SANS 15708-2-2005 Non-destructive testing - Radiation methods - Computed tomography Part 2 Examination practices《无损检测 辐射方法 电脑断层 第2部分 检验方法》.pdf

1、 Collection of SANS standards in electronic format (PDF) 1. Copyright This standard is available to staff members of companies that have subscribed to the complete collection of SANS standards in accordance with a formal copyright agreement. This document may reside on a CENTRAL FILE SERVER or INTRA

2、NET SYSTEM only. Unless specific permission has been granted, this document MAY NOT be sent or given to staff members from other companies or organizations. Doing so would constitute a VIOLATION of SABS copyright rules. 2. Indemnity The South African Bureau of Standards accepts no liability for any

3、damage whatsoever than may result from the use of this material or the information contain therein, irrespective of the cause and quantum thereof. ICS 19.100 ISBN 0-626-16054-5 SANS 15708-2:2005Edition 1ISO 15708-2:2002Edition 1 SOUTH AFRICAN NATIONAL STANDARD Non-destructive testing Radiation metho

4、ds Computed tomography Part 2: Examination practices This national standard is the identical implementation of ISO 15708-2:2002 and is adopted with the permission of the International Organization for Standardization. Published by Standards South Africa 1 dr lategan road groenkloof private bag x191

5、pretoria 0001 tel: 012 428 7911 fax: 012 344 1568 international code + 27 12 www.stansa.co.za Standards South Africa SANS 15708-2:2005 Edition 1 ISO 15708-2:2002 Edition 1 Table of changes Change No. Date Scope Abstract Describes computed tomography (CT) procedures that can provide non-destructive t

6、esting and evaluation. Requirements intend to control the reliability and quality of CT images. Applicable for the systematic assessment of the internal structure of a material or assembly. Provides a basis for the formation of a program for quality control. Keywords computed tomography, diagrams, d

7、imensioning, examination, materials testing, mathematical calculations, non-destructive testing, nuclear technology, protection ratio, quality control, radiation protection, rules, safety. National foreword This South African standard was approved by National Committee StanSA SC 5120.20A, Engineerin

8、g materials Non-destructive testing, in accordance with procedures of Standards South Africa, in compliance with annex 3 of the WTO/TBT agreement. Reference numberISO 15708-2:2002(E)ISO 2002INTERNATIONAL STANDARD ISO15708-2First edition2002-07-01Non-destructive testing Radiation methods Computed tom

9、ography Part 2: Examination practices Essais non destructifs Moyens utilisant les rayonnements Tomographie informatise Partie 2: Pratiques dexamen ISO 15708-2:2002(E) PDF disclaimer This PDF file may contain embedded typefaces. In accordance with Adobes licensing policy, this file may be printed or

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13、eans, electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISOs member body in the country of the requester. ISO copyright office Case postale 56 CH-1211 Geneva 20 Tel. + 41 22 749 01 11 Fax + 41 22 749 09 47 E-mail cop

14、yrightiso.ch Web www.iso.ch Printed in Switzerland ii ISO 2002 All rights reserved ISO 15708-2:2002(E) ISO 2002 All rights reserved iiiContents Page Foreword.iv Introduction.v 1 Scope 1 2 Normative reference1 3 Terms and definitions .1 4 Summary 1 5 System configuration2 6 Documentation.5 7 System s

15、et-up and optimization 8 8 Performance measurement 12 9 CT examination interpretation18 10 Records, reports, and identification of accepted material18 11 Safety conditions.18 12 Precision and bias .18 ISO 15708-2:2002(E) iv ISO 2002 All rights reserved Foreword ISO (the International Organization fo

16、r Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the

17、 right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. Internati

18、onal Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication

19、as an International Standard requires approval by at least 75 % of the member bodies casting a vote. Attention is drawn to the possibility that some of the elements of this part of ISO 15708 may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent

20、 rights. ISO 15708-2 was prepared by Technical Committee ISO/TC 135, Non-destructive testing, Subcommittee SC 5, Radiation methods. ISO 15708 consists of the following parts, under the general title Non-destructive testing Radiation methods Computed tomography: Part 1: Principles Part 2: Examination

21、 practices ISO 15708-2:2002(E) ISO 2002 All rights reserved vIntroduction Computed tomography (CT), as with conventional radiography and radioscopic examination, is broadly applicable to any material or test object through which a beam of penetrating radiation passes, including metals, plastics, cer

22、amics, metallic/non-metallic composite material and assemblies. The principal advantage of CT is that it provides densitometric (i.e., radiological density and geometry) images of thin cross sections “slices” through an object. Because of the absence of structural superposition, images are much easi

23、er to interpret than conventional radiological images. CT images correspond closely to the way the human mind visualizes 3D structures than conventional projection radiology. Because CT images are digital, the images may be enhanced, analysed, compressed, archived, input as data into performance cal

24、culations, and compared with digital data from other non-destructive evaluation (NDE) modalities. CT images can also be transmitted to other locations for remote viewing. This part of ISO 15708 describes CT procedures that can provide for non-destructive testing and evaluation. Requirements in this

25、part of ISO 15708 are intended to control the reliability and quality of the CT images. This part of ISO 15708 is applicable for the systematic assessment of the internal structure of a material or assembly and may be used to prescribe operating CT procedures. It also provides a basis for the format

26、ion of a programme for quality control and its continuation through calibration, standardization, reference samples, inspection plans and procedures. INTERNATIONAL STANDARD ISO 15708-2:2002(E) ISO 2002 All rights reserved 1Non-destructive testing Radiation methods Computed tomography Part 2: Examina

27、tion practices 1 Scope This part of ISO 15708 gives guidelines for procedures for performing CT examinations. It is intended to address the general use of CT technology and thereby facilitate its use. This part of ISO 15708 implicitly assumes the use of penetrating radiation, specifically X-ray and

28、-ray. 2 Normative reference The following normative document contains provisions which, through reference in this text, constitute provisions of this part of ISO 15708. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. However, parties to agreem

29、ents based on this part of ISO 15708 are encouraged to investigate the possibility of applying the most recent edition of the normative document indicated below. For undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC maintain registers of cur

30、rently valid International Standards. ISO 15708-1:2002, Non-destructive testing Radiation Methods Computed tomography Part 1: Principles 3 Terms and definitions For the purposes of this part of ISO 15708 the terms and definitions listed in annex A of ISO 15708-1:2002 apply. 4 Summary This part of IS

31、O 15708 describes CT procedures which can provide for non-destructive testing and evaluation. Requirements in this part of ISO 15708 are intended to control the reliability and quality of the CT images. CT systems are made up of a number of subsystems; the function served by each subsystem is common

32、 in almost all CT scanners. Clause 5 describes the following subsystems: a) source of penetrating radiation; b) radiation detector or an array of detectors; c) mechanical scanning assembly; d) computer system including: 1) image reconstruction software/hardware; ISO 15708-2:2002(E) 2 ISO 2002 All ri

33、ghts reserved 2) image display/analysis system; 3) data storage system; 4) operator interface. Clause 6 describes and defines the procedures for establishing and maintaining quality control of CT examination services. The extent to which a CT image reproduces an object or a feature within an object

34、is influenced by spatial resolution, statistical noise, slice plane thickness and artifacts of the imaging system. Operating parameters shall strike an overall balance between image quality, inspection time and cost. These parameters shall be considered for CT system configurations, components and p

35、rocedures. The setting and optimization of CT system parameters are discussed in clause 7. Methods for the measurement of CT system performance are provided in clause 8. 5 System configuration 5.1 CT System configurations Many different CT examination system configurations are possible and it is imp

36、ortant to understand the advantages and limitations of each. It is important that the optimum system parameters be selected for each examination requirement, through careful analysis of the benefits and limitations of the available system components and the chosen system configuration. 5.2 Radiation

37、 sources 5.2.1 General Whilst the CT examination systems may utilize either gamma-ray or X-ray generators, the latter is used for most applications. For a given focal spot size, X-ray generators i.e., X-ray tubes and linear accelerators (linacs) are several orders of magnitude more intense than isot

38、ope sources. Most X-ray generators are adjustable in peak energy and intensity and have the added safety feature of discontinued radiation production when switched off. However, polychromaticity of the energy spectrum causes artifacts such as “cupping” (the anomalous decreasing attenuation toward th

39、e centre of a homogeneous object) in the image, if left uncorrected. 5.2.2 Electrical radiation generators X-rays produced from electrical radiation generators have focal spot sizes ranging from a few millimetres down to a few micrometres. Reducing the focal spot size reduces geometric unsharpness,

40、thereby enhancing detail sensitivity. Smaller focal spots permit higher spatial resolution, but at the expense of reduced X-ray beam intensity. 5.2.3 Radioisotope sources A radioisotope source can have the advantages of small physical size, portability, low power requirements, simplicity and stabili

41、ty of output. The disadvantages are limited intensity and limited peak energy, primarily due to inefficiency in the process whereby continuous X-rays are generated. Radioisotope sources are typically several orders of magnitude less intense that X-ray generators ISO 15708-2:2002(E) ISO 2002 All righ

42、ts reserved 35.2.4 Synchrotron radiation (SR) sources SR sources produce very intense, naturally collimated, narrow bandwidth, tunable radiation. Thus, CT systems using SR sources can employ essentially monochromatic radiation. With current technology however, practical SR energies are restricted to

43、 less than approximately 20 keV to 30 keV. Since any CT system is limited to the inspection of samples with radio-opacities consistent with the penetrating power of the X-ray used, SR systems can, in general, image only small (about 1 mm) objects. 5.3 Detection system The detection system is a trans

44、ducer that converts the transmitted radiation-containing information about the test object into an electronic signal suitable for processing. The detection system may consist of a single sensing element, a linear array of sensing elements or an area array of sensing elements. The more detectors used

45、, the faster the required scan data can be collected; but there are important tradeoffs to be considered. A single detector provides the least efficient method of collecting data but entails minimal complexity, eliminates cross talk and detector matching, and allows an arbitrary degree of collimatio

46、n and shielding to be implemented. Linear arrays have reasonable scan times at moderate complexity, acceptable cross talk and detector matching, and a flexible architecture that typically accommodates good collimation and shielding. Most commercially available CT systems employ a linear array of det

47、ectors. An area detector provides a fast method of collecting data but entails the transfer and storage of large amounts of information, forces tradeoffs between cross talk and detector efficiency, and creates serious collimation and shielding challenges. 5.4 Manipulation System 5.4.1 General The te

48、st part manipulation system has the function of holding the test object and providing the necessary range of motions to position the volume of interest between the radiation source and detector. Two types of scan motion geometries are most common. 5.4.2 Translate-rotate motion With translate-rotate

49、motion, the test object is translated in a direction perpendicular to the direction of and in the plane of the X-ray beam. Full data sets are obtained by rotating the test article between translations by the fan angle of the beam and again translating the part until a minimum of 180 of data have been acquired. The advantage of this design is simplicity, good view-to-view detector matching, flexibility in the choice of scan parameters and ability to accommodate a wide range of different object sizes includin