Sealing & Emission Control Systems
Seat Sealing
Fire-Safe Soft Seat (Primary/Secondary)
A primary soft (PTFE or similar) seat gives normal bubble-tight shutoff; a secondary metal-to-metal seating surface behind it takes over automatically if the primary seat burns away in a fire, per API 607/API 6FA fire testing.
How does fire-safe soft seat (primary/secondary) work?
Under normal conditions the resilient primary seat seals against the ball or disc for zero leakage. If a fire destroys the elastomer/PTFE primary seat, the ball or disc travels slightly further under line pressure until the secondary metal seating surface makes contact, containing the leak to the fire-test acceptance limit rather than losing containment entirely.
When to Use It
- Any hydrocarbon or flammable-fluid isolation valve where API 607 / API 6FA fire-safe certification is specified
- Standard practice for API 6D pipeline ball valves and most refinery/petrochemical isolation valves
Limitations
- More complex seat design and higher cost than a non-fire-safe soft seat
- Post-fire leakage is contained to the standard's acceptance limit, not zero - the design manages consequence, not eliminates it
Typical MaterialsPTFE or reinforced elastomer primary seat; Stellite-faced or hardened stainless secondary metal seat
Governing Standards
Related Troubleshooting Guides
Typically Specified In
Other seat sealing designs
Reviewed by Process Engineering, Vajra Industrial SolutionsDiscipline: Valve Service SpecificationLast reviewed: 20 June 2026
Connected Engineering
Standards
Failure Modes
Need valves with fire-safe soft seat (primary/secondary)?
We supply Ball Valves / Butterfly Valves with fire-safe soft seat (primary/secondary) to API 607, with full certification. Get a 24-hour quote.
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