Personnel being considered forqualification and certification shouldcomplete sufficient organized training tobecome thoroughly familiar with theprinciples and practices of airborneultrasound related to the level ofcertification desired and applicable to theprocesses to be used. The training shouldinclude examinations to ensure that thenecessary information has beencomprehended. Airborne ultrasoundtraining should consist of references andtechnical source material. The employerwho purchases outside training services isresponsible for ensuring that such servicesare in accordance with governingrequirements.Interpretation of AirborneUltrasound Leak SignalsUltrasonic waves can be generated by theinteraction of higher velocity air or gasmolecules with the atmosphere.Pressurized systems leaking gas underturbulent conditions provide the types ofacoustic signals to which directional196Acoustic Emission Testing
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probes can respond from variousdistances. Hissing sounds are used topinpoint leaks in pressure or vacuumsystems. Pulsed or rhythmic soundsindicate mechanical malfunctions such asfaulty valves or gaskets. Frying or sizzlingsounds are characteristic of electricalleakage. One type of electrical leakage,corona, causes radio interference or highvoltage (arc or spark) insulationbreakdowns in bushings or cables.197Acoustic Leak Testing
Ultrasonic Location ofHigh Pressure LeaksThere are compelling reasons formaintaining the integrity of pressuredistribution systems in industrial plants,power plants and transportation systems.Leakage in poisonous, noxious orexplosive gas systems must beimmediately located and stopped.Ultrasound leak testing units have beenused with considerable success in themaintenance of a wide variety of gaspressure systems. The following discussioncontains general recommendations forultrasound leak testing in high pressuresystems and some suggestions for specificapplications.Technique for UltrasoundDetectors for PressureLeaksFor detecting leaks from pressurizedindustrial systems during operation, theairborne ultrasound signal detector’svolume control should be set atmaximum range for initial scanning forleaks. Reducing the volume controlsetting sharpens the response cone of thedetector and minimizes interference fromlarge adjacent leaks. A preliminary testshould be conducted first. The inspectorcan simply point the scanning moduletoward the inspector’s face and breathe inand out. The ultrasound detector willdetect the sound immediately.Before entering an area such as afactory, the inspector should stand at theentrance and scan for an indication ofleaks; otherwise, the technician mayfollow an apparent reflection from a leakbehind the technician’s back. Largeoverhead leaks often create sonicreflections that give a false indication. Theleak source is always louder than itsreflections. Always verify actual leakage byeliminating the possibility of sonicreflections.
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