Revisiting Drenick's Failure Law of Complex Equipment

• Activity Number: 649
• Type: Contributed
• Date/Time: Thursday, August 7, 2014 : 10:30 AM to 12:20 PM
• Sponsor: Section on Physical and Engineering Sciences
• Author(s): David Collins*+ and Aparna Huzurbazar
• Companies: Los Alamos National Laboratory and Los Alamos National Laboratory
• Keywords: Reliability ; Complex system ; Exponential distribution ; Nuclear power plant

Abstract

Though the exponential distribution is not a good failure time model for most component types, it is applicable to complex repairable systems with large numbers of components, as pointed out by Drenick in 1960. The "failure law of complex equipment" proposes that in series systems with many components which are immediately repaired or replaced when they fail, system failures will be (asymptotically) exponentially distributed regardless of the component failure time distributions. We review necessary conditions for this result, and present some simulation studies to assess how well it holds in systems with finite numbers of components. We also discuss its applicability to estimation of the reliability of piping subsystems in commercial nuclear power plants. These subsystems typically contain thousands of individual piping components in series, each with extremely low failure rate, and meet the required conditions of the "law" quite well. Since available data on failures is insufficient to estimate more than the first moment of the failure time distribution of a single element, the ability to characterize the subsystem failure law as exponential has significant value.