How to Work with an MTBF Requirement
This image comes from Dictionary of French Architecture from 11th to 16th Century (1856) by Eugene Viollet-le-Duc (1814-1879).

How to Work with an MTBF Requirement

Given MTBF? Now What?

Let’s say you join a project as a reliability professional (or an engineer or manager of any type) and you discover that the team as a reliability goal stated as 5,000 hours MTBF.

What are you going to do with that information?

The meaning of the current goal

5,000 hour MTBF might be exactly the right metric and value for the project. It probably is not.

To find out what this value means you need some more information. Ask around and find:

  • What is the primary function of the device?
  • How long should it provide that function for customers?
  • Is there a warranty period or executed lifetime duration?
  • How many hours per year will the device be operated?
  • How many should survive the warranty period or expect useful lifetime?
  • In what environment should it work?

Note these questions help you find each of the four element for a full reliability goal description. Key to this discovery is the duration of useful life (or warranty) along with how many are expected to survive each duration.

The durations are often linked to market expectations. The probabilities (survival) is connected to business objectives of profitability along with customer satisfaction.

Let’s say we determine that there is a one year warranty and the business objectives expect less than 2% of units will fail during the warranty period.

A simple calculation is now possible. Assuming the unit is susceptible to failure every hour of the year, or 8,760 hours, then

No alt text provided for this image

That means the goal is to have only 17% of units survive the warranty period.

That is not very good.

A bit more information

I would show this simple calculation to others and ask if the reliability goal was correct.

Let’s say we quickly learn that the most likely way the product will fail is due to fan failure. And, we discover the unit is only expected to operate 2,000 hours per year.

Changing the calculation to reflect the reliability at 2,000 hours we find

No alt text provided for this image

Which is 67% of units would be expected to survive.

Still not great.

Further discussions

We may find with additional discussion a few reasons for such a poor reliability goal.

It could be

  • Thinking MTBF was a failure free period
  • thinking 5,000 hour MTBF was 2.5x longer than expected 2,000 operation, thus had plenty of margin
  • 5,000 hours was goal for last project and we copied it to this one
  • This is a new high risk project and we set the goal very low on purpose
  • This is an improvement of the last product that had 50% fail in warrantee period

Or, something else.

Whatever, if the business goal is have less than 2% fail in the warranty period and our engineering goal is to expect 33% of device fail, something needs adjusting.

Next Steps

This simple example, which is all too common, illustrates that even a simple calculation to interpret MTBF and compare the results to expectations may cause ‘some discussion’. Hopefully, it helps the organization to adjust the goal and how it is stated to be something meaningful.

Given this situation you may want to take the next steps:

  • Restate the reliability goal in terms of reliability (function, environment, duration, probability) In this case the device will function in an office setting for one year with 98% surviving. Add other duration/probability couplets as needed for clarity.
  • Create an apportionment model for the device and major subsystems/components.
  • Identify past product or similar product performance – also in terms of reliability (not MTBF).
  • Identify high risk of failure areas and focus engineering and supply chain improvements there.

After device launch to the market

Once the product is out there, monitor it’s reliability performance. Again, not in terms of MTBF as we really are not interested in the mean. Rather we are interested in the first 2 percentile point – our target for the warranty period.

Stating reliability clearly helps. Helping others understand the meaning of MTBF also helps.

Go be useful!


Fred Schenkelberg is an experienced reliability engineering and management consultant with his firm FMS Reliability. His passion is working with teams to create cost-effective reliability programs that solve problems, create durable and reliable products, increase customer satisfaction, and reduce warranty costs. If you enjoyed this article consider subscribing to the ongoing series at Accendo Reliability.


要查看或添加评论,请登录

Fred Schenkelberg的更多文章

  • Accendo Weekly Update #490 March 23, 2025

    Accendo Weekly Update #490 March 23, 2025

    Reliability Analysis Courses One using Minitab, the other using Reliasoft Weibull++. Both are collaborations between…

    4 条评论
  • Accendo Weekly Update #489 March 16, 2025

    Accendo Weekly Update #489 March 16, 2025

    Course offered by Industrial Metallurgist Hosted on imetllc.com and taught by Michael Pfeifer.

    3 条评论
  • Accendo Weekly Update #488 March 9, 2025

    Accendo Weekly Update #488 March 9, 2025

    Barringer Process Reliability Introduction A new course by André-Michel Ferrari This is a Beta Launch with a 50%…

    1 条评论
  • Accendo Weekly Update #487 March 2, 2025

    Accendo Weekly Update #487 March 2, 2025

    CMMSradio A podcast series by Greg Christensen All things CMMS, Computerized Maintenance Management Software, including…

    2 条评论
  • Accendo Weekly Update #486 February 23, 2025

    Accendo Weekly Update #486 February 23, 2025

    NoMTBF An article series by Fred Schenkelberg and friends A series of articles devoted to the eradication of the misuse…

    4 条评论
  • Accendo Weekly Update #485 February 16, 2025

    Accendo Weekly Update #485 February 16, 2025

    The RCA An article series by Bob and Ken Latino According to Bob, "I tend to write about all things Root Cause Analysis…

    6 条评论
  • Accendo Weekly Update #484 February 9, 2025

    Accendo Weekly Update #484 February 9, 2025

    Courses offered by Integral Concepts A set of courses offered by Allise and Steven Wachs More than just Applied…

    4 条评论
  • Accendo Weekly Update #483 February 2, 2025

    Accendo Weekly Update #483 February 2, 2025

    The Manufacturing Academy A set of courses offered by Ray Harkins and team Courses designed to teach foundational…

    2 条评论
  • Accendo Weekly Update #482 January 26, 2025

    Accendo Weekly Update #482 January 26, 2025

    Speaking of Reliability A podcast where friends talk shop Enjoy an episode of Speaking of Reliability. Where you can…

    1 条评论
  • Accendo Weekly Update #481 January 19, 2025

    Accendo Weekly Update #481 January 19, 2025

    Everyday RCM Short videos and some articles by Nancy Regan Reliability Centered Maintenance (RCM) is a time-honored…

    1 条评论

社区洞察

其他会员也浏览了