A mill cert is a piece of paper that can hold up a shipment, a payment or an inspection if it is missing, and that nobody looks at if it is not needed. Knowing which jobs need one saves hassle on both sides. Here is what a cert is, when you need it, and how to ask for it so it shows up matching your material.
What a mill cert actually is
A mill cert, also called a mill test report or MTR, is the document the producer issues for a heat of metal. A heat is one batch melted together. The cert lists:
- The specification the material was made to, such as ASTM A36 or A500 Grade C
- The heat number
- Chemical composition, element by element
- Mechanical test results: yield strength, tensile strength and elongation, and sometimes hardness
- For aluminum, the alloy and temper, such as 6061-T651
The heat number is the key. It is marked on the material or its tag and printed on the cert. That link is what makes a piece of metal traceable: you can prove what it is and that it met its spec.
A cert covers the heat, not your individual piece. When material gets cut to size, the heat number has to be carried over to the cut pieces or their paperwork, or the chain breaks.
Jobs that usually require certs
Anything with a customer spec that says so. If your purchase order from the end customer calls for certs, material traceability or “MTRs required,” you need them. This is common with oil and gas, utilities, government and larger industrial customers.
Pressure and piping work. Pressure vessels, piping systems and many code-stamped jobs require documented material. Shops doing oil and gas fabrication run into this constantly.
Structural steel on inspected projects. Building and bridge work often requires certs for A36 plate and shapes, A500 tube and A572, so an inspector or engineer can confirm the material matches the drawings.
Aerospace, defense and medical. These typically require certs and often a specific spec, like an AMS number, with full traceability through every step.
Anything you might have to defend later. A trailer frame, a lifting fixture or a load-bearing bracket that fails will raise the question of what it was made from. A cert in the job file answers it.
Jobs that usually do not
- Prototypes and one-off shop fixtures
- Brackets, guards and covers with no structural role
- Signs, decorative work and trim
- Repair jobs where the customer just wants it fixed
- Practice stock and scrap-bin replacement
For these, ordering certs adds paperwork without adding value. Ask for them only when the job needs them.
How to ask for certs so they match
This is where most cert problems start. The request comes after the material ships, the cut pieces have lost their tags, and the heat cannot be matched anymore.
Ask on the RFQ. Put “certs required” on each line that needs them, not just in a note at the bottom. Different lines can come from different sources, and each one has to be tracked. Our RFQ guide shows where it goes.
Name the spec, not just the grade. “A36” is a spec. “Mild steel” is not. “6061-T651 per ASTM B209” tells the source exactly what the cert must show. If your customer needs a particular spec or revision, say which.
Say if you need one heat. If every piece on a job must come from the same heat lot, say so up front. It narrows where the material can come from.
Keep the heat number on the parts. Once material arrives, carry the heat number onto your traveler or parts. A cert without a way to tie it to the part is just a sheet of paper.
Cert types you might see
Most commercial work uses the producer’s mill test report as issued. Some customers ask for more:
- Certificate of conformance (C of C). A statement from the seller that the material meets the spec. It is not a test report, and some customers accept it where others do not.
- EN 10204 3.1. A European standard format for inspection certificates, sometimes required on export or international work.
- DFARS or domestic melt. Some government work requires material melted in the US or certain qualifying countries, which the cert has to show.
If your customer uses one of these terms, pass it along exactly as written.
Common mistakes
Assuming the grade stamp is enough. Stamped or stenciled grade markings help, but a customer asking for traceability wants the document with test results.
Mixing heats on one job without tracking them. Material from two heats is fine, as long as each piece can be tied to its own cert.
Accepting a cert that does not match. Check that the spec, size range and heat number on the cert line up with what you received. A cert for the wrong heat does not count.
Asking for certs on everything. Certs on a prototype bracket slow the order down for no reason. Save them for the jobs that need them.
How we handle it
Mill certs are available on request with the material we source. Put the requirement on the order, including any spec or single-heat requirement, and we will confirm on the quote what documentation comes with each line. When you are ready, send the list through the quote form and mark each line that needs certs.