Understanding Mean Time to Failure (MTTF) Calculations for Maintenance

What Is Mean Time to Failure? 

Mean Time to Failure (MTTF) is a maintenance metric reflecting the average time a non-repairable system operates before it fails — in other words, it’s the average lifespan of a critical asset. It’s not just a technical measurement but a practical tool that helps you anticipate when a part or asset might need replacement, allowing you to plan effectively and avoid unexpected downtime. 

Understanding MTTF is like having a reliable friend who helps you plan for the future. It allows businesses to be better equipped to keep operations running smoothly, reduce risks and maintain productivity. A higher MTTF shows an asset is less likely to break down, while a lower MTTF indicates a higher risk of breakdowns.

MTTF vs. MTBF vs. MTTR 

Knowing the difference between types of failure metrics is crucial for keeping an organization’s equipment working and failure rate low. While each of these metrics shares some similarities, they serve distinct purposes. How you use MTTF, MTBF and MTTR depends on whether the asset used in the metric is repairable or unrepairable.

• Mean Time to Failure (MTTF): Measures the average amount of time an unrepairable asset works before it fails. It is calculated by dividing the total operational hours by the total number of assets in use.
• Mean Time Between Failure (MTBF): Measures the average time between an asset’s breakdowns — the time in which it remains operational. The asset’s total hours of operation divided by the number of failures that occur during that time gives you the MTBF calculation.
• Mean Time to Repair (MTTR): Measures the average time it takes to repair an asset after it fails. MTTR is calculated by dividing the total repair time by the number of repairs during a specific period. This includes the time the asset’s breakdown is identified, its repair, and the maintenance it needs to become operable. 

How Is MTTF Calculated? 

Now that you know how MTTF is calculated, let’s break it down using an example. Imagine you own three delivery vans — each of which is equipped with a battery. To determine the MTTF (or average lifespan) of the batteries, you need to consider the lifecycle of each battery. 

Let’s say the first battery lasted 8,000 hours, the second lasted 7,500 hours, and the third lasted 9,200 hours. To find the MTTF, you would add the operational hours of all the batteries, which equals 24,700 hours. You then divide 24,700 by the number of batteries — which, in this case, is three. The result gives you an MTTF of 8,233 hours.

Knowing the MTTF allows a company to estimate an asset’s expected operational time before failure occurs and implement a preventive maintenance program to keep it running as long as possible. The calculation reflects an asset’s reliability, enabling a company to make informed decisions about its maintenance.

Key Examples of Using MTTF 

Maintenance teams use MTTF to help prevent disruptions in operations and increase an asset’s lifespan. They may use a run-to-failure maintenance approach, in which an asset is used until it breaks down and needs repair or replacement (for non-critical situations) or a proactive maintenance strategy, in which regular maintenance occurs on an asset to help prevent equipment breakdowns. Businesses use MTTF to assess the lifespan of: 

• Batteries: In a run-to-failure approach, batteries are replaced when they fail, but when using a proactive maintenance approach that tracks battery voltage and performance, a business can schedule battery replacements before failure, minimizing asset disruptions.
• Light bulbs: While a run-to-failure approach in maintenance may be acceptable in circumstances that aren’t critical, replacing bulbs based on preventive maintenance will help avoid sudden lighting outages. 
• Tires: If a business requires fleet maintenance operations, a run-to-failure approach regarding tires can cause a work stoppage. Proactive maintenance, like regular tire inspections, can keep fleets up and running.
• Forklift wheels: Forklift wheels are much like tires, and without working forklifts, operations cease. In a run-to-failure plan, wheels would only be replaced after failure. Preventive maintenance based on forklift usage hours can help maintain operational safety without losing productivity.
• Conveyor belt rollers: A run-to-failure approach to conveyor belt rollers may lead to production stoppages. Proactive maintenance, like scheduled maintenance inspections, can prevent unexpected failures and allow a business to maintain its production goals. 
• Motor fan belts: Motor fan belts need preventative maintenance, such as routine belt inspections and tension adjustments, both of which will keep downtime at a minimum and extend belt life.

The Importance of MTTF 

Because it helps predict how long a spare part or piece of equipment will last before failure, MTTF can help with an organization’s asset management strategy in the following ways: 

Creating a Preventive Maintenance Plan to Prolong Asset Lifespan

MTTF calculations provide a reliable key performance indicator (KPI) that businesses can use to create a preventive maintenance schedule. Using MTTF data that predicts when a part or asset will likely fail, maintenance teams can schedule regular maintenance inspections and servicing or order replacement parts before the predicted failure time. By addressing potential issues early, the asset gains an extended lifespan, and the business saves on maintenance and repair costs overall.

Making Purchasing Decisions That Lead to Profitability

Knowing an asset’s MTTF helps a business choose parts that offer the best value by balancing cost with durability. Opting for parts with a higher MTTF can lower the frequency of replacements and maintenance costs. While these parts may be more costly initially, they’ll be worth the investment over the long term, leading to more profitability overall.

Enhancing Inventory Management

Because an MTTF calculation helps predict when asset failure is likely to occur, a business can have a more holistic approach to inventory management. Team members can plan ahead to ensure that the spare parts needed to repair an asset will be there. Overstocking an item, which can be costly, will no longer be an issue. 

Example of How Calculating MTTF Benefits Businesses

Let’s take a look at Dell Technologies, a globally renowned company in the IT and computing industry. The company manufactures and services a variety of servers and storage solutions, and in order to keep them at top performance, Dell uses MTTF to have a better understanding of the failure rates of their hardware components. 

By calculating MTTF, the tech company can predict the lifespan of its various servers and storage products, allowing them the ability to replace or repair these key assets before a system failure occurs. This leads to not only improved asset reliability, enhanced customer satisfaction and the previously mentioned cost savings, but it also helps Dell’s engineering teams make design improvements to assets that had higher failure rates. 

How to Improve MTTF 

To improve MTTF, companies can focus on the following strategies to enhance an asset’s dependability: 

• Invest in better quality parts and/or equipment: One of the most effective ways to improve MTTF is to buy high-quality parts and equipment for an asset. By using parts and materials of better quality, durability and reliability, a business can improve the MTTF of its assets and reduce breakdowns. While higher-quality parts and equipment may cost more upfront, the long-term benefits of improved MTTF will outweigh the initial investment.
• Use the parts and/or equipment according to the manufacturer recommendations: Misusing or overusing parts or equipment (or the asset itself) can quickly increase wear and tear on the asset, as it reduces MTTF and increases the likelihood of failure. Businesses should train employees on how to use non-repairable assets properly and make sure that when they do use them, they are doing so in their intended manner. 
• Create a preventive maintenance plan: Developing an effective preventive maintenance plan can also improve the lifespan of an asset. This would include scheduling work orders to help maintain an asset and identify potential issues before they happen. Doing so will increase equipment uptime, improve productivity, extend the asset’s lifespan and lessen the need for expensive repairs and part replacements.

Using a CMMS for MTTF Calculations 

Tracking MTTF calculations on a spreadsheet may not only be time-consuming, but manual errors can also occur. That’s where a computerized maintenance management system, also known as a CMMS, comes in handy. CMMS software helps companies manage maintenance tasks and processes and, in doing so, reduces manual error, saves time and keeps operations from disruption. 

A CMMS collects and stores data on an asset’s use, breakdowns and maintenance history. As it monitors these events in real time, it analyzes patterns in an asset’s overall performance, which is vital for calculating an accurate MTTF.  A CMMS tracks an asset’s key maintenance metrics like its hours of operation, the cycles it completes and how often it’s maintained. When breakdowns occur, a CMMS also logs them with all the other data. Over time, it aggregates this information, allowing it to calculate each component’s MTTF. It creates MTTF calculations based on actual performance rather than estimates — leading to more accurate and reliable predictions on an asset’s lifespan.

See how a CMMS like Coast can help you enhance your system reliability by signing up for a free trial!