Failure is the loss of function when you needed the function to occur. Failures for reliability purposes must be precisely defined so they are recorded correctly. Much life data is incomplete because failures are mixed-up with censored/suspended data where aged items may not have failed or they represent removals from service before failure, or they have not yet failed for the mode of failure under study-in short these censored/suspended items represent successes and are a portion of data set for study.
Why: We study failed items for the same reason we do autopsies on humans-we want the data and we want it categorized correctly for making important decisions. Failures require: 1) a time origin which must be unambiguously defined, 2) a scale for measuring the passage of time/starts/stops/etc. which motivates failure, and 3) the meaning of failure must be entirely clear for recording the event.
When: Failure data must be recorded as it occurs to prevent loss of information.
Where: The CMMS system is frequently where most data resides but usually in crude fashion. The failure data is often transferred into the FRACAS system for converting the symptoms of the failure into the root causes of failure. The failure data must be converted into action items for making management decisions about future failures and the corrective action needed.
These definitions are written by H. Paul Barringer and are also posted on his web site at www.barringer1.com
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