Valves in Natural Gas Pressure Reduction Stations: Types, Features, and Selection Criteria

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In high-pressure transmission pipelines, natural gas typically flows at 40–70 bar. However, city networks and industrial facilities require the gas at much lower pressures, usually between 1–20 bar. This adjustment is achieved in pressure reduction stations (PRS). Within these stations, valves play a critical role, not only in reducing pressure but also in ensuring operational safety, efficiency, and continuity.

Valves Used in Pressure Reducing

KEY TYPES OF VALVES IN PRESSURE REDUCTION STATIONS

Pressure Reducing Valves (PRVs)

  • The primary element of PRS, designed to reduce high inlet pressure to a stable and safe outlet pressure.
  • Features:
    • Precise control of downstream pressure
    • Noise and cavitation reduction options
    • Compatible with automation and control systems
  • Standards: EN 334, ISO 23555

By-Pass Valves

  • Provide redundancy in case of regulator failure or during maintenance.
  • Example: Critical installations often employ dual regulators plus a by-pass line to guarantee uninterrupted supply.

Blowdown / Drain Valves

  • Used to depressurize or empty sections of the pipeline.
  • Function: Ensures maintenance safety by isolating sections under pressure.

Safety and Relief Valves

  • Protect the system against unexpected overpressure conditions.
  • Working principle: Opens automatically at a preset pressure to release excess gas.

Control Valves

  • Integrated into SCADA and PLC systems for continuous monitoring.
  • Adjust flow, pressure, and temperature parameters dynamically.
  • Essential in industrial city gate stations with high consumption levels.

VALVE SELECTION CONSIDERATIONS

Flow Range and Capacity

Valves must cover both minimum and maximum consumption scenarios.

  • Example: For a PRS with a design flow of 5,000 Sm³/h, the pressure reducing valve should reliably handle flows between 2,000–7,000 Sm³/h.

Pressure Drop (ΔP)

Pressure reduction is the core task of PRS valves.
ΔP = Pin − Pout

  • Pin: Inlet pressure (bar)
  • Pout: Outlet pressure (bar)

Engineering Note: Rapid fluctuations in outlet pressure can trigger cavitation and noise problems.

Control Characteristics

  • Linear: Flow increases proportionally with valve opening.
  • Equal Percentage: Provides stable control at low openings and rapid flow increase at higher openings.
  • Quick Opening: Best suited for emergency shutoff or rapid actuation.

Cavitation and Noise Control

  • High-pressure drops can cause cavitation inside the valve body.
  • Solution: Multi-stage pressure-reducing valves or silencers.

Actuator Type

  • Pneumatic Actuators: Fast response, most common in PRS.
  • Electric Actuators: Strong integration with SCADA but slower response.
  • Hydraulic Actuators: Used in extra-large valve sizes.

SAFETY AND STANDARDS

  • EN 334 – Gas pressure regulators
  • ISO 23555 – Industrial gas pressure regulation
  • PED (Pressure Equipment Directive) – EU pressure equipment directive
  • ASME – Pressure ratings and design standards

REAL-WORLD APPLICATIONS

  • Istanbul City Gate Stations (Turkey): High-capacity PRVs reduce gas pressure from 70 bar to 19 bar for city distribution.
  • Ruhr Region (Germany): Dual regulators with by-pass valves provide 100% redundancy for enhanced reliability.
  • Japan: Multi-stage noise-reducing valves are installed in urban PRS located near residential areas.

CONCLUSION

Valves in pressure reduction stations are fundamental to safe, efficient, and uninterrupted natural gas distribution. Selection must consider flow ranges, pressure drops, cavitation risk, and automation requirements. Modern PRS increasingly rely on SCADA integration, advanced regulators, and multi-stage valve designs to ensure both operational efficiency and safety. Choosing the right valve technology is not just a matter of performance—it is a cornerstone of reliable and sustainable gas supply.

Types, Features, and Selection Criteria of Valves in Natural Gas Pipelines

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Natural gas plays a vital role in meeting the world’s energy demand, and its safe transmission depends heavily on the performance of valves installed in pipelines. Valves regulate flow, control pressure, isolate sections of the pipeline, and provide emergency shutdown capabilities. Choosing the wrong type of valve not only reduces efficiency but can also lead to severe safety risks.

This article examines the types of valves used in natural gas pipelines, their features, material and standard requirements, and key factors engineers must consider when selecting them.

Natural Gas Pipelines

MAIN VALVE TYPES IN NATURAL GAS PIPELINES

Ball Valves

  • The most widely used valves in natural gas systems.
  • Advantages: Full-bore design minimizes pressure drop. Operated with a quarter-turn (90°), making them ideal for emergency shutoff.
  • Applications: Commonly used in long-distance transmission pipelines and city gate stations.

Gate Valves

  • Preferred in large-diameter transmission lines.
  • Advantages: Minimal flow resistance when fully open.
  • Disadvantages: Slower to operate compared to ball valves.
  • Example: Frequently installed in 36” and larger pipeline sections.

Butterfly Valves

  • Compact and cost-effective solutions for large-diameter lines.
  • Advantages: Lightweight, simple construction, and economical.
  • Applications: More common in distribution networks operating at medium pressure.

Control Valves

  • Designed to regulate flow rate and pressure.
  • Features: Can be integrated into SCADA and automation systems.
  • Example: LNG terminals rely on control valves for continuous adjustment of gas flow.

Safety and Relief Valves

  • Protect pipelines from overpressure events.
  • Operation: Open at a preset pressure, venting gas to the atmosphere.
  • Standard: Designed according to API 520/521.

Check Valves

  • Prevent reverse flow, protecting compressors and downstream equipment.
  • Example: A standard component in compressor stations.

MATERIAL SELECTION AND STANDARDS

  • Common Materials:
    • Carbon steel (ASTM A105, A216 WCB)
    • Low-temperature steels (ASTM A350 LF2)
    • Stainless steels (AISI 304, 316) for corrosive environments
  • Relevant Standards:
    • API 6D – Pipeline valves
    • ASME B16.34 – Pressure-temperature ratings
    • ISO 14313 – International pipeline valve standard

KEY SELECTION CRITERIA

Pressure Class

Valves are designed according to ANSI classes ranging from 150 to 2500.
Example: A 70-bar transmission pipeline typically requires a Class 600 valve.

Flow Coefficient (Cv)

The capacity of a valve is defined by its flow coefficient:

Q = Cv · √(ΔP / G)

  • Q: Flow rate (m³/h)
  • ΔP: Pressure drop (bar)
  • G: Specific gravity of gas

Temperature and Operating Conditions

  • Natural gas is usually transported between -20 °C and +60 °C.
  • Valve seals and body materials must be compatible with this range.

Automation and Remote Control

  • Critical stations require actuated valves (electric, pneumatic, or hydraulic).
  • Example: City gate stations often use pneumatically actuated ball valves integrated into SCADA.

Safety and Maintainability

  • Valves with Double Block & Bleed (DBB) design improve maintenance safety.
  • They also allow testing of pipeline segments under pressure.

REAL-WORLD APPLICATIONS

  • TANAP Project (Turkey): The 1,850 km Trans-Anatolian Natural Gas Pipeline relies on API 6D ball valves for high-pressure transmission.
  • European Distribution Networks: Medium-pressure networks frequently use butterfly and control valves.
  • Compressor Stations: Check valves are indispensable to prevent backflow damage.

CONCLUSION

Valves in natural gas pipelines are essential for safety, efficiency, and operational continuity. From ball and gate valves to butterfly, control, and relief valves, the selection depends on pipe diameter, pressure class, flow capacity, and automation requirements.

Improper valve selection can result in high operational costs or serious safety hazards. Therefore, engineers must rely on API, ASME, and ISO standards, ensuring each valve is designed and chosen for the specific conditions of the pipeline.