MAINTENANCE - Oil India · Maintenance based upon known condition : Redesign to eliminate root...

PRESENTATION

ON

CONDITION MONITORING

By. A.BHAGAWATI

MAINTENANCE •ON FAILURE

•FIXED TIME(PREVENTIVE) •PREDICTIVE •DESIGN OUT

STRATEGY

Upto 1920s : On Failure maintenance 1920-1960s: Preventive Maintenance 1970s : Predictive Maintenance 1985 : TPM- Zero Defects - Zero Breakdown

STRATEGY On Failure Fixed time Predictive Design Out

Definition Fix it when it breaks

Conduct maintenance at regular intervals

Maintenance based upon known condition

Redesign to eliminate root cause of failure

Advantage (when implemented correctly)

Cheap, No pre care or management

Can be planned for spares, labour

Spot a potential failure

Less maintenance required

Disadvantage (when implemented wrongly)

High stock level, loss of production, Unsafe

Unnecessary replacement of parts, spares, can induce failure

Costly if implemented incorrectly.

Cold be highly expensive

Examples Headlights, Streetlights

Oil change Bearings M/c undergoing repetitive failure (Seal)

PREDICTIVE MAINTENANCE

• ADVANTAGEs • Impending equipment failure

can be detected • Can run equipment to near

failure • Maintenance can be planned • Root cause can be detected,

scope for redesign

• DISADVANTAGEs • Can be costly if

implemented wrongly

INTRODUCTION • Human Condition Monitoring - Heart beat, pulse, Pathology, Usg • Industrial Condition Monitoring Early Bearing Condition Analyzer- Screwdriver 1850: Railroad wheel tappers 1945: Oil Analysis, Canadian P. Railways 1970s: Established use of Vibration, Oil analysis, Thermal Imaging 1983: First PC based CM system

CM TOOLS

• VIBRATION ANALYSIS • WEAR DEBRIS MONITORING • THERMOGRAPHY

VIBRATION MONITORING

• Versatile Tool for CM for rotating and reciprocating equipments

• Wide range of techniques and instrumentation • Careful selection & application of techniques

essential for success.

PROBLEM IDENTIFICATION • Unbalance • Misalignment • Looseness • Defective Bearings • Resonance • Eccentricity • Bend shaft • Worn gears • Drive belt problem • Distortion (Soft-foot & Piping strain) • Motor Electrical Problem

VIBRATION • All machines vibrate. • An increase in vibration level is a sign

of trouble & amplitude of vibration depends upon the extent of defect in the machinery component

• Each trouble will create vibration with different characteristics

VIBRATION FUNDAMENTALS • What causes vibration: Induced force & freedom for

movement • It is the motion of mechanical parts back & forth from

its position of rest/neutral position • HARMFUL EFFECTS Increased load on BRGs, reduced BRG life Higher forces on mountings, foundation loosening &

damage of support structure Increased stresses of M/c; Risk of fatigue Decreased equipment efficiency Increased maintenance cost due to more component

failure & unplanned operation Reduced output quality-REJECTION BY QC Unsafe operating Environment

CHARECTERISTICS OF VIBRATION

• AMPLITUDE • FREQUENCY • PHASE Amplitude : Magnitude of Vibration - Displacement (Micron) - Velocity (mm/sec) - Acceleration (g) - Spike Energy (gSE)

AMPLITUDE • RMS: Energy contained in the time wave form • PEAK: 1.41 * RMS • PEAK-TO-PEAK: 2 * PEAK • AVERAGE: Area under curve

FREQUENCY • Period of Vibration is the Time required to

complete one full cycle • Frequency = 1/ time period • If the time required to complete one cycle is

1/60 th of a second, frequency : 60 cycles per second or 60 CPS or 60 Hertz (1 CPS=1 Hertz)

• Vibration frequency is measured in Cycles per minutes (CPM) as it is easier to relate this characteristic to rotational speed of the machine

Hence a vibration occuring at 60 Hz will be expressed occuring at 3600 CPM (1 * RPM)

PARAMETER SELECTION

• Frequency sensitivity Displacement up to 600 CPM Velocity 600-60000 CPM Acceleration > 60000 CPM Spike Energy Ultrasonic range

DISPLACEMENT vs VELOCITY vs ACCELERATION

DISPLACEMENT VELOCITY ACCELRATION

Sensitive to low frequencies. Good guide for imbalance & other low frequency faults

Has average sensitivity th’out frequency range, sensitive for imbalance, misalignment, looseness & later stage of rolling element bearing damage

Sensitive to high frequencies. Good guide for rolling bearing damage, gear related problems & cavitations etc.

BENDING OF A WIRE • Consider the example of repeatedly bending a piece of wire, there are two ways to

reduce the time required to achieve fatigue. One is to increase the distance (DISPLACEMENT) that the wire is bent. The farther the wire is bent each time, the less time it will take to reach fatigue. The other is to increase the number times per minute or second (FREQUENCY) the wire is bent. The more times per minute the wire is flexed, the less time it will take to reach fatigue failure. Thus the severity of vibration is dependent on both Displacement and Frequency.

• An example: a vibration of 6 mils at 120 CPM would be in the GOOD range where as the same vibration at 3600 CPM is considered VERY ROUGH. Hence severity of vibration not only depends on displacement but also on frequency.

• Benefits of Vibration Velocity Measurement over displacement: Vibration velocity is a direct indicator of fatigue since it takes into account both

displacement and frequency. It is not necessary to know the frequency of vibration in order to evaluate the severity

of vibration velocity since frequency is already a part of velocity. A measurement of overall vibration velocity is a valid indicator of the overall

condition of a machine whether the vibration is simple (one frequency) or complex (multiple frequency).

SUMMATION-1 Low Displacement & very high frequency

Accln=d*f*f is very high. Failure is due to applied force

Monitor acceleration

Medium velocity & medium frequency

Velocity= d * f Failure is due to fatigue

Measure velocity

High displacement & low frequency

Vel. is moderate, no fatigue Accln is Low, no failure due to applied force. Failure is due to Stress.

Measure displacement

FREQUENCY ANALYSIS • Characteristics of the Oscillating force caused by individual M/c defect is the

frequency of the oscillating force. • Frequency of vibration is equal to the frequency of this force. • Frequency of vibration is therefore indicative of the type of m/c defects. • Normally any m/c undergo different kinds of defects at a time. • Only the severity of different defects are of different extent. • Vibration components of different frequencies (which is characteristics of the defect)

therefore are present in the m/c simultaneously. • Overall vibration is therefore the resultant of the vibration components of different

frequencies. • In frequency analysis, the overall vibration is sensed.. • Does mathematical calculation to find out the individual vibration components. • Calculate amplitude & frequency of the individual vibration components & display

the information in graphical manner. • The technique is sometime referred to as Spectrum analysis/signature analysis. • FFT TRANSFORM (FAST FOURIER TRANSFORM) • The process of transforming time domain signal to frequency domain. • Time domain signal must first be sampled and digitalized.

SPIKE ENERGY • A measurement parameter designed to detect low amplitude

transient impacts generated within the audiosonic/ultrasonic frequency range by microscopic surface flaws in rolling element bearing and gears.

• The acceleration signal is processed via a high pass filter& a peak detection circuit to produce a numerical value which is the product of : The number and amplitude of the impacts in a unit of time.

• The value is expressed in gSE (IRD) dB (Shock Pulse-SPM) • It is primarily bearing condition monitoring parameter

PHASE • The position of a vibrating part at a given instant w.r.t. a fixed point or

another vibrating object. • The part of a vibration cycle through which one part of object moves relative

to another part. • The unit of phase is degree where one complete cycle of vibration is 360

degree. • Phase analysis Applications: Conforms m/c defect Distinguishes misalignment Vs Bent shaft Distinguishes unbalance Vs eccentricity Detects mechanical looseness Detects resonance Detects type of unbalance Used for balancing.

ADVANCED TECHNIQUES

• Phase Analysis • Time wave analysis • Amplitude Vs Time analysis • Amplitude Vs Phase Vs RPM • Bode Shape analysis • Orbit analysis

CHART Frequency in Terms of RPM

Most Likely cause

Other possible reason

1 * RPM Unbalance

2 * RPM Looseness

3 * RPM Misalignment

<1 * RPM Oil whirl

Synchronous Electrical Prob

2 * syn Fr Torque pulse

Harmonics Bad gears

Very High Fr Bad Bearing(AF

VIBRATION STANDARD

• Published Standard-ISO 2372 • Manufacturer’s guidelines • Comparison • Trending

WEAR DEBIS ANALYSIS • All machines wear out • To predict internal condition of machine in a non intrusive way

by the study of worn particle or debris • SCOPE:Determines: When abnormal wear has begun Root cause of wear/failure Which component is failing Requirement of lubricant replacement Suitability of lubricants Seal/Filter condition CAN PROVIDE EARLIEST DIAGNOSTIC WARNING_

BEFORE VIBRATION CAN SENSE DANGER

7 STEPS FOR WDA

• Sample collection • Codification • Physical & Chemical Test • Incubation • Slide preparation • Microscopic examination • Report Preparation

WDA METHODS • Spectroscopy • Ferrography • Magnetic Plug FERROGRAPHY -Particle Quantifier -Analytical Ferrography- severity of wear Mode of wear size of wear concentration of wear component under wear

THERMOGRAPHY

• Thermography (Thermal imaging) is a methode of redefining the appearance of an object in terms of temperature

• An infrared camera generates only B & W image. By using a complicated algorithms this is converted to colored image.

• A colored thermogram gives immediate feeling of temperature

THANK YOU

A. Bhagawati