MTBF Blues

I will not say that I have the exact answer to your question, but I think that may be this book can help. To be honest I think the amount of downtime that can be tolerated will depend on a lot of parameters. Please go ahead and see if this book found in the Knovel library can help. Here is the link

http://knovel.com/knovel2/Toc.jsp?BookID=1470

Moose:

I don't know how much of my old experience with military control systems can be transferred to today's users of chemical processing equipment, but, for that equipment, at that time, the first requirement was to DESIGN to a predetermined MTBF (Mean Time Between Failures). The requirement began at the contract phase and was carefully tracked in the field. MIL parts were specified to provide predetermined failure rates and purchased at the reliability level required to meet the contract.

Premature failures (Infant Mortality) were induced by rigorous environmental screening prior to shipment and were NOT a part of MTBF. Vibration and thermal cycling were mainstays.

Any indication of a high initial failure rate in the field indicated inadequate factory screening at some level. For products such as fighter engine mounted electronic controls, the analysis and screening were followed by MTBF tracking and FMEAs (Failure Mode And Effects Analysis) for certain failures. This all led to identification of the "Root Cause" for those failures and definition of corrective action.

If all of the foregoing actions were conducted correctly, there were few accident investigations, the ultimate goal.

DickL

Those are the same methods in the CPE (Chemical Process Industries).

One additional method is to determine the "class of quality" during the engineering stage. This is where you would ask questions about redundancy, in line spares, if the What level of failure or repairs is acceptable.

Is it OK to have to shutdown and clear the operating unit to repair a seal failure?

The PHA (Process Hazards Analysis) for those plants that are covered under OSHA Process Safety Management (29CFR1910-119) does similar review.

It may slightly off topic for your letter but the MTBF comment caught my eye. I agree and I've just introduced a system for providing this type of information for rotating machines. It is extremely important for those concerned about reliability and reducing cost in systems using rotating machines-motors, pumps, HVAC, compressors etc If the topic is of interest you can check it out on www.bearinglifeguard.com Vibes