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Flat Gasket

A static sealing element die-cut from flat sheet material and compressed between two flanges to prevent leakage of fluids or gases. The gasket material must be softer than the flange faces to conform to surface imperfections and create a seal. Materials by ascending temperature and pressure capability: (1) Rubber sheet (NR, SBR, NBR, EPDM, CR, silicone, FKM) — up to 100-200°C, 10-20 bar, selected by chemical compatibility. (2) Compressed non-asbestos fiber (CNF — aramid/glass fiber in nitrile or SBR binder) — up to 250°C, 40 bar, general industrial. (3) Flexible graphite sheet (Grafoil/Sigraflex) — -200 to +650°C, 100+ bar, excellent chemical resistance. (4) PTFE sheet — -200 to +260°C, universal chemical resistance, low friction, but cold flows under sustained load. (5) Metal (soft iron, copper, stainless) — highest temperature and pressure. Per ASME B16.21 (non-metallic flat gaskets for ASME flanges). Thickness: typically 1.5-3 mm for rubber, 0.5-3 mm for CNF and graphite. Bolt torque must achieve minimum gasket seating stress without exceeding crush limit. Gasket factors (m and y) per ASME BPVC Section VIII define minimum bolt load requirements. Brands: Garlock, Klinger, Flexitallic, Gore (PTFE).

What you need to know

  • A static sealing element die-cut from flat sheet material and compressed between two flanges to prevent leakage of fluids or gases.
  • The gasket material must be softer than the flange faces to conform to surface imperfections and create a seal.
  • Materials by ascending temperature and pressure capability: (1) Rubber sheet (NR, SBR, NBR, EPDM, CR, silicone, FKM) — up to 100-200°C, 10-20 bar, selected by chemical compatibility.
  • (2) Compressed non-asbestos fiber (CNF — aramid/glass fiber in nitrile or SBR binder) — up to 250°C, 40 bar, general industrial.
  • (3) Flexible graphite sheet (Grafoil/Sigraflex) — -200 to +650°C, 100+ bar, excellent chemical resistance.

Full definition

Flat gaskets are essential sealing elements used in various industrial applications to prevent leakage of fluids or gases between two flanges. They are die-cut from flat sheet materials that must be softer than the flange surfaces, allowing them to conform to surface imperfections and create an effective seal. The choice of material for flat gaskets is critical and depends on the specific operational conditions, including temperature, pressure, and chemical compatibility. For example, rubber sheets made from materials such as natural rubber (NR), styrene-butadiene rubber (SBR), nitrile rubber (NBR), ethylene propylene diene monomer (EPDM), chloroprene (CR), silicone, and fluorocarbon (FKM) can withstand temperatures ranging from 100°C to 200°C and pressures from 10 to 20 bar, making them suitable for general applications.

Compressed non-asbestos fiber (CNF) gaskets, which are typically made from aramid or glass fiber combined with a nitrile or SBR binder, can handle higher operating conditions, tolerating temperatures up to 250°C and pressures of 40 bar. They are widely used in general industrial applications due to their good mechanical properties and resistance to a variety of chemicals. Flexible graphite sheets, such as Grafoil or Sigraflex, offer exceptional performance at extreme temperatures, with a range from -200°C to +650°C and pressure capabilities exceeding 100 bar, making them ideal for high-stress environments.

PTFE (polytetrafluoroethylene) gaskets provide universal chemical resistance and operate effectively between -200°C and +260°C. They exhibit low friction properties but can suffer from cold flow under sustained loads. Finally, metallic gaskets made from soft iron, copper, or stainless steel are utilized in the most demanding applications, offering the highest temperature and pressure resistance. According to ASME B16.21, the thickness of flat gaskets typically ranges from 1.5 to 3 mm for rubber, and from 0.5 to 3 mm for CNF and graphite types. Proper installation requires careful bolt torque application to achieve the minimum gasket seating stress while avoiding crush limits. The gasket factors (m and y) defined in ASME BPVC Section VIII are essential for determining the minimum bolt load requirements for effective sealing.

What you need to know

  • Flat gaskets are made from softer materials than flange faces to ensure a proper seal.
  • Common materials include rubber types (up to 100-200°C, 10-20 bar) and CNF (up to 250°C, 40 bar).
  • Flexible graphite gaskets can withstand temperatures from -200°C to +650°C and pressures over 100 bar.
  • PTFE gaskets resist a wide range of chemicals but may cold flow under sustained load.
  • Thickness typically ranges from 1.5-3 mm for rubber and 0.5-3 mm for CNF and graphite types.

Industrial applications

  • 1Used in piping systems for chemical processing to prevent leaks between flanges.
  • 2Utilized in HVAC systems where sealing against air and refrigerants is critical.
  • 3Applied in automotive engines to seal oil and coolant passages.
  • 4Employed in food processing equipment to maintain hygiene by preventing contamination.
  • 5Utilized in power generation plants for sealing high-pressure steam systems.

Common mistakes

  • ✕Using incorrect gasket material for the intended operating conditions, leading to premature failure.
  • ✕Failing to achieve the correct bolt torque, resulting in insufficient sealing or gasket crush.
  • ✕Not allowing for thermal expansion, which can lead to gasket failure in high-temperature applications.
  • ✕Neglecting to inspect flange surfaces for flatness, which can compromise the gasket's sealing ability.
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Pro tip

Always verify the compatibility of the gasket material with the fluids or gases it will encounter to ensure long-lasting performance.

Technical standards

  • ASME B16.21 - Standard for non-metallic flat gaskets for ASME flanges.
  • ASME BPVC Section VIII - Guidelines for minimum bolt load requirements.

Suppliers of seals & gaskets in Mexico

AguascalientesVer Hule Industrial
Ciudad JuárezVer Hule Industrial
Ciudad de MéxicoVer Hule Industrial
GuadalajaraVer Hule Industrial
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