Predictive maintenance

Fundamentals of Predictive Maintenance

Introduction To
Predictive Maintenance

January 2008

Introduction

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

2

• 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..

Objectives



• This course will present the following topics:

3

– 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

Agenda



4

•
•
•
•
•

Predictive Maintenance
Maintenance Planning
Vibration Analysis
Performance Monitoring
Thermal Analysis

Agenda



•

5

•
•
•
•
•

Lubrication and Tribology (Fluid
Analysis)
Non-destructive Testing and Inspection
Ultrasonic Measurement
Insulation Testing
Balancing
Review


Predictive
Maintenance

Objectives



•

7

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

Terms



8

•
•
•
•

PM means Preventive Maintenance
PdM means Predictive Maintenance
PPM or P/PM means
CMMS means Computerized
Maintenance Management System

How to View Maintenance


9

•
•
•
•

Engineering
Economic
Management
What else?

PM



10

• 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

PdM



11

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

Misconceptions about PM


12

• 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• PM is obsolete due to new technology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

Task Lists


13

• 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

Common Tasks



1. Inspection

14

7. Take Readings

2. Predictive Maintenance 8. Lubrication
3.Cleaning

9. Scheduled Replacement

4. Tightening

10. Interview Operators

5. Operate

11. Analysis

6. Adjustments

Patterns of Failure


15

•
•
•
•
•
•

Random
Infant mortality
Increasing
Increasing then stable
Ending mortality
Bathtub

Bathtub Chart
Break In
Or
Start -up
Number of Failures



Critical
wear point

Normal Life
Time

16

Break Down
Cycle

Predictive Maintenance - PdM



17

• What do we mean by Predictive
Maintenance?

“to declare or indicate in advance”

PdM Definitions


18

• Any inspection (condition based) activity
on the PM task list is predictive.
Condition
• Predictive Maintenance is a way to view
data

PdM Program



• A Predictive Maintenance programs is the
active condition monitoring approach

19

This requires a program to:
– Regularly monitor the mechanical condition
of all critical production equipment.
– Identify outstanding problems.

Equipment Condition Monitoring



20

•
•
•
•
•
•
•

Vibration analysis.
Thermography..
Fluid analysis (tribology).
Visual inspection.
Operational-dynamics analysis.
Electrical monitoring.
Failure analysis.

Condition Monitoring


21

•
•
•
•

Temperature
Vibration
Changes in noise or sound
Visually observed changes and
problems

Temperature


22

Vibration



23

Screwdriver
Listen
Vibration
Probe

Vibration Problems



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

24

– 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

Sound/Noise



• Listening
• Sound Measurements
Sound Intensity and the Human Ear
Change 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.

25

Sight



Loose
Bearing
Housing
Loose
Bolts

Cracked
Housing

26

Seal
Problem

Leaking
Lubrication

Summary



27

• Review Objectives
• Question and Answer session


Maintenance
Planning

Objectives


29

– Define Maintenance Improvement and
Reliability Programs (MIRP)
– Define Critical Path Method (CPM)
– Define Program Evaluation and Review
Technique (PERT)

Maintenance Program Objectives


• The primary objectives of any maintenance
program’s activities include:

30

– 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.

Maintenance Plans


31

• Long range planning
• Short or Mid-range planning
• Immediate planning

Maintenance Improvement and
Reliability Programs


32

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

1- Initialization


33

• 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.

2 - Clear Vision


34

• 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.

3 - Analyze



• Step 3: Analyze the organization.

35

– 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.

4 - Develop


36

• 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.

5 - Assess


37

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

6 - Select



38

• 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?

7 - Measure


39

• 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?

8 - Prepare



• Step 8: Prepare the maintenance
personnel.

40

– 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.

9 - Monitor


41

• 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.

10 - Review


42

• 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.

Critical Path Method - CPM


43

• 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?

Why use CPM?


44

•
•
•
•
•
•
•

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

Building a chart


45

List tasks
and relation
ships

Create start
node

Sequentially
arrange all tasks
from start

Draw arrow
from start to
first task

Repeat process
from successors
to all tasks

Check for missed
relationships

Example chart


Earliest start time followed
by latest start time

TURBINE OVERHAUL
(EXAMPLE)
54-54


8-52

11

Estimated job time

2

12

2

13

60-60

3

2

14

46-46

40

9

2

10
41-49

2

7
4

47-55

4-4

0-0

1

36

4

16

1

2

5

5-13

2

8
4

2

44-53

15

52-60
2

16

3

17

14-56

3

2

2
10-51

18-60
4

19

8

20
70-70

6

10

62-62

49-57

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

46

18

8

6-6

Critical job time

57-57

3

4

Task durations


47

•
•
•
•

Early Start
Early Finish
Late Start
Late Finish

Example Table of Times


48

Work
Segment
Number

Work Description

Estimated
Job time

Earliest
Start
Time

Latest
Start
Time

Earliest
Finish
Time

1-2

Check Stand – by
Unit No:

4

0

0

4

2-3

Check Rebuild
Calibrate
gauges

10

4

4

Dismantle Unit
No:____.
Casing

1

4

Dismantle Unit
No:____
Rotor

2

4

2-5

2-9

3-4

Inspect Clean
Control Lines

Latest
Finish
Time

Float

Critical
Work

4

0

4

14

14

0

4

5

5

0

4

60

20

60

42

14

56

18

62

42

2

Program Evaluation and Review
Technique


49

• 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.



50

• 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.

Terminology


51

•
•
•
•
•
•
•
•

Critical Path
Critical Activity
Lead time
Lag time
Slack
Fast tracking
Crashing critical path
Float

Pert Activity


52

• 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

Implementing PERT


• First, determine the tasks that the
project requires and the order in which
they must be completed.
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

53

Activity

e

3

5

8

5.17

Chart



54

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

PERT Network Diagram


55

40
t=1 mo
10

t=3 mo

t=4 mo

A

30

B

F
D
t=2 mo
E
C

20

t=3 mo

50

Hasse Diagram


56

Summary



57



Vibration
Analysis

Course Objectives



59

• Define the need for analysis
• Define the cause and effects of
equipment vibration
• State how vibration is measured

Benefits from Vibration
Analysis



•

– 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

•
•
•

60

Identifies early stages of machine
defects such as:

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

Vibration CbM Philosophy


• Based on three principles:

61

– All rotating equipment vibrates
– Vibration increases/changes as equipment
condition deteriorates
– Vibration can be accurately measured and
interpreted

Causes of Vibration:


62

• 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)

When Condition of Machinery
Deteriorates


• Dynamic forces increase, cause
increase in vibration

63

– 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

Vibration Demonstration


• Vibration-Single spring and weight in
suspension
Spring
Upper Limit
Weight at
complete rest
Weight

64

Neutral Position
Lower Limit
Time

A Word About Bearings



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

65

Accelerometer

Eddy Current Probe

Bearing

Bearing

bearing
housing

bearing
housing
Soft Metal
(Babbitt)

Oil Wedge
(load zone)

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!

Sensors & Units


Displacement

mils (0.001 inch)
µm (0.001 millimeter)

Velocity

ips (inches/sec)

Velometers &
Integrating
Accelerometers

mm/s (millimeters/sec)

Acceleration

g’s
m/s2(meters/sec2)

66

Eddy Current
Probes

integrate


All sensors are designed to measure one of the three…

Accelerometers

Operation of Piezoelectric
Velocity Pickup


Integrator

67

Insulator
Conductive
Plate
Insulator

Amplifier
Preload
Bolt
Inertial
Mass
Piezoelectric
Crystal

A Non-Contacting Pickup
(NCPU) System


68

Theory of Operation - NCPU


• 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.

RF in

SHAFT
Cutaway of
NCPU Probe Tip
NCPU coil

69

Eddy currents

Generated magnetic field


Displacement


• System Operation

70

Probe Driver
Detector
(-)
V
O
L
T
S

Oscillator

10 20 30 40 50 60 70 80

90 100 110 120

24
20
16
12
8
4

0

MILS

NCPU



• System Static Output

71

(-)
V
O
L
T
S

Linear Range

24
20
16
12

Gap Voltage

8

Gap

4

0

10

20

30

40

50

60

MILS

70

80

90

100

110

120



• System Dynamic Output

72

(-)
V
O
L
T
S

24

Vibration Amplitude

20

Average Gap Voltage

16
12
8
4

0

10

20

30

40

50

60

70

80

TIME (ms)

90

100

110

120



73

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

VIBRATION AMPLITUDE
OVER TIME

74

Amplitude



Time
Peak to Peak Displacement

VIBRATION VELOCITY


75

Peak velocity/Zero acceleration
Amplitude


Zero velocity/Peak acceleration

Time

Zero velocity/Peak acceleration
Period (Time)

VIBRATION FREQUENCY

76

Amplitude


Frequency = 1 / Period

Time

Period (Time)

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

VIBRATION SIGNAL
DETECTION

77

Amplitude



Peak

RMS

Peak to Peak
Time

For Sinusoidal Motion….

78

Peak to Peak = 2 x Peak
RMS = .707 x Peak

Amplitude



RMS

Peak to Peak

Peak

Time

Common Vibration Amplitude
Units


ENGLISH UNITS
• Displacement
– Mils (0.001 inch)
Peak-to-Peak

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

• Acceleration
– G Peak

79

METRIC UNITS
• Displacement

– µm (0.001 millimeter)
Peak-to-Peak

• Velocity
– mm/sec Peak
– mm/sec RMS

• Acceleration
– Meters/Sec2 Peak

RELATIVE PHASE


80

• 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

Frequency Characteristics


81

•
•
•
•

Synchronous Vibration
Asynchronous Vibration
Natural Frequency
Resonance

Resonance



• Spring System – Pillow Block

82

Shaft coupling
Pillow block
housing

Ball bearing

Flex

• Spring System – Machine Base
Machine Base

Flex

V-belt
pulley

Critical Speed


83

• 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 .

Vibration Indicators


84

Vibration Indicators


85

Summary (Amplitude,
Frequency, Phase)



• Amplitude is the amount of vibration

86

– 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.

Overall Velocity Guidelines


87

Overall Alarm Chart


MACHINE TYPE
Cooling Tower Drives

GOOD

FAIR

ALARM

0 - .375
0 - .275
0 - .200

.375 - .600
.275 - .425
.200 - .300

.600
.425
.300

0 - .325
0 - .275
0 - .200
0 - .200
0 - .150

.325 - .500
.275 - .425
.200 - .300
.200 - .300
.150 - .250

.500
.425
.300
.300
.250

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

.300 - .450
.275 - .425
.250 - .375
.250 - .375
.200 - .300
.175 - .275
.175 - .275
.150 - .250

.450
.425
.375
.375
.300
.275
.275
.250

0 - .275
0 - .200

.275 - .425
.200 - .300

.425
.300

0 - .250
0 - .200
0 - .150

.250 - .400
.200 - .300
.150 - .225

.400
.300
.225

0 - .175
0 - .150

.175 - .275
.150 - .225

.275
.225

Vertical Pumps (12' - 20' Height)
0 - .375
0 - .325
0 - .250
0 - .200
General Purpose Horizontal Pump (Direct Coupled) 0 - .200
Boiler Feed Pumps
0 - .200
Hydraulic Pumps
0 - .125

.375 - .600
.325 - .500
.250 - .400
.200 - .300
.200 - .300
.200 - .300
.125 - .200

.600
.500
.400
.300
.300
.300
.200

.100 - .175
.150 - .225
.100 - .175
.075 - .125
.050 - .075

.175
.225
.175
.125
.075

Long Hollow Drive Shaft
Close Coupled Belt Drive
Close Coupled Direct Drive


Compressors
Reciprocating
Rotary Screw
Centrifugal with or without External Gearbox
Centrifugal - Integral Gear (Axial Meas.)
Centrifugal - Integral Gear (Radial Meas.)

Blowers (Fans)

Motor/Generator Sets
Belt-Driven
Direct Coupled

Chillers
Reciprocating
Centrifugal (Open-Air) - Motor & Comp. Separate
Centrifugal (Hermetic) - Motor & Impellers Inside

Large Turbine/Generator
3600 RPM Turbine/Generators
1800 RPM Turbine/Generators

Centrifugal Pumps

Machine Tools

88

Motor
Gearbox Input
Gearbox Output
Spindles:
a. Roughing Operations
b. Machine Finishing

0 - .100
0 - .150
0 - .100
0 - .075
0 - .050



89

Frequency Analysis

Measuring Vibration Amplitude



90

• 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/second
 D = displacement (peak-to-peak) in mils
 F = frequency in CPM

Calculate Acceleration


91

• 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

Time Waveforms


92

Unbalance

Looseness
Output
Shaft

Time

Gearmesh

Conversion to Frequency
Domain

Amplitude

Complex Waveform


A

F.F.T.
T

Time

Amplitude
Freq

A

Frequency
Simple Frequency Spectrum
f

93

Time

Time and Frequency
Domain



Simple Waveform

94

Complex Waveform

FMAX
Amplitude

9X

1X

3X

5X

Time Domain
Frequency Domain
TMAX

Spectrum Analysis!!!

95

Amplitude



a
I
l
m
a
b
n
c
e

r e
B D
p
C
i eFrequency
e c
l
o
n f
a t
i
u
g
n
g

r
G
m
e
e
a
s
h

Frequency

Real Vibration is Complex


96

Resulting Spectrum (FFT)


97



98

Fixed Frequency
vs.
Order Normalization

Fixed Frequency Spectrum
Speed = 500 RPM
Vibration Amplitude



0

1000

2000

3000

Frequency (CPM)

99

4000

5000

Fixed Frequency Spectrum
Speed = 1500 RPM
Vibration Amplitude



0

1000

2000

3000

Frequency (CPM)

100

4000

5000

Order Normalized Spectrum
Speed = 500 RPM
Vibration Amplitude



0

1

2

3

4

5

6

7

Frequency (Orders)

101

8

9 10

Speed = 1500 RPM
Vibration Amplitude



0

1

2

3

4

5

6

7

Frequency (Orders)

102

8

9 10



103

Spectrum Alarm Bands

Alarm Bands

Vibration Amplitude


Speed = 1800 RPM
Band 1 – Unbalance
Band 2 – Looseness
Band 3 – Bearings
Band 4 – Blade Pass

0

1

2

3

4

5

6

7

Frequency (Orders)

104

8

9 10

Alarm Bands

Vibration Amplitude


Speed = 1800 RPM
Band 3 – Bearings

Warning
Danger
Blade Pass
0

1

2

3

4

5

6

7

Frequency (Orders)

105

8

9 10

Trending Band Amplitudes




Band 3 – Bearings


-5

-4

-3

-2

-1

0

Time (Days)

106

1

2

3

4

5

A Pump Example



How many vanes does this one have?

107

Vane Pass



vanes

108

volute
1x

0

The 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.

5x

Hz

This is called the “Vane Pass”
This is called the “Vane Pass”
frequency. It is always equal to the
frequency. It is always equal to the
number of vanes times the speed of
number of vanes times the speed of
the pump.
the pump.
800

In this case…
In this case…
Vane Pass = 5x
Vane Pass = 5x

A Coupling / Alignment
Example



There will be a coupling joining every component on a machine

109

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

coupling

Two Maximum Forces per
Revolution


Imagine that you are this bolt…

110

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

And you would feel a maximum
expansion force here

You would
feel no force
when you
were here

Force is applied in two
directions


111

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

1 Rev.

compression
expansion

Two Maximum Forces per
Revolution
If you drew the same plot of force

(any kind) vs. time you would see…

1 Rev.

112

max.
min.

max compression
max expansion

1x
2x

0

A maximum force is
observed twice per
revolution, so…
Hz

800

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?

113

1x
This type of misalignment would be
felt mostly in the axial direction, but
also somewhat in the radial
direction.

2x

0

Hz

800

Gears

Input =1000 RPM
Output =2000 RPM
Gear mesh=54000 CPM

Drive 54T

Driven 27T

Vibration Amplitude



1x
2x

0

114

20

54x

40
60
80
Frequency (Orders)

100

Rolling Element Bearings

115

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

N=8 (Balls)

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

Vibration Amplitude



FTF
1X
BSF

0

2

BSOR
BSIR

4

6

8

Frequency (Orders)

10

Summary


116

• Question and Answer Session


Performance
Monitoring

Objectives


118

• Define monitoring methods
• Measuring electrical performance
• Measuring fluid performance

Monitoring Methods


119

•
•
•
•

Measuring Electrical Performance
Measuring Fluid Performance
Measuring Temperature
Measuring RPM

Establishing Standards


120

1. Standards which represent absolute
values.
2. Qualitative type of comparative criteria
such as manufacturer’s design limits.

Judging Performance



•

121

•
•
•

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?

Measuring Electrical Performance



122

• First – follow proper safety rules
• Common Electrical instruments
– Voltmeters
– Ammeters
– Ohmmeters
– Megohmmeters
– wattmeters

Basic Instruments- Multimeters


• Combines reading of:

123

– Voltages
– Resistance
– Current

Analog Multimeter

Digital Multimeter

Ohms Law

I=



E
R

124

• 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).

E
I=
R

Measuring Voltage


125

12.000
+
A

V

Battery
A

V
OFF

A

CO M

Voltage Drop Cont’d



7.500

Conductor
Resistance

A

V
OFF

11.500
+

A

A

V

Battery
A

V
OFF

A

126

A

V

COM

COM

Measuring Current



.5000

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

A

V

A

V
OFF

A

COM

+
Battery
-

127

Measuring Current Cont’d


128

Never
clamp
two
wires at
once!

Measuring Resistance


129

Verify zero
setting of meter

Reading
Resistance

0000

5000

V

A

V

A

A

V

A

V
OFF

OFF

A
A

COM

COM

Megohmeter


130

Measuring Power


131

Current

Ammeter

±

A

±

V

Voltage

LOAD

A
SOURCE


Typical single phase wattmeter connection.

Measuring Power Cont’d

132

±

±

A
V

Measuring Power
±

A

±

V

THREE PHASE LOAD

THREE PHASE SOURCE


• Typical single phase wattmeter connection

Protective Devices


133

• Fuses
• Circuit Breakers

Fuse Function

Fuse melts and opens

Load

Fuse
Source



Normal current

Short
BLADE

BODY

ELEMENT

134

High current

FILLER

Circuit Breaker Operation


Pivot point

135

Bimetallic strip
Spring

Breaker
“Made”
Current flow

Breaker
“Tripped”

Hold lever

Contacts
closed

Contacts
open

Measuring Fluid Performance



136

• 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

Pressure and Force


• The force contained by an air
cylinder barrel is the
projected area multiplied by
the pressure
Force = Pressure X Area
Area = Pi X Diameter
4

2

D

Where
=
D = the cylinder bore in inches
P = 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.

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
V1
P1

F3
V2
P2

V3
P3

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

138

Bernoulli’s Principle


139

“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”

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

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

PUMP

B

A
PSI

C
PSI

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

PSI

Pressure Measurement



• Bourdon Style Gage

140

Tube tends to
straighten under
pressure causing
pointer to rotate.

Bourdon
tube

Pressure Inlet

Flow Measurement


141

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

Flow Measurement Cont’d


142

• 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

Elbow Taps


143

• 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

Flow switches


144

• 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.
Switch

Swinging
vane

Turbine Flowmeter


Magnetic pickup

Flow
direction

Rotor
145

Doppler Flowmeters


146

Transmitting
element

Receiving
element

Flow
direction

Summary


147



Thermographic
Analysis

Objectives


149

•Define infrared
•Types of equipment used
•Define thermographic imaging
•Implementing a maintenance program
•List types of faults

Introduction


150

• 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

Infrared Basics


151

• 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.

Energy Emissions


152

•
•
•
•

A = Absorbed energy.
R = Reflected energy.
T = Transmitted energy.
E = Emitted energy.

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

Blackbody Emissions


• A perfect emitting body is called a
“Blackbody”

A

E = A = .7
153

R = .3

T=0

Graybody Emission


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

R
E=A=1

154

R=0

T=0

Infrared Thermometers


155

249°

Line Scanners


156

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

Infrared Imaging


157

Infrared Theory


158

Implementing a Maintenance
Program


159

• 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

Example Inspection Process


160

Overheating Belt/Sheave


161

Overheating Belt Drive


162



163

• Thermal image reveals overheating
bearing on a primary motor



164

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!

Roller, chain and belt
conveyors


165

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

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

Inspect Bearings


166

• 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

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

Printed Circuit Boards


167

Thermal 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,

Building Inspection


168

• 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.

Petroleum and petrochemical
processing


169

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.

Substations and Switchgear



170

• 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.

Monitoring transformers


171

• 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.

Industrial gearboxes


172

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

Reports



173

• 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.

Wind Flow


174

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
4
6
8
10
12
14
16
18

1.00
1.30
1.60
1.68
1.96
2.10
2.25
2.42
2.60

Summary


175



Lubrication

Course Objectives


177

• Define types of lubrication
• Distinguish the difference between
grease and oil
• Discuss the hazards of mixing different
lubrications
• Describe the proper handling of
lubrication

Introduction to Lubrication


• Why use lubricants?

178

– Reduce Friction
– Increase Cooling

Lubrication Functions


179

• Form a lubricant film between
components.
• Reduce the effect of friction
• Protect against corrosion
• Seal against contaminants
• Cool moving parts

Lubrication


180

Friction



181

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

Oil = Low Friction and Heat


182

No Oil = High Friction and Heat


183



Bearing
center

184

Shaft
center

Loaded
area

Oil delivery

Lubrication Prevents Failure of:


185

•
•
•
•

Bearings
Gears
Couplings
Chains

Lubrication Prevents Failure of:


186

•
•
•
•

Engine components
Hydraulic pumps
Gas and Steam Turbines
Any moving parts

Lubricants prevent failure by:


187

•
•
•
•

Inhibiting rust and corrosion
Absorbing contaminates
Displacing moisture
Flushing away particles

Lubricant Selection


188

•
•
•
•
•
•

Operating temperature
Load
Speed
Environment
Grease Lubrication
Oil Lubrication

Grease



189

• Grease is a heavy, non-liquid
lubricant
• Grease can have a mineral, lithium
or soap base
• Grease is pasty, thick and sticky

Grease



190

• 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

Oil



191

• Oil can be a heavy or thin liquid
lubricant
• Oil can have a natural base
(mineral)
• Oil can have a synthetic base
(engineered)

Oil



192

• 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?

How are grease and oil different?


• How oil is used:

193

– 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

How grease is used?


194

– 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

Grease or Oil?


195

• 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.

Viscosity



196

• Liquid oil has lower viscosity than grease
paste
• Grease paste has higher viscosity than
liquid oil

What is Viscosity?


197

Viscosity



198

•
•
•
•

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

Viscosity Rules of Thumb


199

• 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

Viscosity



200

Low
Viscosity

High
Viscosity

Viscosity



201

Temperature affects viscosity.
• Heat decreases viscosity
• Cold increases viscosity
• Viscosity is measured in centistokes
(cSt)

Consistency


202

•
•
•
•
•
•

Fundamental principle
Thickener
Operating temperature
Mechanical conditions
Low temperature effect
High temperature effect

Additives



203

• Antifoaming
• Demulsibility – prevention of emulsions.
• Detergents

Grease Lubrication


204

•
•
•
•

How grease works
Thickening agent
Properties
Where used

Advantages of Grease Lubrication



205

•
•
•
•

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

Grease Selection Factors


206

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

Oil Types



207

• Two types of lubrication oil are:
• Mineral-based
• Synthetic

Mineral-Based Oil


208

• 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

Mineral-Based Oil



• Naphtha Base

209

– Lower viscosity index (40-80 cs)
– Lower pour point
– Less resistant to oxidation and changes
in viscosity index
– Good performance at higher
temperatures

Mineral-Based Oil



• Paraffinic Base

210

– Higher viscosity index (>95cs)
– Higher pour point
– Very resistant to changes in viscosity
index and oxidation
– Thicken at low temperatures

Mineral-Based Oil


211

• 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.

Synthetic Oil


212

• 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

Synthetic Oil


213

• 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

Synthetic Oil


214

• 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

Lubricant Specifications


215

• ISO = International Standards
Organization
• SAE = Society of Automotive
Engineers

ISO Lubricant Specifications


216

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

ISO Lubricants



ISO GRADE

217

Viscosity
40°C
100°C

32

46

68

100

30.4
5.2

43.7
6.6

64.6
8.5

30.4
5.2

222(432)

224(435)

245(473)

262(504)

-36(-33)

-36(-33)

-33(-27)

-30(-22)

Flash Point

°C(°F)

Pour Point
°C(°F)

Using Different Lubricants


218

• Why do we use different lubricants?
• What happens if oils are mixed?

Mixing Lubricants


219

• Consequences of mixing different
lubricants are:
• Change of viscosity
• Stripping of machine’s internal
coatings, damage to seals
• Reduced flash point, risk of fire

Mixing Lubricants


220

•
•
•
•

Loss of corrosion protection
Poor water separation
Foaming
Thermal instability

Fundamentals of Lubrication


• Equipment lubrication

221

– Bearings
– Gears
– Couplings
– Chains

Lubricant Delivery Methods


222

•
•
•
•
•
•

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

Force Feed Lubrication


223

• 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.

Oil Applicators


224

Grease Lubrication


225

Lubrication Check Example



226

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

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

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

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

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

Zerk Fittings


227

• 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.

Lubrication Practices


228

•
•
•
•
•

Using grease gun
Oil samples
Removing contamination
Leaks
Follow lubrication instructions

Summary



229



Tribology
(Oil Analysis)

Course Objectives


231

• Define Tribology
• Oil Analysis Tests
• Discuss the hazards of mixing different
lubrications
• Describe the proper handling of
lubrication

Introduction to Tribology


232

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

Lubricating Oil Analysis Tests



233

•
•
•
•
•
•
•
•
•
•
•

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

TAN



234

• 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

TBN



235

• 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

Wear Particle Analysis


236

• Provides information about the wearing
condition of the machine.
• Particles in lubricant are studied for
– Shape
– Composition
– Size
– Quantity

Types of Wear


237

• 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

Ferrography


238

• 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.

Example Slide



Magnetic Flux Lines

239

Non-Magnetic Particles
Wetting Barrier

Strong Magnet

Ferrogram photos


240

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



241

• Ferrograms of fine rubbing wear and
the occasional larger particle

Spectroscopy


242

• Uses an IR radiation source
• Radiation is passed through the sample
to a detector.

Example FTIR Spectroscopy

Glycol

Sulfation
Antioxidant
Water

Oxidation

Fuel

Soot

3900

243

AW

Nitration

3500

3100

2700

2300
1900
Wavenumber

1500

1100

700

Typical Results of Testing


244



245



246

Analysis Progams


247

• 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.

Benefits



248

• Reduces the frequency of oil changes.
• Decreases consumption and purchase
of virgin oil.
• Reduces the generation of waste oil.
• Provides valuable diagnostic
information.

Disadvantages


249

• 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.

Equipment Audit


250

• An equipment audit should be performed
to obtain:
–
–
–
–
–

knowledge of the equipment
its internal design
the system design
present operating
environmental conditions

Lubricant Audit


251

• 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.

Baseline Signature


252

• 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.

Monitoring


253

These activities are performed to collect
and trend any early signs of deteriorating
lubricant and equipment condition
•Routing Monitoring
•Routes
•Frequency of Monitoring
•Tests

Analysis



254

• Data Analysis
• Root Cause Analysis

Reports



255

– Specific equipment identification
– Data of sample
– Date of report
– Present condition of equipment and
lubricant
– Recommendations
– Sample test result data
– Analyst’s name

Summary



256



Non-Destructive
Testing (NDT)

Objectives


258

• 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

Purpose



• To reduce the rate of machine failure by

259

– 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

Types of Faults


260

–
–
–
–
–
–

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

Types



261

•
•
•
•
•
•

Visual
Liquid Penetrant
Magnetic Particle
Ultrasonic
Eddy Current
Radiography

Direct Visual Inspection


262

• NDE (non-destructive examination)
• Requirements
– Adequate light
– Good eyesight
– Ability to get close to equipment
– Experience/Knowledge
– May need magnification instruments

Remote Visual Inspection


263

• 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

Video Image Scope


264

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

Light guide
cable

Interchangeable
tip adapters

Light guide
connector
CCU
connector

Fiberscope


265

• Differs from video image scope, the
image is seen at the eyepiece
Image guide
Eyepiece
Light guide
Light
source
Focusing eyepiece
Fiber optic light guide

Objective lens

Object
Illumination area

Borescope


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

Light guide
window
Eyepiece

266

Direction indicator
Field of
view
Cap

Liquid Penetrant



• A common method of checking for
cracks due to:

267

– Fatigue
– Grinding
– Welding
– Casting
– Shrinkage
– Lack of bonding
– Delamination
– Etc.

Advantages



• The advantages of liquid penetrant are:

268

– 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.

Disadvantages


269

• 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.

Five steps of Liquid Penetrant



1. Surface
preparation

2. Penetrant
application

4. Developing
270

3. Removal of the
excess penetrant

5. Inspection and
Interpretation

Magnetic Particle Inspection MPI


271

• 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

Basic Principle


272

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 particles

North pole

Magnetic field lines

S

N

South pole

Magnetic Flux and Leakage


Flux lines
A. Uniform Flux Lines
Leakage from
surface flaw
B. Distortion by a surface crack
Leakage from
Subsurface flaw
C. Distortion by Internal Flaw near the Surface

273

Advantages/Disadvantages


274

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.

Three Steps of MPI



•

275

Magnetization of the part

•

Application of the particles

•

Inspection and interpretation

Magnetization



• Four methods

276

– Coil around a piece
– Current through a piece
– Current through a portion
using prods
– Electro-magnetic Yoke.

Application of Particles


277

• 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)

MPI Inspection/Interpretation



278

• 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

Eddy Current Testing - ET


279

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

Eddy Current Principle



Alternating current

280

Probe
Magnetic field

Eddy
Currents
or
secondary
magnetic
field

Fault

Advantages


281

•
•
•
•
•
•
•
•

Crack detection
Material thickness measurements
Coating thickness measurements
Conductivity measurements for:
Material identification
Heat damage detection
Case depth determination
Heat treatment monitoring

Disadvantages


282

• 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

Radiography Testing - RT


283

• Widely used processes to detect subsurface 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

Example Radiography



Source

284

Radiation Beam

Weld

Slag

Film

Sources



285

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

Advantages of X-Rays


286

• 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.

Disadvantages of X-Rays


287

• 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.

Advantages of Gamma Rays



288

• 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.

Disadvantages of Gamma Rays



289

• Radiation hazard and radiation emitted
continuously.
• Penetrating power cannot be adjusted.
• Radioisotope decays in strength requiring
recalibration and replacement.
• Radiographic contrast generally less than Xray.
• Cannot be used on all materials (eg.
aluminum).

Safety



290

• 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

Viewing Radiographs



• Generally viewed on a light-box.

291

Summary



292



Ultrasonic
Measurement

Objectives


294

• Define the basic principles of
ultrasonic detection
• Define the advantages/disadvantages
• Define types of waves

Ultrasonic Testing - UT


295

• 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.

Sound Strategies



• Ultrasonic Inspection Program

296

– Versatile Predictive Maintenance
Technology
– Results Right Out of the Box
– Rising popularity
Condenser Leaks

Steam Traps

Leak Detection

Monitor Bearings

Acoustic Vibration

Sound and Ultrasound


297

• Audible Sound (20
Hz → 20,000 Hz)

Broad or Flat Response - Humans

– 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

20 Hz → 20,000 Hz

Narrow or Steep Response – Ultrasound

20 KHz

40 KHz

60 KHz

Advantages


298

•
•
•
•
•
•
•

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

Disadvantages


299

•
•
•
•

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.

Intensity and transit time


300

• 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

Pulse Echo Example



Start pulse

301

Ending pulse measured in time
CRT

Test Piece

Transducer
Sound energy

Test Piece

Flaw

Types of waves


302

• Longitudinal waves
• Transverse or shear waves
• Surface waves
Transducer

Longitudinal
Waves

Shear
Waves

Ultrasonic Requirements


• High frequency pulse generator
• Transmitting/Receiving probe
(transducers)
• Signal amplifier
• CRT or oscilloscope
• Coupling medium or couplant
Probe
Couplant

303

Test Methods


304

•
•
•
•

Resonant frequency method
Transit time method
Intensity method
Intensity and transit time method

Intensity and transit time method



305

Start pulse
Crack echo

Pulser/Receiver
Transducer

Back
surface
echo

0 2 4 6 8 10 12

Fault

Angle Beam



Transducer

306

Traverse waves
Defect

Intensity Method



• The intensity method requires separate
sending and receiving transceivers
Receiving
probe

Transmitting
probe

Receiver
High Frequency
Generators

With flaw
Receiver

307

Reference
level

Flaw

Disadvantages of Intensity Method



308

– 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.

Piezoelectric Transducers


309

• 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.

Characteristics


310

Example Condition Monitoring



311

Condition Monitoring
•
•
•
•
•
•

Rotating Equipment
Bearings
Gearbox
Pumps
Motors
Compressors

Summary



312



Electrical Insulation
Testing

January 2008

Objectives


314

• Define principle of insulation testing
• Define currents to be tested
• Define testing procedures

Reason for Testing


315

• The most important reason for using an
insulation tester is to insure public and
personal safety.
• It can eliminate the possibility of having a lifethreatening 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.

Principle of Insulation Testing



316

• Insulation systems are capacitive
• Sub currents
– Conductive current
– Capacitive Leakage current
– Resistive current

Insulation Model


317

• Insulation may be simply modeled as
a capacitor in parallel with a resistor.
Total current
AC
voltage

Ic
Capacitive
current

Ir
Resistive
current

DC Insulation Model


318

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

DC

Ida
Dielectric
absorption
current

Current to be measured


Conductive
Leakage
Current

Conductors
319

Capacitive
Charging
Leakage Current

Dielectric
Insulation

Graphical Current Components



320

Insulation
Resistance
(in megohms)
Total current

Capacitive
Charging
Leakage current
Polarization
absorption
leakage current
Conductive
Current
(microamps) Leakage current

0

Time (seconds)

Megger Testing


321

G

L

E

Proof Testing & Procedure


322

Metal
conduit

Insulation

Predictive Maintenance Tests



323

• Spot-reading/short-time resistance
test
• Step voltage test
• Dielectric-absorption/time-resistance
test

Testing Generators/Motors


324

• 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.

Summary



325



Rotor Balancing

Objectives


327

• Describe need for balancing
• Define each type balancing method.
• Determine if equipment is balanced
properly.

Rotor Balancing


328

• Introduction
• Imbalance = unbalance
• Unbalance is one of the most common
causes of machinery vibration.

Balancing Machine


329

Sources of Vibration



• Assembly errors

330

– Center of rotation
– Method of locating
– Cocked rotor

• Incorrect key lengths

Center of Rotation



• Errors

331

– 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

Method of Locating


332

• 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

Cocked Rotor



• For set screw mountings

333

– 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

Key Length


334

• 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.

Unbalance Example


335

½ Revolution
Later
Rotor
Heavy
spot

Centrifugal
Force Pulling
This Way

Centrifugal
Force Pulling
This Way

Unbalance Force



2

336

 RPM 
F = 1.77 × R × W × 

 1000 
– 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 :
W =

F
2

1.77 × R ×  RPM  



 1000  



Theory of Imbalance


337

•
•
•
•

Static
Dynamic
Coupled
Dynamic combinations

Static



338

• Single plane
• Angular relationship
• Force imbalance

Weight
Distribution
Axis

Heavy
Spot

Rotational Axis

Correcting Static Unbalance


339

A

B

C

Heavy
Spot

Heavy
Spot

Heavy
Spot

Balance
weight

BEST

Balance
weights

ACCEPTABLE AT
LOW RPM’S

Balance
weights

NOT
ACCEPTABLE

Dynamic



• Two Correction planes

340

Weight Distribution Axis

Rotational Axis

Couple



• Intersects at rotational axis

341


Rotational Axis

Combination or Quasi-static


342


Rotational Axis

Natural Frequency

a

Displacement

343

Displacement



b

Time

Struck
lightly

Time

Struck
heavily

Before Balancing


344

•
•
•
•

Machine in sound condition
Check for damage
Check rotor
Proper tuning of analyzer

Tools



345

•
•
•
•
•
•

Vibration analyzer
Weight scale
Calculator
Graph paper
Compass, ruler, straight edge
Trial weights

In Place Balancing


346

• Corrected with rotor mounted in its
normal housing

Balancing Methods



Selecting Single Plane, Two Plane, Multi-Plane

347

L/D ration
excluding
shaft
L
D

L
D

D

L

Less than
0.5

Balance Correction
Single
plane

Two plane

Multi-plane

0-1000
RPM

Above 1000
RPM

Not
applicable

More than 0-150 RPM 150-2000
0.5 but
RPM or >
less than 2
70% of first
critical

Above
2000 RPM
or > 70% of
first critical

More than
2

Above 70%
of first
critical

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

Note: RPM = machine operating speed

Summary



348


Predictive maintenance

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