Trunnion Ball Valves

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A trunnion ball valve is a quarter-turn valve that uses a fixed ball supported by trunnions (mechanical anchoring supports) on the top and bottom.
The ball does not float; instead, line pressure moves the seats against the ball to ensure sealing.
 

• Ideal for high-pressure and large-diameter applications due to its reduced torque requirements.
   
• Provides double block and bleed (DBB) functionality, enhancing safety and maintainability.
   
• Typically used in oil & gas pipelines, LNG facilities, petrochemical plants, and severe service applications.
   

• Design Codes & Standards:
   
  • API 6D – Specification for pipeline valves.
     
  • ASME B16.34 – Valve pressure-temperature ratings and design.
     
  • ISO 17292 – Specification for metal ball valves.
     
  • NACE MR0175 / ISO 15156 – Material selection for sour service (H₂S environments).
     
• Key Design Features:
   
  • Anti-blowout stem.
     
  • Fire-safe design (API 607 / ISO 10497).
     
  • Cavity pressure relief system.
     
  • Optional drain, vent, and emergency sealant injection ports.
     
  • Trunnion bearings with low-friction or self-lubricating materials.
     
• Seat Types:
   
  • Soft seats (PTFE, Devlon, PEEK) for standard services.
     
  • Metal seats with coatings like Tungsten Carbide, Chromium Carbide, or Stellite for severe service, erosive, or high-temperature environments.
     

• API 598 – Valve inspection and testing (primarily for general valves).
   
• API 6D – Pressure testing for pipeline valves.
   
• Mandatory tests include:
   
  • Hydrostatic shell test
     
  • Seat leakage test (low and high pressure)
     
  • Gas leak test if specified.
     
• Optional tests:
   
  • Fugitive emissions (per ISO 15848 or API 641).
     
  • Low-temperature and cryogenic testing (especially for LNG service).
     
  • High-cycle or endurance testing (for control or modulating applications).
     

Below is a reference for common ANSI Class–Material combinations used in trunnion ball valves:

• Body: ASTM A216 WCB (Carbon Steel), ASTM A351 CF8M (SS316)
   
• Trim: 316 SS, Inconel overlays for moderate corrosion
   
• Seat: PTFE, RPTFE, PEEK (standard service)
   

• Body: ASTM A105 (CS), A350 LF2 (Low Temp CS), A182 F316/F51 (SS, Duplex)
   
• Trim: Inconel 625, Stellite, or Chromium Carbide coated balls/seats
   
• Seat: Metal seated with HVOF-applied Tungsten Carbide or Stellite
   

• Body: ASTM A182 F22, F91, or F316 for high-temp or corrosive service
   
• Trim: Tungsten Carbide or Stellite-coated ball/seat
   
• Seat: Metal seated with spring-loaded or pressure-assisted sealing
   

• Body: A351 CF8M, CF3M (SS), or special low-temperature alloys like Invar or 9% Ni steel
   
• Trim: SS316, Inconel, or Monel
   
• Seat: PCTFE or modified PTFE; metal seats with special low-temp design
   
• Testing: Per BS 6364 or API 6D with cryogenic leakage testing
   

• Corrosive environments: Duplex (F51), Super Duplex (F53), or Alloy 625/825 for high chloride or sour gas.
   
• Erosive slurry: Tungsten Carbide-coated metal seats and balls.
   
• High-temp steam or hydrocarbon service: Use of Stellite and F22/F91 materials.
   

For complex applications, the exact ANSI Class and material must be selected based on:

• Operating pressure and temperature
   
• Service medium (corrosive, erosive, dirty gas, LNG, etc.)
   
• Actuation and automation requirements