1、raising standards worldwideNO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBSI Standards PublicationBS EN 16016-3:2011Non destructive testing Radiation methods Computed TomographyPart 3: Operation and interpretationIncorporating corrigendum September 2011BS EN 16016-3:2011Natio
2、nal forewordThis British Standard is the UK implementation of EN 16016-3:2011. The UK participation in its preparation was entrusted to Technical Committee WEE/46, Non-destructive testing.A list of organizations represented on this committee can be obtained on request to its secretary.This publicati
3、on does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. The British Standards Institution 2012 Published by BSI Standards Limited 2012 ISBN 978 0 580 77873 5 ICS 19.100 Compliance with a British Standard cannot confer immunity fro
4、m legal obligations.This British Standard was published under the authority of the Standards Policy and Strategy Committee on 30 September 2011.Amendments/corrigenda issued since publicationDate Text affected29 February 2012 Implementation of CEN correction notice 29 September 2011: Corrected wordin
5、g for terms NCand NAin A.2BRITISH STANDARDEUROPEAN STANDARD NORME EUROPENNE EUROPISCHE NORM EN 16016-3 August 2011 ICS 19.100 English Version Non destructive testing - Radiation methods - Computed Tomography - Part 3: Operation and interpretation Essais non destructifs - Mthodes par rayonnements - T
6、omographie numrise - Partie 3: Fonctionnement et interprtation Zerstrungsfreie Prfung - Durchstrahlungsverfahren - Computertomographie - Teil 3: Durchfhrung und Auswertung This European Standard was approved by CEN on 29 July 2011. CEN members are bound to comply with the CEN/CENELEC Internal Regula
7、tions which stipulate the conditions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN member
8、. This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management Centre has the same status as the official versions. CEN
9、 members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, S
10、pain, Sweden, Switzerland and United Kingdom. EUROPEAN COMMITTEE FOR STANDARDIZATION COMIT EUROPEN DE NORMALISATION EUROPISCHES KOMITEE FR NORMUNG Management Centre: Avenue Marnix 17, B-1000 Brussels 2011 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national
11、 Members. Ref. No. EN 16016-3:2011: EEN 16016-3:2011 (E) 2 Contents Page Foreword 3Introduction .41 Scope 52 Normative references 53 Terms and definitions .54 Operational procedure 54.1 General 54.2 CT system set-up .54.2.1 General 54.2.2 Geometry 54.2.3 X-ray source .64.2.4 Detector 64.3 Reconstruc
12、tion parameters 74.4 Visualisation .74.5 Analysis and interpretation of CT images .74.5.1 General 74.5.2 Feature testing/defect testing .74.5.3 Dimensional testing .85 Requirements for acceptable results 105.1 Image quality parameters 105.1.1 Contrast . 105.1.2 Noise 125.1.3 Signal to noise ratio .
13、125.1.4 Contrast to noise ratio . 125.1.5 Spatial resolution 135.2 Suitability of testing 155.3 CT examination interpretation and acceptance criteria 155.4 Records and reports . 155.5 Artefacts 165.5.1 General . 165.5.2 Beam hardening artefacts 165.5.3 Edge artefacts . 175.5.4 Scattered radiation .
14、185.5.5 Instabilities 185.5.6 Ring artefacts 185.5.7 Centre of rotation error artefacts 195.5.8 Motion artefacts 205.5.9 Artefacts due to an insufficient number of projections 215.5.10 Cone beam artefacts 21Annex A (informative) Spatial resolution measurement using line pair gauges . 23A.1 Line pair
15、 gauges . 23A.2 Principle of measurement 24Bibliography . 27BS EN 16016-3:2011EN 16016-3:2011 (E) 3 Foreword This document (EN 16016-3:2011) has been prepared by Technical Committee CEN/TC 138 “Non-destructive testing”, the secretariat of which is held by AFNOR. This European Standard shall be given
16、 the status of a national standard, either by publication of an identical text or by endorsement, at the latest by February 2012, and conflicting national standards shall be withdrawn at the latest by February 2012. Attention is drawn to the possibility that some of the elements of this document may
17、 be the subject of patent rights. CEN and/or CENELEC shall not be held responsible for identifying any or all such patent rights. EN 16016 consists of the following parts: Non destructive testing Radiation methods Computed tomography Part 1: Terminology; Non destructive testing Radiation methods Com
18、puted tomography Part 2: Principle, equipment and samples; Non destructive testing Radiation methods Computed tomography Part 3: Operation and interpretation; Non destructive testing Radiation methods Computed tomography Part 4: Qualification. According to the CEN/CENELEC Internal Regulations, the n
19、ational standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlan
20、ds, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and the United Kingdom. BS EN 16016-3:2011EN 16016-3:2011 (E) 4 Introduction This document gives guidelines for the general principles of X-ray computed tomography (CT) applicable to industrial imaging (in the cont
21、ext of this standard, industrial means non-medical applications); it also gives a consistent set of CT performance parameter definitions, including how these performance parameters relate to CT system specifications. This document deals with computed axial tomography and excludes other types of tomo
22、graphy such as translational tomography and tomosynthesis. BS EN 16016-3:2011EN 16016-3:2011 (E) 5 1 Scope This European Standard specifies an outline of the operation of a CT system, and the interpretation of the results in order to provide the user with technical information to select suitable par
23、ameters. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. EN 16016-1:2011,
24、Non destructive testing Radiation method Computed tomography Part 1: Terminology EN 16016-2:2011, Non destructive testing Radiation method Computed tomography Part 2: Principle, equipment and samples 3 Terms and definitions For the purposes of this document, the terms and definitions given in EN 160
25、16-1:2011 apply. 4 Operational procedure 4.1 General For target-oriented CT inspection procedures, the test and measurement tasks are defined in advance with regard to the size and type of features/defects to be verified; for example, through the specification of appropriate acceptance levels and ge
26、ometry deviations. In the following, the process steps of a CT application are described and information on its implementation provided. 4.2 CT system set-up 4.2.1 General The CT system set-up is oriented towards the requirements for the given task. The required spatial resolution (taking into accou
27、nt the tube focal spot size), contrast resolution, voxel size and the CT image quality can be derived from these requirements. The quality of the CT image is determined by different parameters, which under certain circumstances counteract each other. In the following, system parameters are described
28、 and information is provided on setting up a CT system for inspection. Due to the interactions of the different system parameters, it may be necessary to run through the set-up steps several times in order to acquire optimal data. The optimal energy is that which gives the best signal-to-noise ratio
29、 and not necessarily that which gives the clearest radiograph (the dependency of the detector efficiency on the energy is to be taken into account). However, in order to differentiate between materials of different chemical composition it may be necessary to adjust the accelerating voltage to maximi
30、se the difference in their linear attenuation coefficients. 4.2.2 Geometry The source-detector and source-object distances and thus also the beam angle used should be specified. In order to achieve high resolutions, the projection can be magnified onto the detector. The magnification is equal to the
31、 ratio of the source-detector distance to the source-object distance. Increasing source-detector BS EN 16016-3:2011EN 16016-3:2011 (E) 6 distance leads to a reduced intensity at the detector and thus to a reduced signal to noise ratio. Accordingly, this also applies when using detectors with improve
32、d detector resolution, which can result in a reduction of the signal-to-noise ratio due to the reduced intensity per pixel. In general, for this reason, minimisation of the source-object distance is to be preferred. In order to obtain high beam intensity at the detector, the source-detector distance
33、 should be selected so that it is as small as possible taking into account the required resolution so that the beam cone still fully illuminates the detector. In the case of 3D-CT, the (in general vertical) total cone beam angle measured parallel to the rotation axis should typically be less than 15
34、, but this is specimen dependant, in order to minimise reconstruction-determined (Feldkamp) distortions of the 3D model. In addition, these restrictions do not apply for the perpendicular (in general horizontal) beam angle. For a higher geometric magnification, the object must be positioned as near
35、as possible to the source, taking into consideration the limit on sharpness imposed by focal spot size. The rotation of the object must take place at at least 180 plus beam angle of the X-ray beam, whereby an improved data quality is the result of an increasing number of angular increments. For this
36、 reason, the object is typically turned through 360 . Ideally, the number of angular increments should be at least sizematrix2 where the matrix size is the number of voxels across the sample diameter or the largest dimension. For more information, refer to 5.5. In order to obtain as complete informa
37、tion as possible on the specimen, the requirement in general for a CT is that the object (or the interesting section of the object) is completely mapped in each projection on the detector. For large components that exceed the beam cone, a so-called measurement range extension is used. This measureme
38、nt range extension is accomplished by laterally displacing either the object or the detector, recording the projection data in sequential measurements, and finally concatenating (joining) them. Under certain circumstances, it is also possible to only scan a part of the object (region-of-interest CT)
39、, which may lead to a restricted data quality in the form of so-called truncations. A possible deviation of the recording geometry (offset between the projected axis of rotation and the centre line of the image) must be corrected for in order to obtain a reconstruction which is as precise as possibl
40、e. This can be achieved by careful realignment of the system or be corrected using software. 4.2.3 X-ray source At the X-ray source, the maximum beam energy and tube current are to be set such that sufficient penetration of the test object and tube power with a sufficiently small focal spot are ensu
41、red. The required voltage is determined by the maximum path length, in the material to be X-rayed in accordance with EN 16016-2:2011, 8.2. For the best measurement results, an attenuation ratio of approx. 1:10 should be used. That is the grey level through the sample should be about 10% of the white
42、 level (both measured with respect to the dark level). The optimal range can be achieved through the use of prefilters. It should be noted that every prefilter reduces the intensity. Prefilters have the additional advantage of reducing beam hardening, though further improvements can be made with sof
43、tware correction. 4.2.4 Detector The following detector settings need to be set appropriately for the sample being scanned: Exposure time (Frame rate); Number of integrations per projection; Digitisation gain and offset; Binning. If necessary, corrections for offset, gain and bad pixels (which may d
44、epend on X-ray settings) should be applied. The individual CT projection is determined by the detector properties: its geometric resolution, its sensitivity, dynamics and noise. The gain and exposure time can be adjusted together with the radiation intensity of the source so that the maximum digitis
45、ed intensity does not exceed 90 % of the saturation level. BS EN 16016-3:2011EN 16016-3:2011 (E) 7 To reduce scattered radiation, a thin filter, grid or lamellae can be used directly in front of the detector (post-filtering). The ideal acquisition time is dependent on the required quality of the CT
46、image and it is often limited by the time available for inspection. 4.3 Reconstruction parameters The volumetric region to be reconstructed, the size of the CT image (in terms of voxels) as well as its dynamic range (which should take into account the detector dynamic range) shall be specified. In o
47、rder to achieve sufficient CT image quality, settings for the reconstruction algorithm or corrections should be optimised. The volumetric region is defined by the number of voxels along the X, Y in others it can be fixed only by re-engineering the offending subsystem. Considerable effort is required
48、 to keep these types of errors small compared to other less manageable sources of error, such as those discussed above. 5.5.5 Instabilities Electronic and mechanical nonlinearities and instabilities also represent sources of inaccuracy. These may result from corrigible engineering deficiencies or ba
49、sic physical limitations of the available components. The validity of the data is impacted in either case. In some cases, the problem can be corrected (or reduced) in software; in others, it can be fixed only by reengineering the offending subsystem. Because the bulk of existing information on this crucial topic is commercially sensitive and therefore pro
