Reliability Engineering

Fred Schenkelbergfms@fmsreliability.com

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