17 - 1 maintenance and reliability decisions mgmt3057 © 2011 pearson education

17 - 1

Maintenance and Reliability Maintenance and Reliability DecisionsDecisions

MGMT3057

© 2011 Pearson Education

17 - 2© 2011 Pearson Education

OutlineOutline

The Strategic Importance of Maintenance and Reliability

Reliability Improving Individual Components

Providing Redundancy


Outline – ContinuedOutline – Continued

Maintenance Implementing Preventive

Maintenance

Increasing Repair Capabilities

Autonomous Maintenance

Total Productive Maintenance

Techniques for Enhancing Maintenance


Learning ObjectivesLearning Objectives

When 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 reliability

2. Determine system reliability

3. Determine mean time between failure (MTBF)


Learning ObjectivesLearning Objectives

When 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

5. Describe how to improve maintenance

6. Compare preventive and breakdown maintenance costs

7. Define autonomous maintenance


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 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’s Operation

Reputation

Profitability

Dissatisfied customers

Idle employees

Profits becoming losses

Reduced 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 order

Reliability is the probability that a machine will function properly for a specified time


Important TacticsImportant Tactics

Reliability Improving individual components

Providing redundancy

Maintenance Implementing or improving

preventive maintenance

Increasing repair capability or speed


Maintenance ManagementMaintenance ManagementEmployee Involvement

Partnering with maintenance personnel

Skill trainingReward systemEmployee empowerment

Maintenance and Reliability Procedures

Clean and lubricateMonitor and adjustMake minor repairKeep computerized records

Results

Reduced inventoryImproved qualityImproved capacityReputation for qualityContinuous improvementReduced variability

Figure 17.1


ReliabilityReliability

Improving individual components

Rs = R1 x R2 x R3 x … x Rn

where R1 = reliability of component 1R2 = reliability of component 2

and so on


Overall System ReliabilityOverall System ReliabilityR

elia

bil

ity

of

the

syst

em (

per

cen

t)

Average reliability of each component (percent)

| | | | | | | | |

100 99 98 97 96

100 –

80 –

60 –

40 –

20 –

0 –

n = 10

n = 1

n = 50n = 100n = 200n = 300

n = 400Figure 17.2

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Example 1Example 1

The National Bank processes loan applications through three clerks (each checking different sections of the application in series), with reliabilities of 0.90, 0.80, and 0.99. Find the system reliability.



Rs

R3

.99

R2

.80

Reliability ExampleReliability Example

R1

.90

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 failures

Number of units tested

FR(N) =Number of failures

Number of unit-hours of operating time

Mean time between failures

MTBF =1

FR(N)

17 - 16

Example 2Example 2

20 air conditioning systems designed for use by astronauts in Russia’s Soyuz spacecraft were operated for 1000 hours at a Russian facility. 2 of the systems failed during the test,1 after 200 hours and the other after 600 hours. Find MTBF.



Failure Rate ExampleFailure Rate Example

20 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

20

FR(N) = = .000106 failure/unit hr2

20,000 - 1,200

MTBF = = 9,434 hrs1.000106


Failure Rate ExampleFailure Rate Example

20 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

20

FR(N) = = .000106 failure/unit hr2

20,000 - 1,200

MTBF = = 9,434 hrs1.000106

Failure rate per trip

FR = FR(N)(24 hrs)(6 days/trip)FR = (.000106)(24)(6)FR = .153 failures per trip


Providing RedundancyProviding Redundancy

Provide backup components to increase reliability

+ x

Probability of first

component working

Probability of needing

second component

Probability 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

0.90

R2

0.80

0.80

R3

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

Reliability has increased

from .713 to .94


MaintenanceMaintenance

Two types of maintenance Preventive maintenance –

routine inspection and servicing to keep facilities in good repair

Breakdown 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 fail

High initial failure rates are known as infant mortality

Once a product settles in, MTBF generally follows a normal distribution

Good reporting and record keeping can aid the decision on when preventive maintenance should be performed


Computerized Maintenance Computerized Maintenance SystemSystem

Figure 17.3

Output Reports

Inventory and purchasing reports

Equipment parts list

Equipment history reports

Cost analysis (Actual vs. standard)

Work orders– Preventive

maintenance– Scheduled

downtime– Emergency

maintenance

Data Files

Personnel data with skills, wages, etc.

Equipment file with parts list

Maintenanceand work order

schedule

Inventory of spare parts

Repair history file


Maintenance CostsMaintenance Costs The traditional view attempted to

balance preventive and breakdown maintenance costs

Typically this approach failed to consider the true total cost of breakdowns Inventory

Employee morale

Schedule unreliability


Maintenance CostsMaintenance Costs

Figure 17.4 (a)

Total costs

Breakdown maintenance costs

Co

sts

Maintenance commitment

Traditional View

Preventive maintenance costs

Optimal point (lowestcost maintenance policy)


Maintenance CostsMaintenance Costs

Figure 17.4 (b)

Co

sts

Maintenance commitment

Full Cost View

Optimal point (lowestcost maintenance policy)

Total costs

Full cost of breakdowns

Preventive maintenance costs

17 - 27

Comparing Preventive & Comparing Preventive & Breakdown Maintenance Breakdown Maintenance

CostsCosts“Run until breakdown” policy or contract for preventive maintenance.

1:Compute expected number of breakdowns (history) if the firm continues as is, without the service contract.


17 - 28

Continue..Continue..

2:Compute the expected breakdown cost per month with no preventive maintenance contract.

3: Compute the cost of preventive maintenance.

4: Compare the two options and select the one that will cost less.



Maintenance Cost ExampleMaintenance Cost ExampleShould the firm contract for maintenance on their printers?

Number of Breakdowns

Number of Months That Breakdowns Occurred

0 2

1 8

2 6

3 4

Total : 20Average cost of breakdown = $300


Maintenance Cost ExampleMaintenance Cost Example

1. Compute the expected number of breakdowns

Number of Breakdowns

Frequency Number of Breakdowns

Frequency

0 2/20 = .1 2 6/20 = .3

1 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



2. Compute the expected breakdown cost per month with no preventive maintenance

Expected breakdown cost

Expected number of breakdowns

Cost per breakdown= x

= (1.6)($300)

= $480 per month



3. Compute the cost of preventive maintenance

Preventive maintenance cost

Cost of expected breakdowns if service contract signed

Cost of service contract

=+

= (1 breakdown/month)($300) + $150/month= $450 per month

Hire the service firm; it is less expensive


Increasing Repair Increasing Repair CapabilitiesCapabilities

1. Well-trained personnel

2. Adequate resources

3. Ability to establish repair plan and priorities

4. Ability and authority to do material planning

5. Ability to identify the cause of breakdowns

6. Ability to design ways to extend MTBF


How Maintenance is How Maintenance is PerformedPerformed

Figure 17.5

Operator(autonomous maintenance)

Maintenance department

Manufacturer’s field service

Depot service(return equipment)

Increasing Operator Ownership Increasing Complexity

Preventive maintenance costs less and is faster the more we move to the left

Competence is higher as we move to the right


Autonomous MaintenanceAutonomous Maintenance Employees accept responsibility for

Observe

Check

Adjust

Clean

Notify

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

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 depot service

Training for autonomous maintenance so operators maintain their own machines and partner with maintenance personnel


Techniques for Enhancing Techniques for Enhancing Maintenance Maintenance

Simulation Computer analysis of complex

situations

Model maintenance programs before they are implemented

Physical models can also be used


Techniques for Enhancing Techniques for Enhancing Maintenance Maintenance

Expert systems Computers help users identify

problems and select course of action

Automated sensors Warn 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


Problems With Breakdown Problems With Breakdown MaintenanceMaintenance

“Run it till it breaks” Might be ok for low criticality

equipment or redundant systems

Could be disastrous for mission-critical plant machinery or equipment

Not 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

Typical example – plant relamping

Sometimes misapplied Replacing old but still good bearings

Over-tightening electrical lugs in switchgear


Another Maintenance StrategyAnother Maintenance Strategy Predictive maintenancePredictive maintenance – Using

advanced technology to monitor equipment and predict failures Using technology to detect and predict

imminent equipment failure

Visual inspection and/or scheduled measurements of vibration, temperature, oil and water quality

Measurements are compared to a “healthy” baseline

Equipment that is trending towards failure can be scheduled for repair


Increasing Repair Increasing Repair CapabilitiesCapabilities

1. Well-trained personnel

2. Adequate resources

3. Continual improvement to improve equipment/system reliability

17 - 1 maintenance and reliability decisions mgmt3057 © 2011 pearson education

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