A Mill Test Certificate is the only document that connects the metal physically in front of you to a set of laboratory results. Everything else in the shipping file describes quantities and ownership. The MTC is the one that says what the material actually is.
Most buyers file it. Fewer read it. Fewer still check it. That gap is where substituted grades and falsified paperwork survive all the way to site.
What the certificate is claiming
An MTC (also called a mill certificate, or EN 10204 inspection document) asserts that a specific heat of steel - one furnace charge - was tested and produced the recorded results. It is heat-specific by design. A certificate that does not tie to identifiable heat numbers is not doing its job.
Reading it field by field
Heat / cast number. The anchor of the whole document. This number is rolled, stamped or tagged onto the physical product. If you cannot match the number on the certificate to the number on the bar, coil or plate, you have a certificate for something else.
Product description and dimensions. Should match your purchase order exactly - grade, size, and the standard it was produced to. A certificate for 16 mm bar does not cover the 20 mm in the same bundle.
Standard and grade. For example ASTM A615 Gr 60, BS 4449 B500B, EN 10025 S355JR, API 5L X65. This must match what you bought. A mill that quotes one standard and certifies to a nominally similar national equivalent has substituted, whether or not the material performs.
Chemical composition. Element-by-element percentages - carbon, manganese, silicon, sulphur, phosphorus, and any specified alloying elements. Compare each against the range the standard permits. Everything must sit inside the range, not merely near it.
Watch carbon equivalent (CE or CEV) where weldability matters. It is derived from the chemistry and governs whether the material can be welded without preheat and cracking. A heat can pass every individual element and still exceed the CE limit.
Mechanical properties. Yield strength, tensile strength, elongation, and where specified, impact energy at a stated temperature. For reinforcement bar, also check the yield-to-tensile ratio and bend or rebend results, which are separately specified in B500B and A615 and are where marginal heats tend to fail.
Heat treatment condition. Normalised, quenched and tempered, annealed, as-rolled. This changes the material’s properties substantially. A specification calling for normalised material is not satisfied by as-rolled with the right chemistry.
Additional testing. Depending on service: non-destructive testing, hardness, hydrostatic testing, intergranular corrosion. For sour service, NACE MR0175 / ISO 15156 compliance must be explicitly stated, along with the hardness limits that demonstrate it.
Certificate type and signatures. The EN 10204 designation, the issuing authority, and the signature. This is where 3.1 and 3.2 diverge.
3.1 versus 3.2, and why it matters
| Type | Issued by | Independent of producer? |
|---|---|---|
| 2.1 | Manufacturer, statement of compliance, no test results | No |
| 2.2 | Manufacturer, non-specific test results | No |
| 3.1 | Manufacturer’s quality department, independent of production | Partially - inside the same company |
| 3.2 | Manufacturer and an independent inspector or authorised body | Yes |
A 3.1 is issued by a department that does not report to production, which is a genuine control. It is still the producer certifying its own output.
A 3.2 adds a second signature from someone with no commercial interest in the result - your nominated inspector, or an authorised body. For pressure equipment, sour service, or anything where failure carries safety consequences, 3.2 is normal and worth insisting on. The cost difference is small relative to what it verifies.
Four checks that catch a bad certificate
Falsification is real. It is rarely elaborate: the common pattern is a genuine certificate with numbers adjusted to bring a marginal heat inside specification, or one certificate stretched across several unrelated consignments.
1. Traceability, physically. Take the heat numbers from the certificate and find them on the material. Rolled-in marks on rebar, stamps on plate, tags on coil. A mismatch, or bundles carrying no marking at all, ends the conversation.
2. Internal consistency. Falsified figures often fail basic physics. Yield exceeding tensile is impossible. Elongation that rises with strength across a set of heats is suspicious. A carbon equivalent that does not compute from the stated chemistry indicates the chemistry or the CE was edited. Recalculate it - the formula is published in the standard.
3. Verify with the mill directly. Most reputable mills will confirm whether a given heat number and certificate reference is genuinely theirs. Contact them through details you obtain independently, not the ones printed on the document you are checking. This single step defeats most forgeries.
4. Witness test on a sample basis. Have an independent laboratory pull samples and test them against the certificate. For high-value or critical consignments this is routine, and it converts the certificate from a claim into a verified fact. It is also the only check that catches a technically genuine certificate attached to different material.
Practical red flags
- Identical values repeated across multiple heats - real heats vary.
- No heat numbers, or heat numbers that do not appear on the product.
- Certificate dated after the bill of lading.
- A scanned image with visible inconsistencies in font, alignment or resolution around the numbers.
- Grade or dimension that does not match the purchase order.
- Missing mechanical results for properties the standard requires.
- A 3.2 certificate with only one signature.
Building this into the purchase, not the inspection
Checking certificates on arrival tells you what went wrong. Building the requirement into the order prevents it:
- Specify the certificate type - 3.1 or 3.2 - in the purchase order, not just “mill certificate”.
- Require certificates to be issued and transmitted before shipment, and make final payment conditional on them.
- Appoint an independent inspector to verify heat markings against certificates before the container is sealed.
- Require the standard to be named exactly, and prohibit equivalents without written approval.
- For critical service, include witness testing on a defined sample basis at the supplier’s cost.
The checks themselves take a competent engineer under an hour per consignment. Discovering the problem after the steel is cast into a structure costs considerably more than that - which is why supplier verification and pre-shipment inspection sit at the centre of how we run supplier identification and bulk commodity sourcing.
If you have certificates in front of you that you are not confident about, send them to our desk - verification against the issuing mill is part of what we do on every consignment.