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Numerical standards have been established for the interpretation of radiographs of large solid propellant propulsion units. One numerical method, commonly referred to as the density ratio, is obtained from a comparison of two film density readings taken with a densitometer in teh area of the radiograph containing the suspected defect. The resulting ratio may be used successfully as a standard to differentiate between a normal and a defective area.
Density scans taken normal to the area of the radiograph to be interpreted provide even more possibilities for quantitative analysis of radiographs. Automatic scanning densitometers have been developed which produce highly reliable density scans with relatively good speed. In addition to accuracy, density scans make possible the establishment of several numerical standards including the density ratio.
Numerical standards provide a vital tool for the evaluation of radiographs; relatively inexperienced radiographers can perform the production evaluation of radiographs (or gammagraphs) by using the density ratio or density scan system. Quantitative techniques will find wide application in the solid rocket field for the detection of internal flaws. Numerical inspection data will provide a system for the establishment of firm acceptance-rejection criteria.
Mascis, Richard J.
Special Projects Office, Quality Assurance and Reliability, Washington, D. C.