Towards an innovative lubricant condition monitoring strategy for maintenance of ageing multi-unit systems.

The high acquisition cost retained by replacement of ageing and deteriorating assets triggers operational life-extension for the systems. Subsequently, ageing effects like compromised performance and wear are introduced, adversely affecting system economics and performance. An integrated maintenance and spares strategy incorporating lubricant condition monitoring (LCM) under condition-based maintenance (CBM), corrective maintenance (CM) and preventive maintenance (PM) is proposed, to mitigate the ageing effect challenges. The study considers the lubricant not only as a monitored item, but as a spare like other repairable units, similarly deteriorating, and retaining different maintenance interventions. We link the lubricant degradation (iron and viscosity oil properties) and repairable units’ degradation and performance, by integrating rate-state interactions with imperfect maintenance to derive stochastic dependencies in the degradation model. The applicability of the proposed discrete event simulation model is illustrated for a geothermal drilling rig, whose performance (maintenance cost and lubricant volume) are derived. Results demonstrate system performance dependency on PM intervals and CM strategies for both the lubricant and the repairable units. The significance of LCM policy to maintenance and system performance is substantiated. The developed framework has widespread use in real-life and broader applications that include LCM in deriving maintenance decision support.