Spare Parts Criticality Planner
Decide which spare parts are worth stocking by expected downtime cost avoided, not part price alone, which can badly underrate cheap-but-critical parts.
Criticality
How this works
Deciding which spare parts to stock by part price alone favors expensive parts over cheap-but-critical ones. The value of stocking a part is the expected downtime cost avoided weighed against the annual cost of holding it in inventory.
Key terms
- Expected downtime cost avoided: downtime cost per hour times the extra delay avoided, times the annual probability the part fails.
- Net stocking value: expected downtime cost avoided minus annual holding cost, positive means the part is worth stocking.
Assumptions
- One failure mode per part, holding cost is a flat percentage of part cost
Limitations
- Single part, not a full spares-inventory portfolio optimization
Sources
Standard spare-parts criticality / RCM (reliability-centered maintenance) stocking practice.
Worked example
A price-only ranking would deprioritize a $200 part against a more expensive one. But its $6,000/year expected downtime cost avoided dwarfs its $50/year holding cost, a price-only view would badly underrate how much this cheap part is actually worth stocking.
Common use cases
- Deciding which spare parts justify a stocking budget
- Ranking spare parts by real criticality, not price
- Following up a shutdown-capacity plan with a spares-stocking decision
Frequently asked
- Why isn't part price the main factor in whether to stock it?
- A cheap part that causes expensive downtime when unavailable is worth stocking; an expensive part with a long backlog-remaining runway before it is needed may not be, so expected downtime cost avoided is the real driver.
- What is backlog-remaining and why does it matter?
- It is how much runway exists before a failure would actually stop production (from redundancy, buffer inventory, or slack capacity); a long runway lowers the urgency of stocking a given part.
- How is failure probability estimated?
- It is your own entered estimate from maintenance history or manufacturer data; this model applies it to price expected cost, it does not derive a probability from scratch.
- Does a high net stocking value mean stock the maximum quantity?
- It means stocking at least one unit is justified by expected downtime cost avoided; the optimal quantity beyond one unit depends on failure rate and replenishment lead time, a separate question.