Flange Gasket

1. Core Function and Application Scenarios of Flange Gaskets

1) Core Function

A flange gasket is a static sealing component installed between two flange faces. By applying bolt preload, the gasket is compressed to achieve sealing, with the following purposes:

• Prevent leakage of the medium
• Compensate for machining and installation tolerances of flanges
• Isolate the medium from the external environment or surrounding equipment

In essence: Rubber elasticity and resilience are used to maintain long-term sealing contact stress.

2) Major Application Industries

2. Sealing Mechanism of Flange Gaskets (Engineering Perspective)

Three Key Conditions for Effective Sealing

1)      Initial Sealing Stress

Ÿ  Bolt tightening compresses the gasket

Ÿ  The gasket fills microscopic flange surface irregularities

2)      Long-Term Stress Retention

Ÿ  The gasket must exhibit low CSR (Compression Stress Relaxation) and low compression set

3)      Medium and Temperature Stability

Ÿ  No excessive swelling, softening, hardening, or cracking

Many leakage problems are not caused by “wrong material selection,” but by
excessive stress relaxation of the rubber compound.

3. Common Flange Gasket Designs

1) Flat / Ring-Type Gasket

• Most widely used type
• Typically applied to Raised Face (RF) flanges
• Low cost and easy installation

2) Full Face Gasket

• Covers the entire flange surface
• Commonly used for cast iron flanges or low-pressure systems
• Provides cushioning at bolt holes

3) Gaskets with Locating or Special Structures

• Inner/outer diameter limiting designs
• Prevent extrusion and misalignment
• Suitable for higher pressure or frequent disassembly applications

4. Rubber Materials and Selection Logic for Flange Gaskets

1) Common Rubber Materials Comparison

For drinking water flange gaskets, EPDM is almost the industry standard.

2) Practical Three-Step Selection Method

1. Medium first → Temperature → Pressure
2. Check regulatory requirements (NSF 61, FDA, WRAS, etc.)
3. Cost optimization comes last

5. Key Performance Indicators (More Important Than Hardness)

1) Compression Set

• Directly determines sealing service life
• Recommended target:
• EPDM for water applications: ≤25% (70°C × 24 h)

2) Compression Stress Relaxation (CSR)

• The most critical parameter for flange gaskets
• Determines whether leakage occurs after 3, 5, or 10 years

3) Volume Change

• After immersion in water, oil, or chemicals
• Typical requirement: ±5–10%

4) Property Retention After Aging

• Heat aging and ozone aging
• Hardness change and tensile strength retention

6. Common Failure Modes (Frequently Seen in Factories and at Customer Sites)