T9074-AS-GIB-010/271 Rev 1
3.4 RADIOGRAPHY REQUIREMENTS.
3.4.1 Direction of Radiation. Unless otherwise specified, the direction of the central beam of radiation shall be as nearly central to the area being examined and perpendicular to the surface of the film as possible. 3.4.2 Screens and Filters. All radiographs produced with radioisotopes or a source of 150 kV or greater shall employ a front and back lead screen in contact with the film. Intensifying screens and filters shall be as follows: a. Intensifying screens: For radiation energies up to 300 kV (inclusive), either lead oxide or lead foil intensifying screens may be used. For energies above 300 kV, only lead foil screens may be used. Intimate contact between the screens and the films should be maintained during exposure. b. Front filters: When using radiation sources with energies of 0.7 MeV or greater (including Cobalt-60), a lead filter with a thickness of not less than 0.010 inch shall be placed between the specimen and the film. The filter may be located either in the film holder and may be combined with the intensifying screen, or may be located in front of the film holder. However, if the filter is located in front of the film holder, the screens shall be placed in contact with the film, as in (a) above. c. Back filters: Lead filters shall be used behind the film holder to prevent scattered radiation from the floor, walls, air, or other surrounding objects from fogging the film. Each holder shall have a lead letter “ B ” not less than ½ inch high and not less than 1 ⁄ 16 inch thick positioned behind the film and within the area of film to be read. When performing panoramic exposures, one lead letter “ B ” may be placed in each quadrant. The lead letter “ B ” is not required for radiography of circumferential welds with an inside diameter less than ¾ inch which are performed by the single wall exposure technique. If the image of the letter “ B ” shows a light image on a darker background, the radiograph shall be rejected. A darker image of the letter “ B ” on a lighter background is not cause for rejection provided the darker image does not interfere with the film evaluation. d. Masking: Masking may be used for control of scattered radiation provided the area being viewed for acceptance is masked to the same degree as the penetrameter. 3.4.3 Film. Radiographs shall be made on fine grain, extra-fine grain, or ultra-fine grain, safety base film. High-speed, medium or coarse grain films shall be used only when authorized by NAVSEA or its authorized representative. 3.4.3.1 Film Quality. Radiographs presented for interpretation shall be free from blemishes or film artifacts that might mask or be confused with defects in the material being examined. If doubt exists concerning the true nature of an indication on the film, the radiograph shall be rejected. Typical blemishes are as follows: a. Fogging caused by light leaks in the processing room or cassettes, defective safelights, exposure marks caused by improper processing, or old film.
b. Mechanical processing defects such as streaking, air bells, water marks, or chemical stains. c. Blemishes caused by dirt in cassettes, particularly between intensifying screens and the film. d. Pressure or lead marks, scratches, gouges, finger marks, crimp marks, or static electricity marks. e. Loss of detail caused by poor film-to-screen contact in localized areas.
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