Condition Based Diagnostic Techniques for Predictive Maintenance- A key of Success to Paper Industry...

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

Maintenance

Preventive Maintenance

Breakdown Maintenance or corrective breakdown

Time based Maintenance (TBM)

Condition bases Maintenance

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

•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.

Some techniques of Condition based Predictive Maintenance

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)

• 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

PROBLEMSOURCE

MASS UNBALANCE

A.FORCE UMBALANCE

B.COUPLE UNBALANCE

C.OVERHUNG ROTORUNBALANCE

TYPICALSPECTRUM

PHASERELATONSHIP REMARKS

RADIAL

RADIAL

RADIAL

ILLUSTRATED VIBRATION DIAGNOSTIC CHART(1/3)

1×

1×

1×AXIAL &

(1)Force Unbalance will be in_phase and

steady.

(2)Amplitude due to unbalance will

increase by square of speed.

(1)Coupling Unbalance tends toward 180

degree out_of_phase on same shaft.

(2)Amplitude may varies with square of

increasing speed.

(3)And cause high axial vibration

as well as radial.

(1)Overhung Rotor Unbalance causes high

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

PROBLEMSOURCE

TYPICALSPECTRUM

PHASERELATIONSHIP REMARKS


1×

MISALIGNMENT

A.ANGULARMISALIGNMENT

1× 2×

AXIAL

RADIAL

2×

1× 2×

AXIAL1

23

4

PHASE

1 2:002 5:003 8:004 11:00

MISALIGNMENTB.PARALLEL

C.MISALIGNED BEARINGCOCKED ON SHAFT

(1)Angular misaligment is characterized

by high axial vibration,180 degree

out_of_phase across the coupling.

(2)Typically will have high axial

vibration with both 1X and 2X RPM.

(1)Radial misaligment has similar

symptoms to Angular,but show high

radial vibration which approach 180

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.

(1)Cocked bearing will generate axial

vibration and cause the Twisting

motion with 180 degree phase shift

top to bottom and/or side to side.

(2)Atempt to align coupling or balancing

will not alleviate vibration,Bearing

must be removed and correctly

installed



PROBLEMSOURCE

TYPICALSPECTRUM

PHASERELATIONSHIP REMARKS


ECCENTRIC ROTOR

BENT SHAFT

1XMOTOR

1XFAN

RADIAL

1×

2×

AXIAL

(1) Eccentricity occurs when center of rotation

offset from a sheave,gear,bearing,motor,etc.

(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.

(4)Balancing eccentric rotors result in reducing

vibration in one direction but increasing it

in other direction.

(1)Bent shaft cause high axial vibration

with axial phase difference tending

toward 180 degrees.

(2)Dominant frequency component normally

1X if bent near shaft center,but at

2X if bent near the coupling.



Good Pump Damaged Pump Damaged Pump

DamagedVane

EXAMPLE OF BASIC EXPERIMENTAL DATA

Pressure Fluctuation Analysis of Pump

Good pump

Pump with cut vane

Pump with slightly damaged vane

Pump causing cavitation

EXAMPLE OF BASIC TEST DATA


0

0.05v

-0.05

0

0.05v

-0.05

0

0.05v

-0.05

1

2 3 4 5 6

7

8

10 20 30 40

1

2

3 4 5 6

7

8 9

12

3 4

5 6 7

8

Time for one revolution of shaft



EXAMPLE OF FILED TEST DATA

Good condition

Pump with defected impeller

Pump with eccentric shaft


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 ZoonWavelength 8 to 14 μm

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

What is Infrared?

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.

41

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.

Condition Monitoring

43

Thermal imge of Plastic moulding showing uneven cooling

44

Thermal Image of Ball Bearing

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

46

Leakage from a steam trap

Application of Thermography to Paper Industry

Steam Traps

47

Liquid Storage Tank

Determination of liquid level

48

Pulley System

Hot drive belts

49

Web Process

In this web process, you can easily see the non-uniformity of the sheet along the right side

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.

THANKS

Condition Based Diagnostic Techniques for Predictive Maintenance- A key of Success to Paper Industry...

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