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Reply to "Difference between FMEA and FMECA"

Steve,
quote:
The interval of condition monitoring is set by the PF curve primarily... end of story ... I say it is a second order consideration

I agree entirely with the first part of the above, but you have ignored my comment. "I have not seen many people producing P-F curves". Have you?. Secondly the P-F interval can vary quite a bit, for a single failure mode, there can be quite some uncertainty about the droop. If we suspect the PdM technique, we may use a second method, not more of the same. Thus if bearing vibration readings are not definitive, we might cross check the oil condition or temperature trends. So I cannot agree with your view that 'more frequent' inspection' of doubtful validity will help. Where the degradation rates, and hence droop of the P-F curve can vary a lot, more inspections will help, but it should not be based on Asset criticality at all. After all the droop is a physical phenomenon; it does not have anything to do with criticality - which is totally unrelated to the physical process of degradation. I disagree with you when you say that criticality has a place in the inspection frequency decision at any order, not just the second.
quote:
hard time replacement is determined by safe life
On the one hand you don't want to believe failure data sources; where do you get the safe life from? To those who believe in statistical analysis - and I know you are not in that group, getting safe life is easy, e.g. L10 of ball bearings. Maybe you can explain your process of determining safe or useful life.
quote:
how many data points you recommend to be confident of your answer

I have just explained that errors of 50% in the actual value of the failure rate(or MTBF) will not make a big difference to the maintenance interval. So the answer must be self evident; 'many' is good, but we can live with a 'few', sometimes just 2 or 3. Now, if you are doing a Weibull analysis, we need a lot more, say 7 or 8, since 2 or 3 may get censored, and about 5 (clean) points are necessary to get 90-95% confidence.
RM
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