EN 10204 Type 3.1 MTC Explained: How to Read a Mill Test Certificate (with Annotated Sample)
Quick answer: An EN 10204 Type 3.1 Mill Test Certificate is a batch-level material certificate signed by the manufacturer's independent inspection department. It records the specific heat number of the material, its actual chemistry, actual mechanical test results, dimensional check and applicable standard. Type 3.1 is the buyer's minimum bar for pump, petrochemical, borehole and pressure applications in 2026 — and it's the origin document your UK CBAM reporter and US DOC compliance team will actually accept.
Every serious stainless-steel purchase order in the pump, pressure and petrochemical world asks for an "EN 10204 Type 3.1 MTC" — but a surprising number of buyers can't confidently explain what each line of the document means, what to check, or what a "red flag" MTC looks like. This guide walks through it end-to-end using an anonymised sample from a recent Apurvi Industries lot.
The four EN 10204 certificate types
| Type | Name | Who signs | Traceability | Buyer use case |
|---|---|---|---|---|
| 2.1 | Declaration of compliance | Manufacturer | No specific test data | Low-risk commercial goods |
| 2.2 | Test report | Manufacturer | Non-specific test data | Non-critical service |
| 3.1 | Inspection certificate | Manufacturer's inspection dept (independent of production) | Specific to the heat | Pump, pressure, petrochemical, borehole, CBAM-reported material |
| 3.2 | Inspection certificate | Manufacturer AND external inspection body (SGS / TUV / BV / Lloyd's) | Specific to the heat, third-party witnessed | Highest-risk service (nuclear, offshore, some IBR jobs) |
Type 3.1 is the market default in 2026. Type 3.2 is a step-up for regulated applications and adds the cost of the third-party inspection body. Type 2.2 is rare on serious tube purchases and shouldn't be accepted for pump, pressure or CBAM-reported service.
Anatomy of a Type 3.1 MTC — line-by-line
Here's the schematic of a typical Apurvi Industries EN 10204 Type 3.1 MTC (values altered / anonymised):
How to read each field
① Certificate No. A unique identifier per certificate. Your PO records this number so any future dispute can be traced to a specific document.
② Date of issue Sits within a few days of the final testing date. Suspicious if it's much later than the production date.
③ Buyer / PO Must match your PO number exactly. Verify — this is the buyer's audit trail.
⑤ Product / ⑥ Standard The applicable ASTM / EN / JIS / IS standard. On a dual-cert document you'll see two standards side by side.
⑦ Grade Both the ASTM (TP316L) and EN (1.4404) designations plus the UNS number where applicable. This is the layer where cross-reference happens.
⑧ Heat / Cast number The single most important field on the whole certificate. This is the identifier of the actual melt from which your material was made. It should also be physically stamped on the pipe. When your inspector pulls a pipe from the container, this heat number MUST match a heat number on the MTC.
⑨ Dimension OD × wall × length. On multi-line MTCs, each line has its own dimension.
⑩ Country of melt / ⑪ Country of manufacture These two fields matter more than any other for CBAM (UK) and Section 232 (US) compliance. "Country of melt" is where the raw material was actually melted; "country of manufacture" is where the pipe was made. For CBAM reporting, both must be present. For DOC / Section 232, "country of melt" is the field that determines duty rate.
⑫ Chemistry Actual element percentages vs the required range from the standard. Verify that every element sits inside the range. Read the Mo column carefully — on unreliable "316" pipe you sometimes see Mo below 2%, which is not a legitimate 316.
⑬ Mechanical Yield / ultimate tensile / elongation / hardness measured on a coupon from the actual heat. Verify all values are above (or below, in the case of hardness) the required limits.
⑭ Testing Hydro test (required for pressure service), IGC / ASTM A262-E (inter-granular corrosion resistance test — critical for weldable stainless in corrosive service), PMI, calculated PREN.
⑮ Signature and independence statement This is the fingerprint of the Type 3.1 certificate. The signatory MUST be independent of the production department. If your MTC is signed by the production manager, it is not a valid Type 3.1 — it's effectively a Type 2.2.
Common red flags in a Type 3.1 MTC
Red flag 1: No heat number, or the heat number does not match the pipe stamp. This is the single most common — and worst — MTC issue. Reject the material at inspection.
Red flag 2: Chemistry inside the range but Mo below 2% for a "316" callout. Some mills game a 316 spec by hitting the Cr and Ni range but under-supplying Mo. This material will not perform as a real 316L in chloride service.
Red flag 3: "Country of melt" left blank, or listed as a country different from "country of manufacture". This is a CBAM reporting problem for UK buyers and a Section 232 compliance problem for US buyers. Insist on both fields being filled with the actual origin.
Red flag 4: MTC signed by the production manager, not the inspection / quality department. The independence of the signatory is what makes a document Type 3.1 rather than Type 2.2. If the signatory is not clearly independent of production, ask for a re-issue.
Red flag 5: Certificate date months after the ex-mill / invoice date. Suggests the MTC was reconstructed rather than issued at production. Legitimate MTCs are issued within days of final testing.
Red flag 6: Suspiciously "round" chemistry (e.g. Cr 17.0, Ni 12.0, Mo 2.5 exactly). Real heat chemistry has decimal-place variability. Perfectly round numbers can suggest a fabricated or copied MTC.
How CBAM (UK) and Section 232 (US) use the MTC
UK CBAM (Carbon Border Adjustment Mechanism). The CBAM reporter needs to declare embedded carbon per tonne of imported material. The origin data on the MTC — specifically country of melt and country of manufacture — plugs directly into that declaration. Where the mill can hand the reporter a pre-formatted CSV or PDF with the fields aligned to the CBAM template, the compliance workload drops materially. Apurvi provides this on request.
US Section 232. Section 232 duty rates on steel are set by country of melt. Chinese-origin stainless attracts 50% duty; Indian-origin does not. Your DOC compliance team will look at the "country of melt" field on the MTC to determine duty rate. Get this field right at MTC stage — don't try to fix it at customs.
Common questions
1. Is Type 3.1 always required?
For any pressure, pump, petrochemical, borehole, or CBAM-reported material in 2026 — effectively yes. For a non-pressure decorative railings order, Type 2.2 may be acceptable. Match the certificate type to the risk of the application.
2. Is a Type 3.1 MTC legally binding?
It is a contractual document under the sales agreement. If the MTC is materially inaccurate, that's usually a breach of contract and can trigger rejection or claim.
3. Can I convert a Type 3.1 to a Type 3.2 after the fact?
No. Type 3.2 requires the third-party inspection body (SGS / TUV / BV / Lloyd's) to witness the testing at the mill. It cannot be added retroactively. Request Type 3.2 on the PO, not after shipping.
4. Should the MTC be in English?
Yes for international trade. Indian MTCs are routinely issued in English and match international convention.
5. Do all countries recognise EN 10204 Type 3.1?
Yes — the standard is recognised globally. US buyers accept EN 10204 3.1 as equivalent to an ASTM A751-compliant material certificate. UK / EU buyers require EN 10204 3.1 as the market default. Japanese and Korean buyers routinely accept it too.
6. What if my mill offers "EN 10204 3.1 equivalent"?
Push back. Either the MTC is a proper Type 3.1 signed by an inspection department independent of production, or it isn't. There is no "equivalent" — the definition is precise. If the mill can't issue a real Type 3.1, that's a supplier-quality signal in itself.
Engineer's checklist when reviewing an incoming Type 3.1 MTC
- Heat number on the MTC matches heat number on the pipe stamp
- Standard cited on MTC matches PO (dual-cert if the PO called for it)
- Grade designation and UNS number match PO
- Chemistry values sit inside the spec range for every element
- Mo content is at or above 2.0% for any 316 / 316L callout
- Mechanical test values pass yield / UTS / elongation / hardness limits
- Hydro test result recorded (if required for the service)
- IGC / A262-E test result recorded (if welded stainless in corrosive service)
- Country of melt AND country of manufacture both filled
- Signed by inspection / quality department, not the production manager
- Certificate date within a few days of production / testing
- Chemistry values are not suspiciously "round"
Want to see a real anonymised Apurvi Industries EN 10204 Type 3.1 MTC before you commit?
Request a Sample MTC