An API 6D floating ball valve is a quarter-turn pipeline isolation valve in which the ball is supported only by its two seat rings - line pressure pushes the ball against the downstream seat, so the process fluid itself supplies the sealing force. It is built to API Spec 6D (25th edition, 2021) and its ISO counterpart ISO 14313:2025, in full-bore sizes from NPS ½ to NPS 8 (DN 15 to DN 200), ASME Class 150 to 600, with soft seats holding ISO 5208 Rate A zero-leakage shutoff. Three things decide whether this design is the right one for a line: the pressure class, the isolation function you need, and the temperature limit of the seat material.
GNEE supplies API 6D floating ball valves in carbon steel, low-temperature carbon steel, stainless steel and duplex, with PTFE, RPTFE, PEEK, Devlon or metal seats, lever or gear operated, with ISO 5211 mounting pads for actuation. Every valve is pressure tested before painting and ships with an EN 10204 3.1 material certificate and a pressure test report. Send your size, class, seat material and end connection for a quotation.
Technical Specifications
| Design standard | API Spec 6D, 25th edition (2021) with addenda through Addendum 3 (March 2025); ISO 14313:2025 (supplement to API 6D 25th ed.) |
|---|---|
| Pressure–temperature basis | ASME B16.34:2025 (standard class) |
| Size range | Full bore: NPS ½"–8" (DN 15–DN 200) Reduced bore: extends to NPS 10"–12" (DN 250–DN 300) in Class 150/300 |
| Pressure class | ASME Class 150, 300 and 600 across the size range; Class 900 and 1500 in reduced small bores (NPS 2" / DN 50 and below) |
| Bore | Full bore (full port) or reduced bore (single reduction, typically one pipe size down) |
| Body construction | One-piece (unibody / fully welded), two-piece split body, three-piece; side entry as standard, top entry on request |
| End connections | Flanged RF (Class 150–600), flanged RTJ (Class 900 and 1500), butt weld to ASME B16.25, socket weld and threaded (NPS 2" and below) |
| Flange dimensions | ASME B16.5 (NPS ½"–24"); ASME B16.47 where applicable |
| Face-to-face / end-to-end | ASME B16.10 |
| Temperature range | −46 °C to +200 °C with PTFE seat; to +230 °C with RPTFE; to +260 °C with PEEK; to +540 °C with metal seat. Cryogenic service to −196 °C available with extended bonnet and qualified seat material |
| Seat leakage | Soft seat: ISO 5208 Rate A (no visible leakage). Metal seat: ISO 5208 Rate CD |
| Standard features | Anti-static device, blowout-proof stem, fire-safe construction with graphite body and stem seals, locking device, ISO 5211 actuator mounting pad |
| Operation | Lever, worm gear, pneumatic, electric or hydraulic actuator |
| Inspection and testing | API 6D and API 598 (11th edition, February 2023). Fire test to API 6FA (4th edition, 2020) or API 607:2022 / ISO 10497:2022 as specified |
| Certification | EN 10204 3.1 material certificate, pressure test report, NDE reports; API Monogram on licensed production; NACE MR0175 / ISO 15156 or MR0103 / ISO 17945 for sour service |
Pressure Classes and Maximum Working Pressure
| ASME Class | Max. working pressure | Typical end connection | Notes for floating design |
|---|---|---|---|
| 150 | 19.6 bar (284 psi) | Flanged RF | Full range to NPS 8", reduced bore beyond |
| 300 | 51.1 bar (741 psi) | Flanged RF | Most common floating specification in process and gas distribution |
| 600 | 102.1 bar (1,480 psi) | Flanged RF or RTJ | Practical upper class for a full-bore floating valve at NPS 6"–8" |
| 900 | 153.2 bar (2,220 psi) | Flanged RTJ | Small bores only (NPS 2" and below); otherwise trunnion mounted |
| 1500 | 255.3 bar (3,700 psi) | Flanged RTJ or butt weld | Small bores only; PEEK or metal seat normally required |
| 2500 | 425.5 bar (6,170 psi) | Butt weld or clamp hub | Not offered as a floating design |
Ratings are quoted at ambient temperature. Working pressure falls as design temperature rises; read the value for your design temperature off the ASME B16.34 table for the material group.
Materials of Construction
| Component | Standard material (ASTM) | Used for |
|---|---|---|
| Body and adapter | A216 WCB / WCC (cast), A105 (forged) | General hydrocarbon, water, steam |
| Body and adapter | A352 LCB / LCC, A350 LF2 (forged) | Low-temperature service, down to −46 °C |
| Body and adapter | A351 CF8 / CF8M, A182 F304 / F316 | Corrosive media, offshore topsides |
| Body and adapter | A182 F51 / F53 / F55, A995 4A / 6A | Chloride service, high-pressure offshore |
| Ball | A182 F316 / F304; A105 with ENP or hard chrome | ENP is the standard coating for carbon steel balls; hard chrome is used for higher wear resistance |
| Ball | Stellite 6 or tungsten carbide overlay on metal-seated designs | Abrasive or high-temperature service |
| Stem | 13Cr, A182 F316, 17-4PH, XM-19, F51, Inconel 718 | Matched to seat and body material |
| Seat ring | PTFE, RPTFE, PEEK, Devlon V, nylon, PCTFE | Soft-seated variants - see the temperature table below |
| Seat ring | Stainless or duplex carrier with Stellite 6, tungsten carbide or chrome carbide facing | Metal-seated variants |
| Body and stem seals | Graphite (body gasket and stem packing), Viton / FKM, HNBR, NBR, FFKM for O-rings | Graphite is what makes the fire-safe claim work |
| Bolting | A193 B7 with A194 2H; A320 L7 with A194 7 for low temperature | API 6D 25th edition requires pressure-boundary bolting from suppliers conforming to API 20E (carbon steel) or API 20F (corrosion-resistant) |
Seat Materials and Their Service Limits
| Seat material | Service temperature | Strengths | Watch for |
|---|---|---|---|
| Virgin PTFE | −45 °C to +200 °C | Nearly universal chemical resistance, lowest friction, lowest cost | Cold flow (creep) under sustained load; not for explosive decompression service |
| RPTFE (15–25 % glass-filled) | −45 °C to +230 °C | Better creep and wear resistance; the default for higher pressure and higher cycle counts | Glass filler is attacked by hydrofluoric acid and strong caustics |
| PEEK | −45 °C to +260 °C | Highest temperature and pressure capability among polymers; almost no cold flow | Attacked by concentrated sulfuric acid and strong oxidising acids; higher torque and cost |
| Devlon V | −45 °C to +177 °C | Very high compressive strength, good cold sealing - used in high-pressure gas | Limited chemical resistance against acids |
| Nylon | −30 °C to +100 °C | High compressive strength, economical | Poor acid resistance; temperature ceiling is the lowest of the group |
| Metal (Stellite 6, tungsten carbide, chrome carbide) | −45 °C to +540 °C | Fire-safe by construction, handles abrasion and high temperature | Metal-to-metal contact cannot reach bubble-tight shutoff; leakage acceptance is ISO 5208 Rate CD, and breakaway torque is materially higher |
Do not treat a soft-seat temperature limit as a pressure rating. PTFE does not simply stop working at 200 °C - it deforms progressively as temperature rises, so the differential pressure the seat can hold falls with it. Published seat pressure–temperature tables commonly show the allowable seat pressure at 200 °C falling to roughly one fifth of its ambient value. A valve selected on "the seat handles 200 °C" and then operated near that temperature at full class pressure will creep, lose preload and leak. Read the pressure and the temperature together, off the same chart.
How a Floating Ball Valve Seals
The ball is free. It is not pinned to the stem at the bottom, and it is not carried on trunnions. Its position is set by the two seat rings and by whatever pressure is acting on it.
Pressure moves the ball. With the valve closed, upstream pressure acts on the full projected area of the ball and pushes it downstream, into the outlet seat ring.
Contact stress becomes the seal. The pushed ball compresses the outlet seat against the ball surface. The higher the pressure, the higher the contact stress - so shutoff quality improves as pressure rises, which is why a soft-seated floating valve passes a high-pressure seat test so readily.
The inlet seat stops being a seal. Because the ball has moved away from the upstream seat, that seat is no longer loaded by the ball. This is the mechanical reason a standard floating design does not provide two independently sealing seats.
Thermal expansion needs somewhere to go. Liquid trapped in the body cavity expands when it warms. API 6D requires cavity over-pressure relief - either a self-relieving seat or an external relief connection - so the cavity cannot be pressurised by a warming liquid slug.
One consequence of that sequence deserves its own line, because it is the most misread part of the design: a floating ball valve seals because of differential pressure, so it cannot be relied on to seal at zero differential pressure. After a pump start, during low-pressure commissioning, and during pipeline pigging isolation, the upstream pressure may be only a few bar. The seat has no meaningful force acting on it and leakage past the outlet seat is possible. Trunnion-mounted valves use spring-loaded seats that seal independently of line pressure, and that is the specific reason they are specified for those duties.
Advantages
Pressure-assisted sealing. The harder the line pressure pushes, the tighter the ball seats against the outlet seat. No spring preload or external force is needed to achieve bubble-tight shutoff at working pressure - soft-seated valves are tested to ISO 5208 Rate A, which means no visible leakage for the full test duration.
Compact and light for the duty. Without trunnion bearings, a heavier body and a spring-loaded seat assembly, a floating valve in DN 100 Class 300 is substantially lighter and shorter than the trunnion equivalent. That reduces pipe support and structural cost at the tie-in point.
Low cost of ownership in small sizes. Floating designs typically cost 30 to 50 percent less than trunnion-mounted valves of the same size and class. In a plant with hundreds of small isolation points, the difference is a procurement line item, not a rounding error.
Fast, quarter-turn operation. A 90° stroke from fully open to fully closed is what makes a ball valve suitable for emergency isolation and for actuation. Manual operation stays practical across most of the floating range, with no multi-turn stem travel.
Simple maintenance. Fewer moving parts and, on split-body versions, a seat that can be reached by removing one body half. Field service does not require the bearing and spring-stack work that trunnion seats demand.
Documented integrity. An API 6D valve ships with material test reports, non-destructive examination records, and both high-pressure and low-pressure seat test results - evidence a generic "API-style" valve does not carry.
Applications
Floating ball valves sit where lines are small or medium, pressures are moderate, cycling is occasional, and the cost of a trunnion-mounted valve cannot be justified. Six duties account for most of the demand.
Utility and instrument isolation
Impulse lines, gauge roots, sample points, drain and vent connections, and utility headers up to DN 80. Bore is small, flow is near zero in normal operation, and the requirement is a positive, visible shutoff rather than a flow characteristic. Reduced bore is normal here.
City gas distribution and metering skids
Distribution mains, regulator station laterals and meter runs typically run Class 150 to 300 in DN 25 to DN 150. RPTFE or nylon seats plus a fire-safe secondary metal seat are the common specification, because a soft seat alone will not survive a downstream fire.
Chemical, pharmaceutical and water lines
Virgin PTFE seats are the default where chemical compatibility and clean media matter more than pressure. Their near-universal resistance and lowest-in-class friction keep operating torque low, which matters when the valve is hand-operated and reached by a short lever.
Small-bore high-pressure connections
Injection lines, hydraulic power units and pressure-test headers in DN 15 to DN 50 use floating ball valves in Class 900 or 1500 with PEEK or metal seats. This is the one place where a floating design is specified above Class 600 - the bore is small enough that the seat load stays manageable.
Tank farm and terminal laterals
Loading arms, pump suction and discharge branches, and drain lines on tanks. Full bore is preferred on pump suction to keep velocity head loss low and protect NPSH; reduced bore is acceptable on branches that are closed in normal operation.
Repair and replacement stock
Maintenance groups keep floating ball valves in common sizes and classes on the shelf. Their simple two- or three-piece construction allows seat and seal replacement in the line on split-body versions, which is why they remain the standard spare for small-bore isolation points.
Why Source from GNEE
Valve and pipe from one supplier. GNEE supplies both the API 6D valve and the matching line pipe, flanges and fittings, so bore, class and material are matched at the point of order rather than at site.
Documentation that matches the claim. Material certificates to EN 10204 3.1, PMI and hardness records, NDE reports, and full pressure test reports including the low-pressure seat test - not a summary sheet.
Seat and trim selection as engineering, not catalogue picking. We will tell you when PEEK is unnecessary and when PTFE will fail, and we will not quote a Class 900 floating valve in a size where the design does not work.
Sour and low-temperature service handled explicitly. Hardness control to 22 HRC, NACE MR0175 / ISO 15156 or MR0103 / ISO 17945 documentation, charpy-tested materials for design temperatures below −29 °C, and low-temperature bolting.
Third-party inspection welcome. Witnessed factory acceptance testing, pre-shipment inspection and client-nominated inspection bodies can all be arranged before the order is placed.
Send your floating ball valve requirement
Give us size, class, bore type, seat material or service conditions, end connection and design temperature, and we will come back with a compliant quotation and a drawing. If you are not yet sure whether the duty belongs to a floating or a trunnion-mounted valve, send the line data and we will tell you which one the mechanics allow.
FAQ
What is an API 6D floating ball valve?
It is a quarter-turn ball valve for pipeline and piping isolation, built to API Spec 6D, in which the ball is held only by the two seat rings. Line pressure pushes the ball into the downstream seat, and that contact stress provides the seal. It is supplied in sizes from NPS ½" to NPS 8" and ASME Class 150 to 600, with soft or metal seats.
What size and pressure class can a floating ball valve cover?
Full bore from NPS ½" to NPS 8" (DN 15 to DN 200) and reduced bore out to NPS 10"–12" in Class 150 and 300. Class 150 to 600 applies across the size range; Class 900 and 1500 are offered only in small bores, typically NPS 2" and below. Floating designs are not produced in Class 2500.
What is the difference between a floating ball valve and a trunnion-mounted ball valve?
In a floating valve the ball moves and the seats are fixed. In a trunnion-mounted valve the ball is fixed on top and bottom trunnions and the seats move, held against the ball by springs. That difference makes trunnion torque nearly independent of pressure, allows sealing at near-zero differential pressure, and makes double block and bleed possible - which is why large-diameter and high-pressure isolation duty goes to trunnion-mounted valves.
Can a floating ball valve provide double block and bleed?
Not as a standard single-piston-effect design. When the valve closes, the ball moves away from the upstream seat, so only the downstream seat is loaded and there are not two independently sealing surfaces to bleed between. If the data sheet requires DBB or DIB, specify a trunnion-mounted valve with dual-piston-effect seats or an equivalent arrangement.
What is the difference between API 6D and API 608 for a ball valve?
API 6D covers valves in pipeline transportation systems; API 608 covers metal ball valves in process facilities such as refineries and chemical plants. The practical boundary is usually the first block valve at the facility fence. API 6D demands more: full-opening availability, cavity relief, extended shell testing for buried service and more extensive documentation. Since the 7th edition of API 608 took effect in October 2025, small-bore high-pressure flanged ball valves (DN 15–DN 50, Class 900–2500) fall under both standards, so the purchase order must state which one governs.
Which seat material should I choose - PTFE, RPTFE, PEEK or metal?
Work up the list and stop at the first option that clears your duty with margin: virgin PTFE to 200 °C for general service, RPTFE to 230 °C where pressure or cycling is higher, PEEK to 260 °C for high temperature and high pressure, and metal seats above that or where abrasion or mandatory fire-safe shutoff applies. Always check the allowable pressure at the operating temperature, not just the temperature limit - a PTFE seat's usable differential pressure falls sharply as temperature rises.
Is an API 6D floating ball valve fire-safe?
A fire-safe design is available and is normally supplied as standard: graphite body and stem seals, plus a metal secondary seat contact that takes over when the polymer seat is destroyed. The design is qualified by type test - 30 minutes of flame exposure with the valve closed and pressurised, followed by cooling, cycling and a post-fire seat leakage measurement. For an API 6D valve the referenced test is API 6FA; API 607 and ISO 10497:2022 are also commonly specified.
What tests are performed before shipment?
Hydrostatic shell test at 1.5 times the pressure rating, hydrostatic seat test at 1.1 times the rating on each seat, a low-pressure gas seat test, a backseat test where fitted, an anti-static continuity test (≤ 10 Ω), and a torque or operability check - all completed before painting, with results recorded and issued. NDE and PMI are added according to the quality specification level on the order.
Summary
An API 6D floating ball valve is the right answer for small and medium isolation points in Class 150 to 600, where its pressure-assisted seal gives bubble-tight shutoff, its cost is a fraction of a trunnion design, and its limits are respected. Those limits are specific: full bore to NPS 8", no reliable sealing at zero differential pressure, no true double block and bleed, and soft-seat performance that has to be read off a pressure–temperature chart rather than a single temperature figure. Specify it inside those limits and it will outlast the line. Specify it outside them - as some datasheets still do, at 36 inches and Class 2500 - and it will not work at all.