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Vibration Analysis Report
AN Other Company Limited, Example Report:25th October 2011.
Report Content s):
Run Up/Coast Down Analysis on Calorifier Pumps
Details of Engineer, Site Representative and Report Author
Report Prepared By
Tony Riseley
Dynaseq Monitoring Group Phone+44 (0) 1352 710600Greenfield Business Centre Fax +44 (0) 1352 710703Greenfield, HOLYWELL Email [email protected]. North Wales. Web www.dynaseq.co.uk
Date of Survey(s):25th October 2011.
Our Reference Number:ANCL11-08.
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Table of Contents
PART ONE: The Report Section
Introduction Page 3
Site details, diagrams and additional notes.
Run Up / Coast Down Analysis on Sensitising Calorifier Pumps Page 6
Site details, diagrams and additional notes.
PART TWO: Discussion
Conclusions Page 10
Advice and recommendations
Further Remarks Page 11
Basic concepts of vibration analysis and other details
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Part
1Report Section
Introduction; Machine Listings; Site Details and Relevant Data
Introduction
Preface
A real-time run up/coast down analysis was requested by AN Other Company to investigate the vibration
levels occurring on the Sensitising P1023A and P1023B 82C Calorifier Pumps since installing a variable
speed drive (VSD) inverter on the installations.
The purpose of this survey was to determine if there were any significant increases in vibration amplitude
when operating at certain speeds, where an offset motor misalignment has been identified on regular
occasions during the routine condition monitoring inspections.
Machine Listings
The following machinery located within the Sensitising Plant at AN Other Company has been monitored during
the course of the survey as follows:-
(a) Ten individual horizontallymounted belt driven2.1b (Upper Plant Room) SensitisingBox Section
Fans, each of approximately 2920 RPM, 15 kW capacity and labelled consecutively from No. 1through to
No. 10and identified as follows: (i) K1102; (ii) K1107; (iii) K1103; (iv) K1108; (v) K1104; (vi) K1109; (vii)
K1105; (viii) K1110; (ix) K1106 and (x) K1111.
(b) One single horizontallymounted 2.1b (Upper Plant Room) SensitisingExtraction Fan, identified as:
K1118, of 960 RPM, 11.0 kW capacity.
(c) Two individual horizontallymounted belt driven2.1a Sensitising (Lower Plant Room) Main Conditioner
Fansas follows: (i) Main Conditioner Fan No. 1 K1101of 1460 RPM, 25 Hp capacity and (ii) AuxiliaryConditioner Fan No. 1 K1117of 1460 RPM, 22.0 kW capacity.
(d) Two identical horizontallymounted variable-speed, direct-coupled 2.1 a Sensitising (Lower Plant Room)
82 C Calorifier Pumps, identified as: P1023A and P1023B, each of 2950 RPM, 40 Hp capacity.
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Data Collection
The machines were monitored using an SKF DC460 dual channeldigital FFT analyser which is a combined
portable data collector and sophisticated signal analyser, capable of detecting the following fault types:
bearing damage
lubrication problems
imbalance
positional misalignment
angular misalignment
loading anomalies
looseness
gearbox component wear/damage
conveyor belt tracking
resonance and structural related problems
foundation movement
coupling damage
excessive stress points
inadequate support
application problems
hysteresis whirl
faulty belt drives
The analysis conducted on site highlights any of the above fault types and on detection will be documented in
this report, stating the exact defect, cause and severity.
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Spectrum Analysis: Description and Purpose
Before presenting this report in further detail, it may be necessary to explain some of the terminology used
when referring to the recorded spectra:
Velocity Spectrum
Velocityis movement expressed in terms of time and in our case, measured in mm/sec.. The ISO10816-3
vibration severity standardcategorises certain types of machinery (in accordance with capacity; rotational
speed and operating circumstances) into certain zonessuch as: Excellent; Acceptable; Unsatisfactory
and Unacceptable.
Acceleration Spectrum
Accelerationis the rate of change ofvelocity(in other words, movement per second per second) and is
measured in G. Acceleration is a high frequencyspectral signal relating to typical faults such as: bearing
fatigue; gear wear; complex or multiple component damage; excessive loading anomalies and aerodynamic
related problems on rotors or impellers.
Enveloped Spectrum
Envelopingis the relatively new technique, which filtersandprocessesthe normal high frequency
characteristics naturally produced by the combinedcomponents of a bearing. In the past, conventional
techniques only permitted the analysis of the overallsignal, which could actually indicate an array of anomalies
other than a bearing defect. This method became an increasingly unreliable and misleading technique,especially when levels began to rise - for example, it was impossible to distinguish between a genuinebearing
defect and a typical loading related problem.
When utilising the envelopingtechnique, the following processes take place:
The complexsignal is demodulatedby use of a band pass filtercentred on the resonant carrier waveform.
The entire process is enveloped(half wave rectified). The individualcomponents of a bearing such as faulty
inner/outer races; cages and rollers/balls are now detectable at specific frequencies.
The technique is particularly useful on slow running machinery (e.g., below 10 RPM) where conventional
methods fail to produce any relevant signals to analyse.
The investigation can now be classified into the following areas:
1. Site Details.
2. Vibration Measurements on the machines.
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Run Up / Coast Down Analysis on Calorifier Pumps
Inspection of the Supporting Structure and Operating System
The Calorifier Pumps selected for monitoring appeared to be adequately placed upon suitable foundations and
supporting structures. Hence, the survey was primarily concerned with the vibration levels obtained from the
machine itself as opposed to foundations and structural related problems.
Run Up / Coast Down Analysis
During this particular test, the 2.1a Sensitising Plant 82C Calorifier Pumps P1023A and P1023B were allowed
to operate from standstill to full rotational speed (run up analysis) and from full speed down to standstill (coast
down analysis). The purpose of these tests was to highlight any shaft critical frequencies, random impacts
and/or other anomalies that can easily be missed using stationary signal analysis alone.
Data was collected in real-time at each of the following monitoring positions: (i) motor non drive end
(horizontal)and (ii) motor drive end (horizontal). It has long been suspected that these pumps have been
operating close to a shaft critical frequency since installing a pressure sensitive variable speed drive on each
installation, whereby an offset misalignment of the motor has been observed during the routine condition
monitoring surveys at approximately 81 - 85 % operating speed.
Figure 1:Photograph identifying the dual channel sensor locations on the
non drive endand drive endpositions of the 2.1a Sensitising Plant 82C
Calorifier Pump motor, using magnetic mounted accelerometers connected
to an SKF DC460 analyser.
The following results were obtained during the coast up analysis at 2x rotational frequency from the motor non
drive endand motor drive endbearings, all within the horizontalplane:-
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Coast Up/Down Analysis Results on 2.1a Sensitising 82C Calorifier Pumps P1023A and P1023B
Freq. Pump P1023A Pump P1023B
Notes and observationsmtr-nde mtr-de mtr-nde mtr-de
Hz mm/s mm/s mm/s mm/s
73.4 2.73 2.63 1.36 2.49 Both motors operating normally
75 3 2.86 1.45 2.59 -
76.6 3.32 3.05 1.60 2.52 -
78.1 4.49 4.24 2.01 3.04 First observation of significant 2x rpm vibration on P1023A motor
79.7 7.12 6.71 2.42 3.75 P1023A motor now operating above ISO 10816-3 Unusable Zone
81.3 9.39 8.63 3.42 5.27 First observation of significant 2x rpm vibration on P1023B motor
82.8 7.32 6.66 4.86 7.51 Both P1023A & P023B operating above the ISO 10816-3 Unusable
84.4 4.99 4.65 6.61 10.2 Decreasing amplitudes on P1023A & increasing amplitudes on P1023B
85.9 4.36 4 7.15 10.9 P1023A Satisfactory Zone / P1023B Unusable Zone
87.5 3.57 3.12 6.19 9.32 P1023B continuing to operate in the ISO 10816-3 Unusable Zone
89.1 2.61 2.46 5.15 7.6 P1023B continuing to operate in the ISO 10816-3 Unusable Zone
90.6 2.61 2.36 4.22 6.1 P1023B operating in the ISO 10816-3 Unsatisfactory Zone
92.2 2.52 2.15 3.48 4.92 P1023B operating in the ISO 10816-3 Unsatisfactory Zone
93.8 2.17 1.79 2.87 3.95 Both motors operating normally
95.3 1.78 1.42 2.63 3.45 -
96.9 1.64 1.33 2.43 3.21 -
98.4 1.40 1.19 2.18 2.83 -
Table 1:Table 1 identifying potential shaft critical frequencies (measured in Hz) and velocity amplitudes (measured in mm/sec. RMS) during the
run up / coast down analysis conducted on the motor non drive end and motor drive end monitoring positions of the Sensitising 2.1a 82C
Calorifier Pumps P1023A and P1023B. The dark green, light green, yellow and red boxes correspond with the ISO Vibration Severity Standard:
10816-3 Group 3 (15 kW300 kW pump with external driver rigid mount) ratings of: Excellent, Satisfactory, Unsatisfactory and Unusable
consecutively.
As observed in the table above, there is a potential shaft critical zone between the operating speed of 2351 -
2490 rpm (79.7% - 84.4% running speed) occurring on Pump P1023A and 2399 - 2720 rpm (81.3% - 92.2%
running speed) occurring on Pump P1023B, culminating in the highest velocity amplitude of 10.9 mm/sec. at
85.9 Hz (2xrotationalfrequency) on the motor drive endbearing of Pump P1023B. The prolonged use of
these motors operating in this speed range should be avoided if possible.
The following pages contain the coast up spectral analysis obtained from each motor and clearly illustrate the
problem area.
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P1023A 82 C Calorifier Pump Run Up Analysis
Figure 2:Run Up Analysis conducted on the motor non drive endbearing of 2.1a Calorifier Pump P1023Ashowing significant emergence of 2x rpm
vibration (misalignment) at 81.3 Hz (corresponding to 81.3% operating speed) over a 131 second sample (32768 samples/21 spectra/40KHz spacing).
Figure 3:Run Up Analysis conducted on the motor drive endbearing of 2.1a Calorifier Pump P1023Ashowing significant emergence of 2x rpm vibration
(misalignment) at 81.3 Hz (corresponding to 81.3% operating speed) over a 131 second sample (32768 samples/21 spectra/40KHz spacing).
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P1023B 82 C Calorifier Pump Run Up Analysis
Figure 4:Run Up Analysis conducted on the motor non drive endbearing of 2.1a Calorifier Pump P1023Bshowing significant emergence of 2x rpm
vibration (misalignment) at 85.9 Hz (corresponding to 85.9% operating speed) over a 131 second sample (32768 samples/21 spectra/40KHz spacing).
Figure 5:Run Up Analysis conducted on the motor drive endbearing of 2.1a Calorifier Pump P1023Bshowing significant emergence of 2x rpm vibration
(misalignment) at 85.9 Hz (corresponding to 85.9% operating speed) over a 131 second sample (32768 samples/21 spectra/40KHz spacing).
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Part
2Discussion
Advice and Recommendations
1 Recommendations for 2.1a 82 C Calorifier Pumps P1023A & P1023B
2.1a Sensitising 82 C Calorifier Pumps P1023A & P1023B - URGENT PRIORITY (operating at
shaft critical frequency)
The Sensitising 82 C Calorifier Pumps P1023A and P1023B proved to be operating above the
Unacceptable Zone as specified by the Vibration Severity Standard: ISO10816-3.
The Coast Up/Coast Down Analysis clearly highlighted a potential shaft critical zone between the operating
speed of 2351 - 2490 rpm (79.7% - 84.4% running speed) occurring on Pump P1023A and 2399 - 2720 rpm
(81.3% - 92.2% running speed) occurring on Pump P1023B, culminating in the highest velocity amplitude of
10.9 mm/sec.at 85.9 Hz (2xrotationalfrequency) on the motor drive endbearing of Pump P1023B (should be
less than 4.5 mm/sec.).
The prolonged use of operating these motors in this speed range should be avoided if possible; there is a
potential risk of the internal rotor catching the stator or secondary induced mechanical damage may be causedto the coupling or bearings.
There are three solutions to overcome this problem:-
1. Operate the pumps at 100% speed only (the motors in use are not dynamically balanced to run at any
other speed).
2. Operate the pumps outside the shaft critical speed zone in each case (highlighted above).
3. Replace BOTH motors and fit a variable speed rated motor to each installation.
If there is any aspect of this report you wish to discuss in greater detail, or any further points you would like to raise yourself, thenplease do not hesitate to contact Tony Riseleyon Tel. 01352 710600or [email protected].
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Further RemarksBasic Concepts of Vibration Analysis
What is Vibration?
Introduction
Vibration is the disturbance from equilibrium, which propagates in time from one place to another and exists in
all rotating and reciprocating machinery. An ideal machine would produce no vibration at all because all
energy would be channelled into the machine function. A good design will produce low levels of inherent
vibration, however, as the machine wears, foundations settle and parts deform, subtle changes in the dynamicproperties of the machine begin to occur. Shafts become misaligned, parts begin to wear, rotors become
unbalanced and tolerances increase. All of these factors are reflected in an increase in vibration energy, which
dissipates throughout the machine, excites resonance and puts considerable strain on bearings. Cause and
effect reinforce each other and the machine progresses towards ultimate breakdown.
A machine may contain many complex vibrations, made up of a wide-range of superimposed sinusoidal and
random components. This multi-complex signal can be broken down into its constituent frequency
components by using F.F.T. analysis (Fast Fourier Transform) commonly referred to as a Spectrum. The
following table highlights the many common faults and their characteristic frequencies in terms of rotation
speeds:
Nature of Fault Frequency of DominantVibration (Hz=rpm/60)
Direction Remarks
Rotating members out ofbalance
1 x rpm RadialA common cause of excess vibrationin machinery.
Misalignment & Bent ShaftsUsually 1 x rpm; Often 2 xrpm and sometimes 3 or 4 xrpm
Radial & Axial A common fault.
Damaged rolling elementbearings (ball, roller etc.)
Impact rates for theindividual bearing
componentAlso vibrations at highfrequencies (2 to 60 KHz)often related to radialresonance in bearings
Radial and Axial
Uneven vibration levels, often withshocks. Impact Rates f (Hz)
Outer Race defect: f(Hz) = n/2 x fr(1-
BD/PD x Cos )
Inner Race defect: f(Hz) = n/2 x fr(1+BD/PD x Cos )
Ball defect: f(Hz) = PD/BD x fr [1-
(BD/PD x Cos )2]
N = number of balls or rollersfr= relative rev./s between races
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Journal bearings loose inhousing
Sub-harmonics of shaft rpm,exactly or 1/3 x rpm
Primarily RadialLooseness may only develop atoperating speed and temperature(e.g. turbo machines).
Oil film whirl or whip injournal bearings
Slightly less than half shaftspeed (42% to 48%) Primarily Radial
Applicable to high speed (e.g. turbo)machines.
Hysteresis Whirl Shaft critical speed Primarily Radial
Vibrations excited when passingthrough critical shaft speed aremaintained at higher shaft speeds.Can sometimes be cured bychecking tightness of rotorcomponents.
Damaged or worn gearsTooth meshing frequencies(shaft rpm x number ofteeth) and harmonics
Radial and Axial
Sidebands around tooth meshingfrequencies indicate modulation (e.g.eccentricity) at frequencycorresponding to sideband spacings.Normally only detectable with verynarrow-band analysis and cepstrum.
Mechanical looseness 2 x rpmAlso sub and inter-harmonics, as forloose journal bearings.
Faulty belt drive 1,2,3 & 4 x rpm of belt RadialThe precise problem can be usuallyidentified visually with the help of astroboscope.
Unbalanced reciprocatingforces and couplings
1 x rpm and/or multiples forhigher order imbalance
Primarily Radial
Increased turbulenceBlade and vane passingfrequencies and harmonics
Radial and AxialIncreasing levels indicate increasingturbulence.
Electrically induced
vibrations
1 x rpm or 1 or 2 times
synchronous frequency Radial and Axial
Should disappear when turning off
the power.
Figure 6:Table identifying common machinery faults and characteristic frequencies in terms of rotational speed.
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Evaluation of Rotating Machine Condition using ISO10816-3 Vibration Severity Standard
The ISO Committee have completely revised the old ISO2372 Vibration Severity Standard for evaluating in-
situ performance of rotating machines. The new standard: ISO10816-3accommodates the many changes thathave taken place in the design and operating frequencies of modern process machinery.
The vibration criteria in this standard applies to the machine sets, with for example steam turbine or electric
drives, having a capacity above 15 kW and operating between speeds of 120 RPM and 15000 RPM. Machine
sets covered by this standard include: (i) Steam Turbines with a capacity up to 50 MW; (ii) Steam turbine sets
with a capacity greater than 50 MW and speeds below 1500 RPM; (iii) Rotary Compressors; (iv) Industrial gas
turbines up to 3.0 MW capacity; (v) Pumps of centrifugal, mixed or axial flow type; (vi) Electrical motors of any
type and (vii) Blowers or fans, not of lightweight sheet metal construction.
Classification according to Machine Type and Application
Significant differences in the design; type or bearings and support structures requires a separation into
different groups. Machines in these groups may have horizontal, vertical or inclined shafts and can bemounted on rigid or flexible supports.
Group 1:Large machines rated above 300 kW; electrical machines with a shaft height H 315 mm. Group 2:Medium machines with a rated power above 15 kW up to and including 300 kW: electric machines with a
shaft height 160 mm H 315 mm. Group 3:Pumps with multi vane impeller and separate driver, rated above 15 kW capacity. Group 4:Pumps with multi vane impeller and integrated driver, rated above 15 kW capacity.
ISO10816-3 Vibration Severity Standard
RMS RMSV
elocity
10-1000Hzr>600rpm
2-
1000Hzr>120rpm
11 0.447.1 0.28
4.5 0.18
3.5 0.11
2.8 0.07
2.3 0.04
1.4 0.03
0.71 0.02
mm/sec. inch/s
rigid flexible rigid flexible rigid flexible rigid flexible FOUNDATION
Pumps > 15 kW radial, axial, mixed flowMedium sized
machines 15 kW