基于matlab的扇形束投影CT重建（南航）
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Validation of Procedures for Welding Inspection Using Computed Radiography Davi F. OLIVEIRA1,2, Joseilson R. NASCIMENTO2, Alessandra S. MACHADO2, Carla A. MARINHO3, Marcos AIUB4, Joo M. HOHEMBERGER4, Eduardo IGUCHI4, Ricardo T. LOPES2 1Physics Institute, State University of Rio de Janeiro. E-mail: davi.oliveirauerj.br 2 Nuclear Instrumentation Laboratory, Federal University of Rio de Janeiro. E-mail: davilin.ufrj.br, joseilsonlin.ufrj.br, ricardolin.ufrj.br 3Leopoldo A. Miguez de Melo Research Center, CENPES/PETROBRAS 4SEQUI/PETROBRAS Abstract The introduction of digital radiography replacing conventional film radiography is becoming a reality in the inspection of materials and equipment. For this to happen in the oil and natural gas industry with quality, it is necessary to qualify and validate Radiographic Inspection Procedures, in particular for welding. This work is part of a project that aims at producing a comparative study between the techniques of film and computed radiography (CR) applied to weld inspection. For this purpose, images using five CR systems available on the market were obtained with their respective phosphor plates. Radiographic tests were performed with film and computed radiography for SWSI, DWSI and DWDI techniques. Test samples that consist of plates and steel pipes of different diameters and thickness were used. Radiographs were taken with X-ray and rays sources. The evaluation criteria for approval of the images were, namely, detectability (in comparison with film radiography) and the compliance with specific image quality parameters (contrast, basic spatial resolution and signal to noise ratio normalized). As a result of this study, the equipments that were able to reach positive results for specific ranges of thickness had their procedures duly validated, and are therefore apt to carry out reliable inspections for defect detection. Keywords: Computed Radiography, Inspection Procedure Validation, Weld Inspection. 1. Introduction In past few years, the use of digital radiography in replacing conventional film radiography is becoming a reality in the inspection of materials and equipment. Computed Radiography (CR) is proving itself to be an efficient technique and has been gaining relevance as a method of inspection which has several advantages over film radiography, especially for applications in the Oil & Gas industry. However, the test procedures are based in experimentations of trial and error due to the lack of an established methodology for choosing the parameters, as is the case with film radiography. Due to such lack of methodology, it is impossible to ensure that the CR technique is indeed able to detect the same types of defects as film radiography. In order for that to happen, it is necessary to validate inspection procedures, especially for welds, so as to establish an equivalence of detectability when compared to the conventional technique 1. Computed Radiography equipment are currently being manufactured by several companies who aim at working with NDTs. Each manufacturer produces its own phosphor plates, also known as imaging plates and IPs, according to their own specifications. All systems follow the same working principle, even though certain features may vary depending on the manufacturer, and that is the reason why it is of utmost importance to assess all responses with regard to the sensitivity of detection of discontinuities, such as the ones which are often found on welded joints 2,3. 11th European Conference on Non-Destructive Testing (ECNDT 2014), October 6-10, 2014, Prague, Czech RepublicThus, the main purpose of this study was to develop and validate procedures using CR on welding inspections in real field situations by using three radiography techniques and comparing them with the same techniques applied in film radiography. 2. Materials and methodology 2.1 Radiographic Testing Radiographic tests were performed with film and computed radiography for SWSI, DWSI and DWDI techniques. Test samples that consist of plates and steel pipes of different diameters and thickness were used. The images were considered approved once they achieved the required values for the following image quality parameters 4-10: Basic Spatial Resolution (BSR), Signal to Noise Ratio Normalized (SNRN) and contrast, besides defect detectability equivalent to the conventional film technique. Figure 1 portraits the test samples employed in the experiment and figures 2 to 4 show an illustration of the setup for each technique. Figure 1 Test Samples Figure 2 SWSI Setup Figure 3 DWSI Setup Figure 4 DWDI Setup Tables 1 to 3 show the test samples specifications, the exposure values and the image quality requirements for the three radiographic techniques. Table 1 Samples Specifications (SWSI). X-Rays -Rays Group Nominal Thickness (mm) Total Thickness (mm) High Voltage (kV) Isotope Wire IQI (ISO 19232-1) BSR ( m) (N 2821-B) SNRN (N 2821-B) I 5.33 6.93 140 12 II 6.35 7.95 150 12 III 7.11 10.31 150 11 IV 9.53 12.73 160 10 V 12.70 15.90 190 Se-75 10 VI 18.26 22.26 225 9 VII 25.40 29.40 270 8 VIII 35.71 40.51 320 Ir-192 7 100 (X-Rays) 160 (-Rays) 100 Table 2 Samples Specifications (DWSI). X-Rays -Rays Group Nominal Diam. (inch) Outer Diam. (mm) Nominal Thick. (mm) Total Thick. (mm) High Voltage (kV) Isotope Wire IQI (ISO 19232-1) BSR ( m) (N 2821-B) SNRN (N 2821-B) I 6.02 7.62 170 Se-75 13 II 8.56 11.76 225 Se-75 12 III 13.49 17.49 290 Ir-192 11 IV 4 114.3 17.12 21.12 320 Ir-192 10 V 6.35 7.95 170 Se-75 13 VI 7.11 10.31 200 Se-75 12 VII 12.7 15.9 280 Ir-192 11 VIII 6 168.3 18.26 22.26 330 Ir-192 10 IX 8 219.1 25.4 29.4 350 Ir-192 9 X 5.33 6.93 160 Se-75 13 XI 10 273.0 9.53 12.73 260 Ir-192 11 XII 14 355.6 35.71 40.51 420 Ir-192 8 100 (X-Rays) 160 (-Rays) 100 Table 3 Samples Specifications (DWDI). X-Rays -Rays Group Nominal Diam. (inch) SCH Nominal Thick. (mm) Total Thick. (mm) High Voltage (kV) Isotope Wire IQI (ISO 19232-1) BSR ( m) (N 2821-B) SNRN (N 2821-B) I 80 3.73 5.33 160 Se-75 13 II 0.50 160 4.78 6.38 160 Se-75 13 III 40 2.87 4.47 160 Se-75 13 IV 80 3.91 5.51 160 Se-75 13 V 160 5.56 7.16 160 Se-75 12 VI 0.75 XXS 7.82 11.02 160 Ir-192 11 VII 80 4.55 6.15 160 Se-75 13 VIII 160 6.36 7.96 160 Se-75 12 IX 1.00 XXS 9.09 12.29 180 Ir-192 11 X 80 5.08 6.68 160 Se-75 12 XI 1.50 160 7.14 10.34 160 Ir-192 11 XII 40 3.91 5.51 160 Se-75 13 XIII 80 5.54 7.14 160 Se-75 12 XIV 160 8.74 11.94 160 Ir-192 11 XV 2.00 XXS 11.07 14.27 225 Ir-192 10 XVI 40 5.16 6.76 160 Se-75 12 XVII 2.50 80 7.01 10.21 180 Ir-192 11 XVIII 40 5.49 7.09 160 Se-75 12 XIX 3.00 80 7.62 10.82 180 Ir-192 11 100 (X-Rays) 160 (-Rays) 100 2.2 Detectors For the film radiography test, class I and II films were used. For the computed radiography test, five CR systems were used, each one with its own corresponding imaging plate (IP). Table 4 correlates the CR system, the IP type and the scanning parameters. Table 4 CR systems and scanning parameters. CR System IP Type Laser Spot Size ( m) Pixel Size ( m) S1 87 70 S2 IPA 50 50 S3 50 50 S4 IPB 30 50 S5 IPC 50 50 2.3 Radiation Sources For the radiographic testing, X-ray and gamma ray sources were used, as shown in tables 5 and 6. Table 5 - X-ray specifications. Maximum High Voltage (kV) Maximum Current (mA) Focal Spot Size (mm) Equipment model 200 10.0 1.0 GE IT (Eresco 200 MF4-R) 225 2.8/8.0 1.0/5.5 Yxlon (XMB 225) 450 2.0/10.0 2.5/5.5 GE IT (Isovolt Titan 450) Table 6 - Gamma ray sources. Isotope Maximum Activity (Ci) Focal Spot Size (mm) Irradiator model Iridium-192 80 3.0 x 2.0 Sentinel (880 SIGMA) Selenium-75 80 3.0 x 3.0 Sentinel (880 DELTA) 3. Results 3.1 SWSI Technique Table 7 shows the results of the images acquired with film radiography for mapping the defects on the test samples. Those images were used as reference for evaluating the detectability of the computed radiography systems. Table 7 - Film radiography results. X-rays -Rays Group Exp. (mA.s) Wire IQI (ISO 19232-1) Exp. (x103Ci.s) Wire IQI (ISO 19232-1) Film Class I 440 13 8.70 13 II II 440 13 9.37 12 II III 480 14 10.57 12 II IV 600 12 12.82 12 II V 495 12 15.21 12 II VI 336 11 10.35 12 II VII 270 11 14.58 11 II VIII 280 11 20.11 11 II Tables 8 to 12 show the results of the images acquired through computed radiography. Besides the parameters employed for exposure and the extracted image quantity values, detectability results are also presented and classified as Approved (AP) or Failed (F). Table 8 S1 results using the SWSI technique. X-Rays -Rays Group Exp. (mA.s) Wire IQI (ISO 19232-1) BSR ( m) SNRN Detec. Exp. (x103Ci.s) Wire IQI (ISO 19232-1) BSR ( m) SNRN Detec. I 40 14 100 150 AP 17.4 13 100 160 AP II 44 13 100 165 AP 17.2 12 100 145 AP III 56 13 100 150 AP 15.7 12 100 150 AP IV 120 13 100 170 AP 16.2 12 100 140 AP V 63 13 100 150 AP 21.2 11 100 160 AP VI 126 12 100 185 AP 19.4 9 160 90 F VII 144 11 100 180 AP 26.3 10 160 105 F VIII 168 9 130 130 F 39.6 8 160 104 F Table 9 S2 results using the SWSI technique. X-Rays -Rays Group Exp. (mA.s) Wire IQI (ISO 19232-1) BSR ( m) SNRN Detec. Exp. (x103Ci.s) Wire IQI (ISO 19232-1) BSR ( m) SNRN Detec. I 360 14 80 170 AP 25.5 13 100 160 AP II 120 14 80 110 AP 26.6 12 100 150 AP III 320 14 80 150 AP 28.3 13 100 160 AP IV 880 13 80 175 AP 20.6 12 100 160 AP V 495 12 100 120 AP 22.3 12 100 150 AP VI 728 12 100 135 AP 40.6 10 160 120 F VII 2340 11 100 175 AP 92.1 10 160 117 AP VIII 2772 9 130 135 F 61.2 9 130 128 F Table 10 S3 results using the SWSI technique. X-Rays -Rays Group Exp. (mA.s) Wire IQI (ISO 19232-1) BSR ( m) SNRN Detec. Exp. (x103Ci.s) Wire IQI (ISO 19232-1) BSR ( m) SNRN Detec. I 120 14 50 210 AP 62.5 13 50 210 AP II 120 13 50 195 AP 62.5 13 63 165 AP III 140 14 50 190 AP 63.4 12 63 160 AP IV 280 13 50 195 AP 91.2 12 80 180 AP V 172 13 50 200 AP 89.2 11 80 115 AP VI 232 12 63 155 AP 181.0 11 130 101 F VII 450 11 80 140 AP 173.0 9 160 76 F VIII 330 9 130 135 F 344.0 8 160 79 F Table 11 S4 results using the SWSI technique. X-Rays -Rays Group Exp. (mA.s) Wire IQI (ISO 19232-1) BSR ( m) SNRN Detec. Exp. (x103Ci.s) Wire IQI (ISO 19232-1) BSR ( m) SNRN Detec. I 152 15 50 210 AP 45.7 13 65 140 AP II 120 14 50 200 AP 53.1 13 80 135 AP III 180 14 63 160 AP 50.3 13 80 155 AP IV 260 13 63 205 AP 45.9 12 80 125 AP V 198 13 80 145 AP 54.2 12 80 125 AP VI 364 12 80 130 AP 114.0 11 130 93 F VII 360 11 80 130 F 145.0 9 130 90 F VIII 515 9 100 100 F 61.2 9 160 54 F Table 12 S5 results using the SWSI technique. X-Rays -Rays Group Exp. (mA.s) Wire IQI (ISO 19232-1) BSR ( m) SNRN Detec. Exp. (x103Ci.s) Wire IQI (ISO 19232-1) BSR ( m) SNRN Detec. I 120 15 50 225 AP 36.7 14 63 170 AP II 40 14 50 155 AP 39.3 13 63 180 AP III 144 14 50 220 AP 33.0 13 63 155 AP IV 192 13 50 200 AP 39.6 12 80 130 AP V 165 13 50 210 AP 54.2 12 80 130 AP VI 216 12 63 160 AP 90.0 10 130 102 F VII 270 11 80 140 AP 109.7 10 160 79 AP VIII 588 10 100 120 F 58.9 9 160 55 F For the SWSI technique using an X-Ray source, results showed that all of the tested systems presented satisfactory results for thicknesses up to the ones of group VII, except for system 4, in which the images were approved only up to group VI. For the VIII group thickness, none of the systems were able to detect all of the defects observed with conventional radiography, even though in some cases the image quality requirements were met (S4 and S5). With gamma ray sources, good results were obtained only for thicknesses up to the ones of group V (thickness range of Se-75), even though systems 2 and 5 managed to approve images for group VII. In this case, it is believed that the non-approval for group VI is due the kind of defect found on those test samples: it is a type of defect which is harder to detect than the ones of group VII. As it was the case for the X-Ray source inspections, none of the systems were able to detect all defects for the thicknesses of group VIII. For both radiation sources, there have been cases in which, although meeting the minimum image quality requirements, the images were not approved, since the detectability was not equivalent to the one of film radiography. Figures 5 and 6 display a comparison between the exposure values of the systems using the SWSI technique with X-ray and gamma ray sources, respectively. In such images, only the values for the groups considered approved are shown. 110100100010000Exposure (mA.s)IIIIIIIVVVIVIIGroupSWSI - X-RaysFilmS1S2S3S4S5 Figure 5 Exposure values for X-ray sources (SWSI). 1101001000Exposure (x103 Ci.s)IIIIIIIVVVIIGroupSWSI - -RaysFilmS1S2S3S4S5 Figure 6 Exposure values for gamma ray sources (SWSI). Analyzing the results obtained with an X-Ray source through the images shown above, a trend of exposure reduction can be observed if compared to conventional radiography, except for system 2, which displayed higher exposure values for thicknesses higher than the ones of group IV. However, with gamma-ray sources, the exposure was higher than the one used for conventional radiography for all of the systems. Tables 13 and 14 display the systems final evaluation results using the SWSI for X-Ray and gamma ray sources, respectively. Table 13 Systems evaluation results using an X-Ray source (SWSI). Group S1 S2 S3 S4 S5 I Approved Approved Approved Approved Approved II Approved Approved Approved Approved Approved III Approved Approved Approved Approved Approved IV Approved Approved Approved Approved Approved V Approved Approved Approved Approved Approved VI Approved Approved Approved Approved Approved VII Approved Approved Approved Failed Approved VIII Failed Failed Failed Failed Failed Table 14 Systems evaluation results using gamma ray sources (SWSI). Group S1 S2 S3 S4 S5 I Approved Approved Approved Approved Approved II Approved Approved Approved Approved Approved III Approved Approved Approved Approved Approved IV Approved Approved Approved Approved Approved V Approved Approved Approved Approved Approved VI Failed Failed Failed Failed Failed VII Failed Failed Failed Failed Approved VIII Failed Failed Failed Failed Failed Figures 7 and 8 depict the final comparison result among the systems for both sources using the SWSI technique. On those images, the approval percentages are shown for each system, thus ranking their performance. Figure 7 Approval percentages for each system using X-rays (SWSI). Figure 8 Approval percentages for each system using gamma ray (SWSI). 3.2 DWSI Technique Table 15 shows the results of the images acquired with film radiography for mapping the defects on the test samples using the DWSI technique. Those images were used as reference for evaluating the detectability of the computed radiography systems. Table 15 Film radiography results. X-Rays -Rays Group Exp. (mA.s) Wire IQI (ISO 19232-1) Exp. (x103Ci.s) Wire IQI (ISO 19232-1) Film Class I 105.0 15 10.7 13 I II 22.4 13 3.2 12 II III 37.2 12 3.6 11 II IV 46.4 11 5.5 10 II V 168.8 14 8.5 13 I VI 19.2 13 4.2 13 II VII 44.8 12 4.5 11 II VIII 67.5 11 7.3 10 II IX 300.0 10 20.2 10 II X 340.0 14 15.1 13 I XI 30.6 12 5.8 12 II XII 1134.0 10 102.8 9 II The DWSI technique could not be used with system 1, since there were a number of technical complications which could not be handled in a timely manner for that purpose. Tables 16 to 19 show the results of the images acquired with computed radiography. Besides the parameters used for exposure and the image quality values obtained, detectability results are also presented and classified as Approved (AP) or Failed (F). Table 16 S2 results using the DWSI technique. X-Rays -Rays Group Exp. (mA.s) Wire IQI (ISO 19232-1) BSR ( m) SNRN Detec. Exp. (x103Ci.s) Wire IQI (ISO 19232-1) BSR ( m) SNRN Detec. I 2625.0 13 80 197 AP 24.9 13 100 208 AP II 2240.0 12 80 196 AP 54.5 12 100 224 AP III 620.0 12 80 167 F 59.0 0 200 217 F IV 1676.2 12 100 164 F 24.7 11 200 201 F V 2250.0 13 80 179 AP 20.3 13 100 183 F VI 2240.0 13 80 190 AP 19.5 12 100 171 F VII 3196.8 11 100 185 AP 26.7 11 160 204 AP VIII 2697.3 11 130 110 F 24.9 9 200 185 F IX 2497.5 10 160 102 F - - - - - X 4800.0 13 80 184 AP 15.0 13 100 120 F XI 3396.6 12 100 180 AP 56.3 11 160 187 F XII 1470.0 10 160 45 F - - - - - Table 17 S3 results using the DWSI technique. X-Rays -Rays Group Exp. (mA.s) Wire IQI (ISO 19232-1) BSR ( m) SNRN Detec. Exp. (x103Ci.s) Wire IQI (ISO 19232-1) BSR ( m) SNRN Detec. I 67.5 13 50 145 AP 19.9 12 65 141 F II 53.2 13 50 140 F 18.9 11 80 142 F III 124.0 11 80 144 F 44.6 11 200 130 F IV 203.0 10 100 144 F 75.9 9 200 122 F V 82.5 13 50 135 AP 25.1 12 80 139 F VI 76.8 13 50 136 AP 40.3 11 65 130 F VII 92.8 12 80 120 F 38.9 10 200 128 F VIII 229.5 9 100 100 F - - - - - IX 675.0 8 130 75 F - - - - - X 176.0 13 50 135 AP 10.3 12 80 134 F XI 176.8 13 50 215 F 67.5 10 130 128 F XII 1907.5 8 130 80 F - - - - - Table 18 S4 results using the DWSI technique. X-Rays -Rays Group Exp. (mA.s) Wire IQI (ISO 19232-1) BSR ( m) SNRN Detec. Exp. (x103Ci.s) Wire IQI (ISO 19232-1) BSR ( m) SNRN Detec. I 48.8 13 65 186 AP 16.9 12 80 191 F II 50.4 13 80 195 F 38.0 12 80 190 AP III 108.5 11 80 198 F 37.4 10 160 160 F IV 159.5 11 100 192 F 12.9 8 200 155 F V 82.5 13 65 211 AP 33.8 13 80 139 F VI 64.0 13 80 212 AP 22.6 12 80 131 F VII 102.4 12 80 130 F 55.7 11 130 210 F VIII 205.2 9 100 100 F - - - - - IX 675.0 9 130 78 F - - - - - X 128.0 13 65 209 AP 28.2 13 65 156 F XI 190.4 12 65 165 F 72.0 11 100 216 F XII 2497.5 8 200 47 F - - - - - Table 19 S5 results using the DWSI technique. X-Rays -Rays Group Exp. (mA.s) Wire IQI (ISO 19232-1) BSR ( m) SNRN Detec. Exp. (x103Ci.s) Wire IQI (ISO 19232-1) BSR ( m) SNRN Detec. I 52.5 13 50 227 AP 10.9 13 65 235 F II 30.8 12 80 207 AP 16.4 12 80 219 AP III 111.6 12 80 232 F 24.9 11 160 218 F IV 133.4 11 82 215 F 61.7 11 160 200 F V 56.3 13 65 204 AP 69.2 12 80 208 F VI 48.0 13 50 213 AP 17.6 12 80 137 F VII 83.2 12 80 209 AP 78.9 10 160 210 F VIII 164.7 10 100 85 F 48.2 8 200 224 F IX 450.0 10 100 100 F 70.4 8 250 202 F X 120.0 13 50 220 AP 53.1 12 80 201 F XI 88.4 12 80 203 AP 56.3 11 130 230 F XII 4500.0 9 200 57 F 210.9 8 320 152 F As it was the case with the SWSI technique, there are situations in which, even if the established image quality requirements are met, the images were not approved due to the fact that their detectability were not equivalent to conventional radiography. With X-Ray sources, systems S3 and S4 were approved only for thicknesses up to 7.11 mm, regardless of their diameter, proving that such equipment is not reliable for inspecting larger thicknesses using the DWSI technique. On the other hand, systems 2 and 5 proved to be efficient for detecting defects in thicknesses of up to 12.7 mm. Using gamma ray sources, systems 4 and 5 were only able to detect defects for group IIs test samples. System 2 reached an equivalent detectability level for groups I and VII also. It is thus possible to ascertain that those test samples were manufactured with defects which were easier to detect. This explains how it was possible that the images of system 2 were approved for the thickness of 12.7 mm, even though it was impossible to visualize such defects in smaller thicknesses. Figures 9 and 10 display a comparison between the exposure values among the systems using the DWSI technique with X and gamma ray sources, respectively. Those figures show only the values for the groups considered approved. 110100100010000Exposure (mA.s)IIIVVIVIIXXIGroupDWSI - X-RaysFilmS2S3S4S5 Figure 9 Exposure values for X-ray sources (DWSI). 110100Exposure (x103 Ci.s)IIIVIIGroupDWSI - -RaysFilmS2S4S5 Figure 10 Exposure values for gamma ray sources (DWSI). By analyzing the results obtained with an X-Ray source, a reduction on the exposure values could be observed for systems 3, 4 and 5 only for thicknesses of up to 6.35 mm. This is due to the fact that, for those thicknesses, class 1 films were used for conventional radiography tests. It was also possible to observe that the exposure values for system 2 were much higher than the ones of conventional radiography for all of the approved thicknesses, reaching a factor of 115 times that value in the most extreme case. This large accrual is due to a limitation in this equipment when it comes to working with low laser power, generating images with less noise but with low signal intensity, which has to be compensated with the exposure time. For gamma-ray sources, higher exposure values were necessary when compared to conventional radiography so that the images could be approved, repeating therefore the behavior observed with the DWSI technique. Tables 20 and 21 show the systems final evaluation result using the DWSI technique with X and gamma ray sources, respectively. Table 20 Systems evaluation results using an X-Ray source (DWSI). Group S2 S3 S4 S5 I Approved Approved Approved Approved II Approved Failed Failed Approved III Failed Failed Failed Failed IV Failed Failed Failed Failed V Approved Approved Approved Approved VI Approved Approved Approved Approved VII Approved Failed Failed Approved VIII Failed Failed Failed Failed IX Failed Failed Failed Failed X Approved Approved Approved Approved XI Approved Failed Failed Approved XII Failed Failed Failed Failed Table 21 Systems evaluation results using gamma ray sources (DWSI). Group S2 S3 S4 S5 I Approved Failed Failed Failed II Approved Failed Approved Approved III Failed Failed Failed Failed IV Failed Failed Failed Failed V Failed Failed Failed Failed VI Failed Failed Failed Failed VII Approved Failed Failed Failed VIII Failed - - Failed IX - - - Failed X Failed Failed Approved Failed XI Failed Failed Failed Failed XII - - - Failed Figures 11 and 12 display the final result of the comparison among the systems for both kinds of sources using the DWSI technique. On those images, the approval percentages are shown for each system, thus ranking their performance. Figure 11 Approval percentages for each system using X-rays (DWSI). Figure 12 Approval percentages for each system using gamma rays (DWSI). 3.3 DWDI Technique The DWDI technique could not be used with system 1, since there were a number of technical complications which could not be handled in a timely manner for that purpose. Tables 22 to 25 list the results of the images acquired with computed radiography. Besides the parameters used for exposure and the image quality values obtained, the tables also show detectability results which were classified as Approved (AP) or Failed (F); Table 22 S2 results using the DWDI technique. X-Rays -Rays Group Exp. (x 102 mA.s) Wire IQI (ISO 19232-1) BSR ( m) SNRN Detec. Exp. (x103Ci.s) Wire IQI (ISO 19232-1) BSR ( m) SNRN Detec. I 77.7 13 80 120 AP 115.7 13 100 92 F II 85.1 13 80 147 AP - - - - - III 13.7 13 80 113 AP 74.6 12 160 101 F IV 77.7 13 80 166 AP V 99.9 12 80 170 AP 120.4 11 130 91 F VI 12.0 0 100 147 F - - - - - VII 111.0 13 80 113 AP 106.8 11 160 163 F VIII 111.0 12 100 189 AP - - - - - IX 75.0 11 100 177 F - - - - - X 122.1 13 80 160 AP 105.2 12 160 105 F XI - - - - - 87.0 12 200 140 F XII - - - - - 106.8 12 160 106 F XIII - - - - - 128.3 11 200 88 F XIV - - - - - - - - - - XV 192.0 12 130 163 F - - - - - XVI - - - - - 106.8 11 160 103 F XVII - - - - - XVIII - - - - - 123.2 11 250 72 F XIX - - - - - - - - - - Table 23 S3 results using the DWDI technique. X-Rays -Rays Group Exp. (x 102 mA.s) Wire IQI (ISO 19232-1) BSR ( m) SNRN Detec. Exp. (x103Ci.s) Wire IQI (ISO 19232-1) BSR ( m) SNRN Detec. I 55.0 13 50 135 AP 107.5 0 100 111 F II 67.0 13 50 136 F 105.6 0 80 125 F III 40.0 13 50 108 AP 81.9 12 100 101 F IV 54.0 13 80 120 F 99.1 12 130 97 F V 64.0 12 50 214 F 136.9 11 130 85 F VI 120.0 0 200 111 F - - - - - VII 61.0 13 65 113 F 99.2 10 130 82 F VIII 155.0 12 65 146 F - - - - - IX 40.0 11 100 134 F - - - - - X 100.0 12 50 103 F 104.9 13 160 104 F XI 340.0 12 80 149 F 87.9 10 250 107 F XII 120.0 13 50 140 AP 142.5 10 200 55 F XIII 100.0 12 65 151 F - - - - - XIV 195.0 11 65 119 F - - - - - XV 75.0 11 100 140 F - - - - - XVI 100.0 12 65 148 F 141.6 10 200 50 F XVII 160.0 11 65 102 F 87.0 10 200 103 F XVIII 157.0 12 65 147 F 144.4 11 250 47 F XIX 240.0 11 65 129 F - - - - - Table 24 S4 results using the DWDI technique. X-Rays -Rays Group Exp. (x 102 mA.s) Wire IQI (ISO 19232-1) BSR ( m) SNRN Detec. Exp. (x103Ci.s) Wire IQI (ISO 19232-1) BSR ( m) SNRN Detec. I 2.2 13 50 170 AP 82.4 12 100 91 F II 3.2 13 65 183 F 105.0 0 100 88 F III 1.6 13 65 151 AP 60.5 12 100 90 F IV 2.8 13 80 163 F 99.1 13 130 145 F V 3.4 12 65 131 F 136.9 11 130 147 F VI 4.8 12 65 179 F - - - - - VII 4.1 13 65 139 F 95.6 12 130 72 F VIII 6.7 12 65 188 F - - - - - IX 4.1 11 100 168 F - - - - - X 4.8 13 65 138 F 102.7 10 160 52 F XI 8.1 12 65 183 F 87.0 11 250 153 F XII 5.2 13 65 110 AP 89.0 12 160 60 F XIII 3.7 12 80 136 F 116.7 11 200 53 F XIV 8.4 11 65 178 F - - - - - XV 6.7 11 130 172 F - - - - - XVI 4.3 12 65 120 F 109.8 10 200 49 F XVII 6.9 12 65 183 F 87.0 10 200 146 F XVIII 5.4 13 65 130 F 116.2 10 250 35 F XIX 5.9 11 65 178 F - - - - - Table 25 S5 results using the DWDI technique. -Rays Group Exp. (x103Ci.s) Wire IQI (ISO 19232-1) BSR ( m) SNRN Detec. I 83.3 12 80 200 F II 99.8 13 100 190 F III 59.9 12 160 101 F IV 78.2 13 100 198 F V 116.9 12 100 179 F VI - - - - - VII 92.6 11 160 163 F VIII - - - - - IX - - - - - X 102.7 12 160 105 F XI 70.3 12 250 189 F XII 89.0 12 160 106 F XIII 113.8 11 200 88 F XIV - - - - - XV - - - - - XVI 109.8 10 200 49 F XVII 87.0 10 200 146 F XVIII 116.2 10 250 35 F XIX - - - - - Generally speaking, the performance of the tested systems was not good for both radiation sources. With X-Ray sources, system 5 was not tested, since the detectability results had already been obtained previously. Systems 3 and 4 (same manufacturer) presented good results only for thicknesses up to 3.91 mm. System 1 was able to detect discontinuities in thicknesses up to 6.36 mm. The groups with larger diameters could not be inspected with this system, since it presented technical issues. However, observing the results with smaller diameters, it is believed that it would have a good performance, if it had been tested. For gamma ray sources, none of the systems were able to detect the defects present on the test samples. Since the DWDI technique requires the magnification of the weld located on the source side, the large focal size of the gamma sources creates a very intense unsharpness, which is a determining factor for loss of detectability. Figure 13 shows the comparison among all systems for the exposure values using DWDI technique with an X-Ray source. On those images, only the values for the groups considered approved are shown. It is possible to observe that, as it is the case with the other techniques, the exposure time for system 2 was the highest when compared with the other systems. 1101001000Exposure (x102 mA.s)IIIIIIIVVVIIVIIIIXXXIIGroupDWDI - X-RaysS2S3S4 Figure 13 Exposure values for X-ray sources (DWDI). Tables 26 and 27 show the systems final evaluation result using the DWDI technique with X and -ray sources, respectively Table 26 Systems evaluation results using an X-Ray source (DWDI). Group S2 S3 S4 I Approved Approved Approved II Approved Failed Failed III Approved Approved Approved IV Approved Failed Failed V Approved Failed Failed VI Failed Failed Failed VII Approved Failed Failed VIII Approved Failed Failed IX Failed Failed Failed X Approved Failed Failed XI - Failed Failed XII - Approved Approved XIII - Failed Failed XIV - Failed Failed XV Failed Failed Failed XVI - Failed Failed XVII - Failed Failed XVIII - Failed Failed XIX - Failed Failed Table 27 Systems evaluation results using gamma ray sources (DWDI). Group S2 S3 S4 S5 I Failed Failed Failed Failed II - Failed Failed Failed III Failed Failed Failed Failed IV - Failed Failed Failed V Failed Failed Failed Failed VI - - - - VII Failed Failed Failed Failed VIII - - - - IX - - - - X Failed Failed Failed Failed XI Failed Failed Failed Failed XII Failed Failed Failed Failed XIII Failed - Failed Failed XIV - - - - XV - - - - XVI Failed Failed Failed Failed XVII - Failed Failed Failed XVIII Failed Failed Failed Failed XIX - - - - Figure 14 depicts the final comparison result among the systems for the X-Ray source using the DWDI technique. On those images, the approval percentages are shown for each system, thus ranking their performance. Figure 14 Approval percentages for each system using X-rays (DWDI). 4. Conclusions This paper aimed at analyzing the performance of five computed radiography systems for inspecting welded joints by using SWSI, DWSI and DWDI inspection techniques with both X-Ray and gamma ray sources. The systems had their inspection procedures approved for the radiography techniques and the sources used once the results produced discontinuity detection images whose quality was equivalent to conventional radiography. Such procedures, if reproduced according to the same test parameters described here, shall guarantee that the detectability will be reached for the evaluated thickness ranges. It was observed that the acceptable values for basic spatial resolution of the image (not superior to 100 m for X-Ray sources and 160 m for gamma ray sources, according to the observed penetration thickness order) and normalized signal-to-noise ratio (superior to 100) prescribed as a standard are perfectly coherent and attainable, though unable to guarantee detectability in 100% of the cases. It was possible to ascertain that the effects caused by the fading and by the sensitivity to low-energy radiation was crucial when using gamma ray sources. All approved procedures used sources with activity higher than 30 Ci, on average. When activity reduction by natural decay was observed, an increase on the exposure time, even though common practice in conventional radiography, did not prove to be beneficial and the images were not approv
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