1. 10/16/2010
Maintenance and
17 Reliability
Outline
Global Company Profile: Orlando
Utilities Commission
The Strategic Importance of
PowerPoint presentation to accompany
Heizer and Render
Maintenance and Reliability
Operations Management, 10e
Principles of Operations Management, 8e Reliability
PowerPoint slides by Jeff Heyl
Additional content from Gerry Cook
Improving Individual Components
Providing Redundancy
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Outline – Continued Learning Objectives
Maintenance When you complete this chapter you
should be able to:
Implementing Preventive
Maintenance
1. Describe how to improve system
Increasing Repair Capabilities reliability
li bilit
Autonomous Maintenance 2. Determine system reliability
Total Productive Maintenance 3. Determine mean time between failure
Techniques for Enhancing (MTBF)
Maintenance
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Learning Objectives Orlando Utilities
When you complete this chapter you
Commission
should be able to: Maintenance of power generating plants
Every year each plant is taken off-line
4. Distinguish between preventive and for 1-3 weeks maintenance
breakdown maintenance Every three years each plant is taken
E th h l ti t k
5. Describe how to improve maintenance off-line for 6-8 weeks for complete
overhaul and turbine inspection
6. Compare preventive and breakdown
maintenance costs Each overhaul has 1,800 tasks and
requires 72,000 labor hours
7. Define autonomous maintenance
OUC performs over 12,000 maintenance
tasks each year
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Orlando Utilities Strategic Importance of
Commission Maintenance and Reliability
Every day a plant is down costs OUC
$110,000
The objective of maintenance and
Unexpected outages cost between
reliability is to maintain the
$350,000 d $600,000
$3 0 000 and $600 000 per d
day
capability of the system
Preventive maintenance discovered a
cracked rotor blade which could have
destroyed a $27 million piece of
equipment
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Strategic Importance of Maintenance and Reliability
Maintenance and Reliability
Failure has far reaching effects on a firm’s Maintenance is all activities involved
in keeping a system’s equipment in
Operation working order
Reputation
Reliability is the p
y probability that a
y
Profitability machine will function properly for a
Dissatisfied customers specified time
Idle employees
Profits becoming losses
Reduced value of investment in plant and
equipment
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Important Tactics Maintenance Management
Employee Involvement
Reliability Partnering with
maintenance personnel
Improving individual components Skill training Results
Reward system
Reduced inventory
Providing redundancy Employee empowerment
Improved quality
Improved capacity
Maintenance Reputation for quality
Maintenance and Reliability Continuous improvement
Implementing or improving Procedures Reduced variability
preventive maintenance Clean and lubricate
Monitor and adjust
Increasing repair capability or speed Make minor repair
Keep computerized records
Figure 17.1
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Overall System Reliability
Reliability 100 –
Reliability of the system (percent)
Improving individual components 80 –
60 –
Rs = R1 x R2 x R3 x … x Rn
e
40 –
where R1 = reliability of component 1
20 –
R2 = reliability of component 2
0 |–
and so on 100
| |
99
| |
98
| |
97
| |
96
Average reliability of each component (percent)
Figure 17.2
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Reliability Example Product Failure Rate (FR)
Basic unit of measure for reliability
R1 R2 R3
Number of failures
.90 .80 FR(%) = x 100%
.99 Rs Number of units tested
Number of failures
FR(N) =
Reliability of the process is Number of unit-hours of operating time
Rs = R1 x R2 x R3 = .90 x .80 x .99 = .713 or 71.3% Mean time between failures
1
MTBF =
FR(N)
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Failure Rate Example Failure Rate Example
20 air conditioning units designed for use in 20 air conditioning units designed for use in
NASA space shuttles operated for 1,000 hours NASA space shuttles operated for 1,000 hours
One failed after 200 hours and one after 600 hours One failed after 200 hours and one after 600 hours
2 Failure rate per trip
2
FR(%) = (100%) = 10% FR(%) = (100%) = 10%
20 20
FR = FR(N)(24 hrs)(6 days/trip)
2 FR2= (.000106)(24)(6) failure/unit hr
FR(N) = = .000106 failure/unit hr FR(N) = = .000106
20,000 - 1,200 20,000 - 1,200failures per trip
FR = .153
1 1
MTBF = = 9,434 hrs MTBF = = 9,434 hrs
.000106 .000106
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4. 10/16/2010
Providing Redundancy Redundancy Example
Provide backup components to A redundant process is installed to support
increase reliability the earlier example where Rs = .713
R1 R2 R3
Probability Probability Probability Reliability has
of first of second of needing 0.90
0 90 0.80
0 80 increased from
component + component x second
working component .713 to .94
working
0.90 0.80 0.99
(.8) + (.8) x (1 - .8) = [.9 + .9(1 - .9)] x [.8 + .8(1 - .8)] x .99
= .8 + .16 = .96 = [.9 + (.9)(.1)] x [.8 + (.8)(.2)] x .99
= .99 x .96 x .99 = .94
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Maintenance Implementing Preventive
Maintenance
Two types of maintenance Need to know when a system requires
service or is likely to fail
Preventive maintenance –
routine inspection and servicing
p g High initial failure rates are known as
to keep facilities in good repair infant mortality
Breakdown maintenance – Once a product settles in, MTBF
emergency or priority repairs on generally follows a normal distribution
failed equipment Good reporting and record keeping can
aid the decision on when preventive
maintenance should be performed
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Computerized Maintenance
System
Data Files
Maintenance Costs
Output Reports
Equipment file
with parts list Inventory and
purchasing reports
The traditional view attempted to
balance preventive and breakdown
Maintenance
and work order
schedule
Equipment
parts list maintenance costs
Repair
Equipment
history reports
hi t t
Typically this approach failed to
yp y pp
history file
Cost analysis
consider the true total cost of
Inventory of
(Actual vs. standard)
breakdowns
spare parts
Work orders
– Preventive
Inventory
maintenance
Personnel data
with skills,
– Scheduled
downtime
– Emergency
Employee morale
wages, etc. maintenance
Schedule unreliability
Figure 17.3
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Maintenance Costs Maintenance Costs
Total
costs Total
costs
Preventive Full cost of
maintenance breakdowns
osts
sts
costs
Cos
Co
Breakdown
maintenance Preventive
costs maintenance
costs
Maintenance commitment Maintenance commitment
Optimal point (lowest Optimal point (lowest
cost maintenance policy) cost maintenance policy)
Traditional View Full Cost View
Figure 17.4 (a) Figure 17.4 (b)
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Maintenance Cost Example Maintenance Cost Example
Should the firm contract for maintenance 1. Compute the expected number of
on their printers? breakdowns
Number of Number of Months That Number of Frequency Number of Frequency
Breakdowns Breakdowns Occurred Breakdowns Breakdowns
0 2 0 2/20 = .1 2 6/20 = .3
1 8 1 8/20 = .4 3 4/20 = .2
2 6
3 4 Expected number
of breakdowns = ∑ Number of
breakdowns x
Corresponding
frequency
Total : 20
= (0)(.1) + (1)(.4) + (2)(.3) + (3)(.2)
Average cost of breakdown = $300 = 1.6 breakdowns per month
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Maintenance Cost Example Maintenance Cost Example
2. Compute the expected breakdown cost per 3. Compute the cost of preventive
month with no preventive maintenance maintenance
Expected Expected number Cost per Cost of expected
breakdown cost = of breakdowns x breakdown Preventive
e e t e Cost of
o
breakdowns if service +
=
maintenance cost service contract
contract signed
= (1.6)($300) = (1 breakdown/month)($300) + $150/month
= $480 per month = $450 per month
Hire the service firm; it is less expensive
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Increasing Repair How Maintenance is
Capabilities Performed
1. Well-trained personnel Operator
(autonomous Maintenance Manufacturer’s Depot service
2. Adequate resources maintenance) department field service (return equipment)
3. Ability to establish repair plan and Competence is higher as we
priorities move t the right
to th i ht
Preventive
4. Ability and authority to do material maintenance costs less and
is faster the more we move to the left
planning
Increasing Operator Ownership Increasing Complexity
5. Ability to identify the cause of
breakdowns
6. Ability to design ways to extend MTBF Figure 17.5
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Autonomous Maintenance Total Productive
Maintenance (TPM)
Employees accept responsibility for
Observe Designing machines that are
reliable, easy to operate, and easy
Check to maintain
Adjust
Emphasizing total cost of
Clean ownership when purchasing
Notify machines, so that service and
Predict failures, prevent maintenance are included in the
breakdowns, prolong equipment life cost
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Total Productive Techniques for Enhancing
Maintenance (TPM) Maintenance
Developing preventive Simulation
maintenance plans that utilize the Computer analysis of complex
best practices of operators, situations
maintenance departments and
departments, Model maintenance programs
depot service before they are implemented
Training for autonomous Physical models can also be used
maintenance so operators maintain
their own machines and partner
with maintenance personnel
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7. 10/16/2010
Techniques for Enhancing More on Maintenance –
Maintenance
Supplemental Material
Expert systems
A simple redundancy formula
Computers help users identify
problems and select course of action Problems with breakdown and preventive
maintenance
Automated sensors Predictive maintenance
Warn when production machinery is Predictive maintenance tools
about to fail or is becoming damaged Maintenance strategy implementation
The goals are to avoid failures and Effective reliability
perform preventive maintenance
before machines are damaged
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Providing Redundancy – Problems With Breakdown
An Alternate Formula Maintenance
The reliability of one pump =
The probability of one pump not failing = 0.8 “Run it till it breaks”
P(failing) = 1- P(not failing) = 1 - 0.8 = .2 Might be ok for low criticality
If there are two pumps with the equipment or redundant systems
same probability of not failing
Could be disastrous for mission-
P(failure of both pumps) = critical plant machinery or
P(failure) pump #1 x P(failure) pump #2 equipment
P(failure of both pumps) = 0.2 x 0.2 = .04 Not permissible for systems that
P(at least one pump working) = could imperil life or limb (like
aircraft)
1.0 - .04 = .96
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Problems With Preventive Another Maintenance Strategy
Maintenance Predictive maintenance – Using
“Fix it whether or not it is broken” advanced technology to monitor
equipment and predict failures
Scheduled replacement or
adjustment of parts/equipment with Using technology to detect and predict
imminent equipment failure
q p
a well established service life
well-established
Visual inspection and/or scheduled
Typical example – plant relamping measurements of vibration, temperature,
oil and water quality
Sometimes misapplied
Measurements are compared to a
Replacing old but still good bearings “healthy” baseline
Over-tightening electrical lugs in Equipment that is trending towards failure
switchgear can be scheduled for repair
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8. 10/16/2010
Predictive Maintenance Predictive Maintenance
Tools Vibration Analysis
Vibration analysis Using sensitive transducers and
instruments to detect and analyze
Infrared Thermography vibration
Oil and Water Analysis Typically used on expensive mission-
expensive,
critical equipment–large turbines,
Other Tools: motors, engines or gearboxes
Ultrasonic testing Sophisticated frequency (FFT) analysis
Liquid Penetrant Dye testing can pinpoint the exact moving part that
is worn or defective
Shock Pulse Measurement (SPM)
Can utilize a monitoring service
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Predictive Maintenance Predictive Maintenance
Infrared (IR) Thermography Oil and Water Analysis
Taking oil samples from large
Using IR cameras to look for
gearboxes, compressors or turbines for
temperature “hot spots” on equipment
chemical and particle analysis
Typically used to check electrical
Particle size can indicate abnormal
equipment for wiring problems or
wear
poor/loose connections
Taking cooling water samples for
Can also be used to look for “cold (wet)
analysis – can detect excessive rust,
spots” when inspecting roofs for leaks
acidity, or microbiological fouling
High quality IR cameras are expensive –
Services usually provided by oil
most pay for IR thermography services
vendors and water treatment companies
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Maintenance Strategy
Predictive Maintenance Comparison
Other Tools and Techniques Resources/
Ultrasonic and dye testing – used to Maintenance
Strategy Advantages Disadvantages
Technology
Required
Application
Example
find stress cracks in tubes, turbine Breakdown No prior Disruption of May need Office copier
blades and load bearing structures work production, labor/parts
required injury or death at odd
Ultrasonic waves sent through metal hours
Preventive Work can Labor cost, Need to Plant
Surface coated with red dye, then be may replace obtain relamping,
scheduled healthy labor/parts Machine
cleaned off, dye shows cracks components for repairs lubrication
Shock-pulse testing – a specialized Predictive Impending
failures can
Labor costs,
costs for
Vibration, IR
analysis
Vibration
and oil
form of vibration analysis used to detect be detected detection equipment analysis of a
& work equipment and or large
flaws in ball or roller bearings at high scheduled services purchased gearbox
frequency (32kHz) services
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Maintenance Strategy Is Predictive Maintenance
Implementation Cost Effective?
Percentage of Maintenance Time by Strategy In most industries the average rate of
100%
return is 7:1 to 35:1 for each predictive
80%
maintenance dollar spent
Predictive
Vibration analysis IR thermography and
analysis,
60%
Preventive oil/water analysis are all economically
40%
proven technologies
Breakdown
The real savings is the avoidance of
20%
manufacturing downtime – especially
0%
crucial in JIT
1 2 3 4 5 6 7 8 9 10
Year
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Predictive Maintenance and How Predictive Maintenance
Effective Reliability Improves Effective Reliability
Effective Reliability (Reff) is an extension Example: a large gearbox with a reliability
of Reliability that includes the probability of .90 has vibration transducers installed
of failure times the probability of not for vibration monitoring. The probability of
detecting imminent failure
g early detection of a failure is .70. What is
y
Having the ability to detect imminent the effective reliability of the gearbox?
failures allows us to plan maintenance Reff = 1 – (P(failure) x P(not detecting failure))
for the component in failure mode, thus Reff = 1 – (.10 x .30) = 1 - .03 = .97
avoiding the cost of an unplanned
breakdown Vibration monitoring has increased the
effective reliability from .90 to .97!
Reff = 1 – (P(failure) x P(not detecting failure))
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Effective Reliability Caveats Increasing Repair
Predictive maintenance only Capabilities
increases effective reliability if:
1. Well-trained personnel
You select the method that can detect
the most likely failure mode 2. Adequate resources
You monitor frequently enough to have 3. Proper application of the three
high likelihood of detecting a change in maintenance strategies
component behavior before failure
4. Continual improvement to improve
Timely action is taken to fix the issue
and forestall the failure (in other words
equipment/system reliability
you don’t ignore the warning!)
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