Criticality-based spare parts stocking

Maintenance strategy · Industrial practice · Updated 2026-07-15

Criticality-based spare parts stocking decides which spares to hold, and how many, based on the consequence of the parent equipment failing and the lead time to obtain the part — not on past usage alone. It concentrates stock value on parts whose absence would cause serious downtime while avoiding overstock of low-consequence items.

What it is

This practice replaces stocking by habit or simple reorder points with a deliberate analysis. Each spare is assessed for the criticality of the equipment it serves, the likelihood of needing it, and its replenishment lead time. The combination determines whether the part is stocked, how many are held, and whether it is held on site, by a supplier or not at all. It is an inventory strategy driven by reliability risk.

Why it is done

Spares inventory ties up significant capital, yet the parts that matter most — long-lead, single-source items on critical machines — are often the ones not in stock when needed, while shelves fill with cheap, easily-bought items. Criticality-based stocking aligns inventory to risk, cutting both the carrying cost of unnecessary stock and the downtime caused by missing critical spares.

How it is done

Equipment is ranked by criticality, then the bills of material of the critical assets are reviewed for parts whose failure would stop production. Each candidate part is scored on consequence, demand probability and lead time, and a stocking decision and quantity are set accordingly — including deliberate decisions not to stock low-risk items. Min/max levels are loaded into the stores system, and the analysis is revisited as equipment, suppliers and lead times change.

1. Rank equipment criticality
2. Review critical BOMs
3. Score consequence & lead time
4. Set stocking decision
5. Load min/max levels
6. Review periodically

What to watch for

Stocking purely from historical usage ignores the long-lead critical part that has never failed but would be catastrophic, which is exactly the part to hold. Setting levels once and never revisiting them leaves obsolete spares on the shelf as equipment changes.

Related practices

Related topics

Asset Criticality · Spare Parts Optimisation · Unplanned Downtime

Common in: Chemicals · Power Generation · Cement · Steel & Metals · Paper & Packaging

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