MTC 3.1 vs 3.2 Certificate

Quick Answer: An MTC 3.1 certificate is issued and signed by the manufacturer’s authorized representative based on specific inspection of the delivered product. An MTC 3.2 certificate contains the same test data but is additionally validated and co-signed by an independent third-party inspector (TPI). The key difference is independent verification: 3.2 adds a layer of assurance that the test results were witnessed by an external body.

MTC 3.1 vs 3.2: Detailed Comparison

Both certificate types are defined by EN 10204 and contain test results from specific inspection—meaning the chemical analysis, mechanical properties, and any NDE results are traceable to the exact heat and lot delivered. The distinction lies in who verifies and signs the document.

Feature	EN 10204 Type 3.1	EN 10204 Type 3.2
Issued by	Manufacturer’s authorized QC representative	Manufacturer’s representative + independent TPI
Test basis	Specific inspection (actual delivered product)	Specific inspection (actual delivered product)
Chemical analysis	From specific heat (ladle analysis)	From specific heat (ladle analysis)
Mechanical properties	From specific lot/heat	From specific lot/heat
Heat traceability	Yes	Yes
Third-party witness	No	Yes; TPI witnesses testing and co-signs
Relative cost	Moderate	Higher (+15-30% for TPI coordination)
Lead time impact	+1-2 weeks for lab testing	+2-4 weeks (TPI scheduling + witnessing)
Common applications	Standard pressure piping, ASME B31.3	Sour service, subsea, nuclear, PED Cat. IV

When to Specify 3.1 vs 3.2

The choice between MTC 3.1 and 3.2 depends on the project’s risk level, applicable codes, and client specifications:

• 3.1 is sufficient for most onshore oil and gas projects, standard pressure piping per ASME B31.3, and commercial-grade piping components.
• 3.2 is required when the project specification, end client, or regulatory framework mandates independent witnessing. Typical cases include NACE MR0175 sour service, subsea pipelines (DNV/NORSOK), nuclear piping, and EU Pressure Equipment Directive Category III/IV.

Common Mistake

Specifying 3.2 certificates on every line item “just to be safe” is a costly error. TPI coordination adds 2-4 weeks to delivery and increases material cost. Reserve 3.2 for genuinely critical applications and use 3.1 for standard pressure piping. Review the project piping class index to determine which service classes truly require third-party witnessed certification.

Cost and Procurement Impact

Factor	Type 3.1	Type 3.2
TPI fee	None	Charged per inspection day or per heat
Scheduling	Manufacturer schedules testing internally	Must coordinate mill, lab, and TPI availability
Documentation	Single signature (manufacturer QC)	Dual signature (manufacturer QC + TPI)
Rejection handling	Retest arranged by manufacturer	Retest must be re-witnessed by TPI
Typical use in PO	”Certificates per EN 10204 Type 3.1"	"Certificates per EN 10204 Type 3.2 with TPI by [agency name]”

During pipe inspections, always verify that the certificate type matches the purchase order requirement. Accepting a 3.1 when the PO specifies 3.2 is a non-conformance that can delay shipment approval.

Read the full guide to mill test certificates