31 shaft rotor cracks
DESCRIPTION
investigate the UniqueCharacteristics of Shaft/Rotor Crackusing Vibration Analysis or other Techniques.TRANSCRIPT
Suri Ganeriwala
Spectra Quest Inc.
8227 Hermitage Road, Richmond, VA, 23228
www.spectraquest.com, [email protected]
Shaft/Rotor Cracks
Vibration Signature Analysis
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
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
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
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
Introduction
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
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
Condition Monitoring Sensors
� Vibration Analysis
o Accelerometers and Proximity Probes
� Acoustic Emission
� Motor Current Signature Analysis
Shaft/Rotor Crack Diagnosis
Crack Type and Mechanism
�Open Crack�Breathing Crack
�Transverse Crack�Torsional Crack
�Mixed Mode
Shaft/Rotor Crack Diagnosis
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
Shaft/Rotor Crack Diagnosis
Shaft/Rotor Crack Diagnosis
Shaft/Rotor Crack Diagnosis
Fig. 4 Time waveform of the start-up and cost-down test for “all bolts
tight” condition.
Shaft/Rotor Crack Diagnosis
Intensity plot of the stat-up in
the flange-simulated crack test.
Shaft/Rotor Crack Diagnosis
Waterfall plot of the start-up and coast-down in the flange-simulated crack test
Shaft/Rotor Crack Diagnosis
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
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
Shaft/Rotor Crack Diagnosis
Fig. 7 Changes of critical speeds as the crack conditions change
Shaft/Rotor Crack Diagnosis
Spectra filled (breathing) crack
Shaft/Rotor Crack Diagnosis
Axial Response of filled (breathing) crack
Shaft/Rotor Crack Diagnosis
Spectra of fully open crack
Steady State at 50 Hz, Open
Outboard Bearing HorizontalInboard Bearing Vertical
Steady State at 50 Hz, Breathing
Outboard Bearing HorizontalInboard Bearing Vertical
Steady State at 65 Hz, Open
Outboard Bearing HorizontalInboard Bearing Vertical
Steady State at 65 Hz, Breathing
Outboard Bearing HorizontalInboard Bearing Vertical
Steady State at 80 Hz, Open
Outboard Bearing HorizontalInboard Bearing Vertical
Steady State at 80 Hz, Breathing
Outboard Bearing HorizontalInboard Bearing Vertical
Steady State at 50 Hz
Outboard Bearing HorizontalInboard Bearing Vertical
IMC-2011
Misalignment
IMC-2011
Misalignment
IMC-2011
Misalignment
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.