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—the mill, foundry, or manufacturer—and travels with the material through distribution.

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 is the hard data it contains. Chemical analysis proves the alloy composition matches the specification. Mechanical testing proves the material meets strength requirements. The heat number enables traceability back to the exact production batch. And third-party verification is possible because anyone can test your material against the stated heat to confirm authenticity.

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.

A typical CoC states the material specification and grade, declares that the material meets specification requirements, references supporting documentation like MTRs or test reports, and includes the supplier’s signature and date.

The critical distinction between a CoC and MTR is trust. 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 real verification; a standalone CoC requires you to trust your supplier’s quality system and integrity.

Test Report

A test report documents testing performed after material leaves the mill—typically by an independent laboratory or your own quality organization. Common scenarios include verification testing when an MTR is unavailable, additional testing beyond what the MTR covers (impact testing, corrosion testing, etc.), receiving inspection results, and customer-witnessed testing for critical applications.

Certificate of Analysis (CoA)

Similar to an MTR but typically used for chemicals, polymers, and processed materials where “heat number” doesn’t apply. A CoA contains lot identification, composition, and relevant test data specific to the material type.

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 that should be rejected or require deviation approval.

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 are specified). Note that actual values typically exceed minimums by a comfortable margin—material that just barely meets spec often indicates marginal quality control.

Heat Number / Lot Number

The heat number uniquely identifies the production batch. This number enables traceability from your final part back to the raw material source, recall identification if problems emerge later, correlation of your material to mill production records, and independent verification by testing your material against the stated heat.

The traceability chain flows from mill heat number to distributor lot to your receiving documentation to the part serial number on the finished component.

When You Need Certifications

Always Require MTR

Certain applications demand full MTR documentation. Safety-critical applications like pressure vessels, lifting equipment, and structural components require traceable material. Regulated industries including oil and gas equipment and pressure equipment mandate MTRs by code. Customer specifications often require traceability as a contractual obligation. Quality system requirements under ISO 9001 often specify certified suppliers. High-value components where material failure is costly justify the MTR premium. And any product where failure causes injury or property damage creates liability exposure that MTRs help address.

CoC May Be Sufficient

For many applications, a Certificate of Compliance provides adequate assurance at lower cost. Non-critical applications like fixtures, tooling, and general commercial products rarely justify MTR costs. Low liability exposure situations where failure doesn’t create safety or major cost issues can rely on CoCs. Long-term relationships with trusted suppliers who have verified quality systems provide confidence without MTR documentation. And cost-sensitive procurement where MTR premiums aren’t justified by risk reduction makes CoCs the practical choice.

No Documentation Needed

Some situations don’t warrant formal documentation at all. Prototype and development work where material specifics don’t matter yet, general commercial use with standard fasteners and non-critical components, and disposable items where replacement is easier than documentation all fall into this category.

Verification and Authentication

Is This MTR Legitimate?

Material fraud exists—counterfeit materials with falsified documentation do enter supply chains. For critical applications, take steps to verify authenticity.

Review for completeness first. Legitimate MTRs include all specification-required data. Missing sections suggest the document was fabricated by someone who didn’t understand what’s required.

Check specification compliance by verifying all values fall within specification limits. MTRs showing exact specification limits instead of actual test values are suspicious—real test results almost never land exactly on spec limits.

Verify mill identity by confirming the mill is a recognized producer of this material. Unknown mills warrant investigation before acceptance.

Cross-reference heat numbers for repeat purchases to verify heat numbers are unique. Seeing the same heat number across multiple purchases suggests someone is copying documents.

For highest-criticality applications, send samples for independent lab testing. Results should align with MTR data within normal measurement variation.

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 the MTR, identify mixed or substituted material, and provide receiving inspection confidence without waiting for lab results.

PMI doesn’t replace MTRs because it doesn’t verify mechanical properties—but it confirms chemistry quickly and non-destructively, which catches the most common substitution errors.

Industry-Specific Requirements

Pressure Equipment (ASME)

ASME Section II requires MTRs for pressure-retaining materials. You’ll also need impact testing at design temperature for low-temperature service, heat treatment documentation showing actual time and temperature cycles, and welding procedure and welder qualifications for fabricated components.

Oil and Gas (API, NACE)

Oil and gas applications require MTRs with chemistry and mechanical properties as baseline documentation. Sour service materials need NACE compliance documentation. Heat treatment records and hardness verification are standard for most wellhead and downhole components.

Practical Procurement Tips

Specify Requirements Upfront

Include documentation requirements in RFQs to avoid surprises. Specify exactly what you need: “MTR required traceable to mill heat number” or “Certificate of Compliance to [specification]” or “Independent lab testing per [standard].” Establishing requirements before ordering prevents disputes about documentation charges later.

Budget for Documentation

MTR materials cost more than commercial grades—typically 5-20% premium depending on material and market conditions. This premium covers mill testing and certification, lot segregation and traceability systems, documentation handling through the supply chain, and generally higher-quality material (mills that certify tend to produce better product).

Verify at Receiving

Don’t file documentation without review. Confirm material marking matches the MTR, verify heat/lot numbers align between marking and paperwork, check specification compliance against limits, and note any anomalies before acceptance. A few minutes of verification prevents major problems later.

Maintain Records

Keep material documentation for product liability protection, customer audit support, recall and traceability needs, and warranty claims. Retention periods vary by industry—aerospace often requires permanent retention while other industries may specify 7-10 years minimum.

Working With NextGen Components

We provide appropriate documentation with every order. Standard orders include a Certificate of Compliance confirming material specification. Orders requiring MTRs receive full mill test reports traceable to heat/lot number. Specialty requirements including additional testing, certifications, or documentation per customer specification are available on request.

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.