T9074-AS-GIB-010/271 Rev 1
3.4.3.2 Film Density. The density shall be 1.5 to 4.0 for single film viewing and 2.0 to 4.0 for superimposed film viewing in the area being examined for acceptance. For castings and forgings, the density shall be 1.5 to 4.0 in the area being examined for acceptance for both the single and superimposed film viewing. When the thickness of the part varies considerably in the area under examination, two or more films, either of equal or of different speeds, may be exposed simultaneously in the same film holder and the resultant radiograph submitted for interpretation either as single or superimposed film, whichever is better suited for the interpretation of any small portion of the area covered by the exposure. For the small portion of the area under immediate examination, the density of either the single or the superimposed film shall be in accordance with the aforementioned requirements. 3.4.3.3 Multiple Film Techniques. Film techniques with two or more films of the same or different speeds in the same film holder shall be permitted provided the applicable radiographic quality level for a specific area is demonstrated. 3.4.4 Filmless Techniques. Requirements for the use of digital computed radiography for the detection and measurement of pipe corrosion and erosion are attached as Appendix A. For any other application, the use of filmless techniques shall be limited to in-process inspection and shall not be permitted for final acceptance inspection unless specifically approved by NAVSEA. 3.4.5 Radiation Sources. Recommended X-ray machine voltage settings and gamma-ray sources to be used with various specimen thicknesses are shown on figure 3-1, figure 3-2, and figure 3-3. Other voltage settings or sources may be used provided the required quality levels are maintained. Cobalt-60 sources shall not be used on welds with a specimen thickness (T s ) less than 2.5 inches or on any material with a nominal thickness less than 1 inch. Cobalt-60 may be used on casting repair welds where the specimen thickness is greater than or equal to 1 inch.
3.4.6 Source-To-Film Distance.
3.4.6.1 Calculations. The source-to-film distance SFD shall be such that the geometric unsharpness (U g ) values of figure 3-4 are not exceeded. Source-to-film distance shall be calculated as follows:
Where:
U g = Geometric unsharpness in inches. F = Maximum effective radiation source dimension in inches (see 3.2.2). t = Specimen thickness T s in inches. SFD = Distance, in inches, between radiation source and film.
3.4.6.2 Film-Specimen Contact. When the film cannot be placed in intimate contact with the specimen, and a gap exists between the specimen and the film, the minimum SFD (as calculated per 3.4.6.1) shall be multiplied by the ratio of:
3.4.6.3 Reduced Source-To-Film Distance. When accessibility does not permit compliance with the above, a shorter source-to-film distance is allowed provided the following conditions are met: a. The required quality level is obtained. b. The greatest possible source-to-film distance is used. c. The radiographic record shows what accessibility conditions limited the source-to-film distance and indicates the actual source-to-film distance used.
3-4
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