Application of Measurement Models to Specification of Ultrasonic Inspections
for economic reasons, there is an increasing tendency to perform automated ultrasonic scans of near net-shaped forgings, which can have rather complex shapes, as opposed to inspection of simpler, sonic shapes, which typically have only planar inspection surfaces. A difficulty in the former approach is that the surface curvature of forgings causes the ultrasonic beam to focus or defocus within the component and, therefore, the ultrasonic sensitivity to internal defects changes as compared to inspection through a flat surface. It is certainly possible to account for this sensitivity variation by using curved calibration or reference blocks. However, a more convenient and cost effective approach is to use analytical models to predict the UT instrument gain corrections required for the curved surface inspections as compared to sensitivity levels measured from standard flat surface calibration blocks. This paper describes such models and their application to specification of ultrasonic inspection parameters for scanned ultrasonic inspection of curved forgings using both planar and focused transducers. Examples of these applications will be presented via case histories from the electric generation and aircraft engine industries.