Understanding MTBF, Calculation Methods, and Real-World Applications

MTBF is an important metric that helps track downtime and if equipment needs maintenance to improve availability and reliability. Tracking MTBF is mission-critical because breakdowns can cause your business to bleed money.

The MTBF calculation involves (1) taking the total operating time (in hours) of a machine and (2) dividing it by the number of failures during the same time frame.

According to Reliable Plant, large plants lose 323 production hours a year. This translates into an average cost of lost revenue, financial penalties, idle staff time, and restarting lines worth $532,000 per hour—totaling $172 million per plant a year.

In this post, we explain MTBF, how to calculate it, and how you can track uptime using MTBF.

What Is MTBF?

Mean Time Between Failure (MTBF) is the average time a piece of equipment or component runs before failure.

MTBF calculation often takes place in the context of maintaining industrial systems, where component failures result in downtime and safety issues. Moreover, MTBF can measure the overall reliability of various components and equipment, including manufacturing units and energy grids.

Remember that mean time between failure doesn’t guarantee that a piece of equipment or component will fail only at the end of the MTBF period. It’s just the average time your equipment or component has historically functioned between failures and offers insight into how long you can reasonably expect it to run.

Mean time between failure also has limitations. For example, MTBF doesn’t account for any exceptional circumstances or the impact of a specific failure event on operations and safety.

MTBF Calculation and Example

Here’s the MTBF formula:

MTBF = Total operating time (in hours) / # of breakdowns during the same time

Suppose one of your machines ran for 3,000 hours over the past six months and failed four times during that time.

The MTBF value for this machine is 750 hours (3,000 / 4).

You can expect the machine to run for 750 hours without failure. However, failure may occur before or after 750 hours of operation. In exceptional circumstances, the machine might fail within a few days of the previous repair.

MTBF vs. MTTF vs. MTTR

Mean Time to Failure (MTTF) and Mean Time to Repair (MTTR) are also valuable metrics for reliability engineers and the maintenance team. However, they measure uptime from a different perspective and, therefore, provide unique insights into asset management.

MTTF measures the total operating hours of a machine. That might sound similar to MTBF. However, the difference is that MTTF measures the total period of time that the machine operates until the end of its useful life, i.e., the point at which the machine can’t be repaired.

You can use the following formula to calculate MTTF:

MTTF = Total hours of operation / Total # of assets in use

MTTR measures the amount of time your team takes to diagnose, repair, and recover equipment after failure. MTTR and MTBF are typically used together when trying to maximize total uptime.

Here’s the formula for MTTR:

MTTR = Total maintenance time / # of repairs

How to Use MTBF

MTBF can inform the following:

• Maintenance schedule
• Inventory management
• Repair vs. replace decisions

Maintenance Schedule

The first step to mitigating failure is to understand when to expect it. There’s no way to be certain about failure, but MTBF helps establish a baseline on the frequency of failure. This can be a significant first step towards lowering the failure rate and unplanned downtime.

Once you’ve calculated the mean time between failure, factor this information into your preventive maintenance strategy by scheduling a recurring work order. It’s best to use work order software since it allows you to automate and streamline your preventive maintenance schedule.

For example, if a machine’s MTBF is 1,000 hours, it’s best to schedule preventive maintenance every 750 hours. Because 1,000 hours is an approximation of how long a machine will operate before its next failure, performing maintenance at 750 hours gives you a reasonable margin of safety.

Inventory Management

Having an approximate timeline for equipment failure can help optimize your MRO (maintenance, repairs, and operations) inventory. The timeline is critical if you follow the just-in-time inventory system because you’ll have a clearer idea of the safety stock you should maintain and the frequency of orders to place based on lead times.

Repair vs. Replace Decisions

According to Plant Engineering, 40% of unplanned downtime is caused by aging equipment. It doesn’t always make sense to repair equipment. When a repair significantly reduces the mean time between failure, or it has been low for a while, replacing the asset might make more financial sense.

For example, suppose the cost of repairing a fully depreciated machine is $2,000, and the MTBF is three months. On the other hand, the depreciation of a new machine will be $1,500 for the same three months. Replacing the machine makes more sense in that case.

MTBF and System Availability

System availability is a maintenance metric that measures the total time you can use an asset for production, expressed as a percentage. It’s essentially the probability of the machine experiencing downtime when it’s in use.

The system availability formula uses MTBF and MTTR.

System availability = MTBF / (MTBF + MTTR)

Just like MTBF is part of the system availability formula, availability is part of another KPI called overall equipment effectiveness (OEE). That’s why improving MTBF is mission-critical.

How to Improve MTBF

There’s no standard method to determine if your equipment’s mean time between failure is too low or too high. However, you can use the MTBF of the same or similar assets as an internal benchmark. Once you have a benchmark, interpret the MTBF in the context of the equipment’s age and other factors.

If an asset’s MTBF is too low, you can improve it with proactive scheduled maintenance.

You need insights into various parts of operations, including problems that lead to failure, the effectiveness of repairs, and maintenance efficiency, to improve MTBF. You’ll need to collect information during operations to get these insights.

Modern manufacturers use IIoT (Industrial Internet of Things) devices to collect information. They store this information in a computerized maintenance management system (CMMS). Top CMMS solutions like MaintainX generate insightful reports based on the collected information, which enable you to optimize maintenance strategies.

This information can reduce repair times (MTTR) by providing the information needed for root cause analysis (RCA). Once you’ve determined the root cause, you can find a long-term solution that improves the mean time between failure.

Maintenance software can also help implement advanced maintenance technologies like condition-based maintenance and preventive maintenance. These techniques help prevent breakdowns by identifying and preparing for problems before they occur.

MaintainX: Your Silver Bullet to Lower MTBF

MaintainX can help track MTBF. If you’re dealing with a low-MTBF asset, use MaintainX CMMS to adjust the asset’s maintenance schedule. Technicians can view the updated maintenance schedule on their mobile devices.

If needed, MaintainX allows technicians to seek help in real time with its built-in chat feature. You can even set up recurring work orders outside of the maintenance schedule for assets that require extra care.

If that sounds interesting, try MaintainX today!