digital radiography r High-energy DT Applications lior Pick, Ron Pincu and Ofra Kleinberger over film radiog- p P This advanced

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2 igital Radiography r High-energy DT Applications lior Pick, Ron Pincu and Ofra Kleinberger p P ortable digital radiography has gained popularity raphy and film replacements process-free films) by providing (Light, 2008). immediate system enables reduction This advanced and benefits to users allows for creating images for any compromise t also requires no repositioning. over film radiog- radiography many additional Digital radiography analysis, without of nondestructive (computerized on image quality due to speed. A reliable and portable digital radiography of work time and costs while increasing the profits testing (NDD service providers. technology has been recognized by new NDT standards and codes (ASME, 2010; ASTM, 2007; BSS, 2003; BSS, 2003). t enables detailed results and provides the basis for high-level, detectors limited on-site NDT analysis. available with this kind of technology, levels of energy. Portable amorphous systems are available radiography and high-energy The special structure electronic components inspection based to work with digital array (DDA) imager, in which are not placed behind the imaging area, allows for and works in high levels of energy with only a external shield. The portable site and can be operated on battery-power designed levelsisotopes. of a digital detector almost no backscattering, minimal silicon (a-so flat-panel that have been specially Most of the however, usually work with systems are small, can be used at the by one person. The systems can operate for an entire workday, APRL 2011 so there is no need for external power MATERALS EVALUATON 453

3 ME FEATURE DGTAL RADOGRAPHY FOR NDT APPLCATONS The speedy image acquisition process does not cause any:compromise to image quality. The layers: X-ray ---:~~ D Scintillator Electronic modules D D System interface in the inspection area. These characteristics make for mobile and reliable inspection equipment. This paper presents case studies from various locations around the world that utilized digital radiography systems that were combined levels. For applications with high-energy such as small bore pipes, welding, boilers and shipyard NDT, portable a-si based systems provide a laboratory experience in the field, enable immediate high-quality results for analysis onsite, and offer mobile, efficient testing anywhere. Digital Flat-panel Technology The a-si digital flat-panel is composed and an array of a-si photodiodes of a scintillator (Thales, 2011). The X-ray tube sends an X-ray beam through a target. The photons that are not absorbed by the target reach the a-si detector and strike the layer of scintillating material that converts them into visible light photons. The light photons reach the photodiodes, which convert them into electrons that activate the pixels in the a-si, The electronic data that are generated from this process are The process: X-rays transmitted through x-rav the object Scintillator converts { X-rays into light ""-'--'--" (Fluorescent effect) {}»> Substrate Array of amorphous silicon ~ photodiodes convert light to electrons Low noise readout of electrical signal of each pixel Signal processing for each pixel High-speed interface to transfer image to system Figure 1. Amorphous silicon (a-si) flat-panel structure. converted to a digital signal that is received by the computer. The software then converts this information into a high-quality image (shown in Figure 1). Digital Radiography Advantages in Field NDT Digital radiography can be a sufficient, and even improved, replacement for X-ray film or other film replacements. t can provide advantages that do not exist with other technologies, as well as enhance the work experience of the NDT technician (Pick and Kleinberger, 2009). Among these advantages is the ability to produce images in nearly real-time. With just a click of the mouse, a high-quality image is immediately available on the computer screen. A few more simple steps with the software, such as window leveling, sharpening or histogram equalization, and the images are ready for advanced analysis. The X-ray source can also be controlled by the system, enabling the best synchronization between the actual shooting of X-rays and the time the digital imager reads the data stored in the a-si plate. As this process can be immediate, the data remain unspoiled. The speedy image acquisition process does not cause any compromise to image quality. The sensitive digital imager can provide images of the highest quality on the spot. At last, the professional user can make the most of the capabilities of X-rays. By achieving an image that is immediately visible on the laptop screen, the results are immediately known and there is no need to remain blind on-site. Repeated shots are cost-free and the best position to take an X-ray image can be determined on the spot. The operator can immediately reposition the X-ray source, correct the distance from the imager, change exposure time, or place the imager in a better location to create the perfect image, all according to the previous results that appear immediately on the screen. There is no need to go back to a laboratory to develop or scan results. Despite these advantages, in those applications where high energy is required, much of the NDT market has avoided the transition to digital radiography. The main problem experienced with digital radiography is the shorter lifetime of the DDA imager if it is exposed to high levels of energy. This shorter lifetime makes it difficult to return the investment made in the imager itself. This paper will investigate this problem in more detail and suggest a possible solution. The Problem: High-energy NDT and Digital Detector Array mager Lifetime High-energy NDT is defined as tests that require the use of X-ray energy levels that are higher than MATERALS EVALUATON' APRL 2011

4 or tests that involve the use of isotopes (for example, the r-l92 isotope, which generates approximately 450 kv on average). Historically, the OOA imager lifetime is calculated by recording the time of the first dose-related failure in the imager. These first failures are typically caused by problems in the electronic components of the imager. Electronic parts are relatively low-cost among the components of the imager, and can be easily replaced. The a-si layer inside the imager can continue to function much longer than the electronics, even if it is exposed to high doses of energy. The first step toward enabling the transition to digital radiography in high-energy NOT applications is to understand that the true lifetime of an a-si plate is much longer than the typical declared lifetime of the imagers. t should be understood that faulty electronic parts could be replaced at a relatively low cost, allowing the imager to operate with the original a-si panel for a longer period of time. The Solution: Avoid High-dose Exposure of Electronics The major problem when working with OOA imagers in high doses is the failure caused to electronic parts due to exposure to high-energy radiography. The key to avoiding electronic failures related to the radiography dose is to shield the electronics. The solution therefore needs to be found in the early stages of imager planning. There are two main technological solutions that may be incorporated into the initial design of the imager. These two solutions are optional, and cannot be implemented together. 1. A layer of shielding material (such as lead or tungsten) should be placed inside the imager between the a-si plate and the electronic components. Thus, the a-si plate absorbs most of the X-rays and translates them to an image, and any X-rays that go through it are blocked by the internal shield. The electronics are fully protected. The advantage to this solution is that the shield is integrated into the imager. Figure 2 shows graphics of a digital panel that has the electronics located behind the a-si plate (Thales, 2011). 2. Moving the electronics from behind the a-si plate. When the electronic parts are located to the side of the a-si plate, they are not directly impacted by the X-rays shot toward the imaging area. An external shield can easily provide foolproof protection of the electronic parts of the imager at a low cost, with an adequately cut lead or tungsten plate (shown in Figure 3). The main advantages to this solution are that the original weight of the imager is maintained and the backscattering effect is reduced to a minimum. A disadvantage may be found in the increase of the surface area of the panel. n the first solution, there are panels that already have internal shielding for the electronic parts, but this is a thin layer of metal that blocks most of the Scintillator a-si Plate l Linedriverl integrated circuits ("'1 "" X-ray Detector matrix Figure 2. Flat-panel with electronics behind the a-si plate. L ++Panel 20 mm ~ Active <, 4 imaging - - area - - L ~ ~ctiv~l maging area mm External shielding ----Panel Figure 3. mager and designated external shielding. APRL 2011 MATERALS EVALUATON 455

5 c DlG,,' DlOG y ro DJ X-rays (but cannot provide complete PU 10 5 protection), is The two main disadvantages to the first solution limited to 160 kv and serves to maintain the declared are imager weight and backscattering lifetime as the time resulting of the panel (which is calculated to first dose related fault, and which typically the electronic parts). This is not the kind of internal shield that will serve as a solution applications. occurs in for high-energy A thicker layer of shielding, which is also shielding material increased. original weight without applications resulting The layer adds a disproportionate amount of weight to the imager compared to its the internal shield. Also, in where high energy is not required, NDT technician heavier, is required. effect. The imager weight is significantly the has to always work with the heavier panel. Another problem with moving the shield plate is that it throws back many X-rays that reach it because of its proximity to the a-si plate, causing a heavy backscatteri ng effect. The scattered X-rays then return and light up the a-si pixels once more. The resulting images may be unclear due to the excess of X-rays. A detailed view of the effects caused by the second solution show that it entails many advantages. The original weight ofthe imager is maintained. in various makes its placement matter. By maintaining required, it also to each inspection site. n where high energy is not one continues lightweight This a simple its original weight, remains easy to transport most applications locations to work normally, with a panel and without shielding. The a-si based DDA imager is sensitive enough to enable great results in low doses. Sometimes, working with digital radiography, when it may not be necessary to use the same energy level as is used when working with film. High-energy dose levels can be avoided, which increases operator safety. (a) When shielding is required, a simple external shield will suffice. maging area is not lost because only the sides of the imager (where the electronics located) are require protection. The thickness of the external shield can be deterto the energy level used. This mined according means its weight can be optimized to the type of work required. The imaging area can start from the edges of the panel (on the corner where the a-si plate is located). The imager is thin. The entire depth of the imager can be reduced because the electronics are located on the side. An almost entirely backscatter-free because there is nothing will cause radiation inherent The advantages the beginning ratio and image quality. of digital radiography upon request, analysis anywhere, Figure 4. X-ray images of mm (8 in.) diameter steel pipe, 19 mm (0.75 in.) wall thickness that were taken with: (a) iridium; (b) selenium. MATERALS EVALUATON. APRL 2011 available mentioned of this paper (high-quality and no compromise 456 to return to it. This reduces the noise in the images, as well as increases the signal-to-noise (b) panel is created behind the a-si plate that in images no repositioning on quality of results) can all be in high-energy applications.

6 Relevant Applications Applications that require high-energy levels usually require penetration of thick metallic components. Such NOT inspections include pipe welding and pipe erosion tests, welding in boilers or ship hulls, and quality control inspections in casting facilities. The following case studies contain various high-energy testing examples in which a portable digital radiography system was used. Pipe nspection: Reducing Dose A pipe test was conducted by an NOT service company using an imager with r-192 (iridium isotope) and Se-75 (selenium isotope) sources alternatively. This test showed two interesting results. Testing that is usually conducted with r-192 at a specific level of activity can be also conducted with a lower level of activity. This means longer usage of the same source is achieved and good results are maintained. Testing that is usually conducted with r-l92 can be done with the weaker Se-75 source, and produce images of higher quality (due to the better focal spot and lower radiation energy spectra). A more specific example from these tests can be seen in Figures 4a and 4b. X-ray images of a mm (8 in.) diameter pipe with 19 mm (0.75 in.) wall thickness (total wall thickness 38.1 mm [1.5 in.]) were taken with r-192 and Se-75 isotopes. Table 1 organizes the condition details of the images in Figures 4a and 4b. n the image taken with Se-75, an extra fifth wire is clearly visible. Both images were taken under the same setup conditions, with the exception of the isotope type and exposure times. Pipe nspections: Reducing Exposure Tme Table 2 contains results of on-site tests that were conducted by an NOT service provider on pipes using r-192 combined with a digital radiography system TABLE 1 maging conditions Conditions Ci (a'verageenergy in kv) Exposuretime (per image) Averaging (to improve SNR) Total exposure time for averaged Finalimage Focalspot Distance between source and detector Se Ci (265 kv) 10 s 20 images 200 s mm (0.139 in.) Contact technique mm (9 in.) r Ci (353 kv) 0.6 s 20 images 12 s mm (0.146 in.) Contact technique mm (9 in.) SNR= signal-to-noise ratio. TABLE 2 sotope energy with digital radiography flat-panel versus isotope energy with film results tem inspected Firewater hose Glass fiber profile Processwater pipe Steam cooler Low pressure steam pipe Fuellye pipe Pipe diameter Material Wall thickness 208 mm (8.19 in.) 700mm (27.56 in.) 150 mm (5.91 in.) 250 mm (9.84 in.) plus insulation 400 mm (15.75 in.) plus insulation mm ( in.) ST mm (0.28 in.) -25 mm (0.98 in.) Total one wall 6 mm (0.24 in.) Total one wall 40 mm (1.58 in.) Glass fiber CrMo Liquid content Exposuretime (proprietary digital radiography solution*) Exposuretime (film"') None 30 s 3 min. None 30 s Water 70 pulses* (-4.6 s) 20 s None 50 s 1h 15 min. ST35 12 mm (0.47 in.) None 30 s 20 min. SS2343 6mm (0.24 in.) lye 15 s 10 min. * = test conducted with pulsed XRS-3source. t = film and r-l92. Exposuretime only, not including film developing. :j: = a-si panel and r-192. Time to image. APRL 2011 MATERALS EVALUATON 457

7 ME FEATURE DGTAL RADOGRAPHY FOR NDT APPLCATONS TABLE 3 Time to results Material Outer diameter Wall thickness Total wall thickness Energy Exposure time Carbonsteel mm 2.9mm -e mm 270 kv 4.3 s (2.32 in.) ro.n in.) (0.24 in.) Carbonsteel mm 2.9 mm -s rnrn 270 kv 3.54 s (2.37 in.) (0.11 in.) (0.24 in.) Carbonsteel mm 3.62 mm -6.4 mm 270 kv 2.3 s (3.50 in.) (0.14 in.) (0.25 in.) andor film. The comparison clearly shows that exposure times have been cut tenfold. n a large test conducted in cooperation with a refinery in France,several pipe-welding samples with intentional discontinuities, such as slag, undercut, corrosion, porosity and cracks, were tested with a high-energy compatible a-si panel in the laboratory with a portable pulsed X-ray sourcacrlterta for the success of the tests were the time taken to achieve an image, the visibility of the discontinuities and the image quality indicator wires. Table 3 shows typical tested items and time results. Further tests were conducted in the refinery itself with an r-l92, 16 Ci gamma ray source (real piping in the field). The set-up example is shown in Figure 5. Criteria for the success of the tests were the time to set up the detector and source on-site, time to take a good image, quality of images in comparison with known images of the tested object, and analysis tools available on-site (Pincu and Kleinberger, 2009). The tests in the refinery proved a reduction of exposure time from an average of 4 to 5 min. down to 8 to 16 s. The X-ray conditions were the same (X-raygamma ray source, 500 mm [19.69 in.] distance between imagerfilm to the source, sample or pipe inspected); the only difference was that the film was replaced with a DDA imager. Thirty-three images were taken in just 3 h. Reducing exposure times from minutes to seconds means a significantly faster rate of inspection that translates to shorter refinery shutdown periods and increased inspection efficiency. Conclusion t is possible to use digital radiography with highenergy levels, provided a suitable imager is used. Such an imager can also contribute to shortening exposure times and reducing dose levels, making many applications once considered high-energy easier and quicker to accomplish. (a) (b) Figure 5. Set-up of an a-si panel: (a) in a refinery; (b) the corresponding X-ray image. 458 MATERALS EVALUATON' APRL 2011

8 Additional inherent digital radiography advantages technology safety due to lower exposure increased NOT profitability operator (time and dose) and caused by the shortening time to results (cost and time are considerably saved because many images can be taken per day with a digital radiography imager). The true lifetime of the a-si based OOA imager is long enough to allow fast return of investment, energy tests. REFERENCES ASME, ASME Boiler and Pressure Vessel Code, Section \, Ar ticle, American Society of Mechanical Engineers, New York,2010. to working witn are improved even when conducting high- AUTHORS Lior Pick: Vidisco, Ltd., 32 Haharoshet St., Or Yehuda 60375, srael; Ron Pincu: Vidisco, Ltd., 32 Haharoshet St., OrYehuda 60375, srael; of ASTM, E : Standard Practice for Manufacturing Characterization of Digital Detector Arrays, ASTM nternational, West Conshohocken, Pennsylvania, BSS, BSS 7044: Radiologic nspection, Digital Radioscopic, Boeing Specification Support, Chicago, llinois, BSS, BSS 7045: Radiologic nspection, Composite Structures, Boeing Specification Support, Chicago, llinois, Light, G., "Demonstration of Pulsed X ray Machine Radiography as an alternative to ndustry Radiography Cameras: Demonstration Pilot Project," Materials Evaluation, Vol. 66, No.3,2008,pp Pick, l. and O. Kleinberger, "Technical Highlights of Digital Radiography for NOT," Materials Evaluation, Vol. 67, No. 10, 2009, pp Ofra Kleinberger: Vidisco, Ltd., 32 Haharoshet St., Or Yehuda 60375, srael; Pincu, R. and O. Kleinberger, "The Transition from Conventional Radiography to Digital Radiography," Materials Evaluation, Vol. 67, No.5, 2009, pp ACKNOWLEDGMENT The authors would like to thank Vidisco, Ltd., for providing images that were included as figures in this paper. Thales Group, "Digital Detectors," 2011, ,1 Feb APRil 2011 MATERALS EVAL_--