Steel Flange Types and Standards: ANSI, DIN, JIS, GB Complete Reference

Steel flanges are essential components in piping systems, providing connectable joints for pipes, valves, pumps, and other equipment. With multiple international standards governing flange dimensions, pressure ratings, and materials, selecting the right flange can be complex. This guide covers all major flange types and their specifications across ANSI, DIN, JIS, and GB standards.

1. Types of Steel Flanges

1.1 Weld Neck Flange (WN)

The most common flange for high-pressure and high-temperature applications. Features a long tapered hub that provides structural reinforcement at the weld joint. Used in critical piping systems for oil & gas, power plants, and chemical processing.

1.2 Slip-On Flange (SO)

Slides over the pipe and is welded both inside and outside. Lower cost than weld neck but limited to lower pressure applications. Suitable for water, air, and low-pressure steam lines.

1.3 Blind Flange (BL)

Solid disc with no bore, used to close off pipe ends, valves, or pressure vessel openings. Essential for pressure testing and system isolation.

1.4 Threaded Flange (TH)

Connects to pipes via internal threads — no welding required. Used where welding is impractical, such as explosive environments or small-bore instrumentation lines.

1.5 Socket Weld Flange (SW)

Similar to slip-on but with a counterbore for socket-weld connection. Provides better flow characteristics than threaded flanges. Common in small-diameter high-pressure piping.

1.6 Lap Joint Flange (LJ)

Used with a stub end for systems requiring frequent disassembly. The flange itself doesn’t contact the fluid, allowing use of cheaper flange material with expensive alloy stub ends.

2. Pressure Classes Comparison

3. Material Grades by Standard

4. Dimensional Standards Overview

• ANSI/ASME B16.5: Covers NPS ½ to 24, Classes 150-2500. The dominant standard in Americas and Middle East.
• ANSI/ASME B16.47: Covers NPS 26 to 60, Classes 75-900. For large-diameter piping.
• EN 1092-1: European standard covering PN 2.5-400, DN 10-4000. Replaces DIN 2501 series.
• JIS B2220: Japanese standard covering 5K-40K classes, 10A-600A sizes.
• GB/T 9112-9124: Chinese national standard, largely harmonized with EN 1092-1.

5. Selection Guidelines

• Match the standard: Use the standard specified in your piping design — mixing standards causes fit-up problems
• Pressure rating: Always select flanges rated for the maximum operating pressure plus safety margin
• Material compatibility: Flange material should match or exceed pipe material grade
• Gasket surface: Raised face (RF) is standard; flat face (FF) for low-pressure cast iron systems
• Bolt specification: Ensure bolt material is compatible with flange material and service environment

Conclusion

Steel flanges are critical components that require careful specification. Understanding the differences between ANSI, DIN, JIS, and GB standards helps you source the right flanges for any piping system, regardless of the design origin. CoreMetal supplies carbon steel and stainless steel flanges to all major international standards — send us your specifications for competitive pricing.