Predictive maintenance

Fundamentals of Predictive Maintenance

January 2008

Introduction To Predictive Maintenance

Ejercicios de ¿Qué Pasa Si? y de Diagnóstico y Solución de ProblemasF

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Introduction

• The purpose of this course is to introduce and provide individuals with an overview of predictive maintenance and a basic understanding of the methods and tools required..


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Objectives• This course will present the following topics:

– Define predictive maintenance programs– Define maintenance planning requirements and

review Critical Path Method (CPM)– Examine the principles of Vibration Theory and

Analysis.– Examine the basics of Lubrication and Analysis

(Tribology).– Examine the basics of Ultrasonic Analysis– Examine the basics of Thermographic Analysis– Examine the principles of Electrical Insulation

Testing– Define inspection and performance

measurement techniques


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Agenda

• Predictive Maintenance

• Maintenance Planning

• Vibration Analysis

• Performance Monitoring

• Thermal Analysis


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Agenda

• Lubrication and Tribology (Fluid Analysis)

• Non-destructive Testing and Inspection

• Ultrasonic Measurement• Insulation Testing • Balancing• Review


Predictive Maintenance


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Objectives

• – Define preventive maintenance.– Define predictive maintenance.– Define patterns of failure– Define condition monitoring


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Terms

• PM means Preventive Maintenance

• PdM means Predictive Maintenance

• PPM or P/PM means

• CMMS means Computerized Maintenance Management System


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How to View Maintenance

• Engineering

• Economic

• Management

• What else?


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PM

• PM (Preventive Maintenance) is a series of tasks which are performed at sequence of time, quantity of production, equipment hours, mileage or condition for the purpose of:– Extending equipment life– Detect critical wear or impending

breakdown


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PdM

• PdM (Predictive Maintenance) is any inspection carried out with technological tools to detect when failures will occur.


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Misconceptions about PM

• PM is the only way to determine when and what will break down.

• PM systems are the same

• PM is extra work/costs more.

• Unskilled people can do PM tasks

• PM is obsolete due to new technology

• PM will eliminate breakdowns


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Task Lists

• The task list is the heart of the PM system.– What to do– What to use– What to look for– How to do it– When to do it


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Common Tasks

1. Inspection 7. Take Readings

2. Predictive Maintenance 8. Lubrication

3.Cleaning 9. Scheduled Replacement

4. Tightening 10. Interview Operators

5. Operate 11. Analysis

6. Adjustments


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Patterns of Failure

• Random

• Infant mortality

• Increasing

• Increasing then stable

• Ending mortality

• Bathtub


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Bathtub Chart

Normal Life

Break InOr

Start -up

Break Down Cycle

Time

Nu

mb

er

of

Fa

ilure

s

Critical wear point


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Predictive Maintenance - PdM

• What do we mean by Predictive Maintenance?

“to declare or indicate in advance”


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PdM Definitions

• Any inspection (condition based) activity on the PM task list is predictive. Condition

• Predictive Maintenance is a way to view data


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PdM Program• A Predictive Maintenance programs is the

active condition monitoring approach

This requires a program to:– Regularly monitor the mechanical condition

of all critical production equipment.– Identify outstanding problems.


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Equipment Condition Monitoring

• Vibration analysis.

• Thermography..

• Fluid analysis (tribology).

• Visual inspection.

• Operational-dynamics analysis.

• Electrical monitoring.

• Failure analysis.


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Condition Monitoring

• Temperature

• Vibration

• Changes in noise or sound

• Visually observed changes and problems


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Temperature


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Vibration

Vibration Probe

Screwdriver

Listen


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Vibration ProblemsMany vibration problems can be solved by studying the history of the machine:

– operational changes– maintenance changes

•Talk to the operators and maintenance people, and review the maintenance records.• Knowledge of the machine and its internal components will be of value in this diagnosis


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Sound/Noise• Listening• Sound Measurements

Sound Intensity and the Human EarChange in Sound Density

Human Ear Response

1 dB Detect change under controlled conditions

3 dB – 5 dB Noticeable difference in loudness

6 dB Significant increase in loudness

10 dB Appears almost twice as loud to the human ear

10 dB – 20 dB Unbelievably louder

Example: a 6 dB change in sound intensity will be a significant increase in loudness or a 10 dB change in sound intensity is 3.162 x sound pressure, or almost twice as loud as the original sound heard.


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Sight

Cracked Housing

Seal Problem

Leaking Lubrication

Loose Bolts

Loose Bearing Housing


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Summary

• Review Objectives

• Question and Answer session


Maintenance Planning


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Objectives

– Define Maintenance Improvement and Reliability Programs (MIRP)

– Define Critical Path Method (CPM)– Define Program Evaluation and Review

Technique (PERT)


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Maintenance Program Objectives• The primary objectives of any maintenance

program’s activities include:– To ensure that the equipment operates safely and

relatively trouble-free for long periods of time.– To maximize the availability of machinery and

equipment necessary to meet the planned production and operational objectives.

– To consistently maintain the plant equipment in order to minimize wear and premature deterioration.

– To make the equipment reliable so it can be counted on to perform to set standards and conditions.


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Maintenance Plans

• Long range planning

• Short or Mid-range planning

• Immediate planning


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Maintenance Improvement and Reliability Programs

• The following ten steps outline a plan when a company is considering developing an effective Maintenance Improvement and Reliability Program (MIRP).


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1- Initialization

• Step 1: Begin by initiating a “total maintenance” approach. Production and maintenance must collectively work together.

• The maintenance department has to be viewed as being an integral part of the organization.


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2 - Clear Vision

• Step 2: Establish a clear vision by having the employees and management identify the problems.

• Then specify the goals and objectives that must be set in order to achieve success.


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3 - Analyze

• Step 3: Analyze the organization. – Will the organization, as a whole, support

the type of improvements required? – If not, consider changing the organizational

structure and/or redesign the system to meet the identified needs.

– Review the production and operational policies and procedures, as they may not be suited to the maintenance improvement and reliability program.


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4 - Develop

• Step 4: Begin to develop an ‘action plan.” – Identify what is going to be attempted, who

is to be involved, what are the resources required, etc.

– Action plans take on many different forms, but it is important that the plan contain inputs drawn from the reviews and analysis rather than from complaints.


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5 - Assess

• Step 5: Assess the condition of the equipment and facilities. – Be objective in the assessment.– Determine which equipment requires

immediate attention.


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6 - Select• Step 6: Select the appropriate maintenance

program. is a computerized maintenance system needed? – What technique will be employed, - reactive,

preventive or predictive maintenance?– Determine the order maintenance activities will be

carried out, first, then second, etc.? – What type of reporting system will be used to track

and record the data collected when measuring the performance of each piece of equipment?


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7 - Measure

• Step 7: Measure equipment condition.

• When measuring for equipment condition which method(s) will be considered:– vibration analysis?– fluid analysis?– non-destructive testing?– performance monitoring methods?


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8 - Prepare• Step 8: Prepare the maintenance

personnel. – As the maintenance program activities and

methods are implemented ensure that the maintenance personnel are:

• trained to understand the program• why the activities and methods are performed.

– Without this step no type of maintenance improvement and reliability program will succeed.


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9 - Monitor• Step 9: Monitor equipment and machinery

effectiveness to the detail the maintenance program requires.

• Monitor for:– performance– reliability– quality

• Over time, the recorded information can be used to evaluate the machinery and equipment condition and situation.

• This is an on-going activity of any quality maintenance program.


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10 - Review• Step 10: Initiate periodic reviews• Equipment and machinery effectiveness is

based on scheduled predictive and preventive maintenance activities.– The review of these activities may indicate common

problems and trends which identify any design or operational changes required.

– Include engineering, maintenance and production personnel in these periodic reviews.

– Ensure that action plans develop from these review sessions, not just complaints.


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Critical Path Method - CPM

• Flow chart method of representing specific job activities of a project

• Questions to ask:– How long will it take to complete the

project?– Which tasks determine total project time?– Which activity times should be shortened or

how many resources should be allocated to each activity?


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Why use CPM?

• Which tasks must be carried out

• Where parallel activity can be done

• Shortest time of a project

• What resources are needed

• Sequence of tasks

• Scheduling and timing

• Priorities


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Building a chart

List tasks and relation

ships

Create start node

Draw arrow from start to

first task

Sequentially arrange all tasks

from start

Repeat process from successors

to all tasks

Check for missed relationships


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Example chart

1 2

9

3

11

5

7

6

8

10

12 13 14 18

15 16 17 19 20

4

0-0 4-4

14-56

4

2

6-6

2

28-52

40

8

46-46

10

1

5-13

4

4

2

4

10-51

36

16

41-49

2 2

47-55

44-53

54-5457-57

3 3 2

2

3 2

2

60-60

49-57

52-60 62-62

8

70-70

18-60

CRITICAL PATH: 1 - 2 – 9 10 – 12 – 13 – 14 19 - 20

TURBINE OVERHAUL (EXAMPLE)

Earliest start time followed by latest start time

Estimated job time

Critical job time


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Task durations

• Early Start

• Early Finish

• Late Start

• Late Finish


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Example Table of Times

Work Segment Number

Work DescriptionEstimated Job time

Earliest Start Time

Latest Start Time

Earliest Finish Time

Latest Finish Time

FloatCritical Work

1-2 Check Stand – by Unit No:

4 0 0 4 4 0 4

2-3 Check Rebuild Calibrate gauges

10 4 4 14 14 0

2-5 Dismantle Unit No:____. Casing

1 4 4 5 5 0

2-9 Dismantle Unit No:____ Rotor

2 4 60 20 60 42 2

3-4 Inspect Clean Control Lines 4 14 56 18 62 42


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Program Evaluation and Review Technique

• The Program Evaluation and Review Technique (PERT) is a network model that allows for randomness in activity completion times. It has the potential to reduce both the time and cost required to complete a project.– PERT was developed in the late 1950’s for

the U.S. Navy’s Polaris project having thousands of contractors.


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• A PERT chart is a tool that facilitates decision making; The first draft of a PERT chart will number its events sequentially in 10s (10, 20, 30, etc.) to allow the later insertion of additional events.

• Two consecutive events in a PERT chart are linked by activities

• The events are presented in a logical sequence and no activity can commence until its immediately preceding event is completed.

• The planner decides which milestones should be PERT events and also decides their “proper” sequence.

• A PERT chart may have multiple pages with many sub-tasks.


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Terminology

• Critical Path

• Critical Activity

• Lead time

• Lag time

• Slack

• Fast tracking

• Crashing critical path

• Float


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Pert Activity

• A PERT activity: is the actual performance of a task. It consumes time, it requires resources

• Optimistic Time (O)

• Pessimistic Time (P)

• Most likely time (M)

• Expected time (TE)– TE = (O + 4M + P) ÷ 6


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Implementing PERT• First, determine the tasks that the

project requires and the order in which they must be completed.

Activity Predecessor Opt.O

Norm.M

Pess.P

TE

(o + 4m + p)/6

a -- 2 4 6 4.00

b -- 3 5 9 5.33

c a 4 5 7 5.17

d a 4 6 10 6.33

e b, c 4 5 7 5.17

f d 3 4 8 4.50

g e 3 5 8 5.17


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Chart

• Once this step is complete, one can draw a Gantt chart or a network diagram


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PERT Network Diagram

10 30

40

50

20

DF

E

C

t=2 mo

t=3 mo

t=1 mo

t=4 mo

t=3 mo

A

B


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Hasse Diagram


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Summary




Vibration Analysis


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Course Objectives

• Define the need for analysis

• Define the cause and effects of equipment vibration

• State how vibration is measured


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Benefits from Vibration Analysis

• Identifies early stages of machine defects such as:– Unbalance of Rotating Parts

– Misalignment of Couplings & Bearings

– Bent Shafts

– Bad Bearings – Anti Friction Type

– Bad Drive Belts and Drive Chains

– Worn, Eccentric, or Damaged Gears

• Provides for time to plan maintenance activities

• Saves Cost of Unnecessary Repairs

• Evaluates work done

– Loose or broken parts

– Torque Variations

– Improper Lubricant

– Hydraulic or Aerodynamic Forces

– Rubbing

– Electrical problems

– Resonance


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Vibration CbM Philosophy

• Based on three principles:– All rotating equipment vibrates– Vibration increases/changes as equipment

condition deteriorates– Vibration can be accurately measured and

interpreted


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Causes of Vibration:• Forces that change in direction with time (e.g.,

Rotating Unbalance)• Forces that change in amplitude or intensity

with time (e.g., Motor Problems)• Frictional Forces (e.g., Rotor Rub)• Forces that cause impacts (e.g., Bearing

Defects)• Randomly generated forces (e.g., Turbulence)


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When Condition of Machinery Deteriorates

• Dynamic forces increase, cause increase in vibration– Wear, corrosion, or buildup of deposits increases

unbalance– Settling of foundation may increase misalignment

forces

• The stiffness of the machine reduces, thus increasing vibration– Loosening or stretching of mounting bolts– Broken weld– Crack in the foundation– Deterioration of grouting


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Vibration Demonstration

• Vibration-Single spring and weight in suspension

Upper Limit

Neutral Position

Lower Limit

Spring

Weight at complete rest

Weight

Time


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A Word About BearingsThe vast majority of bearings are one of two types: Fluid Film Bearings and Rolling Element, or “Anti-friction” Bearings

bearing housing

Bearing

bearing housing

Oil Wedge (load zone)Soft Metal

(Babbitt)

Eddy Current ProbeAccelerometer

FLUID FILM: Capable of supporting very high loads, high temperatures, high speed. Expensive and associated rotor dynamics are very complex.

ROLLING ELEMENT: Low cost, simple to apply. But are capable of only moderate speeds and relatively light loads. Rotor dynamics aren’t bad but diagnostics can be complex due to all those spinning balls!

Bearing


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Sensors & Units

Displacement

Velocity

Acceleration

inte

grat

e

mils (0.001 inch)

µm (0.001 millimeter)

ips (inches/sec)

mm/s (millimeters/sec)

g’s

m/s2(meters/sec2)

Accelerometers

All sensors are designed to measure one of the three…

Eddy Current Probes

Velometers & Integrating Accelerometers


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Amplifier

InertialMassPiezoelectricCrystal

Insulator

ConductivePlate

Insulator

Preload Bolt

Integrator

Operation of Operation of Piezoelectric Velocity PickupVelocity Pickup


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A Non-Contacting Pickup (NCPU) System


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Theory of Operation - NCPU

SHAFT

Cutaway ofNCPU Probe Tip

NCPU coil

Generated magnetic field

Eddy currents

RF in

• NCPU system works on the eddy current principle.

• The tip of the probe contains a coil of wire that is connected to a driver. When energized, the probe induces eddy currents in the rotating shaft.


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• System Operation

Probe Driver

OscillatorDetectorNCPU

0 10 20 30 40 50 60 70 80 90 100 110 120

24

20

16

12

8

4

(-)VOLTS

MILS

Displacement


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• System Static Output

(-)VOLTS

MILS0 10 20 30 40 50 60 70 80 90 100 110 120

24

20

16

12

8

4

Linear Range

Gap Voltage

Gap


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• System Dynamic Output

TIME (ms)0 10 20 30 40 50 60 70 80 90 100 110 120

24

20

16

12

8

4

(-)VOLTS

Vibration AmplitudeAverage Gap Voltage


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• There are five measurable characteristics of vibration. – Frequency– Displacement (or amplitude)– Velocity– Acceleration– Phase


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VIBRATION AMPLITUDE OVER TIME

Am

pli

tud

e Time

Peak to Peak Displacement


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VIBRATION VELOCITYA

mp

litu

de Time

Period (Time)

Zero velocity/Peak acceleration

Peak velocity/Zero acceleration

Zero velocity/Peak acceleration


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VIBRATION FREQUENCYA

mp

litu

de

Time

Period (Time)

Frequency = 1 / Period

Example:

If it takes .1 seconds for one cycle (the Period), thenFrequency = 1 / .1 or 10 Cycles Per Second (Hertz)


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VIBRATION SIGNAL DETECTION

Am

pli

tud

e

Time

Peak to PeakPeak RMS


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For Sinusoidal Motion….

Am

pli

tud

e

Time

Peak to Peak PeakRMS

Peak to Peak = 2 x PeakRMS = .707 x Peak


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Common Vibration Amplitude Units

ENGLISH UNITS

• Displacement– Mils (0.001 inch)

Peak-to-Peak

• Velocity– Inches/sec Peak– Inches/sec RMS

• Acceleration– G Peak

METRIC UNITS

• Displacement– µm (0.001 millimeter)

Peak-to-Peak

• Velocity– mm/sec Peak– mm/sec RMS

• Acceleration– Meters/Sec2 Peak


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RELATIVE PHASE• Comparative phase readings show “how” the

machine is vibrating• Note how relative phase causes significant

changes in vibration seen at the coupling with little to no change in the amplitudes measured at points 1 and 2


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Frequency Characteristics

• Synchronous Vibration

• Asynchronous Vibration

• Natural Frequency

• Resonance


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Resonance

• Spring System – Pillow Block

• Spring System – Machine Base

Flex

FlexPillow block housing

Ball bearingV-belt pulley

Shaft coupling

Machine Base


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Critical Speed

• Critical Speed is defined as being a type of resonance which occurs when a shaft or rotating machine component revolves at a speed close to its natural frequency .


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Vibration Indicators


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85

Vibration Indicators


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Summary (Amplitude, Frequency, Phase)

• Amplitude is the amount of vibration– Measured in units of Acceleration, Velocity,

or Displacement– Signal Detection is Peak to Peak, Peak, or

RMS

• Frequency is the number of cycles per second (Hertz) or cycles per minute (CPM) that a part is vibrating

• Phase is used to determine how one part is vibrating relative to another part.


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Overall Velocity Guidelines


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Overall Alarm ChartMACHINE TYPE GOOD FAIR ALARMCooling Tower Drives

Long Hollow Drive Shaft 0 - .375 .375 - .600 .600Close Coupled Belt Drive 0 - .275 .275 - .425 .425Close Coupled Direct Drive 0 - .200 .200 - .300 .300

CompressorsReciprocating 0 - .325 .325 - .500 .500Rotary Screw 0 - .275 .275 - .425 .425Centrifugal with or without External Gearbox 0 - .200 .200 - .300 .300Centrifugal - Integral Gear (Axial Meas.) 0 - .200 .200 - .300 .300Centrifugal - Integral Gear (Radial Meas.) 0 - .150 .150 - .250 .250

Blowers (Fans)Lobe-Type Rotary 0 - .300 .300 - .450 .450Belt-Driven Blowers 0 - .275 .275 - .425 .425General Direct Drive Fans (with Coupling) 0 - .250 .250 - .375 .375Primary Air Fans 0 - .250 .250 - .375 .375Large Forced Draft Fans 0 - .200 .200 - .300 .300Large Induced Draft Fans 0 - .175 .175 - .275 .275Shaft-Mounted Integral Fan (Extended Motor Shaft) 0 - .175 .175 - .275 .275Vane-Axial Fans 0 - .150 .150 - .250 .250

Motor/Generator SetsBelt-Driven 0 - .275 .275 - .425 .425Direct Coupled 0 - .200 .200 - .300 .300

ChillersReciprocating 0 - .250 .250 - .400 .400Centrifugal (Open-Air) - Motor & Comp. Separate 0 - .200 .200 - .300 .300Centrifugal (Hermetic) - Motor & Impellers Inside 0 - .150 .150 - .225 .225

Large Turbine/Generator3600 RPM Turbine/Generators 0 - .175 .175 - .275 .2751800 RPM Turbine/Generators 0 - .150 .150 - .225 .225

Centrifugal PumpsVertical Pumps (12' - 20' Height) 0 - .375 .375 - .600 .600Vertical Pumps (8' - 12' Height) 0 - .325 .325 - .500 .500Vertical Pumps (5' - 8' Height) 0 - .250 .250 - .400 .400Vertical Pumps (0' - 5' Height) 0 - .200 .200 - .300 .300General Purpose Horizontal Pump (Direct Coupled) 0 - .200 .200 - .300 .300Boiler Feed Pumps 0 - .200 .200 - .300 .300Hydraulic Pumps 0 - .125 .125 - .200 .200

Machine ToolsMotor 0 - .100 .100 - .175 .175Gearbox Input 0 - .150 .150 - .225 .225Gearbox Output 0 - .100 .100 - .175 .175Spindles: a. Roughing Operations 0 - .075 .075 - .125 .125

b. Machine Finishing 0 - .050 .050 - .075 .075c. Critical Finishing 0 - .030 .030 - .050 .050


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Frequency Analysis


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Measuring Vibration Amplitude• The three vibration characteristics,

displacement, velocity, and acceleration are inter-related.

• When displacement and frequency values are known, velocity (peak) can be calculated.

• To Calculate Velocity (peak):V = 52.3 x D x F x 106

• Where:V = velocity (peak) in inches/secondD = displacement (peak-to-peak) in milsF = frequency in CPM


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Calculate Acceleration• When displacement and frequency are

known, acceleration (peak) can be determined by using the following calculation:

• To Calculate Acceleration (peak):g (peak) = 14.2 x D (F/I 000)2 x i0

• Where:g = acceleration (peak) due to gravity D = displacement (peak-to-peak) in mils F = frequency in CPM


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Unbalance

Output Shaft Gearmesh

Time

Time Waveforms

Looseness


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Time

Complex WaveformAmplitude

Freq

TimeF.F.T.

FrequencySimple Frequency Spectrum

Amplitude

A

T

A

f

Conversion to Frequency Domain


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Time and Frequency Domain

Time DomainFrequency Domain

Amplitude

Complex Waveform

Simple Waveform

TMAX

FMAX

1X1X3X3X

5X5X

9X9X


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FrequencyI B Dmb

alance

Cou

pling

Gea

rmesh

ea

ring

ef

ectFrequency

Am

plit

ude

Spectrum Analysis!!!


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Real Vibration is Complex


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Resulting Spectrum (FFT)


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Fixed Frequencyvs.

Order Normalization


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Fixed Frequency Spectrum

0 50004000300020001000

Frequency (CPM)

Vib

rati

on

Am

plit

ud

e

Speed = 500 RPM


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Fixed Frequency Spectrum

0 50004000300020001000

Frequency (CPM)

Vib

rati

on

Am

plit

ud

e

Speed = 1500 RPM


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Order Normalized Spectrum

0 105431

Frequency (Orders)

Vib

rati

on

Am

plit

ud

e

Speed = 500 RPM

2 6 7 8 9


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Order Normalized Spectrum

0 105431

Frequency (Orders)

Vib

rati

on

Am

plit

ud

e

Speed = 1500 RPM

2 6 7 8 9


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Spectrum Alarm Bands


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Order Normalized Spectrum Alarm Bands

0 105431

Frequency (Orders)

Vib

rati

on

Am

plit

ud

e

Speed = 1800 RPM

2 6 7 8 9

Band 1 – UnbalanceBand 2 – LoosenessBand 3 – BearingsBand 4 – Blade Pass


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Order Normalized Spectrum Alarm Bands

0 105431

Frequency (Orders)

Vib

rati

on

Am

plit

ud

e

Speed = 1800 RPM

2 6 7 8 9

Band 1 – UnbalanceBand 2 – LoosenessBand 3 – BearingsBand 4 – Blade Pass

WarningBlade Pass

DangerBlade Pass


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Time (Days)

-5 50-1-2-4 -3 1 2 3 4

Trending Band Amplitudes

Band 1 – Unbalance

Band 2 – Looseness

Band 3 – Bearings

Band 4 – Blade Pass


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A Pump Example

How many vanes does this one have?


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Vane PassThe pressure output to the volute will vary as the vanes pass depending on how exactly the vanes line up with the outlet (volute) at any given moment. So with any centrifugal pump there will be a pulsation (pressure pulse) that occurs at a frequency equal to the number of vanes times the speed of the pump.

Hz 0 800

1x 5x

volute This is called the “Vane Pass” frequency. It is always equal to the number of vanes times the speed of the pump.

This is called the “Vane Pass” frequency. It is always equal to the number of vanes times the speed of the pump.

vanes

In this case…

Vane Pass = 5x

In this case…

Vane Pass = 5x


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A Coupling / Alignment Example

This is called “angular” misalignment (you don’t really need to know that though)

There will be a coupling joining every component on a machine

coupling


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Two Maximum Forces per Revolution

And you would feel a maximum expansion force here

Imagine that you are this bolt…

When you were here, you would feel a maximum compressive force

You would feel no force when you were here


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Force is applied in two directions

If you drew a plot of the force relative to expansion or compression, vs. time over one revolution you would see…

compression

expansion

1 Rev.


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Two Maximum Forces per Revolution

If you drew the same plot of force (any kind) vs. time you would see…

max.

min.

1 Rev.

Hz 0 800

1x

2x A maximum force is observed twice per revolution, so…

max compression max expansion


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How Would You Orient The Sensor?

If you were going to attach a sensor to detect this problem, in what direction (relative to the shaft) would you place it?

Hz 0 800

1x

2x This type of misalignment would be felt mostly in the axial direction, but also somewhat in the radial direction.


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Gears

Drive 54T Driven 27T

Input =1000 RPMOutput =2000 RPMGear mesh=54000 CPM

0 10040Frequency (Orders)

Vib

rati

on

Am

plit

ud

e

20 60 80

1x

2x 54x


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Rolling Element Bearings

N=8 (Balls)

Estimation EquationsDefect on Outer Race ~.5xN – 1.2Defect on Inner Race ~.5xN + 1.2Ball Spin Frequency ~.2xN-1.2/NTrain Frequency ~.5xN-1.2/N

0 104

Frequency (Orders)

Vib

rati

on

Am

plit

ud

e2 6 8

BSIR

Estimation EquationsDefect on Outer Race .5x8 – 1.2 = 2.8Defect on Inner Race .5xN + 1.2 = 5.2Ball Spin Frequency .2xN-1.2/N = 1.45Train Frequency .5-1.2/N = .35

BSOR1X

BSF

FTF


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Summary


• Question and Answer Session

Performance Monitoring



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Objectives

• Define monitoring methods

• Measuring electrical performance

• Measuring fluid performance


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Monitoring Methods

• Measuring Electrical Performance

• Measuring Fluid Performance

• Measuring Temperature

• Measuring RPM


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Establishing Standards

1. Standards which represent absolute values.

2. Qualitative type of comparative criteria such as manufacturer’s design limits.


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Judging Performance

• What seems to be out of its limit or has changed?

• By how much have the limits changed?

• Are the changes occurring slowly or rapidly?

• Are there any other changes which either confirm or contradict the initial observations?


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Measuring Electrical Performance

• First – follow proper safety rules

• Common Electrical instruments– Voltmeters– Ammeters– Ohmmeters– Megohmmeters– wattmeters


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Basic Instruments- Multimeters

• Combines reading of:– Voltages– Resistance– Current

Digital Multimeter

Analog Multimeter


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Ohms Law• The amount of current flowing in an

electrical circuit (I - Measured in amperage) is dependent upon the value of electrical pressure (E - measured in volts) and the amount of opposition to the flow of current (R - measured in ohms).R

EI

R

EI


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Measuring Voltage

+

Battery

-

V

V

A COM

12.000

A

OFFA


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Voltage Drop Cont’d

+

Battery

-

Conductor Resistance

V

V

A COM

11.500

A

OFFA

V

V

A COM

7.500

A

OFFA


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Measuring Current

+

Battery

-

A

V

A COM

.5000

V

AOFF

Break circuit to connect meter. Note: meter leads are moved to different inputs for current testing.


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Measuring Current Cont’d

Never clamp two wires at once!


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Measuring Resistance

A

V

A COM

5000

V

AOFF

A

V

A COM

0000

V

AOFF

Verify zero setting of meter

Reading Resistance


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Megohmeter


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Measuring Power

Typical single phase wattmeter connection.S

OU

RC

E

A

LOA

D

A

V

Voltage

Current

Ammeter

±

±


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• Typical single phase wattmeter connectionT

HR

EE

PH

AS

E S

OU

RC

E

TH

RE

E P

HA

SE

LO

ADA

V

±±

A

V

±

±

Measuring Power

Measuring Power Cont’d


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Protective Devices

• Fuses

• Circuit Breakers


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Fuse FunctionS

ourc

e

Fuse

Short

LoadNormal current High current

Fuse melts and opens

BLADE BODY

ELEMENT

FILLER


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Circuit Breaker Operation

Bimetallic stripSpring

Pivot point

Contactsclosed

Contactsopen

Hold lever

Current flow

Breaker“Made”

Breaker“Tripped”


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Measuring Fluid Performance• Pascal’s Law simply stated

says: “Pressure applied on a confined fluid is transmitted undiminished in all directions, and acts with equal force on equal areas, and at right angles to the surface.”

Pressure exerted by fluid equal in all directions


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• The force contained by an air cylinder barrel is the projected area multiplied by the pressure

Force = Pressure X Area

D

=WhereD = the cylinder bore in inchesP = the pressure in pounds per square inch (psi)Note = area of rod must be subtracted from total area if calculating area of pressure at rod end.

Pi X Diameter 2

Area =4

Pressure and Force


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Boyles Law

• “if the temperature of a confined body of gas is maintained constant, the absolute pressure is inversely proportional to the volume.”

F1

F2

F3V1P1 V2

P2 V3P3

P1 X V2 = P2 X V3 = P3 X V3 = constant where P = pressure and V= volume


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Bernoulli’s Principle

PSI PSI PSI

PUMP

In the small section pipe, velocity is maximum. More energy is in the form of motion, so pressure is lower.

“in a system with a constant flow rate, energy is transformed from one form to the other each time the pipe cross-section size changes”

Velocity decreases in the larger pipe. The kinetic energy loss is made up by an increase in pressure.

Ignoring friction losses, the pressure again becomes the same as at “A” when the flow velocity becomes the same as at “A.”

A B C


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Pressure Measurement

• Bourdon Style Gage

Bourdon tube

Pressure Inlet

Tube tends to straighten under pressure causing pointer to rotate.


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Flow Measurement

• By determining the rate of flow to what the recommended flow rate is supposed to be is essential for determining pumping capabilities and efficiencies.


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Flow Measurement Cont’d• Types of flow measurement devices are the

list following are but a few of the most common types– Elbow tap switches– Flow switches– Turbine Flow meters– Rotameter Flow meters– Orfice Flow meters– Venturi tube flow measurement– Doppler Flow meters– Volumetric Flow meters


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Elbow Taps• Elbow Taps: A flow measurement using elbow taps

depends on the detection of the differential pressure developed by centrifugal force as the direction of fluid flow is changed in a pipe elbow

Elbow tap

Elbow tap

Flow Indicator


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Flow switches

Swinging vane

Switch

• Flow switches are used to determine if the flow rate is above or below a certain value. One type of flow switch is the swinging vane flow switch.


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Turbine Flowmeter

Magnetic pickup

Flow direction

Rotor


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Doppler Flowmeters

Transmitting element

Receiving element

Flow direction


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Summary




Thermographic Analysis


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Objectives

•Define infrared

•Types of equipment used

•Define thermographic imaging

•Implementing a maintenance program

•List types of faults


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Introduction

• Thermography is a predictive maintenance technique that can be used to monitor the condition of plant machinery, structures, and systems.

• Involves the measurement or mapping surface temperatures as heat flows to, from and/or through an object


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Infrared Basics• Objects with a temperature above absolute

zero emit energy or radiation• Infrared radiation is one form of this emitted

energy.• Three sources of energy

– Emitted energy– Reflected energy– Transmitted energy

• Only emitted energy is important in a predictive maintenance program.


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Energy Emissions• A = Absorbed energy. • R = Reflected energy. • T = Transmitted energy. • E = Emitted energy.

A

R

T

A + R + T = 1E = AE + R + T = 1


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Blackbody Emissions

• A perfect emitting body is called a “Blackbody”

E = A = .7 R = .3 T = 0

A


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Graybody Emission

• Bodies that are not blackbodies will emit some amount of infrared energy.

E = A = 1 R = 0 T = 0

A

R


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Infrared Thermometers

249°


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Line Scanners

• This type of infrared instrument provides a single-dimensional scan or line of comparative radiation.


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Infrared Imaging


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Infrared Theory


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Implementing a Maintenance Program

• Gain support from management .• Practice reading thermographic images • Meet regularly with managers, line supervisors

and other co-workers • Integrate with other predictive maintenance

efforts • Establish written inspection procedures• Create inspection routes• Reporting results


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Example Inspection Process


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Overheating Belt/Sheave


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Overheating Belt Drive


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• Thermal image reveals overheating bearing on a primary motor


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This panel circuit breaker is hot! Is it a problem? Without a load reading, diagnosis is difficult. This may be the only energized breaker in the entire panel!


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Roller, chain and beltconveyors

• Thermal imaging is especially useful for monitoring low-speed mechanical equipment like conveyors.

These hot spots most likely indicate poor bearing lubrication or componentwear problems.


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Inspect Bearings

overheating shaft and bearing may be an indicator of bearing failure, lack of proper lubrication, or misalignment.

• When a motor bearing fails, the motor heats up and lubrication begins to break down. The windings overheat and then the temperature sensor cuts out and stops the motor. Worst case, the shaft binds up,

the rotor locks up and the motor fails completely


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Printed Circuit BoardsThermal imagers capture two-dimensional representations of the surface temperatures of electronics, electrical components and other objects. Since overheating may signal that a trace, a solder joint, or a component (chip, capacitor, resistor, etc.) is malfunctioning,


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Building Inspection

• Thermal imaging or thermography can capture two-dimensional representations of the surface temperatures of parts of buildings, including roofs, walls, doors, windows and

construction joints.


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Petroleum and petrochemical processing

This nitrogen pump had a persistently leaky seal and had to be changed out regularly. Thermal imaging revealed a restriction preventing the seal from receiving enough cool airflow. As a result, the seal was overheating and melting.


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Substations and Switchgear • Since overheating as well as abnormally cool

operating temperatures may signal the degradation of an electrical component, thermal imagers provide the predictive capabilities required for substation and switchgear maintenance.

For equipment that always has a high operating temperature, establish a baseline or standard acceptable temperature range to compare readings to.


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Monitoring transformers

• Most transformers are cooled by either oil or air while operating at temperatures much higher than ambient

At 94 ºF, one of the terminals on this 1320V– 480 V main transformer is running about 20 ºF hotter than it should.


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Industrial gearboxes

The gearbox on this conveyor belt motor assembly is abnormally warm. The clue is the white-hot shaft at the center.


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Reports

• When an image reveals a situation that may require repairs, a report should be created describing what the image shows and possibly suggesting a remedy. The report can then be circulated to personnel responsible for equipment reliability, who can investigate the problem further.


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Wind will affect your temperature readings due to convection cooling. This can be compensated in outdoor predictive maintenance applications by multiplying your temp. reading by the correction factors listed below.

Wind Speed (Miles Per Hour) Correction Factor

2 1.004 1.306 1.608 1.68

10 1.9612 2.1014 2.2516 2.4218 2.60

Wind Flow


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Summary




Lubrication


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Course Objectives

• Define types of lubrication

• Distinguish the difference between grease and oil

• Discuss the hazards of mixing different lubrications

• Describe the proper handling of lubrication


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Introduction to Lubrication

• Why use lubricants?– Reduce Friction– Increase Cooling


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Lubrication Functions

• Form a lubricant film between components.

• Reduce the effect of friction

• Protect against corrosion

• Seal against contaminants

• Cool moving parts


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Lubrication


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Friction

• Grease and oil lubricate the moving parts of a machine

• Grease and oil reduce friction, heat, and wear of moving machine parts


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Oil = Low Friction and Heat


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No Oil = High Friction and Heat


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Bearing center

Shaft center

Loaded area

Oil delivery


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Lubrication Prevents Failure of:

• Bearings

• Gears

• Couplings

• Chains


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Lubrication Prevents Failure of:

• Engine components

• Hydraulic pumps

• Gas and Steam Turbines

• Any moving parts


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Lubricants prevent failure by:

• Inhibiting rust and corrosion

• Absorbing contaminates

• Displacing moisture

• Flushing away particles


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Lubricant Selection

• Operating temperature

• Load

• Speed

• Environment

• Grease Lubrication

• Oil Lubrication


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Grease

• Grease is a heavy, non-liquid lubricant

• Grease can have a mineral, lithium or soap base

• Grease is pasty, thick and sticky


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Grease

• Some greases remain a paste from below 0°C to above 200°C.

• The flashpoint of most greases is above 200°C

• Grease does not become a mist under pressure


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Oil

• Oil can be a heavy or thin liquid lubricant

• Oil can have a natural base (mineral)

• Oil can have a synthetic base (engineered)


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Oil

• Oil remains liquid from below 0°C to above 200°C.

• The flashpoint of many oils is above 200°C

• The flashpoint is very low for pressurized oil mist. Why?


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How are grease and oil different?

• How oil is used:– Oil used in closed systems with pumps.

An oil sump on a diesel engine pumps liquid oil.

– Oil is used in gas and steam turbines– Oil is used in most machines that need

liquid lubricant


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How grease is used?

– In areas where a continuous supply of oil cannot be retained, (open bearings, gears chains, hinged joints)

– Factors to be considered when selecting greases are:• Type. Depends on operating

temperatures, water resistance, oxidation stability etc

• Characteristics. Viscosity and consistency


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Grease or Oil?

• What determines whether a machine needs grease or oil?

• The manufacturer specifies what lubricant is used in their machines, based on the properties of the lubricant. One important property is VISCOSITY.


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Viscosity

• Liquid oil has lower viscosity than grease paste

• Grease paste has higher viscosity than liquid oil


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What is Viscosity?


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Viscosity• Viscosity is a liquid’s resistance to flow• Viscosity affects the thickness of a liquid• High viscosity liquids are hard to pour• Low viscosity liquids are easy to pour


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Viscosity Rules of Thumb

• the lower the temperature, the lighter the oil

• the higher the temperature, the heavier the oil

• the heavier the load, the heavier the oil

• the lighter the load, the lighter the oil

• the faster the speed, the lighter the oil

• the slower the speed, the heavier the oil


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Viscosity

High High ViscosityViscosity

Low Low ViscosityViscosity


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Viscosity

Temperature affects viscosity.

• Heat decreases viscosity

• Cold increases viscosity

• Viscosity is measured in centistokes (cSt)


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Consistency

• Fundamental principle

• Thickener

• Operating temperature

• Mechanical conditions

• Low temperature effect

• High temperature effect


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Additives

• Antifoaming

• Demulsibility – prevention of emulsions.

• Detergents


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Grease Lubrication

• How grease works

• Thickening agent

• Properties

• Where used


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Advantages of Grease Lubrication

• Reduction of dripping and splattering

• Hard to get points

• Reduction of frequency of lubrication

• Helps seal out contaminants and corrosives.

• Ability to cling to part

• Used to suspend other solids


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Grease Selection Factors– Load condition– Speed range– Operating conditions– Temperature conditions– Sealing efficiency– External environment


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Oil Types

• Two types of lubrication oil are:

• Mineral-based

• Synthetic


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Mineral-Based Oil

• Mineral-based oil is refined from crude oil hydrocarbons

• Mineral-based oil has 2 types of base:– Naphtha Base

• A naphtha base is solvent-like

– Paraffin Base• A paraffin base is waxy


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Mineral-Based Oil

• Naphtha Base– Lower viscosity index (40-80 cs)– Lower pour point– Less resistant to oxidation and changes

in viscosity index– Good performance at higher

temperatures


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Mineral-Based Oil

• Paraffinic Base– Higher viscosity index (>95cs)– Higher pour point– Very resistant to changes in viscosity

index and oxidation– Thicken at low temperatures


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Mineral-Based Oil

• Mineral-based oils are cheaper to buy than synthetics.

• Mineral-based oils can contain traces of sulfur and nitrogen. These impurities can cause oil to form sludge.


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Synthetic Oil

• Synthetic oil is NOT refined from crude oil hydrocarbons

• Synthetic oil is made without a mineral base

• Synthetic oil is made by careful control of a chemical reaction that yields a “pure” substance


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Synthetic Oil

• Synthetic oils are chemically engineered to be pure. They do not contain the traces of sulfur or nitrogen present in mineral-based oils.

• Synthetic oils are expensive


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Synthetic Oil

• Synthetic oil is less flammable than mineral-based oil at low pressure. (Pressure causes most oils to become more flammable)

• Synthetic oils are generally more expensive than mineral based oils


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Lubricant Specifications

• ISO = International Standards Organization

• SAE = Society of Automotive Engineers


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ISO Lubricant Specifications

• ISO Grade lubricants are for industrial use. ISO specifications exist for lubricants in extreme industrial environments.


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ISO Lubricants

ISO GRADE 32 46 68 100

Viscosity

40°C

100°C30.4

5.2

43.7

6.6

64.6

8.5

30.4

5.2

Flash Point

°C(°F)222(432) 224(435) 245(473) 262(504)

Pour Point

°C(°F) -36(-33) -36(-33) -33(-27) -30(-22)


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Using Different Lubricants

• Why do we use different lubricants?

• What happens if oils are mixed?


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Mixing Lubricants

• Consequences of mixing different lubricants are:

• Change of viscosity

• Stripping of machine’s internal coatings, damage to seals

• Reduced flash point, risk of fire


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Mixing Lubricants

• Loss of corrosion protection

• Poor water separation

• Foaming

• Thermal instability


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Fundamentals of Lubrication

• Equipment lubrication– Bearings– Gears– Couplings– Chains


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Lubricant Delivery Methods

• Force Feed Lubricant• Oil Mist• Constant Circulation• Oil Slinger• Zerk Fittings• Surface Application (brush or spray)


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Force Feed Lubrication

• A force feed lubricant system is like an automated version of the hand held oil can. An automatic plunger applies pressure to deliver a few drops at predetermined time intervals.


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Oil Applicators


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Grease Lubrication


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Check Windup Gear Boxes (Quarterly) Oil type ISO360 (Mobil Gear 636)

Grease Variable Pitch Pulley (Quarterly) 1 to 2 Pumps of (Mobil XHP222)

Grease support wheel bearings (Quarterly) 1 to 2 pumps with (Mobil XHP222)

Hand grease square slide shaft and worm shaft (Monthly) 1 to 2 pumps per shaft of (Mobil XHP222)

Hand Oil Roller Chain, [behind guard] (Quarterly) (LPS) (24810)

Lubrication Check Example


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Zerk Fittings

• Zerk Fittings are grease fill points that have an internal check valve that prevents contaminates from entering the fitting. Always clean the Zerk fitting before applying grease.


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Lubrication Practices

• Using grease gun

• Oil samples

• Removing contamination

• Leaks

• Follow lubrication instructions


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Summary




Tribology (Oil Analysis)


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Course Objectives

• Define Tribology

• Oil Analysis Tests

• Discuss the hazards of mixing different lubrications

• Describe the proper handling of lubrication


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Introduction to Tribology

• Tribology is the general term that refers to oil analysis, spectrographic analysis, ferrography, and wear particle analysis.


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Lubricating Oil Analysis Tests• Viscosity• Contamination• Fuel Dilution• Solids Content• Fuel Soot• Oxidation• Nitration• Total Acid Number (TAN)• Total Base Number (TBN)• Particle Count• Spectrographic Analysis


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TAN

• Measures of the acid concentration of the oil• As oil ages and oxidizes small amounts of

acid are formed• Indication of the amount of degradation of oil• TAN above 4.0 is highly corrosive, attacking

bearings and other metals


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TBN

• Measures of the alkalinity the oil

• Engine oil has additives to neutralize acids generated during combustion

• Indication of the amount of degradation of oil

• Once depleted the oil can become highly corrosive, attacking bearings and other metals


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Wear Particle Analysis

• Provides information about the wearing condition of the machine.

• Particles in lubricant are studied for – Shape– Composition– Size– Quantity


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Types of Wear

• Five basic types of wear can be identified according to the classification of particle– Rubbing wear– Cutting wear particles– Rolling fatigue– Combined Rolling and Sliding wear– Severe Sliding Wear


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Ferrography

• Similar to spectrography except a magnetic field is used to separate particles.

• Particles larger than 10 microns can be separated.

• Analytical Ferrography utilizes microscopic analysis to identify the composition of material present.


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Example Slide

Wetting Barrier

Non-Magnetic Particles

Strong Magnet

Magnetic Flux Lines


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Ferrogram photos

• Photographs of ferrograms showing severe sliding wear during break-in


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• Ferrograms of fine rubbing wear and the occasional larger particle


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Spectroscopy

• Uses an IR radiation source

• Radiation is passed through the sample to a detector.


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Example FTIR Spectroscopy

3900 3500 3100 2700 2300 1900 1500 1100 700

Wavenumber

Soot

Oxidation

Nitration

SulfationGlycol

Antioxidant

WaterFuel

AW


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Typical Results of Testing


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Analysis Progams• Lubricant analysis programs are tests used to

determine whether a lubricant remains effective.

• A lubricant analysis program may allow longer intervals between changing lubricants.

• In this program, samples of lubricant are collected and either analyzed in the field (using test equipment) or sent to an analytical laboratory for analysis.

• Representative sample collection is critical to ensure that the sample being analyzed is indicative of the lubricant's overall condition.


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Benefits

• Reduces the frequency of oil changes.

• Decreases consumption and purchase of virgin oil.

• Reduces the generation of waste oil.

• Provides valuable diagnostic information.


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Disadvantages

• Higher level of knowledge is required to perform the diagnostic tests or take representative samples.

• Data must be collected over time and analyzed to determine trends.

• Results are subject to interpretation.

• Oil analyzers must be calibrated to the type and manufacturer of the oil being used.


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Equipment Audit

• An equipment audit should be performed to obtain:– knowledge of the equipment– its internal design– the system design– present operating – environmental conditions


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Lubricant Audit• Equipment reliability requires a lubricant that

meets and maintains specific physical, chemical, and cleanliness requirements.

• A detailed trail of a lubricant is required, beginning with the oil supplier and ending after disposal of spent lubricants.

• Sampling and testing of the lubricants are important to validate the lubricant condition throughout its life cycle.


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Baseline Signature• The baseline signature should be designed to

gather and analyze all data required to determine the current health of – the equipment– lubricant

• The baseline signature or baseline reading requires a minimum of three consecutive, timely samples, preferably in a short duration (i.e., one per month) to effectively evaluate the present trend in the equipment condition.


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Monitoring

These activities are performed to collect and trend any early signs of deteriorating lubricant and equipment condition

•Routing Monitoring

•Routes

•Frequency of Monitoring

•Tests


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Analysis

• Data Analysis

• Root Cause Analysis


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Reports– Specific equipment identification– Data of sample– Date of report– Present condition of equipment and

lubricant– Recommendations– Sample test result data– Analyst’s name


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Summary




Non-Destructive Testing (NDT)


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Objectives

• Upon completion of this course students will be able to: – Define the purpose of non-destructive

testing– Define visual inspection– Define liquid penetrant testing– Define magnetic particle testing


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Purpose

• To reduce the rate of machine failure by– Checking for defects that may cause a part

to fail– Verify a part is within specified tolerances– Conditions will allow machine to operate at

maximum efficiency


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Types of Faults– Cracks– Erosion– Wear– Loss of coating– Reductions in thickness or wall size– Weld integrity

An assembled machine can also be checked for:– Correct assembly– Loose parts– Damage– Blockages


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Types

• Visual

• Liquid Penetrant

• Magnetic Particle

• Ultrasonic

• Eddy Current

• Radiography


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Direct Visual Inspection

• NDE (non-destructive examination)

• Requirements– Adequate light– Good eyesight– Ability to get close to equipment– Experience/Knowledge– May need magnification instruments


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Remote Visual Inspection

• RVI allows the detection, observation or analysis of defects inaccessible to the eye.– The simplest tool is a swivel type mirror

• Main tools are– Videolmagescope– Fiberscope– Borescope


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Video Image Scope

• The scope has a camera built into the end of a flexible probe.

Interchangeable tip adapters

Articulation Control

Light guide cable

Light guide connector

CCU connector


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Fiberscope

• Differs from video image scope, the image is seen at the eyepiece

Eyepiece

Light guide

Light source

Focusing eyepiece

Objective lens

Object

Illumination areaFiber optic light guide

Image guide


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Borescope

• The borescope is another instrument for remotely inspecting the inside of a machine by optical means.

Field of view

Eyepiece

Eye cup

Focus controlDirection indicator

Light guide window

Cap


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Liquid Penetrant• A common method of checking for

cracks due to:– Fatigue– Grinding– Welding– Casting– Shrinkage – Lack of bonding– Delamination– Etc.


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Advantages

• The advantages of liquid penetrant are:– Can be used on a wide variety of materials.– Simple to use and does not require

extensive training.– Does not require expensive and dedicated

equipment.


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Disadvantages

• The disadvantages of liquid penetrant are:– Does not detect sub-surface faults.– Does not indicate the width or depth of a

crack.– Cannot be used on porous materials or

materials that do not have a smooth surface.


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Five steps of Liquid Penetrant

1. Surface preparation

2. Penetrant application

3. Removal of the excess penetrant

4. Developing 5. Inspection and Interpretation


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Magnetic Particle Inspection - MPI

• Magnetic particle inspection (MPI) is a nondestructive testing method used for defect detection.

• MPI uses magnetic fields and small magnetic particles (iron filings) to detect flaws in components.

• The only requirement is that the component being inspected must be made of a ferromagnetic material such as iron, nickel, cobalt, or some of their alloys


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Basic Principle

South poleNorth pole

Any place that a magnetic line of force exits or enters the magnet is called a pole. A pole where a magnetic line of force exits the magnet is called a north pole and a pole where a line of force enters the magnet is called a south pole.

Magnetic field lines

Magnetic particles

NS


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Magnetic Flux and Leakage

A. Uniform Flux Lines

B. Distortion by a surface crack

C. Distortion by Internal Flaw near the Surface

Flux lines

Leakage from surface flaw

Leakage from Subsurface flaw


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Advantages/Disadvantages

The advantages of the Magnetic Particle method are:– sensitive to flaws of almost any size shape and

composition.– can detect flaws that are just below the surface.

The disadvantages of the Magnetic Particle method are:– can only be applied to ferromagnetic material.– if the magnetic flux is parallel to the crack it will not

show, therefore perhaps requiring two or more tests.


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Three Steps of MPI

• Magnetization of the part

• Application of the particles

• Inspection and interpretation


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Magnetization

• Four methods – Coil around a piece

– Current through a piece

– Current through a portion using prods

– Electro-magnetic Yoke.


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Application of Particles

• The particles consist of a fine iron oxide powder that are elongated to assist in polarization and lubricated to enhance their mobility.

• Two types of particles– Dry (usually dyed)– Wet (usually treated with fluorescent

material)


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MPI Inspection/Interpretation

• Flaw detection depends on a number of factors– Strength of magnetic field– Orientation of fault to flux lines– Depth of the flaw– Strength of current used– Location of prods, yoke or coil


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Eddy Current Testing - ET

• Used to inspect electrically conducting specimens for defects, irregularities in structure, and determining coating thickness


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Eddy Current Principle

Probe

Alternating current

Magnetic field

Eddy Currents or secondary magnetic field

Fault


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Advantages

• Crack detection

• Material thickness measurements

• Coating thickness measurements

• Conductivity measurements for:

• Material identification

• Heat damage detection

• Case depth determination

• Heat treatment monitoring


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Disadvantages• Only conductive materials can be inspected • Surface must be accessible to the probe • Skill and training required is more extensive

than other techniques • Surface finish and roughness may interfere • Reference standards needed for setup • Depth of penetration is limited • Flaws such as delaminations that lie parallel to

the probe coil winding and probe scan direction are undetectable


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Radiography Testing - RT

• Widely used processes to detect sub-surface defects and faults

• Permanent record is produced in the form of an image created on a film that was exposed to a source of radiant energy


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Example Radiography

Source

Radiation Beam

Weld Slag

Film


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Sources

• There are two sources of penetrating waves which are suitable for radiography:– X-ray– Gamma Ray


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Advantages of X-Rays• No residual radiation is generated or retained

when the power is switched off.• Penetrating power is adjustable through

varying the high voltage (kV) input.• Can be used on all materials (including

aluminum).• Provides radiographs with good contrast and

sensitivity.• Sufficient size machines exist to radiograph

through 20 inches (500 mm) of steel.


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Disadvantages of X-Rays

• High initial cost.

• Requires source of electrical power.

• Equipment not very portable, also relatively fragile.

• Tube head usually large in size, unusable in tight locations.

• Electrical hazard from high voltage.


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Advantages of Gamma Rays

• Small initial and low maintenance costs.• Rugged construction, more suited to

industrial locations.• No electric power required or concern of

electrical hazard.• High penetrating power.• Portable with access into small areas

with source tube.


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Disadvantages of Gamma Rays

• Radiation hazard and radiation emitted continuously.

• Penetrating power cannot be adjusted.• Radioisotope decays in strength requiring

recalibration and replacement.• Radiographic contrast generally less than X-

ray.• Cannot be used on all materials (eg.

aluminum).


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Safety• Ionizing radiation can be very

damaging to the human body depending on the concentration of the exposure.

• Illness produced from ionizing radiation ranges from nausea, vomiting, headache, and diarrhea to loss of hair and teeth, reduction in red and white blood cells, hemorrhaging, sterility, and death


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Viewing Radiographs

• Generally viewed on a light-box.


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Summary




Ultrasonic Measurement


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Objectives

• Define the basic principles of ultrasonic detection

• Define the advantages/disadvantages

• Define types of waves


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Ultrasonic Testing - UT

• The application of high frequency sound waves is used to detect internal flaws in materials and also for thickness gauging.

• When there is a discontinuity (such as a crack) in the wave path, part of the energy will be reflected back from the flaw surface.


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Sound Strategies

• Ultrasonic Inspection Program– Versatile Predictive Maintenance

Technology– Results Right Out of the Box– Rising popularity

Steam Traps

Leak Detection

Condenser Leaks Acoustic Vibration

Monitor Bearings


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Sound and Ultrasound

• Audible Sound (20 Hz → 20,000 Hz)– Average peak human

range is 16 → 17 kHz– Human response is

very “flat” or broad• Ultrasound (20,000

Hz +)– Well beyond the

range of humans– Ultrasonic response

is very “steep” or narrow

Broad or Flat Response - Humans

20 Hz → 20,000 Hz

Narrow or Steep Response – Ultrasound

20 KHz 40 KHz 60 KHz


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Advantages• Sensitive to surface/subsurface discontinuities• Superior depth of penetration• Only single-sided access needed• Highly accurate• Minimal part preparation• Instantaneous results• Details can be produced on an automated

system• Can also be used for thickness measurement


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Disadvantages• Surface must be accessible• Extensive training required• Requires a coupling medium• Rough, thin or irregular shapes are difficult to

inspect• Cast iron or course grained material difficult to

inspect• Linear defects parallel to beam go undetected• Reference standards are required.


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Intensity and transit time

• The pulse echo procedure is the most common intensity and transit time method

• Pulse echo procedures– normal probe or straight beam– angle beam– surface wave


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Pulse Echo Example

Test Piece Test Piece

CRT

FlawTransducer

Sound energy

Start pulseEnding pulse measured in time


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Types of waves

• Longitudinal waves

• Transverse or shear waves

• Surface wavesTransducer

LongitudinalWaves

ShearWaves


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Ultrasonic Requirements

• High frequency pulse generator

• Transmitting/Receiving probe (transducers)

• Signal amplifier

• CRT or oscilloscope

• Coupling medium or couplant

Couplant

Probe


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Test Methods

• Resonant frequency method

• Transit time method

• Intensity method

• Intensity and transit time method


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Intensity and transit time method

0 2 4 6 8 10 12

Crack echo

Start pulse

Back surface echo

Pulser/Receiver

Transducer

Fault


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Angle Beam

Transducer

Traverse waves

Defect


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Intensity Method• The intensity method requires separate

sending and receiving transceivers

High Frequency Generators

Transmitting probe

Receiving probe

Flaw

Receiver

Reference level

Receiver

With flaw


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Disadvantages of Intensity Method

– The test piece is required to have parallel sides and access to both sides is required.

– The probes must be positioned exactly opposite one another.

– Two probes double the chance of having problems with the fluid coupling.

– The location (depth) of the fault is not indicated.


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Piezoelectric Transducers

• Conversion of electrical pulses to mechanical vibration and back is the basis of ultrasonic testing.

• Piezoelectric ceramic uses the phenomenon, known as electrostriction, to perform this effect.


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Characteristics


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Example Condition Monitoring

• Rotating Equipment• Bearings• Gearbox• Pumps• Motors• Compressors

Condition Monitoring


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Summary




January 2008

Electrical Insulation Testing


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Objectives

• Define principle of insulation testing

• Define currents to be tested

• Define testing procedures


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Reason for Testing• The most important reason for using an

insulation tester is to insure public and personal safety.

• It can eliminate the possibility of having a life-threatening short circuit or short to ground.

• This test is usually performed after the initial installation of the equipment.

• This process will protect the system against miswired and defective equipment and protect against fire or shock.


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Principle of Insulation Testing

• Insulation systems are capacitive

• Sub currents– Conductive current– Capacitive Leakage current– Resistive current


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Insulation Model

• Insulation may be simply modeled as a capacitor in parallel with a resistor.

Ic Capacitive

current

IrResistive current

AC voltage

Total current


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DC Insulation Model

• An extra capacitor is added to the AC model of insulation.

DC

Ida Dielectric

absorption current


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Current to be measured

Conductive Leakage Current

Capacitive Charging

Leakage Current

Dielectric Insulation

Conductors


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Graphical Current Components

Insulation Resistance

(in megohms)

Time (seconds)0

Current(microamps)

Conductive Leakage current

Capacitive Charging

Leakage current

Polarization absorption

leakage current

Total current


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Megger Testing

GL E


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Proof Testing & Procedure

Metal conduit

Insulation


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Predictive Maintenance Tests

• Spot-reading/short-time resistance test

• Step voltage test

• Dielectric-absorption/time-resistance test


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Testing Generators/Motors

• When testing generators, motors, or transformers each winding/phase should be tested in sequence and separately while all the other windings are grounded. In this way, the insulation between phases is also tested.


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Summary




Rotor Balancing


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Objectives

• Describe need for balancing

• Define each type balancing method.

• Determine if equipment is balanced properly.


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Rotor Balancing

• Introduction

• Imbalance = unbalance

• Unbalance is one of the most common causes of machinery vibration.


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Balancing Machine


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Sources of Vibration

• Assembly errors– Center of rotation– Method of locating– Cocked rotor

• Incorrect key lengths


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Center of Rotation

• Errors– Placement of shaft after balancing rotor– Balancing shaft tolerances– Shifting rotational center from center it was

balanced on

• Best results – balance on its own shaft rather than balancing shaft


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Method of Locating

• End clamped rotors out of position after balancing– Unbalanced if shaft not marked for point of

bore and shaft contact– May result in more serious vibration

• Correction requires following precise procedures for disassembly/reassembly


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Cocked Rotor• For set screw mountings

– If a rotor is cocked in a position different from original imbalance can result

– Can be caused by reversing order of set screw tightening during balancing vs. mounting

• Prevention requires:– Tighten set screw gradually– Clean mating surfaces– Clean bolt holes


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Key Length

• Introduces machine vibration if key length different from on used in operation.

• Male/Female. – One half of weight is shafts male portion– One half of weight is coupled female portion

• Prevention – always use actual (recorded) key length.


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Unbalance Example

Centrifugal Force Pulling

This Way

Centrifugal Force Pulling

This Way

Rotor

Heavy spot

½ Revolution Later


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Unbalance Force

– F = The force generated in pounds– R = Radius of the out of balance weight in

inches– W = Weight of the out of balance in

ounces

For calculating trial weight the formula is :

2

100077.1

RPM

WRF

2

100077.1

RPMR

FW


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Theory of Imbalance

• Static

• Dynamic

• Coupled

• Dynamic combinations


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Static

• Single plane

• Angular relationship

• Force imbalance

Rotational Axis

Weight Distribution

Axis

Heavy Spot


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Correcting Static Unbalance

Heavy Spot

Heavy Spot

Heavy Spot

Balance weight

Balance weights

Balance weights

NOT ACCEPTABLE

ACCEPTABLE AT LOW RPM’S

BEST

A B C


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Dynamic

• Two Correction planes

Rotational Axis

Weight Distribution Axis


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Couple

• Intersects at rotational axis

Rotational Axis



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Combination or Quasi-static

Rotational Axis



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Natural Frequency

a

b

Time

Time

Struck lightly

Struck heavily

Displacement

Displacement


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Before Balancing

• Machine in sound condition

• Check for damage

• Check rotor

• Proper tuning of analyzer


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Tools

• Vibration analyzer

• Weight scale

• Calculator

• Graph paper

• Compass, ruler, straight edge

• Trial weights


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In Place Balancing

• Corrected with rotor mounted in its normal housing


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Balancing MethodsSelecting Single Plane, Two Plane, Multi-Plane

L/D ration excluding

shaft

Balance Correction

Single plane

Two plane Multi-plane

Less than 0.5

0-1000 RPM

Above 1000 RPM

Not applicable

More than 0.5 but less than 2

0-150 RPM 150-2000 RPM or > 70% of first critical

Above 2000 RPM or > 70% of first critical

More than 2

0-100 RPM Above 100 RPM to 70% of first critical

Above 70% of first critical

Note: RPM = machine operating speed

D

L

D

L

DL


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Summary



Business

Predictive maintenance