Mill Test Certificate (MTC): EN 10204 3.1 vs 3.2

Quick Reference

A Mill Test Certificate (MTC) is a certified document from a steel manufacturer that reports the actual chemical composition and mechanical properties of a product. The EN 10204 standard defines four certificate types: 2.1 (declaration of compliance), 2.2 (test report with non-specific results), 3.1 (inspection certificate with specific test results), and 3.2 (inspection certificate with third-party validation). MTCs are shipped with other export documents and are the primary quality record for steel products in piping, pressure equipment, and structural applications.

What Is a Mill Test Certificate?

A mill test certificate (MTC), also called a mill test report (MTR) or material test certificate, is a quality document issued by a steel manufacturer that certifies the chemical and mechanical properties of the supplied material. The MTC provides traceable evidence that the product meets the requirements of the applicable material specification (e.g., ASTM A106, ASTM A182, API 5L) and the purchaser’s order.

The terms MTC and MTR are used interchangeably. MTC is the standard abbreviation in European and international projects, while MTR is more common in North American practice. Regardless of the term used, the document serves the same purpose: providing heat-traceable, certified test data for metallic products.

For processed products like pipe fittings (elbows, tees, reducers), the manufacturer must provide MTCs for both the finished product and the “mother” material (the raw pipe or plate used to fabricate it).

Why MTCs Matter

Reason	Explanation
Quality assurance	Traceable record that materials meet required standards and specifications
Code compliance	Required for projects adhering to ASME, API, EN, and PED requirements
Safety	Verifies material strength and composition for pressure-containing and structural applications
Traceability	Links each item to its heat number, allowing recall and root-cause analysis if failures occur
Risk management	Reduces risk of substandard materials causing in-service failures, unplanned shutdowns, and accidents
Contractual obligation	Purchase orders and project specifications mandate specific certificate types; non-compliance is grounds for rejection

Field Note

When materials arrive on site, always match the heat numbers on the physical product against the MTC. It takes five minutes and prevents major headaches; I’ve seen entire shipments rejected during client audits because one elbow had a mismatched heat number.

Information Shown on an MTC

A standard MTC (EN 10204 Type 3.1) contains the following sections:

Section	Contents
Header	Manufacturer name/address, document title, date, certificate type (e.g., “EN 10204 3.1”), page numbering
Order details	Customer name, purchase order reference, product definition, applicable standard
Product description	Type (e.g., “Seamless Pipes”), manufacturing process (HFS, CDS, ERW), surface finish, dimensions (NPS x WT x length)
Quantities	Number of pieces, nominal weight, net/gross weight
Chemical composition	Element percentages (C, Mn, P, S, Si, Cr, Mo, Ni, Cu, V, Nb, Ti, etc.) per heat, compared against spec limits
Mechanical properties	Tensile strength, yield strength, elongation, hardness (HRC/HBW), impact test values (Charpy V-notch at specified temperature)
Heat treatment	Condition of supply (normalized, quenched and tempered, annealed, solution annealed, etc.)
Additional tests	Hydrostatic test, ultrasonic testing, MPI, flattening, flaring, metallographic examination, SSC/HIC results (if sour service)
Marking	Product marking details (heat number, size, grade, manufacturer logo) for traceability
Validation	Manufacturer QA signatures (independent of production); third-party inspector signatures for Type 3.2

MTC Types per EN 10204

The EN 10204 standard (“Metallic products; Types of inspection documents”) defines four certification levels, from basic declarations to fully third-party validated inspection certificates:

Type 2.1: Declaration of Compliance

A declaration that the products comply with the order requirements. No test results are included. No third-party verification. Type 2.1 is suitable for non-critical applications (general structural steel, low-risk components, pipe supports, non-pressure accessories) where material properties are not safety-critical. In piping projects, Type 2.1 is typically limited to gaskets, standard bolting, and non-pressure-bearing items.

Type 2.2: Test Report

In addition to declaring compliance, the manufacturer confirms products were tested per the applicable standard. Non-specific test results are provided (summary statements or typical values, not the actual test data from the supplied batch). No third-party verification. Used when buyers need more assurance than 2.1 but do not require heat-specific test data. Type 2.2 is common for commercial structural steel per EN 10025.

Watch Out

Do not confuse a Type 2.2 test report with a proper MTC. A 2.2 certificate contains test results, but these results may come from a different heat or lot than the material actually delivered. This breaks heat traceability, which is unacceptable for pressure piping under ASME B31.3 and the EU Pressure Equipment Directive. Always verify that the certificate type matches your PO requirement.

Type 3.1: Inspection Certificate

With a Type 3.1 certificate, the mill provides specific test results (actual chemical composition and mechanical properties) measured on the supplied batch. The certificate must be validated by the manufacturer’s authorized inspection representative, who must be independent of the manufacturing department. Full traceability via heat/batch numbers.

This is the standard certificate type for oil & gas, chemical processing, petrochemical, and power generation projects. When a purchase order specifies “MTC required” without further detail, EN 10204 Type 3.1 is typically expected.

Historical Designation (pre-2004)	Current Equivalent	Notes
3.1A	3.2	Issued by an independent third-party inspector
3.1B	3.1	Issued by the manufacturer’s own QA department
3.1C	3.2	Issued by the customer’s designated inspector

Pro Tip

Always request MTCs before the shipment leaves the factory, not after arrival. Chasing missing paperwork while materials sit idle at the port costs storage fees and delays commissioning. Build MTC submission deadlines into your PO terms; for example, “MTCs to be submitted for approval minimum 5 working days before shipment.”

Type 3.2: Inspection Certificate with Third-Party Validation

Same as 3.1, plus an independent third-party inspector witnesses the tests and co-signs the certificate. The third party can be the purchaser’s designated representative or an accredited inspection agency (SGS, Bureau Veritas, Lloyd’s, TUV, DNV, etc.). Required for critical applications where material failure could have catastrophic consequences: subsea pipelines, nuclear components, high-pressure/high-temperature service, and aerospace.

Type 3.2 certificates cost more and add 2-4 weeks to the delivery schedule because the third-party inspector must be scheduled, must travel to the mill, and must witness each test. For large orders, this coordination overhead is significant and must be factored into the procurement timeline.

Sample mill test certificate; EN 10204 Type 3.1 for Tenaris seamless steel pipes. Note the heat number, chemical analysis, tensile test results, and manufacturer’s QA validation stamp.

MTC Comparison Table

Type	English Name	German	French	Test Results	Validated By
2.1	Declaration of compliance	Werkbescheinigung	Attestation de conformite	None	Manufacturer
2.2	Test report	Werkzeugnis	Releve de controle	Non-specific	Manufacturer
3.1	Inspection certificate	Abnahmeprufzeugnis 3.1	Certificat de reception 3.1	Specific (per heat)	Manufacturer QA (independent of production)
3.2	Inspection certificate	Abnahmeprufzeugnis 3.2	Certificat de reception 3.2	Specific (per heat)	Manufacturer QA + third-party inspector

Key Differences: 3.1 vs 3.2

Aspect	2.1 / 2.2	3.1	3.2
Test results	None / Non-specific	Actual values per heat	Actual values per heat
Third-party witness	No	No	Yes
Traceability	Limited	Full (heat/batch)	Full (heat/batch)
Cost impact	Lowest	Moderate	Highest (inspection fees)
Lead time impact	None	+1-2 weeks	+2-4 weeks
Typical use	General engineering, non-critical	Oil & gas, power generation, chemical plants	Subsea, nuclear, HP/HT, aerospace

When to Specify 3.1 vs 3.2

The choice between Type 3.1 and Type 3.2 depends on the criticality of the application and the governing design code:

Application / Service	Recommended Type	Rationale
Standard process piping (ASME B31.3 Normal Fluid Service)	3.1	Adequate assurance for non-critical hydrocarbon and utility services
Power piping (ASME B31.1)	3.1	Standard requirement for boiler and power plant piping
Sour service piping (NACE MR0175 / ISO 15156)	3.1 or 3.2	Hardness, impact, and SSC/HIC testing verification; 3.2 if project spec requires TPI
Lethal service (ASME B31.3 Category M)	3.2	Material failure could cause release of lethal fluids; highest assurance needed
Subsea pipelines (DNV-OS-F101 / NORSOK)	3.2	Third-party witnessed testing mandatory per DNV and NORSOK standards
Nuclear piping (ASME Section III)	3.2	Nuclear safety requirements demand independent verification
High-pressure/high-temperature (HP/HT)	3.2	Extreme operating conditions warrant maximum material assurance
General structural steel	2.2 or 3.1	Per EN 10025; 3.1 if specified by the structural engineer
Non-pressure accessories (supports, clamps)	2.1	Low criticality; compliance declaration sufficient

For oil and gas, chemical processing, and power generation projects, EN 10204 Type 3.1 is the standard certificate type; providing specific test results validated by the manufacturer’s authorized inspection representative. For critical applications where material failure could be catastrophic (subsea, nuclear, high-pressure/high-temperature), Type 3.2 adds independent third-party validation. Types 2.1 and 2.2 should only be accepted for non-critical, low-risk components.

How to Read and Verify a Mill Test Certificate

Reading an MTC correctly requires checking chemical composition, mechanical properties, and traceability data against the applicable material specification. Follow this step-by-step process:

Step 1: Confirm the Material Grade

Verify that the material specification and grade on the MTC (e.g., ASTM A106 Gr. B, API 5L X65 PSL2, ASTM A312 TP316L) match the purchase order exactly. A common error is receiving a lower grade (e.g., Gr. A instead of Gr. B) or a different PSL level.

Step 2: Check Chemical Composition

The MTC lists the percentage of each element detected in a ladle analysis (heat analysis) or product analysis. Compare each value against the specification limits:

Element	Symbol	Why It Matters
Carbon	C	Controls strength and hardness; excess C reduces weldability
Manganese	Mn	Increases strength and toughness; high Mn improves impact resistance
Phosphorus	P	Impurity; must be below spec maximum; causes brittleness
Sulfur	S	Impurity; must be below spec maximum; causes hot cracking
Silicon	Si	Deoxidizer; improves strength
Chromium	Cr	Corrosion resistance; defines alloy and stainless steel grades
Molybdenum	Mo	High-temperature strength; creep resistance
Nickel	Ni	Toughness at low temperatures; corrosion resistance
Carbon Equivalent	CE/CEV	Weldability indicator; typically CE ≤ 0.43 for field welding without preheat

Watch Out

Pay attention to the Carbon Equivalent (CE) value. Even if individual elements are within spec, a high CE indicates poor weldability and may require preheat or PWHT. Many project specifications set a maximum CE of 0.43 for carbon steel piping.

Step 3: Verify Mechanical Properties

Test	What It Measures	Typical Check
Tensile strength	Maximum stress before fracture (MPa or psi)	Must fall within spec range (e.g., ASTM A106 Gr.B: 415-585 MPa)
Yield strength	Stress at 0.2% offset (MPa or psi)	Must meet minimum (e.g., A106 Gr.B: >=240 MPa)
Elongation	Ductility as % stretch before fracture	Must meet minimum (e.g., A106 Gr.B: >=30% for standard specimens)
Hardness	Resistance to indentation (HRC, HBW, or HV)	Must be below maximum; for sour service (NACE MR0175): HRC <=22
Impact test	Toughness at specified temperature (Joules)	Required for low-temperature service; must meet minimum absorbed energy

Step 4: Cross-Reference Heat Numbers

Every MTC must include data that links the certificate to the physical product:

• Heat number (also called “cast number”): unique identifier for the steel melt. Must match the marking on the product.
• Lot/batch number: groups items from the same heat that were processed together.
• Item marking: the physical marking on each pipe, fitting, or flange should show heat number, size, grade, schedule/class, and manufacturer.

Step 5: Verify Heat Treatment

Confirm the heat treatment condition on the MTC matches the requirement of the material standard. For example, ASTM A106 requires normalizing for wall thicknesses above a certain limit; ASTM A312 stainless steel pipes require solution annealing. An incorrect heat treatment condition is grounds for rejection.

Step 6: Check the Certificate Type and Signatures

Confirm the EN 10204 type stated on the MTC matches the purchase order requirement. A Type 3.1 is not acceptable when 3.2 is specified. For Type 3.2, verify that both the manufacturer’s QA representative and the third-party inspector have signed and stamped the certificate.

Step 7: Review Supplementary Requirements

Check for any additional tests specified in the purchase order: impact testing at a specific temperature, NACE MR0175 compliance (SSC/HIC testing, maximum hardness), PMI verification, or special NDT requirements. These results must appear on the MTC or on attached supplementary test reports.

Verification Checklist

Before accepting a shipment, cross-reference: (1) heat number on the MTC matches the product marking, (2) all chemical values are within specification limits, (3) all mechanical values meet minimums/maximums, (4) the certificate type matches your PO requirements (3.1 or 3.2), (5) heat treatment condition is correct, (6) signatures and stamps are present, and (7) supplementary test results are complete.

MTC Requirements by Product Standard

Different product standards have specific testing and certification requirements that must appear on the MTC:

Standard	Product	Key MTC Requirements
API 5L	Line pipe	Chemical composition (heat + product analysis for PSL2), tensile, yield, elongation, Charpy impact (PSL2), hardness (sour service), hydrostatic test, NDT (UT/RT), CVN transition temperature
ASTM A106	Seamless CS pipe	Chemical composition, tensile, yield, elongation, hydrostatic test, flattening test; normalizing for thick walls
ASTM A312	Seamless/welded SS pipe	Chemical composition, tensile, yield, elongation, flattening/flaring, hydrostatic/pneumatic test, intergranular corrosion test (if specified)
ASTM A333	Low-temperature CS pipe	Chemical composition, tensile, yield, elongation, Charpy impact at design temperature, hydrostatic test
ASTM A335	Alloy pipe (Cr-Mo)	Chemical composition, tensile, yield, elongation, hardness, heat treatment condition
ASTM A234	BW fittings (CS/alloy)	Chemical composition (mother material + finished product), tensile, yield, elongation, hardness, hydrostatic test of mother pipe
ASTM A182	Forged fittings/flanges	Chemical composition, tensile, yield, elongation, hardness, heat treatment, PMI for alloy grades
ASTM A105	Forged CS flanges	Chemical composition, tensile, yield, elongation, hardness, heat treatment
ASME B16.5	Pipe flanges	Material per ASME Section II; MTC per referenced ASTM standard; marking per B16.5
ASME B16.34	Valves	Material per ASME Section II; pressure-temperature rating basis; body and trim MTC required

ASME vs EN Standards

EN 10204 is a European standard, but it is universally referenced in international piping procurement. ASTM material specifications do not reference EN 10204 directly; instead, they define their own testing and certification requirements. In practice, mills issue certificates that comply with both the ASTM specification and the EN 10204 type specified in the purchase order.

Traceability Requirements

Heat number traceability is the system that links every piping component back to the original steel melt (heat) from which it was produced. The heat number is assigned by the steel mill at the time of melting and must be maintained throughout the entire manufacturing chain, from raw billet or slab through the finished product.

Traceability Chain

The traceability chain for a typical piping component follows this path:

1. Steel melt (heat): The mill assigns a unique heat number to each melt.
2. Semi-finished product: The billet, bloom, or slab carries the heat number.
3. Finished product: The pipe, fitting, or flange is marked with the heat number during manufacturing.
4. Shipping and receiving: The packing list references the heat number, linking to the MTC.
5. Installation: The as-built documentation records which heat number was installed at each location.

Transfer Marking

When a pipe or fitting is cut, machined, or otherwise processed such that the original heat number marking is removed, the fabricator must transfer the heat number to the new piece before removing the original marking. Transfer marking must be witnessed by a QC inspector per the project quality plan. Failure to maintain transfer marking is one of the most common traceability non-conformances in fabrication shops.

Code Requirements for Traceability

Code / Standard	Traceability Requirement
ASME B31.3	Material traceability mandatory for all pressure components
ASME B31.1	Material identification and traceability for all piping components
NACE MR0175 / ISO 15156	Heat-level traceability mandatory for all sour service materials
PED (2014/68/EU)	Full traceability for Category II-IV pressure equipment
DNV-OS-F101	Heat-level traceability with third-party witness for subsea pipelines
NORSOK M-650	Qualification of manufacturers with full traceability systems
ASTM A530	Marking requirements for steel pipes (heat number mandatory)
ASTM A961	Marking requirements for flanges and forged fittings

Common Issues with MTCs

Fake MTCs: Risks and Prevention

Counterfeit Certificates

Fake MTCs are a serious problem in the global steel supply chain. Substandard materials with forged certificates have caused equipment failures, project delays, and safety incidents. The problem is most common with materials sourced through intermediaries rather than directly from reputable mills.

Risk	Impact
Safety	Materials that don’t meet specs can fail in service under pressure, temperature, or corrosive conditions
Legal liability	Regulatory penalties, product recalls, project shutdowns, criminal prosecution
Financial loss	Replacement costs, construction delays, litigation, insurance claims
Reputation damage	Loss of customer trust, blacklisting from future projects

How to Detect and Prevent Fake MTCs

Method	Action
Direct mill verification	Contact the manufacturer directly using independently sourced contact details (not those on the MTC) to confirm the certificate is genuine
Third-party inspection	Engage independent agencies (SGS, Bureau Veritas, Lloyd’s, TUV, DNV) to witness tests at the mill and validate material properties
PMI testing	Perform positive material identification with XRF or OES on arrival to verify the alloy matches the MTC
Check inconsistencies	Review formatting, fonts, logos, spelling, and data; compare against known genuine certificates from the same mill
Verify traceability	Cross-reference heat/batch numbers on the MTC against physical product markings; check that quantities and dimensions match
Supplier qualification	Audit suppliers’ quality systems (ISO 9001, PED/CE, API monogram) and maintain an approved vendor list
Independent sample testing	Send random samples to an accredited lab for chemical and mechanical testing to verify MTC claims

Common Mistake

Accepting photocopies or scanned PDFs of MTCs from unknown intermediaries without verifying with the original mill. Genuine MTCs carry a wet signature or embossed stamp. If a supplier provides only digital copies, request the mill’s direct contact for verification before accepting the material.

Transcription Errors

Even genuine MTCs can contain transcription errors: incorrect heat numbers, swapped test values, wrong units (MPa vs. psi), or misidentified grades. These errors are usually unintentional but can cause costly delays during inspection. Always cross-check the MTC data against the physical marking and the applicable specification. If a value seems unusual (for example, a tensile strength that is exactly at the minimum or maximum limit), request clarification from the mill.

Missing Data

Common omissions on MTCs include:

• Impact test results omitted when the PO requires low-temperature service qualification
• Hardness values missing for sour service materials (NACE MR0175 requires a maximum of 22 HRC)
• Heat treatment condition not stated or stated as “as-rolled” when the standard requires normalizing
• Carbon Equivalent (CE) not reported when the project specification requires a maximum CE for weldability
• Product analysis missing when the standard requires both heat (ladle) and product analysis (e.g., API 5L PSL2)

An incomplete MTC must be flagged as a non-conformance. The material should be placed on hold until the missing data is provided and verified.

Digital MTCs and Blockchain Traceability

Digital tools are beginning to replace paper-based MTC workflows:

Technology	Application
Blockchain-based MTCs	Immutable, tamper-proof records that cannot be altered after creation; each MTC is tied to a unique hash
Digital twin certificates	Each physical product linked to a unique blockchain record containing its full MTC data and chain of custody
QR/RFID linking	Physical products tagged with QR codes or RFID chips that link directly to the verified digital MTC
Smart contracts	Automated verification of material compliance before payment is released to the supplier
Cloud-based MTC platforms	Centralized repositories where mills upload certificates directly, eliminating the risk of intermediary tampering

Several major steel producers and industry consortia are piloting blockchain-based MTC systems. The benefits include eliminating fake certificates, reducing paperwork, enabling instant verification, and providing a complete chain of custody from melt to installation. Challenges include establishing industry-wide standards, maintaining secure physical-to-digital linking, and achieving regulatory acceptance. Adoption is growing steadily in critical supply chains (oil & gas, nuclear, aerospace).

Standards Reference

Standard	Title	Relevance to MTCs
EN 10204	Metallic products: Types of inspection documents	Defines certificate types 2.1, 2.2, 3.1, 3.2
ASME Section II	Materials	Material specifications and allowable stress values; referenced in MTCs for ASME code construction
ASME B31.3	Process Piping	Requires material certification for all pressure components
ASME B31.1	Power Piping	Mandates MTCs for boiler and power plant piping
NACE MR0175 / ISO 15156	Materials for use in H2S environments	Hardness, SSC/HIC testing requirements; heat-level traceability mandatory
PED 2014/68/EU	Pressure Equipment Directive	EU regulation requiring specific inspection and traceability for pressure equipment
API 5L	Line Pipe	Chemical, mechanical, and NDT testing requirements for line pipe; PSL1 vs PSL2 certification levels
API Q1	Quality Management System	Quality system requirements for API-licensed manufacturers
DNV-OS-F101	Submarine Pipeline Systems	Third-party witnessed testing requirements for subsea applications
NORSOK M-650	Qualification of Manufacturers	Qualification criteria for piping material manufacturers, including MTC requirements

Frequently Asked Questions

What does MTC stand for?

MTC stands for Mill Test Certificate. It is also referred to as a Mill Test Report (MTR), Material Test Certificate, or Material Test Report. All these terms refer to the same document: a certified record of a material's chemical and mechanical properties issued by the manufacturer. MTC is the preferred term in European and international projects; MTR is more common in North America.

What is the difference between EN 10204 Type 3.1 and Type 3.2?

Both EN 10204 Type 3.1 and Type 3.2 provide specific, heat-traceable test results for the supplied material. The key difference is that Type 3.2 requires an independent third-party inspector to witness the tests and co-sign the certificate, while Type 3.1 is validated solely by the manufacturer's own QA department (independent of production). Type 3.2 costs more and adds 2-4 weeks to the delivery schedule due to inspector coordination, but provides the highest level of material assurance. It is required for subsea, nuclear, HP/HT, and aerospace applications.

Is an MTC the same as a Certificate of Compliance (CoC)?

No. A Certificate of Compliance (CoC) is an EN 10204 Type 2.1 document, a simple declaration that products meet order requirements, with no test results. An MTC (Type 3.1 or 3.2) includes actual test data (chemical composition, tensile strength, hardness, impact values) for the specific heat supplied. For pressure-containing piping materials, an MTC is almost always required; a CoC alone is insufficient. The cost difference between a CoC and an MTC is marginal compared to the risk of installing non-conforming material.

What information must a mill test certificate contain?

An MTC must include: manufacturer name and address, product description, material specification and grade, heat/cast number, dimensions (OD, wall thickness, length), heat treatment condition, chemical composition (ladle analysis and/or product analysis), mechanical test results (tensile strength, yield strength, elongation, hardness), NDT results where applicable (hydrostatic test, UT, RT), EN 10204 certificate type designation, and authorized signatures. For Type 3.2, the third-party inspector's signature and stamp must also be present.

How long should mill test certificates be retained?

MTCs are part of the project data book and should be retained for the entire operational life of the equipment or piping system. The industry standard is a minimum of 25 years, though many operators retain them indefinitely. Digital storage and cloud-based archival systems have made long-term retention practical and cost-effective. In the event of an in-service failure or regulatory audit, having the original MTC is essential for root-cause analysis and liability determination.