What is a Bolted Bonnet Valve?

A bolted bonnet valve is a critical component in industrial piping systems, designed for high-pressure and high-temperature applications where safety, durability, and easy maintenance are essential. This blog explores its definition, features, types, applications, and key considerations for selection.

1. Definition of Bolted Bonnet Valve

A bolted bonnet valve refers to a valve construction where the bonnet (cover) is secured to the valve body using bolts or studs. This design ensures a pressure-tight seal, making it suitable for demanding environments like oil & gas, petrochemical, and power plants.

Key Features:

• Removable bonnet for easy inspection and maintenance.
• Robust sealing with gaskets or welding (optional).
• High-pressure resistance (PN 10 to PN 420 per ISO 6002 and GB/T 12234 standards).

2. Types of Bolted Bonnet Valves

Bolted bonnet designs are used in various valve types, including:

A. Bolted Bonnet Gate Valves

• Used for on/off flow control (not throttling).
• Common in oil & gas pipelines (API 600/ISO 6002 standards) .
• Subtypes:Rising stem (OS&Y) – Visual position indicator.Non-rising stem (NRS) – Compact design.

B. Bolted Bonnet Globe Valves

• Ideal for throttling and flow regulation.
• Features linear or equal percentage flow characteristics.

C. Bolted Bonnet Check Valves

• Prevents backflow in pipelines.
• Example: ANSI swing check valves with flanged ends .

D. Bolted Bonnet Ball Valves

• Provides bubble-tight shutoff in high-pressure systems.

3. Key Components & Design

A bolted bonnet valve consists of:

1. Body – Main pressure-containing part (carbon steel, stainless steel, or alloy).
2. Bonnet – Removable cover secured with studs/bolts (ASTM A193 B7 bolts common).
3. Stem – Transmits actuator force to the disc.
4. Seat & Disc – Ensures sealing (metal or soft-seated).
5. Gasket/Packing – Prevents leaks (graphite, PTFE, or spiral-wound).

Bonnet Connection Styles:

• Bolted-only – Standard for most applications.
• Seal-welded bolted – Extra leak protection for hazardous fluids (e.g., HF acid) .

4. Advantages of Bolted Bonnet Valves

✅ Easy Maintenance – Bonnet can be disassembled without removing the valve from the pipeline .
✅ High-Pressure Capability – Suitable for PN 100 to PN 420 systems .
✅ Leak Resistance – Gaskets and bolting ensure a tight seal.
✅ Versatility – Works in steam, oil, gas, and corrosive media .

5. Applications

Bolted bonnet valves are widely used in:

• Oil & Gas – Wellheads, refineries, and pipelines (API 6D/API 600 compliant).
• Power Plants – High-temperature steam systems.
• Chemical Processing – Corrosion-resistant alloys (e.g., Hastelloy).
• Marine & Shipbuilding – Seawater cooling systems.

6. Selection Criteria

When choosing a bolted bonnet valve, consider:

1. Pressure & Temperature Rating – Match with system requirements (ASME B16.34).
2. Material Compatibility – Carbon steel (WCB) for general use, stainless steel (CF8M) for corrosive fluids.
3. End Connections – Flanged, threaded, or butt-welded.
4. Standards Compliance – API, ISO, ANSI, or GB/T 12234 for oil & gas.

7. Industry Standards

• ISO 6002 – Specifies bolted bonnet steel gate valves (DN 10 to DN 1000).
• GB/T 12234 – Chinese standard for petroleum & natural gas valves .
• API 600/602 – Covers steel gate/globe valves for refinery use.

Conclusion

A bolted bonnet valve is a robust, maintainable solution for high-pressure systems, offering reliability in critical industries. Whether for gate, globe, or check valves, its design ensures safety and longevity. Always verify material grades, pressure ratings, and standards before selection.

Need help choosing the right valve? Consult industry standards or a valve specialist for tailored solutions!

References:

• ISO 6002 (Bolted Bonnet Steel Gate Valves)
• GB/T 12234 (Petroleum & Gas Valves)
• ANSI Swing Check Valves
• Bolted Bonnet Maintenance Benefits

Would you like a comparison between bolted bonnet and pressure-seal valves? Let us know in the comments!