A pre-shipment inspection report comes back clean. Eighteen pages, photographs, a signature, a conclusion of "pass". Six weeks later the plate arrives under-thickness and the warehouse rejects it.
Nothing was falsified. The inspection did not cover thickness to your drawing — it covered appearance and a sample of dimensions against the mill's own nominal, which is a different question.
Third-party inspection is a scope, not a guarantee. Knowing where the scope usually ends is the difference between buying a check and buying reassurance.
What inspection actually covers
A standard pre-shipment inspection by any of the major houses does roughly the same set of things:
Quantity. Piece counts against the packing list. Sounds trivial; it is the most common finding.
Appearance and workmanship. Visual defects under defined lighting: dents, scratches, stains, corrosion, roll marks, edge condition.
Dimensions. Measured on a sample, against the specification you supplied. Thickness, width, length, squareness, flatness — but only the ones written in the scope, measured at the points the standard sampling plan defines.
Packing and marking. Whether the packing matches the specification, and whether marks match the documents.
Document review. Certificate of analysis present, certificates matching the goods, shipping marks consistent.
Photographs. The part buyers use most, and the part that is least standardised — what gets photographed depends on what the inspector was asked to look at.
What it does not cover, unless you pay separately
This is the list worth reading twice, because these are the things buyers assume are included.
Chemical composition. An inspector does not carry a spectrometer to verify alloy. They check that a mill certificate says 5052. Whether the metal is 5052 is a laboratory question, and it is priced as a separate test.
Mechanical properties. Tensile, yield, elongation, hardness. Again: the certificate is reviewed, not the metal. Independent testing means sending samples to a lab, which means cutting material, which means a longer and more expensive process.
Internal soundness. Laminations, porosity, inclusions. Requires ultrasonic testing, which requires a specialist and a scope line.
Fitness for your process. Whether the material will run on your press, take your weld, or anodize to your color. No inspection can answer this, because it depends on your equipment.
Performance over time. Corrosion resistance, stress corrosion cracking, fatigue. These are properties, not defects, and a visual inspection at loading cannot see them.
The pattern: inspection verifies what can be seen, counted and measured with hand tools on the day. Everything that requires a laboratory or a service history sits outside it.
The sampling plan is where the argument lives
Inspection is almost never 100%. It is a sample, judged against an acceptance plan, most commonly ISO 2859-1 at General Inspection Level II with an AQL — acceptable quality limit — typically 2.5 for major defects and 4.0 for minor ones.
Those two numbers are the whole negotiation, and they are usually left to the inspection company's default.
Define what counts as major. For aluminum, a sensible split:
| Defect | Class | Why |
|---|---|---|
| Wrong alloy or temper marked | Critical | Not usable as supplied |
| Thickness outside ordered tolerance | Major | Affects weight and fit |
| Dents or deformation on edges | Major | Unrecoverable for visible parts |
| Corrosion or white rust | Major | Progressive, worsens in storage |
| Light surface scratches, removable | Minor | Cosmetic, may polish out |
| Marking illegible but traceable | Minor | Administrative |
Left undefined, "major" and "minor" get assigned by whoever is on site, and a batch with 4% edge dents can pass under one reading and fail under another.
If the material is for anodizing, say so in the scope. The surface standard for anodizing quality is stricter than general visual acceptance, and an inspector who has not been told will apply the general one.
Timing changes what you learn
Four inspection points, four different purposes:
Before production (PPI). Checks raw material and confirms the mill can make what was ordered. Useful on a first order, wasteful on a repeat.
During production (DUPRO). Catches a systematic problem while there is still time to correct it. The most valuable and least used.
Pre-shipment (PSI). The default. Confirms finished goods before they are packed or loaded. Requires production to be substantially complete — most inspection companies will not attend before roughly 80% is finished, because there is not enough to sample.
Container loading supervision (CLS). Watches the loading itself: count, condition, packing, blocking and bracing, photographs. For aluminum this is often the highest-value inspection of the four, because a large share of damage happens at loading and in the container, not at the mill.
If you can only pay for one, and your product is flat-rolled and cosmetic, CLS is the one that addresses the failure you are most likely to have.
What inspection cannot do
Three limits worth stating plainly.
It samples. A passing report means the sample passed. On a 25-tonne lot, a 2.5 AQL plan accepts a non-zero number of defects. That is the design, not a flaw.
It records a moment. Material that passes and then sits in a humid warehouse for two months can arrive with white rust that no inspection could have predicted.
It follows your scope. An inspector checks what the work order says. If the work order says "visual and dimensional per supplier's standard", you have bought a check against the supplier's own standard, which is rarely what a buyer intended.
How to write the scope
Six lines cover most of it:
Inspection type: Pre-shipment + container loading supervision
Standard: ISO 2859-1, General Inspection Level II, AQL 2.5 major / 4.0 minor
Dimensions: Thickness (base metal) at 5 points per sheet, 10 sheets per size;
width and length on the same sample
Appearance: No dents, deformation, corrosion or scratches visible at 500 lux
under the specified viewing distance; anodizing quality, no deep marks
Documents: MTC to EN 10204 3.1, heat number matched to bundle marks
Photographs: Bundle before loading, strap and edge protection, container interior
loaded, container number and seal
Two additions that cost little and prevent most disputes: require the raw data as well as the report, and require the inspector to state which dimensions were measured and where. A report that says "dimensions within tolerance" without the readings is not evidence.
What happens when it fails
A failed inspection is not the end of a shipment. It is the cheapest moment in the whole transaction to fix one, because the goods are still at the mill and nothing has been paid for freight.
Three outcomes are available, and it helps to know which you want before the report arrives.
Concession. The defects are real but do not affect the use. Accept with a price adjustment or with the defective pieces excluded from the count. Common for cosmetic marks on material that will be painted.
Sorting. The mill or the supplier re-inspects 100% and removes the defective pieces, shipping the balance. Costly in time, and it works when the defect rate is low. Ask who pays for the sorting and for the re-inspection — this is the clause most contracts omit.
Rejection. The lot is remade or the order is cancelled. Reserve this for defects that make the material unusable, because it costs everyone the most and is the hardest to enforce once a deposit has been paid.
Two things to settle in the purchase order rather than at the moment of failure: who pays for a re-inspection, and what the remedy is for each defect class. Written in advance, a 2% defect rate is an administrative matter. Left open, it is a negotiation conducted while a vessel is waiting.
One clarification worth stating, because it is widely misunderstood: the inspection report is not the acceptance decision. An inspector reports findings against the scope. A conclusion of "pass" means the sample met the acceptance plan — not that the shipment is good, and not that you have accepted it. That decision stays with you, and it is worth making explicitly in writing rather than by silence.
Who books it
Inspection can be booked by either party. Buyers usually book it because they want the report addressed to them and the inspector working to their scope.
Two practical notes. Book early — inspection companies need a few days' notice and peak season is worse. And make sure the supplier knows the date, because an inspector who arrives to find goods not ready bills for the visit anyway.
We book inspections on the mill floor as part of a shipment, and the scope is agreed with the buyer before the date is set. Our quality control process describes what is checked at each stage. If you have a specification and are not sure which inspection point would catch your real risk, send it over and we will tell you where the gaps are rather than which service to buy.