TM 1-1520-253-23
Ultrasonic inspection uses high frequency sound waves as a probing medium to provide-information as to the state of
various materials. This method is effective for the inspection of most metals for surface and subsurface damage. The
method requires that at least one surface of the part be accessible for transducer contact in the vicinity of the area to be
examined. The inspection is accomplished by inducing the ultrasound into the part by coupling the transducer to the part
and picking up reflections of this sound from within the part. Any marked changes in acoustic properties, defect,
interface, or back surface, will reflect sound back to the transducer. The detected ultrasonic reflections are electronically
displayed on a Cathode Ray Tube (CRT) and interpreted for indications of defects. Accessory wedges can be used to
provide adequate transducer mating to curved surfaces or to change the angle of the sound beam.
1.4.12.1 Safety Precautions During Ultrasonic Inspection. Follow safety precautions and instructions contained in this
manual and the Nondestructive Inspection Methods manual listed in Table 1-1.
WARNING
Electrical equipment shall not be operated in areas where combustible gases or vapors may be
present, unless the equipment is explosion-proof.
a. If instrument is operated using AC power, use a grounded power cord.
b. Turn power OFF before connecting or disconnecting transducer cable or power cable.
1.4.12.2 Ultrasonic Instrument Standardization. The ultrasonic equipment used in ultrasonic v inspection procedures
described throughout this manual is listed in Appendix B. Reference blocks, instrument settings, and standardization
instructions for the ultrasonic instrument are included in the individual ultrasonic inspection procedures. Because of
varied circumstances under which the inspections may be performed, instrument settings, as they are given in this
manual, should be considered typical. Slight adjustment to the settings may be necessary to achieve the desired CRT
presentation. Illustrations representing typical CRT presentation will, in most cases, include reference signals
representing initial pulse, transducer, and/or wedge echoes that have been moved off the scope to make room for
relevant indications. An effective ultrasonic inspection will depend largely upon the proper handling of the transducer;
therefore, the following steps are recommended:
a. Clean ultrasonic transducer with a low-lint cloth, MIL-C-85043 or equivalent. Clean all contact surfaces when
using a wedge or delay block. Apply couplant to these contact surfaces and carefully tighten the assembly prior
to test.
NOTE
Scratches or similar surface blemishes remaining on the transducer or wedge may give false
indications.
b. Use prescribed or equivalent couplant and in sufficient quantity to achieve proper coupling. The use of lubricants
containing graphite, silicones, and glycerines is prohibited.
c. Apply adequate pressure to keep transducer in contact with part.
d. Use moderate speed for transducer search pattern. If transducer movement is too fast, a flaw could be passed
over without a proper indication.
