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Inspection Trends - April 2011 - Spring

angle and allowing light to reflect off the surface at an angle. Pressure marks usually appear as lighter areas on the radiograph and may have any size or shape. They are caused by improper film storage (i.e., boxes of film stacked one on top of another rather than stored on edge), or possibly by a heavy part resting on the film holder during the exposure. A pressure mark caused by a heavy object on the cassette occurring after exposure could result in a dark spot. Static are black indications caused by static electricity discharges on the surface of the emulsion when the film is removed rapidly from the film box. Static indications sometimes appear as dark branching lines (tree roots) or as jagged fine lines (lightning). Fingerprints result from handling the film with wet fingers (i.e., developer, fixer, or water on your fingers). Low density spots or smears are due to splashes of fixer solution on the film prior to development of the film. Dark spots or smears are due to splashes of developer on the film prior to it being developed. Lead screen marks are due to defects in the lead screens such as scratches or wrinkles. They usually appear as darker indications often with a lighter halo. Mottle/paper pattern is an overall pattern on the radiograph resulting from failure to remove the interleaving paper from the film when loading the cassette. Image reversal is due to excessive overexposure in which there is a reversal in the image density. In other words, the normally dark areas appear light, and the normally light areas appear dark. This is not a common occurrence as it is the result of extremely excessive overexposure to radiation. Diffraction (mottle) appear on film as numerous dark lines that are often accompanied by light lines. Diffraction patterns on weld radiographs may have a discrete herringbone pattern. A change in beam angle or kilovoltage alters the pattern and therefore allows diffraction mottling to be identified as a spurious indication. Most commonly occur when using an X-ray machine to radiograph cast materials with large grain structure, or materials with a high nickel content. White dots are due to dirt and dust 20 Inspection Trends / April 2011 on the lead screens. Any foreign material between the lead screens and the film will block out the intensifying action, and appear as white spots on the radiograph. Artifacts Occurring during Processing Scratches occur in the emulsion when a film hanger rubs the surface of a film while being immersed in the processing solutions. They may also occur during agitation of the film hangers when films are too close together in the solution tank. Air bells are shown as small rounded areas of lower density, caused by air bubbles trapped on the surface of the film, usually during the early stages of development, due to insufficient initial agitation. Patches or streaks are due to insufficient agitation during development, or failure to agitate in the stop bath or rinsing bath. They may also be due to a residue of solutions in the hanger clips from prior use. Reticulation is puckered or netlike linkages, giving a pebbled surface appearance similar to that of a basketball or football. This condition is due to rupture of the emulsion caused by a sudden and extreme change in the temperature of the solutions. Kiss marks may be either a dark or light patch on the radiograph caused when two films touch (kiss) in the developer or fixer during manual processing. Dirt or scum is contamination in the developer or fixer. Even the material in the rinse tank may adhere to the film’s surface. This is easily verified by allowing light to reflect off the film surface. Drying marks are due to drops or streaks of water remaining on the surface of the film after it has been partially dried. They often occur when attempting to dry films rapidly at a high temperature in a drying cabinet. Pi marks or Pi lines are lines that run across the film or are spots on the film that occur at regularly spaced intervals. Caused by dirty rollers (usually a buildup of processing chemicals) in an automatic processor. The spacing between these artifacts is equal to the circumference of the roller in the processor. These can easily be identified by allowing light to reflect off the film surface. Pressure marks are a buildup of foreign material on the rollers in the automatic processor. Insufficient clearance between the rollers in the processor will also cause pressure marks that appear as lines on the film surface. These can easily be identified by allowing light to reflect off the film surface. Dirt deposits. Contaminated wash water in the automatic processor may result in deposits on the surface of the film that can easily be verified by allowing light to reflect off the film surface. Artifacts Occurring after Processing Fingerprints result from handling the processed film with wet fingers. Scratches and abrasion marks result from rough handling of the dried films. These can easily be identified by allowing light to reflect off the film surface. Water spots. Any liquid spilled on the radiograph, or onto the table or benchtop, will cause spots on the film surface if the film is laid down on a wet benchtop. As with many other film artifacts, these are easily identified by observing the surface while allowing light to reflect off the film surface. Nonrelevant Indications Indications in this classification are the result of known conditions in the test object. Changes in the configuration of the test object will result in film density variations that may cause difficulties in interpretation. The RI must be able to identify these nonrelevant indications, which are predictable and repeatable if the part is reshot. These types of indications will also appear on the radiographs of other similar parts. Familiarity of the test part configuration and a review of the part drawings will help the RI identify nonrelevant indications. Sometimes another radiograph taken with a different part alignment or different angle of the incident radiation may be necessary to verify and confirm the interpretation. Variations in film density due to keyways, drilled holes, or any other change in part geometry would be interpreted as nonrelevant indications.


Inspection Trends - April 2011 - Spring
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