A delay time multi-level on-condition preventive maintenance inspection model based on constant base interval risk : When inspection detects pending failure

The model described in this paper is one of a series, which determines the optimal multi-level inspection-maintenance policy for a stochastically deteriorating multi-state sub-system, using the delay-time concept. The sub-system deterioration is assumed to be a non-decreasing semi-Markov process, where states are self-announced and inspection detects the sign of pending failure. Emphasis is placed on constant availability and reduction of production losses, deterioration rate and subsequent sub-system failure. In this respect, inspection is scheduled in such a way that the risk of failure is a constant for each inspection interval. Two pairs of mathematical models and softwares have been developed, and the policy decisions taken have been based on two criteria for optimisation. These decisions have then been validated by carrying out a simulation exercise using the ProModel simulation package.