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Reliability Maintenance Engineering Day 1 session 5 Measuring Reliability Three day live course focused on reliability engineering for maintenance programs. Introductory material and discussion ranging from basic tools and techniques for data analysis to considerations when building or improving a program.
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MEASURING RELIABILITY TO IMPROVE SAFETY AND AVAILABILITY
Day 1 Session 5
Objectives
• Reliability and the bathtub curve• Calculating PDF plot• What to do if you don’t have data at failure
mode level• Measuring reliability of Line Replaceable Units• Developing the next generation reliability
growth analysis
Early Life Failures
Decreasing hazard rate
Typical failure causes• Manufacturing defect• Shipping damage• Installation damage
Useful Life
Constant hazard rate
Typical failure causes
• Overstress• Random events
Note: rarely occurs in real life – may be useful if change in hazard rate is small enough
Wear out
Increasing hazard rate
Typical failure causes
• Material wear• Rust/Oxidation• Creep/Crack growth• Embrittlement
Discussion & Questions
Probability Distribution Plot
• Like a histogram• Construction notes
• Continuous distributions
• Discrete distributions
How to use PDF plot
• Probability plots
• How many will survive
• How many will fail
Discussion & Questions
Data and Level
• Failure mechanism level
• Subunit level (LRU)
• Unit Level
• System level
Plots and levels
• CDF with system and subunit information
• Continuous Distributions
• Discrete Distributions
time
Prob
abili
ty o
f Fai
lure
(log
sca
le)
Repairable Equipment
• MCF example
• How to interpret– Concave– Convex– Straight
Time
Cum
ulati
ve F
ailu
res
Discussion & Questions
Reliability Growth
• CDF reflecting changes
• Look for change in slope
• Look for change in scale
time
Prob
abili
ty o
f Fai
lure
(log
sca
le)
or
Cumulative Failures over time
• During development or improvement projects
• Plot total failures over time (more later with Duane and related plots)
Discussion & Questions
Summary
• Reliability and the bathtub curve
• Calculating PDF plot• What to do if you don’t
have data at failure mode level
• Measuring reliability of Line Replaceable Units
• Developing the next generation reliability growth analysis
Measuring Reliability to improveSafety and Availability
