Condition-based maintenance for complex systems:coordinating maintenance and logistics planning for the process industries

Maintenance planning in the process industries is extremely complex for various reasons. Plants often run nonstop, allowing little time for performing preventive maintenance. Failures should be prevented, however, as they can lead to system downtime and high losses of revenue. Corrective maintenance strategies are thus not suitable. Moreover, preventive maintenance strategies, such as time- or age-based maintenance, are generally too conservative, by scheduling maintenance more often than strictly necessary. Condition-Based Maintenance (CBM) therefore offers a lot of potential, as it bases the maintenance decisions on the actual system condition. Besides, in the process industries, systems generally comprise multiple components subject to various inter-component dependencies. In such cases, the optimal policy for one component may not result in a close-to-optimal solution at the system level.In this thesis, we focus on obtaining insights into the optimal CBM policy structure for systems subject to various types of dependencies, thereby focusing on decisions such as when to inspect, when to maintain, when to add a redundant component, and when to order spares. Our key finding is that CBM planning extends beyond merely using monitoring information to schedule maintenance right before component failure. Component dependencies can severely complicate the (maintenance) decisions at the system level. Many complex systems require a custom-fit, dynamic CBM policy, as classical maintenance policies or threshold CBM policies can be significantly more expensive. The insights obtained in this thesis constitute an important step towards such customized CBM policies