Optimal maintenance policy for a two-unit parallel system using proportional hazards model

In this paper, we present an optimal opportunistic maintenance policy for a two-unit parallel system, where economic dependency exists between the units. Both units are subject to deterioration and condition monitoring and the units operate independently. At each inspection epoch, condition information for both units is available. The failure rates of both units are described by the age and by the covariate values obtained at inspection times. The covariate processes representing the two units deterioration have three states: healthy, warning and a high deterioration state. The units can fail independently and the failures can occur at any time. Proportional hazards model is proposed to combine condition monitoring and the age information. The objective is to find an optimal opportunistic maintenance policy minimizing long-run expected average cost per unit time. Numerical example is developed to demonstrate the proposed model.