Study of optimal replacement strategy of degradation system components for system availability

In support process of equipment systems, spare inventory strategy, turnaround time, and product maintenance strategies have a great impact on system support time, and support time is one of the most important factors for the readiness and the task persistence of systems. Therefore, the use of reasonable spare inventory strategy, as well as maintenance and support decisions to systems is essential to improve system availability, security and system cost reducing. Maintenance strategy can be formulated based on the situation in which the products are monitored. For a single-component system, current research around its multi-state transferring have been quite mature, in which the conversion rate defined in a different state in Markov process can be clearly showed by conversion relationship between different state. However, the state transition process involved mostly considers the processes of repairing only, and rarely considers the impact to system availability by the transition of failure rate caused by changes in components, spare replacement strategies and spare supply. To solve this problem, this paper considered a single-component system with two derating states, and discussed its steady-state availability through variable spare replacement probability and different spare fill rate levels. With model of the system with two derating states established, generalized Markov method was used to solve the relationships between replacement timing and system availability with the level of spare fill rate considered. Finally, through the analysis of results, the preliminary conclusions were obtained. The results could clearly reveal the impacts of spare replacement strategy and spare fill rate in single-component system.