A double block and bleed plug valve is a plug valve whose two sealing faces block pressure from both ends and let the cavity between them be vented, replacing two block valves and a spool with up to 66 % fewer flange joints. Typical supply covers NPS 2–42 (DN 50–1050), ASME Class 150–1500, and carbon, stainless and duplex bodies rated from −46 °C to 200 °C.
A double block and bleed (DBB) plug valve is a quarter-turn isolation valve that combines a cavity-free plug flow path with the verified two-barrier DBB function. API 6D defines double block and bleed as one valve whose two seating surfaces block pressure from both ends and vent the body cavity. A plug valve achieves this through an expanding or twin-seal mechanism: two independent seals engage the upstream and downstream faces while the hollow plug body forms the bleed cavity. As a DBB plug valve for oil and gas, LNG, refining and chemical duty, it is built as an API 6D plug valve to API 6D and API 599 from ASTM A216 WCB to ASTM A995 duplex.
Technical Specifications
The table below lists the supply envelope for a typical API 6D and API 599 plug valve, covering lubricated, twin seal plug valve and expanding designs. Where shown, a value is verified by the cited standard; other values are manufacturer ranges to confirm against the purchase specification. The same envelope supports a NACE MR0175 plug valve and an ISO 15848-1 plug valve with qualified bodies and low-emission packing.
| Parameter | Typical range / value | Standard |
|---|---|---|
| Size (NPS) | NPS 2–42 (DN 50–1050); API 599 covers NPS 1/2–24 | ASME B16.10 |
| Pressure class | ASME Class 150–1500 (PN 20–260); API 6A to 15,000 psi (103 MPa) | ASME B16.34 |
| Body material | A216 WCB (yield 240 MPa), A352 LCC (yield 255 MPa, −46 °C), A351 CF8M (yield 205 MPa), A995 4A/5A duplex (yield 450/550 MPa) | ASTM |
| Seat / seal | Metal-to-metal or resilient (PTFE / NBR); renewable sealant film on lubricated types | API 599 |
| End connection | RF, FF, RTJ, BW | ASME B16.5 / B16.47 |
| Operation | Lever, worm gear, electric, pneumatic, hydra-pneumatic | MSS SP-25 |
| Temperature | −46 °C to 200 °C (elastomer/PTFE limited); special to +230 °C | ASME B16.34 |
| Seat leakage | Zero visible leakage at 1.1× rated, each side (ISO 5208 Rate A equivalent) | API 6D / ISO 5208 |
| Fire-safe | API 607 or API 6FA | API 607 / 6FA |
| Fugitive emission | ISO 15848-1 low-emission packing available | ISO 15848-1 |
| Sour service | NACE MR0175 / ISO 15156 qualified bodies on request | NACE MR0175 |
Main Part Materials
| Part | Standard material | Optional |
|---|---|---|
| Body / bonnet | A216 WCB, A352 LCC, A351 CF8M | A351 CF8 / CF3 / CF3M, A995 duplex, Monel, Inconel |
| Plug | A105 + ENP, F304, F316 | F22, F316L, hard-faced |
| Seat ring | PTFE / PPL (resilient) | Graphite-loaded, metal-to-metal |
| Packing | Graphite / PTFE | Low-emission ISO 15848-1 set |
| Bolts / nuts | B7 / 2H | L7 / 4, B8 / 8, B8M / 8M |
DBB Plug Valve vs. Two Separate Block Valves
| Criterion | Single DBB plug valve | Two block valves + bleed |
|---|---|---|
| Flange joints | One body, up to 66 % fewer | Two bodies + spool + bleed |
| Face-to-face | Matches a single valve (ASME B16.10) | Longer spool assembly |
| Isolation integrity | One certified valve, API 6D DBB | Two independent valves |
| Maintenance | One valve; in-line reseal (lubricated) | Three valves to maintain |
| Typical use | Pig traps, metering, injection, skids | Battery-limit, plant-to-pipeline tie-ins |
Standards and Editions in Force
| Standard | Subject | Status / note |
|---|---|---|
| API 6D | Pipeline valves (ball, gate, plug, check) | Current; defines DBB function and seat test |
| API 599 | Metal plug valves | Current; plug-valve specific |
| API 6A | Wellhead and tree equipment | Current; to 15,000 psi plug valves |
| API 598 | Valve inspection and testing | Current; pressure test basis |
| API 607 / API 6FA | Fire testing of quarter-turn / 6D valves | Current |
| ISO 5208 | Industrial valve seat leakage rates | Use Rate A / CD / D (not ANSI/FCI 70-2) |
| ISO 15848-1 | Fugitive emission | Current low-emission reference |
| NACE MR0175 / ISO 15156 | Sour service | Current; H₂S qualification |
| ASME B16.5 / B16.10 | Flanges / face-to-face | Current dimensional basis |
DBB is a function, not a valve type. A plug valve is one way to implement double block and bleed; ball valves and API 6A wellhead valves do so as well, while an API 6D gate valve is single-block-and-bleed (SBB), not DBB. The choice between DBB vs DIB is made on the purchase order: specify DBB for one self-relieving seat; specify DIB-2 where redundant bidirectional isolation is mandatory. Confirm the seat arrangement rather than assuming the product name defines the barrier.
Applications
DBB plug valves are specified wherever a single valve must prove positive isolation before any break-in work, particularly in hydrocarbon and hazardous-fluid systems.
Pipeline isolation and pigging: DBB plug valves serve as mainline block valves and at pig-launcher and -receiver stations, where the bleed connection confirms seat integrity before the trap door opens. They cover NPS 2–42 (DN 50–1050) at ASME Class 150–1500 and meet API 6D, isolating a section without a separate bleed assembly.
Metering and custody-transfer skids: On fiscal metering runs, a DBB plug valve isolates individual meters for proving without shutting the entire line, holding each seat to zero leakage at 1.1× rated pressure per API 6D. This protects calibration accuracy and keeps the run online during meter change-out and inspection.
Chemical injection and sampling points: At injection quills and instrument take-offs, DBB or DIB-1 isolation lets crews change drums or sampling cylinders without exposing the process line to pressure. NACE MR0175 / ISO 15156 compliance is available for sour chemical services above 5,000 ppm H₂S, preventing sulfide-stress cracking in the body.
Tank farms, terminals and loading: Refinery and terminal manifolds use DBB plug valves to prevent product cross-contamination between grades and to secure loading arms. The cavity-free plug body avoids a trapped heel that could mix batches or release vapour during break-in, an advantage over valves with a body recess.
Wellhead and high-pressure service: API 6A DBB plug valves isolate christmas-tree master and wing valves at working pressures to 15,000 psi (103 MPa), providing the double barrier required for well intervention and workover. A single valve replaces two block valves plus a bleed valve, cutting weight on offshore topsides.
Test and inspection
Send your requirement - NPS and DN, ASME class, body and trim material, seat arrangement (DBB or DIB-2), end type, and quantity - to sale@gneetube.com or call +8615824687445, we return a technical submittal and itemized proposal, with MTR, NACE and ISO 15848-1 options on request.
FAQ
What is a DBB plug valve?
A double block and bleed (DBB) plug valve is a quarter-turn isolation valve that combines the cavity-free flow path of a plug valve with the verified two-barrier isolation of the DBB function. API 6D defines DBB as a single valve with two seating surfaces that block pressure from both ends and provide a connection for venting the body cavity. A plug valve achieves this through an expanding or twin-seal mechanism in which two independent seals engage on the upstream and downstream faces while the hollow plug body forms the bleed cavity.
DBB plug valve vs ball valve: which should I specify?
Both can provide DBB, but the designs fit different services. A plug valve has a cavity-free body and a wiping, field-restorable seal, so it suits slurries, sticky or toxic media and in-line resealing. A ball valve gives full-bore piggability, lower torque and easier automation, so it dominates clean high-pressure transmission lines. Above roughly NPS 6 and high class, plug-valve torque rises sharply, which favors the ball valve unless a cavity-free body is the deciding factor.
What standards apply to DBB plug valves?
Pipeline DBB plug valves are built to API 6D, with API 599 covering metal plug valves specifically. Seat leakage is verified to ISO 5208 Rate A (zero visible leakage at 1.1x rated pressure, tested from each side per API 6D). Ends and face-to-face follow ASME B16.5 and ASME B16.10; fire-safe testing uses API 607 or API 6FA, and sour service uses NACE MR0175 / ISO 15156. Avoid the control-valve leakage terms ANSI/FCI 70-2 Class VI, which do not apply to quarter-turn isolation valves.
What size and pressure range can you supply?
Standard supply covers NPS 2 to 42 (DN 50 to 1050), ASME Class 150 to 1500 (PN 20 to 260), with API 6A versions rated to 15,000 psi (103 MPa) for wellhead duty. Ends include RF, FF, RTJ and BW. Common catalog range is NPS 2 to 24 per API 599; larger sizes are quoted on request with verified actuation torque.
Which materials suit sour or corrosive service?
For general hydrocarbon duty, ASTM A216 WCB carbon steel (minimum yield 240 MPa) is standard. Corrosive or marine service uses ASTM A351 CF8M stainless (yield 205 MPa); sour gas uses NACE MR0175 / ISO 15156-qualified bodies, often CF8M or ASTM A995 duplex. Duplex grades 4A/5A reach 450 to 550 MPa yield and resist chloride pitting. Low-temperature LCC bodies are rated to -46 deg C.
Can a DBB plug valve be resealed without removing it from the line?
Yes, for lubricated designs. Sealant is injected through external fittings with a standard grease gun, renewing the sealing film and restoring bubble-tight performance as the valve ages. This in-line reseal avoids the workshop seat replacement that a soft-seated ball valve requires once its seats are worn, which is why plug valves are common in hard-to-shut-down plants.
What documents and certificates come with an order?
Each valve ships with an EN 10204 3.1 material test report (MTR), a hydrostatic and seat-test report per API 6D / API 598, and marking to MSS SP-25. NACE MR0175, ISO 15848-1 low-emission and third-party inspection (e.g. SGS, BV, TUV) certificates are available on request. PMI, UT, RT, PT and MT are offered as options.
What are your MOQ, lead time and warranty?
MOQ is negotiable and often starts at one piece for standard sizes. Typical lead time is 4 to 8 weeks depending on material and certification; expedited builds are possible. We provide an 18-month warranty from shipment and supply spare seals and grease fittings. OEM and ODM with your nameplate and drawings are supported. Confirm exact figures with our sales team before ordering.