What is MTBF Formula Calculation and Significance

MTBF is defined as Mean Time Between Failure. MTBF is a calculation that is used to predict the time between the failures of a particular asset. Below we will discuss what is MTBF and how we can calculate the MTBF and how we can improve the MTBF of machines.

Understanding MTBF

MTBF gives us a better idea of how long equipment can stay in the running condition over a period of time between unplanned breakdowns. MTBF measures Availability and Reliability. Let us first understand what is Availability and what is Reliability.

Availability

Availability is the time a machine or asset is operational and it is being used when it is required to produce goods. In other words, we can say that availability is the state that a machine can perform at any given time. Mathematically it can be written as

Availability = MTBF / ( MTBF + MTTR)

While calculating the Overall Equipment Effectiveness (OEE), availability is one of the three contributing factors.

Reliability

Reliability is the ability of any machine or equipment to perform its required functions under some conditions for a predetermined period of time. In other words, we can say that it is a likelihood that machinery will continue to run what it means to do without any failure. Mathematically, it can be written as

Reliability = e(time/MTBF)

Why MTBF is helpful?

MTBF is an important indicator of the expected performance of a machine. Equipment failure can be very expensive and it is damaging to the organization. If the MTBF value is low, it generally means that you are experiencing a significant number of breakdowns of a particular asset. MTBF generally doesn’t carry the planned maintenance but it can be used to calculate the frequency of preventive replacements or maintenance.

It is known that an asset will likely run for a certain number of hours before it is going to the breakdown. Introducing preventive maintenance like lubrication and greasing can help prevent failure. So by improving MTBF, we can save money and reduce breakdown time.

How to calculate MTBF?

The equation of the MTBF calculation is easy just like in the case of MTTR. It is the sum of the total operating time divided by the total number of failures. Mathematically, it can be written as

MTBF = total operational time/ total number of failures

Let us understand MTBF by an example given below:

Suppose the machine is working and designed to operate for 10 hours per day. The machine got breakdown after a normal operation of 5 days so MTBF, in that case, is 50 hours as calculated below.

MTBF = (10 hours per day * 5 days) / 1 breakdown = 50 hours

Let us take another example in which there is an increased occurrence of breakdown for a longer period of time. Now let us assume that the machine runs for 10 hours per day and breakdown two times in the span of 10 days. The first breakdown occurs at 25 hours from the start time and took 3 hours to repair and the second breakdown occurred 50 hours from the start time and took 4 hours to repair.

Given the total uptime and number of breakdown, the calculation of MTBF is as follow.

MTBF = (25 hours + 22 hours + 46 hours) / 2 breakdowns = 93 hours / 2 breakdowns = 46.5 hours

What does MTBF tell you?

MTBF can help you inform in the following:

Frequency of failure

MTBF shows how frequently your equipment got a breakdown. The higher the value of MTBF the longer the system will likely run before failing. If the MTBF value is lower the equipment will fail frequently.

Cost of Breakdowns

MTBF can help you to reduce the cost of the breakdown. With the help of the MTBF metric, you can plan the maintenance or repair of the machine in advance before it gets fails.

When to use the MTBF?

We can use it in the following ways:

• Budgeting Capex
• PM performance indicator
• Planning of maintenance schedule
• Inventory planning

How to increase MTBF?

There are many things by which we can improve the MTBF

Proactive maintenance

by doing proactive maintenance it is less likely to have a critical failure of the machine. You can create the maintenance schedule as per the manual given by the machine manufacturer and as per the experience of operators and engineers.

Quality of spares

While doing the PM or any breakdown one must replace the spare parts with good quality spares. If we are using the cheapest spares, then the machinery will not run longer and the wear and tear will get increase.

Proper working conditions

You need to make sure that there should be the proper working condition of a particular machine. For example, we know that generally, the hydraulic system works well if the temperature of oil remains within a particular limit. If it goes beyond that limit there is leakage of valves and damage to seals occurs.

Replacing old asset

One must ensure that if there is any old equipment or any old aging assets then if the cost is getting increased and the breakdowns are coming frequently then the management should think about replacement of that asset.

Frequently Asked Questions

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