A novel modeling framework for a degrading system subject to hierarchical inspection and maintenance policy

Most engineering systems exhibit degrading performance in their designated service times as influenced by their working conditions. Thus, inspection and maintenance actions are crucial for maintaining their performance. Among these, critical engineering systems, such as compressors and safety valves, are typically subject to a multi-level inspection scheme consisting of partial and full inspections. In this study, inspired by this inspection scheme, we propose a hierarchical maintenance model to incorporate collected system performance information from these inspection interventions. Partial inspections verify whether the system is functional or not, and then partial preventive maintenance is performed; a more accurate system state is known at the instant of full inspections, which serve as windows for the conduction of condition-based maintenance. The proposed maintenance policy is then applied to a system undergoing monotone stochastic degradation. Subsequently, the average cost per unit time in the operational phase and the sensitivity analysis with respect to variables, such as the preventive maintenance threshold, inspection intervals, and the maintenance effect factors, are investigated. Theoretical results and numerical examples are obtained to examine the applicability of the generalized model. © 2023 The Author(s).