Ultrasound Tips

With many thousands of ultrasound inspectors world wide using our technology to improve reliability, reduce energy waste, and ensure product quality and corporate sustainability, you can bet we've got a few good tips for helping you get the most from your ultrasound inspection program. On this page we

• Share our knowledge with you,
• Post knowledge shared by other ultrasound inspectors
• Invite you to share your tips with us for the GLOBAL ultrasound community to browse

The fire-eye is one of the most crucial safety devices in a boiler. It uses an infrared eye to detect if the boiler's flame is still on. It is designed to trigger the shut down of incoming fuel into the boiler in the absence of a flame.

Buddy OQuinn from Goodyear Chemical sends us this excellent tip for inspecting your older style boiler fire eyes using airborne ultrasound.

"Older style fire eyes on some boilers have a shutter system in them that will photo the flame to ensure there is in fact a flame. Most burners have two of these installed one of them has to visualize a flame at all times or the burner will shut down. These can be easily checked with the ultra sound while the burner is running by touching the housing of the fire eye with your dectector. You will hear a clicking noise every 8 to 15 seconds if the eye is working properly. If you do not hear the noise on one of them it possible to repair it with out shutting the burner down now that you know witch is not working.

The ultrasound community thanks Buddy for sharing this imaginative tip

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Extend Your Distance and Your Efficiency 

How can overhead piping and air lines that are hard to reach be included in a compressed air leak survey without continuously going up and down scissor lifts and ladders?  The use of Extended Distance Sensors and Parabolic Dishes has grown in popularity to improve efficiency and safety of any ultrasonic inspection.  Instead of climbing ladders all day, which introduces fatigue and safety concerns, draw out a map of your overhead system and find the leaks from the floor.

Extended Distance Sensors (EDS) are designed specifically to receive and focus low energy ultrasound pressure waves created by compressed air leaks.  These sensors are low cost and easy to use while extending normal leak detection beyond 50’.  Parabolic sensors that are designed for receiving ultrasound signals are quite small; as small as 10’ diameter.  Because ultrasound waves can be as small as 3/8” there is no need to use huge dishes.  The parabolic shape captures more signals which are focused onto a super sensitive piezo-electric transducer.  Laser sights project a small red dot when a leak is found.

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Tagging System Ensures Leaks Are Fixed

A 2-tag or 3-tag system manages found leaks and closes the loop from discovery to repair.  In either system a brightly colored tag is attached to the leak to identify it for repair.  On the tag itself there are two or three perforated sections with matching identification numbers.  Section one needs ample space for a written description of the leak and its location in the plant.  This section is removed by the ultrasound inspector during a leak survey and is used to generate a work order for repair.  The second section is left at the leak site and only removed after the repair is completed.  There is space on this section to describe the actions taken to affect the repair.  Details may include name of repair personnel, parts required to make the repair, and the time required for the job.  If a third section is used, it is left at the leak site.  During the next tour by the ultrasound inspector the repair will be confirmed.  If no leak is found the inspector removes the third tag to close out the job. 

Finding leaks doesn’t save energy until they are repaired.  Use a tagging system like the one described here to ensure leaks are not only found, but fixed.

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Respecting Personal Safety

Ultrasonic detectors are super sensitive devices capable of hearing extremely low energy high-frequency sound pressure waves.  In some cases the source of ultrasound is quite weak and so the electronics must apply tremendous amplification to the signal.  Otherwise, it would remain undetectable. 

When performing a leak survey our tendency is to continually increase the gain of the detector so that even micro leaks are discovered.  The peril that confronts our own personal hearing is when we enter a zone of the plant where sudden bursts of high energy ultrasound are present.  One such zone is the compressor room where blow-off valves open and close at unpredictable intervals.  If the detector is set to amplify that signal to the max the resulting audible signal heard in the headset can be quite loud and uncomfortable.

As a precaution, always keep the amplifiers set to low and bring them up gradually to the level required for the inspection.

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While performing a quarterly ultrasonic leak inspection on the plant’s compressed air system, our inspector picked up what sounded like a leak coming from a brick wall.  He was miffed.  How could a brick wall have a compressed air leak? 

The Answer… Play the bounce. 

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Corona Leak Damages Insulator

While scanning medium voltage distribution lines with an SDT170 ultrasound meter and the Extended Distance Sensor a steady low level buzzing was detected atop one pole.  Further investigation by the local utility revealed a hairline crack in the insulator. This was a sure sign trouble was approaching.  The linesman explained to me that once cracked, the insulator no longer functions at 100% and an electrical leak happens. This phenomenon is commonly known as “Corona Leak” or “Corona Discharge.”  Corona produces lots of problems including loss of energy, and chemical by-products with corrosive consequences for insulators. Moisture, dirt, and other contaminants penetrate the crack and cause further problems.  The results can vary from minor power loss to a major outage when the insulator finally fails.

Corona leaks are easily detected with an ultrasonic detector.  Set your detector in airborne mode and scan in the direction of the insulators using a back-and-forth and up-and-down motion. For longer distances use a laser sighted parabolic dish.  Good insulators should be quiet while corona discharge will produce a steady or buzzing sound.

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Acoustic Re-Lubrication Pointers Part 1

Condition based lubrication programs rely on ultrasound data collection to alarm when re-greasing is required. Techs re-lubricate bearings with an ultrasonic grease gun interface to ensure the right amount of grease is added. Some confusion about how much grease is enough still remains a question mark. Our advice: 

• Send your lube techs to an ultrasonic training class.

• Alarm bearings for re-lubrication at 8-10 dBµV over baselines established in ultrasonic condition monitoring. 8 dBµV, 16 dBµV, and 24 dBµV are considered SDT’s escalating levels of failure (8 = lubrication, 16 = failure mode started, 24 = catastrophic failure mode entered).

• For consistency use the same ultrasonic instrument for condition monitoring and re-lubrication. Preferably, the ultrasonic device should provide digital measurement and listening capabilities. “Listen-only” units can be subjective amongst multiple users.

• Apply grease slowly while listening and measuring ultrasonically. Your target is to return the dBµV values back to baseline.

• Grease… then wait. Don’t hurry at the expense of doing the job correctly. Allow the grease to work into the cage, rollers, and grease cavity. The bearing may initially go quiet, and then loud again as the grease is worked in.

The 8-16-24 dBµV rule works in most instances, however statistics are a poor substitute for common sense. Use these guideline in harmony with you company’s established greasing protocol to arrive at a unique procedure that suites your needs.

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