Mean Time To Failure (MTTF)

What is Mean Time To Failure (MTTF)?

Mean Time To Failure (MTTF) is the average time a non-repairable part or piece of equipment remains in operation until it needs to be replaced. It is a very basic measure that helps predict the lifecycle for components that cannot be repaired.

Understanding MTTF vs MTBF (mean time between failures) can be a challenge because they are somewhat similar. Here how to tell them apart:

MTTF

• Applies to non-repairable systems or assets
• Measures the amount of time between a device’s first day of use and the last
• Represents the entire lifecycle of a product or device 

MTBF 

• Applies to repairable assets
• Measures the amount of time between each individual failure incident
• Takes failure rate or number of failures into account
• Predicts when an item may need to be repaired next

Table of Contents

Why MTTF metrics are important
What MTTF means for your organization
How to calculate MTTF
How to improve MTTF & productivity
Take the guesswork out of MTTF

Why MTTF metrics are important

Mean Time to Failure helps organizations estimate the lifespan of non-repairable assets. This is helpful for planning of replacement inventory for these parts.  

Some common examples are: 

• Fan belts in automobiles
• Light bulbs in our homes and offices
• Batteries used in vehicles or other large equipment

By knowing how often these parts will be used, maintenance teams can better manage parts inventory and prepare for inevitable replacement work.

What MTTF means for your organization

MTTF is particularly useful as a reliability metric. Engineers can use it to estimate how long a component of critical machinery or equipment may last. Having an awareness of your MTTF allows you to: 

• Evaluate the effectiveness and quality of parts and components
• Forecast replacement needs and plan preventive maintenance tasks
• Perform proper inventory management to ensure resources and replacement parts are available 

Shorter MTTF means more frequent replacements. And more replacements mean more downtime, less uptime, higher costs, and other impacts on productivity. That’s why learning how to extend it is so worthwhile.

When to use MTTF 

First, MTTF helps determine spending on both your capex and opex budgets for existing procedures. It tells you how often will you be replacing things, and at what costs. 

Second, MTTF is also particularly useful for evaluating new procedures. If you are planning to invest in a new process that requires specific equipment, MTTF can give you insight into how much additional labor and parts spend a new process will either save or cost you. This will help you evaluate the cost-effectiveness of certain processes, and determine project budgets.

You can sometimes find information about MTTF from the OEM, but that can sometimes be misleading. These estimates may vary depending on a number of different factors. It is best to run your own MTTF reporting to keep track of your asset lifespans. 

Calculating MTTF doesn’t have to be hard. As long as you’ve tracked the total hours of operation and the number of components you use in the same length of time, you have everything you need. 

The data needed to find your MTTF

Because MTTF is an average lifespan, you will be calculating it for a component that you have or use many of. MTTF is the total operational hours, divided by the total number of units throughout that period of time.

A simple MTTF formula

Let’s assume we tested 3 desktop hard drives. The first one failed after 62,000 hours, the second one failed after 28,000 hours, and the third hard drive failed after 42,000 hours in use. MTTF in this instance would be:

MTTF = (62,000 + 28,000 + 42,000) / 3 units

MTTF = 132,000 / 3

MTTF = 44,000 hours

We can now assume that this particular type and model of hard drive is likely to fail after about 44,000 hours of use.

How to calculate MTTF using Excel and other reporting tools

While it is good to know how to measure MTTF by hand, it is impractical to plan to do it that way every time. A simple spreadsheet makes calculating MTTF easy as long as you are making note of the correct data. But a CMMS software basically does all the work for you.

With a CMMS, equipment failures are logged through the work request process, tracking downtime and operational time automatically. As a result, your mean time metrics begin calculating the second you begin using the system, building a dashboard of useful key performance indicators (KPIs). 

However, if you aren’t quite ready to take the CMMS plunge, we have created a handy calculator. Download it, and see how nice it is to have the work done for you!

How to increase MTTF and productivity

Increasing your MTTF can greatly improve your productivity because you are ensuring that you get the longest lifecycle possible out of your assets, and that you are ready and prepared with a replacement when it fails. Below are a few steps you can take to increase your MTTF: 

Use the best quality components 

Parts that are made from more durable materials and have gone through a thorough quality control process may cost more but will provide more dependability, requiring fewer replacements in the long run. 

Take action to improve asset lifespan

Make sure the parts and components you use are used for their intended purpose and in the conditions (humidity, heat, pressure, voltage, etc.) they are designed for. You can store equipment operating and maintenance manuals in your CMMS to easy reference to ensure they are properly installed/retrofitted every time. 

Use your time, budget, and resources wisely

Because these parts are not intended to be repaired, scheduling maintenance to keep them up is not an option here. You can wipe off the dust or run high-level diagnostics to estimate remaining useful life, but your technicians’ time is better spent where it counts.