Table Of Content

KeithMobley/MaintenanceFundamentals FinalProof 15.6.2004 4:42pm page i MAINTENANCE FUNDAMENTALS 2nd Edition KeithMobley/MaintenanceFundamentals FinalProof 15.6.2004 4:42pm page ii PLANT ENGINEERING MAINTENANCE SERIES Vibration Fundamentals R. Keith Mobley Root Cause Failure Analysis R. Keith Mobley Maintenance Fundamentals R. Keith Mobley KeithMobley/MaintenanceFundamentals FinalProof 15.6.2004 4:42pm page iii MAINTENANCE FUNDAMENTALS 2nd Edition R. Keith Mobley AMSTERDAM • BOSTON (cid:127) HEIDELBERG (cid:127) LONDON (cid:127) NEW YORK (cid:127) OXFORD PARIS (cid:127) SAN DIEGO (cid:127) SAN FRANCISCO (cid:127) SINGAPORE (cid:127) SYDNEY (cid:127) TOKYO KeithMobley/MaintenanceFundamentals FinalProof 15.6.2004 4:42pm page iv ElsevierButterworth–Heinemann 200WheelerRoad,Burlington,MA01803,USA LinacreHouse,JordanHill,OxfordOX28DP,UK Copyright#2004,ElsevierInc.Allrightsreserved. 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ISBN:0-7506-7798-8 ForinformationonallButterworth–Heinemannpublications visitourWebsiteatwww.bh.com 04050607080910 10987654321 PrintedintheUnitedStatesofAmerica KeithMobley/MaintenanceFundamentals FinalProof 15.6.2004 4:42pm page v CONTENTS Chapter1 ImpactofMaintenance 1 Chapter2 FundamentalRequirementsofEffective PreventiveMaintenance 11 Chapter3 DesigningaPreventiveMaintenanceProgram 25 Chapter4 PlanningandScheduling 35 Chapter5 ScheduledPreventiveMaintenance 45 Chapter6 MaintenanceEngineeringRolesandResponsibilities 55 Chapter7 ShaftAlignment 71 Chapter8 RotorBalancing 112 Chapter9 Bearings 125 Chapter10 Couplings 171 Chapter11 GearsandGearboxes 201 Chapter12 Compressors 231 Chapter13 ControlValves 266 Chapter14 Conveyors 287 Chapter15 Fans,Blowers,andFluidizers 299 Chapter16 DustCollectors 317 Chapter17 Pumps 331 Chapter18 SteamTraps 365 Chapter19 PerformanceMeasurementandManagement 374 Glossary 390 Index 416 v KeithMobley/MaintenanceFundamentals FinalProof 15.6.2004 4:42pm page vi This page intentionally left blank KeithMobley/MaintenanceFundamentals FinalProof 15.6.2004 4:44pm page 1 1 IMPACT OF MAINTENANCE Maintenance costs, as defined by normal plant accounting procedures, are normallyamajorportionofthetotaloperatingcostsinmostplants.Traditional maintenancecosts(i.e.,laborandmaterial)intheUnitedStateshaveescalatedat a tremendous rate over the past 10 years. In 1981, domestic plants spent more than$600billiontomaintaintheircriticalplantsystems.By1991,thecostshad increasetomorethan$800billion,andtheywereprojectedtotop$1.2trillionby the year 2000. These evaluations indicate that on average, one third, or $250 billion, of all maintenance dollars are wasted through ineffective maintenance management methods. American industry cannot absorb the incredible level of inefficiencyandhopetocompeteintheworldmarket. Because of the exorbitant nature of maintenance costs, they represent the greatest potential short-term improvement. Delays, product rejects, scheduled maintenance downtime, and traditional maintenance costs—such as labor, overtime, and repair parts—are generally the major contributors to abnormal maintenancecostswithinaplant. Thedominantreasonforthisineffectivemanagementisthelackoffactualdata that quantify the actual need for repair or maintenance of plant machinery, equipment, and systems. Maintenance scheduling has been and in many instances still is predicated on statistical trend data or on the actual failure of plantequipment. Untilrecently,middleandcorporatelevelmanagementhaveignoredtheimpact of the maintenance operation on product quality, production costs, and more importantlyonbottom-lineprofit.Thegeneralopinionhasbeen‘‘maintenanceis 1 KeithMobley/MaintenanceFundamentals FinalProof 15.6.2004 4:44pm page 2 2 MaintenanceFundamentals a necessary evil’’ or ‘‘nothing can be done to improve maintenance costs.’’ Perhaps these were true statements 10 or 20 years ago. However, the develop- mentsofmicroprocessororcomputer-basedinstrumentationthatcanbeusedto monitor the operating condition of plant equipment, machinery, and systems have provided the means to manage the maintenance operation. They have provided the means to reduce or eliminate unnecessary repairs, prevent cata- strophic machine failures, and reduce the negative impact of the maintenance operationontheprofitabilityofmanufacturingandproductionplants. MAINTENANCE PHILOSOPHIES Industrialandprocessplantstypicallyutilizetwotypesofmaintenancemanage- ment:(1)run-to-failure,or(2)preventivemaintenance. Run-to-FailureManagement The logic of run-to-failure management is simple and straightforward. When a machinebreaks,fixit.This‘‘ifitain’tbroke,don’tfixit’’methodofmaintaining plantmachineryhasbeenamajorpartofplantmaintenanceoperationssincethe first manufacturing plant was built, and on the surface sounds reasonable. A plant using run-to-failure management does not spend any money on maintenance until a machine or system fails to operate. Run-to-failure is a reactive management technique that waits for machine or equipment failure before any maintenance action is taken. It is in truth a no-maintenance approach of management.Itisalsothemostexpensivemethodofmaintenancemanagement. Few plants use a true run-to-failure management philosophy. In almost all instances, plants perform basic preventive tasks (i.e., lubrication, machine adjustments,andotheradjustments)eveninarun-to-failureenvironment.How- ever, in this type of management, machines and other plant equipment are not rebuiltnorareanymajorrepairsmadeuntiltheequipmentfailstooperate. The major expenses associated with this type of maintenance management are: (1)highsparepartsinventorycost,(2)highovertimelaborcosts,(3)highmachine downtime, and (4) low production availability. Since there is no attempt to anticipatemaintenancerequirements, aplantthatusestrue run-to-failureman- agementmustbeabletoreacttoallpossiblefailureswithintheplant.Thisreactive methodofmanagementforcesthemaintenancedepartmenttomaintainextensive sparepartsinventoriesthatincludesparemachinesoratleastallmajorcompon- entsforallcriticalequipmentintheplant.Thealternativeistorelyonequipment vendorsthatcanprovideimmediatedeliveryofallrequiredspareparts.Evenifthe latterispossible,premiumsforexpediteddeliverysubstantiallyincreasethecosts KeithMobley/MaintenanceFundamentals FinalProof 15.6.2004 4:44pm page 3 ImpactofMaintenance 3 ofrepairpartsanddowntimerequiredforcorrectingmachinefailures.Tominim- ize the impacton production createdby unexpected machine failures, mainten- ancepersonnelmustalsobeabletoreactimmediatelytoallmachinefailures. Thenetresultofthisreactivetypeofmaintenancemanagementishighermain- tenance cost and lower availability of process machinery. Analysis of maintenance costs indicates that a repair performed in the reactive or run-to-failure modewillaverageaboutthreetimeshigherthanthesamerepairmadewithina scheduled or preventive mode. Scheduling the repair provides the ability to minimize the repair time and associated labor costs. It also provides the means ofreducingthenegativeimpactofexpeditedshipmentsandlostproduction. PreventiveMaintenanceManagement There aremany definitionsof preventive maintenance,but allpreventive maintenance management programs are time driven. In other words, maintenance tasks are based on elapsed time or hours of operation. Figure 1.1 illustrates an exampleofthestatisticallifeofamachine-train.Themeantimetofailure(MTTF) orbathtubcurveindicatesthatanewmachinehasahighprobabilityoffailure, because of installation problems, during the first few weeks of operation. After thisinitialperiod,theprobabilityoffailureisrelativelylowforanextendedperiod of time. Following this normal machine life period, the probability of failure increases sharply with elapsed time. In preventive maintenance management, machinerepairsorrebuildsarescheduledonthebasisoftheMTTFstatistic. s e ur ail of f er b m u N Break in or Equipment start up Normal life worn out Time Figure1.1 Bathtubcurve.