LECTURE 14,15,16reliability analysis.ppt

Reliability Analysis

1. 4S-1
Learning Objectives
Define reliability
Perform reliability computations
Explain the purpose of redundancy in a
system

2. 4S-2
Reliability
Reliability: The ability of a product, part,
or system to perform its intended
function under a prescribed set of
conditions
Failure: Situation in which a product,
part, or system does not perform as
intended
Normal operating conditions:The set
of conditions under which an item’s
reliability is specified

3. 4S-3
Probability that the product or system
will:
Function when activated
Function for a given length of time
Independent events
Events whose occurrence or
nonoccurrence do not influence each other
Redundancy
The use of backup components to increase
reliability
Reliability is a Probability

4. 4S-4
Improving Reliability
Component design
Production/assembly techniques
Testing
Redundancy/backups
Preventive maintenance procedures
User education
System design

5. Transparency Masters to accompany
Heizer/Render –Principles of Operations
Management, 5e, and Operations
© 2004 by Prentice Hall, Inc., Upper Saddle River, N.J. 07458
17-5
Describe or Explain:
How to measure system reliability
How to improve maintenance
How to evaluate maintenance
performance

6. Transparency Masters to accompany
Heizer/Render –Principles of Operations
Management, 5e, and Operations
© 2004 by Prentice Hall, Inc., Upper Saddle River, N.J. 07458
17-6
The Strategic Importance of
Maintenance and Reliability
Failure has far reaching effects on a
firm’s
operation
reputation
profitability
customers
product
employees
profits

7. Transparency Masters to accompany
Heizer/Render –Principles of Operations
Management, 5e, and Operations
© 2004 by Prentice Hall, Inc., Upper Saddle River, N.J. 07458
17-7
Maintenance
Procedures
Employee
Involvement
Maintenance
Performance
© 1995 Corel Corp.
© 1995
Corel
Corp.
Maintenance Performance

8. Transparency Masters to accompany
Heizer/Render –Principles of Operations
Management, 5e, and Operations
© 2004 by Prentice Hall, Inc., Upper Saddle River, N.J. 07458
17-8
Good Maintenance &
Reliability Strategy
Requires:
Employee involvement
Maintenance and reliability procedures
To yield:
Reduced inventory
Improved quality
Improved capacity
Reputation for quality
Continuous improvement

9. Transparency Masters to accompany
Heizer/Render –Principles of Operations
Management, 5e, and Operations
© 2004 by Prentice Hall, Inc., Upper Saddle River, N.J. 07458
17-9
Employee Involvement
Information
sharing
Skill training
Reward system
Power sharing
© 1995 Corel Corp.

10. Transparency Masters to accompany
Heizer/Render –Principles of Operations
Management, 5e, and Operations
© 2004 by Prentice Hall, Inc., Upper Saddle River, N.J. 07458
17-10
Maintenance & Reliability
Procedures
Clean and lubricate
Monitor and adjust
Minor repair
Computerized
records
Maintenance
Procedures
© 1995
Corel
Corp.

11. Transparency Masters to accompany
Heizer/Render –Principles of Operations
Management, 5e, and Operations
© 2004 by Prentice Hall, Inc., Upper Saddle River, N.J. 07458
17-11
Lower
operating
costs
Continuous
improvement
Faster, more
dependable
throughput
Higher
productivity
Improved
quality
Improved
capacity
Reduced
inventory
Maintenance
Maintenance Benefits

12. Transparency Masters to accompany
Heizer/Render –Principles of Operations
Management, 5e, and Operations
© 2004 by Prentice Hall, Inc., Upper Saddle River, N.J. 07458
17-12
Tactics for
Reliability and Maintenance
Reliability Tactics
improving individual components
providing redundancy
Maintenance Tactics
implementing preventive maintenance
increasing repair capabilities

13. Transparency Masters to accompany
Heizer/Render –Principles of Operations
Management, 5e, and Operations
© 2004 by Prentice Hall, Inc., Upper Saddle River, N.J. 07458
17-13
Reliability of
Components in Series
R = R
1* R
2 * R
3* ...

14. Series Systems
14
R
S= R
1R
2... R
n
1 2 n

15. Series Systems (Example)
15
So a two component series system with failure
rates of 0.001 and 0.004 per hour:
R
s(T) = e
-(0.004+0.001)T
 e
-0.005T
The probability of survivalfor 100 hours would
be:
R
s(100) = e
-0.005(100)
 e
-0.5
0.6065 or
60.65%

16. Parallel Systems
16
R
S= 1 -(1 -R
1)*(1 -R
2)...*(1 -R
n)
1
2
n

17. Series-Parallel Systems
Convert to equivalent series system
17
A B
C
C
D
R
A R
B
R
C
R
D
R
C
A B C’ D
R
A R
B R
D
R
C’= 1 –(1-R
C)(1-R
C)

18. Reliability Engineering
Standardization (Certified
Components)
Redundancy (Series systems vs.
Parallel)
Physics of failure (Weathering)
Reliability testing
Accelerated life testing
Burn-in
Component Stress Testing
Infant Mortality Periods
18

19. 4S-19
Rule 1
.90 .80
Lamp 1 Lamp 2
.90 x .80 = .72

20. 4S-20
Rule 2
.90
.80
.90 + (1-.90)*.80 = .98
Lamp 1
Lamp 2 (backup)

21. 4S-21
Rule 3
.90
.80
.70
1-[(1-.90)*(1-.80)*(1-.70)] = .994
1 –P(all fail)
Lamp 1
Lamp 2 (backup for Lamp1)
Lamp 3 (backup for Lamp 2)

22. 4S-22
Example S-1 Reliability
Determine the reliability of the system shown
.98 .90
.90 .92
.95

23. 4S-23
Example S-1 Solution
The system can be reduced to a series of three
components
.98 .90+.90(1-.90) .95+.92(1-.95)
.98 x .99 x .996 = .966

24. 4S-24
Failure Rate
Figure 4S.1
Few (random) failures
Infant
mortality
Failures due
to wear-out
Time, T
Failure Rate

25. 4S-25
Normal Distribution
Reliability
0 z
Figure 4S.3

26. 4S-26
Availability
The fraction of time a piece of equipment
is expected to be available for operationAvailability
MTBF
MTBFMTR


MTBF = mean time between failures
MTR = mean time to repair

27. Availability
availability
27MTRMTBF
MTBF
A
O


MTBF = mean time between
failures
MTR = mean time to repair

28. Transparency Masters to accompany
Heizer/Render –Principles of Operations
Management, 5e, and Operations
© 2004 by Prentice Hall, Inc., Upper Saddle River, N.J. 07458
17-28
Reliability
Probability that an item will function for a
given time
Mean time between failures (MTBF)
Average time between failures of a
repairable item
Failure rate
Reciprocal of MTBF
Evaluating Maintenance

29. Transparency Masters to accompany
Heizer/Render –Principles of Operations
Management, 5e, and Operations
© 2004 by Prentice Hall, Inc., Upper Saddle River, N.J. 07458
17-29
Failure Rate (%)
Number of failures
FR(%) = *
100%
Number of units tested

30. Transparency Masters to accompany
Heizer/Render –Principles of Operations
Management, 5e, and Operations
© 2004 by Prentice Hall, Inc., Upper Saddle River, N.J. 07458
17-30
Lifetime Failure Rates
Infant
mortality
and
improper use
failure
“normal” failure
Wearout
failure
Failure
rate
Lifetime

31. Transparency Masters to accompany
Heizer/Render –Principles of Operations
Management, 5e, and Operations
© 2004 by Prentice Hall, Inc., Upper Saddle River, N.J. 07458
17-31
Failures Per Operating Hour
Number of Failures
FR(n) =
Operating Time

32. Transparency Masters to accompany
Heizer/Render –Principles of Operations
Management, 5e, and Operations
© 2004 by Prentice Hall, Inc., Upper Saddle River, N.J. 07458
17-32
Mean Time Between Failures
1
MTBF =
FR(N)

33. Transparency Masters to accompany
Heizer/Render –Principles of Operations
Management, 5e, and Operations
© 2004 by Prentice Hall, Inc., Upper Saddle River, N.J. 07458
17-33
Providing Redundancy
Probability of
first
component
working
Probability of
second
component
working
+
Probability of
needing
second
component
* =P(R)

34. Transparency Masters to accompany
Heizer/Render –Principles of Operations
Management, 5e, and Operations
© 2004 by Prentice Hall, Inc., Upper Saddle River, N.J. 07458
17-34
How much preventive & breakdown
maintenance
Who performs maintenance
Centralized, decentralized, operator etc.
Contract or in-house
When to replace or repair
How much to replace
Individual or group replacement
Maintenance Decisions

35. Transparency Masters to accompany
Heizer/Render –Principles of Operations
Management, 5e, and Operations
© 2004 by Prentice Hall, Inc., Upper Saddle River, N.J. 07458
17-35
Mean Time Between Failure
and Preventive Maintenance
Frequency
of failure
Mean Time Between Failure
Candidate for preventive
maintenance will have
distribution with low
variability

36. Transparency Masters to accompany
Heizer/Render –Principles of Operations
Management, 5e, and Operations
© 2004 by Prentice Hall, Inc., Upper Saddle River, N.J. 07458
17-36
Centralized maintenance department
Does all maintenance (PM & breakdown)
Decentralized maintenance department
Useful if different equipment used in
different areas of company
Contract maintenance
Used if little equipment or expertise
Operator ownership approach
Organizing the
Maintenance Function

37. Transparency Masters to accompany
Heizer/Render –Principles of Operations
Management, 5e, and Operations
© 2004 by Prentice Hall, Inc., Upper Saddle River, N.J. 07458
17-37
Operator does preventive maintenance
Equipment condition is their responsibility
Learns equipment better
Increases worker’s pride
Reduces repair time & PM costs
Maintenance department is backup
Handles non-routine problems
Provides maintenance training
Has plant-wide responsibilities
Operator-Ownership Approach

38. Transparency Masters to accompany
Heizer/Render –Principles of Operations
Management, 5e, and Operations
© 2004 by Prentice Hall, Inc., Upper Saddle River, N.J. 07458
17-38
Maintenance Costs
Full Cost View
Maintenance
Commitment
Cost
Optimal
Total costs
Full cost of
breakdowns
Preventive
maintenance costs

39. Transparency Masters to accompany
Heizer/Render –Principles of Operations
Management, 5e, and Operations
© 2004 by Prentice Hall, Inc., Upper Saddle River, N.J. 07458
17-39
Increasing Repair
Capabilities:Features of A Good
Maintenance Facility
Well-trained personnel
Adequate resources
Ability to establish a repair plan and
priorities
Ability and authority to do material
planning
Ability to identify the cause of
breakdowns
Ability to design ways to extend MTBF

40. Transparency Masters to accompany
Heizer/Render –Principles of Operations
Management, 5e, and Operations
© 2004 by Prentice Hall, Inc., Upper Saddle River, N.J. 07458
17-40
Operations Manager Must
Determine How Maintenance
Will be Performed
OperatorMaintenance
Department
Manufacturer’s
field service
Depot Service
(return equipment)
Competence is higher as we more
to the right
Preventive maintenance costs
less and is faster as we move
to the left

41. Transparency Masters to accompany
Heizer/Render –Principles of Operations
Management, 5e, and Operations
© 2004 by Prentice Hall, Inc., Upper Saddle River, N.J. 07458
17-41
Techniques for Establishing
Maintenance Policies
Simulation -enables one to evaluate the
impact of various maintenance policies
Expert systems -can be used by staff to help
diagnose faults in machinery and equipment

42. © 2004 by Prentice Hall, Inc., Upper Saddle River, N.J. 07458
17-42
Maintenance
Mean time between failures
Redundancy
Preventive maintenance
Breakdown maintenance
Infant mortality

43. Failure Rate Curve
(Bathtub Curve)
43
“Infant
mortality
period”