A Certificate of Conformance (CoC) for metals is a declaration that a product meets the requirements of the applicable specification. Unlike a full Mill Test Certificate, a CoC does not include actual test data. Understanding when a CoC is sufficient — and when it is not — is critical for procurement and quality compliance.
Quick Answer
Quick Answer
A Certificate of Conformance for metals is a written declaration by the manufacturer that the product meets the specified standard. EN 10204 defines four inspection document types: 2.1 (declaration only) and 2.2 (test data from non-specific inspection) are conformance certificates; 3.1 and 3.2 include specific test data and are true Mill Test Certificates. For pressure-retaining applications, 3.1 minimum is typically required.
EN 10204: The Governing Framework
EN 10204:2004 (Metallic products — Types of inspection documents) is the European standard that defines inspection document types. It is referenced globally — in ASME code contracts, API datasheets, and procurement specifications worldwide.
Document Type Summary
| EN 10204 Type | Test performed by | Certified by | Contains test data | Commonly called |
|---|---|---|---|---|
| 2.1 | Manufacturer | Manufacturer | No | Certificate of Conformance, CoC |
| 2.2 | Manufacturer | Manufacturer | Yes (non-specific) | Test Report |
| 3.1 | Manufacturer | Manufacturer's Auth. Rep. | Yes (specific to order) | Mill Test Certificate (MTC) |
| 3.2 | Manufacturer + Third Party | Both Auth. Rep. and Third-Party Inspector | Yes (specific to order) | Dual-certified MTC |
"Specific" means the test data is traceable to the specific heat, lot, and product supplied under the order. "Non-specific" means data from a similar product in the production run — not the specific items delivered.
When a CoC (2.1 or 2.2) Is Acceptable
A pure conformance certificate (EN 10204 2.1 or 2.2) is acceptable for:
- Non-pressure-retaining components: structural members, brackets, grating, handrails, standard hardware
- Commercial off-the-shelf items where the manufacturer's established QMS and product certification provide sufficient assurance
- Low-risk applications where material substitution would have no safety consequence
- Bulk consumables such as standard fasteners, paint, gaskets below a specified pressure class
Some procurement contracts allow 2.2 for secondary structural members in process plants where the specification explicitly permits it.
When a Full MTC (3.1 or 3.2) Is Required
A CoC is not sufficient for:
- Pressure-retaining materials under ASME BPVC (Section VIII, B31.3) — specific heat chemistry and mechanical test results are required
- Cryogenic service materials — Charpy impact test results at the design temperature are mandatory
- Sour service (H₂S environments) — NACE MR0175/ISO 15156 compliance requires documented hardness and chemistry
- Nuclear applications — ASME Section III requires documented traceability to the specific material
- Materials under EN 1092 flanges in Group 1 dangerous fluid service (PED Category III/IV equipment)
- Any specification that explicitly calls for EN 10204 3.1 or 3.2
What a CoC Must Contain
Even though a CoC does not include test data, it must be a meaningful document. A valid CoC for metals should state:
- Manufacturer name and address
- Order reference and date
- Product description — material specification, grade, product form, dimensions
- Quantity and delivery unit identification (heat/lot number or tag reference)
- Applicable standard(s) — e.g., "This material conforms to ASTM A106 Grade B"
- Explicit conformance statement — "We hereby certify that the above product meets the requirements of..."
- Authorized signatory — name, title, signature, date
- Quality system reference — ISO 9001 certificate number (optional but adds credibility)
A CoC that simply states "material is certified" without naming the specific standard is worthless for audit purposes.
CoC vs. MTC: Common Procurement Mistakes
Mistake 1: Accepting a CoC when the specification requires 3.1
Many procurement teams accept any document labeled "Mill Certificate" without checking whether it actually contains heat-specific test data. A document stamped "Certified" with no chemistry values is a 2.1 CoC, not a 3.1 MTC.
Mistake 2: Confusing 2.2 with 3.1
A 2.2 test report contains real test data but from a non-specific (typical) heat. It is useful for process control but provides no traceability to the specific material delivered.
Mistake 3: Not verifying the heat number
Even a genuine 3.1 MTC is worthless if the heat number on the certificate does not match the heat number stamped or stenciled on the actual material. This check must be performed on receipt.
Mistake 4: Missing the authorized representative signature
EN 10204 3.1 requires the manufacturer's authorized inspection representative to sign — not a commercial sales signature. Verify the signatory's role.
Requesting the Correct Document at Order Placement
The correct way to specify inspection documents is in the purchase order, not after delivery. Use one of these formulations:
- "Mill Test Certificates to EN 10204 Type 3.1 are required for all pressure-retaining materials."
- "Certificates of Conformance to EN 10204 Type 2.1 are acceptable for standard hardware items as defined in Attachment A."
Ambiguous language such as "material certificates required" without specifying the EN 10204 type will result in inconsistent document types from different suppliers.
Is ASTM A6 the same as EN 10204 3.1?
No. ASTM A6 is a material specification for rolled structural steel. It includes requirements for material test reports (MTRs) that are broadly equivalent to EN 10204 3.1 in concept — heat-specific chemistry and mechanical test data certified by the manufacturer. However, the two standards have different field requirements and are not interchangeable by name.
Can a distributor issue an EN 10204 3.1 certificate?
A distributor (service center, stockholder) can re-issue or pass through the original mill's 3.1 certificate. They can also issue a new 3.1 certificate if they have performed additional testing and employed an authorized representative. However, a distributor's declaration referencing the mill's original test without an authorized signatory is not a valid 3.1 document.
What does 'non-specific inspection' mean in EN 10204 2.2?
Non-specific inspection means the test data recorded in the document comes from tests on products of the same type, grade, and heat treatment condition — but not necessarily the specific items delivered under this order. The manufacturer certifies that these results are representative. It provides more information than a pure declaration (2.1) but less traceability than a specific inspection (3.1).
Do US standards use the EN 10204 designation?
EN 10204 originated in Europe but is widely referenced globally, including in US projects with international clients. US-based fabricators working to European codes (EN 13480, EN 13445) or exporting to Europe must supply EN 10204 documents. US domestic projects typically reference ASTM material standards that define their own MTR requirements.
How do I verify that an MTC is genuine and not falsified?
Key checks: (1) Heat number on the certificate matches the physical marking on the material. (2) Chemistry and mechanical values are plausible for the stated grade. (3) The issuing mill is the actual manufacturer of record. (4) The certificate format matches known examples from that mill. For high-risk applications, PMI testing or independent laboratory verification should be used to corroborate the chemistry data.
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