Hardness Testing in Mill Test Certificates (MTCs) for Stainless Steel Tubes

09/28/2025

Mr. Toey

Introduction

Mill Test Certificates (MTCs) are essential documents for stainless steel tubes, certifying that products comply with ASTM, ASME, EN, and JIS standards. Among the critical mechanical properties included, hardness values (Brinell, Rockwell, Vickers) are especially important for ensuring suitability in demanding applications like boilers and heat exchangers.

1. Hardness in MTCs

Location: Listed under the Mechanical Properties section.
Typical Representation:
- Brinell: HBW 10/3000 = 160
- Rockwell: HRB 85 / HRC 22
- Vickers: HV10 = 190
Example: ASTM A213 TP316L tubes typically specify maximum HBW 192.

2. Why Hardness Testing Appears in MTCs

Verify Heat Treatment: Ensures proper annealing or quenching.
Confirm Compliance: ASTM and EN standards specify hardness limits.
Guarantee Reliability: Prevents tube failures in high-pressure, high-temperature operations.

3. How to Interpret Hardness Data

Compare values with standard limits.
Cross-check with tensile and elongation data.
Note conversion tables (ASTM E140) when multiple scales appear.

4. DLSS Quality Control

At DLSS, hardness testing is mandatory before issuing MTCs:

Brinell (HBW): For thick-walled tubes and forgings.
Rockwell (HRB/HRC): For seamless tubes and fittings.
Vickers (HV): For thin-walled tubes, welds, and precision parts.

All MTCs from DLSS include accurate hardness values, ensuring customers receive products that meet both international standards and end-use requirements.

Conclusion

Hardness values in Mill Test Certificates are vital indicators of stainless steel tube quality. By reviewing Brinell, Rockwell, and Vickers results, engineers and inspectors can confirm product reliability and compliance.

DLSS provides detailed MTCs with transparent hardness data, reinforcing our commitment to quality assurance for global clients.