Seat
The sealing surface inside the valve body against which the disc, ball, gate, or plug closes to achieve shutoff. Seat leakage class (ANSI/FCI 70-2) defines acceptable leakage: Class IV (metal seat, 0.01% of max Cv or less), Class V (metal, 0.0005% or less), Class VI (soft seat, zero leakage per ANSI tables).
Related Terms
Applicable Standards
Valve Inspection and Testing
API 598 is the universal valve testing and inspection standard, defining acceptable leakage rates (leak classes) for hydrostatic shell tests, seat leakage tests, and backseat tests.
Industrial Valves - Pressure Testing of Metallic Valves
ISO 5208 is the international standard for pressure testing of metallic valves.
Frequently Asked Questions
What is a Seat in a valve?
The sealing surface inside the valve body against which the disc, ball, gate, or plug closes to achieve shutoff. Seat leakage class (ANSI/FCI 70-2) defines acceptable leakage: Class IV (metal seat, 0.01% of max Cv or less), Class V (metal, 0.0005% or less), Class VI (soft seat, zero leakage per ANSI tables).
What materials are used for the Seat?
Seat material selection depends on the process fluid, operating temperature and pressure, and required corrosion resistance. Standard materials include carbon steel (A216 WCB/A105), austenitic stainless steel (SS316/316L), and corrosion-resistant alloys (Hastelloy C-276, Inconel 625, duplex stainless steel 2205/2507) for aggressive service. All materials must be certified with EN 10204 Type 3.1 MTCs traceable to the heat number.
What standards govern the design of the Seat?
Valve component design is governed by ASME B16.34 for pressure-temperature ratings, API 600/602 for gate valves, API 609 for butterfly valves, and API 6D for pipeline valves, as applicable. Third-party inspection to these standards ensures compliance. Vajra Industrial Solutions supplies valves with full documentation packages including dimensional inspection records and material certificates.
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Related Troubleshooting
- ModerateGate Valve Leaking Past Seat (Internal Leak)
- ModerateBall Valve Leaking Past Seat (Internal Leak)
- ModerateButterfly Valve Not Sealing / Seat Leakage
- ModerateCheck Valve Passing in Reverse / Back Leakage
- ModerateGlobe Valve Seat Leakage / Wire-Drawing Erosion
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