On most new plants the spares question gets answered by three documents: the OEM’s recommended spares list, the spares purchase order, and the commissioning contractor’s consumables list. Together they look complete. Then a critical pump fails in the first months of running, and the part that fixes it is weeks away, because nobody linked the spares list to the way that pump fails.
A new plant needs its spares built the same way its maintenance readiness is built: from the equipment’s failure modes and the maintenance tasks, with the vendor’s list as one input. This guide sets out the three holdings a plant needs before start-up, why the OEM list falls short, how we build the list, and when it has to be ordered.
Quick Links
The short answer
A new plant needs three spares holdings in place before start-up: commissioning spares to get through commissioning and early running, operating spares for the planned maintenance tasks, and critical spares (often called insurance spares) for the failures the plant cannot afford to wait on. Build the list from failure modes and maintenance tasks, use the OEM’s recommended list as one input, make one stocking decision per critical line, and order early enough that long-lead parts are on site and receipted before the plant needs them.
The three spares holdings at a glance
| Holding | What it covers | How the quantity is set | What happens without it |
|---|---|---|---|
| Commissioning spares | Parts consumed or damaged during commissioning and early running: seals, gaskets, filters, fuses, wear parts used in testing | The vendor’s commissioning list, checked against the commissioning plan | Commissioning stalls on a part worth a fraction of the delay |
| Operating spares | Everything the planned maintenance consumes: filters, service kits, belts, lubricants, test gases | The maintenance task list and its intervals | Planned work is deferred for want of parts, and the plant drifts into breakdown maintenance |
| Critical spares | Parts for failures with a high consequence and a long lead time: gearboxes, motors, liners, major bearings, sometimes complete pumps | One stocking decision per line, from equipment criticality, the failure mode and the lead time | Weeks of lost production waiting on a single part |
You will also hear capital spares: high-value items, often whole assemblies, that many owners account for as capital rather than stock. Most capital spares are critical spares by another name. How they are accounted for is a decision for your finance team; whether to hold them is a decision about risk, and it belongs in the same list.
Why the OEM recommended list is not enough
The OEM’s recommended spares list is a good starting point and a poor finishing one. It is written by the vendor, for the equipment, without knowing your plant. In practice it falls short in five places:
- It does not know your criticality. The same pump gets the same list whether it is a duty pump with a standby or the only feed to the mill.
- The holding basis is unclear. Quantities are often per unit when you hold per train, or the reverse. Unless someone checks, the order quietly doubles or halves.
- It misses what the maintenance tasks consume. Filters, kits, lubricants and gases sit in the work instructions, not the spares list. An accumulator pre-charge needs nitrogen; an OEM spares list rarely mentions it.
- Sub-supplier parts sit elsewhere. Motors, couplings, gearboxes and instruments come with their own manuals and their own parts lists, often in a separate document set.
- It arrives late. On a greenfield build the lists turn up with the vendor data, package by package, sometimes after the parts should already be on order.
How we build a new plant’s spares list
- Write the data requirement into the purchase orders. Recommended spares lists, parts lists and lead times are a deliverable of every EPC and OEM purchase order, specified before the order is executed.
- Extract every part from every source. The recommended spares list, the general arrangement drawing bills of materials, the installation and operating manuals, and each sub-supplier manual. The spares purchase order is reconciled line by line against what was recommended.
- Tie every part to the maintenance tasks. Every task that replaces or consumes something has its parts in the list, against the same plant item, so the parts arrive with the work order.
- Make the critical spares call from failure modes. A critical spare is justified by the equipment’s criticality and the way it fails: hidden failures, high-consequence failures and long lead times. Each critical line carries its reason, so the decision can be defended at budget time.
- Put complete units to the owner as a risk decision. A spare pump, motor or gearbox is a deliberate choice about risk and capital. We set out the consequence and the lead time; the owner decides.
- Load it, ready to stock. Catalogue items, bills of materials and stock holdings delivered as load sheets in the plant’s CMMS format, structured to ISO 14224, alongside the maintenance strategies they support.
What good looks like at start-up: every critical line has a stocking decision and the reason behind it, the parts for every planned task are catalogued against the work order, and the critical spares are on site and receipted before the first productive work on the asset.
When the spares must be ordered
The spares list has two deadlines, and the first one arrives well before anyone thinks about stores. Vendor data requirements, including spares lists and lead times, must be written into the EPC and OEM purchase orders before those contracts are executed, around 24 months before first ore. Miss it and the data is bought back later, at the contractor’s price.
The second deadline is the one the operating team feels. Under the First Work-Level Readiness test, the spares the maintenance strategy calls for must be physically on site and receipted before the first productive work on the asset. Work back from that date by each critical line’s lead time, and the order dates usually land during construction. The readiness checklist carries both dates, counted back from first ore.
Restarts: check the store, not the register
A plant coming back from care and maintenance has a store and a spares register, and neither can be trusted until it has been checked. Parts degrade on the shelf, get cannibalised for other sites, and stop matching equipment that has since been modified. The register describes the plant as it was. On a restart, re-verify what is physically in the store against the plant that exists, then rebuild the critical list from current criticality. Greenfield vs brownfield vs restart covers how the rest of readiness shifts.
Where this has been done
- A new iron-ore plant: a critical spares register and bills of materials, SAP-ready, delivered with 353 planned routine tasks before commissioning. Read the case study
- Three newly commissioned treatment plants: failure-mode analysis on every maintainable group with a draft stocking recommendation, then register-ready critical spares, one stocking call per line, across 577 assets on the largest site.
- A nickel concentrator restart: asset criticality and integrity assessed, then baseline maintenance strategies and a critical spares list, for a plant being prepared to restart after five years in care and maintenance. Read the case study
- Hydraulic excavator fleets: critical spares determined with reliability block diagram modelling, where the consequence justified the analysis. Read the case study
- A West African greenfield gold plant (in delivery): spares and bills of materials built from vendor data as it arrived, in the client’s CMMS format. Delivering readiness in West Africa
Spares list due before handover?
If your project is relying on the vendor lists to arrive complete, find out now which critical lines have no order behind them. Spares are part of the maintenance readiness our operational readiness consultants build and assure, and the free readiness scorecard shows where your project stands across the nine readiness areas in about five minutes.
Frequently asked questions
What are critical spares?
Critical spares are the parts held for failures a plant cannot afford to wait on: failures with a high production, safety or environmental consequence where the replacement has a long lead time. They are justified line by line from the equipment’s criticality and the way it fails.
What is the difference between critical, insurance and capital spares?
Critical and insurance spares are largely the same thing: parts held against a high-consequence failure, which may never be used. Capital spares are high-value items, often whole assemblies, that many owners account for as capital rather than stock. Most capital spares are also critical spares. The accounting treatment is a finance decision; whether to hold the part is a risk decision.
When should spares for a new plant be ordered?
The spares data requirements go into the EPC and OEM purchase orders before they are executed, around 24 months before first ore. The parts themselves are ordered against each line’s lead time so that the spares the maintenance strategy calls for are on site and receipted before the first productive work on the asset. For long-lead critical spares, that usually means ordering during construction.
Is the OEM recommended spares list enough?
It is a good input and an incomplete answer. The OEM list does not know your plant’s criticality, often leaves the holding basis unclear, misses the consumables your maintenance tasks need, leaves sub-supplier parts in separate manuals, and can arrive after the parts should be on order. Use it, then build the list from failure modes and tasks.
How many critical spares should a new plant hold?
There is no defensible ratio. The number is the sum of individual decisions, one per critical line, each based on the consequence of the failure, how the part fails, how long a replacement takes to arrive, and whether a standby unit covers the risk. A list built that way can be defended at budget time; a percentage cannot.