Predicting operational availability for systems with redundant, repairable components and multiple sparing levels

The Strategic Petroleum Reserve (SPR) is a multi-mission project required by law to maintain a prescribed degree of readiness and a mandated performance criteria. The prediction of operational availability is essential to determine operational readiness to satisfy mission requirements. This is accomplished through, the use of availability models utilizing a reliability block diagram (RED) of mission critical components. The RED model calculations incorporate sparing criteria and components using a multi-state model of the operation. Individual component data include: capacity, meantime-between-failure (MTBF), and mean-down-time (MDT) assuming repairable components and instantaneous switching. An accurate site model addresses all of these concerns and provides a good prediction of operational availability. An example of a system without a spare and the same system with a spare is presented to illustrate one method of incorporating sparing into the prediction of operational availability.