Material Certifications Explained: MTRs, CoCs, and Traceability

Material certifications answer a simple question: “How do I know this is really what you say it is?”

In industries where material failures create safety hazards, liability exposure, or regulatory violations, verbal assurance isn’t enough. Formal documentation establishes material identity, verifies properties, and creates traceability from mill to finished product.

This guide explains the documentation you may need, what each document contains, and when different certification levels are appropriate.

Types of Material Documentation

Mill Test Report (MTR) / Mill Certificate

An MTR (also called a Mill Test Certificate, Mill Cert, or MTC) is the primary document proving material identity and properties. It’s generated by the material producer (mill, foundry, or manufacturer) and travels with the material through distribution.

What an MTR contains:

Section	Information
Material Identification	Specification (ASTM, AMS, SAE), grade, temper/condition
Heat/Lot Number	Unique identifier linking to production batch
Chemistry	Actual chemical composition vs. specification limits
Mechanical Properties	Test results: tensile, yield, elongation, hardness
Dimensions	Form, size, quantity
Mill Information	Producer name, location, test date
Certifications	Applicable standards, special certifications

What makes an MTR valuable:

• Chemical analysis proves alloy composition
• Mechanical testing proves material properties
• Heat number enables traceability to production batch
• Third-party verification possible by testing against stated heat

Certificate of Compliance (CoC) / Certificate of Conformance

A Certificate of Compliance is a statement from a supplier (distributor, processor, or manufacturer) that material conforms to specified requirements. Unlike an MTR, a CoC doesn’t contain actual test data—it’s a declaration of conformance.

CoC typically states:

• Material specification and grade
• That material meets specification requirements
• Reference to supporting documentation (MTR, test reports)
• Supplier signature and date

CoC vs. MTR: A CoC is only as credible as the supplier providing it. Without underlying test data, you’re trusting the supplier’s word. A CoC backed by MTR data provides verification; a standalone CoC requires supplier trust.

Test Report

A test report documents testing performed after material leaves the mill—typically by an independent laboratory or the end-user’s quality organization.

Common test report scenarios:

• Verification testing when MTR is unavailable
• Additional testing beyond MTR data (impact, corrosion, etc.)
• Receiving inspection results
• Customer-witnessed testing

Certificate of Analysis (CoA)

Similar to an MTR but typically used for chemicals, polymers, and processed materials where “heat number” doesn’t apply. Contains lot identification, composition, and relevant test data.

Understanding MTR Content

Chemical Composition

The chemistry section shows actual measured composition versus specification limits. For example, an MTR for 316 stainless steel might show:

Element	Spec Min	Spec Max	Actual
Carbon	-	0.08%	0.042%
Chromium	16.0%	18.0%	17.2%
Nickel	10.0%	14.0%	11.8%
Molybdenum	2.0%	3.0%	2.34%

All actual values must fall within specification ranges. Values outside limits indicate non-conforming material.

Mechanical Properties

Mechanical testing results demonstrate the material meets strength requirements:

Property	Spec Min	Actual
Tensile Strength	75,000 psi	84,200 psi
Yield Strength (0.2%)	30,000 psi	42,100 psi
Elongation	40%	52%

Values must meet or exceed minimums (or fall within ranges if both min and max specified).

Heat Number / Lot Number

The heat number uniquely identifies the production batch. This number enables:

• Traceability from final part back to raw material source
• Recall identification if problems emerge
• Correlation of your material to mill production records
• Independent verification by testing your material against stated heat

Traceability chain: Mill heat number → Distributor lot → Your receiving documentation → Part serial number

When You Need Certifications

Always Require MTR

• Safety-critical applications: Aerospace, pressure vessels, lifting equipment, medical devices
• Regulated industries: Nuclear, defense, oil and gas, FDA-regulated products
• Customer specifications requiring traceability
• Quality system requirements: AS9100, ISO 13485, NADCAP
• High-value components: Where material failure is costly
• Liability exposure: Products where failure causes injury or property damage

CoC May Be Sufficient

• Non-critical applications: Fixtures, tooling, general commercial products
• Low liability exposure: Failure doesn’t create safety or major cost issues
• Trusted suppliers: Long-term relationships with verified quality systems
• Cost-sensitive procurement: When MTR cost premium isn’t justified

No Documentation Needed

• Prototype/development work: When material specifics don’t matter yet
• General commercial use: Standard fasteners, non-critical components
• Disposable items: Low-cost parts where replacement is easier than documentation

Verification and Authentication

Is This MTR Legitimate?

Material fraud exists—counterfeit materials with falsified documentation. For critical applications, consider:

Review for completeness Legitimate MTRs include all specification-required data. Missing sections suggest problems.

Check specification compliance Verify all values fall within specification limits. MTRs showing exact specification limits (instead of actual test values) are suspicious.

Verify mill identity Is the mill a recognized producer of this material? Unknown mills warrant investigation.

Cross-reference heat numbers For repeat purchases, verify heat numbers are unique (not duplicated across purchases).

Independent testing For highest-criticality applications, send samples for independent lab testing. Results should align with MTR data.

Positive Material Identification (PMI)

PMI uses portable XRF (X-ray fluorescence) or OES (optical emission spectroscopy) analyzers to verify alloy chemistry in-house. PMI can:

• Verify incoming material matches MTR
• Identify mixed or substituted material
• Provide receiving inspection confidence

PMI doesn’t replace MTRs (it doesn’t verify mechanical properties) but confirms chemistry quickly and non-destructively.

Industry-Specific Requirements

Aerospace (AS9100, NADCAP)

• MTR required for flight-critical materials
• Full traceability from raw material to finished part
• Approved supplier lists for material sources
• Shelf life management for age-sensitive materials
• Flow-down of requirements to sub-tier suppliers

Medical Devices (ISO 13485, FDA)

• Material traceability required for implants and Class III devices
• Biocompatibility documentation (ISO 10993)
• Lot history records maintained
• Supplier qualification and monitoring

Pressure Equipment (ASME, PED)

• MTR required per ASME Section II
• Impact testing at design temperature
• Heat treatment documentation
• Welding procedure and welder qualifications

Oil and Gas (API, NACE)

• MTR with chemistry and mechanical properties
• NACE compliance for sour service materials
• Heat treatment records
• Hardness verification

Practical Procurement Tips

Specify Requirements Upfront

Include documentation requirements in RFQs:

• “MTR required traceable to mill heat number”
• “Certificate of Compliance to [specification]”
• “Independent lab testing per [standard]”

Avoid surprises by establishing requirements before ordering.

Budget for Documentation

MTR materials cost more than commercial grades—typically 5-20% premium depending on material and market conditions. The cost covers:

• Mill testing and certification
• Lot segregation and traceability
• Documentation handling
• Typically higher-quality material

Verify at Receiving

Don’t file documentation without review:

• Confirm material marking matches MTR
• Verify heat/lot numbers align
• Check specification compliance
• Note any anomalies before acceptance

Maintain Records

Keep material documentation for:

• Product liability protection
• Customer audit support
• Recall/traceability needs
• Warranty claims

Retention periods vary by industry—aerospace often requires permanent retention; others may specify 7-10 years.

Working With NextGen Components

We provide appropriate documentation with every order:

Standard: Certificate of Compliance confirming material specification With MTR: Full mill test report traceable to heat/lot number Specialty: Additional testing, certifications, or documentation per customer specification

Material certifications add cost but provide value when needed. We help customers determine appropriate documentation levels—avoiding over-specification that wastes money while ensuring critical applications get proper traceability.

Questions about documentation requirements? Contact us to discuss your specific needs.