Maintenance and its types-corrective, preventive, predictive, condition based

1. MAINTENANCE ENGINEERING
MODULE II
Prepared By
Dhanesh S
Assistant Professor
Department of Mechanical Engineering

2. Maintenance Strategies
■ Maintenance strategy:A long-term plan, covering all aspects of
maintenance management which sets direction for maintenance
management, and contains firm action plans for achieving a desired
future state for the maintenance function
■ Maintenance system: methodology and strategy for establishing a good
maintenance management principles and providing a framework for
identifying, mapping and controlling the elements of maintenance
functions
■ Maintenance types-what kind of maintenance functions are to be
performed and what type of maintenance methodology is to be chosen to
plan and execute those functions in most efficient way

3. Maintenance Strategies
■ Maintenance Policy: tool for maintenance personnel to plan their
appropriate maintenance strategies.
■ Maintenance policy consist of five major components and different
maintenance strategies are developed form these components
■ Five major components are:
– Length of time for maintaining for their present use
– The life requirement of the buildings and their findings, services
– The standard to which building and its services are to be maintained
– The reaction time required between defects occurring and repair
being carried out
– The legal and statutory requirements shall also be considered

4. Maintenance Strategies
■ Significance of maintenance policy are:
– Ensures that equipment is always in ready and reliable
condition.Ensures company which is able to respond to any sudden
change in demand
– Ensure that equipment is always calibrated to provide good quality
products and competitive advantage.Ensures no sudden and frequent
breakdowns and reduce production of defective products
– Ensures that there are no major breakdowns. Ensures there is no loss
of inventory or market share of companies
– Ensures that costs are always controlled
– Particularly important in capital intensive industries

5. Maintenance Strategies
■ Failure to implement maintenance policy lead to :
– Full capacity utilization not achieved
– Increase in production cost as fixed labour cost cannot be reduced
– Increase in maintenance cost as more spare parts are required
– Reduction in product quality and increase in wastage
– Safety of workers and operators in risk
Basis of Selection:
■ Various reasons for evaluating/considering/selecting maintenance strategies such as
– Which set of tasks that should be performed and their frequency
– With aging of the plant a different mix of tasks is needed to maintain reliability
– Perhaps with reduced staff it is not possible to perform all the tasks that used to be done and only the
most effective tasks are selected
– The plant operators may want to reduce maintenance expenditures without elevating risk or reducing
reliability
– Downtime a problem
– Availability of equipment to carry out maintenance

6. Integrated Information System for
Maintenance Strategy

7. Types of Maintenance Strategies

8. Maintenance Decision Diagram

9. Breakdown Maintenance
■ In this type of system, maintenance repair is done after failure has already occurred. The
equipment is allowed to run undisturbed till it fails.
■ Only when equipment fails to perform designated functions or comes to a grinding halt,
any maintenance or repair job is taken.
■ Also called Reactive Maintenance
■ This system works good in small factory/plant where
– Number of equipments are few
– Equipments are simple and repair does not call for specialists or special
tools/tackles
– When sudden stoppage/failure of equipment will not cause severe financial loss in
terms of delivery commitment or further damage to other equipments
– When sudden failure will not cause any severe safety or environmental hazards

10. Breakdown Maintenance
■ In small factories-no specialized maintenance crew are kept and
maintenance is normally done by persons operating the machine and
other concerned persons
■ Outside agency may also be approached.
■ Does not work in big industries, having large number of equipment's
some of which may be quite intricate

11. Breakdown Maintenance
■ Flow diagram of breakdown maintenance

12. Breakdown Maintenance
Advantages Disadvantages
Lowers Initial Cost Increased cost due to unplanned downtime of
equipment
Requires less staff:complex repairs are
outsourced
Increased labour cost, including overtime and
outside help
No planning required:repairs when failed and
hence no time spent for planning
Cost involved with repair and replacement of
equipment
Possible secondary equipment or process
damage for equipment failure
Insufficient use of staff or internal resources
Shorter life expectancy of assets
Interferes with planned work
Collateral damage
Indirect costs,repeat issues etc

13. Corrective Maintenance
■ Means maintenance actions for correcting or restoring a failed unit or a
unit going to fail.
■ Include different types of actions, from small actions like typical
adjustments and minor repairs to minor design of equipment
■ Mostly unplanned action, but may include few planned/scheduled actions
as well
■ Actions in corrective maintenance may be sub-divided according to
priority as follows:
– Emergency work, high priority, generally offline, i.e.after stopping
the equipment, giving normally less than 24hours notice to take up
the job

14. Corrective Maintenance
– Deferred works-jobs of lower order priority;generally off-line
– To eliminate/reduce repetitive breakdowns
– Specific reconditioning or redesign jobs, generally small or medium
in volume
■ Corrective maintenance-generally one time task,once taken up,completed
fully.
■ Bigger corrective maintenance jobs have following stages:
– Collection of data/information and analysis
– Identify likely causes
– Find out best possible solution to eliminate those likely causes
– Implement these solutions etc.

15. Corrective Maintenance
■ Difference between corrective maintenance and preventive maintenance
are:
– PM jobs are generally taken before the equipment has stopped
working but corrective may be taken before or after equipment has
stopped working
– Level and type of PM jobs are normally decided within maintenance
department whereas in corrective maintenance, help of other
departments may be taken
– PM jobs are planned well in advance whereas corrective
maintenance jobs may be taken at shorter notice
■ Corrective maintenance may include some od design-out maintenance
jobs

16. Preventive Maintenance
■ Any action to prevent equipment downtime/failure
■ Include-periodical evaluation of critical equipment, machinery to detect
problem and schedule maintenance tasks to avoid degradation in operating
conditions
 Objectives of Preventive Maintenance:
 To minimize the number of breakdowns on critical equipment
 To reduce the loss of production that occurs when the equipment failures
takes place
 To increase the productive life of all capital equipment
 To acquire meaningful data relative to history of all capital equipment so
that sound decisions are to repair, overhaul or replacement
 To permit better planning and scheduling of required maintenance work
 To promote better safety and health of the work force

17. Preventive Maintenance
■ Various components of PM:
– Check drawing, design and installation of equipments including
subsequent redesign and minor modifications, depending on specific
nature of problems
– Proper identification of all items, proper documentation and
codification,check-
■ History cards/records
■ Spares catalogues, equipment catalogues and inventory lists
■ Job manuals and standard maintenance practises
■ Maintenance workorders and other pending workorders

18. Preventive Maintenance
■ Periodic inspection of plant and equipment-
– Use of checklists by inspectors and its frequency; shift-wise, daily, weakly and
monthly
– Well qualified and experienced inspectors
– Use of necessary aids,test equipments, vibration meters, ultrasonic and x-ray
equipments etc
– Preparing total defect/failure list and its categorization
■ Repetitive servicing, repairs, upkeep and overhaul
– Minor repairs
– Medium repairs
– Major overhauls or capital repairs
– Emergency repairs or corrective repairs
– Recovery or salvaging

19. Preventive Maintenance
■ Adequate lubrication, cleaning and painting of equipments;changing of oils and
lubricants of systems as per inspection reports
■ Typical failure analysis and plan for their elimination
■ Organization for PM
■ Budget provision and control for repairs and PM
 Elements of Preventive Maintenance:
 Inspection
 Servicing
 Calibration
 Testing
 Alignment
 Adjustment
 Installation

20. Preventive Maintenance
■ PM schedules-generally two types
– Fixed Time Maintenance(FTM) Schedules
– Condition Based Maintenance (CBM ) Schedules
■ Planning and scheduling of all activities of PM-done beforehand to avoid
following delays
– Waiting for job orders at the start of shift and also after finishing one job
– Visiting the site or other place to find out what to do and how to do
– Unncessary trips to stores as complete list of tools/spares are not available
at the start of shift and tools are brought from stores as and when needed
– Operating personnel not clearly aware of time of sparing the machine and
doing their preparatory jobs before handling the machine to maintenance
for PM
■ Loosing time because of non-availability of safety clearance/permit in time

21. Preventive Maintenance
■ Process Flow of Steps Involved in Preventive Maintenance:
– Step 1: Analyzing the maintenance system
– Step 2: Reviewing the systems
– Step 3: Prioritizing the maintenance
– Step 4:Training the maintenance staffs
– Step 5: Implementing the maintenance plan
 Frequency of Major Repair in PM:
 Scheduled periodic/cyclic major repair-important component of PM
 Interval between the two PM major repairs for same equipment, i.e.frequency may not
be same throughout the lifecycle of the equipment
 Frequency-dictated by bathub curve
 Failure developing period(FDP) can also be used to decide preventive maintenance
frequency
 FDP-Time period from when it is possible to detect a failure until a breakdown occurs
or it is the time difference between failure and breakdown

22. Preventive Maintenance

23. Preventive Maintenance
■ Graph shows rough curve for major repairs of preventive maintenance
■ X1,X2, X3….represent working period of an equipment when its condition
deteriorates from good(nearly 100%) condition to bad when the failure
rate is expected to be unacceptable
■ Y1, Y2, Y3…is period of PM major repair, when the equipment is restored
to nearly 100%.
■ In actual practice X1, X2, X3..and Y1, Y2,Y3…may not be the same, but is
often nearby

24. Preventive Maintenance
Advantages Disadvantages
1. Cost effective in many capital intensive
processes
1. Catastrophic failures still likely to occur
2. Flexibility allows for the adjustment of
maintenance periodicity
2. Labour intensive
3. Increased component life cycle 3. Included performance of unneeded
maintenance
4. Energy savings 4. Potential for incidental damage to
components in conducting unneeded
maintenance
5. Reduced equipment or process failure

25. Preventive Maintenance
■ Sources for PM Procedure Development:
– Vendor Recommended PM: Maintainance manuls provided by
equipment manufacturers can be used to build a PM procedure if not
fully adopted also
– Plant Developed PM: Mechanics who work on equipment and
operators who run it can help define PM that might be specific to
equipment environment
– Generic PM: Developed for general classes of equipment can be
modified to fit a specific facility requirement.