Airborne & Structure borne Ultrasonic Testing

Some of the most common plant applications are: leak detection in pressure and vacuum systems (i.e., boilers, heat exchangers, condensers, chillers, distillation columns, vacuum furnaces, specialty gas systems), bearing inspection, steam trap inspection, valve blow-by, pump cavitations, detection of corona in switch gear, compressor valve analysis, integrity of seals and gaskets in tanks, pipe systems and large walk-in boxes.

All operating equipment and most leakage problems produce a broad range of sound. The high frequency ultrasonic components of these sounds are extremely short wave in nature, and a short wave signal tends to be fairly directional. It is therefore to isolate these signals from background noises and detect their exact location. In addition, as subtle changes begin to occur in mechanical equipment, the nature of ultrasound allows these potential warning signals to be detected early, before actual failure.

Airborne ultrasound instruments, often referred to as "ultrasonic translators", provide information two ways: qualitatively, due to the ability to "hear' ultrasounds through a noise isolating headphone, and quantitatively, via incremental readings on a meter. This is accomplished in most ultrasonic translators by an electronic process called "heterodyning", which accurately converts the ultrasounds sensed by the instrument into the audible range where users can hear and recognize them through headphones.

Although the ability to gauge intensity and view sonic patterns is important, it is equally important to be able to "hear" the ultrasounds produced by various equipment. That is precisely what makes these instruments so useful; they allow inspectors to confirm a diagnosis on the spot by being able to discriminate among various equipment sounds.

The reason users can accurately pinpoint the location of a particular ultrasonic signal in a machine or from a leak is due to its high frequency short wave. Most of the sounds sensed by humans range between 20 Hz and 20 kHz (20 cycles per second to 20,000 cycles per second). They tend to be relatively gross when compared with the sound waves sensed by ultrasonic translators. Low frequency sounds in the audible range are approximately 1.9 cm. to 17 meters in length, whereas ultrasounds sensed by ultrasonic translators are only 0.3 - 1.6 cm long. Since ultrasound wave lengths are magnitudes smaller, the ultrasonic environment is much more conducive to locating and isolating the source of problems in loud plant environments.

-::- This site is designed and authored by David Stevens IEng MIET FIDiagE MICML   -::-

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