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What Is Mean Time Between Failure (MTBF)?

April 30, 2021

What Is Mean Time Between Failure (MTBF)?

Mean Time Between Failures (MTBF) is a maintenance metric that measures the standard amount of time between expected equipment failures for an asset performing under normal operational usage. Maintenance professionals use MTBF to inform equipment design, optimize preventive maintenance scheduling, and maintain reliability for their most essential pieces of equipment.

Overview

Mean time between failures (MTBF) is the “up-time” between two failure states of a repairable system. Here’s an illustration: 

MTBF is only used in conjunction with repairable assets. 

Thus, maintenance managers calculate the metric under the assumption that tangible asset failure is inevitable—the question isn’t if the machinery will break down, but when? The higher the MTBF,  the more likely the asset will operate uninterrupted for an extended period. 

The precise definition of Mean Time to Failureis contingent on what gets categorized as a “failure.” Most maintenance departments consider equipment failures to be completely out-of-service states of operation. Minor malfunctions are not classified as failures. 

Who Uses MTBF

The more capital a company has invested in complex mechanical systems, the more likely it is to calculate key performance indicators (KPIs) like mean time between failures (MTBF), Mean Time to Repair (MTTR), and planned maintenance percentage (PMP). 

Complex organizations running several pieces of expensive equipment at once—manufacturers, warehousers, mining companies, oil/gas producers—depend on continuous reliability to meet strict deadlines. 

Thus, minimizing downtime is a crucial component of delivering on time, keeping customers happy, and maintaining profitability. Minimizing downtime is especially important for manufacturers whose profits substantially vary based on how many individual units are produced per hour. 

Why Is MTBF Used? 

MTBF rates help O&M managers anticipate asset failures within given periods more accurately. It’s often paired with other maintenance strategies and key performance indicators (KPIs) like root cause analysis to remedy original causes of repetitive equipment failures. 

Such comprehensive preventive maintenance (PM) strategies allow management to a) minimize unplanned downtime and b) schedule routine upkeep within brief intervals instead of expensive hour-long shutdowns during emergency maintenance. 

Exactly how impactful are MTBF-informed maintenance systems? We’re talking the difference between spending a few hundred dollars in maintenance-related expenses versus hundreds of thousands of dollars in costly downtime! Aberdeen Strategy & Research reports the average cost of downtime across all businesses is a whopping $260K per hour.

MTBF supports maintenance departments that execute several tasks, including: 

  • Optimizing Maintenance Schedules: Again, MTBF provides a baseline for maximizing PM schedules. This allows leadership to schedule maintenance activities before failures occur so that technicians perform condition-based maintenance only when necessary. 
  • Improving MRO Inventory: Tracking MTBF allows managers to fine-tune maintenance, repair, and operations (MRO) inventory purchasing to ensure the optimal number of parts are always available. Accurate parts’ forecasting results in lower repair costs, more liquid capital, and quicker repair times.
  • Replacing Assets: It’s always tricky to decide whether to repair or replace a critical piece of equipment. MTBF helps inform the decision-making process by allowing managers to calculate expected repair costs over time. They can then weigh the data against the cost of purchasing new machinery to determine a cost-effective repurchasing date. 

Additionally, MTBF is an essential KPI calculation for reliability engineering, especially when it comes to critical assets. Maintenance engineers often rely on MTBF when designing safety, mechanical, and electronic systems to ensure optimal results. 

How to Calculate MTBF

Determining the reliability of an asset requires the collection of accurate data. Unfortunately, it’s not uncommon for busy facilities to neglect consistent data collection when relying upon paper forms, Microsoft Excel spreadsheets, or Google documents. 

For this reason, we recommend streamlining data entry with a mobile computerized maintenance management system (CMMS) like MaintainX

To calculate MTBF:

1. Gather the following pieces of information to calculate Mean Time between Failure (MTBF): 

  • Asset operational time in a given period
  • Number of breakdowns/repairs experienced in that given period
  • Number of labor hours spent on maintenance in that given period

If you’re not sure which piece of equipment to calculate MTBF for first, we recommend selecting the one with the highest failure rates. After solving the issue after conducting a root cause analysis, move onto the asset with the next highest failure rate and so on. 

2. Input your data into the following formula: 

MTBF = # of operation hours ÷ # of failures

Divide your asset’s total number of operational hours by the number of failures it experienced within a given period to arrive at an hourly measurement. 

Let’s look at an example: 

A water pump ran for a total of 1,000 hours and broke down twice. 

Water Pump MTBF=1,000 hours ÷ 2 repairs

Water Pump MTBF = 500 hours

Reminder: don’t include planned repair times when calculating MTBF—only factor in unplanned maintenance. It’s important to recognize that failure here doesn’t refer to completely broken down pieces of equipment. It means that an asset isn’t meeting intended production levels as designed. 

Achieving world-class MTBF is challenging. Every piece of equipment operates under different conditions with different expectations. For this reason, we advise investigating the MTBF for each asset and the industry standard for your sector before setting a benchmark. 

How to Improve MTBF

The more equipment failures your facility experiences, the more production hours you will lose, and the more O&M costs you will accrue. You can enhance your MTBF metrics in the following ways:

  • Improve PM Processes: An effective PM program can drastically increase MTBF. Ensure your maintenance technicians are well-trained, equipped with appropriate manufacturer manuals, and have adequate procedural checklists for PM activities.
  • Conduct Root Cause Analyses: Spend more time searching for root causes of equipment failures instead of engaging in temporary fixes. Engaging in investigative maintenance strategies like “The Five Whys” can help address the specific reasons certain assets fail more often than others. In other words, seek long-term solutions to repeat issues.  
  • Understand Aging Assets: Forty percent of unplanned downtime is caused by aging equipment. But maintenance professionals can sometimes do more than they realize is possible to manage these failures. Team leaders should educate themselves on how to best handle aging equipment and address avoidable recurring issues.
  • Adopt Condition-Based Maintenance (CBM): This maintenance strategy uses technology-based diagnostics—vibrations, temperature, pressure, speed, voltage—combined with problem-solving flowcharts to determine when maintenance is needed. Sensor devices monitor the actual conditions of assets in real-time and indicate signs of decreasing performance or impending failure. Technology-aided data collection is particularly effective because every asset operates under different circumstances and is influenced by human factors such as design, assembly, and maintenance. 
  • Streamline Data Collection: Again, the most accurate equipment data stems from using sensory meters with CMMS platforms. MTBF metrics are only as valuable as the data behind them. Use a cloud-based solution like MaintainX to reliably store PM repair dates, parts used, and costs accrued for work orders and work requests. 

Other ways to improve MTBF include using quality replacement parts and sticking with suggested parameters as recommended by manufacturers. Also, don’t underestimate the importance of comfortable working conditions and solid onboarding programs for machine operators.

Conclusion

Equipment failures affect organizational bottom lines, productivity, and safety. Maintenance departments must do everything they can to keep operations running smoothly for all stakeholders. 

Tracking failure metrics such as MTBF can take O&M programs to new heights of reliability.  We recommend using MaintainX to track maintenance metrics, streamline operations, and identify opportunities for program improvements. 

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