Steel Building Mill Test Certificates: What to Request and How to Verify Them
A mill test certificate is the paper trail that proves the steel in your building is the grade you specified. It records the heat number, chemical composition and mechanical properties of the material, and it is one of the documents importers, inspectors and customs officers actually read. This article explains which certificates to request, what EN 10204 3.1 and 3.2 mean, and how to verify them against the delivered steel.
What a mill test certificate actually proves
A mill test certificate (MTC) is issued by the steel mill, not the fabricator, and it describes one heat of steel. It tells you the grade and standard, the heat number, the chemical composition (carbon, manganese, silicon and other elements), the mechanical properties (yield strength, tensile strength, elongation and sometimes impact values) and the dimensions of the batch it covers.
| Field on the certificate | What it tells you |
|---|---|
| Grade and standard | Which specification the steel meets (for example Q235B, Q355B, S355 to its applicable standard) |
| Heat number | The unique identifier that links the certificate to the physical steel |
| Chemical composition | Element percentages that define the grade and weldability |
| Yield and tensile strength | Mechanical capacity used in design |
| Elongation / impact | Ductility and toughness, important in cold climates |
EN 10204 3.1 vs 3.2: the difference that matters
European practice (EN 10204) classifies inspection documents. A 3.1 certificate is issued by the manufacturer, declaring that the product meets the order and that testing was done by the manufacturer’s own qualified personnel. A 3.2 certificate adds an independent inspection body that witnesses the testing and signs the document. For most steel buildings, 3.1 certificates for the primary frame are sufficient; 3.2 is requested on critical projects or where the contract or local authority demands independent verification. Ask your supplier which type their mill can issue and whether 3.2 is available at additional cost.
Which members should carry certificates
Primary structural members — columns, rafters and other load-bearing sections — should have traceable certificates. Secondary members such as purlins and girts are often covered by batch certificates from the same heat or rolling batch. It is reasonable to request certificates for all primary steel and to agree in advance how secondary steel will be documented, so the documentation package matches the inspection expectations at your end.
How to verify a certificate against the delivered steel
Verification is simple in principle: the heat number on the certificate must match the heat number marked on the physical member. During fabrication, members are marked with their code and often with the heat or batch reference; check a sample of members against the certificates at the factory or at arrival. Confirm the grade marking (for example Q355B) matches the certificate and the order. If heat numbers cannot be matched, treat the material as unverified and ask the supplier to explain before erection.
Where certificates fit in the documentation package
Mill certificates sit alongside the packing list, bill of lading and inspection reports in the shipment documentation. Customs officers and third-party inspectors use them to confirm the declared material, and your own pre-shipment quality inspection can include a certificate-to-steel check. Keep the certificate set with the project file — it is also your evidence if a material dispute ever arises.
FAQ
What if the heat number doesn’t match the member?
Stop and verify before erection. Unmatched heat numbers mean the certificate cannot be tied to the steel, so the grade is unproven. Ask the supplier to reconcile the marking or provide the correct certificate, and consider independent testing if it cannot be resolved.
Can the factory provide 3.2 certificates?
Sometimes, depending on the mill and the order volume. 3.2 inspection is arranged with an independent body and usually adds cost and lead time. Ask at quotation stage if your project requires it, so it is priced and scheduled from the start.
Do mill certificates cover secondary steel like purlins?
Purlins and girts are often supplied with batch certificates rather than individual heat certificates. Agree with your supplier how secondary steel will be documented, and check that the batch reference appears on the certificate and the material.
Need certified steel for your building project? Send us your steel grade and certificate requirements, and we will confirm the documentation package — mill certificates included — in the quotation.
