How to Calculate MTBF: The Mean Time Between Failure Numbers That Matter for Plant Asset ReliabilityJune 21, 2018
Downtime is dollars. That means keeping your assets healthy is the same thing as keeping your business healthy. If a pivotal centrifuge, cooling system, or pump goes offline, your plant or facility could be exposed to hundreds of thousands of dollars’ worth of lost production.
Ensuring your assets stay on their feet comes down to knowing them and checking in on them, same as you do for your people. Specifically, by knowing the mean time between failure (MTBF) for each of your critical assets, you can establish maintenance procedures that minimize the risk of unexpected failure and increase plant asset reliability. Let’s take a look at how to calculate MTBF.
Defining and Calculating MTBF
Mean time between failure, simply stated, is the average amount of time between instances of repairable asset failure. It’s different from the mean time to failure, which is the average amount of time until an asset fails, cannot be repaired, and must be replaced.
The Basic MTBF Formula
MTBF is calculated by dividing an asset’s total uptime by its number of failures:
MTBF = Uptime / Number of Failures
This calculation can be performed in aggregate with multiple assets. The more relevant company or industry-wide historical data on larger numbers of assets that becomes available, the closer your calculation will come to producing a true mean.
However, as differences in assets can vary widely by make, usage, location, maintenance schedules, and production year, the mean times produced by aggregate data should be compared against mean times produced by assets you manage yourself, or ones very similar. The data on the assets under your control should be available in maintenance and production records collected by your Mobile Field Workers, and should be compiled in sequential reports.
How to Calculate MTBF for Assets with Multiple Functions
Large pieces of production equipment are complex systems comprised of myriad smaller mechanisms. These smaller networks within the greater system have different tiers of function, from inessential to critical. You can perform MTBF calculations on any system or combination of systems, from external lighting to belts, pumps, turbines, coolant piping or control systems. So which one should you use?
The answer will be unique to your assets, and your workplace. You can define failure as the cessation of a single critical function, or perform multiple calculations to schedule a tiered framework of failure points. Define failure for each of your assets individually or in classes, based on the continuance of the essential functions of each piece of equipment. Minor failures should be grouped and monitored as they contribute to the entire system you’re monitoring.
Using MTBF to Reduce Unscheduled Downtime
The failure calculations you perform for your assets or their internal systems should be the ones you expect to be worth monitoring. In other words, only perform needed calculations. Knowing the mean time between failure for each system allows you to schedule maintenance intervals. Scheduled maintenance helps you catch problems before they arise. You’ll know when something is likely to break, so you can take immediate action it before it does.
…it’s not enough to simply set a schedule and expect the world to follow it.
Even so, it’s not enough to simply set a schedule and expect the world to follow it. To be sure that assets on your field or in your plant don’t fail unexpectedly, you’ll need Mobile Field Workers to perform regular inspections. If these workers can pass along timely information on the current condition of your equipment, you can dispatch repair teams to respond to any emerging or immediate maintenance situations.
Triage of Limited Resources to Prevent Unscheduled Downtime
In a world of limited resources, sometimes maintenance budgets or available equipment are not adequate to cope with temporary or chronically-elevated levels of repair needs. Ideally, this issue is prevented ahead of time. It is the responsibility of Plant Managers to accurately diagnose the expected equipment and manpower needed to provide maintenance, and to budget accordingly.
Sometimes factors beyond control contribute to a lack of resources, such as:
- Unexpected increases in production
- Unexpected weather events or natural disasters necessitating many repairs
- A lack of corporate funding
In these instances, when repair resources are inadequate, unscheduled downtime can still be reduced by establishing a proactive plan for triage. Maintenance can be scheduled to prioritize higher tier functions and emergency needs over less essential aspects. Needless to say, untended issues grow more costly over time and are best remedied as soon as feasible.
Preventing Unscheduled Downtime with Timely Information Collection
A less-recognized obstacle to the prevention of unschedule downtime is lack of sufficient and actionable information. It’s easy to not know what you don’t know. When you’re tasked with keeping million-dollar assets on a continuous production schedule, what you don’t know can be very costly.
In order to get ahead of asset downtime using your asset performance management process, you need to know when that downtime will likely occur.
In order to get ahead of asset downtime using your asset performance management process, you need to know when that downtime will likely occur. This is the primary reason why you perform MTBF calculations. You also need to collect and analyze data on the ongoing current condition of the assets under your care. For many plants, facilities, and fields, this aspect of downtime prevention can be a hidden bottleneck.
It’s difficult to collect and compile data for maintenance logs on far-flung assets spread across the plant or campuses you work on. Many important observations can’t be instrumented, and need to be inspected visually in person. Operators have to cover anywhere from acres to square miles, sometimes in rugged terrain, without cell service or wireless connectivity.
Comparing the Methods of Plant Asset Data Collection
To collect all this asset maintenance and reliability information, many Operators still rely on paper checklists and clipboards. When Rounds are complete, the checklists are gathered together and their information is entered into a computer system in the control room. Often this information isn’t seen the day it’s collected, and may not be analyzed for weeks or even months. Early warning signs of preventable failures can be missed this way, lost in the paperwork.
Much of the inefficiency and redundancy of paper data collection, however, can be eliminated with mobile technology.
Much of the inefficiency and redundancy of paper data collection, however, can be eliminated with mobile technology. Field Operators can fill in checklists on their tablets or smartphones, transferring information instantly to a central location. Programs in the central IT system can automatically analyze the data collected and generate reports on asset conditions. By viewing these reports, Plant Operations Managers and Frontline Supervisors can detect any warning signs of needed maintenance, with plenty of time to take corrective action. As a result, mobile technology is replacing paper checklists as the most efficient, effective method of plant asset data collection.
MTBF is an important indicator for Plant Operations Managers to keep an eye on. By knowing when your assets are expected to fail, you can schedule maintenance to maximize uptime. It’s also important to head off any unexpected issues with timely and actionable information on the condition of your assets. While paper checklists have long been the workplace standard, advances in mobile technology greatly improve upon their timeliness and efficiency, better enabling Plant Operations Managers to make the smartest decisions possible.
GoPlant was built around a simple idea: making plant operations easier. Relying on our deep experience designing and implementing a successful plant floor data collection system, we developed a mobile system ideal for power plants, chemical facilities, oil fields, and wastewater treatment centers.
Image courtesy MAGNIFIER