A nearly optimal inspection policy for a two-component series system

This paper deals with a condition based maintenance policy for a series system made of two components subject to gradual deterioration and whose failures are not self-announcing and can be detected only through inspection. An inspection consists in measuring one control parameter for each component and comparing the obtained value with a predefined corresponding alarm threshold level. At this point, a decision should be made based on the inspections results, doing preventive or corrective replacements respectively when one component threshold level is exceeded or when it is found in a failure state, or do nothing in case neither of the two alarm thresholds is found above the corresponding alarm threshold level. A preventive replacement of a component is performed in case the other one has to be replaced. A mathematical model and a numerical procedure are developed in order to generate a nearly optimal inspection sequence (inspection instants) which minimizes the average total cost per time unit induced by both inspection and maintenance actions over an infinite horizon. Numerical results are presented and discussed.