MTTR prediction

[Bucky88]

Would anyone know where I can get my hands on some MTTR prediction data for mechanical parts??

Is there a such thing as a handbook for this?

HELP!!!

:confused:

[David]

You might want to check out the following document from the US Army.

Publication Number: TM 5-698-5
Title: Survey of Reliability and Availability Information for Power Distribution, Power Generation, and Heating, Ventilating and Air Conditioning (HVAC) Components for Commercial, Industrial, and Utility Installations

This document can be found at http://www.usace.army.mil/publications/armytm/tm5-698-5/.

I hope this helps.

[Bucky88]

Thx for your help...

I know there is actually a database for predicting MTTR, same concept as NPRD-95..

Item Soft uses it in their software.

I'm just wondering if there anyway of purchasing a hard copy of this database.

[Bucky88]

NSWC-98 Handbook

would anyone know if this is a similar concept to NPRD95 but made to maintenance..

[David]

The NSWC-98 is the same as MIL-STD 217, but for mechanical components. Maintenance is not mentioned in NSWC-98.

[Bucky88]

I deal with mainly mechanical components - so this should help me then?

[David]

NSWC predicts a system failure rate based on the assumption that all components are arranged in series and their failure times follow an exponential distribution. However, it does not mention maintenance in the standard.

[Relman]

Element data can be obtained from RADC-TR-70-89, Maintainability Prediction and Demonstration Techniques, and MIL-HDBK-470A, Appendix D

[Norbyzuka]

NSWC = http://www.everyspec.com/USN/NSWC/

[Sushant Mohan Dewal]

NSWC predicts a system failure rate based on the assumption that all components are arranged in series and their failure times follow an exponential distribution. However, it does not mention maintenance in the standard.

Dear David,

In NSWC it is metioned that mechanical components does not follow an exponential distribution.. but does exponential distribution fairly fits for the failure times?

Best,

Sushant

[Kathleen]

Hi Sushant,

You are correct, NSWC-98 and NSWC-07 state that failure rates of mechanical components are not usually described by a constant failure rate distribution because of wear, fatigue and other stress-related failure mechanisms resulting in equipment degradation.

Regarding your question on whether the exponential distribution fairly fits the failure times. Given that all you have are failures in a period of time, the closest distribution that could be used to describe that situation is the exponential distribution. However, you are assuming a constant failure rate, which may not be true.

I hope that this helps.

Thank you,
Kathy

[Sushant Mohan Dewal]

Dear Kathleen,

Thanks for the clarification. Does it means that to be on the safe side only MTTF/ MTBF predictions from NSWC can be made.

Regards,

Sushant

[csasun]

Hello all!

Interesting post and some of my views are as follows:

NSWC provides models for estimating failure rate - average failure rate. Also, we know that the mechanical parts donot follow exponential distribution. Therefore, it is not prudent to estimate MTTF/MTBF using NSWC models (MTTF would be too optimistic)

On the other hand, since the handbook considers all types of failure modes (eg. chain link: roller wear, breakage, corrosion etc.) in computing failure rate, it is expected to approach constant failure rate - as a system. Therefore, it is important to know the correlation between the NSWC and one's own application (in terms of model parameter values) and then decide the time line duration within which the average failure rate is valid.

Any other views or responses are welcome.
Sasun