Mean Time Between Failure (MTBF) is the average time between two successive failures.  Over a long period of time, the asset under consideration would have failed multiple times and MTBF is calculated as the arithmetic mean of the elapsed time between successive failures. 

MTBF is an indicator of how long equipment is operating continuously without any failures or downtime.  Thus, it’s a measure of the reliability of the asset and gives an indication of the likely future failure.  Higher MTBF for an asset indicates a long lead time between two successive failures and thus is considered more reliable than an asset with lower MTBF.

Why do we measure MTBF?

  1. MTBF gives a good idea of the likely occurrence of failure and helps the organization prepare for that.
  2. Analysis of MTBF by failure modes can give insights on strengthening the Preventive Maintenance program.
  3. Increasing MTBF can be used as a measure of the effectiveness of Preventive Maintenance programs.
  4. MTBF along with other condition monitoring parameters can be a factor in determining Predictive Maintenance.
  5. Tracking MTBF and instituting measures for improvement increases equipment reliability.   
  6. Avoidance of a costly breakdown and associated unplanned downtime can improve Overall Equipment Effectiveness (OEE) and help meet the business goals significantly.
MaintWiz_MTBF Software

How do you calculate MTBF?

Often MTBF is quickly calculated as Total Uptime / Number of Failures.  This calculation includes the uptime since the last failure and thus has a mathematical error.

MTBF is elapsed time between successive failures and is not an indication of the run hours.  MTBF is usually expressed in a number of hours.  MTBF calculations include only unplanned downtime due to sudden failures and explicitly exclude planned downtime for scheduled maintenance, calibration etc. 

Maintenance organizations used to keep a track of uptime and downtime in their logbooks and use them to calculate MTBF.  Modern Computerized Maintenance Management Systems (CMMS) track all the unplanned downtime associated with breakdowns systematically to calculate MTBF.

What are the related terms used along with MTBF?

Downtime:  Downtime is measured as the total time during which the equipment is not available for use or operations.  Downtime can be planned, say for Preventive Maintenance, or unplanned due to sudden failures.

Uptime:  Uptime is measured as the total time during which the equipment is available for use or operations.  Utilization will be less than or equal to uptime.

Mean Time To Repair (MTTR):  MTTR is the average time to repair the equipment and restore it to usable condition, after an outage.

Mean Time To Failure (MTTF):  MTTF is similar to MTBF.  While MTBF is used to denote the average time between two successive failures for a repairable system, MTTF is used to denote a similar metric for a non-repairable system.

How do Enterprises use MTBF?

The impacts of unplanned downtime can be costly and significant for organizations.   The cost of downtime is often much more for the organization.  It involves lost production from the failed machine, under-utilization of operators and other related production equipment in the line and involves break-fix costs.

MTBF is the expected period of time in which an asset fails.  MTBF thus can be a useful tool to schedule preventive maintenance to avoid costly breakdowns.

MTBF can be calculated in a granular way by failure mode. The number of occurrences by failure mode and their corresponding MTBF can provide additional insights for planners in defining preventive maintenance programs for the asset. 

It can also be used in the prioritization of Preventive Maintenance activities within a given period.

Based on MTBF by failure mode, Spares inventory can be planned in anticipation and helps in reducing the response time and resolution of a failure.

As assets age, the number of failures increases.  MTBF and downtime can also be used as evaluation factors in repair vs replace decisions.

MTBF along with other condition monitoring parameters can be used as factors in Predictive Maintenance.

How can MaintWiz help you in improving MTBF?

MaintWiz industry 4.0 CMMS software gathers comprehensive information on your breakdowns, including Root Cause Analysis, Counter-Measures and Corrective Actions and Preventive Actions (CAPA).  It supports detailed failure mode capture with Issue Codes (Production observed) and Failure Codes (Maintenance found).  

Work Order Metrics can calculate MTBF by Issue Codes and Failure Codes to give a comprehensive picture of the failure modes recurrence.   MaintWiz provides analytics and visual reports to help the maintenance team derive insights.  MTBF by failure mode can be computed for individual equipment or aggregate analysis can be done at peer class level or for a group of equipment/plant.

The Preventive Maintenance Program is done to avoid unplanned downtime.  MTBF trends can be useful in defining Preventive Maintenance programs.  PM Schedules can be defined in such a way that they carry out the preventive maintenance before the likely failure and tasks can be defined to address the individual failure modes and their MTBF.

MTBF can be used to determine the prioritization of maintenance work orders in a given period to ensure equipment that needs attention can be worked on first.

MTBF and MTBF by failure modes can be presented along with the Preventive Maintenance Work Order for the technician to get an insight into the equipment failure history and current status.

Equipment Scorecards provide the MTBF metric and the MTBF by key failure modes.  The composite risk score can be computed with the MTBF trend as a factor.

Besides MTBF, MaintWiz provides a lot of equipment metrics and information – other failure metrics, performance metrics, financial metrics, failure history and peer class metrics.  Overall MaintWiz helps you improve your overall asset uptime and efficiency.