USING FIELD AND TEST DATA TO ESTIMATE RELIABILITY
Day 1 Session 4
Objectives
• Discussing reliability data types• Considering complete and censored data• Analyzing trend plotting, 80-20 plots and
statistical plots• Drawing a best-fit regression line with Weibull• Recording data related to reliability
performance• Providing continuity in data collection systems
Reliability Data Types
• CMMS data
• Process data
• Life data
• Time to Failure data
Reliability Data Types
• Pass/Fail data• Attribute data
• Time or cycles to failure• Variables data
• Start and stop definitions
Reliability Data Types
• Complete data– All units have failed
• Censored data– Right censored – not all
have failed yet– Left censored – not sure
when some started– Interval censored – not
sure when failure occurred between inspections.
Reliability Data Types
• Non-repairable data
All start at time zero
Reliability Data Types
• repairable data
All start at time zero
Discussion & Questions
Trend Plotting
Advantages• Easy
• Visual
• Actual data
Disadvantages• Difficult to see changes
• Lagging indicator
• May require adjustments for scheduled downtime
80 – 20 or Pareto plotting
Advantages• Easy
• Visual
• Prioritization build in
Disadvantages• Difficult to see changes over
time
• Doesn’t include costs impact
Coun
t or F
requ
ency
Life Data CDF
Advantages• Accounts for all data
• Visual
• Easy to read
Disadvantages• Difficult to see changes
• Requires probability paper or software
• Requires time to failure data
CDF – Cumulative Distribution Function -
MCF plotting
Advantages• Very Easy to create
• Easy to see patterns
Disadvantages• Difficult to summarize
• Requires more than two failures/repairs per equipment
• Doesn’t account for scheduled downtime or extended repairs
MCF – Mean Cumulative Function
Wayne Nelson, Graphical Analysis of Repair Data
Discussion & Questions
Weibull Plotting with Weibull++
• Data preparation• Basic algorithm• Censored data handing
• For more details• www.weibul.com
Reading a Weibull CDF Plot
MCF plotting
• Data Preparation• Basic algorithm
• For more information• Trindade paper, book,
Nelsons paper, book
Reading an MCF plot
Discussion & Questions
Plot labeling
• Title• Data source• Data timeframe
• Axis labels and units
Report Data
• Regular reports
• Project reports
• Analysis reports
• Recommendation reports
Comparisons over time
• Break up data by time– Before/after change– Before/after experiment– Before/after overhaul
• Labels• Show magnitude of
impact clearly, if any.
Data collection over time
• Vendor data• Installation• Maintenance• Decommissioning
Discussion & Questions
Summary
• Discussing reliability data types
• Considering complete and censored data
• Analyzing trend plotting, 80-20 plots and statistical plots
• Drawing a best-fit regression line with Weibull
• Recording data related to reliability performance
• Providing continuity in data collection systems
Using field and test data to estimate reliability
