This document discusses vibration signature analysis and provides a case study example. It begins with an introduction to machine fault detection and an overview of vibration signature analysis techniques in the time, frequency, and quefrency domains. It then presents a case study of a high pressure multistage pump that was experiencing high noise levels. Analysis found the noise was caused by cavitation of the first stage impeller due to flow perturbations from erosion of serrations on the pump's balancing drum. Replacing the worn balancing drum components resolved the noise issue.

1. Vibration Signature Analysis and Case study
DONE BY:
GIRISH RAGHUNATHAN
M.Tech in Machine Design
Assignment
on
1

2. OUTLINE
• Introduction
• Necessity of Machine Fault Detection
• Vibration Signature Analysis
• Time Domain
• Frequency Domain
• Quefrency Domain
• Case Study
2

3. Introduction
• When a fault takes places, some of the machine parameters are subjected to
change.
• The main causes of mechanical vibration are unbalance, misalignment, looseness
and distortion, defective bearings, gearing and coupling inaccuracies, critical
speeds, various form of resonance, bad drive belts, reciprocating forces,
aerodynamic or hydrodynamic forces, oil whirl, friction whirl, rotor/stator
misalignments, bent rotor shafts, defective rotor bars, and so on.

4. Fig. 1 : Machine Unbalance Fig. 2 : Misalignment
Fig. 3 : Bad Bearings
Fig. 4 : Bad Drive Belts Fig. 5 : Looseness

5. Necessity of Machine Fault Identification
• Classification of failure causes are as follows:
Inherent weakness in material, design, and manufacturing;
Misuse or applying stress in undesired direction;
Gradual deterioration due to wear, tear, stress fatigue, corrosion,
and
• There are certain objectives of machine fault identification:
Prevention of future failure events.
Assurance of safety, reliability, and
Maintainability of machineries.
Fig. 6 : Residual Stresses
Fig. 7 : Corrosion

6. Vibration Signature Analysis
• Vibration signature analysis techniques for
machine fault identification based on the
principle that all the system produces vibration.
• Change in vibration spectrum of machine due to
fault.
• The vibration signals obtained from the vicinity
of a bearing assembly contain rich information
about the bearing condition.
Fig. 8 : Broken Gear Tooth
Fig. 9 : Corresponding peak in Signature

7. Vibration Signature Analysis
• Signatures are extensively used as a diagnostic
tool for mechanical system.
• Signal processing is undertaken on those signals
in order to enhance or extract specific features of
such vibration signatures.
• Type and range of transducers used as pickup for
capturing vibration signal.
• Noise Reduction
Fig. 10 : Vibration Pickups
Fig. 11 : DAQ System and Control

8. 1) Time-Domain Analysis
• The time domain refers to a display or
analysis of the vibration data as a
function of time.
• Little or no data are lost prior to
inspection.
• Often too much data for easy and clear
fault diagnosis.

9. • A time-domain analysis focuses principally on statistical characteristics of vibration signal
such as peak level, standard deviation, skewness, kurtosis, and crest factor.
• Time-domain analysis of vibration signals can be subdivided into the following categories:
1. Time-waveform analysis,
2. Time-waveform indices,
3. Time-synchronous averaging,
4. Negative averaging,
5. Orbits,
6. Probability density moments
Fig. 12 : Vibration Signature (Time Domain)

10. 2) Frequency Domain Analysis
• The frequency domain refers to a display
or analysis of the vibration data as a
function of frequency.
• Fast Fourier transform (FFT) algorithm.
• Repetitive nature of the vibration signal is
clearly displayed as Frequency peaks.
• Easy for early detection and diagnosis of
faults.
Fig. 13 : Time and Frequency Domain

11. • Significant amount of information (transients, non-repetitive signal components) may be
lost during the transformation process. Not retrievable unless a permanent record of the
raw vibration signal has been made.
• The various methods of frequency-domain vibration signature analysis are - Band pass
analysis, Shock pulse (spike energy), Enveloped spectrum, Signature spectrum, and
Cascades (waterfall plots).

12. Fig. 14 : Fast Fourier Transform (FFT)

13. 3) The Quefrency Domain
• The quefrency is the abscissa for the
cepstrum which is defined as the
spectrum of the logarithm of the
power spectrum.
• It is used to highlight periodicities
that occur in the spectrum.
• Cepstrum Analysis.
Fig. 15 : Quefrency and Cepstrum

14. Case Study: Rectification of High Noise Problem of High Pressure
Multistage Pump
S.No Particulars Value
1 Pump Make M/s KSB
2 Type Horizontal, centrifugal modular design pump
3 Number of Stages 7
4 Motor Specs 220 HP , 1500 rpm motor, 29 A
5 Pump Speed 5130 rpm
6 Pump Rated Capacity 27 cubic meter / hour
7 Total Head Developed 450 LPM at 830 meter head
8 Noise Level near suction
nozzle
106 dB
Table 1: Pump Parameters

15. Case Study: Rectification of High Noise Problem of High Pressure
Multistage Pump
Following observations were noticed:
• Overall vibration of suction pipeline varied between 20 to 50 mm/sec (peak) at
different locations.
• This was higher than the 12 mm/sec acceptable limit for piping vibration as per
ASME O & M code for nuclear piping.
• The vibration amplitude corresponding to pump rpm at 87.5 Hz was very low.
Whereas vibration peaks of high amplitude found at 365.2 Hz, 1 KHz, 1.5 KHz etc.

16. Case Study: Rectification of High Noise Problem of High Pressure
Multistage Pump
Fig. 16 : Pump Vibration Signature

17. Case Study: Rectification of High Noise Problem of High Pressure
Multistage Pump
• Probable causes of high vibration were
either rubbing or amplification of
unbalance forces due to mechanical
looseness or both.
• This caused deterioration of pump and
result in increase in vibration within a
short span of time.
Fig. 17 : Pump Sectional View

18. Case Study: Rectification of High Noise Problem of High Pressure
Multistage Pump
• This high noise problem was due to flow
perturbation in the pump suction which resulted in
the cavitation of 1st stage impeller at its entrance.
• This perturbation was caused by high pressure water
entry in the pump suction due to erosion of
balancing drum serration which was due to increase
in radial clearances between balancing drum and
balancing sleeve.
Fig. 18 : Pump Suction Nozzle

19. Case Study: Rectification of High Noise Problem of High Pressure
Multistage Pump
Fig. 19 : Erosion and Corrosion in Pump Balancing drum

20. Conclusion
• Systematic vibration signature analysis has assisted in solving the above specific
cases of high vibration.
• So, vibration signature analysis is very important diagnostic tool for reliability
centered maintenance.

21. THANK YOU