beams of radiation 54-67 respectively emanating from the radiation sources 43-45 will be directed through the

openings

60, 62 and 64 in the bar. On the other hand, when the masking bar 58 is shifted to the right to the dashed-line position shown at 68 in FIG. 3, the

openings

60, 62 and 64 will be out of registration with the radiation passages 5557 and the

openings

59, 61 and 63 will instead be aligned with these radiation passages. The significance of these alternative positions of the masking bar 58 will subsequently be explained with reference to FIGS. and 7.

To accurately locate the masking bar 58 in either of its two alternative operating positions as well as to releasably secure the masking bar in these positions, the preferred embodiment of the present invention includes manually-operable detent means such as a pair of longitudinally-movable rods or

bolts

69 and 70 which are mounted in the shielding block 48 and respectively disposed in

elongated slots

71 and 72 in the ends of the bar. Biasing means such as compression springs 73 and 74 are cooperatively arranged to normally urge the

bolts

69 and 70 upwardly but still allow the bolts to be manually shifted downwardly as required to displace the lower

enlarged heads

75 and 76 of the bolts below the lower face of the masking bar 58. By respectively providing eccentrically-located counterbores, as at 77 and 78, on the outer edges of the

slots

71 and 72, when the masking bar 58 is shifted so as to align one of the counterbores with the head of its respective bolt, as at 69 (or 70), the enlarged head 75 (or 76) will be snugly retained in the counterbore by the spring 73 (or 74) so as to retain the masking bar in that position. The opposite result is, of course, obtained when the bolt 69 is momentarily depressed to remove the enlarged head 75 from the counterbore 77 to permit the masking bar 58 to be shifted transversely to its position at 68 to then align the enlarged head 76 with the counterbore 78.

It will also be noted from FIGS. 3 and 5 that the radioactive sources 4345 are uniquely arranged so that the separate beams of radiation 65-67 are each directed at spaced intervals along a selected transverse plane intersecting the inspection axis 17. In particular, in the preferred embodiment of the invention, the radiation means 26 are arranged so that two of the three

radiation beams

65 and 67 are respectively directed on opposite sides of the axis 17 and the third beam of radiation 66 will intersect the inspection axis to define a composite radiation pattern of selected intensity and lateral width. Accordingly, as illustrated in FIG. 5, when the mask 58 is positioned as shown and the detector is coincidentally aligned with the inspection axis 17, the radiation beam 66 from the central radioactive source 44 will be directly impinged on the detector and the exterior or flanking beams of

radiation

65 and 67 will substantially uniformly straddle the detector. ,On the other hand, as schematically depicted by the dashed

circles

79 and 80, should the detector 25 be shifted laterally to either side of the inspection axis 17, the active portion of the detector will progressively receive more radiation from one or the other of the two flanking beams 65 (or 67) and correspondingly receive a lesser amount of radiation from the central beam 66. The significance of this will best be appreciated by the respective response curves for the detector 25 as graphically depicted in FIG. 6.

Accordingly, as schematically represented in FIG. 6, by selecting a given energy or intensity for the central radioactive source 44, the detector 25 will respond to irradiation from this source as graphically depicted by the centrally-located response curve 81. As represented there, so long as the detector 25 remains coincidentally aligned with the inspection axis 17, the maximum intensity of the central radioactive source 44 will be received thereby so as to produce the maximum output as represented by the peak of this central response curve 81. On the other hand, lateral movement of the detector 25 to either one. side or the other of the inspection axis 17 will progressively diminish the radiation intensity being received from the central source 44 by the detector and produce a correspondinglyreduced output signal generally as indicated by the portions of the central response curve 81 that asymptotically approach the distance" axis on either side of the intensity maximum. The same results will, of course, be obtained for each of the two flanking sources 43 and 45 (FIG. 5) as shown by their respective response curves 82 and 83 (FIG. 6).

Accordingly, by selecting the

sources

43 and 45 to have equal but lesser strengths than the central source 44 and cooperatively arranging the two flanking radioactive sources in the manner depicted in FIGS. 3 and 5, as the detector 25 shifts to one side or the other of the inspection axis 17, the detector will be irradiated by a combination of one of the two flanking radiation beams, for example the left-hand beam 65, as well as the central radiation beam 66. Thus, as shown in FIG. 6, as the detector 25 moves further to the left, the progressively-increasing signal (as depicted by the response curve 82) produced by the weaker radioactive source 43 will be added to the progressivelydiminishing signal (as shown by the response curve 81) produced by the central radioactive source 44 so as to produce a combined or composite output as represented by the overall response curve 84. The same response will, of course, be obtained whenever the detector 25 shifts to the right-hand side of the inspection axis 17 except that the right-hand radioactive source 45 will produce a progressively-greater output signal (as shown by the response curve 83) as the output signal contributed solely by the central radioactive source 44 progressively diminishes. It will, of course, be appreciated that the strengths of the two flanking

sources

43 and 45 are cooperatively selected in accordance with their lateral spacing from the central source 44 to obtain the additional intensity to make the combined out put substantially constant across the expected rangeof lateral movements of the detector 25 for the larger sizes of pipe as at 16.

It will be appreciated, therefore, that with the mask 58 in the position shown in FIGS. 3 and 5, the new and improved radiation means 26 of the present invention will produce a substantially-uniform output signal for a given thickness of metal between the radiation sources 43-45 and the detector 25 so as to at least minimize the effects which would otherwise be caused by lateral shifting of the detector in relation to the inspection axis 17.

should also be noted that even though the detector 25 may bounce upwardly and downwardly (vertically as viewed in FIG. 5) as the pipe 16 is being moved over the detector, the radiation means 26 of the present invention will also provide substantially-uniform signals over an acceptable range of vertical movement of the detector inasmuch as the radiation beams 67 are well collimated and the sides of each beam are relatively parallel so that the flux density of each beam will be substantially equal at different vertical positions within the expected range of vertical movement of the detector. Thus, the vertical movements of the detector 25 are usually within a range where the axes of the radiation beams 6567 can be perfectly parallel and still maintain a substantially-equal flux density within this range. It has been found, however, that by arranging the

outer radiation passages

55 and 57 to converge the flanking beams 65 and 67 slightly inwardly a few degrees, the outer radiation patterns will be moved slightly inwardly toward the central radiation pattern to produce a more-uniform flux density over a greater range of vertical movments of the detector 25 without reducing its range of lateral movements.

It has been found that where typical oil-filed tubular goods are being inspected, the efficiency of the new and improved thicknessmeasuring apparatus is significantly improved where the radioactive sources 43-45 are selected for producing a substantial count rate at the detector 25 in the order of 10 to 10 counts/second as a tubular member is being inspected. With count rates of this magnitude, it will be appreciated that the detector 25 will be operated at optimum statistical accuracy so that pipes, as at 16, can be moved through the inspection apparatus 10 at reasonably-high axial speeds without unduly compromising the accuracy of the resulting thickness measurements.

To produce such high count rates while there is an intervening pipe wall between the radiation means 26 and the detector 25 will, of course, cause the detector to be subjected to much-greater count rates when a pipe is not positioned over the detector. It has been found, however, that with even the highest-quality radioactivity detectors, the prolonged exposure of the detector 25 to such greatly-increased count rates will rapidly cause the detector to begin drifting and that this drift or error is accelerated at an exponentiallyincreasing rate so long as the exposure is continued. Moreover, it has been found that even brief direct exposures of even a high-quality radioactivity detector to such greatly-increased count rates will quickly initiate unreliable or unstable operation of the detector 25 which will not be corrected until the detector has been inserted into a pipe for a considerable period of time. Those skilled in the art will, of course, recognize that a typical inspection operation cannot be reliably conducted with sufficient rapidity to always assure that the detector 25 will be inserted into a pipe so as to prevent the occurrence of such unstable operation of the detector. Such unpredictable operation of the detector 25 will, therefore, either result in unreliable measurements being obtained or make it necessary to delay the inspection of another pipe for at least a considerable period of time until the radioactivity detector has again stabilized.

Accordingly, as described in more detail in US. Pat. No. 3,683,187 the shutter means 52 are operatively arranged for selectively attenuating the radiation beams 65-67 at all times that a pipe, as at 16, is not positioned over the detector 25. Thus, by reducing the intensity of radiation intercepted by the detector 25 to at least a reduced level that will not create the aforementioned unstability or drifting of the detector, the new and improved thickness-measuring apparatus 10 can be operated at efficient inspection rates without compromising the accuracy of the resulting measurements.

Referring again to FIGS. 2 and 3, it will be noted that in the preferred embodiment of the shutter means 52 employed for use in the present invention, a flat plate is cooperatively arranged for sliding movement within a complementary passage 86 formed in the shutter block 54 parallel to the axis 17 and intersecting the radiation passages 5557 therein. In the preferred embodiment of the thickness-measuring apparatus 10, the intersecting passage 86 is parallel to the inspection axis 17 and the shutter plate 85 is of sufficient length that it will project outwardly from the forward and rearward faces of the

flanges

34 and 35.

As best seen in FIGS. 2 and 3, in its preferred embodiment the shutter plate 85 is appropriately sized in relation to the passage 86 so as to be capable of movement completely out of alignment with the radiation passages 5557 when the radiation-emitting means 26 is being used to perform an inspection operation. On the other hand, the shutter plate 85 is particularly formed to have a thickness of a selected and predetermined magnitude so that upon movement of the plate to position the plate in alignment with the radiation passages 5557, the radiation intercepted by the radiation detector 25 will be reduced to produce a selected count rate at the detector.

Accordingly, the new and improved thicknessmeasuring appartus 10 is operatively arranged for selectively moving the shutter plate 85 to shift it out of alignment with the radiation passages 5557 just as the leading end of the pipe 16 approaches the detector 25 and then repositioning the shutter plate to bring it back into alignment with the radiation passages as the trailing end of the moving pipe passes over the detector. It will be appreciated, therefore, that these alternatelydirected movements of the shutter plate 85 between its respective positions will assure that the detector 25 will be protected from exposure to excessive radiation intensities that could otherwise create the aforementioned problems with unstability or drifting of the detector.

In the preferred manner of accomplishing these alternately-directed movements of the shutter plate 85 and as disclosed and claimed in US. Pat. No. 3,684,887, rounded knobs, as at 87 and 88, are mounted on the outer ends of an elongated rod 89 coupled to the shutter plate. To allow unimpeded passage of the radiation beam 66 when the shutter plate 85 is in the position illustrated by the dashed lines at 90 in FIG. 4, an opening 91 is arranged in the actuating rod 89 to be in registration with the radiation passage 56 when the shutter plate is in its open position. Since the shutter plate 85 will follow a circular path upon rotation of the rotating body 27, straps, as at 93 and 94 (FIG. 1), of a relatively-flexible material are respectively secured to the forward and rearward portions of the housing 33 and operatively arranged for pivotal movement from first positions away from the housing to second positions immediately adjacent thereto which respectively intercept the paths of rotation on the forward and rearward knobs 87 and 88. Selectively-

operable solenoid actuators

95 and 96 are arranged adjacent to the straps 93 and 94, respectively, and so located that, upon energization of the first actuator 95, the strap 93 will be moved into the rotational path of the knob 87 and will accordingly shift the shutter plate 85 to the position illustrated in FIG. 2 before the rotating body 27 completes a full revolution. Conversely, by energizing the second acutator 96, the shutter plate 85 will be quickly shifted in the reverse direction to its alternate position for opening the radiation passages 5557. In the preferred embodiment of the thickness-measuring apparatus 10, the selective operation of the

solenoid actuators

95 and 96 is accomplished by arranging typical limit switches, as at 97 and 98 in FIG. 1, for contact by the pipe 16 as it passes. along the conveyor 13 to shift the shutter plate 85 back and forth in proper coordination with the operation of the thickness-measuring apparatus.

Turning now to FIG. 7, it will be appreciated that the thickness-measuring apparatus has been adjusted for inspecting smaller sizes of tubular members by shifting the masking bar 58 to the right so as to now position the

openings

59, 61 and 63 in registration with the radiation passages 55-57. Moreover, as will subsequently be explained, the detector 25 has now been removed and a new and improved detector 25 is now mounted on the lance 21. All other elements of the new and improved apparatus 10 remain the same as previously described with reference to FIG. 5. As illustrated, the pipe 16 which is to be inspected is of a smaller diameter than the pipe 16.

As best illustrated in FIGS. 4 and 7, the opening 61 in the masking bar 58 is unimpeded and the

openings

59 and 63 are respectively plugged or blocked with

members

99 and 100 of a suitable radiation-attenuating material, such as tungsten or lead, of sufficient thickness to block the passage of most, if not all, of the two flanking radiation beams 65 and 67. Thus, as depicted in FIG. 7, only the central radiation beam 66 is permitted to emanate from the radiation means 26 for intersecting the wall of the pipe 16'. In other words, only the central radiation source 44 is effective when the masking bar 58 is in the position shown in FIG. 7.

It will, of course, be appreciated that it may be desired to select the radiation source 44 so that the intensity of the radiation beam 66 is of a substantial magnitude when the masking bar 58 is in the position shown in FIG. 7 and is of a somewhat lesser magnitude when the masking bar is in the position shown in FIG. 5. Thus, in the preferred embodiment of the present invention, the opening 62 in the masking bar 58 is partially obstructed either with a slight radiation attenuator or by leaving a web 101 of predetermined thickness in the opening. In this manner, the intensity of the central radiation beam 66 is somewhat reduced when the masking bar 58 is in the position shown in FIG. 5 so as to better achieve the cooperation between the three sources 43-46 as depicted in FIG. 6.

Referring again to FIG. 7, it will be noted that the central radioactive source 44 and the radiation passage 56 are cooperatively arranged to direct the beam of radiation 66 along a radial radiation axis intersecting the inspection axis 17. It will also be noted that, as indicated by the dashed

circles

102 and 103, the detector 25' is capable of moving laterally on opposite sides of the inspection axis 17 within the pipe 16. Thus, only so long as the detector 25 is coincidentally aligned with the inspection axis, will the radiation beam 66 be uniformly impinged on radiation-sensitive means, such as a scintillation crystal 104 of unique design which is cooperatively arranged within the detector; and, in the other positions of the detector (as at 102 and 103), the

radiation beam will be unsymmetrically aligned in relation to the active portion of the crystal. It will be appreciated, therefore, that since the output of the scintillation crystal 104 is directly related to the intensity of the radiation beam 66 as well as to the total effective crosssectional area of the active portion of the crystal which is being irradiated at any given time. the lateral position of the detector 25' in relation to the inspection axis 17 would significantly affect the output of the detector as shown at 105 in FIG. 8 unless the principles of the invention described in the aforementioned copending application, Ser. No. 189,306 are followed.

Accordingly, in keeping with the objects of the invention described in the aforementioned application, the detector 25 is uniquely arranged to provide a uniform output signal for a given flux of the radiation beam 66 over a wide range of lateral movements of the detector within the pipe 16 on either side of the inspection axis 17. In the preferred manner of accomplishing this unique result, the scintillation crystal 104 is selectively shaped so as to make the effective volume of its active portion which is intersected by the radiation beam 66 when the detector 25 is coincidentally aligned with the inspection axis 17 substantially equal to the effective volume of the active portion which is intersected by the beam when the detector is on either side of the inspection axis. Thus, as shown in FIG. 7, where the scintillation crystal 104 is a cylinder, a longitudinal bore 106 is symmetrically formed therein for removing a sufficient volume from the central portion of the crystal to achieve a selected reduction in the output response of the crystal when it is coincidentally aligned with the axis 17. As best seen in FIG. 8, therefore, the crystal 104 is selectively hollowed in a symmetrical fashion to obtain an output response similar to that illustrated at 107. It will, of course, be appreciated that the particular dimensions of the axial bore 106 will be wholly dependent upon the physical size of the crystal 104 as well as the range of lateral movement of the detector 25 and the intensity and width of the radiation beam 66 at the axis 17.

Accordingly, as schematically represented in FIG. 8, at a given energy level or intensity for the radioactive source 44, the detector 25' will respond to irradiation from the source as graphically depicted by the response curve 107. As represented there, so long as the detec tor 25 remains coincidentally aligned with the inspection axis 17, the maximum intensity of the radioactive source 44 will be received thereby so as to produce the reduced output as represented by the center of the flat portion of the response curve 107. On the other hand. lateral movement of the detector 25' to either one side or the other of the inspection axis 17 will progressively diminish the radiation intensity being received from the source 44 by the detector but a substantially equal output will be produced as represented by the outer portion of the flat-top curve portion. A correspondinglyreduced output signal (as generally indicated by the flank portions of the response curve 107 that asymptotically approach the distance axis on either side of the curve) will, of course, be produced should the detector 25 move outwardly beyond either of its

eccentric positions

102 and 103.

It will be appreciated, therefore, that the unique radiation detector 25' will produce a substantially-uniform output signal for a given thickness of metal between the radiation source 44 and the detector so as to at least minimize the effects which would otherwise be caused by lateral shifting of the detector within the pipe 16'. It should also be noted that even though the detector 25 may bounce upwardly and downwardly (vertically as viewed in FIG. 7) as the pipe 16' is being moved thereover, the new and improved radiation detector of the present invention will also provide substantiallyuniform signals over an acceptable range of vertical movement of the detector inasmuch as the radiation beam 66 is well collimated and the sides of the beam are relatively parallel so that its flux density will be substantially equal at different vertical positions within the expected range of vertical movement of the detector.

As previously mentioned with respect to the detector 25, the efficiency of the new and improved thicknessmeasuring apparatus is significantly improved where the radioactive source 44 is selected for producing a substantial count rate atthe detector in the order of 10 to lO -counts/second as a tubular member is being inspected. Hereagain, with count rates of this magnitude, it will be appreciated that the detector 25' will be operated at optimum statistical accuracy for typical inspections. Moreover, such greatly-increased count rates will similarly require the use of the shutter means 52 to assure reliable and stable operation of the detector 25.

It will, of course, be appreciated that as far as the requirements of the present invention are concerned, circuitry such as that shown in FIG. 8 of US. Pat. No. 3,565,310 can be efficiently employed for obtaining adequate records with the new and improved thickness-measuring apparatus 10. In the preferred embodiment of the thickness-measuring apparatus 10, it is preferred, however, to employ new and improved circuitry such as schematically depicted at 108 in FIG. 9 of the present application and described in greater detail in US. Pat. No. 3,683,187. As disclosed in greater detail in this last-mentioned application, the new and improved circuitry 108 is uniquely arranged for cooperation with the shutter means 52.

In general, the circuitry 108 is uniquely arranged so that each time the shutter plate 85 is in its radiationblocking positions, a calibration measurement is made of the thickness of the plate. Then, as a pipe, as at 16 (or 16') is being inspected, the resulting thickness measurements being obtained are compared with the previously-obtained calibration measurement for determining the accuracy of these thickness measurements.

As described in greater detail in the aforementioned patent, the circuitry 18 is appropriately arranged for converting the output signal of the radiation detector 25 (or 25) to a meaningful record. To accomplish this, the output signal of the detector 25 (or 25') is coupled by way of

suitable conductors

109 and 110 and an amplifier 111 to an indicator, such as a recorder 112, that is appropriately arranged for progressively providing a continuous first indication representative of the wall thickness of a tubular member passing through the inspection apparatus 10. As an additional feature, the circuitry 108 also includes a time-averaging circuit 113 appropriately tuned to average the output of the detector 25 (or 25') for each revolution of the radiation means 26 to provide a second indication, as on a typical recorder 114, representative of the transverse crosssectional metal area through that portion of the tubular member scanned in that revolution. In this manner, by driving the

recorders

112 and 114 at speeds related to the axial speed of the pipe 16 (or 16) past the apparatus l0, continuous meaningful records will be obtained fo the actual metal thicknesses along the generallyhelical inspection path around the pipe as well as of successive transverse cross-sectional metal areas along the length of pipe. The circuitry 108 further includes alarm indicators, as at 115 and 116, coupled to the

recorders

112 and 114 and adapted for warning the operator of the apparatus 10 that the representative thick ness and area measurements are less than some selected minimum value.

To provide the aforementioned calibration measurements, the circuitry 108 further includes a normallyopen relay 117 which is appropriately connected to the solenoid actuator 96 and adapted to be closed when the shutter plate 85 is in its radiation-blocking position. In this manner, when the radiation passages -57 are closed, the output of the detector 25 (of 25) will be temporarily coupled by way of an adder 118, a follower 119, and an adder 120 to the amplifier 111 to produce an input signal at the recorder 112 that corresponds to the known thickness of the shutter plate 85. A selectively-adjustable reference signal, such as provided by a constant-voltage source 121 and a potentiometer 122, is coupled to the other input of the adder 118 for accurately resetting the recorder 112 before the first pipe that is to be inspected is passed through the thickness-measuring apparatus 10. Once this reference signal is correctly set, the potentiometer 122 is not changed until such time that the thicknessmeasuring apparatus 10 is again recalibrated.

For reasons that will subsequently be explained, the adder 118 is a signal-inverting adder so that the combination of the detector output signal and the reference signal will be inverted by the adder to provide a calibration signal. The calibrated output signal from the inverting adder 118 is stored by a capacitor 123 and, by employing the high-impedance follower 119, will remain as a fixed input to the adder 120 after the relay 117 is opened. It will be appreciated, therefore, that when the relay 117 is closed and the reference signal is applied to the inverting adder 118, the inversion of the signals by the adder 1 18 will produce an output signal from the adder 120 that equals only the reference signal. On the other hand, the signal initially stored by the capacitor 123 will be the inverted summation of the reference signal and the output signal of the detector 25 (or 25).

Accordingly, once the reference signal has been properly set to obtain the correct reading at the recorder 112, the potentiometer 122 is left alone and the first pipe, as at 16 (or 16) is inspected'As these measurements are being obtained, it will be appreciated that the output signal of the adder 120 will be equal to the algebraic summation of the reference signal and the difference in the output signals of the detector 25 (or 25) at that moment and at the time that the recorder 112 was calibrated. Thus, the recorder 112 will, in effect, be recording the differences between the various wall thicknesses of the pipe 16 (or 16) and the known thicknesses of the shutter plate 85. These readings can, of course, be presented either as a true thickness measurement or as a difference between this known thickness.

Once the first pipe has been inspected, the shutter plate will, of course, be reclosed and the relay 117 will again be reclosed just before the next pipe is inspected. At this time, if there has been drifting of the detector 25 (or 25'), the calibration signal that is then stored on the capacitor 123 will be the inverted algebraic summation of the unchanged reference signal and the output signal of the detector which will be then produced as a result of any drifting. It will be recalled that the potentiometer 122 is not changed. Thus, with the relay 117 being reclosed, the output of the adder 120 will'again be equal to only the original unchanged reference signal which will indicate that the circuitry 108 is still properly calibrated.

Once the next pipe is moved through the thickness measuring apparatus 10 and the relay 117 is reopened, the resulting output signal from the adder 120 will again be equal to the algebraic summation of the reference signal and the difference in the output signals of the detector (or 25) at that moment and at the time the second calibrating signal was stored on the capacitor 123. Hereagain, the resulting signal recorded by the recorder 112 will be representative of the differences in the thicknesses of the pipe being inspected and the known thickness of the shutter plate 85. 7

It will be appreciated that a more-precise calibration signal can be stored in the capacitor 123 if the detector 25 (or 25') is in a known position in relation to the radiation sources 43-45 at that time. Accordingly, in the preferred embodiment of the thickness-measuring apparatus 10, means are also provided for temporarily fixing the detector 25 (or 25) in a selected position as the calibration measurements are being obtained.

Accordingly, as more-fully explained in 1.1.8. Pat. No. 3,683,187, in the preferred manner of accomplishing this, first and second selectively-operable clamping devices 124 and 125 (FIGS. 1 and 2) are arranged at opposite ends of the tubular member 32 and cooperatively arranged to secure the detector 25 (or 25) in coincidental alignment with the inspection axis 17 as a calibration measurement is being obtained. In general, each of the

clamping devices

124 and 125 is comprised of an opposed pair of horizontal bars, as at 126 and 127, which are respectively disposed above and below the conveyor 13 and operatively carried for vertical movement on suitable guides or uprights 128 stationed on opposite sides of the conveyor. Suitable devices, such as solenoid-actuators or hydraulic piston actuators as at 129 and 130, are operatively coupled to the clamping bars 126 and 127, respectively, and suitably arranged for moving the opposed bars in unison into clamping engagement on the respective end portions of the detector housing 28 for coaxially positioning the detector 25 (or 25 therein when a calibration measurement is to be made. Once the-calibration measurement is completed, the

actuators

129 and 130 are reversed to return the clamping bars 126 and 127 to their normal positions so that the pipe 16 (or 16) can freely pass through the clamping

devices

124 and 125.

It will be appreciated, therefore, that the present invention has provided new and improved radiation apparatus for accurately and quickly measuring the wall thicknesses of elongated tubular members of many different sizes. By arranging the new and improved radiation means to produce a plurality of narrowly-focussed beams of radiation which are transversely distributed across the longitudinally-directed inspection axis, depending upon the position of the masking means as a tubular member is advanced along this axis and over a radiation detector, either one or all of the radiation beams will be intercepted thereby even though the detector is erratically moving and does not remain in coincidental alignment with the axis. Thus, by further selecting the several radioactive sources and selectively positioning the masking means as described in detail herein, the output of the detector can be efficiently modified to provide a substantially-constant signal for a given thickness of metal over a predetermined range of eccentricity from the inspection axis irrespective of whether the pipe being inspected is large in diameter or relatively small in diameter.

While a particular embodiment of the present invention has been shown and described, it is apparent that changes and modifications may be made without departing from this invention in its broader aspects; and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

What is claimed is:

1. Apparatus adapted for alternative use with a first radiation detector adapted for loose insertion within tubular members of a first size range moving longitudinally along a predetermined inspection axis and a second smaller radiation detector adapted for loose insertion within tubular members of a second smaller size range moving longitudinally along said inspection axis and comprising:

a plurality of radiation sources arranged in a side-byside relationship positioned exterior of a tubular member moving along said inspection axis;

radiation-focussing means including a radiation shield between said radiation sources and said inspection axis and having a corresponding number of side-by-side focussing passages respectively aligned with said radiation sources for directing individual radiation beams toward spatially-disposed locations on a transverse plane crossing said inspection axis; and

radiation-controlling means cooperatively arranged between said radiation sources and said inspection axis and including a radiation-masking member positioned for selective movement in relation to said focussing passages between selected masking positions, first means on said masking member operable upon movement of said masking member to one of its said masking positions for passing all of said radiation beams to produce a composite radiation pattern of a selected intensity lying across said spatially-disposed locations on said transverse plane and having a lateral width greater than that of the first radiation detector, and second means on said masking member operable upon movement of said masking member to another of its said masking positions for passing less than all of said radiation beams to produce a reduced radiation pattern of a selected intensity lying across less than all of said spatially-disposed locations on said transverse plane and having a lateral width less than that of the second radiation detector.

2. The inspection apparatus of claim 1 wherein:

said first means include first radiation-passage means in said masking member adapted to be aligned with said focussing passages upon movement of said masking member to its said one masking position; and

said second means include second radiation-passage means in said masking member adapted to be aligned with less than all of said focussing passages upon movement of said masking member to its said other masking position, and radiation-blocking means on said masking member adapted to be aligned with the remaining ones of said focussing passages upon movement of said masking member to its said other masking position.

3. The inspection apparatus of claim 1 wherein:

said first means include a series of radiation passages spatially disposed along said masking member and adapted to be respectively aligned with all of said focussin g passages upon movement of said masking member to its said one masking position; and

said second means include a radiation passage in said masking member adapted to be aligned with one of said focussing passages upon movement of said masking member to its said other masking position, and radiation-blocking means on said masking member adapted to be aligned with the remaining ones of said focussing passages upon movement of said masking member to its said other masking position.

4. The inspection apparatus of claim 3 wherein:

said one radiation passage is between said radiationblocking means.

5. The inspection apparatus of claim 3 wherein:

said first means further include radiation-attenuating means in one of said radiation passages for selectively reducing the intensity of the radiation beam passing therethrough when said masking member is in its said one position.

6. The inspection apparatus of claim 5 wherein:

said one radiation passage is separated from said series of radiation passages.

7. The inspection apparatus of claim 1 wherein:

said first means include a series of first radiation passages spatially disposed along said masking member and adapted to be respectively aligned with said focussing passages upon movement of said masking member to its said one masking position; and

said second means include a series of second radiation passages spatially disposed along said masking member and adapted to be respectively aligned with said focussing passages upon movement of said masking member to its said other masking position. and radiation-blocking means in all but one of said second radiation passages for blocking said radiation beams from all but one of said radiation sources upon movement of said masking member to its said other masking position.

8. The inspection apparatus of claim 7 further including:

radiation-attenuating means in one of said first radiation passages for selectively reducing the intensity of the radiation beam passing therethrough when said masking member is in its said one masking position.

9. The inspection apparatus of claim 7 wherein:

said first and second radiation passages are alternately disposed along said masking member.

10. Apparatus adapted for alternative use with a first radiation detector adapted for loose insertion within tubular members of a first size range moving longitudinally along a predetermined inspection axis and a second smaller radiation detector adapted for loose inser- 6 tion within tubular members of a second smaller size range moving longitudinally along said inspection axis and comprising:

a plurality of radiation sources arranged in a side-byside relationship for rotation about the exterior of a tubular member moving along said inspection axis; radiation-focussing means including a radiation shield carrying said radiation sources and having a corresponding number of inwardly-directed focus sing passages respectively aligned with said radiation sources for directing individual radiation beams therefrom toward spatially-disposed locations on a transverse plane crossing said inspection axis; and radiation-controlling means cooperatively arranged between said radiation sources and said inspection axis and including a radiation-masking member positioned for selective movement in relation to said focussing passages between selected masking positions, first means on said masking member operable upon movement of said maskin'g member to one of its said masking position for passing all of said radiation beams to produce on said transverse plane a composite radiation pattern of a selected intensity and of a lateral width greater than that of the first radiation detector, and second means on said masking member operable upon movement of said masking member to another of its said masking positions for passing less than all of said radiation beams to produce on said transverse plane a reduced radiation pattern of a selected intensity and of a lateral width less than that of the second radiation detector. 11. The inspection apparatus of claim 10 wherein: there is an odd number of said radiation sources and focussing passages with one of said radiation sources and focussing passages being directed along a radiation beam axis intersecting said inspection axis and the remaining ones of said radiation sources and said focussing passages being equally disposed on opposite sides of said one radiation source and focussing passage for distributing said radiation patterns symmetrically across said inspection axis. 12. The inspection apparatus of claim 10 wherein: said first means include first radiation passages spatially disposed along said masking member and adapted to be respectively aligned with said focussing passages upon movement of said masking member to its said one masking position; and said second means include second radiation passages spatially disposed along said masking member and adapted to be respectively aligned with said focussing passages upon movement of said masking member to its said other masking position, and radiation-blocking means in all but one of said second radiation passages for blocking said radiation beams from all but one of said radiation sources upon movement of said masking member to its said other masking position. 13. The inspection apparatus of claim 12 further including:

radiation-attenuating means in one of said first radiation passages cooperatively arranged for selectively reducing the intensity of the radiation beam passing therethrough when said masking member is in its said one masking position. 14. The inspection apparatus of claim 12 wherein:

said first and second radiation passages are alternately disposed along said masking member. 15. Apparatus adapted for inspecting tubular members moving longitudinally along a predetermined inspection axis and comprising:

means adapted to support an elongated tubular member for axial movement along a selected inspection axis;

a body of radiation-attenuating material mounted for rotation about a tubular member moving along said inspection axis and carrying at least three radiation sources arranged in a side-by-side relationship;

radiation-focussing means on said rotatable body including a first focussing passage arranged therein in alignment between a first one of said radiation sources and a selected point of intersection with said inspection axis to direct an inwardly-directed narrowly-focussed first radiation beam toward said inspection axis for producing a substantiallyuniform reduced radiation pattern of a selected reduced dimension extending transversely across said point of intersection, and at least second and third focussing passages respectively arranged in said rotatable body in alignment with second and third ones of said radiation sources and on opposite sides of said first focussing passage to direct inwardlydirected narrowly-focussed second and third radiation beams on opposite sides of said reduced radiation beam for producing in conjunction with said first radiation beam a substantially-uniform composite radiation pattern of a selected enlarged dimension extending transversely across said inspection axis; and

radiation-controlling means cooperatively arranged on said rotatable body and including a radiationmasking member positioned for selective movement across said focussing passages between first and second masking positions, first means on said masking member cooperatively arranged for substantially blocking said second and third radiation beams whenever said masking member is in its said first masking position, and second means on said masking member cooperatively arranged for substantially passing all of said radiation beams when ever said masking member is in its said second masking position.

16. The inspection apparatus of claim wherein:

said first means include first and second radiationattenuation means cooperatively located on said masking member to be respectively situated in a beam-blocking position in said second and third focussing passages only upon movement of said masking member to its said first masking position.

17. The inspection apparatus of claim 15 wherein:

said second means include radiation passage means cooperatively located in said masking member to be in registration with all of said focussing passages only upon movement of said masking member to its said second masking position.

18. The inspection apparatus of claim 17 wherein:

said first means include first and second radiationattenuating means cooperatively located on said masking member to be respectively situated in a beam-blocking position in said second and third focussing passages only upon movement of said masking member to its said first masking position.

19. The inspection apparatus of claim 17 wherein:

said radiation-passage means include first, second and third ports in said masking member respectively adapted for alignment with said first, second and third focussing passages only upon movement of said masking member to its said second masking position.

20. The inspection apparatus of claim 19 further including:

radiation-reducing means in said first port cooperatively arranged to selectively reduce the radiation intensity of said first radiation beam only upon movement of said masking member to its said second masking position.

21. The inspection apparatus of claim 15 further including:

radiation-detecting means including a radiationsensitive element positioned in said transverse plane and adapted for loose reception in a tubular member moving along said inspection axis for operation only when said masking member is in its said first masking position and cooperatively, shaped for producing uniform output signals for a given wall thickness and material of a tubular member upon random movements therein of said radiation-sensitive element across said reduced radiation pattern.

22. The inspection apparatus of claim 15 further including:

Claims

1. Apparatus adapted for alternative use with a first radiation detector adapted for loose insertion within tubular members of a first size range moving longitudinally along a predetermined inspection axis and a second smaller radiation detector adapted for loose insertion within tubular members of a second smaller size range moving longitudinally along said inspection axis and comprising: a plurality of radiation sources arranged in a side-by-side relationship positioned exterior of a tubular member moving along said inspection axis; radiation-focussing means including a radiation shield between said radiation sources and said inspection axis and havIng a corresponding number of side-by-side focussing passages respectively aligned with said radiation sources for directing individual radiation beams toward spatially-disposed locations on a transverse plane crossing said inspection axis; and radiation-controlling means cooperatively arranged between said radiation sources and said inspection axis and including a radiation-masking member positioned for selective movement in relation to said focussing passages between selected masking positions, first means on said masking member operable upon movement of said masking member to one of its said masking positions for passing all of said radiation beams to produce a composite radiation pattern of a selected intensity lying across said spatially-disposed locations on said transverse plane and having a lateral width greater than that of the first radiation detector, and second means on said masking member operable upon movement of said masking member to another of its said masking positions for passing less than all of said radiation beams to produce a reduced radiation pattern of a selected intensity lying across less than all of said spatially-disposed locations on said transverse plane and having a lateral width less than that of the second radiation detector.

2. The inspection apparatus of claim 1 wherein: said first means include first radiation-passage means in said masking member adapted to be aligned with said focussing passages upon movement of said masking member to its said one masking position; and said second means include second radiation-passage means in said masking member adapted to be aligned with less than all of said focussing passages upon movement of said masking member to its said other masking position, and radiation-blocking means on said masking member adapted to be aligned with the remaining ones of said focussing passages upon movement of said masking member to its said other masking position.

3. The inspection apparatus of claim 1 wherein: said first means include a series of radiation passages spatially disposed along said masking member and adapted to be respectively aligned with all of said focussing passages upon movement of said masking member to its said one masking position; and said second means include a radiation passage in said masking member adapted to be aligned with one of said focussing passages upon movement of said masking member to its said other masking position, and radiation-blocking means on said masking member adapted to be aligned with the remaining ones of said focussing passages upon movement of said masking member to its said other masking position.

4. The inspection apparatus of claim 3 wherein: said one radiation passage is between said radiationblocking means.

5. The inspection apparatus of claim 3 wherein: said first means further include radiation-attenuating means in one of said radiation passages for selectively reducing the intensity of the radiation beam passing therethrough when said masking member is in its said one position.

6. The inspection apparatus of claim 5 wherein: said one radiation passage is separated from said series of radiation passages.

7. The inspection apparatus of claim 1 wherein: said first means include a series of first radiation passages spatially disposed along said masking member and adapted to be respectively aligned with said focussing passages upon movement of said masking member to its said one masking position; and said second means include a series of second radiation passages spatially disposed along said masking member and adapted to be respectively aligned with said focussing passages upon movement of said masking member to its said other masking position, and radiation-blocking means in all but one of said second radiation passages for blocking said radiation beams from all but one of said radiation sources upon movement of said masking member to its said other masking position.

8. The inspection apparaTus of claim 7 further including: radiation-attenuating means in one of said first radiation passages for selectively reducing the intensity of the radiation beam passing therethrough when said masking member is in its said one masking position.

9. The inspection apparatus of claim 7 wherein: said first and second radiation passages are alternately disposed along said masking member.

10. Apparatus adapted for alternative use with a first radiation detector adapted for loose insertion within tubular members of a first size range moving longitudinally along a predetermined inspection axis and a second smaller radiation detector adapted for loose insertion within tubular members of a second smaller size range moving longitudinally along said inspection axis and comprising: a plurality of radiation sources arranged in a side-by-side relationship for rotation about the exterior of a tubular member moving along said inspection axis; radiation-focussing means including a radiation shield carrying said radiation sources and having a corresponding number of inwardly-directed focussing passages respectively aligned with said radiation sources for directing individual radiation beams therefrom toward spatially-disposed locations on a transverse plane crossing said inspection axis; and radiation-controlling means cooperatively arranged between said radiation sources and said inspection axis and including a radiation-masking member positioned for selective movement in relation to said focussing passages between selected masking positions, first means on said masking member operable upon movement of said masking member to one of its said masking position for passing all of said radiation beams to produce on said transverse plane a composite radiation pattern of a selected intensity and of a lateral width greater than that of the first radiation detector, and second means on said masking member operable upon movement of said masking member to another of its said masking positions for passing less than all of said radiation beams to produce on said transverse plane a reduced radiation pattern of a selected intensity and of a lateral width less than that of the second radiation detector.

11. The inspection apparatus of claim 10 wherein: there is an odd number of said radiation sources and focussing passages with one of said radiation sources and focussing passages being directed along a radiation beam axis intersecting said inspection axis and the remaining ones of said radiation sources and said focussing passages being equally disposed on opposite sides of said one radiation source and focussing passage for distributing said radiation patterns symmetrically across said inspection axis.

12. The inspection apparatus of claim 10 wherein: said first means include first radiation passages spatially disposed along said masking member and adapted to be respectively aligned with said focussing passages upon movement of said masking member to its said one masking position; and said second means include second radiation passages spatially disposed along said masking member and adapted to be respectively aligned with said focussing passages upon movement of said masking member to its said other masking position, and radiation-blocking means in all but one of said second radiation passages for blocking said radiation beams from all but one of said radiation sources upon movement of said masking member to its said other masking position.

13. The inspection apparatus of claim 12 further including: radiation-attenuating means in one of said first radiation passages cooperatively arranged for selectively reducing the intensity of the radiation beam passing therethrough when said masking member is in its said one masking position.

14. The inspection apparatus of claim 12 wherein: said first and second radiation passages are alternately disposed along said masking member.

15. Apparatus adapted for inspecting tubular members moving longitudinally along a predetermined inspection axis and comprising: means adapted to support an elongated tubular member for axial movement along a selected inspection axis; a body of radiation-attenuating material mounted for rotation about a tubular member moving along said inspection axis and carrying at least three radiation sources arranged in a side-by-side relationship; radiation-focussing means on said rotatable body including a first focussing passage arranged therein in alignment between a first one of said radiation sources and a selected point of intersection with said inspection axis to direct an inwardly-directed narrowly-focussed first radiation beam toward said inspection axis for producing a substantially-uniform reduced radiation pattern of a selected reduced dimension extending transversely across said point of intersection, and at least second and third focussing passages respectively arranged in said rotatable body in alignment with second and third ones of said radiation sources and on opposite sides of said first focussing passage to direct inwardly-directed narrowly-focussed second and third radiation beams on opposite sides of said reduced radiation beam for producing in conjunction with said first radiation beam a substantially-uniform composite radiation pattern of a selected enlarged dimension extending transversely across said inspection axis; and radiation-controlling means cooperatively arranged on said rotatable body and including a radiation-masking member positioned for selective movement across said focussing passages between first and second masking positions, first means on said masking member cooperatively arranged for substantially blocking said second and third radiation beams whenever said masking member is in its said first masking position, and second means on said masking member cooperatively arranged for substantially passing all of said radiation beams whenever said masking member is in its said second masking position.

16. The inspection apparatus of claim 15 wherein: said first means include first and second radiation-attenuation means cooperatively located on said masking member to be respectively situated in a beam-blocking position in said second and third focussing passages only upon movement of said masking member to its said first masking position.

17. The inspection apparatus of claim 15 wherein: said second means include radiation passage means cooperatively located in said masking member to be in registration with all of said focussing passages only upon movement of said masking member to its said second masking position.

18. The inspection apparatus of claim 17 wherein: said first means include first and second radiationattenuating means cooperatively located on said masking member to be respectively situated in a beam-blocking position in said second and third focussing passages only upon movement of said masking member to its said first masking position.

19. The inspection apparatus of claim 17 wherein: said radiation-passage means include first, second and third ports in said masking member respectively adapted for alignment with said first, second and third focussing passages only upon movement of said masking member to its said second masking position.

20. The inspection apparatus of claim 19 further including: radiation-reducing means in said first port cooperatively arranged to selectively reduce the radiation intensity of said first radiation beam only upon movement of said masking member to its said second masking position.

21. The inspection apparatus of claim 15 further including: radiation-detecting means including a radiation-sensitive element positioned in said transverse plane and adapted for loose reception in a tubular member moving along said inspection axis for operation only when said masking member is in its said first masking position and cooperatively, shaped for producing uniform output signals for a given wall Thickness and material of a tubular member upon random movements therein of said radiation-sensitive element across said reduced radiation pattern.

22. The inspection apparatus of claim 15 further including: radiation-detecting means including a radiation-sensitive element positioned in said transverse plane and adapted for loose reception in a tubular member moving along said inspection axis for operation only when said masking member is in its said second masking position and having an effective width less than that of said composite radiation pattern for producing uniform output signals for a given wall thickness and material of a tubular member upon random movements therein of said second radiation-sensitive element across said composite radiation pattern.