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How to Read a Mill Test Certificate (MTC)
How to Read a Mill Test Certificate (MTC)
A Mill Test Certificate (MTC, also called mill cert or material test report) is the document that proves the steel you received matches the grade you ordered. For structural, pressure-vessel and export projects, the MTC is not a nice-to-have — it is a contractual document. Yet many buyers receive a thick PDF and do not actually check what is in it. This guide walks through the fields that matter.
What an MTC Is
An MTC is issued by the steel mill that produced the material. It lists the heat (batch) number, the chemical composition, the mechanical test results and the dimensional inspection for that specific heat. It is not a generic “we sell 304” document — every heat has its own certificate. ÎN 10204 3.1 is the most common requirement for export; 3.2 means an independent inspector has witnessed the tests.
The Fields You Must Check
- Purchase order number and material / grade — they must match your order exactly (e.g. ASTM A36, Q355B, 304 / 316L).
- Heat number — this is the batch ID. It should match the stamping / labels on the material itself.
- Chemical composition — every element should fall inside the standard range. If carbon is high or chromium is low for stainless, reject the material.
- Mechanical properties — yield, tensile, elongation and impact (Charpy) values. Yield must meet the minimum, not just “close”.
- Dimensional check — thickness, lăţime, length and flatness tolerances.
- Mill stamp / signature — the cert should be signed or carry the mill’s authorized stamp.
Common Red Flags
If the MTC shows composition values that are copied from a standard table rather than tested, or if the heat number on the cert does not match the stamp on the material, treat it as suspect. Mismatched heat numbers are the most common sign of “cert shopping” — a trader mixing heats and printing a generic cert. For critical projects, require third-party inspection (SGS, BV, TÜV) at the mill before shipment.
Which Products Need an MTC?
All structural grades (Q235B / Q355B / ASTM A36 / A572) and all stainless grades should ship with an MTC. In our range, every Q355B plate, 316L plate, 20# seamless pipe and Q355B round bar ships with a mill cert. For decorative or non-critical trim (anodized aluminum angle, color sheet), a MTC is usually available but may carry a small documentation fee.
Why It Matters for You
When a welded structure fails or a pressure vessel is inspected, the MTC is the document that proves the material was correct. If you are the fabricator or the end customer, keeping a correct MTC on file is your legal and insurance protection. If you are an importer, customs and your customer’s QA team will ask for it. Ordering material “without cert” to save a few dollars almost always costs more later.
