Flange gaskets, as the core sealing components in flange connections, are undeniably critical to system integrity. These circular ring-shaped materials, capable of plastic deformation while maintaining structural strength, work in conjunction with flanges and fasteners to ensure leak-proof connections and reliable sealing between pipelines, valves, and equipment. Despite their importance,gasketselection is often overlooked during design and application. This article comprehensively examines the classification, standardization, and selection criteria of flange gaskets, emphasizing their indispensable role in industrial systems.

1. Classification of Gasket Materials and the National Standard System
Gasket materials are vital to sealing performance and can be categorized into three groups: metallic, non-metallic, and metal-nonmetal composites. Each type has distinct properties and must comply with national standards to ensure reliability.

1.1 Gasket Classification by Material
Gaskets are classified into four primary categories based on composition:

Non-metallic: Rubber, asbestos rubber sheets, non-asbestos fiber rubber sheets, and polytetrafluoroethylene (PTFE) sheets.

Semi-metallic: Spiral-wound gaskets and toothed composite gaskets.

Metallic-coated: A hybrid category combining metal and non-metal layers.

Metallic: Solid metal ring gaskets (e.g., octagonal or elliptical rings) for high-pressure flange sealing.

1.2 National Standard System for Gaskets
In 2019, China consolidated 13 flange standards (GB/T 91129124-2010) into two new systems:

European (PN series)

American (Class series)

This reform also impacted gasket standards, shifting from traditional sizing guidelines to a performance-based framework. Key current standards include:

GB/T 13403-2008: Large-diameter steel pipe flange gaskets

GB/T 13404-2008: Non-metallic PTFE-coated gaskets

GB/T 15601-2013: Metallic-coated gaskets

GB/T 19066-2020: Metallic wave-tooth composite gaskets

GB/T 19675-2005: Metallic toothed plate flexible graphite gaskets

GB/T 4622-2022: Spiral-wound gaskets

GB/T 9128-2003: Metallic ring gaskets

These standards ensure uniformity in material properties, dimensions, and testing methods.

2. National Standard Flange Gaskets: Types and Applications
2.1 Non-Metallic Gaskets
Materials: Rubber, asbestos rubber, non-asbestos fiber rubber, and PTFE.
Applications: Compatible with flat, raised, grooved (tongue-and-groove), and concave-convex sealing surfaces.

2.2 PTFE-Coated Gaskets
Structure: A PTFE outer layer bonded to an inner core (asbestos rubber, fluororubber, or EPDM).
Types: A (standard), B (integral positioning ring), and C (adjustable ring).
Use Case: Ideal for raised-face flanges but unsuitable for vacuum or corrosive media.

2.3 Spiral-Wound Gaskets
Design: V-shaped/W-shaped metal strips (stainless steel) with non-metallic fillers (graphite, PTFE).
Advantages: Elasticity and compression recovery for high-pressure systems.
Applications: Small-diameter flanges; one of the four most widely used gasket types.

2.4 Metallic Toothed Composite Gaskets
Features: Concentric grooves create line contact, generating high localized stress for superior sealing.
Variants:

Type A: For tongue-and-groove or concave-convex flanges.

Type B/C: For flat/raised faces with fixed/adjustable positioning rings.

2.5 Metallic Wave-Toothed Composite Gaskets
Structure: Metal framework with graphite/PTFE layers.
Benefits: Combines rigidity (metal) with flexibility (graphite); resists crushing.
Temperature Limit: ?450C for graphite layers.

2.6 Flexible Graphite Metal-Reinforced Gaskets
Types:

A (Basic): Raised-face flanges.

B (Inner Flange): Concave-convex flanges.

C (Inner/Outer Flange): Tongue-and-groove flanges.

2.7 Metallic-Coated Gaskets
Construction: 0.30.5 mm metal shell with flexible graphite/asbestos/PTFE filler.
Types: Flat (Code F) and corrugated (Code C) for recessed sealing faces.

2.8 Large-Diameter Flange Gaskets
Standards: GB/T 13403-2008 for oil, water, and nuclear cooling pipelines.
Recommendations: Use raised-face seals with spiral-wound or ring gaskets in critical applications.

2.9 O-Ring and Metal Ring Gaskets
O-Rings: Selected per GB 3452 for dynamic seals.

Metal Rings: Octagonal/elliptical shapes for high-pressure joint connections.

3. Key Selection Guidelines
Fluid and Operating Conditions: Consider pressure, temperature, and chemical compatibility.

Flange Surface: Roughness and geometry must match the gasket type.

Material Limits:

Avoid PTFE-coated gaskets in vacuums or corrosive environments.

Limit flexible graphite to ?450C; rubber to ?80C.

Low-Pressure Systems (PN < 16): Prefer spiral-wound, metallic-coated, or ring gaskets for welded flanges.

Conclusion
Flange gaskets are pivotal to sealing performance, and their selection requires careful evaluation of materials, standards, and operational demands. By adhering to national guidelines and understanding each gaskets unique properties, engineers can ensure system safety and longevity.