An aerospace or defense customer's receiving inspection operates at a different standard than a structural steel customer's. They're not checking whether a cert exists. They're checking the chain of custody: can you prove, document by document, that this specific strip of stainless came from this specific melt, was processed under these conditions, and was not commingled with any other heat?
Most service centers, even well-run ones, cannot fully answer that question for slit material. The cert looks complete. Under aerospace scrutiny, it isn't.
What Aerospace Customers Look for in Slit-Coil Documentation
An AS9100-certified aerospace supplier or a NADCAP-accredited processor has a defined expectation for incoming material documentation. For slit strip, that expectation typically includes:
1. Original mill cert with heat number and melt number. Not just a reference to a cert number — the actual document, showing chemistry and mechanical test results for the specific heat.
2. Processing record showing which coil was slit. Date of slitting, coil ID or heat number, resulting strip IDs, slit dimensions, and the operator or equipment used. This is a first-party document — issued by the service center, not the mill.
3. Heat number carried on every strip's physical label and on every shipping document. Not the lot number, not the order number — the mill heat number.
4. No evidence of commingling. Strips from different heats must not be mixed on the same skid or pallet. Each skid or pallet should contain material from a single heat only.
If any of these four elements is missing or incomplete, aerospace receiving inspection will reject the shipment or place it on hold pending additional documentation.
The Commingling Problem
Slitting operations create a commingling risk that doesn't exist for unprocessed coil. A single slitting run typically processes one coil from start to finish — but in a high-volume facility, the slitter operator may run a second coil on the same line in the same shift. If strips from two different coils intermingle during recoiling or stacking, the heat-specific traceability of both heats is compromised.
For commercial structural customers, this is rarely a critical issue. For aerospace customers, it is a disqualifying finding. AS9100 Section 8.4 and NADCAP requirements on material traceability explicitly address the risk of material commingling. A supplier who cannot demonstrate that commingling was prevented — not just that it probably didn't happen — will receive a corrective action request.
The operational fix requires strict segregation during slitting: one coil at a time, strips stacked by coil, pallets labeled with heat number before the next coil starts. This is operationally inconvenient. It is a condition of doing business with aerospace customers.
The Documentation Gap: What Service Centers Miss
Most service centers issue a slit-coil report that shows the original coil's heat number, the date of processing, and the resulting strip dimensions. This document satisfies commercial customers.
What it typically does not show: a strip-level traceability record that ties each specific strip ID to the original coil's heat number and, critically, to the strip's position or sequence in the slitting run. Aerospace auditors ask for the strip-level document.
The distinction is important. A slit-coil report at the coil level tells the auditor that a coil with heat number X was processed into strips. A strip-level document tells the auditor that strip ID Y-007, specifically, is traceable to heat number X and was not commingled with heat number Z during processing.
The strip-level document requires a more granular logging step during the slitting operation. It cannot be reconstructed from coil-level records after the fact.
What the Audit Finding Looks Like
The NADCAP or AS9100 finding for this gap is written as: "Unable to verify traceability of slit strips to source coil heat number. Processing records do not identify individual strips. Risk of commingling not controlled or documented."
This is classified as a major finding at most aerospace certifying bodies. It requires a corrective action plan with root cause analysis, a defined corrective action, and evidence of implementation before the finding can be closed. In some cases, shipments on hold pending the finding closure cannot be released until the corrective action is verified.
The business impact of a major finding at a NADCAP audit extends beyond the immediate shipment. It affects the service center's approved supplier status with every aerospace customer that uses NADCAP acceptance.