1. Maintenance Strategies
Dr David Baglee
School of Computing and Technology

2. Background Maintenance strategy is becoming a more important issue
Today machines are integrated
Very little inventory stock held
Automation of processes increasing
Downsizing of workforce

3. Hidden Losses Labour Visible Costs Materials Breakdowns Plant Trips
Operability
Reduced
Throughput
Restart Losses
Poor Quality
Poor Integrity
Low Morale

4. Maintenance Strategies
Reactive Maintenance (1)
Preventive Maintenance (2)
Conditional Maintenance
Predictive Maintenance (3)
Total Productive Maintenance (TPM)
Reliability Centred Maintenance (RCM)
Reactive: Breakdown Maintenance, Run-to-failure Maintenance, Unscheduled Maintenance, Corrective Maintenance
Preventive: Planned Maintenance, Scheduled Maintenance, Periodic Maintenance
[Conditional: Opportunity Maintenance]
Predictive: Condition Based Monitoring, Condition Monitoring

5. Reliability Domains Reliability Centered Maintenance
Total Productive Maintenance
Predictive Maintenance
Planned Maintenance
Reactive Maintenance
MAINTENANCE EXPENSE

6. Reactive Maintenance Allow machinery to run to failure
Traditionally the exclusive maintenance mode until fairly recently
Continues to be the predominate method of maintenance
Many major industrial companies still operate in this mode
Repair or corrective action is taken after the fault has occurred
Reactive or Corrective Maintenance (CM) is the old “if it ain’t broke don’t fix it” line. This approach is the perennial run to failure mode. It is simplicity itself, requires no forethought, and (at least up to the point of machinery failure) requires the least support from the O&M crew and infrastructure. In this particular case, the problem initiator was the pump starting to cavitate the day it was installed This degradation mechanism was responsible for extreme erosion of both the impeller and the pump casing, leading to failure in 6 months.
This situation created a reactive scenario showing in the slide.
In a reactive mode, little, if any, attention is paid to ensuring that the operating conditions are within the design envelope and, consequently, the actual service performance and life-span of the equipment are substantially below the estimates of the manufacturer. The equipment is simply run until it either catastrophically fails, or it no longer can provide its intended function. At that time (usually around 2 a.m.) the equipment must be replaced.
While reactive maintenance does make economic sense in some instances (replacing a light bulb for instance), in a vast majority of process applications it is by far the most expensive O&M mode going. It is still, surprisingly, the predominant method of plant operation in the U.S. despite the high product loss, capital equipment loss, total manpower expenditure, and accident rate that result.

7. Advantages Disadvantages
Low direct costs
Less staff required
Appropriate for certain applications
High costs due to unplanned downtime of equipment
Increased labor costs, especially if overtime is needed
Costs involved with repair or replacement of equipment
Possible secondary equipment or process damage from equipment failure
Inefficient use of staff resources
Does not support the true definition of maintenance

8. Preventive Maintenance
Actions that detect, prevent, or mitigate degradation of a component or system
Aims to sustain or extend useful life by controlling degradation to an acceptable level.
Actions performed periodically prior to functional failures to achieve desired safety or reliability levels.
Preventive Maintenance (PM) is the art of periodically checking the performance or material condition of a piece of equipment to determine if the operating conditions and resulting degradation rate are within the expected limits. If they are not, a search for the reason for the more rapid degradation must be sought so the problem can be corrected, or at least mitigated, before the machine fails.
The method is illustrated in the slide.
The tests, inspections, servicing or parts-replacement actions are done on a service life (e.g. hours of operation) or purely on a time-in-service basis. Note that for our hypothetical case, the service life was extended by a factor of four to 24 months, due to an awareness of the rapid decline in pump condition caused by cavitation and an attempt to slow down this degradation mechanism. Unfortunately we still do not have a grip on the root cause. Although accurate failure statistics allow the test interval to be optimized, catastrophic failures are still likely to occur. The PM method is also very labor intensive, much unneeded maintenance is performed, and incidental damage to equipment is widely reported as a result of poor maintenance practices. A PM system can, however, be a cost effective strategy when the life span of the equipment is well understood and consistent. Studies in the utility industry report a reactive-to-preventive life cycle cost savings in the 12 to 18% range. Thus this methodology, while it significantly reduces the O&M cost over the purely reactive variety, still allows abrupt failures to spoil an otherwise good night’s sleep.

9. Preventive Maintenance
A step forward from reacting to breakdowns to preventing breakdowns:
Pioneered by the U.S. Navy.
Analogous to an automobile schedule of maintenance.
Time intervals based on manufacturer recommendations and machinery history experience.

10. Preventive Maintenance
Scheduled maintenance activities are based on specific time intervals
Calendar days
Run time
Parts produced
Includes routine tasks such as:
Changing oil
Replacing filters
Greasing bearings
Instrument calibration

11. Preventive Maintenance
Includes measurement of degradation prone areas for rapid changes in out-of-tolerance conditions.
Wear rings
Alignment
Shaft end play
Useful against age related modes of failure:
Wear
Fatigue
Corrosion

12. Advantages Disadvantages
Cost effective in many capital intensive or potentially high impact processes.
Flexibility allows for the adjustment of maintenance periodicity.
Increased component life-cycle.
Energy savings.
Reduced equipment or process failures.
Catastrophic failures still likely to occur.
Labor intensive.
Performance of unneeded maintenance.
Incidental damage to components through poor maintenance practices.
Time-Directed Tasking: Proven to save 12% - 18% over “Run to Failure”

13. Conditional Maintenance
Maintenance actions conducted as result of a specific condition, or as a result of specific circumstances or events.
Examples of Conditional Inspections
Aircraft hard landing
Unscheduled disassembly
Power Interruption
Over/Under Voltage
Lightning strike
Over stress
Unscheduled or scheduled shut-down
AKA Opportunity Maintenance

14. Predictive Maintenance
Measurements that detect the onset of a degradation mechanism thereby allowing causal stressors to be eliminated or controlled prior to any significant deterioration in the component physical state.
Results indicate current and future functional capability.
Involves use of specialised equipment to monitor the condition of machines (Vibration, Oil Analysis, Thermography, Acoustic Emission, etc)
Predictive Maintenance (PDM) advocates measurements aimed at the detection of degradation mechanisms themselves, thereby allowing the degradation to be understood and eliminated or controlled, prior to significant physical deterioration of the equipment.
These usually nonintrusive measurement methods allows us to detect and correct the potential for degradation considerably earlier in the equipment degradation scenario. Technologies such as vibration analysis, oil analysis, thermography and condition monitoring pushes our problem recognition capability to the leading edge of the degradation envelope. So now our time line now looks like the one shown in the slide.
The application of this technology results in :
• marked increased equipment life
• earlier corrective actions taken
• decreased process downtime
• decreases in maintenance parts and labor
• better product quality
• decreased environmental impact
• energy savings.
The sum of these advantages adds another 8 to 12% to the savings over a good PM program. Root cause can usually be understood and, consequently, mitigation can be better targeted and repeating failures are history. On the negative side, the up-front investment in diagnostic equipment and the high level of staff training make this a more difficult pitch to an ever wary, cost conscious management. The savings are now usually in terms of avoided cost (a hard concept for management to grasp) and therefor become much more difficult to demonstrate and easier to forget.

15. Predictive Maintenance
Schedule maintenance activities when mechanical or operational conditions warrant to repair or replace deteriorated equipment before obvious problems occur.
Allows assessment of whether equipment will fail during some future period
Hence indicates best time to perform repairs or maintenance

16. Advantages Disadvantages
Increased component operational life/availability
Allows for pre-emptive corrective actions
Reduced equipment or process downtime
Decreased costs for parts and labor
Better product quality
Improved worker and environmental safety
Improved worker morale
Energy savings
Increased investment in diagnostic equipment
Increased investment in training of staff
Savings potentials not readily seen by management
Additional 8% - 12% savings over a good preventive maintenance program

17. Total Productive Maintenance
JIT based approach
Workers perform preventive maintenance on the machines they operate
Skilled maintenance personnel train the operators and develop ‘one-point lessons’.
Maintenance department moves from a ‘fire-fighting’ mode to a prevention mode & re-engineering
Restore deteriorated equipment through Improvement-Related Maintenance.
Identify design weaknesses and improve equipment
Preventive (equipment manufacturers/operators data)
Predictive (data analysis and periodic diagnostic tests)

18. Reliability Centered Maintenance
Process used to determine maintenance requirements of any physical asset in its operating context.
Plan is based upon reliability criteria with priority given to the most critical components.
Determine what types of failures are likely to occur.
Focuses on preventing failures whose consequences are likely to be serious.
Emphasizes the use of predictive maintenance practices.
Utilizes previous aspects of reactive and preventive maintenance concepts, in concert with root cause analysis.

19. Strategy Development Advantages Disadvantages
Towards more efficient maintenance programmes.
Eliminating unnecessary maintenance or overhauls.
Minimize frequency of overhauls.
Reduced chance of sudden equipment failure.
Focuses maintenance activities on critical components.
Increased component reliability.
Root causes of problems identified.
Disadvantages
Can have significant startup cost
Training
Equipment
etc.
Savings potential not readily seen by management.
Changes take time to implement
TPM and RCM

20. Costs Total Cost Predictive Direct Cost Preventive Reactive
Indirect Cost

21. Trade-off between Repairs and PM
Minimum Total
Maintenance Cost
Total
Maintenance
Costs
Annual Cost
Preventive
Maintenance
Cost
Breakdown
and Repair
Cost
Degree of Preventive Maintenance

22. Service Organizations
Maintenance issues are not limited to manufacturing
Transportation firms (airlines, railways, haulage, dispatch companies, etc) must maintain vehicles in good operating condition
Highways Department must maintain roads
Office personnel are reliant on computers, printers, copiers and fax machines working properly
As services become increasingly automated, service firms face more and more maintenance issues

23. Trends in Maintenance
Production machinery is becoming more and more complex and maintenance personnel must keep pace
Special training programs to maintain worker skill level
Subcontracting service companies
Production workers maintain own equipment
Computer assistance in maintenance