Condition Based Diagnostic Techniques for
Predictive Maintenance- A key of Success
to Paper Industry
by
Sanjay Tyagi, B. P. Thapliyal, R. M. Mathur and A. K. Ray
Central Pulp and Paper Research Institute, Saharanpur
Purpose of Maintenance of Industry
• Fundamental purpose of maintenance in any
process industry is to provide the required
capacity for production at the lowest cost.
• Should be regarded as a RELIABILITY
function , not as a REPAIR function
Objective of the Maintenance
To achieve the correct level of operational
reliability and best possible personal
safety at minimum cost
Cost of Maintenance in Few Industries
S. No.
Industries
Maintenance cost (%
of total sales)
1.
Pharmaceuticals Industry
16 %
2.
Car manufacturing
4%
3.
Chemical Industry
6%
4.
Engine manufacturing
7%
5.
Casting/Forging
8%
6.
Paper Manufacturing
10%
7.
Steel Industry
15%
8.
Electronics
2%
Classification of Maintenance
Time based
Maintenance (TBM)
Preventive
Maintenance
Condition bases
Maintenance
Maintenance
Breakdown
Maintenance or
corrective breakdown
Corrective or Break Down
Maintenance (Run to breakdown)
•
It covers the measures carried out in order to correct or repair
faults after they have occurred.
• Referred as “repair work” in everyday language.
• If industry running too many in expensive machines where
process duplicates , less of production is not significant as spares
machines can take care off production.
• In case of process industries like paper if large unduplicated
process machine run to breakdown it severely affected
production.
Time Based Preventive Maintenance
Plant management decides to take some actions with
the aim of preventing failure occurring or at least
reducing the chance of failure.
•
Maintenance on fixed or duty basis
• Opportunity Maintenance
• Design out maintenance
• Management Policy
• Experience has shown that in a vast majority
of cases, above time based maintenance is
UNECONOMICAL.
• Instead of the reducing failure rate of the
machine by replacing wear parts regularly, the
opposite often happens.
• Reliability of newly serviced machine is
reduced temporarily by the interference.
• As the actual failure pattern for each
individual machine cannot be predicted,
an individual approach is therefore
needed.
• Here role of ON-CONDITION maintenance
comes
On - Condition Maintenance
• Each machine is considered individually by making
fixed interval condition measurement to obtain a
quantitative value of the ‘health’ of the machine.
•
In this way servicing is only allowed when
measurements show it is necessary.
• Basis is that most mechanical components give
some warning of their impending failure.
Predictive Maintenance
•
Predictive
maintenance
technique
use
sensing
instruments to determine health in much the same
way a doctor uses medical instruments to determine
human health
•
Instead of stethoscope, blood pressure , X-rays , ECG
etc, Predictive maintenance use technologies like
Thermography , vibration analysis , oil analysis ,
ultrasonic measurements to gain early warning in
order to plan corrective action.
Why condition based diagnostic techniques
for predictive maintenance preferred ?
• Only 11-17% of failure are time or age related.
• On average 83 – 89 % of failure are random.
Today’s Maintenance is too Costly
• 65% of maintenance performed is corrective
• 30 % of maintenance is preventive of which
60% is unnecessary
• 5% is predictive
Use of condition based Predictive
maintenance has dramatically reduces
non- value added maintenance by
eliminating the need of unnecessarily
shutdown of the equipment for
maintenance checks
Principle of Condition Monitoring
Some techniques of Condition based Predictive Maintenance
•Thermography: infrared imaging to detect abnormal
temperature or hot spots.
•Vibration monitoring: accelerometer instruments can
be used to detect abnormal or high vibration
particularly in bearings.
•Oil Analysis: Analysis of oil can detect the
deterioration or breaking down of an internal
equipment part.
•Ultrasonic measurement: Use of ultrasonic
technologies to detect leaks or blockages on utility
system.
Vibration Monitoring
• Best known technique for rotating machines such
as pumps, air compressor steam turbine etc.
• All machines to have some level of small vibration
•
Increase in the level of vibration is the indication
of some mechanical fault in machine.
• Vibration analysis uses accelerometer instruments to
detect these vibration movements .
•
Results can be plotted (magnitude v/s frequency)
using a mathematical representation called Fast
Fourier's Transform (FFT). Which highlight the level of
vibration and identifies which frequencies they are
present in.
Relation Between Vibration and Mechanical Component
Typical vibration analysis FFT plot (magnitude vs. frequency)
21
• Vibration analysis plot contain multiple fault
frequencies
• Analyst
needs a detailed knowledge of the
operating characteristics of the equipment
(such as number of fan blades , RPMs, pulley
ratios, bearing types etc)
Following type of problems can be determined using
vibration analysis
• Unbalance of rotary components
• Mechanical looseness
• Misalignment of drive system , shafts etc.
• Belt deflection
• Bearing deterioration and gear wear
Machine Condition and Vibration Spectrum
ILLUSTRATED VIBRATION DIAGNOSTIC CHART(1/3)
PROBLEM
SOURCE
MASS UNBALANCE
PHASE
RELATONSHIP
TYPICAL
SPECTRUM
1×
RADIAL
REMARKS
(1)Force Unbalance will be in_phase and
steady.
(2)Amplitude due to unbalance will
increase by square of speed.
A.FORCE UMBALANCE
1×
RADIAL
(1)Coupling Unbalance tends toward 180
degree out_of_phase on same shaft.
(2)Amplitude may varies with square of
increasing speed.
B.COUPLE UNBALANCE
(3)And cause high axial vibration
as well as radial.
(1)Overhung Rotor Unbalance causes high
C.OVERHUNG ROTOR
UNBALANCE
1×
AXIAL &
RADIAL
1X RPM in both Axial and Radial.
(2)Axial reading tend to be in_phase
whereas radial phase reading might be
unsteady.
Cited from Technical Associate Co. USA
Machine Condition and Vibration Spectrum
ILLUSTRATED VIBRATION DIAGNOSTIC CHART(2/3)
PROBLEM
SOURCE
MISALIGNMENT
A.ANGULAR
MISALIGNMENT
B.PARALLEL
MISALIGNMENT
PHASE
RELATIONSHIP
TYPICAL
SPECTRUM
REMARKS
(1)Angular misaligment is characterized
by high axial vibration,180 degree
1× 2×
out_of_phase across the coupling.
(2)Typically will have high axial
AXIAL
1×
vibration with both 1X and 2X RPM.
2×
(1)Radial misaligment has similar
symptoms to Angular,but show high
radial vibration which approach 180
RADIAL
degree out_of_phase across coupling.
(2)2X often larger than 1X,but it depend
on coupling type and construction.
(3)Misaligment become severe,much higher
harmonics(4X-8X) can be generated.
C.MISALIGNED BEARING
COCKED ON SHAFT
1×
(1)Cocked bearing will generate axial
2×
vibration and cause the Twisting
AXIAL
1
2
3
4
2:00
5:00
8:00
11:00
motion with 180 degree phase shift
1
PHASE
4
top to bottom and/or side to side.
2
3
(2)Atempt to align coupling or balancing
will not alleviate vibration,Bearing
must be removed and correctly
installed
Cited from Technical Associate Co. USA
Machine Condition and Vibration Spectrum
ILLUSTRATED VIBRATION DIAGNOSTIC CHART(3/3)
REMARKS
(1) Eccentricity occurs when center of rotation
offset from a sheave,gear,bearing,motor,etc.
1X MOTOR
ECCENTRIC ROTOR
PHASE
RELATIONSHIP
TYPICAL
SPECTRUM
1X FAN
PROBLEM
SOURCE
(2)Largest vibration occurs at 1xRPM of eccentric
components in a direction thru centers of the
two rotors.
(3)Horizontal and vertical phase readings usually
differ either by 0 or 180 degrees.
RADIAL
(4)Balancing eccentric rotors result in reducing
vibration in one direction but increasing it
in other direction.
BENT SHAFT
1×
(1)Bent shaft cause high axial vibration
AXIAL
with axial phase difference tending
toward 180 degrees.
2×
(2)Dominant frequency component normally
1X if bent near shaft center,but at
2X if bent near the coupling.
Cited from Technical Associate Co. USA
Pressure Fluctuation Analysis of Pump
EXAMPLE OF BASIC EXPERIMENTAL DATA
Damaged
Vane
Good Pump
Damaged Pump
Damaged Pump
Pressure Fluctuation Analysis of Pump
EXAMPLE
Good
Pump
Pump
Pump
OF
BASIC
TEST
DATA
pump
with
with
cut
vane
slightly
causing
damaged
cavitation
vane
Pressure Fluctuation Analysis of Pump
EXAMPLE
Good
v
0.05
OF
FILED
TEST
DATA
condition
7
1
3
2
0
5
4
10
20
6
8
30
40
-0.05
Time
v
0.05
for
one
revolution
Pump
of
with
1
3
shaft
defected
impeller
7
4
5
2
6
9
8
0
-0.05
Time
for
one
revolution
Pump
v
0.05
with
of
shaft
eccentric
3
4
2
-0.05
Time
for
one
revolution
8
5
1
0
of
shaft
shaft
6
7
Thermal Imaging or Thermography
• Thermography is a temperature profiling of
surface or point based on IR Technique
• It is based on the principle that every object
units certain amount of IR energy and the
intensity of this IR radiation is a function of
temperature.
Thermal imaging is used primarily on electrical
panels to identify loose connection but now it
is use in other applications .
•
Checking for blockages in pipes.
• Carrying out heat survey in plants.
• Mill drive train misalignment
• Leakages from steam traps.
• Misaligned pumps.
What is Thermography?
The term "Thermography" refers to the capturing
of thermal patterns and data emitted by an
object with the use of an infrared imaging and
measurement camera.
An image is then produced with the camera that
can give you data that is otherwise unattainable.
Infrared Zoon
Wavelength 8 to 14 μm
What is Infrared?
Infrared light is not visible to the naked eye because infrared
wavelengths are too high on the electromagnetic spectrum.
The wave lengths are longer than those of visible light and
shorter than those of radio waves. This part of the
electromagnetic spectrum is what we perceive as heat or
“heat radiation”.
Infrared is mostly associated with “hot spots”, but did you
know that ANYTHING above absolute zero emits infrared
heat?
34
INFRARED CAMERA
Hot Connector Diagnostics
Thermal Image of Compressor
Use of Thermography in Maintenance
Monitoring of temperature and thermal patterns on
• Pumps
• Motors
• Bearings
• Pulleys
• Fans
•
Drives
• Conveyors etc while equipment is on line and
running under full load.
Condition Monitoring
Industrial pumps are known to work continuously
for many hours. If a pump stops working or starts to
wear, this can cost a factory much needed time.
Using an IR camera to monitor the temperature of
these type pumps, a maintenance worker can spot
troubled pumps BEFORE the failure and address
with little or no down time - saving you time and
money.
41
42
Thermal imge of Plastic moulding showing uneven cooling
43
Thermal Image of Ball Bearing
44
Advantage of Thermography
• It is non destructive and non contact type technique
• It gives fast, reliable and accurate measurements.
• Capable of catching moving targets in real time
• Large surface area can be scanned
• Measurement in areas inaccessible for hazardous for other methods
Disadvantages
• Duality cameras are expensive having + 2 or worsen accuracy
• Ability to only measure surface areas. Unable to detect the inside
temperature
Application of Thermography to Paper Industry
Steam Traps
Leakage from a steam trap
46
Liquid Storage Tank
Determination of liquid level
47
Pulley System
Hot drive belts
48
Web Process
In this web process, you can easily see the non-uniformity of the sheet along the right side
49
50
Motor Coupling
Thermal image showing high temperature rise in motor bearing due to
misaligned pump
Paper Roll
Thermal image of paper roll showing moisture variation
Tribology based Diagnosis Technology or
Lubricant Analysis
Tribology:- Branch of science dealing with lubricants and friction
in rolling system.
•
Tribology based diagnosis technology (Lubricant analysis) is
now becoming one of the major methods for maintenance
engineering.
Lubrication Program Followed in Industry
- Time based
- Oil Lubricant analysis
Lubricant Analysis
-
Lubricant analysis indicates when an lubricant change out is
required.
-
Allows condition based approach to lubricant change would
super cede the change frequency based on running hours.
-
High Iron content indicating wear and tear ( may require
further investigation of equipment)
-
Breakdown in oil additives
-
High water content
-
Change in viscosity levels.
Tribology based diagnosis technique give prediction
regarding machine wear out much earlier as compared to
other predictive maintenance techniques.
Damage process of machine and lubrication system diagnosis
Ultrasonic Measurement
What is ultrasonic detection?
• Sounds above 20 kHz are ultrasonic
• Ultrasonic detectors convert ultrasound to
audible sounds.
• Ultra sonic inspection can measure efficiency
and overall health of your production equipments.
• Most versatile maintenance technology available.
• Ultrasonic measurement instruments translate high
frequency sounds produce by steam or air leaks into
the audible range which can be heard through
headphones and can be visualized on meter on
display.
Use of Ultrasonic Testing for Steam Traps
•
Steam traps are temperature and condensate sensitive devices that open
or closes automatically to allow condensate passes to drain.
•
Steam traps can fail open (in this case both steam and condensate passes
to drain)
•
Steam traps fail closed (this result in internal build up of condensate in
steam line)
• The fail open steam trap can be detected by the ultrasonic frequencies
present from the steam and condensate continuously leaking through the
trap.
• Failed closed trap can be detected by the absence of ultrasonic frequencies
at the trap.
Acoustic Emission
• This is relatively new technique for the detecting the initiation
of cracks in machine structures.
•As crack is initiated propagated through material, a stress pulse
is generated and transmitted through a material, a stress pulse is
generated and transmitted through the material as stress wave.
•A transducer mounted on the surface, will detect the disturbance
and produce on electric out put.
•The source of the wave or location of the crack can be found by
using three or more transducers.
• The transducers detect high frequencies of 200 kHZ or
more. Counters with a threshold limit register a count
each time the signal level exceed the threshold values.
Several other parameters like rise time, event duration
etc. are also used for analysis
• Acoustic emission has been successfully used in a number
of applications testing of pressure vessels, detection of
leaks, cavitations detection, corrosion fatigue crack
detection, seal failure detection , detection of damage in
rolling .
Conclusions
• A diagnostic condition – based model can be used for
predictive maintenance of equipments and plants in
paper industry
• Condition monitoring based maintenance may be
component of total maintenance system,, involving
use of other maintenance strategies as well. It is also
to be a part of manufacturing system for machine
and production control.
• Predictive maintenance is widely accepted approach to the
maintenance strategy for paper mills. The benefits of PdM
can be extended to promotes a proactive approach to
maintenance. Not only in maintenance, this approach also
useful as energy conservation measure for plants.
• The above strategy would lead to economic benefits and
avoidance of unscheduled breakdowns and safety especially
for large capacity high speed machines.