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Asset Management Failure Metrics: What are MTTF, MTBF, and MTTR?

by Nathan Jeans on October 5, 2021
 
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When it comes to measuring key performance indicators (KPIs) in business, there’s an overwhelming focus on success. But when it comes to asset management, you should pay attention to your failures, too.

In this quick guide, we’ll explain the three key asset management failure metrics that can provide valuable insights into your maintenance strategy and discuss when they can be used.

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What is MTTF?

MTTF is an initialism (acronyms have to be pronounceable e.g. NASA) for Mean Time To Failure. It measures the average lifespan of a device or asset so that its failure rate can be predicted.

It can be calculated by adding up the total lifespan of a set of assets or devices and dividing that value by the total asset count.

MTTF = total lifespan across assets / no. of assets

MTTF can only be used to measure the failure rate of assets that are replaceable or non-repairable. More specifically, MTTF applies to two types of non-repairable and replaceable assets:

  • Replaceable assets that can’t be repaired

Mean time to failure allows facility managers to predict when assets that can’t be repaired will fail so you can keep an adequate number of replacements in inventory.

  • Replaceable subsystems within repairable assets

Although a subsystem within an asset such as a piece of machinery can fail, the subsystem itself can be replaced so the machinery can continue to operate. In this case, the MTTF metric helps you to budget. It tells you how much you’ll need to spend on smaller subsystems to avoid the cost of replacing the larger asset.

When to use MTTF

MTTF is an indication of an asset's reliability. Tracking this metric enables organizations to understand which brand of an asset lasts the longest and how much inventory of that asset it should keep. It can also determine whether a new asset is outperforming the one it replaced.  

The limitations of MTTF

MTTF works well when it’s used to calculate the average lifetime of assets with a relatively short lifespan. The difficulty comes when you measure assets that last much longer. In that case, MTTF falls short.

Why? Well, when calculating MTTF, organizations typically run an asset (let’s use the example of a lightbulb) for a set period and count how many fail. If only one of 100 lightbulbs fails within 12 months, that gives you an MTTR value of 1,200 months or 100 years.

Is each lightbulb going to last 100 years? Probably not, and that’s where the limitations of this metric lie.

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What is MTBF?

MTBF is short for Mean Time Between Failures. It uses past data and observations to predict the average time between failures of a system that can be repaired. It is used to track both the reliability and the availability of an asset and has its origins in the aviation industry, where failures can have serious consequences in terms of cost and human life.

You can calculate MTBF by adding up the total lifespan of assets and dividing it by the number of failures.

MTBF = total lifespan of assets / no. of failures

Commonly used by manufacturing businesses, the goal is to keep the MTBF high, with as many weeks, months, and years between failures as possible. Importantly, as the metric is used to track reliability, the total lifespan does not include the time to repair the device. Instead, it focuses on outages and issues.

When to use MTBF

The mean time between failures is an important metric for facilities and manufacturing managers as it indicates the reliability and quality of assets. If you improve your MTBF, it means that a device is either lasting longer between failures or that any failures are being resolved more quickly.

Calculating the MTBF as well as other KPIs will help you make educated decisions about issues such as inventory management and maintenance scheduling.

The limitations of MTBF

Like any statistical measurement, MTBF only provides an estimate of likely failure rates based on past events, so its accuracy is limited. For that reason, rather than predicting when an asset will fail, it’s better used to estimate how many spares will be needed to support your assets.

The mean time before failure can also be distorted by a poor selection of assets or time periods. For example, starting your measurement shortly after one failure and ending before the next will lead to inaccurate results. That’s why it’s important to have agreed standards in place to calculate MTBF in a consistent and meaningful way.

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What is MTTR?

MTTR is an initialism for the Mean Time To Repair. It measures the time it takes to repair an asset and get it running properly once it has failed. Taking too long to repair an asset drives up the cost in the long run due to the downtime involved. Many businesses purchase spares so they can install a replacement quickly.  

MTTR is calculated by adding the total time spent repairing an asset and dividing that by the number of repairs.

MTTR = total time spent repairing / no. of repairs

Mean time to repair is a valuable metric because it measures how quickly your business responds to an unforeseen problem. So, the smaller this number, the better. A typical MTTR value varies a lot depending on the size and type of the organization. Generally though, an MTTR of no more than five hours could be considered a good goal.

When to use MTTR

Mean time to repair is a metric that maintenance and support teams use to keep their repairs on track. By performing repairs quickly, they can reduce downtime and lower the costs associated with a failure. The goal of a facilities or manufacturing manager is to get this number as low as possible by increasing the efficiency of their repair teams.

As an example of MTTR in practice, if you have 20 repairs over a week that are actively repaired for 80 hours, you’ll have an MTTR value of four hours. You can decide whether that’s a figure you’re happy with based on the standard repair times in your industry.

The limitations of MTTR

As with all metrics, there are limitations of MTTR. In some cases, there can be a lag between the failure occurring, the failure being detected, and the subsequent repair. That can lead to a value that does not represent the outage itself.

The metric is also only a measure of how quickly your maintenance staff can make a repair. It does not help you identify problems that you may have spotting a failure in the first instance or the existence of pre-repair delays. Both of those are important factors when assessing the success of your maintenance teams.  

Time is of the Essence

There’s no time to waste when a failure occurs. That’s why these metrics, although limited in their scope, can provide vital information about how you respond to repairs and where you can make improvements.

Although they are sometimes used interchangeably, these asset failure metrics provide the clearest picture of your team’s performance when used together. That’s when they provide incident management insights that enable you to make data-backed decisions and improvements.  

How EAM Software Can Help

Advanced EAM software like ManagerPlus® can help you keep your critical assets running better for longer. It enables you to track and access important information on your repairs and analyze trends. You can then produce intelligent reports on the performance of your maintenance strategies and make improvements.

Importantly, ManagerPlus is always connected and lives in the cloud. That enables you to access real-time data on everything happening in your operations so you can always keep your assets running efficiently.

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Executive Summary

Asset management failure metrics can provide valuable insights into the efficiency of your maintenance strategies. MTTF, MTBF, and MTTR are three of the most useful metrics to use, with each providing different insights that combine to create a complete picture. Learn what each of these metrics is, when it can be used, and discover how ManagerPlus EAM software helps you track the most valuable data about your maintenance performance.

Nathan Jeans
About the author

Nathan Jeans

Nathan is a long-serving freelance copywriter with a specialism in B2B software. When he's not busy writing transformative content, he likes to spend his time trying to get some sleep.

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