Radiation Source Use and Replacement Abbreviated Version (2008) / Chapter Skim
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8 INDUSTRIAL RADIOGRAPHY
8 INDUSTRIAL RADIOGRAPHY
Pages 135-146
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From page 135... ...
With ongoing developments in ultrasonic inspection technologies as well as in x-ray radiography, satisfactory alternatives for many of the gamma-ray radiography applications exist. There are, however, a number of specific applications, such as pipeline inspection in remote locations, underwater, and in chemical plants with wrapped or closely spaced piping, where the advantages of mobility, ease of use, and low power requirements of radionuclide-based radiography may make replacement difficult and uneconomic, at least with current alternative technologies.
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From page 136... ...
For certain specialized applications, selenium-75 and ytterbium-169 are also used. These radionuclides are listed along with their half-lives and the average energy of their gamma rays in Table 8-1.
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From page 137... ...
Furthermore, the relatively low cost of gamma sources, their portability, straightforward image interpretation, and simple radiological safety measures makes entry into the market relatively inexpensive for small companies. Also, the use of portable gamma sources allows radiography to be carried out in remote locations where electric power may not be readily available.
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From page 138... ...
Each dashed line indicates the approximate location of the average energy for the gamma rays emitted by the radionuclide with which it is labeled. Note that the actual half-value is slightly higher for radionuclides that emit some higher-energy gamma rays, such as iridium-192.
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From page 139... ...
Those performing radionuclide radiography are subject to much greater radiation exposures than those in the medical irradiator sectors, where exposures are not routine parts of the job. Occupational doses to workers using radiation generators are much lower.
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From page 140... ...
Table 8-2 lists commonly used methods of nondestructive testing and their effectiveness in detecting particular kinds of defects, relevant to the inspection of pressure vessels and pipes where radiography has traditionally been a principal tool. Refinery owner issues RFQ for inspection of pipes Insurance carrier stipulates Service company responds acceptable methods with quote based on technical codes Service company selects NDI tools Codes based on discussions In technical community FIGURE 8-4 Process for selecting nondestructive testing method on the left, and factors that influence or dictate the process on the right.
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From page 141... ...
INDUSTRIAL RADIOGRAPHY 141 TABLE 8-2 Common Imperfections and the Nondestructive Examination Methods That Are Generally Capable of Detecting Them SOURCE: Reprinted from ASME 2004 Boiler and Pressure Vessel Code, Section V, by permission of ASME. All rights reserved.
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From page 142... ...
, x-ray radiography is already becoming more widely used as a quality control tool in manufacturing, especially with the development of compact, microfocus x-ray tubes. These industrial applications typically occur in factory settings where components can be inspected in a fixed location and the higher cost of x-ray facilities is outweighed by their increased productivity, improved imaging resolution, or higher energy for greater penetration.
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From page 143... ...
There are several characteristics of ultrasonic waves that can be utilized in addition to simple absorption used in radiography, including frequency, polarization, and phase. Major breakthroughs in the development of ultrasonic testing have included transducers that generate only shear waves, enabling other types of discontinuities to be detected; the development of time-of-flight diffraction which allows the top and bottom edges of discontinuities to be displayed and provides better accuracy in through-thickness measurement; and phased-array testing, which produces images of internal structures similar to that of medical ultrasound.
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From page 144... ...
. Over the past two decades, these and other advances in computational imaging and electromagnetic acoustic transducers have made ultrasonic techniques a viable alternative for many weld and structural inspection purposes.
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From page 145... ...
, about 50 percent of industrial radiography performed today could be performed by ultrasonic methods, and a further 25 percent could be inspected using x-ray radiography as opposed to gamma radiography. With the prospect of continuing advances in computational resources, low-cost sophisticated analysis software, and image-matching algorithms, it is likely that ultrasonics and x-ray radiography (as well as other inspection technologies not discussed in this report)
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