Towards a reliable condition index for condition-based maintenance decision-making

This paper aims at analyzing the effectiveness of some well-known condition indices for condition-based maintenance decision-making. The study is based on a single-unit system subject to competing risks due to multiple degradation paths of stress corrosion cracking (SCC). The system is assumed to be failed whenever the number of cracks or the sum of all crack sizes reach critical thresholds. A periodic inspection scheme is used to monitor the system health state. Each inspection returns the perfect diagnostic information (i.e., the number of cracks and the corresponding crack size, as well as the failure/working state of the system). Based on this information, two kinds of prognostic condition indices (i.e., average type and quantile type of the system residual useful life) are constructed. The associated predictive maintenance strategies and cost models are also developed and compared with the ones whose maintenance decisions are based on diagnostic condition indices. The comparison results allow us to conclude on the performance and on the robustness of the prognostic indices compared to the diagnostic ones, hence giving some suggestions on the choice of condition indices for maintenance decision-making.