An Age Based Maintenance Policy Model for Unavailability Analysis of Dormant Systems

Abstract

Repairable systems with latent failures are systems where special inspections are realized regularly, with a fixed period, to reveal a failure. If a failure is revealed, the renewal procedure is started at the earliest possible inspection time. Maintenance policies for such systems can be categorized into two main classes: age based and calendar based policies. In the age based policy we suppose that maintenance actions are realized at a given time interval starting from the latest time of maintenance, whereas in the calendar based policy, the system inspections and maintenance are realized periodically at planned times known in advance. In the age based policy, real calendar time of maintenance actions is unknown in advance, due to random times of failures and random times necessary for restorations. Relevant issue of the paper is to formulate reliability mathematics describing the time based maintenance policy model, here denoted as Model III. The paper results from innovative stochastic reliability models, recently developed and used for unavailability quantification of repairable and maintained systems with latent failures. Models are transformed into numerical codes to be demonstrated on both a referenced simple system with the Weibull ageing and real complex system from practice. For the reason of system unavailability analyses, the directed acyclic graph was used in this study, which showed to be a suitable system representation of complex systems.