Joint optimization of maintenance and spares inventory policy for a series-parallel system considering dependent failure processes

•An optimal joint policy of maintenance and inventory for a series-parallel system with software and components is studied.•The components will be opportunistically inspected when the software failure occurs.•The components are subject to mutually dependent failure processes.•The inspection interval, preventive replacement threshold and order point are optimized. This paper investigates the joint optimization of condition-based opportunistic maintenance and spare inventory policies for a series-parallel system consisting of software and components. Software failure follows a homogeneous Poisson process. Components are subject to mutually dependent competing failure processes. When the software failure occurs, an opportunistic inspection will be implemented for the components. Besides the maintenance policy, the (s, S) inventory policy is applied for components. The maintenance and order decisions will be made according to the conditions of the components and inventory level at each inspection. The state transition probabilities and expected sojourn times can be obtained by the formulated semi-Markov decision process. The optimal inspection interval, the preventive replacement threshold of the component, and the order point can be derived by minimizing the expected average cost rate. Finally, the effectiveness and superiority of the proposed joint optimization model are verified by an illustrative example.