SPARE PARTS MANAGEMENT BY AMAR P. NARKHEDE

INTRODUCTION CHARACTRISTICS OF SPARE PARTS Spare parts management needs special treatment, somewhat different from inventory management of regular items since keeping a stock of these is different to serve as a replacement to the worn out parts in the machinery. The statistics of failure is of much importance in the management of spare parts. Moreover, spare parts are not always available during the entire life time of the equipment. Spare parts are special independent demand items deriving their demand from the failure characteristics of the component and with a specialized supply situation

CLASSIFICATION OF SPARE FOR STOCKING POLICY ANALYSIS Maintenance of breakdown spares: These are the spares which are required in large quantities at more or less frequent periodic intervals as and when the breakdowns occur. These resemble, some what the regular inventory items in their consumption patterns. The rate of consumption of spares can be derived from historical data regarding failure of different components in the machinery

Insurance spares: As the name indicates, the purpose of these spares is to provide an insurance against the relatively remotely possible breakdown or failure of an equipment/components. The probability that such a component/equipment will survive the life time of the machinery or plant is quite high. The reliability of such spare has been observed to be high as 95 to 99% over the life span of the machinery. These spare are sparingly needed. But they are needed all the same because they may hold up production resulting in considerable for want of them. Many of these spares are also high value items. These spares are, by and large produced along with the capital euipments

Capital spares: These are high reliability spares, but not as high as the insurance spares. The reliability is not as low as the maintenance spares. Moreover these spares have relatively higher purchase cost than the breakdown spares. The decision regarding these spares is usually made at the time of purchase of the capital equipment itself. The analysis for the capital spares inventory policy is therefore somewhat different from that of insurance spares. A spare has to be procured only if the expected value of the down time costs exceeds the purchase value of the spare

Rotable spares: These are reusable spare pats, which after their breakdown can be reconditioned and reused. Typical examples are the stepney in the car, jet engine in aircrafts, tyre tubes in cycle, electrical motors. Since these have more than one life, the cycle of their various lives needs to be taken into consideration in the analysis of their inventory policy. For example, jet engine or an electric motor can be reconditioned after failure and put back in operation. These are called rotable spares