AMMTIAC Quarterly, Vol. 2, No. 2 - Advanced Materials ...

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techsolutions 5 However, with today’s technology it is now possible to generate images of higher quality and sensitivity. The higher quality of radiographic images is primarily due to improved films that have a wider variety of available grain sizes. Also, with the addition of computers and other advanced electronic systems to the process, the advent of digital radiography has proved to be a large advancement within the industry. With the use of digital radiography, a radiographic image captured today can theoretically be preserved forever and sent anywhere in the world almost instantly. In earlier cases, there had to be concerns with deterioration of the image that no longer have to be taken into account today. This ability to continually improve the process has led to growth of radiography into numerous industries. Radiography has seen expanded use in industry to inspect welds and castings, airbags and canned foods, to name a few. The area of metallurgical material identification and security systems has also employed radiography NDT at airports and other facilities with security needs.[1, 5] CONCLUSION Radiography is a mature NDT method that can be used to effectively detect several types of discontinuities embedded within a variety of types of materials and components. Since the method has been in use for many years, the drawbacks and shortcomings are well-known. Some of these limitations have been overcome with the rapid advancement of digital technology. Radiography has continued to evolve by embracing certain aspects of the digital era, and consequently it has become a more flexible and viable method for nondestructive evaluation. REFERENCES [1] “Radiography in Modern Industry,” 4th Edition, R.A. Quinn and C.C. Sigl, Editors, Eastman Kodak Company, 1980, http:// www.kodak.com/eknec/documents/87/0900688a802b3c87/Radiogra phy-in-Modern-Industry.pdf [2] “Radiography Testing,” Engineer’s Handbook, http://www.engi neershandbook.com/MfgMethods/ndtrt.htm [3] “Radiographic Inspection,” ASM Metals Handbook, Ninth Edition, Vol. 17, Nondestructive Evaluation and Quality Control, ASM International Metals Park, OH, pp. 296-357. [4] “Industrial Radiography Radiation Safety Personnel,” ASNT Practice No. ASNT-CP-IRRSP-1A, 2001 Edition, American Society for Nondestructive Testing, http://www.asnt.org/certification/irrsp/ cp-irrsp-1a.pdf. [5] “Introduction to Radiographic Testing,” NDT Resource Center, http://www.ndted.org/EducationResources/CommunityCollege/Radio graphy/Introduction/presentstate.htm. Table 1. Radiography Summary Discontinuity types (e.g. what types the method can detect) Size of discontinuities Limitations Advantages Inspector training (level and/or availability) Inspector certification required Equipment Relative cost of inspection • Voids • Inclusions • Cracks • Non-uniformity of material • Density changes • Weld defects • Discontinuities that exhibit 1% or more absorption difference relative to surrounding region • Advanced systems can detect flaws as small as 0.001 inches • Orientation of inspection sample • Not suitable for surface defects • As thickness increases, detection effectiveness decreases • Large amounts of equipment required for non-portable setup • Film limitations • Manual image interpretation • Can be used to detect defects in a variety of materials • Can detect internal defects • Permanent inspection record • Objects radiographed range in size from micro-miniature electronic parts to large missile components • Makes it easier to maintain a defect-free and uniform product line • Variety of programs available nationally to study the science of radiology • Radiation safety training is critically important • ASNT offers certification for radiography safety • Portable or fixed setups depending on industry/company requirements and desired function • Traditional radiography requires film development facilities and equipment • Depends on setup, but cost can be greatly reduced with the use of portable equipment that requires less space 10 The AMMTIAC Quarterly, Volume 2, Number 2
Greg A. Levcun Naval Facilities Engineering Command Northwest Christopher S. Mahendra Naval Air Systems Command INTRODUCTION Like many other Navy regions, Commander Navy Region Northwest (CNRNW) was faced with replacing its aging chemical and film-based radiographic imaging systems that were being used for nondestructive testing (NDT). At CNRNW, several activities acquired computed radiography (CR) systems via the Pollution Prevention Equipment Program (PPEP) to replace the conventional NDT systems. The new CR systems have been installed and used, and the intent of this article is to report on the benefits, requirements, concerns, and problems associated with implementing this new technology for CNRNW. Why the Move Away from Film Several factors are influencing the move away from film-based X-ray techniques toward CR systems. CR systems eliminate costly chemicals and resulting hazardous waste, provide an adaptable image medium, reduce other consumables that filmbased systems require, protect worker health and safety, improve productivity by reducing work turn-around time and make test results readily available to off-site experts. Each of these benefits is described in the following sections. THE BASICS OF COMPUTED RADIOGRAPHY SYSTEMS Computed radiography is a type of digital radiography. Similar to conventional radiography, CR systems create an X-ray image of the part under inspection. Unlike a filmbased system, however, the end result is a digital image. (The sidebar contains a summary of three radiography inspection technologies). CR systems have four main elements, including a phosphor image plate (IP), an IP reader (see Figure 1), a central processing station with special software (see Figure 2), and a high-resolution monochrome X-ray monitor. The IP surface is coated with storage phosphors that capture and store the incident radiation energy from the X-ray source to create a latent image on the plate. After the IP is exposed to the radiation energy it is processed in the IP reader where a low energy laser is used to release visible light from the stored energy. The visible light is then converted into an electrical signal which can be converted into digital data. The storage image phosphors will retain the latent image for periods ranging from several hours to days, depending on screen phosphor material and exposure duration; however, the plates can be reused numerous times once the latent image is cleared. Similar to conventional X-ray film, phosphor plates are stored in cassette format. Figure 1. An NDI Inspector Works with the IP and Reader. Figure 2. An Inspector Looks at Two Views of a Defect. Elimination of Chemicals and Hazardous Materials With CR systems, images are generated on a medium that does not require the chemical bath processing used for producing traditional film. Moreover, traditional film chemicals must be used within a limited timeframe, which requires processing labs to maintain a fresh stock of chemicals. The cost of procuring and maintaining these supplies is expensive, and the film developing chemicals must be disposed of as hazardous waste. Therefore, by utilizing the CR systems, chemicals and hazardous materials are eliminated. http://ammtiac.alionscience.com The AMMTIAC Quarterly, Volume 2, Number 2 11
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