AE06.pdf

Personnel being considered for qualification and

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Personnel being considered for qualification and certification should complete sufficient organized training to become thoroughly familiar with the principles and practices of airborne ultrasound related to the level of certification desired and applicable to the processes to be used. The training should include examinations to ensure that the necessary information has been comprehended. Airborne ultrasound training should consist of references and technical source material. The employer who purchases outside training services is responsible for ensuring that such services are in accordance with governing requirements. Interpretation of Airborne Ultrasound Leak Signals Ultrasonic waves can be generated by the interaction of higher velocity air or gas molecules with the atmosphere. Pressurized systems leaking gas under turbulent conditions provide the types of acoustic signals to which directional 196 Acoustic Emission Testing
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probes can respond from various distances. Hissing sounds are used to pinpoint leaks in pressure or vacuum systems. Pulsed or rhythmic sounds indicate mechanical malfunctions such as faulty valves or gaskets. Frying or sizzling sounds are characteristic of electrical leakage. One type of electrical leakage, corona, causes radio interference or high voltage (arc or spark) insulation breakdowns in bushings or cables. 197 Acoustic Leak Testing
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Ultrasonic Location of High Pressure Leaks There are compelling reasons for maintaining the integrity of pressure distribution systems in industrial plants, power plants and transportation systems. Leakage in poisonous, noxious or explosive gas systems must be immediately located and stopped. Ultrasound leak testing units have been used with considerable success in the maintenance of a wide variety of gas pressure systems. The following discussion contains general recommendations for ultrasound leak testing in high pressure systems and some suggestions for specific applications. Technique for Ultrasound Detectors for Pressure Leaks For detecting leaks from pressurized industrial systems during operation, the airborne ultrasound signal detector’s volume control should be set at maximum range for initial scanning for leaks. Reducing the volume control setting sharpens the response cone of the detector and minimizes interference from large adjacent leaks. A preliminary test should be conducted first. The inspector can simply point the scanning module toward the inspector’s face and breathe in and out. The ultrasound detector will detect the sound immediately. Before entering an area such as a factory, the inspector should stand at the entrance and scan for an indication of leaks; otherwise, the technician may follow an apparent reflection from a leak behind the technician’s back. Large overhead leaks often create sonic reflections that give a false indication. The leak source is always louder than its reflections. Always verify actual leakage by eliminating the possibility of sonic reflections.
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  • Fall '19
  • Acoustic Emission

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