Abstract
Most work on reliability analysis assumes binary state spaces of the system and its components. In the practice, components deteriorate from perfect functioning to complete failure, passing through several intermediate deteriorating states. This paper considers general multistate coherent systems and proves the existence theorem of series and parallel multistate coherent systems, the IFRA and NBU closure theorems, and the fact that the preservation of IFR property determines the structure of a coherent system uniquely as a series system. Furthermore a generalization of the concept of modules and hazard transform is presented.
