Radiography in Modern Industry - Kodak

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Figure 93: Double-exposure (parallax) method for localizing defects.If the flaw is sufficiently prominent, both exposures may be made on the same film. (Oneexposure "fogs" the other, thus interfering somewhat with the visibility of detail.) The distance ofthe flaw above the film plane is given by the equation:whered = distance of the flaw above the film plane,a = tube shift,b = change in position of flaw image, andt = focus-film distance.If the flaw is not sufficiently prominent to be observed easily when both exposures are made onthe same film, two separate radiographs are necessary. The shadows of the marker (M 2 ) aresuperimposed and the shift of the image of the flaw is measured. The equation given in thepreceding paragraph is then applied to determine the distance of the flaw from the film.Often it is sufficient to know to which of the two surfaces of the part the flaw is nearer. In suchcases, the shifts of the images of the flaw and the marker (M 1 ) are measured. If the shift of theimage of the flaw is less than one-half that of the marker (M 1 ), the flaw is nearer the film plane; ifgreater, it is nearer the plane of the marker (M 1 ).The above methods of calculation assume that the image of the bottom marker (M 2 ) remainsessentially stationary with respect to the film. This may not always be true--for example, if thecassette or film holder is not in contact with the bottom surface of the specimen or in a situationwhere large tube shifts are used.In such cases, a graphical solution is convenient. It can be shown that if the markers are placedfairly close to the flaw, the image shifts are proportional to the distances from the film plane.Thus, a straight line graph can be drawn of image shift against distance from the bottom (filmside) of the specimen.Radiography in Modern Industry 152
To illustrate, let us assume that the image of the bottom marker (M 2 ) on a specimen 2 inchesthick moved 1/16 inch and that of the top marker (M 1 ) moved 1/4 inch. A graph similar to that inthe figure below is drawn, with image shift on the horizontal axis and specimen thickness on thevertical. Points M 1 and M 2 are plotted at the appropriate image shift and thickness values, and astraight line is drawn between them. (Note that for convenience in plotting, 0 specimen thicknessis considered to be on the film side of the specimen.) If the image of a discontinuity has shifted,for example, 3/16 inch, its distance from the film side of the specimen--15/16 inch--can be readdirectly from the graph as shown in the dashed line of Figure 94. It should be emphasized thatFigure 94 is not a general curve, but is for illustration of the method only. A graph of the sametype must be drawn for each particular set of circumstances.Note that in this method it is not necessary to know either source-film distance or amount of tubeshift. This often makes the method convenient even in those cases where the image of thebottom marker (M 2 ) shifts only imperceptibly. The point (M 2 ) of Figure 94 then coincides with theorigin of the graph.Figure 94: Example of the graphical method for localizing a discontinuity by the parallax(double-exposure) technique.Thickness MeasurementOccasionally, it is necessary to measure the thickness of a material in a location where it isdifficult or impossible to use gauges, calipers, or the like. In these cases, radiography cansometimes be applied. One example of this would be the measurement of the wall thickness of ahollow air-craft-propeller blade.The technique is simple, involving the simultaneous radiography of the item in question and astepped wedge of the same material. The stepped wedge should be wide or, if narrow, should bemasked with lead in order to avoid difficulties and errors due to the undercut of scattered radiationinto the area of the stepped wedge. The stepped wedge should be placed as close as possible tothe area to be measured to avoid errors from differences in radiation intensity across the field.Ideally, the stepped wedge and the specimen should be radiographed on the same film. If this isnot possible, as for instance when a film is inserted into a hollow propeller blade, the steppedwedge should be radiographed on film from the same box. Care should be taken that the screensused to radiograph specimen and wedge are the same. If separate films are used for wedge andspecimen, they should be processed together. These precautions avoid errors caused bydifferences in x-ray exposure and errors in processing.A curve is drawn relating thickness of the stepped wedge to the density obtained. Thicknesses inthe part under test are then determined by reference to this curve. Plotting a calibration curve forRadiography in Modern Industry 153
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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 (
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Hole Type PenetrametersThe common p
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of the same thickness as the specim
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Chapter 9: Industrial X-ray FilmsMo
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Figure 70 indicates the direction t
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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 and 142: In summary, use of the test papers
Page 143 and 144: narrow angle would be very thick, e
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: The radiograph exposed in the right
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
Page 193 and 194: e noted here. Although the average
Page 195 and 196: Chapter 17: Film Graininess; Signal
Page 197 and 198: The ratio of signal to noise has a
Page 199 and 200: Chapter 18: The Photographic Latent
Page 201 and 202: 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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Radiography in Modern Industry - Kodak

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