ultrasound condition monitoring ue v7

8/10/2019 Ultrasound Condition Monitoring Ue v7

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1 2009 UE Systems, Inc all rights reserved

ULTRASONIC CONDITION MONITORINGAlan Bandes

UE Systems, Inc

Abstract:

Instruments based on airborne/structure

borne ultrasound technology offer many

opportunities for reducing energy wasteand improving asset availability in

plants. They expand the concept of

Condition Monitoring to include muchmore than basic mechanical fault

inspections. Since these instrumentsdetect friction, ionization and turbulence,

their inspection capabilities range from

trending bearing condition to

determining lack of lubrication, locating

compressed air leaks and detecting

arcing, tracking and corona emissions inboth open and enclosed electric

equipment. Portable, instruments basedon this technology are used to trend and

analyze bearing condition, detect leaks

(pressure and vacuum), test valves and

steam traps, identify electrical problems

and identify potential problems in gears,motors and pumps. This presentation

will provide a brief overview of the

technology, its applications, energy

savings cost analysis and suggestedinspection techniques.

Overview:

In todays environment, generating revenuesfor any industry is important. Profit marginsare shrinking and often the differencebetween a profit and a loss can be as simpleas preventing loss and improvingefficiencies. Locating sources of energywaste, identifying failure conditions inelectrical and mechanical systems allcontribute to helping improve the bottom

line. In some cases it can be a dramaticimprovement.

Ultrasound inspection offers a uniqueposition for condition monitoring as both astand-alone inspection technology and asan effective screening tool that can speedup the inspection process and helpinspectors determine effective follow-upactions for mechanical, electrical and leakapplications.

Whether you refer to proactive inspectionsas predictive maintenance or conditionmonitoring, the goal is the same; to note adeviation from a normal or baseline

condition in order to determine whether ornot to take corrective action in a plannedorderly manner and to prevent an unplannedincident.

The ideal end result is to maintain assetavailability, reduce maintenance overheadand improve safety conditions. Not onetechnology can cover everything. Therecommendation is to incorporate as manytechnologies as possible into inspectionprocedures to assure reliable results.

This paper will review the basics ofultrasound technology, what is new to thetechnology and how it is used for conditionmonitoring to locate safety hazards, reduceenergy waste and improve equipmentavailability.

Ultrasound TechnologyAirborne/structure borne ultrasoundinstruments receive high frequencyemissions produced by operatingequipment, electrical emissions and by


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leaks. These frequencies typically rangefrom 20 kHz to 100 kHz and are beyond therange of human hearing. The instruments

electronically translate ultrasoundfrequencies through a process calledheterodyning, down into the audible rangewhere they are heard through headphonesand observed as intensity and or dB levelson a display panel. The newer digitalinstruments utilize data managementsoftware where information is data loggedon the instrument and downloaded to acomputer for analysis. Some instrumentscontain on board sound recording to capturesound samples for spectral analysis.

Sounds are received two ways: through theair and through solid surfaces (structures).

Airborne sounds such as leaks or electricalemissions are received through a scanningmodule. The structure borne ultrasounds,such as generated by bearing or leaksthrough valves, are sensed through a wave-guide or contact module.

What makes airborne ultrasound soeffective? All operating mechanicalequipment, electrical emissions (arcing,tracking, corona) and most leakageproblems produce a broad range of sound.

The high frequency ultrasonic componentsof these sounds are extremely short wave innature. A short wave signal tends to befairly directional and localized. It is thereforeeasy to separate these signals frombackground plant noises and to detect theirexact location. In addition, as subtlechanges begin to occur in mechanicalequipment, the subtle, directional nature ofultrasound allows these potential warningsignals to be detected early, before actualfailure.

Most of the sounds sensed by humansrange between 20 Hertz and 20 kilohertz (20cycles per second to 20,000 cycles persecond). The average human highfrequency threshold is actually 16.5 kHz.Low frequencies tend to be relatively largewhen compared with the sound wavessensed by ultrasonic translators. Thelengths of low frequency sound waves in theaudible range are approximately 1.9 cm(3/4") up to 17 m (56'), where-as ultrasoundwave lengths sensed by ultrasonictranslators are only 0.3 cm (1/8") up to 1.6

cm (5/8") long. Since ultrasound wavelengths are magnitudes smaller, the"ultrasonic environment" is much more

conducive to locating and isolating thesource of problems in loud plantenvironments.

The high frequency, short wavecharacteristic of ultrasound enables users toaccurately pinpoint the location of a leak,electrical emission or of a particular sound ina machine.

The basic advantages of ultrasound andultrasonic instruments are:

1. Ultrasound emissions aredirectional.

2. Ultrasound tends to be highlylocalized.

3. Ultrasound provides early warningof impending mechanical failure

4. The instruments can be used inloud, noisy environments

5. They support and enhance otherPDM technologies or can stand ontheir own in a maintenance program

When used as part of a condition monitoringprogram, ultrasound instruments helpimprove asset availability and save energy.

Once established, ultrasound can be usedas the first line of defense to:

Inspect equipment fast

Screen out anomalies Set up alarm groups for detailed

analysis and further action

Lets examine the possibilities of what canbe done to save time, locate deviations andsave energy. First listen to the translatedultrasound and observe the decibel level.Note any deviations from previous readingsas you continue your route. Record the dataand any sound anomalies. Then analyzethe data and sounds to consider if additionalaction is necessary. All of this can beaccomplished very quickly.

In order to understand the scope and depthof inspection opportunities airborne structureborne ultrasound offers, lets look at how thetechnology has progressed over the pastthree decades.


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Initially these instruments were analog.Early versions received the raw ultrasoundsignal and by the electronic process of

heterodyning translated them down into theaudible range where users heard thesesounds through headphones. Some of theinstruments had intensity level meters togive the user an indication of soundamplitude. As time progressed, frequencytuning was initiated so that when confrontedwith a variety of test environments userscould change the frequency in order to helpmake a received signal clearer. Theseinstruments were all basically search andlocate in that they were used to identify anissue. Data was manually entered on achart or sheet.

The primary applications for theseinstruments were to locate leaks such as incompressed gas and steam systems and tocheck for arcing, tracking and corona insubstations and along distribution lines.

As the industry has changed, so, too hasultrasound instrumentation. The need fordocumentation, trending, reporting andanalysis of equipment condition has broughtabout changes that improve inspectioncapabilities and equipment availability. Asthese instruments are incorporated into

reliability and energy conservation programsthe meantime between failure rates improvealong with a reduction of energy loss.

The changes in instrumentation have beensubstantial. No longer analog based, mostof the newer instruments are digital. Thisallows users to view intensity levels asdecibels, which provides more reliability foranalysis of test results. In addition, data isnow logged on-board the instruments anddownloaded into data managementsoftware. The software enables users to

review test results, compare current datawith baseline data and trend changes. Italso produces reports which can bereviewed by all involved.

In addition to on-board data logging, someof the new digital instruments incorporateon-board sound recording so that users cancapture sound samples of equipment forsound analysis. The recorded soundsamples can be viewed in spectral analysissoftware. An important feature of thespectral analysis software, in addition to

viewing sound samples in spectral, time andwaterfall screens, is the ability of users tohear the sound sample as it is played.

Using both the visual and audible modalitiesin this manner adds a new dimension forenhanced diagnostics.

Being digitally based, the technology is nowcapable of incorporating a range ofdiagnostic and analytical software tools thatwill keep users informed of the savingsgenerated through compressed gas surveysand steam surveys. In fact newdevelopments in compressed gas softwareprovides users the ability to manage theirleak programs while demonstrating savingsin energy and carbon gases. Should acompany become involved with carbontrading, these reports can prove to beextremely useful.

Another advancement over the years hasbeen in the area of specialized moduledevelopment. Recognizing that not onereceiving module can be used in all testenvironments, new modules have beencreated to meet specific needs. Forexample, a magnetically mountedtransducer is used to test bearings toprovide consistency in test approach and

results.

Parabolic modules can double the detectiondistance of standard scanning modules andcan be used to safely identify electricalemissions in transmission lines orsubstations without inspectors getting tooclose.

When equipment needs to be monitoredover time or when remote monitoring iscalled for, remote sensors can be mountedon test points. Some of these sensors have

cables that can run out to an accessiblearea where an inspector using a portableinstrument can attach the cable end to asensing module and log the data. Othertypes use 4-20 mA , 0-10V andheterodyned outputs to transmit data to acontrol panel, alarm or recording device.

While many of these remote sensors areused to monitor bearing wear, with theincreased awareness of arc flashprevention, some of these sensors are


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placed in enclosed electric cabinets to alarmwhen arcing, tracking or corona are present.

Applications

There are three generic categories ofapplications in power plants: leak detection,mechanical inspection and electricinspection.

Leak Detection:Leaks can form practically anywhere in aplant. This includes pressurized systemsand systems under a vacuum. Leaks canoccur internally through valves and steamtraps, in heat exchanger and condensertubes or to atmosphere.

While it is important to locate potential safetyhazards from leaks, loss of gases throughleaks costs facilities lots of money. Onearea that can show fast returns is throughestablishing a compressed air leak surveyprogram. In fact, the US Department ofEnergy has started a compressed airchallenge. The reason? They estimatedthat of all the compressed air used in the USby industry, about 30 percent is lost to leaks.They estimate this to cost from 1 to 3.2

billion dollars annually.1

Based on 100 psi, at a cost of $0.25/mcf forone year (8760 hours), a leak as small as1/16 (.16 cm) can cost $846.00 annually.By doubling this to 1/8 (.125 cm), the cost

jumps to $3,389.00 annually. If your planthad 10 leaks or 50 leaks, imagine thesavings! Weve had reports of users who,after performing a leak survey and repairingthe leaks, have eliminated the use of anextra compressor.

New compressed gas survey softwareorganizes results so that when data isdownloaded, the software will calculate thecfm loss per leak in terms of dollars lost. Itwill also provide information on gases thatcontribute to the carbon footprint.

In addition to the results of the survey, thesoftware keeps tabs on what has beenrepaired and what leaks have not. Thishelps users manage their survey andprovides information on actual money savedand carbon gas emissions cut.

Here are two images of a typicalcompressed gas report. The report shows

annualized results for both dollars saved(Table 1) and carbon gases saved (Table 2).In addition you will note that it has columnsthat detail leaks found and leaks repaired.

Electric emissionsUltrasound inspection works on all voltages,

low, medium and high to detect arcing,tracking and corona in both enclosed andopen access equipment. Arcing, trackingand corona ionize the air molecules aroundthem, which produces ultrasound.

With the advantage of digital soundrecording and spectral analysis, inspectorscan analyze sound samples to determinethe type and severity of an electric emission.

Below are some examples of corona,tracking and arcing. As you will note in the

FFT screen as the condition becomes moresevere, there are fewer harmonics of 60cycles. If this were in Europe, we would seethe same with harmonics of 50 cycles.The first image is Corona (Figure 1) followedby Tracking (Figure 2) and then by Arcing(Figure 3).

Figure 1Corona

Table 2

Table 1


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>38.5C

25.0

30.0

35.0

The following demonstrate the effectivenessof ultrasound when used with infrared. An

inspector who utilizes both ultrasound andinfrared technologies was inspectingswitchgear. Some of the doors could not beopened. There were no IR ports on theclosed cabinets and therefore thisswitchgear could not be tested with infrared.By scanning the door seams and air ventswith the ultrasound instrument, the inspectorheard a very distinctive arcing sound. Herecorded the sound and after the cabinetswere opened he took visual and infraredimages (Figures 8,9). Below are the results.

This is the spectral image of arcing (Figure6). Below this is the time series view (Figure7) of arcing.

The infrared image shows (Figure 8) thatthis failure condition could have resulted inflashover at any monent which would haveproduced a catastrophic event.

Mechanical InspectionAs ultrasound technology has evolved intothe digital age it has created manyopportunities for detecting, trending,analyzing and reporting changes inoperating mechanical equipment to improveasset availability. Data can be stored,uploaded and downloaded into datamanagement software. The software isused to produce trend charts, generate

Figure 2Tracking

Figure 6 & 7

Figure 8

Figure 9

Figure 3Tracking


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reports with selected criteria, alarm levelscan be set to create work orders forequipment in need of corrective action.

When changes in mechanical equipmentexceed an alarm value over baseline,spectral analysis can be used to analyzesound samples for accurate diagnosis(Figures 10 & 11). Fault frequencies can bedetermined for bearings or gears. It isrecommended that baseline readings betaken both as stored decibel levels and withrecorded sound samples. Baseline soundswill be very useful in determining whether ornot changes have occurred in equipmentand if corrective action should be taken.

In the sample below (Figure 12), whileinspecting bearings a user noticed anunusual sound in a nearby gearbox. Herecorded the sound and played it back in thespectral analysis software where heconfirmed the sound was in fact gear relatedby noting gear mesh harmonics. He usedthis recording as a baseline. The lower

spectra line was the baseline. You will notethat as the condition worsened theamplitude increased to a point where

corrective action was taken.

Condition Based Lubrication

Ultrasound is sensitive to friction and for thisreason it is effective in identifying lack oflubrication and also preventing overlubrication. Over lubrication is one of themost common causes of bearing failure.Condition based lubrication, as opposed totime based preventive lubrication programsprevent over lubrication. The traditional timebased programs traditionally call forlubricating all bearings at set intervals with a

set amount of lubricant. This overlooks oneproblem; not all bearings need lubrication oras much as called for in these procedures.Condition based lubrication utilizes the newadvancements in the technology of datamanagement and specialized sensors todetermine specifically which bearings needlubrication and when the lubricant is applied,when to stop adding the grease.

Conclusion

Over the past few years ultrasoundtechnology has advanced from using simpleanalog search and locate troubleshooting instruments to a comprehensive,sophisticated technology that is digitallybased offering systematic approaches toleak management, electrical monitoring andmechanical inspection including bearingcondition analysis and trending. Theyprovide savings in energy and improvemeantime between failure rates. Powerplants can improve their efficiencies plant

Figure 12

Figure 11

Faulty Bearings: Note Harmonics

Figure 10

Good Bearin : Note No Harmonics


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wide which will lead to improved productivityand cost reduction.

1. US Department of Energy. Energy Efficiencyand Renewable Energy

www1.eere.energy.gov/industry/bestpractices

Glossary of Terms:Arcing:An electric discharge through normallynon-conductive media such as air. It is a failurecondition in electric equipment and can lead to fireor an explosion.CBM: Condition Based MaintenanceCorona: An electric discharge around conductorswhen the surrounding air is stressed beyond itsionization point without developing flashover.

FFT: Fast Fourier Transfer A digital processingof a recorded signal representing data in terms ofits component frequencies.IR (Infrared): infrared cameras and infraredthermometers sense the infrared (below red) lightwhich is not detected by the human eye. Theseemissions are usually related to temperatureemissions.

kHz: KiloHertz. One kHz= 1000 Hz or 1000ncycles per secondPdM: Predictive MaintenanceTracking:Electricity follows a pathway to groundutilizing dirt and other contaminants until it reachesflashover.

ultrasound condition monitoring ue v7

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