Soft sealing seat F53

I. Core material characteristics of alloy valve seat

• Stainless steel alloy (such as 316L and 2507 dual-phase steel): strong corrosion resistance, suitable for acid-base medium and seawater environment;
• Nickel-based alloys (such as Inconel 625 and Hastelloy C-276): resistant to strong corrosion, high temperature and high pressure, and commonly used in chemical industry and energy fields;
• Copper alloy (such as aluminum bronze and beryllium bronze): wear-resistant and cavitation-resistant, suitable for water systems and low-pressure valves;
• Titanium alloys (such as TA2 and TC4): lightweight, resistant to seawater and chloride ion corrosion, mostly used in marine engineering and ship valves.

II. Core role in valves

1. Realize the sealing function: the foundation support of hard seal and soft seal.

• Hard seal core carrier: The metal-to-metal rigid seal is realized under high pressure by directly bonding the alloy sealing surfaces with high precision grinding (such as the gate and valve seat of gate valves), which is suitable for high temperature and particle-containing media (such as power station steam valves).
• Soft seal support structure: provide installation base and mechanical support for rubber, PTFE and other soft sealing rings (such as valve seat groove of ball valve) to prevent the sealing ring from deformation and failure due to medium pressure or mechanical load. For example, in the butterfly valve, the rubber sealing ring is fixed in the annular groove of the alloy valve seat to ensure that it is uniformly stressed when opening and closing.

2. Withstand high pressure and mechanical load

• Adaptability to high-pressure working conditions: the high strength of alloy material (such as tensile strength of 2507 dual-phase steel ≥700MPa) can resist the impact of ultra-high pressure medium (such as the fracturing valve of oil and gas well bears more than 100MPa pressure), so as to avoid plastic deformation or rupture of the valve seat.
• Anti-vibration and impact: In high-frequency vibration scenes such as compressor outlet, the rigid structure of alloy valve seat can reduce the gap between sealing surfaces caused by vibration and prevent medium leakage (such as pressure regulating valve of natural gas pipeline).

3. Resist environmental damage such as corrosion and wear.

• Chemical corrosion resistance: Nickel-based alloys (such as Hastelloy C-276) have excellent resistance to strong corrosive media such as concentrated hydrochloric acid and aqua regia, and are suitable for chemical reactor valves; Titanium alloy valve seat can resist pitting corrosion of seawater and chloride-containing solution, and is often used in seawater treatment system of offshore platform.
• Erosion and wear resistance: through surface hardening treatment (such as surfacing tungsten carbide and nitriding), the alloy valve seat can withstand high-speed erosion of solid particle-containing media (such as slurry pipeline valves) and prolong its service life. For example, the slag slurry valve in coal mine washing plant adopts wear-resistant alloy valve seat, which reduces the wear by more than 80% compared with ordinary steel valve seat.

4. Adapt to high and low temperature environment

• High-temperature stability: the alloy material (such as Inconel 600) still maintains its mechanical properties above 500℃, which is suitable for high-temperature steam in power stations (540℃), cracking gas in refining and chemical industry (450℃) and other scenes to avoid sealing failure caused by high-temperature softening of the valve seat.
• Anti-embrittlement at low temperature: after low temperature treatment, austenitic stainless steel (such as 316L) can maintain toughness in-196℃ liquid nitrogen environment (such as LNG storage tank valve) to prevent valve seat from cracking at low temperature.

III. Adaptation between Typical Application Scenarios and Working Conditions

IV. Key Points of Structural Design and Performance Optimization

1. Sealing surface design

• Conical/plane sealing surface: gate valves usually use plane sealing surface (grinding accuracy Ra≤0.8μm), and ball valves/globe valves usually use conical sealing surface, which is sealed by the wedging force between the valve core and the valve seat, and the matching angle (such as 60 conical surface) needs to be optimized according to the pressure grade.
• Surface hardening treatment: surfacing stellite alloy (hardness HRC≥55) on the easily worn parts (such as throttle valve seat), or laser cladding tungsten carbide coating to improve the erosion resistance.

2. Thermal expansion compensation

• Under high-temperature working conditions (such as power station valves), an expansion gap (0.5-1mm) is reserved between the alloy valve seat and the valve body, or an elastic support structure (such as a spring-loaded valve seat) is adopted to avoid the sealing surface from being blocked due to thermal expansion and contraction.

3. Anti-sticking design

• For easy-to-crystallize media (such as sodium carbonate solution), the surface of the valve seat can be plated with hard chromium (5-10μm in thickness) or coated with molybdenum disulfide to reduce the adhesion of the sealing surface caused by the crystallization of the media and facilitate the opening and closing of the valve.

V. Synergy with other components

• Matching with the valve core: the sealing surfaces of the alloy valve seat and the valve core need to be ground in pairs (such as cemented carbide valve seat+cemented carbide valve core), or a “hard-soft” combination (such as alloy valve seat+PTFE valve core) is adopted to balance the sealing accuracy and wear resistance.
• Coordination with sealing ring: In the scene where soft sealing is needed (such as low-pressure gas valve), alloy valve seat provides rigid support for rubber sealing ring to prevent it from being squeezed out under medium pressure, and at the same time, the position of sealing ring is fixed through sealing groove structure (such as O-ring groove) to ensure sealing reliability.

VI. Limitations and Alternatives

1. Limitations

• High cost: high-performance alloys (such as nickel-based alloys) are expensive, which limits their application in ordinary civil valves;
• Difficult processing: high-precision sealing surface grinding requires special equipment (such as CNC grinder), and the surface hardening treatment (such as surfacing) process is complex, which increases the manufacturing cycle;
• Limitations of pure hard seal: it is difficult to completely avoid tiny leakage when the alloy valve seat is attached to the metal under micro-pressure or vacuum conditions, so it is necessary to cooperate with soft sealing ring (such as FFKM) to assist the seal.

2. Alternatives

• Cast iron/carbon steel valve seat: suitable for low pressure, non-corrosive media (such as civil water pipes), with low cost but poor corrosion resistance;
• Non-metallic valve seats (such as PTFE and PEEK): used in normal temperature and weakly corrosive media (such as food and beverage pipelines), but with low strength, they cannot withstand high pressure or high temperature.