Abstract
The invention discloses a scanning method and apparatus suitable for scanning a pipeline or process vessel in which a beam of gamma radiation from a source is emitted through the vessel to be detected by an array of detectors which are each collimated to detect radiation over a narrow angle relative to the width of the emitted radiation beam.
Claims
1. A method of inspecting an underwater pipeline to determine wall thickness or information about the contents of the pipeline, the method comprising: interposing the pipeline between a gamma radiation source and an array of detector units, the source and the detector units being mounted in a fixed relationship with each other on a support so that the radiation emitted by the source passes along a plurality of paths through a portion of the pipeline and impinges upon the detector units; rotating the support, the source, and the detector units around a circumference of the pipeline and acquiring data at a plurality of radially offset positions around the pipeline to acquire density data at a variety of angles through the pipeline; and presenting a representation of the pipeline or contents of the pipeline using the density data.
2. The method according to claim 1, wherein the support, the source, and the array of detector units are provided on an apparatus that comprises a buoyancy material.
3. The method according to claim 2, wherein the apparatus is hinged so that the apparatus is configured to be opened and closed around the pipeline.
4. The method according to claim 1, wherein the representation is a representation of the composition of the pipeline or its contents.
5. The method according to claim 1, wherein the representation is built using tomography algorithms.
6. The method according to claim 1, further comprising detecting a void in the pipeline.
7. The method according to claim 1, further comprising detecting a crack in the pipeline.
8. The method according to claim 1, further comprising detecting wall thinning in the pipeline.
9. The method according to claim 1, further comprising detecting a gas hydrate within the pipeline.
10. The method according to claim 1, further comprising detecting scale within the pipeline.
11. The method according to claim 1, further comprising detecting a change in density relative to a reference value.
12. The method according to claim 11, wherein the reference value is a calculated value.
13. The method according to claim 11, wherein the reference value is a value from an adjacent portion of the pipeline.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0062] The invention will be further described with reference to the attached drawings, which are:
[0063] FIG. 1: a schematic view of a scintillator suitable for use in the scanning method and apparatus of the invention
[0064] FIG. 1A: A view of the scintillator of FIG. 1 from direction A.
[0065] FIG. 1B: A schematic view of an alternative scintillator suitable for use in the scanning method and apparatus of the invention.
[0066] FIG. 2: a schematic view through a section of a detector unit.
[0067] FIG. 3: a schematic view through a longitudinal section of a detector unit
[0068] FIG. 4: a schematic view of a detector block forming part of a radiation detector according to the invention.
[0069] FIG. 5: a schematic view of a photomultiplier mounting block forming part of a radiation detector according to the invention.
[0070] FIG. 6: a schematic view of a collimator block forming part of a radiation detector according to the invention.
[0071] FIG. 5: a schematic sectional view of a radiation detector according to the invention.
[0072] FIG. 7: a schematic view through a section of an alternative detector unit
[0073] FIG. 8: a view of a front elevation of the detector unit of FIG. 7.
[0074] FIG. 9: a diagrammatic view of a preferred arrangement of the apparatus.
[0075] FIG. 10: a schematic view of an array of detector units for an apparatus according to the invention
[0076] FIG. 11: a schematic view of a part of an apparatus according to the invention.
[0077] FIG. 12: a schematic elevation view of an apparatus according to the invention
[0078] FIG. 13: a schematic perspective view of the apparatus shown in FIG. 12;
[0079] FIG. 14: a schematic elevation view of an apparatus according to the invention, and
[0080] FIG. 15: a schematic elevation view of an apparatus according to the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0081] FIGS. 1 and 1A show a bismuth germanate (BGO) scintillator crystal 10 having a thickness t of 5 mm, a height h of 30 mm and a depth d of 75 mm. The detecting surface 12 is opposite the collecting surface 14. All surfaces of the bismuth germanate (BGO) scintillator crystal 10 except the detecting surface 12 and collecting surface 14 are coated in a highly reflective coating. FIG. 1B shows an alternative bismuth germanate (BGO) scintillator crystal 10.
[0082] FIG. 2 shows, a transverse cross-section through a detector unit 30, comprising a block of heavy alloy 16 which is highly attenuating to radiation, of the type used as shielding material for gamma radiation. The block of heavy alloy 16 has collimation channels 18 extending from the front face to the opposed rear face of the block of heavy alloy 16. In use, a bismuth germanate (BGO) scintillator crystal 10 is housed in the block of heavy alloy 16, with the detecting surface 12 of the bismuth germanate (BGO) scintillator crystal 10 at the front face of the block of heavy alloy 16 and the collecting surface 24 optically connected to photomultiplier tube (PMT) 20. Photomultiplier tube (PMT) 20A is connected to an adjacent bismuth germanate (BGO) scintillator crystal 10 (not shown), and is shown to demonstrate the packing of the photomultiplier tubes (PMTs) within the detector unit 30. The detector unit 30 comprises nineteen detectors, each comprising a bismuth germanate (BGO) scintillator crystal 10 and a photomultiplier tube (PMT) 20 and mounted in register with a collimation channel 18 in the block of heavy alloy 16.
[0083] FIG. 3 shows a longitudinal section through an assembled radiation detector comprising a collimator block 40, a detector block 200 and a PMT mounting block 300, each shown individually in FIGS. 4-6. The blocks are mounted together so that channels 46, 36 and 26 are all in register, together forming channels extending from the front face of the collimator block 40 to the rear of the PMT mounting block 300. A scintillator crystal 10 is housed within channel 26 and a PMT 50 is housed within channel 36. The PMT 50 may be connected to electronic data processing and control apparatus by means of connectors accessible from the rear of the channel 36. Channels 46a, 36a and 26a and the scintillator 10a and PMT 50a are shown in dashed outline because they are not in the same plane as the respective channels and components in solid outline. In the embodiment shown, the longitudinal axes of the channels 26, 36, and 46 form an angle of between 1 and 2° with the longitudinal axis 51 of each block 200, 300, and 400.
[0084] FIG. 4 shows a detector block 200 which comprises a rectangular block of heavy alloy 21 which is highly attenuating to radiation, of the type used to as shielding material for gamma radiation. The rectangular block of heavy alloy 21 has channels 26 extending from the front face 22 of the rectangular block of heavy alloy 21 to the opposed rear face 24. Blind sockets 28 are provided for locating and mounting a collimator block. The channels 26 are sized to house a scintillator crystal. In use, a scintillator crystal is housed in each channel 26, with the detecting surface of the scintillator crystal at the front face 22 of the rectangular block of heavy alloy 21 and the collecting surface at the rear face 24.
[0085] FIG. 5 shows a photomultiplier mounting block 300 which comprises a rectangular block of white plastic material such as polytetrafluoroethane. Channels 36 extend from the front face 32 of the photomultiplier mounting block 300 to the opposed rear face 34. The channels 36 are each of an appropriate size to house a small photomultiplier tube. The channels 36 are positioned in the photomultiplier mounting block 300 in such a way that each opening at the front face 32 of the photomultiplier mounting block 300 butts against the collecting surface 14 of a scintillator crystal 10 mounted in an adjacent detector block 200 when the rear face 24 of the detector block 200 is placed against the front face 32 of the PMT mounting block 300. Blind sockets 38 are provided for locating and mounting to the detector block 200.
[0086] FIG. 6 shows a collimator block 40 comprising a rectangular block of heavy alloy which is highly attenuating to radiation, of the type used to as shielding material for gamma radiation. The collimator block 40 has channels 46 extending from the front face 42 of the collimator block 40 to the opposed rear face 44. Blind sockets 48 are provided for locating and mounting a detector block 200. The block channels 46 have a width and height which is slightly less than the width and height of the channels 26 in the detector block 200. In an assembled radiation detector, rear face 44 of collimator block 40 is mounted against the front face 22 of detector block 200 such that channels 46 are in register with channels 26.
[0087] In FIG. 10, a detector unit 30 consisting of 19 collimation channels 18, scintillator crystals 10 and photomultiplier tubes (PMTs) 20 is shown, in which the collimation channels 18 are formed into a single block being spaced apart and angled from each other by an angle of about 1 degree of arc.
[0088] FIGS. 7 and 8 show an alternative arrangement for a detector unit. In FIG. 7, the steel block 60 forming the collimator 62 and holding the scintillator 64 and PMT 66 is formed from a stainless steel. The PMT 66 is mounted out of alignment with the radiation direction in order to reduce the total depth of the detector unit. The direction of radiation is indicated by the arrow. FIG. 8 shows an elevation from the direction of the arrow. Layers 68 and 69 of a dense heavy alloy shielding material are positioned above and below the steel block 60. This material provides additional shielding for the detectors from scattered radiation impinging on the detector unit.
[0089] FIG. 11 shows a support 70 joined rigidly at one end to a generally arcuate shaped detector housing 72, all formed of an aluminium alloy, and at the other end to a source unit 74. An arrangement of the source unit 74 and detector units is shown in FIG. 9. The direction of three collimator channels is illustrated in order to show that they align with the direction of the source unit 74 and are not aligned with the radius Rt of the structure. The source unit 74 and detector housing 72 is arranged to rotate about a central point on the structure on a path having a radius Rt. The source unit 74 comprises a caesium source 78 of gamma radiation surrounded by heavy alloy shielding material 76 including a slot for collimating radiation in a fan shaped beam 80 towards the detector housing 72. The detector housing 72 comprises an aluminium alloy cage and, in the embodiment shown, contains two arcuate arrays of detector units 30, one at each end. The detector housing 72 includes rails along which the detector units may be moved to different locations within the detector housing 72. The detector housing 72 shown could accommodate one or more additional detector unit arrays if required.
[0090] FIGS. 12 and 13 show an apparatus for scanning steel pipe 82, having an internal diameter of about 234 mm and a wall thickness of about 43 mm, to detect changes and flaws in the wall. The pipe wall is surrounded by a layer of insulating material 84. A support member 86 is clamped to the pipeline by means of clamps 88 hydraulically operated by arms 90. The support member 86 also supports rails 92 which support the support 70, detector housing 72 and source unit 74. A motor 94 mounted on the detector housing 72 is operable to move the detector housing 72 and source unit 74 along the rails 92 and thereby to rotate the position of the source and detectors around the pipeline. At each position, radiation emitted by the source towards each detector in the two detector units forms a number of radiation paths through the pipe wall and insulation equal to the number of detectors, which in this case is (19×2)=38 separate paths which can be scanned at the same time. When the apparatus is rotated to a different position along the rails 92, a further 38 paths can be scanned. Data in the form of counts detected by the detectors is processed and stored by a data processor housed in housing 96 located towards the top of the support 70. Deployment of the detector units in the positions shown is particularly suitable for scanning the pipeline walls and insulation to detect flaws and changes between different locations in the pipe.
[0091] In the detector housing 72 shown, there is space for one or more detector units to be placed in the central portion of the housing 96. In that position, a detector unit would detect radiation which has passed through the lumen of the pipe 82 and its contents. Use of a detector unit in such a position would therefore be suitable for conducting tomography scans of the pipe 82 and contents.
[0092] FIGS. 14-15 show another embodiment of a scanning apparatus according to the invention. The apparatus comprises two parts of a hinged housing 102 which together form a clamp with jaws which can be opened (FIG. 14) and closed (FIG. 15) around the pipe 82 by operation of a hydraulic cylinder 98. When closed, the hinged housings 102 surround the pipe 82 but are spaced apart from the surface of the pipe 82. Rollers 100 contact the surface of the pipe 82 and maintain the spacing of the hinged housing 102 from the pipe 82. Hinged housing 102 covers and contains a detector housing for one or more arrays of detector units and a source unit 72 as described above. The source and detector unit are mounted in a fixed relationship to one another and are arranged to move along a track within the jaws so as to rotate around the circumference of the pipeline. Adjustable grippers 104 are present either side of the pipe 82 which are operable by means of a hydraulic cylinder 108 to grip the pipe 82 and centralise it within the space between the jaws and the pipe 82. When the hinged housing 102 is closed around the pipe 82 and centralised by the adjustable grippers 104, the source unit 74 and detector housing 72 are rotated around the pipe 82 so that density information can be acquired by the detectors at a plurality of angular locations around the pipe 82. The data is then processed to produce a tomography image or an indication of one or more properties of the pipeline at different locations around the path of the scanning operation. When sufficient data has been acquired, the hinged housing 102 is opened and moved to a different location along the pipeline for new scanning data to be acquired.
