31 shaft rotor cracks
DESCRIPTION
investigate the UniqueCharacteristics of Shaft/Rotor Crackusing Vibration Analysis or other Techniques.TRANSCRIPT
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Suri Ganeriwala
Spectra Quest Inc.
8227 Hermitage Road, Richmond, VA, 23228
www.spectraquest.com, [email protected]
Shaft/Rotor Cracks
Vibration Signature Analysis
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Objective of this work was to investigate the Unique
Characteristics of Shaft/Rotor Crack
using Vibration Analysis or other Techniques
Motivation:
Electric Power Research Institute estimates direct and
indirect losses (repair, replacement, and loss of
revenue) at around 1 billon US dollars in the
conventional and nuclear power industry alone.
Shaft/Rotor Crack Diagnosis
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Questions:
� How Crack Signature is Different than Unbalance, Looseness, or misalignment?
� Is there an Unique Spectral/Time Signature of a Crack and if yes What is it?
� Does 2X frequency dominate the response?
� How 2X frequency amplitude varies with crack size and location?
� Does crack produce sub-harmonic excitation?
Shaft/Rotor Crack Diagnosis
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Outline
� Introduction – A quick overview of Condition Monitoring/Diagnostics
� Review of Shaft/Rotor Crack Monitoring/Diagnostics
� Details of Experimental Study done at SpectraQuest
� Results and Discussion of Results
� Cause/Sources of Confusion � Concluding Remarks
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Introduction
• Condition Based Maintenance (CBM) promises
to deliver improved maintainability and
operational availability of rotating machinery
while reducing life-cycle costs.
• The three critical components of CBM are:
condition indications, diagnostics, and
prognostics
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Introduction
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The emphasis of the academic community has
taken a three-fold approach on machine
condition monitoring & diagnostics/prognostics :
(1) Data based methods,
(2) Model based diagnostics and prognostics, and
(3) Data mining (or probabilistic) approaches.
Academic Approach
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Primarily signal based and is done in the following
way:
• Define measurement locations on machines
• Install different types of sensors
• Create a measurement structure or database
• Collect data, perform time and frequency domain analysis and
define trend parameters
• Periodically repeat measurements and generate historic trends
• Create statistical threshold based on historical experience
• Make maintenance decision when parameters cross set
thresholds
Industrial Approach
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Condition Monitoring Sensors
� Vibration Analysis
o Accelerometers and Proximity Probes
� Acoustic Emission
� Motor Current Signature Analysis
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Shaft/Rotor Crack Diagnosis
Crack Type and Mechanism
�Open Crack�Breathing Crack
�Transverse Crack�Torsional Crack
�Mixed Mode
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Shaft/Rotor Crack Diagnosis
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1. Crack simulation study based on the Jeffcott rotor models
2. Modeling critical speeds/resonances and monitoring the
shift in them
3. Modeling bi-directional total frequency spectrum and
observing the change
4. Treat Crack as transient phenomenon
5. Torsinal vibration and determine shift in natural
frequencies
6. Multiple sensor approach--AE to locate the shaft crack,
and the vibration signal to determine the depth.
7. Combined fracture mechanics with rotordynamics to
calculate compliance matrix and predict spectra shift
Research Approaches
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Shaft/Rotor Crack Diagnosis
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Shaft/Rotor Crack Diagnosis
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Shaft/Rotor Crack Diagnosis
Fig. 4 Time waveform of the start-up and cost-down test for “all bolts
tight” condition.
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Shaft/Rotor Crack Diagnosis
Intensity plot of the stat-up in
the flange-simulated crack test.
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Shaft/Rotor Crack Diagnosis
Waterfall plot of the start-up and coast-down in the flange-simulated crack test
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Shaft/Rotor Crack Diagnosis
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Shaft/Rotor Crack Diagnosis
Change in the critical speed
Conditions Critical speed (Hz)
All bolts tight 65.62
One bolt loose 65.00
Two bolts loose 64.37
Three bolts loose 64.37
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Shaft/Rotor Crack Diagnosis
Change in the critical speed
Conditions Critical speed (Hz)
Intact 65.00
Filler fully tightened 62.50
Filler partially tightened 62.50
No-filler 60.00
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Shaft/Rotor Crack Diagnosis
Fig. 7 Changes of critical speeds as the crack conditions change
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Shaft/Rotor Crack Diagnosis
Spectra filled (breathing) crack
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Shaft/Rotor Crack Diagnosis
Axial Response of filled (breathing) crack
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Shaft/Rotor Crack Diagnosis
Spectra of fully open crack
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Steady State at 50 Hz, Open
Outboard Bearing HorizontalInboard Bearing Vertical
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Steady State at 50 Hz, Breathing
Outboard Bearing HorizontalInboard Bearing Vertical
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Steady State at 65 Hz, Open
Outboard Bearing HorizontalInboard Bearing Vertical
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Steady State at 65 Hz, Breathing
Outboard Bearing HorizontalInboard Bearing Vertical
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Steady State at 80 Hz, Open
Outboard Bearing HorizontalInboard Bearing Vertical
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Steady State at 80 Hz, Breathing
Outboard Bearing HorizontalInboard Bearing Vertical
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Steady State at 50 Hz
Outboard Bearing HorizontalInboard Bearing Vertical
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IMC-2011
Misalignment
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IMC-2011
Misalignment
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IMC-2011
Misalignment
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Shaft/Rotor Crack Diagnosis
Conclusions:
�The critical speed decreases with the increase in crack
�The 1X, 2X and even 3X frequency responses increases
�Increases in higher harmonics were more severe near critical speed
�No serious sub-harmonic excitation was seen
�Results are consistent with the theoretical predictions of crack.
�The results of this study do not provide a unique signature of crack
�Further research is needed to develop for modeling of rotor crack.