Mean Time Between Failures (MTBF)

What is MTBF?

 Mean time between failures (MTBF) is calculated as the average time between failures for repairable items.  MTBF is used as a performance indicator (PI) of the reliability of manufacturing equipment.  The concept of “Mean time Between…”  is also applicable to, e.g. entire packing lines (mean time between touch MTBT), quality (mean time between quality defects – MTBQD), and other areas.

When to use MTBF?

MTBF is a good indicator of the reliability of manufacturing equipment and components.  As such, it is a valuable measure of how well the plant and equipment are maintained (strategy, practices) and of the success of, e.g. risk-based inspection programs and reliability improvement projects: MTBF increases as reliability increases.  MTBF is also directly correlated to Breakdown and Minor Stoppage TPM losses: as the losses decrease, MTBF increases.

MTBF is used in the calculation of the Availability, which in turn is used to calculate overall equipment effectiveness (OEE):

Example: Series system (most packing lines)

Availability of an individual plant item (series system)

Av₁ = 1 – MTTR/(MTBF + MTTR)

(Where MTTR = mean time to repair = average time to return a failed component to service)

Availability of system = Av₁ x Av₂ x Av₃…

And

Overall Equipment Effectiveness = Availability x Performance x Quality