Random Failure
Definition
A failure that occurs with approximately constant probability per unit time, independent of the item's age or accumulated operating time (Weibull beta approximately 1). Random failures are caused by unpredictable combinations of stress and strength, external events, or operating conditions that cannot be anticipated by age-based inspection or maintenance. They are equally likely to occur at any point during the useful life period.
Context
Random failures represent the useful life phase of the bathtub curve. They are significant because time-based preventive maintenance cannot prevent them — the failure probability is the same for a new item as for one that has operated for years. Condition monitoring and redundancy are the primary strategies for managing random failure modes.
Examples
- Lightning strikes on instrumentation cause random failures that cannot be predicted or prevented by time-based maintenance. The appropriate strategy is redundancy and surge protection.
- Foreign object damage (FOD) to a compressor is a random failure mode — it depends on the coincidence of debris ingestion and operating conditions, not on equipment age.
Applicable Standards
- IEC 60300-3-1
- SAE JA1011
Related Terms
A graph of the hazard rate versus time that describes the typical life cycle of a population of items, characterized by three distinct phases: (1) Infant Mortality — a decreasing failure rate period caused by manufacturing defects, installation errors, or design weaknesses; (2) Useful Life — a period of approximately constant, low failure rate representing random failures; (3) Wear-Out — an increasing failure rate period caused by age-related degradation mechanisms.
Infant MortalityThe early-life period of a component or system characterized by a higher-than-normal failure rate that decreases over time (Weibull beta < 1). Infant mortality failures are caused by latent defects introduced during manufacturing, installation, or commissioning — they are not age-related degradation but rather quality problems that manifest early. Common causes include material defects, welding flaws, installation errors, contamination, and incorrect settings.
Wear-OutThe late-life period of a component or system characterized by an increasing failure rate over time (Weibull beta > 1), caused by progressive degradation mechanisms such as fatigue, corrosion, erosion, creep, and material aging. Wear-out failures are predictable and age-related, making them amenable to time-based or condition-based preventive maintenance strategies.
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).
Condition MonitoringThe process of monitoring a parameter of condition in equipment (vibration, temperature, pressure, flow, oil quality, acoustic emission, electrical properties) to identify significant changes indicative of a developing failure. Condition monitoring is the technical enabler of predictive maintenance, detecting degradation at the P point on the P-F curve to allow planned intervention before functional failure.
Where this appears in Reliatic
This concept is used in the Reliability Analytics module.