Analysis of Oblique Angle Scanning in the Imaging of Multilayered Targets
The ultrasonic scanning of multilayered targets, using pulse-echo detection, results in reverberations which complicate the direct characterization of the boundaries. In the nondestructive material evaluation, the problem of reverberation arises frequently. In fact some structures by their very nature are so reverberant that the reverberations comprise the entire received signal. A practical example of such a problem occurs in connection with the inspection of steam generator tubing. Steam generators currently in use contain inconel tubing which is held loosely within a steel support structure. The integrity of the tube/support structure can be evaluated by sending ultrasonic pulses through the tube wall which are highly reverberant. The multilayered model of the tube/support structure is shown in Figure 1, where Region I is inside the tube, Region II is the tube wall, Region III is the water gap, and Region IV is the support plate. Through earlier investigations [1, 2], an ultrasonic classification technique using a normal incident angle scheme has been developed that facilitates the imaging of targets (Region IV) hidden by highly reverberant thin layers (Region II).
KeywordsShear Wave Longitudinal Wave Mode Conversion Scanning Angle Support Plate
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