A renewal process model with failure based PM and imperfect CM for unavailability exploration

Abstract

PurposeThe paper aims to explore unavailability of dormant systems that are under both preventive and corrective maintenance. Preventive maintenance is considered as a failure based maintenance model, where full renew is realized at the occurrence of every nth failure. It proposes the imperfect corrective maintenance model, where each restoration process deteriorates the system lifetime, probability distribution of which is gradually changed via increasing failure rate.Design/methodology/approachBasic reliability mathematics necessary for unavailability quantification of a system which undergoes a real aging process with maintenance has been derived proceeding from renewal theory. New renewal cycle was defined to cover the real aging process and the expectation of its length was determined. All events resulting in the failure of studied system were explored to determine their probabilities. An integral equation where the unavailability function characterizing studied system is its solution was derived.FindingsPreventive maintenance is closely connected with the occurrence of the nth failure, which starts its renew. The number n can be considered as a parameter which significantly influences the unavailability course. The paper shows that the real aging process characterized by imperfect repairs can significantly increase the unavailability courses in contrast with theoretical aging. This is true for both monitored and dormant systems.Originality/valueAlthough mathematical methods used in this article were inspired and influenced by the work of reference (van der Weide and Pandey, 2015), derivation of final formulas for unavailability quantification considering the new renewal cycle is original. Idea of the real aging process is new as well. This paper fulfils an identified need to manage the maintenance of realistically aging systems.

Really Ageing Systems Undergoing a Discrete Maintenance Optimization

“…The corresponding reliability mathematics for the unavailability quantification of terminal nodes was derived in this article because this unavailability is used as the main input in system unavailability quantification using AGs as the system representation. Although the renewal process model that originates from the new renewal cycle was only developed in this article, in general, we can conclude that it is a limited case of the model developed in [31] where the length of the inspection period approaches zero. A cost model respecting the imperfect CM process with FBM was further introduced because it is indispensable for discrete maintenance optimization.…”

“…The starting point for the development of this methodology lies in our previous work introduced in [31], where dormant systems under inspection were investigated. The main difference is in the renewal cycle.…”