A double block and bleed ball valve, built to API 6D, is a quarter-turn isolation valve with two independent seals and a vented cavity, so an isolated section can be depressurized and proved safe before work begins. The API 6D ball valve achieves this with two self-relieving seats, each passing the seat test from either side at 1.1 times the rated pressure. Common sizes span NPS 2–48 (DN 50–1200) and classes from ASME 150 to 2500, in bodies of ASTM A216 WCB, A105, A350 LF2, A351 CF8M and duplex F51. One compact unit replaces two block valves and a spool, cutting flange joints by up to 66 %.
Technical Specifications
The DBB ball valve size range covers NPS 2–48 (DN 50–1200) and the DBB ball valve pressure class spans ASME 150–2500, as listed below. Figures below are the standard supply range for API 6D double block and bleed ball valves. Values outside this range (e.g. NPS 56, subsea, API 6A wellhead) are quoted per project data sheet.
| Parameter | Range / Specification | Standard |
|---|---|---|
| Size range | NPS 2–48 (DN 50–1200); small-bore NPS 1/2–2 | API 6D |
| Pressure class | ASME Class 150–2500 (PN 16–PN 420); API 6A wellhead to 15,000 psi | ASME B16.34 / API 6A |
| Design type | Floating (≤ NPS 8 / Class 600) and trunnion mounted (full range) | API 6D |
| Bore | Full bore (FB) or reduced bore (RB) | API 6D |
| End connections | RF / RTJ flanged, butt-weld, socket-weld | ASME B16.5 / B16.47 / B16.25 / B16.11 |
| Face to face | Long pattern | API 6D / ASME B16.10 |
| Temperature | −29 °C to +200 °C (soft seat); −46 °C (LCC); −196 °C (cryogenic); +425 °C (metal seat) | ASTM material / API 607 |
| Seat options | PTFE, RPTFE, PEEK, Devlon, SS + graphite (fire-safe) | - |
| Operation | Lever, gear, pneumatic, electric, hydraulic (ISO 5211) | ISO 5211 |
| Leakage class | Zero visible leakage, soft seat | ISO 5208 Rate A / API 598 |
| Fire-safe | Secondary metal-to-metal seal | API 607 / ISO 10497 |
| Fugitive emission | Live-loaded packing (optional) | ISO 15848-1 / 15848-2 |
| Sour service | Low-hardness trim, controlled hardness | NACE MR0175 / ISO 15156 |
Body and trim materials
| Material (ASTM) | Type | Min. yield strength | Typical service |
|---|---|---|---|
| A216 WCB | Cast carbon steel | 240 MPa (35 ksi) | General pipeline, ambient |
| A105 | Forged carbon steel | 250 MPa (36 ksi) | General, flanged bodies |
| A350 LF2 | Forged low-temp carbon | 250 MPa (36 ksi) | Low temperature to −46 °C |
| A352 LCC | Cast low-temp carbon | 240 MPa (35 ksi) | Cryogenic to −46 °C |
| A351 CF8M / A182 F316 | Stainless 316 | 205 MPa (30 ksi) | Corrosive, sanitary |
| A182 F51 | Duplex (S31803) | 450 MPa (65 ksi) | Sour / seawater |
| A182 F53 | Super duplex (S32750) | 550 MPa (80 ksi) | Severe corrosive |
| A217 WC6 | 1.25Cr-0.5Mo | 280 MPa (40 ksi) | High temperature |
Isolation type selection (DBB / DIB)
| Type | Seat design | Isolation | Cavity relief | Specify when |
|---|---|---|---|---|
| DBB | Two SPE seats | Both ends, self-relieving | Automatic both sides | Standard isolation, cost priority |
| DIB-1 | Two DPE seats | Full bidirectional | External device required | Critical, high-integrity isolation |
| DIB-2 | One DPE + one SPE | Hybrid, one side full | Automatic one side | Balanced safety and cost |
Advantages
The double block and bleed arrangement reduces installed cost and risk compared with a two-valve isolation spool while keeping isolation verifiable.
Fewer leak paths: A single DBB ball valve replaces two block valves and a spool piece, cutting flange joints by up to 66 % and weight by up to 60 % versus a conventional assembly. Fewer connections mean fewer leak points across the isolated boundary, directly lowering fugitive-emission exposure and the inspection load on a pipeline or plant.
Verifiable isolation: The bleed connection lets an operator vent the body cavity and confirm both seats hold before breaking containment, turning isolation from an assumption into a test. API 6D requires each seat to pass a test performed from each side at 1.1× rated pressure, so a dry bleed proves the downstream side is safe to open for maintenance or hot work.
Fire-safe performance: Soft-seated DBB ball valves are built to API 607 / ISO 10497, with a secondary metal-to-metal seal that engages after the seat insert burns away in a fire. The stem and body seals use graphite, and spiral-wound gaskets keep the bonnet sealed at temperature, so the valve retains shutoff when non-metallic parts are destroyed.
Lower operating torque: A trunnion mounted ball valve carries seat load on bearings rather than line pressure, so torque stays low and predictable from Class 150 to 2500 and across NPS 2–48. That lets smaller actuators be specified and protects the seats from overloading, an advantage for automated and large-bore valves where floating designs would need oversized, high-cost operators.
Sour-service capability: DBB ball valves are supplied to NACE MR0175 / ISO 15156 for H2S service, using low-hardness bodies such as A350 LF2 or duplex F51 and graphite or PEEK seats. Hardness control and material selection prevent sulfide-stress cracking, so the valves suit sour gas gathering, processing and injection where standard carbon-steel trim would fail under wet H2S exposure.
Applications
The DBB ball valve for oil and gas, chemical and power service is specified wherever a process section must be isolated and verified depressurized before maintenance or pressure testing proceeds.
Pipeline isolation and pigging: DBB ball valves serve as main-line block valves on oil and gas transmission lines from NPS 2 to 48 (DN 50–1200), where full-bore designs let pigs pass without restriction. API 6D qualifies them to Class 2500 (PN 420), and the bleed port confirms both seats hold before the line is opened for inspection or weld tie-in.
Wellhead and manifold isolation: At wellheads and production manifolds, DBB ball valves give verified isolation between the tree and downstream equipment, cutting the risk of trapped hydrocarbons during workover. API 6A covers wellhead versions to 15,000 psi, while API 6D pipeline versions handle gathering duty from −46 °C to 200 °C with soft seats or higher with metal seats.
Instrument and sampling isolation: Small-bore DBB ball valves (NPS 1/2–2, DN 15–50) isolate pressure transmitters, gauges and analyzers so instruments can be calibrated or replaced without stopping the process. The cavity bleed protects sensitive equipment from line pressure and lets trapped fluid drain safely, a routine need in refinery and chemical-injection service where uptime matters.
Tank farm and loading isolation: In storage and loading terminals, DBB ball valves isolate tanks and meters for fiscal proving, maintenance and overfill protection. Their bubble-tight shutoff per ISO 5208 Rate A prevents product loss at the seal, and a single body replaces a two-valve arrangement, lowering installation cost and the count of potential leak points across a tank-farm network.
Power and utility isolation: DBB ball valves isolate feedwater, cooling-water and fuel-gas lines, including high-pressure steam systems where metal-seated versions rated to 425 °C are used. They support safe isolation during turbine and boiler maintenance, and ISO 5211 mounting lets plants add electric or pneumatic operators for remote ESD duty without re-flanging the valve.
DBB Ball Valve packaging and shipping
Send us your DBB ball valve specification-size (NPS/DN), pressure class, body and seat material, end connection, bore type, seat configuration (DBB / DIB-1 / DIB-2), medium, operating temperature and required tests or certificates. Our engineering team returns a data sheet and lead time within 24 hours.
FAQ
What is a double block and bleed ball valve?
A double block and bleed (DBB) ball valve is a quarter-turn isolation valve with two independent self-relieving seats and a vented body cavity. Per API 6D, each seat passes the seat test performed from each side at 1.1 times the rated pressure, so both ends are isolated and the cavity can be bled to confirm a safe, depressurized section before maintenance.
What sizes and pressure classes are available for DBB ball valves?
Pipeline API 6D ball valves span NPS 2–48 (DN 50–1200) and ASME Class 150–2500 (PN 16–PN 420). Floating designs are common up to NPS 8 / Class 600; trunnion-mounted designs cover the full range including large bore and high class. Small-bore instrument versions run NPS 1/2–2. API 6A wellhead versions reach 15,000 psi.
What is the difference between DBB, DIB-1 and DIB-2?
DBB uses two self-relieving (SPE) seats and vents the cavity to the lower-pressure side automatically. DIB-1 uses two double-piston-effect (DPE) seats for full bidirectional isolation but needs an external cavity-relief device. DIB-2 combines one DPE and one SPE seat, giving hybrid isolation with one-sided automatic relief. Select by flow direction, cavity-relief need and risk-not preference.
Which materials are used for sour and low-temperature DBB ball valves?
For sour (H2S) service, bodies such as A350 LF2 or duplex F51 with graphite or PEEK seats are supplied to NACE MR0175 / ISO 15156, with controlled hardness to avoid sulfide-stress cracking. For low temperature, A352 LCC bodies are rated to −46 °C and cryogenic packages to −196 °C. Material traceability is documented under EN 10204 3.1.
What testing and certification are provided with DBB ball valves?
Every valve is hydrostatically shell-tested at 1.5× the working pressure and seat-tested at 1.1× with zero visible leakage for soft seats per ISO 5208 Rate A / API 598. Fire-safe performance is verified to API 607 / ISO 10497, and fugitive-emission packing to ISO 15848 when specified. EN 10204 3.1 material certificates, ITP and test reports are supplied.
What is the difference between floating and trunnion mounted DBB ball valves?
A floating ball is pushed against the downstream seat by line pressure, so torque rises with pressure and it suits small bore (NPS 2–8) and Class 150–600. A trunnion mounted ball valve is carried on bearings, so seat load does not depend on line pressure and torque stays low and predictable across NPS 2–48 and Class 150–2500-preferred for large bore, high class and automated duty.
What are your MOQ, lead time and quotation requirements for DBB ball valves?
Minimum order quantity starts from 1 piece for standard designs; typical lead time is 4–8 weeks depending on material and actuation. For a quotation, provide size (NPS/DN), pressure class, body and seat material, end connection, bore type, seat configuration (DBB/DIB-1/DIB-2), medium, temperature and required tests or certificates.
Do DBB ball valves meet fire-safe and fugitive-emission standards?
Yes. Soft-seated DBB ball valves are built to API 607 / ISO 10497 with a secondary metal-to-metal seal that engages after the seat insert burns away, and graphite stem and bonnet seals. For low-emission duty, ISO 15848-1 / 15848-2 live-loaded packing is offered and the emission class and test cycles are stated on the data sheet.
Conclusion
Double block and bleed ball valves provide verified two-way isolation in a single body, a practical choice for pipeline, wellhead, instrument, tank-farm and power isolation where safety and leak control matter. Built to API 6D with self-relieving seats, fire-safe API 607 compliance and optional NACE MR0175 / ISO 15848 fugitive-emission packages, they span NPS 2–48 (DN 50–1200) and ASME Class 150–2500. The bleed port turns isolation into a checkable step instead of an assumption, and the compact design cuts flange joints by up to 66 % versus a two-valve spool.