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Main factor to be consider in the fan
during Operation & Maintenance otherthan routine Check
High gas temperature
Erosion or Wear and corrosion
Vibration
Fan Operation &maintenance
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The fan should not operate over above themaximum design temperature. If so
Material strength
Material yield strength, as well as creep andrupture strength, properties drop dramaticallywith slight increase in temperature.
Thermal expansion
With high temperature, loosening of hub inshaft may occur. Resulting vibration and
movement of the rotor on the shaft.
Thermal Fatigue
Fast rate of temperature change may cause
premature rotor failure because of Thermalfatigue.
Gas TemperatureEffect
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High Temperature corrosion
Sulfidation and carburization may occur andform surface pitting, embrittlement corrosion ofweld material.
Rotor inlet seal
Required more clearance to take care expansionor it will damage the inlet cone and rotor.
Expansion Joints
Expansion Joints are essential for hightemperature fan and it should be providedAdequate
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Shaft cooling and Seal Gland cooling is requiredfor fan operating at higher temperature (> 650deg C).
While heating or cooling we have to maintained
40 Deg C per hour rate.
In Emergency Shutdown, it is important that thefan should be rotated at 40 rpm rate until the
gas temperature decreases to 100 Deg C. Otherwise it will lead to permanent distortion of theshaft.
General Procedure
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Erosion (Wear) is a major problem in induced draftfans while handling dust mixture gas.
High dust loading combined with high inlet velocitiescan result in dangerous Break downs
To avoid Erosion wear liners will help, but while
selecting the system the following points shouldbe considered to minimize the problem.
Reduce the particulate (dust) flow rate
Reduce the average particle size
Install high efficiency dust collector to separatethe dust from air stream.
Cause of Erosion
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The kinetic energy (KE) generated over theparticles is square of the velocity.
Reduce the gas (with dust) velocity at fan inlet.
For reducing the fan inlet velocity we have to selectlower speed fan and larger diameter fan
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We can select Double inletfan instead of single inletfan to reduce the fan inletvelocity.
For clean air application,we can use Mild steel
material.
Bolting type wear liner is not safe for high speedand long operating hours fans.
Chequred pattern hard facing will not solve full
wear problem.
For dusty air we have to use hard facing impeller.
Some Hard facing electrode for fanL&T CPE-063 Diffusion-Abroloy 3000D
Advani
Weld arc SV-6 Wear Resist
XL-CC 60
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Vibrationis a destructive force that leads to thepremature failure of rotating machinery.
Vibration will degrade weaker machine components
until the eventual collapse of the mechanical system.
If allowed to progress to extreme levels, bearinghousings and pedestals, shafts, foundations, andvirtually every connecting member to the machine is goto severe damage.
Vibration is a periodic back-and-forth motion of amachine or Machine parts.
Usually, the first casualties are machine parts likebearings, couplings and mechanical seals
Vibration
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If the part responsible for the vibration can withstandgreater loads than associated machine components, itcould lead to premature failure of these componentswith little damage to the offending part.
For example, gears and couplings can usuallywithstand greater loads than their support bearings.
Vibration is accurately defined by all these commonterms: swinging back-and-forth, oscillating,unbalanced, vibrating and shaking.
Vibration occurs when a machine or machinecomponent moves from its neutral position ornormal position of rest to a lower and upper extremelimit of travel.
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Forced vibrations occur if a system is continuously
driven by an external agency
Vibrations fall into two categories, free and forced
Free vibrations occur when the system is disturbedmomentarily and then allowed to move withoutrestriction.
The cause of vibrations must be due to force, Whichchange its direction or its strength. So each case thevibration has different characteristics.
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Vibration FrequencyIs Number of cycle happenedfor a particular time.
VibrationTerminology
Time
1 Cycle Displacement
Vibration Displacement
Is the total distance traveledby the vibration part from oneextreme limit to other limit(Peak-Peak displacement)
Expressed inMicrons(0.001 mm)
Expressed inCPMCycle per minute)
1 Hz = 1 CPS = 60CPM
Vibration VelocityIs the peak speed of partsdisplacement, which is high atneutral point. Expressed inmm/sec
Peak velocity
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Vibration AccelerationDuring vibration the weightreach zero velocity at peakpoint and again accelerate thespeed after turning thedirection is Vibration
acceleration.
Vibration Terminology
Peak Acceleration
PhasePhase is defined as theposition of a vibration part at a
given instant with reference toa fixed point or anothervibrating part.
Expressed ingie
9.81 m/sec2
Expressed inDegreei.e. 0 deg to 360 deg
Phase = 180 DegPhase = 90 DegPhase = 0 Deg
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Displacement !, Velocity !, or Acceleration ! Whichparameter should we use to monitor the fan health?
Displacement (D) , Velocity (V) , and Acceleration (g)are directly related one to each other along withFrequency.
Velocitypeak= 52.3 * Displacement Peak* Frequency * 10 31000
gpeak= 5.6 * Displacement Peak* Frequency * 10 4
1000
In practical we can directly measure the velocity andacceleration, so the above formula is shown to explainthe relation.
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When a sheet metal is bent repeatedly frontand Back the folding area fail in to fatigue
and break
Increasing the amount of the bending(Displacement) the sheet is more likely to fail
Increasing the rate of bending (Frequency) thesheet is quicker to fail
So the failure severity of sheet metal is depends onamount of displacement and rate of frequency.
Like that Vibration severity is a function ofDisplacement and Frequency i.e. Velocity
Velocity in mm/sec is the Overall Indicator of
Machinery Health.
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Vibration measurementshould be taken in rotorsupport bearing in three
position.
The velocity measured in bearing is show the
combination of vibration level of different parts, likeshaft, bearing, Housing, pedestal and foundation.
Also it may be the combination of different cause.
Axial Inline with shaft
Radial (H) HorizontalPerpendicular to shaft
Radial (V ) VerticalPerpendicular to shaft
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Vibration AmplitudeVibration frequency is a measure of how often amachine or machine component oscillates.Vibration amplitude is a measure of how much orhow far it travels back-and-forth.
The distance traveled, or vibration amplitude can be
measured as a Peak, Peak to Peak or RMS value.Peak (Pk) amplitude measures the amount of travelfrom the neutralposition to the upperextreme limitof travel or from the neutralposition to the lower
extreme limit of travel.
Peak-to-Peak (Pk-Pk) amplitude is the totalamount of travel from the upperextreme limit oftravel to the lowerextreme limit of travel.
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RMS amplitude is Root Mean Square of peak value.
RMSamplitude measures the amount of travel from
the neutralposition to 70.7% of the extreme limit.RMS = 0.707 * Peak or Peak = 1.414 *RMS
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The Vibration may be cause for the following reason.
Unbalance
Misalignment
Bent shaft
Mechanical LoosenessDefective Bearings
Rubbing
Electrical defects
Dynamic air force
Foundation and soil
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Chennai720KHz
Trichy
936KHz
Madurai
1050KHz
Nellai
1150KHz
All rhythms andPitch match to the
Desired level,We get a good Music
The level of Pitch and Speed of music willVary for Karnatic or Western or Pop
Like that Machine parts Vibrate differentfrequency. So each machine have some limitsfor safe vibration
Like that If Machine parts Vibrate to a desiredlevel the machine health condition is OK.
If one station pitch or speed is not match itwill affect Quality of music.
Like that If one part faulty the vibrationVelocity will Increase
To Locate the fault or Which Station Wehave to tune individual frequency andIdentify the Station Which create the fault.
Like that to Locate the faulty part, We haveto analyze the displacement with differentfrequency.
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The Vibration severity level for Fans0 2.5 mm/sec Excellent2.5 6.0 mm/sec Good6.0 - 12.5 mm /sec AlarmMore than 12 .5 mm/sec Shutdown
The Safest level of Vibration in Terms of Velocity is
