GB Standard Forged Steel Pipe Flanges

Product Description

GB Standard Forged Steel Pipe Flanges are manufactured according to Guobiao (Chinese National Standards) for pressure piping, power plants, oil refineries, and municipal fluid systems. The framework harmonizes both European metric (PN series) and American imperial (Class series) dimensioning systems into a unified national standard.

1. Governing GB Standards

Chinese national flange specifications are consolidated under comprehensive standards covering materials, pressure-temperature ratings, and dimensions:

• GB/T 9124.1: Steel pipe flanges - Part 1: PN designated series (European metric framework).

• GB/T 9124.2: Steel pipe flanges - Part 2: Class designated series (American ASME B16.5 framework).

• GB/T 9112 to GB/T 9123: Individual dimensional standards for specific flange types (e.g., GB/T 9115 for Weld Neck, GB/T 9123 for Blind).

• HG/T 20592 & HG/T 20615: Chemical Industry Standards (HG) widely specified alongside GB standards for petrochemical plants.

2. GB Flange Structural Types & Letter Codes

GB standards utilize specific two-letter alphabetical codes to identify flange structural configurations:

3. Sealing Face Configurations (GB Standard)

GB standards use letter designations for flange sealing face profiles:

• RF (Raised Face): Concentric serrated raised seating area; standard for general industrial service.

• FF (Flat Face): Entire face is machined flat; used when mating against fragile or cast iron equipment.

• FM / M (Female / Male Face): Matched recessed and raised step set to retain gaskets under pressure.

• TG / T (Tongue / Groove Face): Interlocking groove joint preventing lateral gasket displacement.

• RJ (Ring Joint): Machined metallic annular groove for solid metal ring gaskets in high-pressure service.

4. Pressure Ratings & Dimensional Systems

GB standards accommodate both global piping philosophies within one specification:

PN Series (Metric / European Origin)

• Pressure Ratings: PN 2.5, PN 6, PN 10, PN 16, PN 25, PN 40, PN 63, PN 100, PN 160.

• Nominal Sizes: DN 10 through DN 2000.

Class Series (Imperial / ASME Origin)

• Pressure Ratings: Class 150, Class 300, Class 600, Class 900, Class 1500, Class 2500.

• Nominal Sizes: DN 15 ($NPS \ 1/2$) through DN 600 ($NPS \ 24$).

5. Standard GB Material Specifications

Forged steel materials for GB flanges correspond directly to international carbon, alloy, and stainless steel grades: