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Predictive Maintenance (Predictive Testing and Inspection).

Predictive testing and inspections (PTI) is sometimes called

condition based monitoring (CBM) or predictive maintenance.

Predictive maintenance is : a management technique that uses

regular evaluation of the actual operating condition of plant

equipment production s!stems and plant management

functions to optimi"e total plant operation. (#iggins $%%&).

Predictive maintenance is the application of advance technolog!

to detect 'hen failures 'ill occur. (evitt $%%).

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)Maintenance Management ( EM 664

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The aim of predictive maintenance or (CBM) is:To predict 'hen equipment failure might occur

To prevent occurrence of the failure b! performingmaintenance.Monitoring for future failure allo's maintenance to be

planned before the failure occurs.

Predictive maintenance or (CBM) advantages is:Better planning of repairers is possible out of production

time.Inconvenient brea*do'ns and e+pensive consequential

damage are avoided.

The failure rate is reduced thus improving plant availabilit!and reliabilit!

The spares inventor! is reduced and parts are ordered 'hen

needed.,nnecessar! 'or* is avoided and equipment life is e+tended.

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Predictive maintenance or (CBM) disadvantages is:

#igh investment costs-dditional s*ills required

Conventional CM Techniques :

There are a host of techniques that can be used for direct(requiring access to the machine) or indirect

measurement each having its o'n advantages and

disadvantages.

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isual Inspection: This simple qualitative technique ma*es use of human senses such

as sight hearing and touch.

Most useful for detection of crac*s sub/surface defects corrosion

e+cessive noise and0or vibration loss of /belt drive and lea*age.

Portable instruments inspections:

,se of portable instruments tends to increase the consistenc! of

the results of different operators.

The problem is that different conclusions ma!

be dra'n for the same machine b! different

inspectors due to individual personal s*ills

and e+perience.

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Condition monitoring techniques

1ifferent predictive maintenance methods and techniques

such as:

ibration anal!sis

Temperature monitoring

-coustic anal!sis

Performance monitoring (Process Parameters)

1!namic c!linder pressure monitoring

Instantaneous angular speed (I-2) anal!sis

Infrared anal!sis ubricant anal!sis (oil anal!sis)

3lectrical condition monitoring.

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ibration and -coustics : The most common problems that

produce vibration and acoustics are:

,nbalance of rotating parts

Misalignment of couplings and bearings

Bent shafts

4orn eccentric or damaged partsBad drive belts and drive chains

Bad bearings

Torque variations

3lectromagnetic forces

-erod!namic forces

#!draulic forces

ooseness

5esonance.

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Parameter Measurement Transducers andInstrumentations

ibration Measurement using (-ccelerometers)6igures sho' online vibration data collection and anal!sis

t!pical of that used in industr! to detect and diagnose faults in

machines.

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-coustic Measurements ,sing (Microphones) :-irborne sound normall! using high/band'idth free/field microphone

operate in the frequenc! range up to $77*#".

T!pical sample of the online ra' data

from the microphone.

Time domain analysis of airborne acoustic signal Spectrum of airborne acoustic signal.

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High-bandwidth microphone

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1!namic C!linder Pressure Monitoring using (pressuretransducer )Previousl! the use of d!namic c!linder pressure as a diagnostic aid has often been seen

as being the concern of the specialist consultant a specialist diagnostic tool

#o'ever d!namic pressure as a condition/monitoring tool is e+tremel! po'erful

8nline pressure measurements and pressure data collectors used in industr! toda!.

Measured internal c!linder pressure signal is plotted against the cran* angle.

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Pressuresignals

from crankend

Online cylinder pressure data readings

Pressuresignal

from headend

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Instantaneous -ngular 2peed (I-2) Monitoring ,sing (2haft3ncoder)

2mall changes in shaft speed to be recorded.

The device produced a square pulse output for ever! angular degree

(thus the term 97 line encoder) for ever! complete revolution.

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!ncoder set up

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Temperature Measurement using (Thermocouples ;Infrared cameras)

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"herma#$% P6 &nfrared #amera(Courtesy of FLIR Systems Ltd, Kent,

UK) [66]

"hermal image of pulley'(earing(Courtesy of FLIR Systems Ltd, Kent,

UK

Online thermocouple digitaloutput

2nd

stage

1st

stage

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$mpli)er

#!* 141plus

+chematic diagram of the compressor test system

,emo )lter)lter$mpli)er

!ncoder

"hermocouple

One pulse - 36pulses

$ccelerometer

Pressure sensor%icrophone

"ank pressuresensor

"ank

Measurement Practice and 1ata Management in the ab.

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Measurement Practice and 1ata Management in the

ab.

2ignal processing: to handle the data or signals

collected for better understanding and interpretation

of the data using .The main methods for data anal!sis are:

Time/domain anal!sis

6requenc!/ domain anal!sis (2pectrum -nal!sis)Time/frequenc! anal!sis.

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DVOH

DVOH

DVOH

DVOH

DVCH

DVCH

DVCH

DVCH

Crank Angle (Deg)

-mplitude

*ischarge pressure .4 psi/


*ischarge pressure . psi/


Time/domain anal!sis

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6requenc!/domain anal!sis

Time < 6requenc! anal!sis

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Documents

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