1. RF (Raised Face)

RF flanges feature a circular raised sealing surface outside the bolt circle, forming an independent compression zone. This structure increases surface pressure under limited bolt torque, enabling the metal gasket to produce plastic deformation and form a reliable metal-to-metal seal.

RF flanges fit most pressure and temperature grades and are the most widely used type in oil, gas and chemical industries.

Characteristics:

• Minimum sealing area, highest surface pressure, fits rigid gaskets
• Standard roughness: Ra3.2–6.3μm (micro grooves help gasket embedding)
• Too smooth surface causes leakage (no micro-deformation)
• Sensitive to bolt preload; thermal cycling may cause stress attenuation
• Unstable sealing under drastic temperature changes and volatile media

  2. FF (Flat Face)

  FF flanges are mainly designed to protect brittle materials such as cast iron. The sealing surface is flush with the bolt face, with the full-area gasket covering from inner diameter to outer diameter.

  It adopts low surface pressure + even compression principle, requiring soft, high-flexibility and high-resilience non-metal gaskets with serrated surface.

  Characteristics:

  • Large sealing area → low surface pressure
  • Only for low-pressure classes (125# / 250#)
  • Cannot match RF flanges (especially hard material RF)
  • Core function: protect flange body from damage

    3. RTJ (Ring Type Joint)

    RTJ is an upgraded heavy-duty version of raised face flange, applied for high pressure & high temperature severe working conditions (above 750°C). Mainly used for Class900 and above.

    RTJ uses solid metal gaskets (R type / RX type / BX type), softer than flange material to ensure plastic deformation and perfect metal-to-metal sealing.

    Characteristics:

    • Oval / Octagonal gasket available (octagonal for better sealing)
    • Groove embedded structure, no direct flange-to-flange contact
    • BX type adopts self-energizing principle: higher pressure = tighter seal
    • Perfect for oil & gas high-pressure pipeline systems

      4. TG / MFM (Tongue & Groove / Male & Female)

      Both structures lock the gasket position physically, preventing radial sliding caused by uneven bolt force, vibration or temperature fluctuation.

      • TG (Tongue & Groove):Strong positioning constraint, specially suitable for soft gaskets
      • MFM (Male & Female):Wider contact surface, more uniform stress, compatible with more gaskets

        Must be used in pairs. Widely used for medium & high reliability industrial projects.

        5. LMF / LCF (Large Male & Female)

        An enhanced version of MFM, mostly used for pressure vessel equipment.

        Wider contact surface allows a wider surface pressure range, reduces machining precision requirements, and greatly improves connection stability and equipment safety.

        6. SJ (Self-Energized Seal)

        Typical types: C-ring, O-ring metal gasket, lens gasket.

        The sealing force increases with medium internal pressure (self-energized effect). Adopts controllable plastic metal gaskets.

        Applied for extreme working conditions: ultra-low temperature, high temperature, pressure pulsation, special chemical and aerospace equipment.