Mill Test Certificate — EN 10204 Types Explained
A mill test certificate documents the chemical and mechanical properties of a material heat. EN 10204 classifies these inspection documents into four types based on who tests and who certifies. This guide covers all four types, when each is required, and how they relate to North American MTRs.
MTR vs. Mill Test Certificate vs. CMTR
The welding industry uses several names for the same document. A mill test report (MTR) is the standard North American term — it is the manufacturer's certified report of chemical analysis and mechanical test results for a specific heat of material. A mill test certificate (MTC) or mill certificate is the international equivalent, particularly common in European, Middle Eastern, and Asian practice. A certified material test report (CMTR) is the formal ASTM/ASME term used in procurement specifications.
All three terms refer to the same core document: a traceable record linking a material’s heat number to its tested properties. The difference is in the classification framework. North American practice (ASTM, ASME) typically requires a CMTR without specifying a type classification. International practice (EN 10204) classifies inspection documents into four types with increasing levels of independent verification.
EN 10204 Certificate Types
EN 10204:2004 “Metallic products — Types of inspection documents” defines four types of inspection certificates. The type required is specified in the purchase order or the governing fabrication code.
| Type | Name | Issued By | Test Basis | Typical Use |
|---|---|---|---|---|
| 2.1 | Declaration of compliance | Manufacturer | No test results — statement of compliance only | Non-critical commercial steel, general construction |
| 2.2 | Test report | Manufacturer | Non-specific inspection — test results from production batch, not necessarily the delivered lot | Standard structural steel, general fabrication |
| 3.1 | Inspection certificate 3.1 | Manufacturer’s authorized inspector | Specific inspection — tests performed on the delivered product, validated by manufacturer’s authorized representative | Pressure vessels (ASME VIII), process piping (B31.3), structural steel (D1.1), most fabrication codes |
| 3.2 | Inspection certificate 3.2 | Manufacturer’s inspector + independent third-party inspector | Specific inspection — witnessed by both the manufacturer and an independent inspector or purchaser’s representative | Nuclear (ASME III), high-pressure critical service, PED Category III/IV, offshore in some jurisdictions |
What Makes 3.1 Different from 3.2?
Both 3.1 and 3.2 certificates provide test results from the specific delivered product — not batch averages or statistical data. The critical difference is who witnesses the testing.
A 3.1 certificate is validated by the manufacturer’s own authorized inspection representative. This person must be independent of the manufacturing department — they work for the same company but report through a quality assurance function, not production. The 3.1 certificate carries the manufacturer’s stamp and the authorized representative’s signature.
A 3.2 certificate requires dual validation: the manufacturer’s inspector AND an independent third-party inspector (or the purchaser’s designated representative) must both witness the testing and sign the certificate. This adds a layer of independent verification that the material was actually tested and the results are genuine. The third-party inspector is typically from a classification society (Lloyd’s, DNV, Bureau Veritas, TUV) or the purchaser’s own inspection agency.
The practical impact: a 3.2 certificate costs more and takes longer because the mill must coordinate testing schedules with the third-party inspector. Lead times for 3.2 material can be 2-6 weeks longer than 3.1 material of the same specification.
When Is Each Type Required?
Type 2.1 or 2.2 — General Construction
Suitable for non-critical applications where the governing specification does not require specific test results per delivered lot. Common for general structural steel (non-coded), commercial fencing, guardrails, and non-pressure-retaining components. Some project specifications accept 2.2 for secondary structural members where failure consequences are low.
Type 3.1 — The Industry Standard
Required by most pressure equipment and structural fabrication codes. ASME Section II Part A material specifications require a CMTR that is functionally equivalent to EN 10204 Type 3.1. D1.1:2025 Clause 7.3 requires the contractor to verify base metal compliance with the WPS — a 3.1 certificate provides the documented evidence. ASME IX Table QW/QB-422 lists over 2,000 material specifications, each requiring traceable documentation per Section II. API standards for pressure vessels, piping, and storage tanks typically require 3.1 as a minimum. This is the default for any coded welding work.
Type 3.2 — Safety-Critical Service
Required when independent verification is mandated by regulation or project specification. The European Pressure Equipment Directive (PED 2014/68/EU) requires 3.2 certificates for Category III and Category IV equipment — pressure vessels and piping where failure could cause serious injury. ASME Section III (nuclear) requires material documentation with independent oversight. Some offshore specifications (NORSOK, API 2W) require 3.2 for primary structural steel in splash zone and submerged applications.
Reading a Mill Test Certificate
Every mill test certificate — regardless of EN 10204 type — should contain the following information. If any of these are missing, the certificate may be incomplete or non-compliant.
Heat number. The unique identifier linking the certificate to the specific melt of steel. This number must match the heat number stamped, stenciled, or painted on the material itself. Without a matching heat number, traceability is broken and the certificate is worthless.
Material specification. The ASTM, ASME (SA-prefix), EN, or other standard to which the material was produced. For example, SA-516 Grade 70, SA-240 Type 304, EN 10025-2 S355J2. The specification determines the allowable chemical composition and mechanical property ranges.
Chemical composition. The actual chemical analysis of the heat — typically reported as percentage by weight for carbon, manganese, phosphorus, sulfur, silicon, and any alloying elements (chromium, molybdenum, nickel, vanadium). These values must fall within the specification limits. For welding under D1.1, the carbon and manganese values feed the Annex B carbon equivalent calculation, and the Table 5.6 base metal group determines preheat requirements per Table 5.11.
Mechanical properties. Tensile strength, yield strength, and elongation from tension testing per ASTM E8. Impact test results (Charpy V-notch per ASTM E23) if required by the specification or purchase order. Hardness values if specified. All values must meet the specification minimums (or maximums, for elements like carbon and phosphorus).
Product form and dimensions. Plate, pipe, tube, bar, forging, or casting. Thickness, width, length, or diameter as applicable. The product form determines which material specification applies and which supplementary requirements may be relevant.
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Ask FluxMill Test Certificate vs. MTR: Practical Differences
For North American fabricators working under D1.1 or ASME codes, the practical difference is minimal. An ASTM CMTR is functionally equivalent to an EN 10204 Type 3.1 certificate — both provide specific test results for the delivered lot, validated by the manufacturer’s authorized representative.
The distinction matters when working on international projects. A European client specifying EN 10204 Type 3.1 expects a certificate formatted and classified per that standard. A North American CMTR satisfies the same technical requirements but may not carry the EN 10204 type designation. If the purchase order or project specification references EN 10204 specifically, ensure the mill issues the certificate with the correct type classification.
For dual-code projects (e.g., ASME VIII vessel with EN 10204 3.1 material requirements), verify that the CMTR from the North American mill meets the EN 10204 classification criteria: specific inspection of the delivered product, validated by an authorized inspection representative independent of the manufacturing department.
Key Takeaways
- MTR, MTC, and CMTR are different names for the same document — a certified record of material test results. MTR is North American, MTC is international, CMTR is formal ASTM/ASME.
- EN 10204 classifies certificates into four types (2.1, 2.2, 3.1, 3.2) based on who tests and who witnesses. Type 3.1 is the industry standard for coded fabrication work.
- The heat number is the traceability anchor. If the heat number on the certificate does not match the heat number on the material, the certificate has no value.
- 3.2 certificates add independent third-party witnessing and are required for nuclear, high-pressure critical, and PED Category III/IV applications. They cost more and add lead time.
"The certificate is only as good as its traceability. A perfect set of test results on a certificate that cannot be linked to the material on your shop floor is a compliance failure waiting to happen."
D1.1:2025 Clause 7.3 requires the contractor to verify that base metals conform to the requirements of the WPS
Frequently Asked Questions
A mill test certificate (MTC) is an inspection document issued by the material manufacturer that certifies the chemical composition, mechanical properties, and heat treatment condition of a specific heat or lot of material. The term is used internationally and is defined by EN 10204:2004, which classifies inspection documents into four types (2.1, 2.2, 3.1, 3.2) based on who performs the inspection and who issues the certificate. In North American practice, the equivalent document is usually called a mill test report (MTR) or certified material test report (CMTR).
The terms mill test report (MTR) and mill test certificate (MTC) refer to the same type of document — a manufacturer's report of material test results. MTR is the standard North American term, while MTC and mill certificate are more common in international and European practice. EN 10204 uses the formal term inspection document and classifies them by type (2.1 through 3.2). ASTM and ASME standards typically reference a certified mill test report or CMTR. Regardless of the name, the document must contain the heat number, chemical analysis, mechanical test results, and material specification compliance statement.
EN 10204:2004 defines four inspection document types. Type 2.1 is a declaration of compliance by the manufacturer with no test results. Type 2.2 is a test report based on non-specific inspection — test results from the production process but not necessarily from the delivered lot. Type 3.1 is an inspection certificate with specific test results from the delivered product, validated by the manufacturer's authorized inspection representative. Type 3.2 is an inspection certificate validated by both the manufacturer's inspector and an independent third-party inspector or the purchaser's designated representative. Most pressure equipment and structural steel projects require 3.1 as a minimum.
A 3.2 certificate is typically required for safety-critical applications where independent verification of material properties is mandated. Common examples include nuclear pressure equipment (ASME Section III), high-pressure piping systems operating above specific thresholds, offshore structural steel in certain jurisdictions, pressure equipment under the European Pressure Equipment Directive (PED 2014/68/EU) for Category III and IV equipment, and projects where the purchaser's specification explicitly requires third-party witnessed testing. The 3.2 requirement adds cost and lead time because an independent inspector must be present during testing at the mill.
Verify the heat number on the certificate matches the heat number stamped or stenciled on the material. Cross-check the chemical composition against the limits in the material specification — for example, SA-516 Grade 70 has maximum carbon of 0.27% per ASTM A516. Verify tensile strength, yield strength, and elongation meet specification minimums. Check that the certificate identifies the testing standard (EN 10204 type, ASTM E8 for tension testing, ASTM E23 for impact testing). For 3.1 certificates, confirm the authorized representative's signature or stamp is present. For 3.2 certificates, confirm both the manufacturer's and the independent inspector's signatures are present.
Reference data from EN 10204:2004 and ASME BPVC II-A. Not affiliated with CEN or ASME.