What is Ultrasonic Testing?

Ultrasound spectral analysis of compressor bearing. Here, ultrasound output is fed into the vibration analyzer to provide a quantitative evaluation of the ultrasound source.

Many electrical and mechanical problems produce sound and vibration at ultrasonic frequencies (greater than 20kHz). Unfortunately, these sounds cannot be detected by the human ear. These sounds can be detected by ultrasonic listening instruments. These instruments have been integrated into our Predictive Testing Service.

Ultrasonic testing is used in two ways in our Predictive Testing Service. First, it permits us to identify faults that cannot be detected by either infrared or vibration tests. Second, it permits an independent verification of problems that can be detected by the infrared or vibration tests.

What problems may be identified by ultrasonic testing?

Any type of impacting mechanical fault will generate ultrasound. Such faults in clude bearing and gear defects as well as mechanical looseness. Ultrasonic testing generally provides earlier warning of these types of faults than vibration or infrared tests.

Other mechanical faults that are found by ultrasound include: defective steam traps; leaks in pipes or vessels due to faulty welds, holes, gasket failures, etc.;leaky valves in liquid or gas lines and leaks in compressed air systems. Compressed air leak surveys can be a particularly valuable process that can easily reduce compressed air demand and electrical usage.

Ultrasonic survey of high voltage power lines. The sensitivity of the instrument is greatly enhanced for this application by using a parabolic signal concentrator.

Ultrasound is extremely valuable for inspections of high voltage electrical systems (above 2,000V). These systems require properly functioning insulation systems. Failure of high voltage insulation systems can result in catastrophic faults. Deterioration of high voltage insulation produces an electrical leakage known as corona, tracking or partial discharge. This condition causes ionization of the surrounding air. The ionization process produces ultrasound which is readily detected by the ultrasound instrument.

Pushing the Ultrasound Envelope

Mid Atlantic Infrared has innovated and expanded the use of ultrasound by developing spectral analysis of ultrasound signatures. This technique permits quantified analysis of both electrical and mechanical ultrasound sources.

Analysis of the resulting spectral patterns reveals the source of high ultrasound. For example, ultrasound signatures readily reveal specific bearing fault frequencies.

Also, ultrasound signatures can distinguish faulty high voltage insulation and arcing from other background ultrasound sources.

Mid Atlantic Infrared has pioneered the use of ultrasound for the evaluation of packing line equipment. This equipment consists of motors, gearboxes and numerous bearings, operating at a wide variety of speeds, often with limited access.

Ultrasound has been proved to be an excellent tool for rapid and dependable identification of problems with this type of equipment.


Ultrasonic Testing Ultrasonic Testing
This plot compares an ultrasound reading and a vibration reading of a failing bearing. The vibration analysis revealed nothing about the condition. The ultrasound analysis readily shows the problem. Ultrasound plots show once per revolution impact on a shaft turning at 66 RPM. Ultrasound is excellent for evaluation of slow speed machinery.

Ultrasonic Testing
High broad band ultrasound results from arcing in high voltage switchgear. The 60 hz components to the left are from magnetically induced vibration in the switchgear. Spectral analysis of ultrasound permits dangerous insulation failures to be distinguished from normal ultrasound noise. Mid Atlantic Infrared pioneered these spectral analysis techniques.

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