Reliability Modelling for Business Decisions. Introduction Definitions Modelling overview Modelling...

Reliability Modelling for Business Decisions

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Introduction

• Definitions• Modelling overview• Modelling construction• Event graph• Results• Business Decisions - Questions answered


Reliability

• The ability of a system or component to perform its required functions under stated conditions for a specified period of time1.

1. Blanchard, Benjamin S. (1992), Logistics Engineering and Management (Fourth Ed.), Prentice-Hall, Inc., Englewood Cliffs, New Jersey.


Maintainability

• The measure of the ability of an item to be retained in or restored to specified condition when maintenance is performed during the course of a specified mission profile (The mission-related system maintainability parameter.)1

1. MIL-STD-721


Availability

• A measure of the degree of a system which is in the operable and committable state at the start of mission when the mission is called for at an unknown random point in time1.

1. MIL-STD-721


Availability

• Inherent availability, Ai

• Achieved availability, Aa

• Operational availability, Ao

1. MIL-STD-721


Modelling and Simulation

AvailabilityCostMaintenanceConfiguration


Availability Simulation

• How is a model built?• It is built to represent the reliability and

maintainability relationships between the items using RBDs

• Data sources are from engineering drawings and workshops with appropriate people

• What data is needed?


Building an RBD



M1

M2

M3



3

59

4564

8951

34

5

78

4

45

76

53

7

48

8

68

9

56

8



Time EventM1 Status

M2 Status

M3 Status

Repair man

Repair Time

DownTime

0 Start Good Good Good Free12 Failed15 Failed17 Failed



Time EventM1 Status

M2 Status

M3 Status

Repair man

Repair Time

DownTime

12 Failed Broken Good Good Free12 Begin Repair Broken Good Good14 Repaired15 Failed17 Failed



Time EventM1 Status

M2 Status

M3 Status

Repair man

Repair Time

DownTime

12 Begin Repair Broken Good Good Busy 214 Repaired15 Failed17 Failed



Time EventM1 Status

M2 Status

M3 Status

Repair man

Repair Time

DownTime

14 Repaired Good Good Good Free 215 Failed17 Failed26 Failed



Time EventM1 Status

M2 Status

M3 Status

Repair man

Repair Time

DownTime

15 Failed Good Broken Good Free15 Begin Repair Good Broken Good17 Failed18 Repaired26 Failed



Time EventM1 Status

M2 Status

M3 Status

Repair man

Repair Time

DownTime

15 Begin Repair Good Broken Good Busy 317 Failed18 Repaired26 Failed



Time EventM1 Status

M2 Status

M3 Status

Repair man

Repair Time

DownTime

17 Failed Good Broken Broken Busy18 Repaired?? Begin Repair26 Failed



Time EventM1 Status

M2 Status

M3 Status

Repair man

Repair Time

DownTime

18 Repaired Good Good Broken Busy 318 Begin Repair Good Good Broken21 Repaired26 Failed33 Failed



Time EventM1 Status

M2 Status

M3 Status

Repair man

Repair Time

DownTime

18 Begin Repair Good Good Broken Busy 321 Repaired26 Failed33 Failed



Time EventM1 Status

M2 Status

M3 Status

Repair man

Repair Time

DownTime

21 Repaired Good Good Good Free 426 Failed33 Failed38 Failed



Time EventM1 Status

M2 Status

M3 Status

Repair man

Repair Time

DownTime

24 End Good Good Good Free26 Failed33 Failed40 Failed



• EG



0

1

2

3

4

5

6

7

8

81.2

81.8

82.4

83.0

83.6

84.2

84.8

85.4

86.0

86.6

87.2

87.8

Availability (%)

Pro

bab

ilit

y D

istr

ibu

tio

n (

%)

0

10

20

30

40

50

60

70

80

90

100

Cu

mu

lati

ve P

rob

abil

ity

(%)

Probability Distribution Cumulative Distribution


Availability SimulationBCIR1.4%LO

1.7%

GS1.8%

Scheduled Outage29.3%

FG16.3%

SECA15.1%

MSHS9.5%

SA7.9%

FW6.8%

CW2.2%

Other8.0%



• Availability M1 – 92%• Availability M2 – 88%• Availability M3 – 83%• Repair man Utilisation 33%• Plant Availability 88%


Questions

• How many spares used?• Which machine caused the most downtime?• Are two repairmen required?• What about levels of repair?• Pro active versus reactive?• How is logistic support allowed for?


Questions

• Where and when is modelling used?– During design to meet requirements and gain

financial sign off– During operating phase to determine

maintenance and other support tactics– During end of life to determine disposal time and

strategy


Reliability Modelling for Business Decisions. Introduction Definitions Modelling overview Modelling...

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