Reliability Metrics 101: Mean Time to Failure (MTTF)

The role of a maintenance and reliability leader is to continuously find methods to optimally use gathered data to track the progress of maintenance activities and to measure the true reliability of their assets.

In earlier articles we shared how Mean Time to Repair (MTTR) and Mean Time Between Failure (MTBF) is used to measure how long it takes to repair and bring an asset back online. However, an important data piece is measuring how long an asset will last before it fails, which is the exact intention of calculating 'Mean Time to Failure'. Understanding MTTF helps in predicting asset failure, which is crucial for optimizing maintenance and asset management strategies.

Mean Time to Failure (MTTF) is a crucial maintenance metric that measures the average time an asset operates before failure. Effectively, MTTF measures the reliability of non-repairable assets by looking at similar assets over a period of time and measuring how long they perform until failure.

An effective preventive maintenance program is essential for improving MTTF. Regular maintenance can identify potential issues early, thereby reducing downtime and enhancing productivity while extending the lifespan of assets.

non-repairable asset is an asset that is generally replaced rather than repaired when it fails as it would be more cost-effective. A few examples of non-repairable assets are lightbulbs, small HP motors, and fan belts.

MTTF Fundamentals

MTTF, or Mean Time to Failure, is a pivotal reliability metric that estimates the average time a non-repairable asset operates before it fails. This metric is indispensable for asset management, as it allows organizations to predict when a component is likely to fail and plan its replacement proactively. By understanding MTTF, maintenance teams can develop effective preventive maintenance programs that minimize costly repairs and enhance overall system reliability. MTTF is particularly relevant for assets and equipment that cannot or should not be repaired, making it a cornerstone of strategic maintenance planning.

How to calculate MTTR

To accurately calculate MTTF, it's essential to track maintenance metrics meticulously. This includes recording the total number of operational hours and the total number of assets in use. This data can be collected manually or, more efficiently, through the use of computerized maintenance management system (CMMS) software. By leveraging CMMS software, organizations can streamline the data collection process, ensuring accurate and timely calculations of MTTF and other critical maintenance metrics.

Calculating MTTF is a straightforward process that involves dividing the total number of hours of operation by the total number of assets in use. The formula for MTTF is:

MTTF = Operating time to failure (in hours) / Number of Assets in Use

Failure = when an asset is no longer able to perform its intended function

Operating time = the timeframe that an asset or component is in operation

It is important to note that this formula assumes a constant failure rate, which may not always be accurate in real-world scenarios.

What is considered a good MTTF failure rate?

There is no specific universal benchmark for the MTTF of non-repairable assets. Rather, it is more effective to consider a few factors when deciding whether an MTTF is "good" or not. Among these factors are the expected lifecycle of the asset, the environmental conditions in which they perform, the quality of the installation, and how it compares to like-assets on the site that share a similar use-case.

Accurate MTTF data is crucial for making informed decisions about asset reliability and maintenance planning.

Comparing MTTF to Other Reliability Metrics

MTTF is often compared to other reliability metrics, such as Mean Time Between Failure (MTBF) and Mean Time to Repair (MTTR). While these metrics are related, they measure different aspects of asset reliability. MTBF measures the average time between failures of repairable assets, providing insights into the overall reliability of systems that can be fixed. On the other hand, MTTR measures the average time it takes to repair a failed asset, highlighting the efficiency of maintenance processes. Understanding the differences between these metrics is essential for developing comprehensive and effective maintenance strategies that enhance asset reliability and performance.

Ways to improve the MTTF for your assets with an effective preventive maintenance program

Conduct a failure analysis

Whenever an unexpected failure occurs, it can prove to be valuable to conduct a Root Cause Failure Analysis (RCFA) or a Failure Mode Effects and Criticality Analysis (FMECA) to help understand why an asset is experiencing a and how to prevent premature failures from happening in the future.

FMECA is a common method used to find problems with the design of a product, the manufacturing process, the materials used, or the installation method.

Consider the quality of the replacement parts used

Consider the context of a personal "asset" like your vehicle. Although there are certain replacement parts that are "good enough," it can sometimes be counterproductive to use a cheaper or inferior replacement just to cut costs. For example, if you live in an urban setting but replace your city tires with all-terrains, you will lose a significant amount of MPGs which can add up to more fuel costs.

Similarly, using quality replacement parts for your assets, specifically OEM parts, will lead to greater reliable because these parts are manufactured to spec for the asset and use the verifiable materials and processes. In general, a quality replacement part is unlikely to fail due to wear or inadequate manufacturing materials.

Download our "MRO Inventory Best Practices Checklist" to make sure you are ready when it is time to replace parts.

Maintain your assets to keep them in good working order

Preventive Maintenance can often be overlooked due to the common misconception that it only applies to large or complex machinery. However, small motors, pumps, valves, fans, heat exchangers, and other pieces of equipment can all be subject to PM. Scheduled maintenance helps to reduce the risk of unplanned downtime, improves efficiency, and decreases costs. Maintenance professionals play a crucial role in implementing preventive maintenance strategies to ensure asset reliability.

Predictive maintenance is a strategy that uses sensor technology to monitor and predict the health of the asset before it breaks down. These sensors can provide information about the condition of the asset and allow you to take steps to avoid breakdowns. This same predictive technology is used to detect the future failure of a non-repairable asset, which can allow for proper planning for its replacement.

Test new assets on an engineering project

An idea to consider for improving the MTTF of your site is to test a new asset on an engineering project to monitor it and evaluate its true performance and cost-effectiveness.

For example, if your site is considering a new centrifugal pump that is a more expensive replacement, then a new engineering project would be the best testing ground to decide whether it is worth the investment. If the pump is more expensive but lasts longer, then this performance could translate across the entire site.

Using CMMS Software for MTTF Calculation

CMMS software can significantly simplify the process of calculating MTTF by automating the collection and analysis of maintenance data. With CMMS software, you can efficiently track maintenance metrics, including the total number of hours of operation and the total number of assets in use. This data is crucial for calculating MTTF and other reliability metrics, such as MTBF and MTTR. By using CMMS software, organizations can optimize their maintenance schedules, reduce unplanned downtime, and improve overall system reliability. The automation provided by CMMS software ensures accurate data collection and analysis, leading to more informed maintenance decisions and enhanced asset management.