Equipment parts that deteriorate gradually during their life cycle should be replaced during planned maintenance activities, and should be purchased by direct-charge or back-order and not be stocked. As a result of prior inspection or for planned maintenance, the departments concerned should requisition normal operating spares. They should be catalogued with price and lead-time so that the fulfilling of Plant Maintenance work orders can be planned. Sufficient time shall be allocated to order the particular spare parts required. Even though the precise timing of the shutdown may be condition-based, a nominal operating interval will have been established and the necessary overhaul kits or spare parts ordered accordingly.