Radiography in Modern Industry - Kodak

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Chapter 14: Special Radiographic Techniques"In-Motion" RadiographyIn most industrial radiography, it is essential that there be no relative motion of radiation source,specimen, and film. Movement of the film with respect to the specimen results in a blurredradiograph; motion of the radiation source with respect to the specimen and film is equivalent tothe use of a larger source size, resulting in increased geometric unsharpness.There are certain cases, however, in which motion between components of the radiographicsystem--source, specimen, and film--has positive benefits, either economic or in producinginformation that could not be otherwise obtained.Extended SpecimensAn example of an extended specimen would be a longitudinal weld in a cylindrical structure. Thelength of the weld could be radiographed using a series of individual exposures. This wouldrequire setup time--placement and removal of films, placement of penetrameters andidentification markers, and movement of tube--for each individual exposure. Economic gains canoften be achieved by radiographing the entire length of the weld in a single exposure either on astrip of film or on a series of overlapping sheets.The x-ray beam is restricted to a narrow angle by means of a diaphragm at the tube. The tube isthen traversed the length of the weld (See Figure 85), each segment of weld being radiographedonly during the time that the beam is incident on it. If there were two or more longitudinal welds,all could be radiographed at once using a rod-anode tube giving a 360-degree radiation beam,the radiation being restricted to a relatively thin "sheet" by lead disks concentric with the axis ofthe tube. In such a case, it is essential that the anode traverse along the axis of the specimen sothat equal densities are obtained on the radiographs of all the welds.Figure 85: "In-motion" radiography of long welds. Left: Single weld. Right: Simultaneousradiography of several welds, using a rod-anode tube with disk-shaped collimators.The exposure time--that is, the length of time the tube is operating--is long compared to the totalexposure time for a series of individual exposures. The economic advantage arises from the verygreat savings in setup time, and hence in total time required for the examination.It is for this reason, also, that the technique is applicable largely, if not entirely, to x-rays. Ingamma-ray radiography, the exposure times are usually considerably longer than the setuptimes. The prime advantage of the method is a saving in setup time, and it is not attractive whensetup time is a small part of the total. Also, the jaws required to restrict a gamma-ray beam to a
narrow angle would be very thick, especially for cobalt 60 radiation, and hence difficult to makeand to position.The technique is generally limited to thin specimens or cases where a large source-film distancecan be used. The motion of the tube gives rise to a geometrical unsharpness that can betroublesome for thick specimens or short source-film distances. This unsharpness (U m ) can becalculated from the formula:where t is the thickness; w is the width of the radiation beam at the source side of the specimen,measured in the direction of motion of the tube; and d is the source-specimen distance.If the permissible motion unsharpness can be estimated, the formula can be rearranged to givethe maximum width (in the direction of motion) of the beam at the source side of the specimen:In the above formulae, distances are usually measured in inches and Um is also in terms ofinches. Thus, care must be exercised in comparing values so obtained with values of geometricunsharpness (U g ) calculated from the formula:Because focal spot sizes are usually specified in millimetres, values of U g , from the formulaabove are usually in millimetres also.Since the exposure time T that is required for a single exposure of the specimen is usually knownfrom experience or from an exposure chart of the material, the required rate of travel V of the tuberelative to the specimen can be calculated:where w is the width of the beam (in the direction of travel) at the source side of the specimen.For best results with this technique, the motion of the radiation source must be smooth anduniform. Any unevenness of motion results in parallel bands of overexposure and underexposureat right angles to the direction of motion.Rotary Radiography of Annular SpecimensAnnular specimens often present economic problems if they must be radiographed in quantity.Placed flat on a film, they are wasteful of film area, of exposure and setup time, and of filingspace. Great economies of time and money can be achieved by the use of a variation of thetechnique described above.Film is wrapped around a circular, cylindrical, lead-covered mandrel, and covered with a light tightcovering that is also rugged enough to protect the film from abrasion. Annular specimens are thenslipped on the mandrel, over the film in its protective cover. Clamping means may be required toprevent rotation of the specimens with respect to the mandrel. The "loaded" mandrel is placedbehind a lead shield containing a narrow slit at least as long as the mandrel (See Figure 86).During the course of the exposure, the mandrel is rotated behind the slit, each part of thespecimens being radiographed in turn by the thin "sheet" of radiation passing through the slit. It isnot necessary that radiography be completed in a single turn of the mechanism. Several rotationscan be used but it is important that it be an integral number of turns; otherwise there will be aRadiography in Modern Industry 143
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RadiographyinModernIndustry
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RadiographyinModernIndustryFOURTH E
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ContentsIntroduction...............
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Chapter 1: The Radiographic Process
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Intensifying ScreensX-ray and other
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makes it a very suitable material f
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Figure 6: Typical voltage waveforms
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Table I - Typical X-ray Machines an
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The wavelengths (or energies of rad
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Table III - Industrial Gamma-Ray So
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1. The source of light should be sm
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B and H in the Figure 13 show the e
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Figure 14: Geometric construction f
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Figure 17: Pinhole pictures of the
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The kilovoltage applied to the x-ra
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Figure 21: Schematic diagram of som
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kind of material radiographed, the
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instance, the kilovoltage may be fi
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The technique need not be limited t
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Chapter 5: Radiographic ScreensWhen
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Contact between the film and the le
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Figure 29: The number of electrons
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lead foil screens ran be retained w
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Figure 33: The sharpness of the rad
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Figure 34: Low density (right) is a
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such as a wall or floor, on the fil
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from this source. Since scatter als
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A filter reduces excessive subject
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Definite rules as to filter thickne
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0.010-inch front screen of value be
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Example: Suppose that with a given
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If the milliamperage remains consta
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espectively. In other words, a cons
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Any given exposure chart applies to
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Figure 46: Typical gamma-ray exposu
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where the slope of the characterist
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Figure 49: Characteristic curves of
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Figure 51: Characteristic curve of
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Nomogram MethodsIn Figure 54, the s
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Figure 56: Transparent overlay posi
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Figure 58: Overlay positioned so as
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The problem of radiographing a part
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Figure 62: System of lines drawn on
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Chapter 8: Radiographic Image Quali
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Film contrast refers to the slope (
Page 91 and 92: Hole Type PenetrametersThe common p
Page 93 and 94: of the same thickness as the specim
Page 95 and 96: Chapter 9: Industrial X-ray FilmsMo
Page 97 and 98: Figure 70 indicates the direction t
Page 99 and 100: the lead letters on a radiation-abs
Page 101 and 102: Therefore, protection requirements
Page 103 and 104: 5. Avoid pressure damage caused by
Page 105 and 106: Paddles or plunger-type agitators a
Page 107 and 108: slow, and the development time reco
Page 109 and 110: ubbles make their way to the surfac
Page 111 and 112: When development is complete, the f
Page 113 and 114: soften considerably with prolonged
Page 115 and 116: Figure 77: The roller transport sys
Page 117 and 118: Rapid Access to Processed Radiograp
Page 119 and 120: Figure 78: Film-feeding procedures
Page 121 and 122: Chapter 11: Process ControlUsers of
Page 123 and 124: 3. Age of the developer replenisher
Page 125 and 126: Figure 80: Control chart below for
Page 127 and 128: DiscussionDensitometric data and pr
Page 129 and 130: Figure 82: Plan of a manual x-ray p
Page 131 and 132: Figure 83: A schematic diagram of a
Page 133 and 134: loading-bench activities are carrie
Page 135 and 136: KODAK Quinone-Thiosulfate Intensifi
Page 137 and 138: Methylene-Blue MethodTwo variations
Page 139 and 140: KODAK Hypo Test Solution HT-2Avoird
Page 141: In summary, use of the test papers
Page 145 and 146: When radiation passes through a spe
Page 147 and 148: Figure 89: Demonstration of the eff
Page 149 and 150: Figure 90: The amount of gamma radi
Page 151 and 152: The radiograph exposed in the right
Page 153 and 154: To illustrate, let us assume that t
Page 155 and 156: Figure 95: High-speed x-ray picture
Page 157 and 158: Figure 97: Two methods of neutron r
Page 159 and 160: Duplicating RadiographsSimultaneous
Page 161 and 162: Sometimes, as when sets of referenc
Page 163 and 164: PhotofluorographyIn photofluorograp
Page 165 and 166: discontinuities or of segregation i
Page 167 and 168: from the camera or by reaching down
Page 169 and 170: Figure 106: Schematic diagram of th
Page 171 and 172: valuable technique, for instance, i
Page 173 and 174: The position of the spots is determ
Page 175 and 176: Powder Diffraction File, Internatio
Page 177 and 178: Processing TechniquesRadiographs on
Page 179 and 180: Since this formula applies only to
Page 181 and 182: such that it does not distort the i
Page 183 and 184: Figure 113: A: Representation of a
Page 185 and 186: Figure 115: Characteristic curve of
Page 187 and 188: film fairly well. If high densities
Page 189 and 190: Density = 1.5 Density = 2.5Film Rel
Page 191 and 192: In most industrial radiography, the
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e noted here. Although the average
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Chapter 17: Film Graininess; Signal
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The ratio of signal to noise has a
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Chapter 18: The Photographic Latent
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Thus, the change that makes an expo
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Figure 130: Stages in the developme
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electrons by successive Compton int
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Development is essentially a chemic
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Chapter 19: ProtectionOne of the mo
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duct is brought into the x-ray room
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