Heizer om10 ch17

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Heizer om10 ch17

  1. 1. 17 - 1© 2011 Pearson Education, Inc. publishing as Prentice Hall17 Maintenance andReliabilityPowerPoint presentation to accompanyHeizer and RenderOperations Management, 10ePrinciples of Operations Management, 8ePowerPoint slides by Jeff HeylAdditional content from Gerry Cook
  2. 2. 17 - 2© 2011 Pearson Education, Inc. publishing as Prentice HallOutline Global Company Profile: OrlandoUtilities Commission The Strategic Importance ofMaintenance and Reliability Reliability Improving Individual Components Providing Redundancy
  3. 3. 17 - 3© 2011 Pearson Education, Inc. publishing as Prentice HallOutline – Continued Maintenance Implementing PreventiveMaintenance Increasing Repair Capabilities Autonomous Maintenance Total Productive Maintenance Techniques for EnhancingMaintenance
  4. 4. 17 - 4© 2011 Pearson Education, Inc. publishing as Prentice HallLearning ObjectivesWhen you complete this chapter youshould be able to:1. Describe how to improve systemreliability2. Determine system reliability3. Determine mean time between failure(MTBF)
  5. 5. 17 - 5© 2011 Pearson Education, Inc. publishing as Prentice HallLearning ObjectivesWhen you complete this chapter youshould be able to:4. Distinguish between preventive andbreakdown maintenance5. Describe how to improve maintenance6. Compare preventive and breakdownmaintenance costs7. Define autonomous maintenance
  6. 6. 17 - 6© 2011 Pearson Education, Inc. publishing as Prentice HallOrlando UtilitiesCommission Maintenance of power generating plants Every year each plant is taken off-linefor 1-3 weeks maintenance Every three years each plant is takenoff-line for 6-8 weeks for completeoverhaul and turbine inspection Each overhaul has 1,800 tasks andrequires 72,000 labor hours OUC performs over 12,000 maintenancetasks each year
  7. 7. 17 - 7© 2011 Pearson Education, Inc. publishing as Prentice HallOrlando UtilitiesCommission Every day a plant is down costs OUC$110,000 Unexpected outages cost between$350,000 and $600,000 per day Preventive maintenance discovered acracked rotor blade which could havedestroyed a $27 million piece ofequipment
  8. 8. 17 - 8© 2011 Pearson Education, Inc. publishing as Prentice HallStrategic Importance ofMaintenance and ReliabilityThe objective of maintenance andreliability is to maintain thecapability of the system
  9. 9. 17 - 9© 2011 Pearson Education, Inc. publishing as Prentice HallStrategic Importance ofMaintenance and Reliability Failure has far reaching effects on a firm’s Operation Reputation Profitability Dissatisfied customers Idle employees Profits becoming losses Reduced value of investment in plant andequipment
  10. 10. 17 - 10© 2011 Pearson Education, Inc. publishing as Prentice HallMaintenance and Reliability Maintenance is all activities involvedin keeping a system’s equipment inworking order Reliability is the probability that amachine will function properly for aspecified time
  11. 11. 17 - 11© 2011 Pearson Education, Inc. publishing as Prentice HallImportant Tactics Reliability Improving individual components Providing redundancy Maintenance Implementing or improvingpreventive maintenance Increasing repair capability or speed
  12. 12. 17 - 12© 2011 Pearson Education, Inc. publishing as Prentice HallMaintenance ManagementEmployee InvolvementPartnering withmaintenance personnelSkill trainingReward systemEmployee empowermentMaintenance and ReliabilityProceduresClean and lubricateMonitor and adjustMake minor repairKeep computerized recordsResultsReduced inventoryImproved qualityImproved capacityReputation for qualityContinuous improvementReduced variabilityFigure 17.1
  13. 13. 17 - 13© 2011 Pearson Education, Inc. publishing as Prentice HallReliabilityImproving individual componentsRs = R1 x R2 x R3 x … x Rnwhere R1 = reliability of component 1R2 = reliability of component 2and so on
  14. 14. 17 - 14© 2011 Pearson Education, Inc. publishing as Prentice HallOverall System ReliabilityReliabilityofthesystem(percent)Average reliability of each component (percent)| | | | | | | | |100 99 98 97 96100 –80 –60 –40 –20 –0 –Figure 17.2
  15. 15. 17 - 15© 2011 Pearson Education, Inc. publishing as Prentice HallRsR3.99R2.80Reliability ExampleR1.90Reliability of the process isRs = R1 x R2 x R3 = .90 x .80 x .99 = .713 or 71.3%
  16. 16. 17 - 16© 2011 Pearson Education, Inc. publishing as Prentice HallProduct Failure Rate (FR)Basic unit of measure for reliabilityFR(%) = x 100%Number of failuresNumber of units testedFR(N) =Number of failuresNumber of unit-hours of operating timeMean time between failuresMTBF =1FR(N)
  17. 17. 17 - 17© 2011 Pearson Education, Inc. publishing as Prentice HallFailure Rate Example20 air conditioning units designed for use inNASA space shuttles operated for 1,000 hoursOne failed after 200 hours and one after 600 hoursFR(%) = (100%) = 10%220FR(N) = = .000106 failure/unit hr220,000 - 1,200MTBF = = 9,434 hrs1.000106
  18. 18. 17 - 18© 2011 Pearson Education, Inc. publishing as Prentice HallFailure Rate Example20 air conditioning units designed for use inNASA space shuttles operated for 1,000 hoursOne failed after 200 hours and one after 600 hoursFR(%) = (100%) = 10%220FR(N) = = .000106 failure/unit hr220,000 - 1,200MTBF = = 9,434 hrs1.000106Failure rate per tripFR = FR(N)(24 hrs)(6 days/trip)FR = (.000106)(24)(6)FR = .153 failures per trip
  19. 19. 17 - 19© 2011 Pearson Education, Inc. publishing as Prentice HallProviding RedundancyProvide backup components toincrease reliability+ xProbabilityof firstcomponentworkingProbabilityof needingsecondcomponentProbabilityof secondcomponentworking(.8) + (.8) x (1 - .8)= .8 + .16 = .96
  20. 20. 17 - 20© 2011 Pearson Education, Inc. publishing as Prentice HallRedundancy ExampleA redundant process is installed to supportthe earlier example where Rs = .713R10.900.90R20.800.80R30.99= [.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 = .94Reliability hasincreased from.713 to .94
  21. 21. 17 - 21© 2011 Pearson Education, Inc. publishing as Prentice HallMaintenance Two types of maintenance Preventive maintenance –routine inspection and servicingto keep facilities in good repair Breakdown maintenance –emergency or priority repairs onfailed equipment
  22. 22. 17 - 22© 2011 Pearson Education, Inc. publishing as Prentice HallImplementing PreventiveMaintenance Need to know when a system requiresservice or is likely to fail High initial failure rates are known asinfant mortality Once a product settles in, MTBFgenerally follows a normal distribution Good reporting and record keeping canaid the decision on when preventivemaintenance should be performed
  23. 23. 17 - 23© 2011 Pearson Education, Inc. publishing as Prentice HallComputerized MaintenanceSystemFigure 17.3Output ReportsInventory andpurchasing reportsEquipmentparts listEquipmenthistory reportsCost analysis(Actual vs. standard)Work orders– Preventivemaintenance– Scheduleddowntime– EmergencymaintenanceData FilesPersonnel datawith skills,wages, etc.Equipment filewith parts listMaintenanceand work orderscheduleInventory ofspare partsRepairhistory file
  24. 24. 17 - 24© 2011 Pearson Education, Inc. publishing as Prentice HallMaintenance Costs The traditional view attempted tobalance preventive and breakdownmaintenance costs Typically this approach failed toconsider the true total cost ofbreakdowns Inventory Employee morale Schedule unreliability
  25. 25. 17 - 25© 2011 Pearson Education, Inc. publishing as Prentice HallMaintenance CostsFigure 17.4 (a)TotalcostsBreakdownmaintenancecostsCostsMaintenance commitmentTraditional ViewPreventivemaintenancecostsOptimal point (lowestcost maintenance policy)
  26. 26. 17 - 26© 2011 Pearson Education, Inc. publishing as Prentice HallMaintenance CostsFigure 17.4 (b)CostsMaintenance commitmentFull Cost ViewOptimal point (lowestcost maintenance policy)TotalcostsFull cost ofbreakdownsPreventivemaintenancecosts
  27. 27. 17 - 27© 2011 Pearson Education, Inc. publishing as Prentice HallMaintenance Cost ExampleShould the firm contract for maintenanceon their printers?Number ofBreakdownsNumber of Months ThatBreakdowns Occurred0 21 82 63 4Total : 20Average cost of breakdown = $300
  28. 28. 17 - 28© 2011 Pearson Education, Inc. publishing as Prentice HallMaintenance Cost Example1. Compute the expected number ofbreakdownsNumber ofBreakdownsFrequency Number ofBreakdownsFrequency0 2/20 = .1 2 6/20 = .31 8/20 = .4 3 4/20 = .2∑ Number ofbreakdownsExpected numberof breakdownsCorrespondingfrequency= x= (0)(.1) + (1)(.4) + (2)(.3) + (3)(.2)= 1.6 breakdowns per month
  29. 29. 17 - 29© 2011 Pearson Education, Inc. publishing as Prentice HallMaintenance Cost Example2. Compute the expected breakdown cost permonth with no preventive maintenanceExpectedbreakdown costExpected numberof breakdownsCost perbreakdown= x= (1.6)($300)= $480 per month
  30. 30. 17 - 30© 2011 Pearson Education, Inc. publishing as Prentice HallMaintenance Cost Example3. Compute the cost of preventivemaintenancePreventivemaintenance costCost of expectedbreakdowns if servicecontract signedCost ofservice contract=+= (1 breakdown/month)($300) + $150/month= $450 per monthHire the service firm; it is less expensive
  31. 31. 17 - 31© 2011 Pearson Education, Inc. publishing as Prentice HallIncreasing RepairCapabilities1. Well-trained personnel2. Adequate resources3. Ability to establish repair plan andpriorities4. Ability and authority to do materialplanning5. Ability to identify the cause ofbreakdowns6. Ability to design ways to extend MTBF
  32. 32. 17 - 32© 2011 Pearson Education, Inc. publishing as Prentice HallHow Maintenance isPerformedFigure 17.5Operator(autonomousmaintenance)MaintenancedepartmentManufacturer’sfield serviceDepot service(return equipment)Increasing Operator Ownership Increasing ComplexityPreventivemaintenance costs less andis faster the more we move to the leftCompetence is higher as wemove to the right
  33. 33. 17 - 33© 2011 Pearson Education, Inc. publishing as Prentice HallAutonomous Maintenance Employees accept responsibility for Observe Check Adjust Clean Notify Predict failures, preventbreakdowns, prolong equipment life
  34. 34. 17 - 34© 2011 Pearson Education, Inc. publishing as Prentice HallTotal ProductiveMaintenance (TPM) Designing machines that arereliable, easy to operate, and easyto maintain Emphasizing total cost ofownership when purchasingmachines, so that service andmaintenance are included in thecost
  35. 35. 17 - 35© 2011 Pearson Education, Inc. publishing as Prentice HallTotal ProductiveMaintenance (TPM) Developing preventivemaintenance plans that utilize thebest practices of operators,maintenance departments, anddepot service Training for autonomousmaintenance so operators maintaintheir own machines and partnerwith maintenance personnel
  36. 36. 17 - 36© 2011 Pearson Education, Inc. publishing as Prentice HallTechniques for EnhancingMaintenance Simulation Computer analysis of complexsituations Model maintenance programsbefore they are implemented Physical models can also be used
  37. 37. 17 - 37© 2011 Pearson Education, Inc. publishing as Prentice HallTechniques for EnhancingMaintenance Expert systems Computers help users identifyproblems and select course of action Automated sensors Warn when production machinery isabout to fail or is becoming damaged The goals are to avoid failures andperform preventive maintenancebefore machines are damaged
  38. 38. 17 - 38© 2011 Pearson Education, Inc. publishing as Prentice HallMore on Maintenance – A simple redundancy formula Problems with breakdown and preventivemaintenance Predictive maintenance Predictive maintenance tools Maintenance strategy implementation Effective reliabilitySupplemental Material
  39. 39. 17 - 39© 2011 Pearson Education, Inc. publishing as Prentice HallProviding Redundancy –An Alternate FormulaP(failing) = 1- P(not failing) = 1 - 0.8 = .2 The reliability of one pump =The probability of one pump not failing = 0.8P(failure of both pumps) =P(failure) pump #1 x P(failure) pump #2P(failure of both pumps) = 0.2 x 0.2 = .04P(at least one pump working) =1.0 - .04 = .96 If there are two pumps with thesame probability of not failing
  40. 40. 17 - 40© 2011 Pearson Education, Inc. publishing as Prentice HallProblems With BreakdownMaintenance “Run it till it breaks” Might be ok for low criticalityequipment or redundant systems Could be disastrous for mission-critical plant machinery orequipment Not permissible for systems thatcould imperil life or limb (likeaircraft)
  41. 41. 17 - 41© 2011 Pearson Education, Inc. publishing as Prentice HallProblems With PreventiveMaintenance “Fix it whether or not it is broken” Scheduled replacement oradjustment of parts/equipment witha well-established service life Typical example – plant relamping Sometimes misapplied Replacing old but still good bearings Over-tightening electrical lugs inswitchgear
  42. 42. 17 - 42© 2011 Pearson Education, Inc. publishing as Prentice HallAnother Maintenance Strategy Predictive maintenance – Usingadvanced technology to monitorequipment and predict failures Using technology to detect and predictimminent equipment failure Visual inspection and/or scheduledmeasurements of vibration, temperature,oil and water quality Measurements are compared to a“healthy” baseline Equipment that is trending towards failurecan be scheduled for repair
  43. 43. 17 - 43© 2011 Pearson Education, Inc. publishing as Prentice HallPredictive MaintenanceTools Vibration analysis Infrared Thermography Oil and Water Analysis Other Tools: Ultrasonic testing Liquid Penetrant Dye testing Shock Pulse Measurement (SPM)
  44. 44. 17 - 44© 2011 Pearson Education, Inc. publishing as Prentice HallPredictive MaintenanceVibration Analysis Using sensitive transducers andinstruments to detect and analyzevibration Typically used on expensive, mission-critical equipment–large turbines,motors, engines or gearboxes Sophisticated frequency (FFT) analysiscan pinpoint the exact moving part thatis worn or defective Can utilize a monitoring service
  45. 45. 17 - 45© 2011 Pearson Education, Inc. publishing as Prentice HallPredictive MaintenanceInfrared (IR) Thermography Using IR cameras to look fortemperature “hot spots” on equipment Typically used to check electricalequipment for wiring problems orpoor/loose connections Can also be used to look for “cold (wet)spots” when inspecting roofs for leaks High quality IR cameras are expensive –most pay for IR thermography services
  46. 46. 17 - 46© 2011 Pearson Education, Inc. publishing as Prentice HallPredictive MaintenanceOil and Water Analysis Taking oil samples from largegearboxes, compressors or turbines forchemical and particle analysis Particle size can indicate abnormalwear Taking cooling water samples foranalysis – can detect excessive rust,acidity, or microbiological fouling Services usually provided by oilvendors and water treatment companies
  47. 47. 17 - 47© 2011 Pearson Education, Inc. publishing as Prentice HallPredictive MaintenanceOther Tools and Techniques Ultrasonic and dye testing – used tofind stress cracks in tubes, turbineblades and load bearing structures Ultrasonic waves sent through metal Surface coated with red dye, thencleaned off, dye shows cracks Shock-pulse testing – a specializedform of vibration analysis used to detectflaws in ball or roller bearings at highfrequency (32kHz)
  48. 48. 17 - 48© 2011 Pearson Education, Inc. publishing as Prentice HallMaintenance StrategyComparisonMaintenanceStrategy Advantages DisadvantagesResources/TechnologyRequiredApplicationExampleBreakdown No priorworkrequiredDisruption ofproduction,injury or deathMay needlabor/partsat oddhoursOffice copierPreventive Work canbescheduledLabor cost,may replacehealthycomponentsNeed toobtainlabor/partsfor repairsPlantrelamping,MachinelubricationPredictive Impendingfailures canbe detected& workscheduledLabor costs,costs fordetectionequipment andservicesVibration, IRanalysisequipmentorpurchasedservicesVibrationand oilanalysis of alargegearbox
  49. 49. 17 - 49© 2011 Pearson Education, Inc. publishing as Prentice HallMaintenance StrategyImplementationBreakdownPreventivePredictive1 2 3 4 5 6 7 8 9 10Year100%80%60%40%20%0%Percentage of Maintenance Time by Strategy
  50. 50. 17 - 50© 2011 Pearson Education, Inc. publishing as Prentice HallIs Predictive MaintenanceCost Effective? In most industries the average rate ofreturn is 7:1 to 35:1 for each predictivemaintenance dollar spent Vibration analysis, IR thermography andoil/water analysis are all economicallyproven technologies The real savings is the avoidance ofmanufacturing downtime – especiallycrucial in JIT
  51. 51. 17 - 51© 2011 Pearson Education, Inc. publishing as Prentice HallPredictive Maintenance andEffective Reliability Effective Reliability (Reff) is an extensionof Reliability that includes the probabilityof failure times the probability of notdetecting imminent failure Having the ability to detect imminentfailures allows us to plan maintenancefor the component in failure mode, thusavoiding the cost of an unplannedbreakdownReff = 1 – (P(failure) x P(not detecting failure))
  52. 52. 17 - 52© 2011 Pearson Education, Inc. publishing as Prentice HallHow Predictive MaintenanceImproves Effective Reliability Example: a large gearbox with a reliabilityof .90 has vibration transducers installedfor vibration monitoring. The probability ofearly detection of a failure is .70. What isthe effective reliability of the gearbox?Reff = 1 – (P(failure) x P(not detecting failure))Reff = 1 – (.10 x .30) = 1 - .03 = .97 Vibration monitoring has increased theeffective reliability from .90 to .97!
  53. 53. 17 - 53© 2011 Pearson Education, Inc. publishing as Prentice HallEffective Reliability Caveats Predictive maintenance onlyincreases effective reliability if: You select the method that can detectthe most likely failure mode You monitor frequently enough to havehigh likelihood of detecting a change incomponent behavior before failure Timely action is taken to fix the issueand forestall the failure (in other wordsyou don’t ignore the warning!)
  54. 54. 17 - 54© 2011 Pearson Education, Inc. publishing as Prentice HallIncreasing RepairCapabilities1. Well-trained personnel2. Adequate resources3. Proper application of the threemaintenance strategies4. Continual improvement to improveequipment/system reliability
  55. 55. 17 - 55© 2011 Pearson Education, Inc. publishing as Prentice HallAll rights reserved. No part of this publication may be reproduced, stored in a retrievalsystem, 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.

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