Introduction to Steel Pipe Flange Gasket Selection
Flange gaskets are the critical sealing elements in piping systems. Choosing the wrong gasket can lead to leaks, environmental contamination, and costly downtime. This comprehensive guide covers all major gasket types, materials, pressure-temperature ratings, and selection criteria to help engineers and procurement professionals make informed decisions.
Types of Flange Gaskets
Non-Metallic (Soft) Gaskets
Non-metallic gaskets, also known as soft gaskets, are flat gaskets made from compressible materials. They are suitable for low-to-medium pressure applications and are commonly used in ASME B16.5 Class 150 and 300 flanges.
- Compressed Asbestos Fiber (CAF): Traditional material, being phased out due to health concerns
- Non-Asbestos Fiber (NAF): Made from aramid, glass, or carbon fibers with elastomer binders
- PTFE (Virgin & Filled): Excellent chemical resistance, suitable for temperatures up to 260 degrees C
- Graphite-Filled: High-temperature capability up to 500 degrees C in oxidizing environments
- EPDM: Ideal for water, steam, and mild chemical services
Semi-Metallic Gaskets
Semi-metallic gaskets combine metallic and non-metallic materials to achieve better sealing performance across wider pressure and temperature ranges.
- Spiral Wound Gaskets (SWG): Most common semi-metallic type, made by winding alternating layers of metal and filler. Metal options include 304SS, 316SS, Carbon Steel, Inconel, and Monel. Fillers include graphite, PTFE, and ceramic
- Camprofile Gaskets: Serrated metal core with soft sealing layers, excellent for high-temperature applications
- Klingersil gaskets: Compressed fiber with steel inserts for improved blowout resistance
Metallic Gaskets
Metallic gaskets provide the highest sealing integrity and are used in high-pressure, high-temperature (HPHT) applications common in oil and gas, petrochemical, and power generation industries.
- Ring Type Joint (RTJ) Gaskets: Oval and octagonal cross-sections per ASME B16.20. Available in R, RX, and BX types
- Ring Joint Oval: Used with older flange designs, requires higher bolt loads
- Ring Joint Octagonal: Compatible with newer flanges, lower bolt load requirement
- Pressure energized BX rings: Self-energizing design for extreme pressures
Gasket Material Selection by Service
| Service Media | Recommended Gasket Type | Material | Temperature Range |
|---|---|---|---|
| Water / Steam | Spiral Wound | 304SS + Graphite | -50 to 500 C |
| Hydrocarbons | Spiral Wound | 316SS + Graphite | -200 to 550 C |
| Acid / Caustic | PTFE Envelope | PTFE | -200 to 260 C |
| High-Pressure Gas | RTJ | Soft Iron / Low Carbon Steel | -50 to 500 C |
| Cryogenic | Spiral Wound | 316SS + PTFE | -200 to 260 C |
| H2S Service (Sour) | Spiral Wound / RTJ | Inconel 625 + Graphite | -50 to 650 C |
Key Standards and Specifications
- ASME B16.20 / B16.5: Metallic gaskets for pipe flanges (RTJ, SWG, Camprofile)
- ASME B16.21: Non-metallic flat gaskets
- EN 1514: European standard series for flange gaskets (Parts 1-7)
- API 6A: Ring gaskets for wellhead and christmas tree equipment
- NORSOK M-710: Qualification and selection of sealing materials (Norwegian standard)
Gasket Sizing and Pressure-Temperature Ratings
Proper gasket sizing follows the flange dimensions specified in ASME B16.5. Key dimensions include:
- Inside diameter: Must match the pipe bore to avoid flow obstruction
- Outside diameter: Must fit within the flange bolt circle
- Thickness: Standard thickness is 3mm or 4.5mm for spiral wound gaskets
- Compression ratio: Typically 25-33% for soft gaskets, 7-12% for SWG
Installation Best Practices
- Clean flange faces thoroughly before installation – no old gasket material, rust, or debris
- Inspect flange sealing surfaces for scratches, gouges, or corrosion pits
- Center the gasket properly in the flange before inserting bolts
- Use new bolts and nuts for critical services; inspect reused bolts for thread damage
- Follow star-pattern bolt tightening sequence to ensure even compression
- Apply specified torque values per the gasket manufacturer’s recommendation
- Re-torque after thermal cycling for non-metallic gaskets
Common Gasket Failure Modes
- Blowout: Internal pressure exceeds gasket residual surface stress
- Creep relaxation: Gasket material loses compression over time, especially at elevated temperatures
- Chemical attack: Process media degrades the gasket filler material
- Flange rotation: Uneven bolt loading causes flange faces to separate on one side
- Thermal cycling: Repeated temperature changes cause gasket stress variation
Why Choose CoreMetal Steel for Flange Gasket Supply
CoreMetal Steel supplies a comprehensive range of flange gaskets to match our full inventory of steel flanges and pipe fittings. All gaskets are manufactured per international standards and shipped with full material traceability documentation.
- Spiral wound gaskets in all common materials (304SS, 316SS, Carbon Steel, Inconel)
- RTJ gaskets in R, RX, and BX styles per ASME B16.20
- Non-asbestos fiber gaskets for general service
- PTFE gaskets for chemical resistance applications
- Custom sizes available for non-standard flanges
Contact CoreMetal Steel today for gasket recommendations matched to your flange specifications and service conditions.