Delay-time-based preventive maintenance modelling for a production plant: a case study in a steel mill

This paper presents a case study of delay-time-based preventive maintenance (PM) modelling for a production plant system. Since production stoppages caused by waiting for raw materials provide windows to inspect and maintain the system, these production stoppages can be incorporated into the PM model. Considering the nature of different defects that can cause failures, two types of defects are modelled: small and large defects. Small defects are normally dealt with during production stoppages, but both small and large defects can be dealt with over a longer duration during PM. The parameters of the model are estimated using the maximum-likelihood method based on the real data. The model aims to find the optimal PM interval by minimizing the expected total downtime within an overhaul cycle. Management suggestions are also recommended.