What Are MTRs? How to Read Stainless Steel Certifications

What Are MTRs? How to Read and Verify Stainless Steel Certifications

A Mill Test Report (MTR) is an essential document that verifies the chemical composition, mechanical properties, heat number, and manufacturing details of stainless steel components. In sanitary processing—where material integrity and traceability are critical—MTRs provide the assurance that fittings, tubing, and other components meet required standards such as ASTM A270 or ASME BPE.

This guide explains what an MTR includes, how to read one, and why it matters in hygienic applications.

What Is an MTR?

An MTR (Mill Test Report)—also called a Material Test Report or Certified Mill Test Certificate—is a quality assurance document issued by the stainless steel manufacturer. It validates that the material supplied meets the chemical and mechanical requirements of the specified grade.

An MTR typically certifies stainless steel to standards such as:

• ASTM A270 (sanitary tubing)
• ASTM A240 (plate/sheet for fittings)
• ASME BPE (pharmaceutical tubing and fittings)

MTRs are part of the traceability chain that ensures materials are safe, compliant, and suitable for hygienic processing environments.

Why MTRs Matter in Sanitary Processing

MTRs are vital for applications where material integrity directly affects product quality and regulatory compliance. Key reasons include:

• Verification of alloy type (e.g., 304 vs 316L)
• Chemical composition confirmation to prevent corrosion or contamination
• Traceability from finished component to raw material heat
• Regulatory compliance for FDA, 3-A, or ASME BPE requirements
• Quality assurance for audits or customer documentation

For industries like dairy, brewing, food processing, biotech, and pharmaceuticals, MTRs are often part of standard procurement and validation procedures.

Key Sections of an MTR

An MTR generally includes several critical pieces of information. Here's how to interpret them:

1. Material Specification

This section lists the grade and standard of the stainless steel, such as:

• ASTM A270 316L
• ASTM A240 304
• ASME SA-479 316L

This verifies the intended specification for tubing, fittings, or plate.

2. Heat Number

The heat number is a unique identifier tied to the batch of molten steel used to produce the material. It enables full traceability back to the melt and chemical analysis.

Heat numbers are often stamped or etched on tubing or fitting components.

3. Chemical Composition

This table shows the laboratory-tested percentages of key alloying elements, typically including:

• Chromium (Cr)
• Nickel (Ni)
• Molybdenum (Mo)
• Carbon (C)
• Manganese (Mn)
• Silicon (Si)
• Phosphorus (P)
• Sulfur (S)

For example, 316L stainless will show:

• Cr: 16–18%
• Ni: 10–14%
• Mo: 2–3%
• C: ≤ 0.03%

If chemical values fall outside the specified range, the material does not meet the standard.

4. Mechanical Properties

MTRs also include mechanical property tests, such as:

• Tensile strength
• Yield strength
• Elongation
• Hardness

These properties indicate how the material will perform under stress, pressure, or vibration.

5. Heat Treatment / Processing

Sanitary stainless components are often bright annealed, which restores corrosion resistance and produces a clean, scale-free interior surface. The MTR may note:

• Annealing furnace type
• Annealing temperature or process notes
• Passivation information

6. Compliance Certifications

MTRs often include statements of compliance such as:

• “Meets ASTM A270 requirements”
• “Material conforms to ASME BPE-BM”
• “All chemical composition values within specification limits”

These confirm that the material has been verified against the specified standard.

How to Verify an MTR

To ensure an MTR is valid and accurate, follow these steps:

• Match the heat number on the MTR to the number stamped on the part.
• Verify the chemical composition against the standard.
• Check alloy designation (304 vs 316L) for process compatibility.
• Inspect mechanical property values for anomalies.
• Ensure dimensional tolerances match ASTM A270 or A240 as needed.

For high-criticality applications, PMI (Positive Material Identification) using XRF can confirm chemistry matches the MTR.

Why MTRs Are Requested by Many Facilities

Depending on industry and audit requirements, MTRs may be required for:

• Pharmaceutical or biotech validation
• FDA or 3-A compliance documentation
• New equipment commissioning
• Quality audits and traceability programs
• Warranty or vendor qualification

Even when not explicitly required, many engineering teams request MTRs to ensure consistent sourcing and avoid accidental introduction of incorrect alloys.

How to Request an MTR for a Previous Order

If you need an MTR for stainless steel tubing or fittings purchased from PNW Sanitary, you can request it anytime through our Help Center. Simply provide your order number and the specific items requiring certification.

Click here to request an MTR for a past order.

Need MTRs for Your Sanitary Components?

PNW Sanitary provides MTRs for select stainless steel tubing and fittings upon request. Whether you need certification for 304, 316L, ASTM A270, or ASME BPE-compliant materials, our team can help you obtain the correct documentation.

If you have questions about reading MTRs, verifying alloy compatibility, or selecting the right components for your system, we’re here to help.