The most common types of ball valves in the oil and gas industry are categorized by their ball support design (Floating vs. Trunnion), body assembly (Side Entry, Top Entry, or All-Welded), and bore size (Full Bore vs. Reduced Bore). Most must comply with the API 6D standard for pipeline service.
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API 6D Ball Valve Classification (Construction & Assembly)
| Category | Valve Type (Standard Terminology) | Technical Features & API 6D Requirements |
| Ball Support Design | Floating Ball Valve | The ball is supported by seats and moves downstream under pressure. Generally limited to sizes below NPS 10 (DN250) and Class 150-300. |
| Trunnion Mounted Ball Valve (TMBV) | The ball is fixed by upper and lower bearings (trunnion). The standard configuration for large-bore, high-pressure API 6D pipelines; offers low torque and stable sealing. | |
| Body Assembly Type | Side Entry (Split Body) | Available in 2-piece or 3-piece bolted designs. The most common type; easy to manufacture and maintain for standard pipeline services. |
| Top Entry Ball Valve | Features a monolithic (one-piece) body. Supports In-line Maintenance, allowing repairs without removing the valve from the welded pipeline. | |
| Fully Welded Body Valve | The body is fully sealed by welding with no bolted joints. Eliminates external leak paths; ideal for Buried gas transmission pipelines. |
Bore & Functional Classification Table
| Item | Type | API 6D Definition & Value |
| Bore Diameter | Full Bore (FB) | Bore diameter complies with API 6D Table 1. Supports Pigging operations with minimal flow resistance. |
| Reduced Bore (RB) | Bore is smaller than the pipeline diameter. Offers lower torque and cost; not suitable for pipelines requiring pigging. | |
| Sealing Function | Double Block & Bleed (DBB) | In the closed position, two seats seal against pressure simultaneously, and the cavity can be vented to verify seal integrity. Standard API 6D configuration. |
| Double Isolation & Bleed (DIB-1 / DIB-2) | Provides double isolation. Even if one seat fails, the other maintains sealing through mechanical or fluid pressure. | |
| Operation Mode | Manual, Gear, Actuated | API 6D valves often require actuators (Pneumatic, Hydraulic, or Electric) and must have mounting pads complying with standard dimensions. |
Key Accessories & Critical Features for API 6D Valves
| Features | Technical Description | Application Significance |
| Emergency Injection | Fittings for injecting sealant into the seats and stem. | Provides a temporary secondary seal if the primary soft seat is damaged. |
| Anti-Static Device | Ensures electrical continuity between the ball, stem, and body. | Prevents spark ignition in explosive oil and gas environments. |
| Anti-Blowout Stem | Features an internal shoulder design (internal entry). | Prevents the stem from being ejected under pressure during packing maintenance. |
| Fire-Safe Design | Certified to API 607 or API 6FA. | Ensures a secondary metal seal remains intact if soft seals melt during a high-temperature fire event. |
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FAQ
What is natural gas ball valve
Natural gas ball valves are key control devices in natural gas transmission systems, primarily used in petrochemical, natural gas refueling stations, heating networks, and shipbuilding industries. These valves feature either a floating or fixed design, high wear resistance, excellent sealing performance, and easy operation, enabling the shut-off, connection, or regulation of pipeline media. Different models, such as Q341F-16C and Q41F, are suitable for applications ranging from ambient to cryogenic liquefied natural gas, and offer manual and turbine drive options.
What is the difference between API 6D and API 594?
API Standard 594 covers the design, materials, face-to-face dimensions, pressure-temperature ratings, and inspection, testing, and examination requirements for two types of check valves.
API SPEC 6D adopts ISO 14313: 1999, Oil and gas industry-Pipeline transport systems-Pipeline valves. This international standard specifies and provides recommendations for the design, manufacture, testing, and documentation of ball valves, check valves, gate valves, and plug valves used in pipeline systems.