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10/16/2010
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1717 Maintenance and Reliability
Maintenance and Reliability
17 - 1© 2011 Pearson Education, Inc. publishing as Prentice Hall
PowerPoint presentation to accompany PowerPoint presentation to accompany Heizer and Render Heizer and Render Operations Management, 10e Operations Management, 10e Principles of Operations Management, 8ePrinciples of Operations Management, 8e
PowerPoint slides by Jeff HeylAdditional content from Gerry Cook
OutlineOutline
Global Company Profile: Orlando Utilities CommissionThe Strategic Importance of
17 - 2© 2011 Pearson Education, Inc. publishing as Prentice Hall
Maintenance and ReliabilityReliability
Improving Individual ComponentsProviding Redundancy
Outline Outline –– ContinuedContinued
MaintenanceImplementing Preventive MaintenanceIncreasing Repair Capabilities
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Increasing Repair CapabilitiesAutonomous Maintenance
Total Productive MaintenanceTechniques for Enhancing Maintenance
Learning ObjectivesLearning ObjectivesWhen you complete this chapter you When you complete this chapter you should be able to:should be able to:
1. Describe how to improve system li bilit
17 - 4© 2011 Pearson Education, Inc. publishing as Prentice Hall
reliability2. Determine system reliability3. Determine mean time between failure
(MTBF)
Learning ObjectivesLearning ObjectivesWhen you complete this chapter you When you complete this chapter you should be able to:should be able to:
4. Distinguish between preventive and breakdown maintenance
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breakdown maintenance5. Describe how to improve maintenance6. Compare preventive and breakdown
maintenance costs7. Define autonomous maintenance
Orlando Utilities Orlando Utilities CommissionCommission
Maintenance of power generating plantsEvery year each plant is taken off-line for 1-3 weeks maintenanceE th h l t i t k
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Every three years each plant is taken off-line for 6-8 weeks for complete overhaul and turbine inspectionEach overhaul has 1,800 tasks and requires 72,000 labor hoursOUC performs over 12,000 maintenance tasks each year
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Orlando Utilities Orlando Utilities CommissionCommission
Every day a plant is down costs OUC $110,000Unexpected outages cost between $3 0 000 d $600 000 d
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$350,000 and $600,000 per dayPreventive maintenance discovered a cracked rotor blade which could have destroyed a $27 million piece of equipment
Strategic Importance of Strategic Importance of Maintenance and ReliabilityMaintenance and Reliability
The objective of maintenance and The objective of maintenance and reliability is to maintain thereliability is to maintain the
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reliability is to maintain the reliability is to maintain the capability of the systemcapability of the system
Strategic Importance of Strategic Importance of Maintenance and ReliabilityMaintenance and Reliability
Failure has far reaching effects on a firm’sOperationReputation
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ProfitabilityDissatisfied customersIdle employeesProfits becoming lossesReduced value of investment in plant and equipment
Maintenance and ReliabilityMaintenance and Reliability
Maintenance is all activities involved in keeping a system’s equipment in working orderReliability is the probability that a
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y p ymachine will function properly for a specified time
Important TacticsImportant Tactics
ReliabilityImproving individual componentsProviding redundancy
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MaintenanceImplementing or improving preventive maintenanceIncreasing repair capability or speed
Maintenance ManagementMaintenance ManagementEmployee Involvement
Partnering with maintenance personnel
Skill trainingReward systemEmployee empowerment
Results
Reduced inventoryImproved quality
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Maintenance and Reliability Procedures
Clean and lubricateMonitor and adjustMake minor repairKeep computerized records
Improved qualityImproved capacityReputation for qualityContinuous improvementReduced variability
Figure 17.1
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ReliabilityReliability
Improving individual components
Rs = R1 x R2 x R3 x … x Rn
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where R1 = reliability of component 1R2 = reliability of component 2
and so on
Overall System ReliabilityOverall System Reliability
e sy
stem
(per
cent
)
100 –
80 –
60 –
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Rel
iabi
lity
of th
e
Average reliability of each component (percent)
| | | | | | | | |100 99 98 97 96
40 –
20 –
0 –
Figure 17.2
Rs
R3
.99
R2
.80
Reliability ExampleReliability Example
R1
.90
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Reliability of the process is
Rs = R1 x R2 x R3 = .90 x .80 x .99 = .713 or 71.3%
Product Failure Rate (FR)Product Failure Rate (FR)Basic unit of measure for reliability
FR(%) = x 100%Number of failuresNumber of units tested
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FR(N) = Number of failuresNumber of unit-hours of operating time
Mean time between failures
MTBF = 1FR(N)
Failure Rate ExampleFailure Rate Example20 air conditioning units designed for use in NASA space shuttles operated for 1,000 hoursOne failed after 200 hours and one after 600 hours
FR(%) = (100%) = 10%2
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FR(%) = (100%) = 10%20
FR(N) = = .000106 failure/unit hr220,000 - 1,200
MTBF = = 9,434 hrs1.000106
Failure Rate ExampleFailure Rate Example20 air conditioning units designed for use in NASA space shuttles operated for 1,000 hoursOne failed after 200 hours and one after 600 hours
FR(%) = (100%) = 10%2Failure rate per trip
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FR(%) = (100%) = 10%20
FR(N) = = .000106 failure/unit hr220,000 - 1,200
MTBF = = 9,434 hrs1.000106
FR = FR(N)(24 hrs)(6 days/trip)FR = (.000106)(24)(6)FR = .153 failures per trip
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Providing RedundancyProviding RedundancyProvide backup components to increase reliability
Probability of first
Probability of needing
Probability of second
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+ xof first component
working
of needing second
component
of second component
working
(.8) + (.8) x (1 - .8)= .8 + .16 = .96
Redundancy ExampleRedundancy ExampleA redundant process is installed to support the earlier example where Rs = .713
R1
0 90
R2
0 80
R3Reliability has
17 - 20© 2011 Pearson Education, Inc. publishing as Prentice Hall
0.90
0.90
0.80
0.80 0.99
= [.9 + .9(1 - .9)] x [.8 + .8(1 - .8)] x .99= [.9 + (.9)(.1)] x [.8 + (.8)(.2)] x .99= .99 x .96 x .99 = .94
increased from .713 to .94
MaintenanceMaintenance
Two types of maintenancePreventive maintenance –routine inspection and servicing
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p gto keep facilities in good repairBreakdown maintenance –emergency or priority repairs on failed equipment
Implementing Preventive Implementing Preventive MaintenanceMaintenance
Need to know when a system requires service or is likely to failHigh initial failure rates are known as
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infant mortalityOnce a product settles in, MTBF generally follows a normal distributionGood reporting and record keeping can aid the decision on when preventive maintenance should be performed
Computerized Maintenance Computerized Maintenance SystemSystem
Output Reports
Inventory and purchasing reports
Equipment parts list
Equipment hi t t
Data Files
Equipment file with parts list
Maintenanceand work order
schedule
Repair
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Figure 17.3
history reports
Cost analysis (Actual vs. standard)
Work orders– Preventive
maintenance– Scheduled
downtime– Emergency
maintenance
Personnel data with skills, wages, etc.
Inventory of spare parts
Repair history file
Maintenance CostsMaintenance CostsThe traditional view attempted to balance preventive and breakdown maintenance costs Typically this approach failed to
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yp y ppconsider the true total cost of breakdowns
InventoryEmployee moraleSchedule unreliability
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Maintenance CostsMaintenance CostsTotal costs
osts
Preventive maintenance costs
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Figure 17.4 (a)
Breakdown maintenance costs
Co
Maintenance commitment
Traditional View
costs
Optimal point (lowestcost maintenance policy)
Maintenance CostsMaintenance Costs
sts
Total costs
Full cost of breakdowns
17 - 26© 2011 Pearson Education, Inc. publishing as Prentice Hall
Figure 17.4 (b)
Cos
Maintenance commitment
Full Cost View
Optimal point (lowestcost maintenance policy)
Preventive maintenance costs
Maintenance Cost ExampleMaintenance Cost ExampleShould the firm contract for maintenance on their printers?
Number of Breakdowns
Number of Months That Breakdowns Occurred
0 2
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0 21 82 63 4
Total : 20
Average cost of breakdown = $300
Maintenance Cost ExampleMaintenance Cost Example1. Compute the expected number of
breakdownsNumber of
BreakdownsFrequency Number of
BreakdownsFrequency
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0 2/20 = .1 2 6/20 = .31 8/20 = .4 3 4/20 = .2
∑ Number of breakdowns
Expected number of breakdowns
Corresponding frequency= x
= (0)(.1) + (1)(.4) + (2)(.3) + (3)(.2)= 1.6 breakdowns per month
Maintenance Cost ExampleMaintenance Cost Example2. Compute the expected breakdown cost per
month with no preventive maintenance
Expected breakdown cost
Expected number of breakdowns
Cost per breakdown= x
17 - 29© 2011 Pearson Education, Inc. publishing as Prentice Hall
breakdown cost of breakdowns breakdownx
= (1.6)($300)= $480 per month
Maintenance Cost ExampleMaintenance Cost Example3. Compute the cost of preventive
maintenance
Preventive Cost of expected breakdowns if service Cost of +
17 - 30© 2011 Pearson Education, Inc. publishing as Prentice Hall
e e t emaintenance cost breakdowns if service
contract signedCost oservice contract
=
+
= (1 breakdown/month)($300) + $150/month= $450 per month
Hire the service firm; it is less expensive
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Increasing Repair Increasing Repair CapabilitiesCapabilities
1. Well-trained personnel2. Adequate resources3. Ability to establish repair plan and
17 - 31© 2011 Pearson Education, Inc. publishing as Prentice Hall
priorities4. Ability and authority to do material
planning5. Ability to identify the cause of
breakdowns6. Ability to design ways to extend MTBF
How Maintenance is How Maintenance is PerformedPerformed
Operator(autonomous maintenance)
Maintenance department
Manufacturer’s field service
Depot service(return equipment)
Competence is higher as we t th i ht
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Figure 17.5
Increasing Operator Ownership Increasing Complexity
Preventive maintenance costs less and is faster the more we move to the left
move to the right
Autonomous MaintenanceAutonomous MaintenanceEmployees accept responsibility for
ObserveCheck
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AdjustCleanNotify
Predict failures, prevent breakdowns, prolong equipment life
Total Productive Total Productive Maintenance (TPM)Maintenance (TPM)
Designing machines that are reliable, easy to operate, and easy to maintain
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Emphasizing total cost of ownership when purchasing machines, so that service and maintenance are included in the cost
Total Productive Total Productive Maintenance (TPM)Maintenance (TPM)
Developing preventive maintenance plans that utilize the best practices of operators, maintenance departments and
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maintenance departments, and depot serviceTraining for autonomous maintenance so operators maintain their own machines and partner with maintenance personnel
Techniques for Enhancing Techniques for Enhancing Maintenance Maintenance
SimulationComputer analysis of complex situations
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Model maintenance programs before they are implementedPhysical models can also be used
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Techniques for Enhancing Techniques for Enhancing Maintenance Maintenance
Expert systemsComputers help users identify problems and select course of action
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Automated sensorsWarn when production machinery is about to fail or is becoming damaged The goals are to avoid failures and perform preventive maintenance before machines are damaged
More on Maintenance More on Maintenance ––
A simple redundancy formulaProblems with breakdown and preventive maintenance
Supplemental MaterialSupplemental Material
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Predictive maintenancePredictive maintenance toolsMaintenance strategy implementationEffective reliability
Providing Redundancy Providing Redundancy ––An Alternate FormulaAn Alternate Formula
P(failing) = 1- P(not failing) = 1 - 0.8 = .2
The reliability of one pump =The probability of one pump not failing = 0.8
If there are two pumps with the
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P(failure of both pumps) =P(failure) pump #1 x P(failure) pump #2
P(failure of both pumps) = 0.2 x 0.2 = .04P(at least one pump working) =
1.0 - .04 = .96
same probability of not failing
Problems With Breakdown Problems With Breakdown MaintenanceMaintenance
“Run it till it breaks”Might be ok for low criticality equipment or redundant systems
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Could be disastrous for mission-critical plant machinery or equipmentNot permissible for systems that could imperil life or limb (like aircraft)
Problems With Preventive Problems With Preventive MaintenanceMaintenance
“Fix it whether or not it is broken”Scheduled replacement or adjustment of parts/equipment with a well established service life
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a well-established service lifeTypical example – plant relampingSometimes misapplied
Replacing old but still good bearingsOver-tightening electrical lugs in switchgear
Another Maintenance StrategyAnother Maintenance StrategyPredictive maintenancePredictive maintenance – Using advanced technology to monitor equipment and predict failures
Using technology to detect and predict imminent equipment failure
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q pVisual inspection and/or scheduled measurements of vibration, temperature, oil and water qualityMeasurements are compared to a “healthy” baselineEquipment that is trending towards failure can be scheduled for repair
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Predictive Maintenance Predictive Maintenance ToolsTools
Vibration analysisInfrared ThermographyOil and Water Analysis
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Oil and Water AnalysisOther Tools:
Ultrasonic testingLiquid Penetrant Dye testingShock Pulse Measurement (SPM)
Predictive Maintenance Predictive Maintenance Vibration AnalysisVibration Analysis
Using sensitive transducers and instruments to detect and analyze vibrationTypically used on expensive mission-
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Typically used on expensive, mission-critical equipment–large turbines, motors, engines or gearboxesSophisticated frequency (FFT) analysis can pinpoint the exact moving part that is worn or defectiveCan utilize a monitoring service
Predictive Maintenance Predictive Maintenance Infrared (IR) ThermographyInfrared (IR) Thermography
Using IR cameras to look for temperature “hot spots” on equipmentTypically used to check electrical
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equipment for wiring problems or poor/loose connectionsCan also be used to look for “cold (wet) spots” when inspecting roofs for leaksHigh quality IR cameras are expensive –most pay for IR thermography services
Predictive Maintenance Predictive Maintenance Oil and Water AnalysisOil and Water Analysis
Taking oil samples from large gearboxes, compressors or turbines for chemical and particle analysis
Particle size can indicate abnormal
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Particle size can indicate abnormal wear
Taking cooling water samples for analysis – can detect excessive rust, acidity, or microbiological foulingServices usually provided by oil vendors and water treatment companies
Predictive Maintenance Predictive Maintenance Other Tools and TechniquesOther Tools and Techniques
Ultrasonic and dye testing – used to find stress cracks in tubes, turbine blades and load bearing structures
Ultrasonic waves sent through metal
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Ultrasonic waves sent through metalSurface coated with red dye, then cleaned off, dye shows cracks
Shock-pulse testing – a specialized form of vibration analysis used to detect flaws in ball or roller bearings at high frequency (32kHz)
Maintenance Strategy Maintenance Strategy ComparisonComparison
Maintenance Strategy Advantages Disadvantages
Resources/ Technology Required
Application Example
Breakdown No prior work required
Disruption of production, injury or death
May need labor/parts at odd hours
Office copier
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Preventive Work can be scheduled
Labor cost, may replace healthy components
Need to obtain labor/parts for repairs
Plant relamping, Machine lubrication
Predictive Impending failures can be detected & work scheduled
Labor costs, costs for detection equipment and services
Vibration, IR analysis equipment or purchased services
Vibration and oil analysis of a large gearbox
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Maintenance Strategy Maintenance Strategy ImplementationImplementation
Predictive
100%
80%
Percentage of Maintenance Time by Strategy
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Breakdown
Preventive
1 2 3 4 5 6 7 8 9 10Year
60%
40%
20%
0%
Is Predictive Maintenance Is Predictive Maintenance Cost Effective?Cost Effective?
In most industries the average rate of return is 7:1 to 35:1 for each predictive maintenance dollar spentVibration analysis IR thermography and
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Vibration analysis, IR thermography and oil/water analysis are all economically proven technologiesThe real savings is the avoidance of manufacturing downtime – especially crucial in JIT
Predictive Maintenance and Predictive Maintenance and Effective ReliabilityEffective Reliability
Effective Reliability (Reff) is an extension of Reliability that includes the probability of failure times the probability of not detecting imminent failure
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gHaving the ability to detect imminent failures allows us to plan maintenance for the component in failure mode, thus avoiding the cost of an unplanned breakdownReff = 1 – (P(failure) x P(not detecting failure))
How Predictive Maintenance How Predictive Maintenance Improves Effective ReliabilityImproves Effective Reliability
Example: a large gearbox with a reliability of .90 has vibration transducers installed for vibration monitoring. The probability of early detection of a failure is .70. What is
17 - 52© 2011 Pearson Education, Inc. publishing as Prentice Hall
ythe effective reliability of the gearbox?Reff = 1 – (P(failure) x P(not detecting failure))
Reff = 1 – (.10 x .30) = 1 - .03 = .97Vibration monitoring has increased the effective reliability from .90 to .97!
Effective Reliability CaveatsEffective Reliability CaveatsPredictive maintenance only increases effective reliability if:
You select the method that can detect the most likely failure mode
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You monitor frequently enough to have high likelihood of detecting a change in component behavior before failureTimely action is taken to fix the issue and forestall the failure (in other words you don’t ignore the warning!)
Increasing Repair Increasing Repair CapabilitiesCapabilities
1. Well-trained personnel2. Adequate resources
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3. Proper application of the three maintenance strategies
4. Continual improvement to improve equipment/system reliability
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17 - 55© 2011 Pearson Education, Inc. publishing as Prentice Hall
All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying,
recording, or otherwise, without the prior written permission of the publisher. Printed in the United States of America.