When designing a process facility, a concept called “Sparing Philosophy” is used, i.e., If a certain equipment fails, can I keep the plant running using a spare?
The below image explains the terminology to Assign how many pumps are working (W) & how many are on Standby (S).
Some brief points on how the sparing is arrived at,
1. Life Cycle Cost [LCC] Reduction – The Criticality & Reliability of the unit operation decides the sparing philosophy. To achieve high LCC, time intervals between failures & repairs should also be high.
2. Cost Savings – Every time a pump fails, you lose production, i.e., Downtime. So the sparing is chosen by weighing the Production Losses vs. Cost of purchase, maintenance, labour & cost of capital of the equipment.
3. Spare Inventory – Sparing is chosen depending on, if the spares are available at site or kept in some warehouse elsewhere or one has to call up the vendor to purchase.
4. Interchangeability – Being able to interchange pumps between units during failures to reduce downtime.
Basically, when a pump fails without a spare & you have to wait for all eternity before the pump is fixed, up & running, then you’ve lost the plot about Asset Management!!