Optimization of condition-based maintenance considering partial opportunities

Recent studies have demonstrated the economic benefit of exploiting partial opportunities for maintenance, which arise from the reduction of costs of doing partial maintenance utilizing the opportunity given. A typical example is an externally induced production stop with a duration that may not be sufficient to a complete maintenance activity. This paper combines partial opportunities and condition-based maintenance (CBM) strategies and proposes an innovative maintenance optimization method considering time-varying economic conditions. This scenario naturally fits a broad range of assets with a finite design life (including long-life machinery and infrastructure), operating under variable economic conditions and usage-intensities. The maintenance optimization problem is formulated in this study as a finite-horizon Markov decision process, where the randomly occurring opportunities are accounted for by augmenting the time-varying, decision-dependent transition probabilities. A dynamic programming approach is subsequently used to obtain the optimal CBM policy, consisting of time-varying thresholds on equipment condition and the cost of conducting maintenance during the arrived opportunity. A case study of such a maintenance policy for an induced draft fan of a sugar production system located in Queensland, Australia, is undertaken to evaluate the benefits of the proposed methodology against more traditional approaches that neglect opportunities or consider only replete opportunity durations.