Technical Reports

Procedure to Establish Inspection Intervals of Regularly Maintained In-Service Units Subject to Failure

  • 01
  • May
  • 1996
AUTHOR: Federal Railroad Administration
KEYWORDS: Inspection; Reliability; Failure Rate; Repair; Probability; Simulation; Exponential Failure; Inspection Interval; Statistical Formula; Level of Confidence
ABSTRACT: Procedures have been developed for determining the period between regular inspections that is required to ensure, with a specified level of confidence, that no more than a certain percentage of the units of a population that is in service has failed. The procedure assumes that the units have a uniform random failure rate and that the population is divided into many equal sized groups. These groups are inspected sequentially at a uniform rate over the inspection interval, repaired if necessary, and returned to service. A new inspection interval is calculated based on the number found failed in an initial inspection interval. Comparisons of repeated simulations of the percentage of in-service units of the population using randomly generated data have determined that the procedure is useful when the population is greater than 100 units and the percentage of the population found failed at inspection is less than 1%. These procedures, combined with engineering data and experience, may be applied to the definition of approaches for ensuring safety of equipment in railroad operations.