T.O. 33B-1-15-44Figure 5-47. Angle Beam Inspection.5.3.3.2.3 MultipleSearchUnits.Most angle beam methods use a single search unit with one transducer element for transmitting and receivingultrasonic energy. Special applications may utilize dual angle-beam search units (see Figure 5-32) or two or moreangle beam units, one for transmitting, the rest for receiving.5.3.3.3 SurfaceWaveMethod.NOTEWhen surface waves are used to inspect painted surfaces, the technician shouldexercise caution during set up and interpretation due to the possibility of surfacereflection from scratches and breaks in the painted surface. Rough surfaces or liquidon the surface attenuate surface waves. The area in front of the search unit must bekept free of all but the minimum amount of couplant needed for the inspection.5.3.3.3.1 General.This method uses surface/Rayleigh waves that are refracted in the test part at an angle of 90 degrees. This methodworks only for contact inspection since the part surface along which the surface wave propagates must be bounded byair.5.3.3.3.2 Applications.Surface wave inspections can be utilized in many field NDI applications involving surface cracks or slightly sub-surfacediscontinuities. On smooth surfaces, sound energy can travel long distances with little energy loss. Surface wavestravel around curved surfaces. They reflect at sharp edges (radius less than one wavelength). Even at the sharp edges,complete reflection does not occur. Weak signals pass around the edges shows a typical surface wave inspection.
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