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Mean Distance Between Failures(MDBF)

Reliability Engineering
mechanical

Definition

The average distance traveled or cycles completed between consecutive failures, used for equipment where usage is measured in distance or cycles rather than operating hours. MDBF is the distance/cycle-based equivalent of MTBF, appropriate for mobile equipment, rotating machinery measured in revolutions, or reciprocating equipment measured in strokes.

Context

Used in reliability analysis for equipment where time-based metrics are less meaningful than usage-based metrics. Examples include pipeline pigging equipment (distance), reciprocating compressors (cycles), and relief valves (actuations). MDBF enables more accurate reliability prediction when failure is driven by usage rather than age.

Formula

MDBF = Total Distance (or Cycles) / Number of Failures

Examples

  1. A pipeline inspection gauge (pig) has an MDBF of 500 km, meaning on average one component failure occurs for every 500 km of pipeline inspected.
  2. Reciprocating compressor valves have an MDBF of 10 million cycles, driving a preventive replacement strategy at 8 million cycles.

Applicable Standards

  • ISO 14224:2016
  • IEC 60300-3-1

Related Terms

Mean Time Between Failures(MTBF)

The average time between consecutive failures of a repairable system or component, calculated as the total operating time divided by the number of failures during that period. MTBF is the primary reliability metric for repairable systems and represents the expected time of continuous operation between failure events. Higher MTBF indicates better reliability.

Mean Time To Failure(MTTF)

The average time from the start of operation until the first failure of a non-repairable item, or the average time between replacement and next failure for items that are replaced rather than repaired. MTTF is technically correct for non-repairable components (bearings, seals, filters, lamps) while MTBF applies to repairable systems. In practice, the terms are often used interchangeably.

Failure Rate(Lambda)

The average number of failures per unit of time for a population of items, typically expressed as failures per hour, per year, or per million hours. Failure rate (lambda) is the reciprocal of MTBF for constant-failure-rate systems. It is a statistical average measure, distinct from the instantaneous hazard rate, and is most accurate when the failure rate is approximately constant (beta near 1).

Where this appears in Reliatic

This concept is used in the Reliability Analytics module.