Technical reference
How to read a mill test certificate
A mill test certificate (MTC) reports the actual chemistry and mechanical test results for the specific heat your plate was rolled from. Below is a labeled walkthrough of what's on one and what each section means — select a numbered section.
This is an illustrative diagram of a typical MTC layout, not a scan or reproduction of any real certificate. A genuine MTC, tied to a specific heat number, accompanies every shipment.
Heat number
A traceability number assigned to one specific melt of steel. Every mill test certificate, and the markings on the plate itself, are tied to this number, so a buyer or surveyor can trace a specific plate back to the exact chemistry and test results for the batch it came from.
1. Heat number
A traceability number assigned to one specific melt of steel. Every mill test certificate, and the markings on the plate itself, are tied to this number, so a buyer or surveyor can trace a specific plate back to the exact chemistry and test results for the batch it came from.
2. Chemical composition
The measured percentage of each element controlled for the grade — typically carbon, manganese, silicon, phosphorus, sulphur, and for higher grades, grain-refining elements such as aluminium or niobium. These values are also what a carbon equivalent (Ceq) calculation is based on.
3. Mechanical properties (ReH, Rm, A5)
ReH is the measured yield strength, Rm is the tensile strength, and A5 is elongation after fracture. These are tested on a sample cut from the actual plate and must meet or exceed the grade's minimum requirements.
4. Impact test (Charpy V-notch)
For grades that require it, the energy absorbed by a notched sample at a specified low temperature — a measure of resistance to brittle fracture. Grade A normal-strength plate typically has no mandatory impact-test requirement; D, E and the higher-strength series are tested at progressively lower temperatures.
5. Certificate type: 3.1 or 3.2
A 3.1 certificate is issued and validated by the manufacturer's own authorized quality department. A 3.2 certificate additionally requires countersignature by an independent inspector, typically the classification society surveyor.
6. Witness signature (3.2 only)
On a 3.2 certificate, this is where the independent inspector who witnessed testing countersigns, confirming the results independently of the mill's own quality department.
Section layout and exact wording vary by mill, but these six elements — heat number, chemistry, mechanical properties, impact results, certificate type, and (for 3.2) a witness signature — appear on every EN 10204 mill test certificate for shipbuilding plate.
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