GB2157930A

GB2157930A - Radiography apparatus

Info

Publication number: GB2157930A
Application number: GB08509569A
Authority: GB
Inventors: Ian Geoffrey Brewis Redmayne
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-04-13
Filing date: 1985-04-15
Publication date: 1985-10-30
Also published as: GB2157930B; GB8509569D0

Abstract

Apparatus for the inspection of pipe welds comprises a radiation source 2 for transmitting radiation, say as X-rays, through a pipe weld 15, and a detector in box 16 arranged diametrically opposite the source 2, with respect to the pipe 14, for detecting the transmitted radiation and providing electrical signals which are processed to produce an image of the weld 15. The source 2 and detector are mounted on a frame 1 which is rotatable about an inner frame 11 clamped to the pipe 14. <IMAGE>

Description

SPECIFICATION Radiography apparatus The present invention relates to radiography, and in particularto the inspection of pipe welds where the pipe is fixed in position.

GB 1570310 and WO 83/01509 disclose systems for the inspection of pipe welds in which a source of radiation is positioned within the pipe and a detector intheform of a flourescentscreen is mounted outside ofthe pipe to detect radiation passing through the weld from the source. The pipe is rotated or moved axially dependent upon whether the weld is a girth weld or extends along the pipe. The picture formed on the screen may be viewed by means of a camera and V.D.U. and may be stored.

GB 2042860 and GB 2064929 disclose systems suitable for inspecting a pipe weld with the pipe in situ in which a source of radiation, such as X-rays, is fixed in position on one side of the pipe weld, and a radiation sensitive film is laid againstthe weld diametrically opposite the source, and exposed to the radiation penetrating the pipe walls and the weld. The source is relocated at a number of positions around the pipe to examine the complete weld.

Afirst aspect of the present invention provides apparatusfortheinspection of pipewelds, comprising means for mounting a source of penetrating radiation adjacent the outside ofthe pipe wall, the source being arranged to transmit radiation through the weld, means for mounting a detector adjacent the outside of the pipe wall to detect radiation transmitted through a portion ofthe weld and provide an electrical signal indicative of the transmitted radiation and means for moving the source and detectortogetheraround the circumferenceofthe pipe to build up an imageofthe complete weld.

Very preferably the detector comprises an array of radiation sensitive elements. The radiation will be of a type which can pass th rough the pipe wall, usually X-ray or gamma ray radiation. The sensitive elements may be scintillators which are coupled to photodiodes or the like to provide an electrical signal. A linear array of photosensitive elements may be used, aligned generally in the axial direction ofthe pipe.

The detecting means may comprise an X-ray sensitive vidicon or fluorescent material which is scanned by a T.V. camera or similar device.

The invention thus provides a system which utilises a detector which can provide for real-time analysis of a pipe weld with the pipe in situ.

Preferablythe detecting means is arranged substantially diametrically opposite the radiation source with respectto the pipe. By offsetting the source in the axial direction of the pipe relative to the weld the beam will pass through the pipe wall adjacent the weld and then through the weld diametrically opposite.

The radiation source and the array of elements are stepped automatically or moved continuously around the circumference ofthe pipe to build up a picture of the complete weld.

The signal from the detector, indicative of the radiation passing through the pipe and thus providing an image ofthe pipe weld, may be repeatedly summed over a period oftimeto increase the signal to noise ratio.

In a particular preferred embodiment, a two dimensional array of radiation sensitive elements is used.

The array is stepped through the path ofthe radiation and the signal produced by each row of the array as it detects the radiation passing through a particular region ofthe weld is summed, thereby increasing the signal to noise ratio and, in particular, accounting for variations in sensitivity or response of the elements in a row ofthe array.

Accordingly, a further aspect of the invention provides a detection system for detecting a stream of radiation comprising an array of sensitive elements, means for moving the array relative to the stream of radiation, means for producing from each row of the array a signal indicative ofthe patern of radiation incidentthereupon and means for summing the signals produced by the rows ofthe array.

The radiation source and the detector are moved in a full circle around the pipe weld. The signal from the detector may be stored and used to display on a video screen such as a cathode ray tube a picture of the complete weld, thus providing for realtime analysis of the weld.

The signals may be recorded onto magnetic tape or other recording media before or after (digital) image processing by a computer.

In orderto locate accurately regions of interest in the weld both during and after inspection a datum line may be provided on the pipe. Preferably this datum is in the form of a tape which can be read by the apparatus as it rotates the detector and radiation source, to indicate the position of the detector on the pipe. Very preferably the tape is a recording and/or reproducing medium such asa magnetictapewhich can be read from, and optionally written to, by means of a tape head provided on the apparatus. Other systems, such as opto-electronic systems, e.g. a bar code system, may be used. The tape may be stuck to the pipe and may be left in position after inspection.

The tape may be recorded with information indicating the quality of weld, and possibly with a signal representative of the signal produced by the detector.

The use of a datum line is applicable to other inspection systems where the radiation source and/or detector is moved around the pipe.

Accordingly a third aspect ofthe invention provides a method of inspecting a pipe weld, in which a radiation source and/or detector is moved relativeto the pipe and a datum line is provided on the pipe, said datum line being readable to indicate the position of source and/or detector.

Preferablythemeansformounting andmovingthe source and detector comprises a first member which is fixable in position on a pipe, a second member connected to the first member and extending around su bstantialiy the whole circumference of the pipe and being splitfor location therearound, the source and detector being mounted on the second member.

The first member may carry a rack or otherwise form a pinion which is engaged by a toothed wheel rotatably mounted on the second member. A motor may be provided on the second memberto rotate the toothed wheel to drive the member circumferentially around the pipe.

There may be a degree of backlash in the drive system which is preferably avoided. However, by using the apparatus in conjunction with a fixed readable datum line and with the benefit of storing an imageofthetransmitted radiation itwill be possibleto account readilyfor any backlash.

The means for mounting the detectorand source preferably include means for moving the detector relative to thesource. In particular means may be provided forstepping the detectorthrough the incident radiation beam. Preferably a collimator will be provided between the pipe wall and the detector.

To form a complete picture of the weld it is proposed to adopt a stereoscopic imaging technique.

The weld will be radiographed from two or more angles. This may be achieved in a number of ways.

To form a stereoscopic image in a single pass around the weld a pairofdetectors may be mounted on the pipe. The detectors preferably being spaced from one another circumferentially around the pipe to receive different portions ofthe beam transmitted by the source. As the detectors and source move around the pipe each position ofthe weld will effectively be imaged from two angles as the two detectors pass by it. The beam from the source may be collimated to form two separate beams.

In another arrangement a pair of detectors and a pair of respective sources may be used. They may be arranged so thatthe radiation beams are at 900 to one another.

A common method of forming a pipe weld is to chamfer the pipe ends to form a V-shaped groove where the pipe ends abut. Defects in the weld often occurattheface ofthe V, extending parallel to the face, and these can be difficult to detect ifthey are planar, extending transverse to the direction of the radiation beam. By utilising two beams at an angle of say 10 degrees directed along each face ofthe V such defects can be more readily detected, the transverse beam enabling the inner and outer radial limits ofthe defect to the detected.

The invention will befurtherdescribed byway of example with reference to the accompanying drawings, in which: Figure 1 is an end view of an apparatus according to the invention, shown mounted on a pipe; Figure 2 is a side view, partly cutaway, of Figure 1; and Figure 3 is an underneath view ofthe apparatus of Figure 1.

In the drawings, a pipe 14 has a weld in the region indicated by arrow 15. An X-ray source 2 is mounted in a casing 17 which isfirmly mounted in an outerframe 1 which is mounted on the pipe 14 for rotation therearound. The source 2 emits a beam of radiation which passes diametricallythrough a pipe 14to a detector 3. The detector 3 consists of an array of scintiliators coupled to photodiodes to provide an electrical signal indicative ofthe amount of radiation incident thereupon. Detector3 is mounted in a shielded box 16 secured to outer frame 1 so as to be diametrically opposite the source 2 with respect to the pipe 14.

As seen in Figure 1, the outerframe 1 is split along a diameter, the two halves being hinged together at a pin 12 and the frame is clamped around the pipe 14 by clamp assembly illustrated by a bolt head and a boit (not shown) which is pivotally mounted in the lower frame half 1 a on a pivot 18.

The outerframe 1 is mounted on an inner clamping member 11 which is firmly clamped on the pipe. The inner clamping member may be arranged to contact the pipe l4ata number of points only, say3, to accommodate non-uniform pipe cross-sections. The outerframe 1 is form-locked on the inner clamp 11 against axial movement, for example by running between flanges (notshown). Clamp member 11 carries an external gear 19 which meshes with a gear wheel 20 which is mounted fast on an axle 21 journalled in the frame member 1 and driven by a motor 22.

To ensure accurate and smooth movement the halves of the frame 1 closetogetherfullyand accurately around inner clamp 11. Inner clamp member 11 may have replaceable centre pieces to accommodate different pipe sizes.

The source 2 comprises a tube head 8 housing an X-ray source (not shown) which emits X-raysthrough a collimator 9. The tube head may be retracted within casing 17 when the apparatus is not in use. The beam emitted by source 2 is collimated to form a narrow beam which extends in the axial direction of the pipe 14 as shown by the dashed lines in Figure 2.

The detector 3 consists of a two dimensional array of scintillators having a centre to centre spacing of about 40 microns. The detector3 is movable either continuously or in stepped intervals of say 40 microns, tangentiallyofthe pipe 14so asto position each row of the array in turn diametrically opposite the source 2.

The X-ray beam impinging on the detector is colli ,mated by a collimator7 on the box 16. The aperture of collimator7 extends in the axial direction of the pipe.

The array may be activated or read from one row at a time.

A magnetictape 5 is affixed to the pipe wall and is read from and written to by a reproducing head 6 mounted on an arm 4which is fast with the outer frame 1.

In usethe innerclamp member 11 is clamped onto the pipe 14a predetermined distance from the weld 15. The outer frame member is then clamped onto the inner clamp member 11, with the gearwheel 20 meshing with the external gear 19.

As seen in Figure 1, source 2 is positioned to one side of the weld and arranged so that radiation passes through a plain section of the pipe wall before impinging on the weld diametrically across the pipe.

Detector 3 then monitors the radiation transmitted throughtheweld 15.

Motor 22 is driven to move the frame member 1 stepwise orcontinuously around the pipe 14. The relative position of the detector on the pipe circumference is monitored by means of prerecorded magnetic tape which is fixed to the pipe and read by head 6. An optical system such as a barcode may also be used. By using a magnetictapedata may also be written to the datum line formed by tape 5.

Detector 3 is stepped through the beam passing through collimator 7 and signals from each row of the array as it passes through the beam are summed and stored. Astheframe 1 rotates completely around the pipe a complete picture ofthe weld is built up. The frame 1 may be stepped around the pipe, for example in 0.1 intervals, the array being stepped completely through the beam at each interval. It can be seen that the frame 1 may also be driven continuously if only limited resolution is required.

The signals may be processed and displayed on a cathode ray tube to provide a real-time display ofthe weld, enabling rapid approval or correction ofthe weld and/orthey may be recorded, before or after digital enhancement by a computer.

The signal read from the magnetic tape can be stored and displayed alongside the data obtained from the detectorto enable rapid identifications of defective areas of the weld and if desired summation of repeated passes of the same weld area.

The apparatus when mounted on a pipe may be covered with a radiation absorbentcanopyto protect the user fro stray radiation. The cathode ray tube and a control panel maythen be located a short distance from the apparatus.

In anotherform ofthe device an outer frame encircling the pipe and carries within it an inner frame carrying the source and detector. Both innerand outer frames are split along a diameterto allow them to be mounted on the pipe. The outerframe is clamped in a fixed position on the pipe, preferably bearing on a collar which is attached to the pipe and allows four tolerance in the pipe diameter. The innerframe is driven relative to the outer frame.

The apparatus may be adapted for analysis or inspection of a pipe by other methods, such as visual or photographic inspection, eddy current and magnetic field analysis. The data for each type of insepction may be recorded in a like manner so asto be referable to data obtained by other methods. The apparatus may be arranged so that more than one method of inspection is performed simultaneously.

twill be appreciated that the apparatus ofthe invention may be used with pipes of different materials, the radiation source and detector being changed to suitthe material ofthe pipe. Also means may be provided for moving the source and detector axially of the pipeaswell as circumferentially.

Claims

1. Apparatus for the inspection of pipewelds, comprising means for mounting a source of penetrating radiation adjacent the outside of the pipe wall, the source being arranged to transmit radiation through the weld, means for mounting a detector adjacent the outside ofthe pipe wall for detecting radiation transmitted through a portion of the weld, the detector providing an electrical signal indicative ofthetransmitted radiation, and means for moving the source and detectortogether around the circumference ofthe pipe to build up an image of the complete weld.

2. Apparatus as claimed in claim 1, in which the detector is arranged substantially diametrically opposite the radiation source with resepcttothepipe.

3. Apparatus as claimed in claim 1 or 2, in which the detector is mountable attwo positions relative to the detector.

4. Apparatus as claimed in claim 1 or 2, in which there are provided two detectors and/or sources at spaced locations around the circumference ofthe pipe.

5. Apparatus as claimed in claim 4, in which there are provided two detectors and two sources, spaced at approximately 90 around the pipe and staggered in the axial direction ofthe pipe.

6. Apparatus as claimed in claim 5, wherein a first source and detector combination is arranged to provide and monitor a beam of radiation passing down oneface of the weld and the second source and detector combination is arranged to provide and monitor a beam of radiation passing down the other side face ofthe weld.

7. Apparatus as claimed in any one of claims 1 to 6 in which the said detector comprises an array of radiation sensitive elements.

8. Apparatus as claimed in any one of claims 1 to 7 in which the electrical signal is repeatedly summed over a period of time to increase the signal to noise ratio.

9. Apparatus as claimed in claim 7 in which the array of radiation sensitive elements is a two dimensional array.

10. Apparatus as claimed in claim 9, including means for moving the arraythrough the path of the transmitted radiation and meansforsummingthe signals produced by different rows ofthe array asthey detect radiation passing through a particular region of the weld.

11. Apparatus as claimed in any one of claims 1 to 6 in which the detector comprises a vidicon or fluorescent material scanned by a T.V. camera or similar device.

12. Apparatus as claimed in any one of claims 1 to 11 inciuding means for processing said electrical signal for displaying the image oftheweld, or a part thereof on a video screen.

13. Apparatus as claimed in any one of claims 1 to 2 including means for processing the electrical signal to enhance the image oftheweld.

14. Apparatus as claimed in any one of claims 1 to 13, including means for recording the electrical signals before and/or after processing.

15. Apparatusasclaimedinanyoneofclaimsl to 14, including means for reading a datum line fixed in position on the pipe.

16. Apparatus as claimed in any one of claims 1 to 15 comprising a first member which is attachable in a fixed position on the pipe and a second member carrying the detector(s) and source(s) which is attachable to the pipe and rotatable therearound relative to the first member.

17. Apparatus as claimed in claim 15 in which the second member is attached around the first member.

18. Apparatus as claimed in claim 16, in which the first member includes an external gearwhich encircles the pipe and means for rotating the second member around the pipe comprises a gearwheel driven by a microprocessor controlled motor.

19. Apparatus as claimed in claims 16, or 18, in which the means for reading the datum line is carried bythesecond member.

20. Apapratusforthe inspection ofpipewelds, substantially as hereinbefore described with reference to the accompanying drawings.

21. Detection system for detecting a stream of radiation and comprising an array of sensitive elements, means for moving the array relative to the stream of radiation, means for producing from each row ofthe array a signal indicative ofthe pattern of radiation incident thereupon and means for summing the signals produced by the rows ofthe array.

22. Apparatusforthe inspection of a pipe, comprising means forattachment to the pipe to form a fixed datum line around the circumference of the pipe, meansfor inspecting the pipe at a plurality of positions aboutthe circumferencethereof, and means for moving the inspecting means around the pipe circumference and noting the position of inspection relative to the datum line.