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9/8/98 AC 43.13-1B SECTION 6. RADIOGRAPHY (X-RAY) INSPECTION 5-73. GENERAL. Radiography (x-ray) is an NDI method used to inspect material and components, using the concept of differential adsorption of penetrating radiation. Each specimen under evaluation will have differ- ences in density, thickness, shapes, sizes, or absorption characteristics, thus absorbing dif- ferent amounts of radiation. The unabsorbed radiation that passes through the part is re- corded on film, fluorescent screens, or other radiation monitors. Indications of internal and external conditions will appear as variants of black/white/gray contrasts on exposed film, or variants of color on fluorescent screens. (See figure 5-14.) 5-74. LIMITATIONS. Compared to other nondestructive methods of inspection, radiog- raphy is expensive. Relatively large costs and space allocations are required for a radio- graphic laboratory. Costs can be reduced con- siderably when portable x-ray or gamma-ray sources are used in film radiography and space is required only for film processing and inter- pretation. Operating costs can be high because sometimes as much as 60 percent of the total inspection time is spent in setting up for radi- ography. With real-time radiography, operat- ing costs are usually much lower, because setup times are shorter and there are no extra costs for processing or interpretation of film. 5-75. FILM OR PAPER RADIOGRA- PHY. In film or paper radiography, a two- dimensional latent image from the projected radiation is produced on a sheet of film or pa- per that has been exposed to the unabsorbed radiation passing through the test piece. This technique requires subsequent development of the exposed film or paper so that the latent im- age becomes visible for viewing. 5-76. REAL-TIME RADIOGRAPHY. A two-dimensional image that can be immedi- ately displayed on a viewing screen or televi- sion monitor. This technique converts unab- sorbed radiation into an optical or electronic signal which can be viewed immediately or can be processed with electronic or video equipment. 5-77. ADVANTAGE OF REAL-TIME RADIOGRAPHY OVER FILM RADIOG- RAPHY. The principal advantage of real-time radiography over film radiography is the op- portunity to manipulate the test piece during radiographic inspection. This capability al- lows the inspection of internal mechanisms and enhances the detection of cracks and pla- nar defects by allowing manipulation of the part to achieve the best orientation for flaw detection. Part manipulation during inspection also simplifies three-dimensional dynamic im- aging for the determination of flaw location and size. In film radiography, depth parallel to the radiation beam is not recorded. Conse- quently, the position of a flaw within the vol- ume of a test piece cannot be determined ex- actly with a single radiograph. To determine flaw location and size more exactly with film radiography, other film techniques; such as ste- reo-radiography, triangulation, or simply making two or more film exposures with the radiation beam being directed at the test piece from a different angle for each exposure, must be used. 5-78. COMPUTED TOMOGRAPHY (CT). CT is another important radiological technique with enhanced flaw detection and location capabilities. Unlike film and real- time radiography, CT involves the generation of cross-sectional views instead of a planar Par 5-73 Page 5-37PDF Image | AFS-640
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