Mean downtime (MDT) is a very important concept in maintenance and reliability. MDT is the average amount of time that a system is unavailable for use. This can be due to a variety of factors, such as equipment failure, power outages, human error, and natural disasters. When measuring downtime, it’s important to understand what is included in that calculation. Mean downtime is one common metric used to determine how well a machine is functioning. In this post, we’ll explore what MDT is and how to calculate it.
What is Downtime?
Equipment downtime is the period when an asset is not in use and causes a halt in production. When a facility is noticing low production numbers, equipment downtime is usually the main cause. Downtime is frequently linked to lost output, lost money, and occasionally even lost clients. Additionally, It is common knowledge that downtime is expensive. According to one study, it can cost companies up to $260,000 per hour.
However, the reality is that some downtime is required since maintenance, repairs, upgrades, and replacements have to happen. But, for the greatest success and lowest downtime cost, you have to have a handle on planned and unplanned downtime. That includes having a system to measure and monitor downtime trends for your organization, which is where the MDT metric comes in.
Scheduled Downtime
The time between an asset’s first shutdown and the completion of maintenance tasks is included in scheduled downtime. Scheduled downtime is any downtime that you plan and isn’t a result of an unexpected breakdown. A company’s maintenance philosophy will usually have an impact on the frequency and severity of scheduled downtime.
A few examples of scheduled downtime include:
- Scheduled Repairs
- Preventive Maintenance or Predictive Maintenance
- Turnarounds
- Set-ups
Unscheduled Downtime
When an asset goes offline suddenly and cannot carry out its planned role, this is known as unscheduled or unplanned downtime. Unscheduled downtime also takes into account the time spent waiting for parts to be ordered for repairs. In reality, a lack of adequate spare parts is to blame for about half of all unplanned downtime. Since it causes more than just a manufacturing delay, it directly affects revenue.
In fact, a survey by Efficient Plant found that unplanned downtime affects 1-3% of annual revenue and up to 30-40% of profitability for the manufacturing and heavy process sectors.
Examples of unplanned downtime occurrences are:
- Unexpected Repairs to Machinery
- Failure of Equipment
- Operational Challenges
- Process Failures
- Emergency Work
What is Mean Downtime?
Mean downtime is a metric that measures your average time an asset must be offline for maintenance and repairs. It begins at the point of initial failure and includes the time spent diagnosing, performing lockouts and tagouts, waiting for parts, and repairing the asset. When the asset is functioning properly again and online, the downtime is over.
How to Calculate Mean Downtime
Knowing your MDT can help you make better decisions about maintaining your systems and improving reliability. So, you can calculate your mean downtime by dividing the total downtime by the number of downtime events.
MDT = Total Downtime / # of Downtime Events
Total downtime is the sum of scheduled and unscheduled downtime that prevents an asset from operating. The term “downtime event” encompasses any event where an asset is not functional and cannot perform its intended functions. It is best to measure your mean downtime results in hours or percentages.
Mean Downtime vs. Mean Time to Repair
In contrast to mean time to repair (MTTR), which only considers repair time, mean downtime takes into account all delays. MTTR is still an excellent metric to track. However, MDT gives a complete view of an asset’s downtime and can be used to spot inefficiencies that reduce productivity.
Benefits of Calculating MDT
MDT can give you great insight into equipment downtime, including many benefits such as:
- Tracking improvements in site availability.
- Assessing the effectiveness or maintainability of asset repair strategies.
- Identifying inefficiencies in repair processes.
- Helping you formulate critical spare parts strategies.
- Monitoring the progress of initiatives to reduce downtime.
Mean Downtime: A Valuable Addition to Your Maintenance Metrics
Maintenance teams can measure asset reliability by combining several maintenance metrics, including mean downtime, MTTR, and mean time between failures (MTBF). In addition to ensuring asset performance, reliability is what shapes your organization’s reputation within and outside the organization.
