October - Library - Central Queensland University

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Figure 6: Weibull Curve Generated From Sample Data
The B values shown in Figure 6 represent the times at which 10%, 15%, or 20% of the filters are likely to become blocked. These
a re unreliability values which we can use to decide when we might want to change the filters. At B10 we could expect a 90%
probability that we would not suffer a failure due to blocked filters.
F i g u re 7 shows some various Weibull shapes and the potential maintenance strategy for dealing with them. The maintenance strategy
we use will be very dependent on the business impact of the failures. Weibull only gives us a probability of success. It does not
give us all of the information we need for making the best business decisions.
Curve Description Potential Maintenance Strategy
A: Infant failure followed by a long
period of gradually increasing or
constant failure rate.
B: A long period of gradually increasing
or constant failure rate followed by a
rapid wear out period.
C: Very few initial failures followed by a
short period of rapidly increasing
failures then a long period of gradually
increasing or constant failure rate.
D: Constantly increasing failure rate.
E: Random Failures with constant
failure rate
F: Combination
Figure 7: Weibull Shapes and Potential Maintenance Strategies
Root Cause Failure Analysis to
determine causes of infant failures.
Interim stage parts and personnel if
repairs required. Do not implement
time based maintenance.
Potential for time based replacement
or overhaul at just before the point
where Wearout begins to occur. Root
Cause Failure Analysis if Wearout is
occurring earlier than desired or
required to meet business obectives.
Predictive Maintenance or Constant
Condition Monitoring. Root Cause
Failure Analysis if residual failure rate
is too high.
Time based replacement or overhaul
depending on the level of acceptable
cost or risk.
Run to Failure, Predictive Maintenance,
or Constant Condition Monitoring. Root
Cause Failure Analysis if failure rate is
higher than desired or required to meet
cost and risk needs.
May require different strategies
depending on where in life cycle.