How to Read a Mill Test Certificate for Steel Plate
In short: A mill test certificate (MTC) is the document that ties a delivered steel plate to the heat it was made from. It records the heat number, chemical composition, mechanical properties, dimensions and delivery condition, and it is the only document that lets a buyer prove the plate meets the specified grade after it has left the mill.
What is a mill test certificate?
A mill test certificate is a document issued with a steel delivery that reports the actual test results for that specific heat or plate — not the nominal properties of the grade in a catalogue.
The distinction matters. A grade designation such as Q345R or S355J2 describes what the steel should do. A certificate describes what this plate actually did when it was tested. Buyers accept deliveries against the second, not the first.
EN 10204 2.2 vs 3.1: what is the difference?
Both are inspection documents under EN 10204, and the difference is who signs them.
| Type | Issued by | What it proves |
|---|---|---|
| 2.2 | Manufacturer’s own inspection department | Test results from the manufacturer’s own testing, not independently witnessed |
| 3.1 | Manufacturer’s independent inspection representative | Test results validated by a representative independent of the manufacturing department |
| 3.2 | Manufacturer plus an independent third party or purchaser’s representative | Results validated by a party outside the manufacturer entirely |
For pressure vessel, energy and structural work subject to third-party review, 3.1 is the usual requirement, and 3.2 is specified when the buyer or a classification society wants its own witness. A supplier who cannot state which type it issues is usually issuing 2.2.
What information must a certificate contain?
A usable certificate for plate typically carries:
- Purchaser and manufacturer identification — who ordered and who rolled it
- Certificate number and issue date
- Standard and grade — for example Q345R to GB713, or S355J2 to EN10025-2
- Heat number and plate number — the link between the document and the physical piece
- Chemical composition — C, Si, Mn, P, S and alloying elements, with actual values
- Mechanical properties — yield strength, tensile strength, elongation, and impact energy with test temperature
- Delivery condition — as-rolled, normalized, quenched and tempered, or annealed
- Dimensions and quantity — thickness, width, length, number of pieces, weight
- Additional tests — ultrasonic inspection, Z-direction testing, hardness, grain size, where specified
- Signature and stamp of the issuing inspection body
If item 4 is missing, the certificate cannot be matched to the plate, and the rest of the document is unverifiable.
The 7 checks to run before accepting a delivery
Run these in order. Each one catches a different failure mode.
| # | Check | What it catches |
|---|---|---|
| 1 | Heat number on the certificate matches the stamping on the plate | Plates swapped between heats or between orders |
| 2 | Grade and standard match the purchase order exactly | Substitution to a lower grade or a different standard |
| 3 | Delivery condition matches the order | Normalized steel supplied as-rolled |
| 4 | Chemical values are within the grade limits, not just present | Out-of-spec chemistry presented as compliant |
| 5 | Impact test temperature matches the grade suffix | A “D” grade certified at room temperature |
| 6 | Dimensions and piece count match the packing list | Short delivery concealed by weight rounding |
| 7 | Certificate type (2.2 / 3.1 / 3.2) matches the contract | An internal report presented as independent verification |
Check 5 is the one most often missed. A grade suffix carries the test temperature with it, and impact energy quoted at the wrong temperature looks correct on the page while proving nothing.
Why the heat number is the most important field
The heat number is the only field that connects a document to a physical object. Everything else — chemistry, mechanicals, heat treatment — describes a batch. The heat number says which batch, and therefore whether this particular plate is the one that was tested.
This is also the field that makes traceability possible downstream. Where a supplier runs an ERP and EMS system, each cut part is coded and linked back to the mother plate, so a certificate can still be matched to a component after fabrication, years after delivery.
Without that link, a buyer holding a certificate has a document about some steel, not about their steel.
Common certificate problems and what they usually mean
- Values typed rather than printed from a test system — the document may be a re-creation, not a mill original
- One certificate covering many heats — acceptable only if each heat is listed separately with its own results
- Impact energy given as a single figure without temperature — the test condition is unspecified, so the result cannot be judged
- Grade printed but standard omitted — the same grade name can mean different things under GB, EN and ASTM
- No plate number, only a heat number — traceable to the batch but not to the individual piece
- Certificate dated after shipment — the document was produced for the file, not for the delivery
None of these is automatically fraud. All of them are reasons to ask for the original before accepting.
Frequently asked questions
What does EN 10204 3.1 mean? It is an inspection certificate where test results are validated by an inspection representative independent of the manufacturer’s manufacturing department. It is the standard requirement for pressure vessel and energy applications.
What is the difference between a heat number and a plate number? The heat number identifies the batch of steel melted in one furnace; the plate number identifies the individual rolled piece. A certificate should carry both.
Can I accept a delivery with only an EN 10204 2.2 report? Only if the purchase order permits it. For applications subject to third-party inspection, 3.1 or 3.2 is normally required.
What is an impact test temperature and why does it matter? It is the temperature at which toughness is measured. Grade suffixes such as D, E or F specify it, and a result quoted at the wrong temperature does not demonstrate the required toughness.
How do I verify a certificate is genuine? Match the heat number to the plate stamping, check that values fall inside the grade limits, and confirm the certificate type and issuing body against the contract.
Can a cut part still be traced to its certificate? Yes, where the supplier codes each part and links it to the mother plate through an ERP and EMS system.
Contact
Nanjing Tiange Metal Trading Co., Ltd. Mill-direct steel supply with full certificate traceability Email: postmaster@tigosteel.com Phone / WhatsApp / Telegram: +86 138 1389 7227 Web: www.tigosteel.com Nanjing, Jiangsu, China