How To Select The Sealing Material For A Floating Ball Valve To Adapt To Corrosive Media?

The media type, concentration, temperature, pressure, velocity, corrosion resistance, abrasion resistance, elasticity and temperature adaptability of the sealing material need to be considered. Specific selection principles and application scenarios for commonly used materials are as follows:
I. Selection Principles
Media Compatibility: Sealed materials must be chemically stable with corrosive media (e.g., acids, alkalines, salt solutions, organic solvents, organic solvents, oxidizing media, etc.) to avoid reactions that could lead to leakage or material failure.
hydrofluoric acid, for example, corrodes most metals and polymers and requires the use of special metal seals such as Monel or Hastelloy.
Temperature Adaptability: The sealing material's temperature range must cover the media's operating temperature to prevent high-temperature softening or low-temperature brittleness.
For example: PTFE (polytetrafluoroethylene (PTFE) has a temperature resistance of -200° C C to 260°C, but prolonged exposure to high temperatures (>200°C) accelerates aging; PEEK (PTFE) has a temperature resistance of 250°C, suitable for high-temperature corrosive media.
Pressure and wear resistance;
High pressure media will accelerate wear and tear of the seal, so it is necessary to choose a material with high hardness and wear resistance.
For example, hard metal seals (such as cobalt crusts No. 6) are suitable for high pressure (>10MPa) or medium conditionscontaining particles.
Flexibility and Sealing Compensation Capability
Soft sealing materials such as rubber and PTFE (PTFE) must be elastic to compensate for wear or thermal deformation of the cover.
PTFE valve seats is compensated by elastic deformation, but prolonged high pressure may cause creep leakage.
Industry Standards and Certification
Sealants must meet the corrosion resistance requirements of relevant industry standards (e.g. API 6D and ISO 15848).
For example, NACE MR0175 establishes corrosion resistance requirements for materials used in oil and gas field equipment in environments containing hydrogen sulfide (H2S).
ii. Common Sealing Materials and Their Application Scenario
1.Soft Sealing Materials
Material Type | Corrosion Resistance | Applicable Temperature Range | Typical Application Scenario
(PTFE | Resistant to most acids, alkalis and organic solvents (except molten alkali metals and elemental fluorine), chemically inert | -200°C~260°C | Strongly corrosive media (e.g. concentrated sulfuric acid, hydrochloric acid)
Polytetrafluoroethylene | Similar to polytetrafluoroethylene, but more heat resistant (long-term operating temperature ≤260°C) | -200° C ~C | High temperature, highly corrosive medium
PEEK | Resistant to strong acids, strong alkalis and organic solvents, but not to concentrated sulphuric acid and nitric acid | -60°C~250°C | High temperature, high pressure corrosive media (e.g. chemical reactants)
FFKM (Perfluororubber) | Resistant to strong acids, strong alkalis and organic solvents, 327°C | -20°C~327°C | Ultra-high temperature, highly corrosive media (e.g. semiconductor industry)
Oil, weak acid, weak alkalinity, but strong oxidizing media (e.g., concentrated nitric acid, chromic acid). -Weak corrosive media such as petroleum and fuel oil range from -40 ° C to 120 ° C.
2.Metal Hard Sealing Materials
Material Type | Corrosion Resistance | Applicable Temperature Range | Typical Application Scenario
Tungsten chromium cobalt crusts 6 | high-temperature oxidizing media (e.g. nitric acid and chromic acid), but not resistant to hydrofluoric acid and strong alkalis. ≤650°C applies to high-temperature and high-pressure corrosive media (e.g. power plant boilers).
Resistant to strong acids (e.g. hydrochloric acid, sulfuric acid and phosphoric acid) and organic solvents, but not to concentrated nitric acid. The highly corrosive media in the chemical and pharmaceutical industries range from 196 ° C to 650 ° C.
Resistant to hydrofluoric acid, seawater and alkaline media, but not to strong oxidizing acids (e.g. nitric acid). -100°C~450°C for marine engineering and hydrofluoric acid pipelines.
316L Stainless Steel Resistant general corrosive media (e.g. diluted acid, alkali and salt water) but not to concentrated sulfuric acid and hydrochloric acid. -196° C to 800 °C for weakly corrosive media in food and pharmaceutical industries.
3. Composite Sealing Materials
Material Type | Structural Characteristics | Applicable Scenario
Metal + PTFE: Seat is a metal (e.g., stainless steel) coated with PTFE. Balances strength and corrosion resistance (e.g., chemical pipelines).
Metal + PEEK: The base of the seat is metal and covered with a PEEK layer. Suitable for high temperature and high pressure corrosive media (e.g., oil refineries).
Rubber + PTFE: Rubber skeleton covered with a PTFE layer. Suitable for corrosive media requiring elastic compensation (e.g., vacuum systems).
III. Selection steps
Determine Media Parameters: determine media type, concentration, temperature, pressure, velocity and presence of particles.
Screening of candidate materials: Elimination of inappropriate materials based on media compatibility tables.
Verify temperature adaptability: Ensure that the material's temperature range includes working temperature.
Pressure and wear assessment: Hard metal seals should be preferred for high pressure or granulated media.
Consider cost and service life: Soft seal low cost but short service life, while hard metal seals high cost but long service life.
Testing and certification: verification of material performance through simulated operating conditions, such as immersion tests and high voltage cycle testing.
IV. INTRODUCTION I. INTRODUCTION 1 -6 2
Case 1: Concentrated Sulfuric Acid Pipeline
Medium: 98% concentrated sulfuric acid, temperature 80°C, pressure 2.5MPa.
Material Selection: Polytetrafluoroethylene (PTFE) (PTFE) soft seal (concentrated sulfuric acid resistance, temperature adaptability).
RESULTS: After 3 years of operation, there is no leakage and no corrosion.
Case 2: Hydrogen Sulfide-Containing Oil and Gas Pipeline
Medium: Wet H2S gas, 60°C, pressure 10MPa.
Material Selection: Hastelloy C-276 hard metal seal (H2S resistant, pressure adaptable).
Results: NACEMR0175 was identified as non-corrosive for 5 consecutive years.
Case 3: Semiconductor Industry Ultrapure Water System
Medium: Ultrapure water (pH=6-8), temperature 25°C, pressure 0.6MPa.
Material Selection: FFKM perfluororubber (ultrapure water resistance, no ion precipitation).
RESULTS: To meet the high cleanliness requirements of semiconductor industry.
V. Precautions
Avoid Mixing Media: Combining different corrosive media may result in synergistic corrosion effect (e.g. chlorine gas from hydrochloric acid + sodium hypochlorite).
Consider Erosion Effects: high velocity liquids (flow velocity greater than 10 m/s) accelerate seal wear; abrasionresistant materials (e.g., PEEK) must be selected.
Periodic maintenance: Even anticorrosion materials should be inspected regularly to prevent sudden leakage due to local corrosion.
Compliance: Ensure that materials meet the corrosion resistance requirements of standards such as ASME B16.34 and API 6D.
Through scientific material selection, floating valve can achieve long-term reliable sealing under highly corrosive conditions, reducing maintenance costs and safety risks.