Ultrasonic Testing

Ultraprobe Applications
There are many applications for an Ultraprobe. Sensing high frequency emissions, these instruments are used in most any industry, including general manufacturing, processing, power generation and distribution, printing and transportation. Typical applications include:

Leak Detection
Pressure or vacuum systems, seals and gaskets, wind noise, hatch leaks, vacuum bagging, compressed air, compressors, valves, steam traps, heat exchangers, boilers, condensers, building envelope, glove box, distillation columns,

Mechanical Inspection
Bearing faults (all speeds), lack of lubrication, prevent over lubrication, compressors, pumps (cavitation), motors, gears/gear boxes, hydraulic systems, fans, couplings, trending, trend reports, spectral analysis

Electrical Inspection
(All voltages, open access or enclosed) Arcing, tracking, corona, partial discharge: switchgear, transformers, arresters, insulators, motor control centers, distribution lines, buss bars, breakers/disconnects

Ultrasonic Leak Detection

Ultrasonic leak detection is extremely broad based. Sensing ultrasounds generated by a leak, the ULTRAPROBE can be used to locate leaks in pressurized systems regardless of the type of gas used. This is especially beneficial in areas where there is a saturation of gases or where a wide variety of gases, pressurized vessels and vacuum processes exist.
Time and convenience are also improved with ultrasonic detection since equipment may be tested while on-line.

How Ultrasonic Leak Detection Works
During a leak, a fluid (liquid or gas) moves from a high pressure to a low pressure. As it passes through the leak site, a turbulent flow is generated. This turbulence has strong ultrasonic components which are heard through headphones and seen as intensity increments on the meter. It can be generally noted that the larger the leak, the greater the ultrasound level.


Leak Detection Method
Ultrasound is a high frequency, short wave signal. The intensity of the ultrasound produced by a leak drops off rapidly as the sound moves away from its source. For this reason, the leak sound will be loudest at the leak site. Ultrasound is considered fairly "directional" and therefore, locating the source (i.e. the location) of the leak is quite simple.
For detection, scan the general area of a suspected leak and listen for a hissing sound (similar to the sound you hear when you fill a tire with air). Move in the direction of the loudest sound. If it is hard to determine the direction of the noise, reduce the sensitivity until direction can be established. Follow the sound and continue to reduce the sensitivity to determine the direction of the leak. In order to confirm the leak site, move the scanner back and forth over the suspect area. The sound level should increase as you pass over the leak. In some loud factory environments, frequency tuning may be required.

Ultrasonic Bearing & Mechanical Inspection

Inspection of mechanical equipment with ultrasonic instruments such as the Ultraprobe has many advantages. Ultrasound inspection provides early warning of bearing failure, detects lack of lubrication, prevents over lubrication and can be used on high as well as low speed bearings. In addition, since ultrasound is a high frequency, short wave signal, it is possible to filter out stray, confusing background noises and focus on the specific item to be inspected. Basic inspection methods are extremely simple and require very little training.
Ultrasonic condition analysis is straightforward. Users can observe sound levels while simultaneously listening to sound quality and record both sound and data for analysis through specialized software. Digital instruments provide many possibilities for a comprehensive bearing condition program including sound sample recording, data logging, trending, alarm groups, sound (spectral) analysis and reporting.

How Ultrasound Bearing and Mechanical Inspection Works
Mechanical movements produce a wide spectrum of sound. By focusing on a narrow band of high frequencies, the Ultraprobe detects subtle changes in amplitude and sound quality. It then heterodynes these normally undetectable sounds down into the audible range where they are observed on a meter (for trending and comparison purposes) and heard through headphones.
Based on research by NASA, it was established that ultrasonic monitoring provides early warning of bearing failure. Various stages of bearing failure have been established. An 8 dB gain over baseline indicates pre-failure or lack of lubrication. A 12 dB increase establishes the very beginning of the failure mode. A 16 dB gain indicates advanced failure condition while a 35-50 dB gain warns of catastrophic failure.

Ultrasonic Bearing Inspection Method
There are two basic methods for ultrasonic bearing monitoring: comparative and historical. In order to trouble shoot bearings or to establish a baseline, it is necessary to compare similar bearings for potential differences in amplitude and sound quality. To do this, make a permanent reference point on a bearing housing or use the grease fitting, tune to 30 kHz and adjust the sensitivity to read the intensity/decibel level on the display panel. Then compare this base reading to other similar bearings. An 8 dB gain over a baseline, with no change in sound quality will indicate possible lubrication starvation. Levels, such as 12 dB or higher can signify a potential failed condition. Once a series of bearings have been tested, and a base line set, data is recorded and then compared to future readings for historical trending and analysis. Alarm levels can be set to note any bearings in need of corrective action. Sound anomalies can be recorded for spectral analysis.
Ultrasonic inspection works extremely well with vibration technology. In fact the two technologies complement each other and enhance any PDM, (Predictive Maintenance) program.

Ultrasonic Electrical Inspection

When electrical apparatus such as switchgear, transformers, insulators or disconnects and splices fail, the results can be catastrophic. This is just as true in industrial plants as it is in the power transmission and distribution side. Electrical discharges such as arcing, tracking or corona are all potential for equipment failure. In addition, the problems of RFI and TVI impact on our valuable communication networks. If left undetected, these conditions can become a source of an arc flash incident, which can result in severe injury or death. Arcing, tracking and corona produce ultrasound and are detected with an Ultraprobe.

How Ultrasonic Electrical Detection Works
Arcing, tracking and corona all produce some form of ionization which disturbs the air molecules around it. The Ultraprobe detects the high frequency noise produced by this effect and translates it, via heterodyning, down into the audible ranges. The specific sound quality of each type of emission is heard in headphones while the intensity of the signal is observed on a meter. Normally, electrical equipment should be silent, although some may produce a constant 60 cycle hum or some steady mechanical noises. These should not be confused with the erratic, sizzling frying, uneven and popping sound of an electrical discharge.

Detection Method
Before beginning any inspection of mid or high voltage equipment, be sure to review your plant or company's safety procedures. Essentially, as in generic leak detection, the area of inspection is scanned starting at a high sensitivity level. To determine the location of the emission, reduce the sensitivity and follow the sound to the loudest point. If it is not possible to remove covers, or plates, scan around the seams and vent slots. Any potentially damaging discharges should be detected.
When it is not possible to get close to the test equipment, such as for safety reasons or while inspecting over-head power lines, use a parabolic microphone. UE Systems has two models, the Ultrasonic Waveform Concentrator (UWC) and the Long Range Module (LRM). These highly sensitive, directional sensors double the detection distance of a standard scanning module and provide pinpoint accuracy.

Source: UE Systems Inc.