What is a mill test certificate (MTC)?
A mill test certificate (also called a material test certificate or inspection certificate) is the document in which the producing mill certifies that a given heat, one batch poured from a single melt, meets a named standard. It records the chemical composition, the mechanical properties, the heat-treatment or delivery condition, and any corrosion or non-destructive test results. All of it ties back to one heat / cast / melt number, so the paperwork can be traced to the actual steel.
The certificate turns a stack of metal into an accept-or-reject decision. That heat number: stamped on the plate, printed on the packing list, written on the certificate. It's the thread of material traceability that lets a QA inspector prove the delivered plate is the grade on the purchase order. For the declarative definitions of each document, what separates an MTC from a test report, and how it sits alongside NDT and PMI, see the companion note on mill test certificates, NDT & PMI. This guide takes the other angle: how to actually read and validate one, field by field.
Nandini Steel ships every order with an EN 10204 3.1 or 3.2 mill test certificate tied to the heat. The plate behind it is genuine mill material, sourced from producers like Aperam, Outokumpu, Jindal, POSCO, Nippon Steel and JFE.
EN 10204 certificate types: 2.1, 2.2, 3.1 and 3.2 explained
You can't read a certificate properly until you know its type, because the type sets how much you are allowed to trust the numbers on it. EN 10204 defines four inspection-document types. Two are non-specific (the results don't relate to the actual product delivered), and two are specific (the results come from testing the consignment itself). The governing standard page for this is EN 10204.
| Type | Name | Who tests / inspects | Who validates it | Specific inspection? | Typical use |
|---|---|---|---|---|---|
| 2.1 | Declaration of compliance with the order | Manufacturer | Manufacturer, no test results stated | No (non-specific) | Low-criticality / commodity items |
| 2.2 | Test report | Manufacturer | Manufacturer, results from non-specific inspection | No (non-specific) | General stock, non-critical service |
| 3.1 | Inspection certificate 3.1 | Manufacturer, on the actual consignment | Manufacturer's authorized inspection representative, independent of the manufacturing department | Yes (specific) | The stainless / nickel-alloy / CRA default |
| 3.2 | Inspection certificate 3.2 | Manufacturer, on the actual consignment | The manufacturer's representative and the purchaser's representative or an inspector designated by official regulation | Yes (specific) | Pressure equipment, critical / regulated service |
2.1: declaration of compliance
A 2.1 is nothing more than a plain statement, signed by the manufacturer, saying the material meets the order. There are no test results attached. It's non-specific, too: nothing on the certificate ties back to the actual heat you received. It works fine for low-criticality commodity items, but beyond that, it proves nothing you can actually inspect.
2.2: test report
A 2.2 test report shows results from non-specific inspection: figures the mill keeps on file for that grade and process route, not necessarily pulled from your consignment. The manufacturer issues it. It's fine as background, but it doesn't prove your specific plate was tested.
3.1: inspection certificate (independent of production)
A 3.1 inspection certificate reports specific inspection: testing performed on the actual consignment, validated by the manufacturer's authorized inspection representative, someone independent of the manufacturing department. This is the working default for stainless steels, nickel alloys and other corrosion-resistant alloys. The reason is simple: the numbers relate to the steel in your hands.
3.2: inspection certificate (second-party / third-party validated)
A 3.2 certificate carries the same inspection requirements as a 3.1, but a second party has to countersign it too, either the purchaser's authorized inspection representative or an inspector named by official regulation, say a notified body like TÜV SÜD, Bureau Veritas, DNV, SGS or ABS. This is the certificate you need for pressure equipment and other regulated, safety-critical scopes.
Which type do you actually need?
For most corrosion-resistant plate, sheet and bar, specify 3.1 on the purchase order. Move up to 3.2 when a code, client or regulator requires independent witnessing, which usually means pressure vessels, sour-service equipment, or nuclear and offshore work. Writing the clause (for example "EN 10204 3.1") on the order is what obliges the mill to furnish it. A 2.2 can't be upgraded after the fact.
Before you start: what you need
Reading an MTC is a cross-check, not a one-way read. You need both sides in front of you to compare them properly. Before opening the certificate, gather four things.
- The purchase order, the grade, standard, form and any extra tests you ordered to (for example "ASTM A240 Type 316L plate, solution annealed, A262 Practice E").
- The governing specification, the standard that carries the acceptance limits. For stainless flat product that's ASTM A240 / ASME SA-240. PVQ plate falls under ASTM A516 plus ASTM A20, while Incoloy 825 is covered by ASTM B424.
- The physical material with its stamping, hard-punch or tag, so you can match the heat number.
- The certificate itself, ideally the original or a clean mill-issued PDF.
How to read a mill test certificate, step by step
Work top to bottom, but start with the certificate type. It decides how far you can trust every field that comes after it. The table below maps each field to what it means and what you should check it against; the nine steps walk through that table in order.
| Field on the certificate | What it means | Check it against |
|---|---|---|
| EN 10204 clause | Certificate type / level of validation | The clause stated on your purchase order |
| Heat / cast / melt number | The melt the product was poured from, the traceability key | Plate stamping + packing list + PO |
| Grade, standard & form | Material designation and specification claimed | The grade and standard ordered |
| Chemical composition | Ladle (cast) and/or product (check) analysis, element by element | The standard's composition ranges |
| Mechanical properties | Tensile, 0.2% proof (yield), elongation, hardness | The standard's minima / limits |
| Impact (where required) | Charpy V-notch (CVN) energy at a stated temperature | The spec test temperature and energy |
| Heat treatment / delivery condition | Solution annealed, normalized, etc. | The condition the spec / PO requires |
| Corrosion tests | IGC per ASTM A262, PREN, HIC where ordered | The spec / order requirement |
| NDT & identification | UT, RT, hydrostatic, PMI | The ordered test scope |
| Declaration & signature | EN 10204 clause + authorized signatory | The clause ordered; a valid signature / stamp |
Step 1: Confirm the certificate type (EN 10204 clause)
Find where the certificate lists its EN 10204 clause: 2.1, 2.2, 3.1 or 3.2. This is the first filter. A 3.1 or 3.2 confirms specific inspection on your consignment; a 2.1 or 2.2 doesn't. Missing the clause, or it doesn't match your order? Stop. Query it before you read any further.
Step 2: Match the heat / cast number
Read the heat (cast, melt) number and check it against the hard stamping or tag on the physical plate, then against the packing list. A single mismatch breaks material traceability, and that consignment can't be accepted on that paperwork. One certificate might cover several heats; if so, confirm every piece maps back to a listed heat.
Step 3: Verify the grade, standard and form
Check that the grade, the standard edition, and the product form on the certificate match the purchase order exactly, "ASTM A240 Type 316L plate," say, not just "316" or an edition left unstated. Get the grade right but the standard wrong, or get the form wrong, and it's still a non-conformance.
Step 4: Check the chemical composition
Compare each element against the specification range, and note whether the figures come from ladle (cast) analysis or product (check) analysis, product analysis is taken from the finished item and counts as the stronger evidence. Carbon is the single number that proves an "L" grade: 304L and 316L must show C ≤ 0.03%. That's what suppresses sensitization in the 425–815 °C range. Check the pitting drivers as well: molybdenum on 316/316L, and both Mo and copper on 904L.
Step 5: Check mechanical properties
Confirm that tensile strength, 0.2% proof (yield) strength, elongation and hardness all clear the standard's minimum values. Where low-temperature or pressure service comes into play, Charpy impact (CVN) energy needs to be reported at the required temperature too. If you want to know what each figure actually means and how it's worked out, see mechanical properties.
Step 6: Confirm the heat-treatment / delivery condition
Verify the delivery condition line. Austenitic stainless and most nickel alloys have to show up solution annealed (see solution annealing); PVQ plate meant for low-temperature vessels is usually normalized (PVQ plate). If a grade requires a heat-treatment line and that line is missing or blank, treat it as a red flag.
Step 7: Check corrosion and special tests
When the order calls for it, check the corrosion results. Look at intergranular corrosion per ASTM A262 (see intergranular corrosion (IGC) & sensitization), and don't forget the PREN, which you can recalculate yourself from the certificate chemistry. Hydrogen-induced cracking (HIC) per NACE TM0284 matters too, especially for NACE MR0175 sour service. A passivation record, if it's attached to the certificate, should be checked against passivation requirements.
Step 8: Check NDT / dimensional / marking results
Confirm that any ordered non-destructive tests are reported and passed: ultrasonic (UT), radiographic (RT), hydrostatic, and positive material identification (PMI). Dimensions and marking need to be confirmed too. These fields prove the product, not just the chemistry.
Step 9: Verify the declaration, inspector and signatures
Read the closing declaration: it should restate the EN 10204 clause and carry the signature of the authorized inspection representative, someone independent of the manufacturing department. A 3.2 must also show the second-party or third-party stamp. If a certificate is unsigned, or the signatory isn't identified, treat it as incomplete.
How to calculate PREN from the certificate
The Pitting Resistance Equivalent Number gives you a way to rank pitting resistance right off the chemistry listed on the certificate. Here's the formula:
PREN = %Cr + 3.3 × %Mo + 16 × %N
Pull the ladle or product analysis off the MTC and swap in the real numbers. Say a 904L heat comes back at 20.0% Cr, 4.3% Mo, and 0.10% N:
| Grade (sample heat) | %Cr | %Mo | %N | PREN = Cr + 3.3·Mo + 16·N |
|---|---|---|---|---|
| 904L | 20.0 | 4.3 | 0.10 | 20 + 14.19 + 1.6 ≈ 35.8 |
That result sits comfortably above the roughly 34 nominal floor for 904L, confirming the heat's chloride-pitting class straight from its own documented chemistry. The method is laid out in full under PREN.
Red flags and common pitfalls: how to spot a bad or fake MTC
Most buyers skim the top third of the certificate and call it good. A certified supplier's QA team won't stop there. They hunt for the discrepancies below.
- Heat number mismatch, the number on the certificate does not match the plate stamping or the packing list.
- A "2.2" dressed up as a "3.1", the layout mimics 3.1, but the declared clause stays non-specific, or there's no independent-inspection signature at all.
- A missing heat-treatment line on a grade that must be solution annealed or normalized.
- Chemistry parked suspiciously at a limit, when several elements across unrelated heats sit exactly on a round boundary, that can point to copied data.
- Identical values repeated across different heat numbers, real heats vary; cloned figures do not.
- A retyped or altered PDF, inconsistent fonts, misaligned columns, or a flattened scan with no mill letterhead.
- No inspector name or signature, or a signatory who is clearly part of production rather than independent of it.
- A designation error, for instance, when an order calls the material "Inconel 825" when the alloy is actually Incoloy / Alloy 825 (UNS N08825). This naming mismatch between PO, tag and certificate turns up constantly at receiving inspection. Catching it on the order up front heads off an acceptance dispute later.
How to verify a mill test certificate is genuine
When a field raises doubt, verify rather than reject on suspicion:
Cross-check the heat number with the mill first, confirming it against the original producing mill's records; this step matters especially when the plate is coming through a stockist rather than straight from the source.
Run PMI the moment the material arrives. Positive material identification gives an independent elemental reading on the plate itself, something you can set against the certificate rather than just trusting it.
Commission a third-party re-test. Bring in an independent laboratory or inspector, say TÜV SÜD, Bureau Veritas, DNV, SGS or ABS, and have them re-pull chemistry, mechanicals or IGC.
Finally, walk the traceability chain end to end: heat number on the certificate, then plate stamping, then packing list, then PO. No gaps allowed. The mechanics behind these declarations are covered under mill test certificates, NDT & PMI.
Nandini Steel supplies genuine mill plate against the original heat, and it furnishes the EN 10204 3.1 (or 3.2 on request) for it. So the certificate you get traces back to a nameable mill, not some reissued document.
MTC requirements by material (worked examples)
What you need on the certificate depends on the grade. The table below covers four common cases, and each grade links through to its product page.
| Grade | Governing standard | Must-see chemistry line | Key test on cert | Typical cert type |
|---|---|---|---|---|
| 316L | ASTM A240 / ASME SA-240 | C ≤ 0.03% | A262 IGC | 3.1 |
| 904L plate | ASTM A240 / B625 | Mo ~4.5%, Cu ~1.5%, PREN ~34 | A262 IGC | 3.1 |
| Incoloy 825 | ASTM B424 | Ni 38–46%, Ti-stabilized | NACE MR0175 | 3.1 / 3.2 |
| A516 Gr 70 plate | ASME SA-516 + ASTM A20 | Killed, fine-grain | Charpy; HIC / TM0284 | 3.1 / 3.2 |
316L stainless
Confirm the ASTM A240 composition with C ≤ 0.03%. Where welded corrosion service applies, an ASTM A262 intergranular-corrosion pass is also required. A 3.1 inspection certificate is normally expected.
904L super-austenitic
Check the chemistry on this super-austenitic grade first: roughly 25% Ni, about 4.5% Mo, around 1.5% Cu. Recompute PREN from the certificate, it should come out near 34, and track down the A262 IGC result. Copper is what gives 904L its resistance to sulfuric acid, so make sure it's actually present.
Incoloy 825
Check the Ni-Fe-Cr chemistry against ASTM B424 / ASME SB-424: Ni 38–46%, Mo 2.5–3.5%, Cu 1.5–3%, titanium-stabilized. For sour duty, the heat also needs a NACE MR0175 sour service qualification. Don't let the certificate call it "Inconel 825", it's Incoloy, or Alloy 825.
A516 Gr 70 PVQ
For pressure-vessel plate, confirm the killed, fine-grain chemistry under ASME SA-516 with ASTM A20, check the delivery condition (normalized for low-temperature vessels), and review the Charpy result at the design temperature. For sour service, add the HIC result per NACE TM0284 on the NACE-HIC variant.
How Nandini Steel certifies every order
Nandini Steel has been in business since 2003 and holds ISO 9001:2015 certification as a stockist and supplier (Certificate No. 1283438, Unitas Certification Services UCS-UK, valid to 11 January 2028). Every consignment of stainless, nickel-alloy, alloy-steel and PVQ product ships ex-stock for immediate dispatch, whether it's sheet, plate, coil, pipe, fitting, flange, bar or fastener. Each shipment comes with an EN 10204 3.1 or 3.2 mill test certificate against the heat, and a 3.2 with second-party or third-party witnessing can be arranged on request. The firm specializes in third-party-certified 904L, Alloy 28 / Sanicro 28, Incoloy 800 and Hastelloy plate. Over 20+ years it has delivered 307+ projects for 260+ clients across 36+ export countries.
Need the certificate before you commit? Request a quotation for live pricing and ask for a sample MTC. Call +91 22 43404600, WhatsApp +91 99202 09184, or email reachus@nandinisteel.com (GSTIN 27ADJPA7240C1Z0). Looking for the paperwork that travels with an export shipment? See export & import documentation. To pin the grade before you order, start with selecting the grade, and for welded service, prevent sensitization. Traceable certificates aren't optional in pharmaceutical (hygienic) and fertilizer / acid service work. They're mandatory.