T.O. 33B-1-15-45Figure 5-48. Surface Wave Inspection5.3.3.3.3 SurfaceWaveFamiliarization.a. Use a miniature angle-beam block. Attach a 2.25 MHz surface wave search unit to the ultrasonicinstrument.b. Position the search unit at P-1 as shown in Figure 5-49. Adjust the sweep and gain to obtain a signalfrom corner C.Figure 5-49. Surface Wave Familiarization.c. Moisten a finger with oil and move it across the surface from the search unit toward corner C. Note thatthe corner signal is damped until the finger moves beyond the corner.d. Move the search unit away from corner C toward corner B as shown in Figure 5-49. Note that thecorner C signal moves to the right along the time base.e. Position the search unit at P-2 as shown in Figure 5-49. Orient the search unit perpendicular to edgeAC. Adjust the sweep and gain to obtain a signal from edge AC.f. Rotate the search unit and note that the signal from the edge decreases as the search unit is rotated awayfrom the normal to the edge. This illustrates that surface waves should always be directedperpendicular to the expected plane of cracks (see Figure 5-50).
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