MRO procurement: buying spares before the machine needs them

Criticality is about downtime consequence, not part cost

The right sorting question is what happens to output between the moment the part fails and the moment a replacement can be fitted. A cheap proximity sensor on a single-path conveyor with a long import path can outrank an expensive gearbox on a machine with a parallel route. Build the classification from the equipment side: which assets have no redundancy, which failures stop a whole line rather than a cell, which parts have a long or uncertain replenishment path, and which need a specialist to fit. Value-based classification consistently misplaces the parts that hurt most.

Original equipment parts against qualified equivalents

Machine builders price spares well above the component's open-market level, and for many standard items — bearings, seals, pneumatic fittings, drive belts, common sensors — a catalogue equivalent is the identical component in different packaging. The distinction that matters is whether the part sits inside a controlled function: a safety circuit, a validated process, a metrology chain, or anything covered by a warranty or service agreement that names original parts. Equivalents are sensible for the general population and dangerous inside those boundaries. Decide the rule by category once, and record it, rather than debating it at each failure.

Obsolescence on the machine side, not the product side

Production equipment outlives its control components by a wide margin. Drives, controllers, human-machine interfaces and specialised sensors reach end of support while the mechanical asset still has plenty of life. The plant then faces three options: buy a final stock of the discontinued component, retrofit the control system, or accept the risk of the grey market with its counterfeit exposure. Each is expensive and none is comfortable. What makes the decision manageable is knowing early, which means asking equipment suppliers for support status on control components as a standing question rather than discovering it after a failure.

The storeroom nobody has audited

Spares inventories accumulate. Parts stay on the shelf after the equipment leaves, duplicates arrive under different descriptions from different suppliers, and items with a shelf life — elastomers, adhesives, batteries, certain lubricants — quietly expire in place. A physical review that matches stock against the current asset register usually finds a material share of the value attached to equipment no longer in the building. Cleaning that up releases cash and, more usefully, restores confidence in the records, so maintenance stops keeping private caches because it does not believe the system.

Buying repairs, not only parts

A substantial part of this category is service rather than material: motor rewinds, gearbox overhauls, hydraulic cylinder refurbishment, spindle rebuilds, calibration. These purchases are harder to specify because you are buying a restored condition rather than a described object. Define what the returned item must demonstrate — the test results, the tolerances checked, the parts replaced as standard, the warranty on the work — before it goes out. Repair vendors that report only that the unit was overhauled leave you unable to distinguish a proper rebuild from a clean and a repaint.

Frequently asked questions

How do you decide how many of a critical spare to hold?

Start from how many identical units are installed, how the component actually fails, and how long a replacement genuinely takes to arrive including any specification or approval step. A single installed unit with a long procurement path and a sudden failure mode argues for one on the shelf. Several installed units with gradual, detectable wear may need none, because condition monitoring gives you warning enough to order. Holding by rule of thumb across the whole storeroom produces both shortage and dead stock at once.

Should maintenance or purchasing own the spares decision?

Maintenance owns which part is technically acceptable and what criticality it carries, because that judgement rests on the equipment and the failure mode. Purchasing owns the source, the commercial terms and the replenishment arrangement. Trouble appears when either crosses the line: purchasing substituting an equivalent without engineering sign-off, or maintenance placing direct orders that bypass agreed suppliers and pricing. A joint review of the critical spares list, refreshed as equipment changes, keeps both sides looking at the same register.

What is the risk of buying obsolete machine components on the open market?

Counterfeit and refurbished parts sold as new are a genuine hazard in discontinued electronics and control components, and a failed drive can damage far more than itself. Where you must buy outside the original channel, prefer sources that provide traceability back to the manufacturer, insist on functional testing before the part is accepted into stores, and treat an unusually attractive price on a long-discontinued item as a warning rather than a find.