An API 6D DBB ball valve is a quarter-turn isolation valve that uses two independent seats and a body-cavity bleed to isolate a pipeline section and prove it depressurized before work begins. Built to API 6D with self-relieving (SPE) seats, it covers NPS 2–56 (DN 50–1400), ASME Class 150–2500, and body materials from ASTM A216 WCB to duplex F51, rated from −46 °C to +210 °C.
A double block and bleed (DBB) ball valve is a quarter-turn isolation valve that provides the verified two-barrier isolation of the DBB function through the flow path of a ball valve. API 6D defines double block and bleed as a single valve with two seating surfaces that block pressure from both ends and provide cavity venting. A ball valve achieves this through spring-energized, self-relieving seats that each pass the seat test from either side at 1.1 times the rated pressure. As an API 6D DBB ball valve for oil and gas, LNG, refining and chemical duty, it is built in ASTM A216 WCB to ASTM A995 duplex and replaces two block valves and a spool to cut flange joints by up to 66 %.
Technical Specifications
The DBB ball valve size range is NPS 2–56 (DN 50–1400) and the DBB ball valve pressure class spans ASME Class 150–2500; floating designs serve to NPS 8 / Class 600 while trunnion mounted designs cover the full range, so the floating vs trunnion ball valve choice follows size and pressure. Values outside this range are quoted per project datasheet.
Supply range
| Parameter | Standard range | Note |
|---|---|---|
| Size | NPS 2–56 (DN 50–1400) | Floating common to NPS 8 / Class 600; trunnion covers full range |
| Pressure class | ASME Class 150–2500 (PN 16–PN 420) | API 6A wellhead versions reach 15,000 psi |
| Temperature | −46 °C to +210 °C | Extended bonnet for cryogenic; metal seat to +540 °C |
| Design standard | API 6D, ASME B16.34, EN ISO 17292 | Project specification governs if cited |
| Face-to-face | API 6D / ASME B16.10 | B16.10 short pattern for NPS ≥ 24 |
| Ends | RF, RTJ, BW, SW | ASME B16.5 / B16.47 / B16.25 / B16.11 |
| Bore | Full / reduced | Full bore for piggable lines |
| Operation | Lever, gear, pneumatic, electric, hydraulic | ISO 5211 actuator pad |
| Seat arrangement | DBB (SPE/SPE), DIB-1 (DPE/DPE), DIB-2 (SPE/DPE) | State on order |
Body and trim materials (yield strength)
| Material (ASTM) | Type | Min. yield (MPa) | Min. tensile (MPa) |
|---|---|---|---|
| A216 Gr. WCB | Cast carbon steel | 250 | 485 |
| ASTM A352 Gr. LCC | Cast low-temp carbon steel | 240 | 450 |
| A105 / A350 LF2 | Forged carbon / LT carbon | 250 | 485 |
| A182 F304 / F316 | Stainless 304 / 316 | 205 | 515 |
| ASTM A351 CF8M | Cast 316 SS | 205 | 485 |
| A995 Gr. 1A (F51) | Duplex | 450 | 655 |
| A182 F51 / F53 | Duplex / super-duplex | 450 / 550 | 655 / 795 |
Isolation selection: DBB vs DIB
| Arrangement | Seats | Cavity relief | When to specify |
|---|---|---|---|
| DBB | 2 × SPE (self-relieving) | Automatic to line | Standard pipeline, liquid service, thermal-relief concern |
| DIB-1 | 2 × DPE (bidirectional) | External relief valve required | Critical gas isolation, ESD, redundant sealing |
| DIB-2 | 1 SPE + 1 DPE | SPE side self-relieves | Vessel isolation needing directional redundancy |
Note: DBB is a capability label, not a valve family. A double block and bleed valve may be built as a ball valve, a plug valve or a paired block-and-bleed assembly; a plug valve can also be a DBB valve. An API 6D gate valve is single-block-and-bleed (SBB). Always confirm the seat arrangement on the order, because the product name alone does not define the barrier.
Applications
An API 6D DBB ball valve is specified wherever a pipeline section must be isolated and verified depressurized before isolation, maintenance, or pressure testing proceeds.
Pipeline isolation and pigging: An API 6D DBB ball valve is the main-line block valve on oil and gas lines from NPS 2 to NPS 56 (DN 50–1400). API 6D qualifies it for pipeline service to Class 2500, and the bleed port confirms both seats hold before inspection or weld tie-in for pigging.
Metering and terminal stations: At custody-transfer metering skids and tank-farm terminals, the valve isolates a meter tube or pump set so it can be depressurized under proof of zero energy. The 1.1× rated-pressure seat test from each side, required by API 6D, gives the documented leak-tight isolation that fiscal metering and terminal safety cases demand.
Emergency shutdown and HIPPS: In ESD and high-integrity pressure-protection systems, a trunnion mounted API 6D ball valve with DBB isolation provides the fast, repeatable block that protects downstream equipment from overpressure. API 6D trunnion designs carry seat load on bearings, keeping actuator torque predictable from Class 150 to 2500 across the full NPS 2–56 range.
Offshore and space-limited tie-ins: Where a platform or skid cannot fit two separate block valves and a spool, one API 6D DBB ball valve replaces that assembly and cuts flange joints by up to 66 %. Weight drops by up to 60 %, and the compact body eases layout and maintenance in offshore modules.
Refinery and petrochemical manifolds: In refineries and chemical plants, the valve isolates process sections carrying hydrocarbons, steam or aggressive media so they can be opened for maintenance. Body materials span ASTM A216 WCB, A350 LF2, A182 F316 and duplex F51, while fire-safe API 607 and ISO 15848-1 low-emission packing address the plant's safety and emissions limits.
FAQ
What is the difference between a DBB and a DIB ball valve?
DBB uses two self-relieving (SPE) seats and vents cavity overpressure to the line automatically. DIB-1 uses two double-piston-effect (DPE) seats for two-way redundancy but needs an external cavity relief valve. DIB-2 pairs one SPE and one DPE seat. The choice follows the isolation risk, not the product name.
What size range and pressure class does an API 6D DBB ball valve cover?
Standard supply spans NPS 2–56 (DN 50–1400) 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. Small-bore instrument versions run NPS 1/2–2.
What information is needed for an API 6D DBB ball valve quotation?
Send valve type, size and DN, ASME class, body and trim material, seat arrangement (DBB or DIB-2), end connection, medium, design temperature, operation method, quantity and required document scope (datasheet, ITP, MTC, NDE).
What certificates and test reports are provided?
Each valve is supplied with an EN 10204 3.1 MTC, hydrostatic shell and seat test records to API 6D and ISO 5208 Rate A, and painting/packing documents. Third-party inspection (SGS, TUV, BV) and project ITP are available on request.
What is the MOQ, lead time and warranty?
MOQ starts from 1 piece for standard designs; project orders are quoted per datasheet. Typical lead time is 4–8 weeks depending on material and size. The warranty is 18 months from shipment or 12 months from commissioning, whichever comes first.
Can you supply OEM and sour-service (NACE) versions?
Yes. Private-label (OEM) supply with your nameplate and packaging is available. For H2S service, bodies and trim are supplied to NACE MR0175 / ISO 15156 with controlled hardness and CRA overlays on wetted faces.
Does a DBB ball valve need an external cavity relief valve?
A standard DBB with SPE seats self-relieves cavity overpressure to the line, which API 6D requires. Only DIB configurations with DPE seats need an external relief valve. Specifying the seat arrangement is therefore the first step in any DBB order.
API 6D versus API 608 - which standard applies?
API 6D covers pipeline valves; API 608 covers process-plant metal ball valves. The boundary is the first isolation valve at the plant battery limit. When a datasheet cites both, the project specification governs.