Flange Markings – How to Read and Understand Them Accurately

Tác giả: Administrator
Ngày cập nhật: 03 February 2026
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Steel flanges are essential components in industrial piping systems. To select the correct flange for each application, users must understand the markings engraved or stamped on the flange surface. These markings indicate technical specifications such as standard, material, size, pressure rating, and other critical data.

Sunjin Metals Vina (SJM Vina) will guide you through the most common flange markings and how to read them properly for safe and effective usage.

                                                              


1. Manufacturing Standard

The first marking typically shows the manufacturing standard. Common examples include:

  • ANSI B16.5 – American standard

  • JIS 10K – Japanese standard

  • DIN 2576 – European (German) standard

Example:
The marking “ANSI B16.5” indicates the flange is produced according to American standards, suitable for heavy industries like oil & gas.


2. Flange Type

Flanges come in several types, each with specific abbreviations:

  • WN: Welding Neck Flange

  • SO: Slip-On Flange

  • BL or BLIND: Blind Flange

  • TH: Threaded Flange

  • SW: Socket Weld Flange

Example:
A flange marked “SO” refers to a Slip-On type, commonly used in medium-pressure piping systems for easier installation.


3. Nominal Diameter (DN or NPS)

  • DN: Nominal diameter in millimeters (e.g., DN50, DN100)

  • NPS: Nominal Pipe Size in inches (e.g., NPS 2", NPS 4")

Example:
The marking “DN100” means the flange is designed for a 100 mm nominal pipe size (approximately 4 inches).


4. Pressure Rating

Pressure rating depends on the applied standard:

  • ANSI: Class 150, 300, 600...

  • JIS: 5K, 10K, 16K...

  • DIN: PN10, PN16, PN40...

Example:
The marking “CLASS 300” indicates the flange is rated for 300 psi (~20.7 bar) under standard conditions.


5. Material

Flanges are made from various materials, each with a specific marking:

  • A105: Carbon steel – widely used in general industries

  • 304/316: Stainless steel – for food, chemical, and clean environments

  • F11, F22: Alloy steel – suitable for high-temperature applications

Example:
A flange marked “A105” is made from carbon steel, ideal for water, gas, steam, and oil lines.


6. Year of Manufacture and Manufacturer’s Mark

Many flanges include:

  • Year of production (e.g., “2024”)

  • Manufacturer abbreviation (e.g., “SJM”)

Example:
A flange with the marking “SJM 2024” was manufactured by Sunjin Metals Vina in 2024.


7. Additional Markings

  • HEAT NO: Heat number – used for material traceability

  • LOT NO: Lot number – identifies the production batch

  • MTC: Refers to Mill Test Certificate availability

These markings are essential for quality assurance and certification in critical projects.


Conclusion

Correctly reading and understanding flange markings helps:

  • Ensure proper product selection

  • Avoid installation errors and safety risks

  • Improve system reliability and compliance


Sunjin Metals Vina – Supplying Certified Flanges with Full Markings

At Sunjin Metals Vina (SJM Vina), we provide a full range of JIS, ANSI, and DIN standard flanges with complete markings, technical drawings, and quality certificates.

  • Flange types: WN, SO, BL, TH, SW

  • Materials: A105, SS400, Stainless Steel 304/316

  • Sizes from DN15 to DN600

  • Documentation: CO, CQ, MTC, Drawings available upon request

Address: 628 Le Hong Phong, Ward 10, District 10, Ho Chi Minh City, Vietnam
Hotline: +84 33 4233 127
Email: sjmvina@sunjinmetal.com
Website: www.sjmvina.com.vn

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Sunjin Metals Vina (SJM Vina)

Add: 628 Lê Hồng Phong, Vuon Lai Ward, Ho Chi Minh City, Vietnam

Hotline: +84 33 4233 127

Email: sjmvina@sunjinmetal.com

Tax Code: 0315448500

Website: sjmvina.com.vn

         

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