The mill test certificate, MTC, arrives with every batch and is read before the bundle is opened. In it the mill answers for the steel being made from a specific heat, having a specific composition and having passed specific tests. Everything else, commercial letters, traders’ certificates, “quality passports” without a heat number, does not give that link.
Fields that must be there
- The producing mill, certificate number and date, the buyer’s order number. A certificate on a trader’s letterhead with someone else’s stamp is a reason to request the mill’s original.
- Product, standard and grade: “Hot rolled ribbed bar, GB/T 1499.2-2018, HRB500E”. Standard and grade must match the contract letter for letter.
- Heat number and lot number. The same heat number is on the tag of every bundle: this is the point of reconciliation.
- Size, quantity, weight, line by line, as many lines as there are items in the packing list.
- Chemical composition by ladle analysis: C, Si, Mn, P, S, for rebar the carbon equivalent Ceq, for alloy grades Cr, Ni, Cu, V, Nb. Next to the actual value the standard’s limit is usually printed.
- Mechanical properties: yield strength, tensile strength, elongation, for E-grades the ratios Rm/ReL and ReL/ReL nominal, bend test, and where required impact toughness with the temperature. Test methods to GB/T 228.1, GB/T 229, GB/T 232 or their equivalents.
- Signature and stamp of the mill’s quality control department, and the document type under EN 10204 or GB/T 18253.
Four types under EN 10204
EN 10204:2004 describes not a form but the degree of responsibility for the results. The Chinese GB/T 18253 repeats the same classification with the same numbers, so a “3.1” on a certificate from a mill in Tangshan and a “3.1” on a certificate from Linz mean the same thing.
| Type | Tests | Who validates | Where it is enough |
|---|---|---|---|
| 2.1 | Testsno results: a declaration of compliance with the order | Who validatesthe mill | Where it is enoughfasteners, consumables |
| 2.2 | Testsresults of non-specific inspection: product of the same process was tested, not necessarily this batch | Who validatesthe mill | Where it is enoughnon-critical structures by agreement |
| 3.1 | Testsspecific inspection: this batch, or the test unit it belongs to, was tested | Who validatesthe mill’s inspection representative, independent of production | Where it is enoughrebar, plate, pipe for construction: the bureau’s standard delivery |
| 3.2 | Teststhe same specific inspection | Who validatesthe mill’s representative and the purchaser’s representative or an inspector designated by official regulations | Where it is enoughpressure vessels, pipelines, wherever the project requires it |
Why 3.1 and 3.2 do not replace each other
The difference between 3.1 and 3.2 is not in the scope of testing, which is the same, but in the second signature. Under 3.2 stands a party independent of the mill: the purchaser’s inspector or an inspector of a body designated by regulations. If the project requires 3.2, a 3.1 certificate does not satisfy it, however many mill stamps it carries. The reverse is also true: ordering 3.2 for foundation rebar means paying for an inspector’s presence where neither the standard nor the project requires it. The bureau’s inspection report with photographs is a separate document: it confirms that the batch at the mill’s warehouse matches the certificate and the contract, but it is not a 3.2 certificate and is not called one.
A five-minute check
- The heat number on the bundle tag matches the heat number in the certificate line.
- Standard and grade in the certificate match the contract; for GB rebar the class digit and the letter E are rolled into the bar.
- Every chemistry and mechanics figure lies inside the limit printed next to it; a figure at the edge of the limit is a question to the mill before shipment, not after.
- The weight in the certificate lines agrees with the packing list and with the scale at acceptance.
For a delivery under GOST, the mill certificate is supplemented by a quality document under GOST 7566 and a certificate of conformity issued in Uzbekistan; both are prepared from the MTC data, so neither is issued without the mill certificate.
