MTC Review Checklist for Buyers: EN 10204 3.1 and 3.2 Audit

Why this matters

The Mill Test Certificate (MTC) is the legal record that a heat of steel meets the chemistry and mechanical properties you ordered. EN 10204 defines four certificate types; the two that matter for pressure-piping procurement are 3.1 and 3.2. A clean MTC review takes 15 minutes per heat and prevents the costliest defect a buyer can ship: wrong-grade material installed in service. This MTC review checklist is built around the EN 10204 standard structure documented by Project Materials and Holland Applied Technologies.

Field-by-field MTC review

1. Identification block. PO number, line item, manufacturer name and works address. Cross-check the works address against the supplier's accreditation — material made at an unlisted works is a red flag.

2. Product description. Standard + edition (e.g., ASTM A403-2023), grade (WP316L), size, quantity, and shape must match the PO line. A common error is WP316 quoted but WP316L delivered — the L (low-carbon) is required for welded service.

3. Heat number traceability. Every piece must trace to a heat number, and every heat number must appear in the chemistry table. Mark each PO quantity against a heat: missing pieces mean partial-heat shipment without disclosure.

4. Chemical composition. Verify each element is within the ASTM/ASME range for the ordered grade. For 316L, C ≤ 0.030%. For WPB, C ≤ 0.30%, Mn 0.29–1.06%. Look for elements that are not reported but are required by the spec (e.g., Cu, Mo).

5. Mechanical properties. Tensile, yield, elongation, impact (where required). For A234 WPB: tensile 415 MPa min, yield 240 MPa min, elongation 22% min in longitudinal. Charpy values must include test temperature and direction.

6. Hardness. For sour service per NACE MR0175, hardness must be reported and ≤ 22 HRC. Some mills omit hardness — request it explicitly.

7. Heat treatment record. State of supply (annealed, normalised, solution-annealed) and furnace charge number. Solution-anneal temperature for 316L should be ≥ 1040 °C followed by rapid cooling.

8. NDE results. UT, RT, MT, PT results with the procedure number and acceptance standard (e.g., ASTM A388, ASME V Article 4). Reject "satisfactory" without a procedure number.

9. Hydrostatic test. Test pressure, hold time, and standard reference. Per ASME B31.3, hydrostatic pressure is at least 1.5 × design.

10. PMI. For alloy and stainless: XRF or OES result per heat (or per piece for critical service). XRF cannot read carbon, so 316 vs 316L distinction needs OES or chemistry from melt.

11. Signature block. EN 10204 3.1 requires the manufacturer's authorised inspection representative — this person must be independent of the production department. EN 10204 3.2 adds a second signature from the buyer's inspector or an officially designated body (e.g., a notified body or a TPI agency).

12. Statement of conformity. A clean statement that the product complies with the contract and named standards.

3.1 vs 3.2 — buyer decision points

Use 3.1 for general process piping and water service. Specify 3.2 when the project spec demands third-party endorsement: subsea, nuclear, high-pressure hydrogen, classed marine, or sour service per NACE MR0175. 3.2 typically adds 3–7 days lead time and a TPI fee.

Common buyer mistakes

• Approving an MTC that lists the wrong edition year of the standard.
• Accepting averaged chemistry instead of per-heat chemistry.
• Missing that the inspection representative signature is from the production manager — that violates EN 10204 3.1's independence requirement.
• Filing the MTC without checking each piece can be matched back to a heat stamp on the fitting (per MSS SP-25).
• Assuming PMI on one piece per heat is enough for safety-critical service.

Buyer checklist

• [ ] PO + line + works address verified
• [ ] Standard edition year matches PO
• [ ] Heat numbers cover 100% of pieces shipped
• [ ] Chemistry within spec for every element
• [ ] Mechanical properties + test temperature reported
• [ ] Hardness reported (≤ 22 HRC if sour)
• [ ] Heat-treatment temperature and process reported
• [ ] NDE procedure numbers and acceptance standards listed
• [ ] Independent signatory (3.1) or TPI countersignature (3.2)
• [ ] Conformity statement present and unqualified

Sample PO clause

"EN 10204 Type 3.1 Mill Test Certificate required for every heat. Submit MTC in PDF a minimum of 5 working days before shipment for buyer review. For 316/316L material, OES PMI per piece is mandatory. For sour service items, hardness traverse per NACE MR0175 / ISO 15156-2 must be reported."

Review sample MTC formats in our certificates library, browse seamless butt-welding pipe fittings, or send a pre-shipment MTC for review.

Sources

• EN 10204 explained — Holland Applied Technologies: https://hollandapt.com/what-is-the-difference-between-en-10204-3-1-and-3-2-inspection-certificates/
• Project Materials, MTC 3.1 vs 3.2: https://blog.projectmaterials.com/epc-projects/testing-inspection/mill-test-certificates-3-1-2/
• ASTM A234/A234M scope: https://store.astm.org/a0234_a0234m-19.html
• NACE MR0175 hardness rule (NTI summary): https://ntia.no/en-10204-3-1-vs-3-2/
• EPCLand MTC guide: https://epcland.com/material-test-certificate-en-10204-guide/