Esmaeil Rezaei - Mazandaran University of Science and Technology, Behshahr, Mazandaran, Iran
Din Mohammad Imani - Iran University of Science and Technology, Tehran, Iran

Repairable system is commonly used in different industries and has been more complex. In this paper, two component repairable systems with failure interaction are considered. The failure of these components can be soft or hard. The hard failure causes the system stop and the soft failure does not, but it increases the system operating costs too. The periodic inspections have a fix cost to system. When the first component fails, it remains in a failed state until the next inspection time.Therefore, if the first component failed in each inspection interval, a downtime penalty cost is incurred. The cost is proportional to the elapsed time from failure time to its detection at inspection time. The short inspection interval increase the number of inspection and causethe extra cost for system. As well, long inspection interval cause the greater cost due to long elapse time between real occurrence of thefailure time and the failure detection (penalty cost). On a finite time horizon, the objective is to find the optimal inspection interval for thesoft failure component so that the expected total cost will be minimized. Finally, a sample problem is solved and numerical results are presented.

Periodic inspection interval, Steam turbine rotor, maintenance, soft and hard failures, Failure interaction