Soft sealing seat +FFKM

I. The core function of metal valve seat: structural support and foundation for withstanding severe working conditions.

1. High-strength mechanical support and pressure resistance

• Material characteristics: The metal valve seat (such as stainless steel, nickel-based alloy, titanium alloy, etc.) has extremely high strength and rigidity, and can withstand ultra-high pressure (such as oil and gas well fracturing above 100MPa) and severe pressure fluctuation, so as to avoid plastic deformation of the valve seat due to mechanical load or medium impact.
• Typical scenario: In the deep-sea oil and gas production valve, the metal valve seat needs to resist the dual effects of external static pressure (such as 100MPa) and internal oil and gas pressure in thousands of meters of water depth.

2. High temperature resistance and wear resistance

• High-temperature adaptability: metal valve seat can maintain structural stability in high-temperature environment above 400℃ (such as high-temperature steam valve in power station, the temperature reaches 540℃), its thermal conductivity is better than that of non-metallic materials, and it can quickly dissipate heat to avoid local overheating.
• Anti-erosion wear: In solid particles or high-speed fluid (such as oil pipeline with high sand content), the surface of metal valve seat can resist the wear of sealing surface caused by medium erosion after hardening treatment (such as surfacing tungsten carbide).

3. Limitations

• Shortcomings of pure metal seal: the metal valve seat relies on the fitting of precision machined sealing surfaces to achieve hard seal, but in dynamic working conditions (such as frequent opening and closing of valves) or micro-pressure environment, it is easy to produce tiny gaps due to vibration and wear, resulting in medium leakage;
• Chemical compatibility limitation: some metals (such as stainless steel) may corrode in strong oxidant (such as concentrated nitric acid) or fluorine-containing medium, which needs to be compensated with corrosion-resistant sealing rings.

II.the core function of FFKM sealing ring: elastic sealing and chemical protection in extreme environment.

1. Elastic seal in ultra-wide temperature range

• Temperature resistance: FFKM can maintain elasticity in the range of-20℃~327℃ (far exceeding the upper limit of 260℃ of PTFE), and its molecular structure can still maintain elastic deformation under high-temperature working conditions (such as cracking gas valve in refining and chemical plant, the temperature reaches 300℃), compensating the gap caused by thermal expansion and cold contraction of metal valve seat.
• Low temperature adaptability: In the valve of liquefied petroleum gas storage tank at-20℃, the FFKM sealing ring will not crack due to low temperature hardening, and it can still be sealed by elastic pre-tightening.

2. Super chemical resistance and solvent resistance

• Scope of chemical medium resistance: FFKM has excellent resistance to strong acids (such as sulfuric acid and nitric acid), strong bases (such as sodium hydroxide), strong oxidants (such as hydrogen peroxide), organic solvents (such as ketones and esters) and fluorine-containing media (such as Freon), even resisting aqua regia and most nuclear radiation environments, which is incomparable to PTFE and ordinary rubber.

• Application scenario:

  • In the etching process of semiconductor industry, the valve conveying fluoride gas (such as nitrogen trifluoride) needs FFKM sealing ring to prevent medium corrosion;

  • The sour crude oil pipeline in petroleum refining can resist the corrosion FFKM hydrogen sulfide (HS) and organic sulfur compounds.

3. Dynamic sealing and low gas permeability

• Dynamic adaptability: the elastic modulus and tear strength of FFKM are higher than PTFE, and it can withstand repeated compression deformation without failure in the dynamic process of valve opening and closing (such as the rotation of ball valve), and it is suitable for valves with high frequency operation (such as compressor inlet valve, which is opened and closed more than 100 times a day).
• Low gas permeability: the molecular structure of FFKM is compact, and its permeability to small molecular gases such as hydrogen and helium is extremely low. In vacuum systems (such as valves of vacuum coating equipment), it can achieve “zero leakage” sealing (leakage ≤ 10 PAM/s).

4. Anti-aging and long-life characteristics

• Weathering resistance: FFKM sealing ring is not easy to age in ultraviolet, ozone and high-energy radiation environment, and it is suitable for open-air or nuclear industry valves (such as coolant pipeline valves of nuclear power plants), and its service life can reach more than 10 years, far exceeding that of ordinary rubber sealing rings (2-3 years).

III. Synergistic logic of metal valve seat+FFKM sealing ring

IV. Structural Design and Installation Form

1. Common combination structure

• Embedded sealing groove design: FFKM sealing ring is embedded in the annular groove of metal valve seat (such as U-shaped groove of ball valve seat), and the sealing ring is pushed close to the valve core by medium pressure to form a “self-tight seal”. For example, in a high-pressure natural gas valve, the medium pressure will squeeze the FFKM sealing ring, and the higher the pressure, the tighter the seal.
• Overlapping compound seal: Add FFKM gasket above the sealing surface of metal valve seat (such as the sealing surface of butterfly valve seat), metal provides support, and FFKM is responsible for dynamic seal, which is suitable for occasions that need to resist high pressure and chemical corrosion simultaneously.

2. Design key points

• Compression control: the compression of FFKM is usually controlled at 15%-20% to avoid elastic attenuation caused by excessive compression; At the same time, its “thermal shrinkage rate” at high temperature (about 0.5%/100℃) should be considered, and the gap compensation should be reserved.
• Metal surface treatment: the sealing surface of the valve seat needs mirror grinding (roughness Ra≤0.8μm) to avoid sharp edges and corners scratching the FFKM sealing ring; For media containing particles, wear-resistant alloy (such as Stellit) can be surfacing on the surface of metal valve seat to protect the sealing ring from erosion.

V. Application Limitations and Alternatives

1. FFKM 的局限性

• High cost: the price of FFKM is 10-20 times that of ordinary rubber, and it is difficult to process, which limits its application in ordinary working conditions (for example, NBR or PTFE is usually used for civil pipeline valves).
• Lower limit of low temperature: when the temperature is lower than-20℃, the elasticity of FFKM will decrease significantly, so it is necessary to use fluororubber (FKM, which can withstand the temperature of-25℃~200℃) or metal bellows seal (suitable for liquid nitrogen valves at-196℃).
• Compatibility of molten metal: FFKM can’t resist molten alkali metals (such as lithium and sodium) and high-temperature fluorine gas (> 400℃), so it needs all-metal hard seal (such as Inconel valve seat+metal sealing ring).

2. Substitution combination

• Metal valve seat+FKM sealing ring: It is suitable for medium temperature (≤200℃) and medium corrosive medium (such as general acid and alkali solution), and its cost is lower than that of FFKM, which is common in ordinary pipelines in chemical industry.
• Metal valve seat+metal sealing ring: fully hard sealing structure, suitable for ultra-high pressure (> ＞100MPa) or harsh working conditions containing solid particles (such as shale gas mining valves), but the sealing accuracy is lower than that of the combination with FFKM, and higher machining accuracy is required.