Maintenance -> CM, PM, Inspections

[lowens]

I have established a RBD model within BlockSim6 and have added reliability data from OREDA based on the Exponential distribution since OREDA data is based on the assumption that the failure rate function is constant and independent of time. I am only considering "critical failures" of items.

I am now need to add maintenance data to the model. I have calculated MTTR (hours) from the OREDA data i.e. from the active repair time values given in OREDA. Where active repaire time values are not available, I have used mean repair time (manhours) and assumed two men per repair job. I have entered this data as an Exponential distribution under "Corrective Maintenance" (CM). I am assuming this is right as, for critical failures, this would entail a downtime for the item to be repaired?

I also wish to add Preventitive Maintenance (PM) and Inspections to the model. :confused:

1. Can anyone advise what data (OREDA) I should be input in here. Would it be wrong to assume/ use the exponential distribution again and enter the same MTTR figure I used for CM??

2. For Inspections - am I correct in thinking the Mean time = average mean time per inspection?

[Arai.M]

Hi there,
My answers follow your questions.
Arai

I have established a RBD model within BlockSim6 and have added reliability data from OREDA based on the Exponential distribution since OREDA data is based on the assumption that the failure rate function is constant and independent of time. I am only considering "critical failures" of items.

I am now need to add maintenance data to the model. I have calculated MTTR (hours) from the OREDA data i.e. from the active repair time values given in OREDA. Where active repaire time values are not available, I have used mean repair time (manhours) and assumed two men per repair job. I have entered this data as an Exponential distribution under "Corrective Maintenance" (CM). I am assuming this is right as, for critical failures, this would entail a downtime for the item to be repaired?

This sounds right to me.

I also wish to add Preventitive Maintenance (PM) and Inspections to the model. :confused:
Once you assume your parts have an exponential distribution, preventive maintenance can/should not be added. Because of the properties of the exponential distribution (i.e. constant failure rate, memory less distribution, etc.), you are no better off doing a PM than not doing it at all. Now the reason you want to add PMs is because intuitively, you know these parts are wearing off. However by using OREDA data you are assuming that the parts are not wearing off, they fail at the same rate when they are 10 hours as when they are 100 hours and so forth. If you want more details, here is an article http://www.weibull.com/SystemRelWeb/preventive_maintenance.htm
If you want some general modeling tools, some general idea as to how the parts in your system are related and more of a starting point, OREDA data can help. Now if you want to quantify how maintenance policy with inspections, PMs and so forth will affect your system, you are going to need models that accurately predict the life of your parts (i.e. wear off behavior with an increasing failure rate). If they are truly not wearing off, which is very unlikely, then just repair them when they fail.

1. Can anyone advise what data (OREDA) I should be input in here. Would it be wrong to assume/ use the exponential distribution again and enter the same MTTR figure I used for CM??

2. For Inspections - am I correct in thinking the Mean time = average mean time per inspection?[/quote]