A flange gasket is an elastic material installed between the sealing surfaces of two flanges, used to fill uneven surfaces and prevent fluid or gas leakage. Its function is to withstand pressure, temperature fluctuations, and medium corrosion, ensuring the integrity of the sealing system.
Types of Flange Gaskets and Detailed Introduction
Non-Metallic Gaskets
Materials: Rubber, graphite, PTFE (polytetrafluoroethylene), non-asbestos fiber (NAF), etc.
Characteristics: Good flexibility, low cost, suitable for low-pressure and low-temperature environments.
Rubber Gasket
- Materials: Natural rubber, nitrile rubber (NBR), EPDM, etc.
- Applications: Water, air, and other non-corrosive media; generally for temperatures <100°C.
PTFE Gasket
- Properties: Resistant to strong acids and alkalis, chemically inert, but prone to cold flow (permanent deformation).
- Forms: Pure PTFE sheet, filled/modified PTFE (e.g., with glass fiber).
Graphite Gasket
- Properties: High-temperature resistance (up to 500°C+), self-lubricating, but low strength.
- Applications: High-temperature steam, hot oil systems.
Non-Asbestos Gasket
- Features: Environmentally friendly and safe alternative to traditional asbestos, made of fiber and rubber composites.
Semi-Metallic Gaskets
Structure: Non-metallic core material + metal reinforcement, balancing flexibility and strength.
Spiral Wound Gasket
- Structure: Alternating layers of metal strips (e.g., 304 stainless steel) and graphite/PTFE, with optional inner/outer rings.
- Advantages: Excellent elasticity, high pressure/temperature resistance (up to 800°C), widely used in petroleum and chemical industries.
- Types:
- With inner ring (prevents media erosion inside the gasket).
- With outer ring (enhances positioning and pressure resistance).
Metal Jacketed Gasket
- Structure: Non-metallic core (e.g., graphite) wrapped in a thin metal sheet (e.g., stainless steel).
- Applications: Medium-to-high-pressure pipelines, corrosion-resistant media.
Metallic Gaskets
Materials: Pure metal (copper, aluminum, stainless steel, titanium, etc.), used in extreme conditions.
Ring Joint Gasket (RTJ)
- Shape: Oval or octagonal cross-section, fits into a machined groove in the flange.
- Applications: High-pressure and high-temperature systems (e.g., API 6A valves, wellheads).
Serrated Gasket
- Structure: Concentric serrations on the metal surface; sealing is achieved by deformation under compression.
- Advantages: High-pressure resistance but requires significant bolt preload.
Corrugated Metal Gasket
- Features: Thin corrugated metal sheet with good elasticity, suitable for heat exchanger flanges.
How to Select the Right Flange Gasket?
Selection Process:
Confirm media, temperature, and pressure → 2. Match flange type → 3. Select gasket material → 4. Verify bolt load → 5. Consider cost and maintenance.
1. Determine Key Operating Parameters
(1) Media Properties
Corrosivity: Strong acids/alkalis/solvents require chemically resistant materials (e.g., PTFE, graphite).
Toxicity/Hazard: Flammable/toxic media (e.g., hydrogen, H₂S) demand zero-leakage gaskets (e.g., metal RTJ).
Cleanliness: Food/pharmaceutical industries require FDA-approved materials (e.g., silicone, PTFE).
(2) Temperature Range
Cryogenic (<-50°C): Use cold-resistant rubber (e.g., FKM) or PTFE.
Moderate (-50°C to 200°C): Rubber or non-asbestos fiber gaskets.
High (200°C–800°C): Graphite spiral wound or metallic gaskets (e.g., stainless steel RTJ).
Ultra-high (>800°C): Special alloys (e.g., Inconel) or flexible graphite composites.
(3) Pressure Rating
Low (<150 psi/10 bar): Non-metallic gaskets (rubber, non-asbestos).
Medium (150–1000 psi/10–70 bar): Semi-metallic gaskets (spiral wound, metal jacketed).
High (>1000 psi/70 bar): Metallic gaskets (RTJ, serrated).
(4) Flange Standards and Sealing Face Types
| Flange Type | Suitable Gasket | Example Applications |
| Flat Face (FF) | Soft gaskets (rubber, PTFE) | Low-pressure water/air pipes |
| Raised Face (RF) | Spiral wound/metal jacketed | Chemical/oil pipelines (PN16–40) |
| Ring Joint (RTJ) | Metal ring gaskets (oval/octagon) | High-pressure valves (API 6A) |
| Tongue & Groove (T/G) | Metal serrated/PTFE-filled | High-purity gas/vacuum systems |
2. Select Gasket Type Based on Material Properties
Non-Metallic Gaskets: Low-pressure, non-corrosive media (water, air).
Recommended:
- NBR Rubber: Oil-resistant, for fuel pipelines.
- EPDM Rubber: Resists steam/hot water.
- PTFE: Chemically inert but requires reinforcement.
Semi-Metallic Gaskets: Medium-to-high pressure/temperature, corrosive media.
Recommended:
- Spiral Wound (SWG): 304 stainless steel + graphite/PTFE.
- Metal Jacketed: High compressive strength for reactors/heat exchangers.
Metallic Gaskets: Ultra-high pressure/temperature or zero-leakage requirements.
Recommended:
- RTJ Gasket: API-standard for wellheads/high-pressure valves.
- Serrated Gasket: High bolt load, for steam pipelines.
3. Consider Installation and Maintenance Factors
Bolt Load: Metallic gaskets require higher preload; verify flange strength.
Removability: For frequent disassembly, use elastic gaskets (e.g., spiral wound).
Cost: Non-metallic gaskets are cheaper but less durable; metallic gaskets are costly but long-lasting.
Industry Application Examples
| Industry | Typical Conditions | Recommended Gasket |
| Petrochemical | High temp/pressure, H₂S | Spiral wound/RTJ |
| Food/Pharma | Sterility requirements | PTFE/silicone |
| Power (Steam) | >400°C | Graphite/serrated metal |
| Marine | Saltwater, vibration | Metal jacketed/NBR rubber |
Selection Summary
By systematically analyzing operating conditions and material properties, flange gaskets can ensure long-term sealing reliability and prevent leakage risks.
Example of Wrong Selection:
Mistake: Using a standard rubber gasket for 200°C steam (will degrade and leak).
Solution: Switch to graphite spiral wound or stainless steel serrated gasket.
EN 
DE 
RU 
FA 
ID 
ES 
FR 
NL