metalscan - qualification of an on-line bearing and gear health

Qualification of an On-Line Bearing and Gear Health Monitoring Technique for

In-Service Monitoring of Aircraft Engines and Helicopter Transmissions

Karen Cassidy, PhD

Presenter

Presentation Notes

Thanks also to Tony Boutros, Shaun Horning, Dave Muir, and Oliver Rusch from GasTOPS, for input on this report. Special thanks to Paula Dempsey of AFRL, and recognition to Nelson Forster of AFRL for all their supporting research.

Outline• Introduction

- Aircraft availability depends on engine & transmission health- Why bearings and gears fail- Oil Debris Monitor sensor

• Qualification Process- How to set debris limits, assess damage severity- Early research results, characteristic debris accumulation,

initial condition indicators- Validate the limits using empirical test data

• Sources of Aircraft Engine & Transmission ODM Test Data- Bearing and gear rigs; engine and helicopter test stands- Pre-flight aircraft data

• In-Service Condition Indicator Qualification- Eurofighter Typhoon / EJ200- Pilatus PC-12 / PWC PT6A

CLASS A & B ENGINE-RELATED MISHAP COSTS BY COMPONENT FY00 - FY04 (Millions USD)

FY04 DOLLARS

$0

$50

$100

$150

$200

$250

TURBINES

BEARINGS

COMPRESSORSENG FUEL S

YSTEMPILO

T INDUCED

FAN

OIL SYSTEM

FUEL CONTROLS

COMBUSTOR

TURBINES

BEARINGS

COMPRESSORS

ENG FUELSYSTEMPILOT INDUCED

FAN

OIL SYSTEM

FUEL CONTROLS

COMBUSTOR

The Cost of Aircraft Engine Failures

Source: Forster, Thompson, Toms, & Horning, “Assessing the Potential of a Commercial Oil Debris Sensor as a Prognostic Device for Gas Turbine Engine Bearings” ISHM August 2005

Presenter

Presentation Notes

Note this means about $35 million per year related to bearing failures.

• Bearings fail in-service due to Over Rolling Debris

• Solids contaminationCorrosion Pitting

• Chemical contaminationMechanical Damage

• Dimensional discrepancies • Manufacturing defects• Damage during shipping, install

Classic Fatigue

• Subsequent damage progression results in metallic particles being released into lubricating oil

Why Bearings Fail

Source: FAG Bearings / Aerospace Applications

MetalSCAN Oil Debris Monitor

• On-line full-flow ODM sensor fitted in lube oil line• Detects 100% of particles above minimum particle size• Measures number, size, mass of ferrous & non- ferrous debris• Detects spall initiation, progression, rate• Quantifies damage severity and remaining useful life

MetalSCANTM

• Metallic debris flows through the field coils creating a current in the sense coil

• Processor computes particle size and mass based upon signal amplitude

• Ferrous particles and non-ferrous particles are distinguished based upon signal direction.

ODM Principles of Operation

Presenter

Presentation Notes

Two outer coils set up a magnetic field; a pulse measure by the inner coil measures when particles pass in the field. The amplitude of the pulse measures the size of the particle (larger amp = particle of greater mass), and shape of pulse determines whether the particle is ferrous (positive peak before negative) or non-ferrous (negative peak before positive).

Condition Indicator Development Process• Condition Indicator Development

- Determine measurements that quantify wear and damage severity

• Establish Limits & Guidelines- Theory validated by empirical data

SELECTDAMAGE

MODE

SELECTPOSSIBLE

INDICATORS

SELECTMEASUREMENT

PROCESS

SENSITIVITYTESTS

AMBIGUITYTESTS

STATISTICALBEHAVIOR

OK?

STOP

PROCEDURESDEVELOPMENT OK?

STOP

OK?

STOP

Y

Y

Y

Presenter

Presentation Notes

Sensitivity – is the indicator sufficiently sensitive to the failure mode requiring detection? Any condition indicator must give an advance warning to the operator or maintainer to permit maintenance to be triggered prior to major damage. The measured parameter used as a condition indicator must identify deterioration from the normal operating condition. However, the threshold of detection must allow sufficient time for the machinery to be maintained – or at least put out of service – prior to failure and possible secondary damage. Ambiguity – will the indicator, or combination of indicators, correctly identify the failure mode with a high degree of confidence? A condition indicator must clearly and unambiguously identify a specific mode of failure – either root or secondary – of a piece of machinery. Unless the condition indicator clearly identifies a specific machinery failure mode, it is not suitable for use as a metric to establish health of the machine. Statistically Stable – can reliable warning and alarm limits be established for the level and/or rate of change, which will indicate the severity of the failure mode? The condition indicator must, without exception, detect every instance of machinery degradation. It must also, to be effective, be unable to falsely indicate the identified condition. If the indicator gives false alarms, the credibility associated with it will decrease to the point of its being useless. (repeatable, reliable, low false alarm, no missed alarm)

Qualification Process

• ODM Qualification Process- Correlate debris quantity with actual damaged components- Validate with spall checks, FDA, teardown reports, field data

Analyze Data

Develop Condition Indicators

Validate/Improve Condition Indicators

Field/Rig Data

Early Research Results

• Joint program between GasTOPS, National Research Council Canada, and Pratt & Whitney in the early 1990s

• Aircraft bearing test rigs: bearings were run to failure• Data from over 40 bearings (2” to 18” in diameter; ball and roller)• Initial spall generates a few particles ranging small to large in size• Early damage progression is a series a spall growth events, which

are seen as bursts of particles• Later stage failure: damage is more progressive / accelerated

- Rate is dependent on load and speed- Quantity is dependent on size of bearing- Particle size distribution is independent of bearing size

• Reliable alarm limits can be based upon accumulated quantity• Can correlate spall size to quantity of debris

Characteristic Debris Accumulation

0 20 40 60 80 100 1200

2000

4000

6000

8000

Elapsed Time [% ]

Num

ber o

f Par

ticle

s

> 500 um

> 400 um

> 350 um

> 300 um

> 250 um

> 200 um

> 700 um

*

Particle Size

Source: JL Miller (Pratt & Whitney) and D. Kitaljevich (GasTOPS Ltd.), In-line Oil Debris Monitor for Aircraft Engine Condition Assessment, IEEE 2000

Presenter

Presentation Notes

This data shows one typical test. Note that debris from all size ranges are generated, from 200 to 900 microns. There are two humps in the first, initial spall development, takes a turn for the worse around 50% of time/time to catastrophic failure. Then at t=90%, turns again. This was later confirmed as the point at which the spall length increases enough to include 2 roller elements; vibration jumps (which can be the trigger to stop rig tests) and rate accelerates. This point is the critical alarm limit as defined in the next slide. Note the large number of particles produced over the minimum threshold size, and how the sensor allows analyst to track fault development.

Initial Condition Indicator – Total Mass

• Critical spall arc length: 2 rolling elements (θc = 360°/N)- When 2 elements fit in spall track, get a jump in vibration

• Mass of debris shed is a function of spall width, depth, length, material density; proportional to ball, pitch diameter

• Mass rate is function of load, speed, temp

Alarm limit QALARM = K (360°/N) D d

-Q = Quantity of debris detected-K = Constant (bearing type)-N = Number of rolling elements-D = Bearing pitch diameter-d = Rolling element diameter

Presenter

Presentation Notes

Equation for bearing critical spall arc length and hence mass limit, derived from geometry. Note k is a correction factor that is proprietary and depends upon the specific application; validated by empirical data.

Engine, Gearbox, & Bearing Rig Data

• Bearing and Gear Component Rigs- National Research Council of Canada – small scale bearing rigs- Pratt & Whitney & GasTOPS – full scale aircraft bearings- AFRL 40mm Bearing Rigs - test bearing materials and fluids- NASA Glenn Research Center Component Rigs

• Hybrid bearing, Tapered roller bearing, Spur gear, Spiral bevel gear

• Engine & Transmission Test Stands - NASA OH-58 Kiowa Helicopter – main rotor transmission test stand - CAF Sea King Helicopter – engine & gearbox test facilities- DTSO Bell 206 Helicopter – main rotor transmission test stand- F22 Raptor - F119 engine pre-flight tests - AH-64 Apache Helicopter - transmission test stand

Presenter

Presentation Notes

NRC and Pratt: see slide 9. AFRL see slide 13. NASA see slide 14. F22/F119 see slide 15, CAF Sea King- many flight hours and data… DTSO is Australian Defense Technology & Science Organization. They ran seeded fault tests on 2 helicopter test stands in 2002, to monitor gear and bearing damage: initiation and progression. AH-64 see slide 16.

0

20

40

60

80

100

120

140

160

180

0 20 40 60 80 100 120 140 160Cycles(Millions)

Mas

s Lo

ss(m

g)

52100 278 ksi

52100 278 ksi

52100 250 ksi

M50 NiL 350 ksi

M50 NiL 300 ksi

Critical mass rate

Critical mass loss

52100 278 ksi

AFRL Bearing Rig: M50 NiL Propagation Rates

Critical particle size

Presenter

Presentation Notes

Points to make: 1) rate depends on load and material type, 2) mass rate increases/decreases when increase/decr load during experiment, 3) critical mass loss threshold, and critical mass rate; 4) late stage development, larger particles are generated. AFRL looked at the effect of Hertzian stress on spall propagation rates; determined critical mass loss and mass rate. Fatigue starts as surface defect, but hard materials resist failure. Spall propagates from subsurface cracks. In this figure: 52100 steel at lower stress (250 ksi) takes long to fail, increase to 278ksi and mass rate increases (similar, opposite is true). M50NIL steel resists mass loss even at 300 ksi but increase to 350ksi, mass rate starts to increase. Insert: AFRL determined that late in failure propagation, the particle size becomes much larger (more 800-1000 micron particles).

NASA Glenn Test Rigs

• Goal to quantify debris generation during bearing & gear wear• Test Methods: Spur gears (17 tests), Spiral bevel gears (6 test),

OH-58 helicopter transmission (2 tests), and others• Measured debris progression, total counts, total mass, mean

particle size

ODM mass during spur gear failure

Total Counts vs. Sample #

Source: NASA Glenn Research Center, Cleveland, OH.Ref: P.Dempsey, A. Afieh, D. Lewicki, H. Decker, et al.

Counts

0

100

200

300

400Spur,pittingSpur,pitting

Spur,no pitting

Spur,no pitting

Bevel,pittingBevel,pitting

OH-58,bearingsOH-58,

bearings

Presenter

Presentation Notes

Points 1) monitor mass increase during failure progression, on spur gear rig; 2) compare spur (healthy, faulted) with spiral bevel failures, 3) full scale OH-58 rig has bearing, spiral-bevel, and planetary gears. 4) Failure tests show clear distinction between faulted and healthy. This slide shows multiple papers and research projects; contact Dempsey or Decker for more info.

F119 Engine / F22 Aircraft Pre-Flight Tests

• New engine run on test stand• Damage due to assembly error• Bearing highly over-stressed• Bearing replaced, no secondary

damage occurred• Debris rate returned to normal

Presenter

Presentation Notes

This is one of two occasions where MetalSCAN detected pre-flight failure on the F119. In this case, the bearing assembly was installed backwards. If audience asks about capture of in-flight failures the answer is this: That data is typically retained with the OEM and /or military agency; they tend to not share it with vendors. However, if anyone in the audience is aware of such a case and they can share with us, please do. Also note, MetalSCAN has about 10 million operational hours of experience; most in non-military / industrial apps where the turbines run 24/7.We have much experience here with CI development and validation. It takes a long time to get the op hours on flying aircraft! Due to the long lead time to get the sensor implemented, and the infrequency at which they run and also that they fail.

AH-64 Apache Helicopter Transmission• Application: Naval Air Station at Patuxent River

Helicopter Transmission Test Facility• Condition Indicator: Total Mass

- Right nose gearbox sensor detected high quantity of wear debris• Damage Verification

- Filter Debris Analysis (XRF) showed M50 in right NGB, 100x mass LNGB- Teardown showed one roller over 50% of contact surface had spall;

early signs in other rollers and race

Presenter

Presentation Notes

These data became apparent in spring/summer 2007 and are very recent results. No alarm limits had been set on test stand. Amount of metal was 100x left nose gearbox; 10x two main transmissions. Teardown was performed at Redstone Technical Test Center in Huntsville, AL.

In-Service CI Qualification

• Application: Eurofighter Typhoon / EJ200

• Condition Indicators- Total Mass Accumulation Level and Rate- Large Particle Accumulation Level and Rate

• EJ200 Debris Database- 3 Bench Test Engines- 7 Flying Development Engines

• Validation- Bearing rig tests used for initial condition indicator limits- Correlated MetalSCAN mass rate to legacy debris monitor limits- Database of wear debris data (MetalSCAN, MCD and oil filters) of

healthy and faulted engines used for ongoing limit verification

Presenter

Presentation Notes

Note they increased their minimum detection particle size to ignore sizes generated by healthy data, and to better distinguish between normal and fault condition. Validation data includes statistical analysis of debris captured by magnetic chip detectors and oil filters

In-Service CI Qualification

• Application: Pilatus PC-12 / PWC PT6A Engine

• Condition Indicators- Level 1 Threshold - Total Particle Count Threshold

• Minimum count to allow for new engine break-in- Level 2 Threshold - Short Term Particle Count Rate

• Cockpit CAUTION for aircraft on ground- Level 3 Threshold - Medium Term Particle Count Rate

• Cockpit ALARM for aircraft on ground and in air

• Validation- Normal engine oil contamination rates evaluated in test cells

• Over 100 Production Engines and 50 Repair/Overhaul Engines- Over 350 in-service aircraft

Presenter

Presentation Notes

Note this sensor only counts the particles; does not record size nor distribution. Inspect engine, mag plugs, filters if alarms present.

Summary

• A mature, commercially-available in-line ODM sensor provides quantitative diagnostic and prognostic information about bearing and gear damage

• Over the past 15 years, ODM diagnostic condition indicator formulas have been verified by military and government organizations (DND, AFRL, NASA) and by the OEMs

• Verification process uses parameters including:- Critical mass loss - Critical mass rate- Critical particle size

• GasTOPS is working with AFRL to enhance prognostic capabilities of the ODM sensor algorithms for aircraft engine bearing applications

Presenter

Presentation Notes

Note we would like to work also with OEMs to help develop and validate condition indicators, if possible.

metalscan - qualification of an on-line bearing and gear health

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