BS EN 16407-1:2014 BSI Standards Publication Non-destructive testing — Radiographic inspection of corrosion and deposits in pipes by X- and gamma rays Part 1: Tangential radiographic inspection BS EN 16407-1:2014 BRITISH STANDARD National foreword This British Standard is the UK implementation of EN 16407-1:2014 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 publication does not purport to include all the necessary provisions of a contract Users are responsible for its correct application © The British Standards Institution 2014 Published by BSI Standards Limited 2014 ISBN 978 580 77930 ICS 19.100; 23.040.01 Compliance with a British Standard cannot confer immunity from legal obligations This British Standard was published under the authority of the Standards Policy and Strategy Committee on 31 January 2014 Amendments issued since publication Date Text affected BS EN 16407-1:2014 EN 16407-1 EUROPEAN STANDARD NORME EUROPÉENNE EUROPÄISCHE NORM January 2014 ICS 19.100; 23.040.01 English Version Non-destructive testing - Radiographic inspection of corrosion and deposits in pipes by X- and gamma rays - Part 1: Tangential radiographic inspection Essais non destructifs - Examen radiographique de la corrosion et des dépôts dans les canalisations, par rayons X et rayons gamma - Partie 1: Examen radiographique tangentiel Zerstörungsfreie Prüfung - Durchstrahlungsprüfung auf Korrosion und Ablagerungen in Rohren mit Röntgen- und Gammastrahlen - Teil 1: Tangentiale Durchstrahlungsprüfung This European Standard was approved by CEN on 26 October 2013 CEN members are bound to comply with the CEN/CENELEC Internal Regulations 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 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 members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United Kingdom EUROPEAN COMMITTEE FOR STANDARDIZATION COMITÉ EUROPÉEN DE NORMALISATION EUROPÄISCHES KOMITEE FÜR NORMUNG CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels © 2014 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members Ref No EN 16407-1:2014 E BS EN 16407-1:2014 EN 16407-1:2014 (E) Contents Page Foreword Scope Normative references Terms and definitions Classification of radiographic techniques 5.1 5.2 5.3 5.4 5.5 5.6 5.6.1 5.6.2 General Protection against ionising radiation Personnel qualification Identification of radiographs Marking Overlap of films or digital images Types and positions of image quality indicators (IQI) .9 Single wire or step hole IQIs .9 Duplex wire IQI (digital radiographs) 6.1 6.1.1 6.1.2 6.1.3 6.1.4 6.2 6.3 6.4 6.5 6.5.1 6.5.2 6.6 6.7 6.8 6.9 6.10 6.10.1 6.10.2 6.10.3 Recommended techniques for making radiographs 10 Test arrangements 10 General 10 Radiation source located on the pipe centre line 10 Radiation source located offset from the pipe centre line 11 Alignment of beam and film/detector 13 Choice of radiation source 13 Film systems and metal screens 14 Screens and shielding for imaging plates (computed radiography only) 16 Reduction of scattered radiation 17 Filters and collimators 17 Interception of back scattered radiation 18 Source-to-detector distance 18 Axial coverage and overlap 19 Dimensional comparators 20 Image saturation and use of lead strips to avoid burn-off 21 Selection of digital radiographic equipment 21 General 21 CR systems 22 DDA systems 22 7.1 7.1.1 7.1.2 7.1.3 7.2 7.3 7.4 7.5 7.5.1 7.5.2 7.5.3 Radiograph/digital image sensitivity, quality and evaluation 22 Evaluation of image quality 22 General 22 Maximum grey level in free beam (digital radiographs) 22 Minimum normalized signal to noise ratio (digital radiographs) 22 Density of film radiographs 23 Film processing 23 Film viewing conditions 23 Dimensional calibration of radiographs or digital images 24 General 24 Measurement of distances in radiographic setup 24 Measurement of pipe outside diameter 25 BS EN 16407-1:2014 EN 16407-1:2014 (E) 7.5.4 7.6 7.7 7.7.1 7.7.2 Dimensional comparator 25 Wall thickness measurements for film radiographs 26 Wall thickness measurements for digital radiographs 26 Interactive on-screen measurements 26 Grey-level profile analysis methods 26 8.1 8.2 8.3 8.4 8.5 8.6 8.7 Digital image recording, storage, processing and viewing 27 Scan and read out of image 27 Multi radiograph technique 27 Calibration of DDAs 28 Bad pixel interpolation 28 Image processing 28 Digital image recording and storage 28 Monitor viewing conditions 29 Test report 29 Annex A (normative) Determination of basic spatial resolution 31 Annex B (informative) Choice of radiation source for different pipes 35 Bibliography 36 BS EN 16407-1:2014 EN 16407-1:2014 (E) Foreword This document (EN 16407-1:2014) 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 the status of a national standard, either by publication of an identical text or by endorsement, at the latest by July 2014, and conflicting national standards shall be withdrawn at the latest by July 2014 Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights EN 16407 consists of the following parts, under the general title Non-destructive testing — Radiographic inspection of corrosion and deposits in pipes by X- and gamma rays: — Part 1: Tangential radiographic inspection; — Part 2: Double wall radiographic inspection According to the CEN-CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom BS EN 16407-1:2014 EN 16407-1:2014 (E) Scope This European Standard specifies fundamental techniques of film and digital radiography with the object of enabling satisfactory and repeatable results to be obtained economically The techniques are based on generally recognized practice and fundamental theory of the subject This European Standard applies to the radiographic examination of pipes in metallic materials for service induced flaws such as corrosion pitting, generalized corrosion and erosion Besides its conventional meaning, “pipe” as used in this standard should be understood to cover other cylindrical bodies such as tubes, penstocks, boiler drums and pressure vessels Weld inspection for typical welding process induced flaws is not covered, but weld inspection is included for corrosion/erosion type flaws The pipes may be insulated or not, and can be assessed where loss of material due, for example, to corrosion or erosion is suspected either internally or externally This part of EN 16407 covers the tangential inspection technique for detection and through-wall sizing of wall loss, including: a) with the source on the pipe centre line, and b) with the source offset from it by the pipe radius Part of EN 16407 covers double wall radiography, and note that the double wall double image technique is often combined with tangential radiography with the source on the pipe centre line This European Standard applies to tangential radiographic inspection using industrial radiographic film techniques, computed digital radiography (CR) and digital detector arrays (DDA) Normative references The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application For dated references, only the edition cited applies For undated references, the latest edition of the referenced document (including any amendments) applies EN 14784-1, Non-destructive testing — Industrial computed radiography with storage phosphor imaging plates — Part 1: Classification of systems EN ISO 11699-1, Non-destructive testing — Industrial radiographic films — Part 1: Classification of film systems for industrial radiography (ISO 11699-1) EN ISO 11699-2, Non-destructive testing — Industrial radiographic films — Part 2: Control of film processing by means of reference values (ISO 11699-2) EN ISO 17636-1:2013, Non-destructive testing of welds — Radiographic testing — Part 1: X- and gamma-ray techniques with film (ISO 17636-1:2013) EN ISO 19232-5, Non-destructive testing — Image quality of radiographs — Part 5: Determination of the image unsharpness value using duplex wire-type image quality indicators (ISO 19232-5) BS EN 16407-1:2014 EN 16407-1:2014 (E) Terms and definitions For the purposes of this document, the following terms and definitions apply 3.1 actual wall thickness tact actual wall thickness of the pipe 3.2 basic spatial resolution of a digital detector detector SRb half of the measured detector unsharpness in a digital image which corresponds to the effective pixel size and indicates the smallest geometrical detail, which can be resolved with a digital detector at magnification equal to one Note to entry: plate For this measurement, the duplex wire IQI is placed directly on the digital detector array or imaging Note to entry: The measurement of unsharpness is described in EN ISO 19232-5, see also ASTM E2736 [18] and ASTM E1000 [16] 3.3 comparator C reference object of defined dimension c and material for dimensional calibration of a radiographic image 3.4 computed radiography CR storage phosphor imaging plate system complete system comprising a storage phosphor imaging plate (IP) and a corresponding read-out unit (scanner or reader), which converts the information from the IP into a digital image 3.5 detector D radiographic image detector consisting of a NDT film system (see EN ISO 11699-1) or a digital radiography system using an imaging plate system (CR system) or a DDA system Note to entry: Film systems and IPs can be used as flexible and curved detectors or in planar cassettes 3.6 digital detector array system DDA system electronic device converting ionizing or penetrating radiation into a discrete array of analogue signals which are subsequently digitised and transferred to a computer for display as a digital image corresponding to the radiologic energy pattern imparted upon the input region of the device 3.7 maximum penetrated thickness wmax maximum thickness of material for a pipe which occurs for a tangent to the inner pipe surface BS EN 16407-1:2014 EN 16407-1:2014 (E) 3.8 measured wall thickness tmeas measured wall thickness of the pipe on the radiograph or digital image 3.9 nominal wall thickness t thickness of the pipe material only where manufacturing tolerances not have to be taken into account 3.10 normalized signal-to-noise ratio SNRN signal-to-noise ratio, SNR, normalised by the basic spatial resolution, SRb, as measured directly in the digital image and/or calculated from the measured SNR, SNRmeasured, by: SNRN =SNRmeasured 88,6µm SRb 3.11 object-to-detector distance b distance between the radiation side of the test object and the detector surface measured along the central axis of the radiation beam 3.12 outside diameter De nominal outside diameter of the pipe 3.13 pipe centre to detector distance PDD distance between the pipe centre and the detector 3.14 pixel size geometrical centre-to-centre distance between adjacent pixels in a row (horizontal pitch) or column (vertical pitch) of the scanned image [SOURCE: EN 14096-2:2003, 3.2] 3.15 signal-to-noise ratio SNR ratio of mean value of the linearized grey values to the standard deviation of the linearized grey values (noise) in a given region of interest in a digital image 3.16 source size d size of the radiation source [SOURCE: EN 12679:1999, 2.1] BS EN 16407-1:2014 EN 16407-1:2014 (E) 3.17 source-to-detector distance SDD distance between the source of radiation and the detector measured in the direction of the beam 3.18 source-to-object distance f distance between the source of radiation and the source side of the test object measured along the central axis of the radiation beam 3.19 source-to-pipe centre distance SPD distance between the source of radiation and the pipe centre (pipe axis) measured in the direction of the beam 3.20 storage phosphor imaging plate IP photostimulable luminescent material capable of storing a latent radiographic image of a material being examined and, upon stimulation by a source of red light of appropriate wavelength, generates luminescence proportional to radiation absorbed Classification of radiographic techniques The tangential radiographic techniques are divided into two classes: — basic technique TA; — improved technique TB The basic techniques, TA, are intended for tangential radiography of generalized wall loss, such as that due to erosion or large scale corrosion The improved techniques, TB, should be used for the more demanding tangential radiography of localized corrosion pitting flaws, which require higher sensitivity for detection and sizing Further technique improvements beyond TB are possible and may be agreed between the contracting parties by specification of all appropriate test parameters The choice of radiographic technique shall be agreed between the concerned parties 5.1 General Protection against ionising radiation WARNING — Exposure of any part of the human body to X-rays or gamma-rays can be highly injurious to health Wherever X-ray equipment or radioactive sources are in use, appropriate legal requirements shall be applied Local or national or international safety precautions when using ionizing radiation shall be strictly applied BS EN 16407-1:2014 EN 16407-1:2014 (E) 7.5 Dimensional calibration of radiographs or digital images 7.5.1 General For tangential radiography, when making dimensional measurements of wall thickness, it is necessary to calibrate the distances involved in the radiography, to allow for the image enlargement or “blow-up” The geometric magnification effect for tangential radiography is shown in Figure Key detector Figure — Geometric magnification for tangential radiography showing the measured wall thickness tmeas The following methods can be used for dimensional calibration, to derive the actual wall thickness tact from the measured value tmeas 7.5.2 Measurement of distances in radiographic setup This method involves direct physical measurement of the key distances involved in the radiography For calibration by the distances method, two of the following distances need to be measured accurately (to within a few percent): a) source to detector distance, SDD; b) distance from source to pipe centre line, SPD; c) distance from detector to pipe centre line, PDD In addition, the following distance shall also be recorded: d) 24 lateral offset (if any) of source from pipe centre line, x BS EN 16407-1:2014 EN 16407-1:2014 (E) For offset tangential radiography (with x approximately r), the true wall thickness tact at the tangential pipe position can be calculated from the measured wall thickness tmeas using the approximate formula: = tact SPD ⋅ tmeas SDD (7) NOTE Provided x approximately 0, then the following complex formula can be used to derive the wall thickness tact, from the measured value tmeas: t r SPD − meas 2 SDD SPD − r tact = r − t r 1+ − meas 2 SDD SPD − r (8) where r is half the pipe outside diameter (= De/2) For practical in service radiography, the accurate physical measurements of distances may be difficult to achieve and document reliably If this is considered to be the case, the alternative methods given below shall be used 7.5.3 Measurement of pipe outside diameter Provided the pipe outside diameter is known accurately at the measurement position in the image or radiograph, then dimensional calibration can be achieved by measurement of the imaged size of the pipe outside diameter, De’, on the radiograph or digital image The actual remaining wall thickness tact can then be found from the measured remaining wall thickness value, tmeas, using the ratio of the actual to measured pipe outside diameter: = tact tmeas ⋅ 7.5.4 De De' (9) Dimensional comparator If the pipe outside diameter is not known accurately or reliably, then the alternative dimensional calibrator method, described in 6.8, shall be used With this method, the measured dimension of the comparator, c’, is used to calibrate the distances, so the actual remaining wall thickness tact can then be found from the measured remaining wall thickness value, tmeas, using the ratio of the defined (c) to measured (c’) comparator dimensions: = tact tmeas ⋅ c c' (10) Note that if the pipe outside diameter is known accurately, the method described in 7.5.3 is likely to provide more accurate measurements, since the calibration is made over a larger distance which can be measured more accurately in percentage terms than the smaller distance across a comparator 25 BS EN 16407-1:2014 EN 16407-1:2014 (E) 7.6 Wall thickness measurements for film radiographs Dimensional measurements from film radiographs can be made with callipers, of both the pipe wall thickness and an object of known dimension, for calibration purposes (i.e the ball-bearing comparator or known pipe outside diameter – see 7.5.3 and 7.5.4) 7.7 Wall thickness measurements for digital radiographs 7.7.1 Interactive on-screen measurements CR/DDA systems contain software options which allow on-screen interactive dimensional measurements using a cursor overlaid on the digital images, without reference to the underlying grey level values in the images The user then judges by eye the locations in the image of the inner and outer edges of the pipe wall This method can be subject to significant errors as the apparent wall thickness depends on the contrast and brightness settings used to display the image These errors are larger for pipes having maximum penetrated thickness values, wmax, approaching the maximum of those recommended for the radiation source in use (see Table 1) To reduce these errors, the following techniques can be used: a) High-frequency spatial filtering (sharpening) which emphasises the positions of the edges of the pipe wall in the images, and reduces the dependence on the contrast and brightness settings on the image; b) For some images, display of the image using a logarithmic relation between radiation intensity and grey level reduces the overall image contrast and improves the definition of the inner diameter position Some CR scanners give logarithmic images directly For those scanners and DDA systems that provide nonlogarithmic response images, an appropriate look-up table (LUT) can be used to obtain a digital image with a logarithmic response If this interactive on-screen measurement method is used, it shall be first checked for acceptable accuracy using the current contrast and brightness settings of the displayed image, by application to a section of the pipe with known wall thickness (e.g known to be uncorroded or not eroded) 7.7.2 Grey-level profile analysis methods In addition to on screen measurements, covered in 7.7.1, many CR/DDA systems also allow wall thickness measurement methods based on analysis of a grey level profile taken in a direction orthogonal to the pipe wall axis The software extracts a grey-level profile along this line, which is then generally presented on-screen, superimposed on the image, as illustrated in Figure a) Automated routines Automated analysis routines can increase the reliability of the measured wall thickness values, unless the maximum tangential penetrated thickness, wmax, is approaching the maximum possible, given the radiation source in use (see 7.2) In addition, other factors such as the presence of external scale, corrosion products or irregular internal/external corrosion may affect the accuracy of these automated routines In these cases, the automated routines are subject to uncertainties, and the operator should check the consistency of the derived values with the density profile and the digital radiographic image b) Interactive methods As an alternative to automated routines for wall thickness analysis, the operator can use available interactive facilities for analysis of the grey level profile Accuracy is likely to be improved, especially for pipes having larger wmax values, if the digital images have a logarithmic response and are high-pass filtered 26 BS EN 16407-1:2014 EN 16407-1:2014 (E) Figure shows an example of interactive measurement of wall thickness, using cursors on a grey level profile across the pipe wall, after applying a logarithmic look-up table to the CR image, and high-pass filtering to enhance details The position of the outer diameter corresponds to a clear peak in the profile, and the location of the inner diameter is given by the minimum and pronounced change in gradient of the profile This method, combined with a visual assessment of the image, can in some circumstances give higher measurement accuracy than the automated routines described above Figure — Example of interactive wall thickness measurement using cursors superimposed on a grey level profile taken across the pipe wall The accuracy of all measurement methods decrease as the tangential penetrated thickness, wmax, approaches the maximum value recommended for the isotope in use (see Table 1), since the location of the inner wall becomes increasingly difficult to determine with any reliability due to lack of contrast and increased noise 8.1 Digital image recording, storage, processing and viewing Scan and read out of image Detectors or scanners are used in accordance with the conditions recommended by the detector and scanner manufacturer to obtain the selected image quality The digital radiographs should be free from artefacts due to processing and handling or other causes which would interfere with interpretation 8.2 Multi radiograph technique Different digital radiographs at different exposure conditions may be used to optimise the SNR of the outer wall in one exposure and to optimise the SNR of the inner wall in a second exposure The source and detector position shall not be changed for these exposures The distance between the inner and outer surface may be 27 BS EN 16407-1:2014 EN 16407-1:2014 (E) determined from the different exposures in analogy to multi film viewing A software tool may be used to measure the wall thickness from the different images or from an overlaid image The performance of this technique and any applied software shall be demonstrated with an exposure of a reference pipe sample with known dimensions 8.3 Calibration of DDAs If using DDAs the detector calibration procedure as recommended by the manufacturer shall be applied The detector shall be calibrated with a background image (without radiation) and at least with one gain image (radiation on and homogeneously exposed) Multi gain calibration will increase the achievable SNRN and linearity but takes more time All calibration images shall be taken at least with two times larger exposure dose (mA ⋅ or GBq ⋅ min) as finally used for the production radiographs to minimize the noise introduction of the calibration procedure Calibrated images should be treated as unprocessed raw images for quality assurance if the procedure has been documented The calibration and a bad pixel interpolation shall be performed periodically and if the exposure conditions are changed significantly 8.4 Bad pixel interpolation Bad pixels are underperforming detector elements of DDAs They are described in ASTM E2597 If using DDAs the detector shall be mapped to determine the bad pixel map in accordance with the manufacturer guideline This bad pixel map shall be documented The bad pixel interpolation is acceptable and an essential procedure of radiography with DDAs It is recommended to apply only detectors which have no cluster kernel pixels (CKP) in the region of interest (ROI) 8.5 Image processing The digital data of the radiographic detector shall be evaluated with linearized grey value representation which is directly proportional to the radiation dose for determination of SNR, SRb and SNRN For optimal image display, contrast and brightness should be interactively adjustable Optional filter functions, profile plots and an SNR, SNRN tool should be integrated into the software for image display and evaluation For critical image analysis the operator shall interpret the image with a zoom factor between 1:1 (meaning pixel of the digital radiograph is presented by one monitor pixel) and 1:2 (meaning pixel of the digital radiograph is presented by four monitor pixels) Further means of image processing applied on the stored raw data (e.g high pass filtering for image display) shall be documented, be repeatable and be agreed between the contracting parties 8.6 Digital image recording and storage CR/DDA images should be stored in a file format which supports a minimum of 12-bits/pixel The original images shall be stored in full resolution as delivered by the detector system Only image processing connected with the detector calibration (e.g off-set correction, gain calibration for detector equalization and bad pixel correction (see also ASTM E2597) to provide artefact free detector images shall be applied before storage of the raw data The data storage shall be redundant and be supported by suitable back-up strategies to ensure “loss-less” data storage Any data compression techniques used in the storage of these files shall be “loss-less”, i.e it shall be possible to reconstruct the exact original data from the compressed data 28 BS EN 16407-1:2014 EN 16407-1:2014 (E) 8.7 Monitor viewing conditions The digital radiographs shall be examined in a dimmed room The monitor setup shall be verified with a suitable test image The display for image evaluation shall fulfil the following minimum requirements: a) minimum brightness of 250 cd/m ; b) display of at least 256 shades of grey; c) minimum displayable light intensity ratio of 1:250; and d) display of at least megapixel resolution, with a pixel pitch of < 0,3 mm Test report For each exposure, or set of exposures, a test report shall be made giving information on the radiographic technique used, and on any other special circumstances which would allow a better understanding of the results The test report shall include as a minimum the following information: a) reference to this standard; b) name of the examination body; c) object and pipe isometric and pipe content; d) material type, outer diameter De and nominal wall thickness t of pipe; e) material, thickness and condition of insulation; f) material, dimension and position of the comparator C; g) specification of examination including requirements for acceptance; h) radiographic technique and class; i) test arrangement in accordance with 6.1; j) system of marking used; k) detector position plan; l) radiation source, type and size of focal spot and identification of equipment used; m) detector, screens and filters; n) used tube voltage and current or source activity; o) time of exposure, SDD and PDD; p) film type, film system and film processing; 29 BS EN 16407-1:2014 EN 16407-1:2014 (E) q) CR system, IP type, scanner model, scanner parameters e.g scan speed, gain, laser intensity, laser spot size, pixel size; r) DDA type, operating parameters, pixel size; s) basic spatial resolution of digital detectors; t) measured image parameters: 1) film densities measured at pipe centre (if applicable), in the pipe wall and outside pipe; 2) SNRN, achieved at the pipe centre (if applicable) and in the free beam; u) measured wall thicknesses, including minimum measured wall thickness and its location; v) material loss: inside, outside, pitting or generalized; w) additional observations; x) any deviation from this standard, by special agreement; y) name, certification and signature of the operator; z) date(s) of exposure and test report 30 BS EN 16407-1:2014 EN 16407-1:2014 (E) Annex A (normative) Determination of basic spatial resolution Linearized grey levels are the precondition for the measurement of correct basic spatial resolution values This means the grey values need to be proportional to the radiation exposure at a given location of the image This is typically supported by the manufacturer software The duplex wire IQI shall be positioned directly on the detector surface or cassette surface and shall be read in accordance with EN ISO 19232-5 for determination of the detector basic spatial resolution SRb NOTE If the duplex wire IQI is positioned on a test object, instead of directly on the detector, a measurement of image detector image basic spatial resolution SRb is then obtained, not detector basic spatial resolution SRb (or SRb ) If the first unsharp wire pair cannot be recognized clearly (see EN ISO 19232-5), the 20 % dip method shall be applied as follows: On the digital radiograph, the first wire pair giving a modulation (dip) of less than 20 % in relation to the double peak size (see Figure A.1) shall be documented as the result of the IQI test (e.g D8 as shown in Figure A.1a) A profile function of the image processing software shall be used to recognize the first wire pair with a dip of less than 20 % (when averaged over both minima – see Figure A.1(d)) The profile shall also be averaged (see Figure A.1 b-c) over at least 21 single line profiles to improve the SNR in the profile plot By usage of the duplex wire IQI, conforming to EN ISO 19232-5, the inherent image unsharpness ui shall be determined and the basic spatial resolution SRb of the detector shall be calculated with: SRb = ui (A.1) The duplex wire IQI shall be positioned at an angle of approximately 2° to 5° towards the pixel line or column orientation in order to avoid aliasing effects as shown in Figure A.1 The determination of the basic spatial resolution for a digital detector system (SRb) shall be performed under one of the following exposure conditions without object: a) b) c) Inspection of light alloys: 1) Tube voltage 90 kV; 2) prefilter mm Al Inspection of steel and copper alloys ≤ 20 mm penetrated thickness: 1) Tube voltage 160 kV; 2) prefilter mm Cu Inspection of steel and copper alloys > 20 mm penetrated thickness: 1) Tube voltage 220 kV; 2) prefilter mm Cu 31 BS EN 16407-1:2014 EN 16407-1:2014 (E) d) Gamma radiography or high energy radiography: 1) Use the gamma source as specified or X-ray source > MV; 2) prefilter mm Cu or mm steel for Se 75, Ir 192, and mm Cu or 8mm steel for Co 60 or X-ray voltage > MV The duplex wire shall be positioned directly on the detector surface or cassette surface The source to detector distance shall be (1 000 ± 50) mm The mean grey value in the digital image shall exceed 50 % of the maximum grey value or the SNR shall exceed 100 for standard systems with pixel size ≥ 80 µm or 70 for high resolution systems with pixel size < 80 µm in the reference radiograph The basic spatial resolution (see Formula A.1) as measured in the reference radiograph for the used digital system and the system settings shall be documented in the examination report The detector basic spatial resolution of CR systems shall be measured both perpendicular and parallel to the scanning direction of the laser The higher value of the two SRb-values shall be used as resulting detector detector ) basic spatial resolution (SRb or SRb a) Image of the duplex wire IQI as shown in a radiograph b) Profile of the duplex wire IQI averaged from at least 21 lines 32 BS EN 16407-1:2014 EN 16407-1:2014 (E) c) Zoomed profile of wire pair D7 and D8 d) Scheme for calculation of the dip value (in %) with: dip = 100 x (A+B-2C)/(A+B) Key D7, D8 X Y duplex wire IQI values distance amplitude Figure A.1 — Example for duplex wire IQI evaluation with resulting IQI value D8, being the first one with a dip < 20 % image value, the 20 % dip value should be For improved accuracy in the measurement of the SRb or SRb interpolated from the modulation depth (dip) of the neighbour duplex wire modulations Figure A.2 represents the corresponding procedure for a high resolution CR system 33 BS EN 16407-1:2014 EN 16407-1:2014 (E) a) Profile plot of measured profile of a high resolution system with determined modulation depths (dips) b) Interpolation of modulation depth vs duplex wire diameter NOTE The 20 % value is determined from the intersection with the 20 % line resulting in iSRb = 66 µm Figure A.2 — Example for determination of the interpolated basic spatial resolution (iSRb) by interpolation from the measured modulation (dip) of the neighbour duplex wire elements The dependence of modulation (dip) from wire diameter should be fitted with a polynomial of second order for calculation of the intersection with the 20 % line as indicated in Figure A.2 Modulation values greater than zero shall be used for the interpolation only The interpolated SRb value (see Figure A.2) shall be documented as “interpolated SRb value” or iSRb This value may be used instead of the non-interpolated value SRb by agreement of contracting parties 34 BS EN 16407-1:2014 EN 16407-1:2014 (E) Annex B (informative) Choice of radiation source for different pipes Figure B.1 shows the maximum penetrated steel thickness, wmax, as a function of pipe wall thickness for different pipe outside diameters, derived using Formula (1) The recommended limits on wmax are also shown for the application of the different radiation sources, which allows the appropriate source to be selected for a particular pipe, given the outside diameter and wall thickness Dimensions in millimetres Figure B.1 — Maximum penetrated steel thickness, wmax, as a function of wall thickness, tact The curves in Figure B.1 show the values for pipes of differing outside diameters, De, with dimensions given in millimetres and nominal bore, NB, according to ANSI B36.1 The limits for different radiation sources given in Table for class TA are also illustrated These limits can be increased if digital radiography is used 35 BS EN 16407-1:2014 EN 16407-1:2014 (E) Bibliography [1] EN 444, Non-destructive testing — General principles for radiographic examination of metallic materials by X- and gamma-rays [2] EN 12543-1, Non-destructive testing — Characteristics of focal spots in industrial X-ray systems for use in non-destructive testing — Part 1: Scanning method [3] EN 12543-2, Non-destructive testing — Characteristics of focal spots in industrial X-ray systems for use in non-destructive testing — Part 2: Pinhole camera radiographic method [4] EN 12543-3, Non-destructive testing — Characteristics of focal spots in industrial X-ray systems for use in non-destructive testing — Part 3: Slit camera radiographic method [5] EN 12543-4, Non-destructive testing — Characteristics of focal spots in industrial X-ray systems for use in non-destructive testing — Part 4: Edge method [6] EN 12543-5, Non-destructive testing — Characteristics of focal spots in industrial X-ray systems for use in non-destructive testing — Part 5: Measurement of the effective focal spot size of mini and micro focus X-ray tubes [7] EN 12679:1999, Non-destructive testing — Determination of the size of industrial radiographic sources — Radiographic method [8] EN 14096-2:2003, Non-destructive testing — Qualification of radiographic film digitisation systems — Part 2: Minimum requirements [9] EN 25580, Non-destructive testing — Industrial radiographic illuminators — Minimum requirements (ISO 5580:1985) [10] EN ISO 9712, Non-destructive testing — Qualification and certification of NDT personnel (ISO 9712) [11] EN ISO 19232-1, Non-destructive testing — Image quality of radiographs — Part 1: Determination of the image quality value using wire-type image quality indicators (ISO 19232-1) [12] EN ISO 19232-2, Non-destructive testing — Image quality of radiographs — Part 2: Determination of the image quality value using step/hole-type image quality indicators (ISO 19232-2) [13] EN ISO 19232-3, Non-destructive testing — Image quality of radiographs — Part 3: Image quality classes (ISO 19232-3) [14] EN ISO 19232-4, Non-destructive testing — Image quality of radiographs — Part 4: Experimental evaluation of image quality values and image quality tables (ISO 19232-4) [15] ISO 5576, Non-destructive testing — Industrial X-ray and gamma-ray radiology — Vocabulary [16] ASTM E1000, Standard Guide for Radioscopy [17] ASTM E2597, Standard Practice for Manufacturing Characterization of Digital Detector Arrays [18] ASTM E2736, Standard Guide for Digital Detector Array Radiology 36 This page deliberately left blank NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW British Standards Institution (BSI) BSI is the national body responsible for preparing British Standards and other 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