Selection Guide for Common Valves in Natural Gas Service – Engineering Configuration Essentials from High-Pressure Long-Distance Transmission to LNG Systems

From gas field gathering, purification, and processing to long-distance pipelines, pressure regulation & metering, and LNG receiving & regasification, valves in natural gas systems perform shut-off, regulation, and isolation functions. Different operating conditions impose specific requirements on valve structure, sealing methods, materials, and actuators. Based on engineering project records and current standards, this article organizes the application of regulating valves, ball valves, and butterfly valves in natural gas systems for the reference of design, procurement, and operations & maintenance personnel.

Comprehensive Guide to Natural Gas Valve Selection

I. Typical Operating Condition Characteristics of Natural Gas

Common parameter ranges are as follows:

• Pressure Rating: Class 600 to Class 2500 (PN100 to PN420)

• Differential Pressure Range: Typically 8 to 15 MPa before and after pressure regulating stations

• Temperature Range:

  • LNG storage, transportation, and regasification systems: -196℃ to -162℃

  • Some heat-traced or compression systems: Up to over 450℃

• Medium Types: Dry gas, wet gas, sour gas (containing H₂S/CO₂), small amounts of condensate, and particulates

These conditions directly determine valve structure type, sealing method, material selection, and actuator configuration.

II. Key Application Points for Regulating Valves

Regulating valves are primarily used for continuous flow and pressure control, with typical scenarios including pressure regulation & metering stations, high differential pressure reduction, and LNG regasification flow regulation.

High Differential Pressure Reduction Conditions

When natural gas is throttled under high differential pressure, supersonic jets, noise, and vibration are easily generated.

• Multi-stage pressure reduction structures (maze type or multi-stage orifice type) can dissipate energy in stages, controlling flow velocity and noise levels. Field measurement data shows that under reasonable selection and installation conditions, noise can be controlled to around 85 dB(A).

• Flow velocity calculation is required during selection to avoid the outlet velocity approaching the speed of sound.

Sour Service Conditions with H₂S

When the medium meets the determination criteria of NACE MR0175 / ISO 15156, materials must comply with sulfide stress cracking resistance requirements.

• It is recommended to conduct an environmental assessment based on H₂S partial pressure and provide material qualification certificates.

• A bellows seal structure is recommended where necessary to reduce the risk of external leakage.

LNG Low-Temperature Conditions

Low-temperature systems not only require an extended bonnet structure but also attention to:

• Low-temperature impact toughness of body and bonnet materials

• Charpy impact test reports

• Dimensional stability after cryogenic treatment

Low-temperature valves generally need to comply with BS 6364 to ensure reliable sealing performance at -196℃.

High-Flow Bypass Systems

• A balanced structure can reduce plug stem thrust and improve operational stability.

• In high-flow, low-differential pressure scenarios, Cv margin and rangeability should be verified to avoid small-opening vibration.

III. Key Application Points for Ball Valves

Ball valves are primarily used for isolation and emergency shutdown (ESD), serving as a core safety component in natural gas systems.

Long-Distance Pipelines and ESD Systems

• Trunnion-mounted ball valves are commonly used in medium to high-pressure pipelines. Typical configurations include:

  • Double Block and Bleed (DBB)

  • Double Piston Effect (DPE)

• The action time of ESD valves should be determined based on the project's SIL rating. In practical engineering, main stroke completion is typically required within 1 to 3 seconds, subject to the specific process package and Safety Integrity Level documentation.

• Fire safety performance should comply with API 607.

Regulation or Conditions with Small Amounts of Particulates

• V-port ball valves are suitable for equal percentage control scenarios.

• If the medium contains small amounts of condensate or particulates, an eccentric structure can reduce seal face wear.

Low-Temperature Ball Valves

In LNG storage and transportation systems, the following are commonly used:

• Extended bonnet design

• Low-temperature specific sealing materials

• Anti-contraction structural compensation design

Compliance with API 6D is also required.

IV. Key Application Points for Butterfly Valves

Butterfly valves offer the advantages of compact structure and lower torque in large-diameter systems.

Heat-Traced Systems and Compressor Stations

• Triple-offset metal-seated butterfly valves are suitable for medium to high-temperature systems.

• The leakage class should be determined according to ANSI/FCI 70-2 or project specifications.

Large-Diameter Medium to High-Pressure Isolation

• For pipelines DN600 and above, double-offset or triple-offset structures can be selected based on torque and response time requirements.

• During selection, the following must be performed:

  • Torque calculation

  • Actuator output torque verification

  • Opening/closing time assessment

LNG Low-Temperature Pipelines

• Low-temperature butterfly valves must comply with BS 6364 testing requirements, and material low-temperature impact performance must be verified.

V. Key Configuration Points for Actuators and Accessories

Natural gas systems have high reliability requirements for actuators. The following should be considered:

• Explosion protection rating (Ex d / Ex ia)

• Air supply pressure stability

• SIL certification matching (ESD systems typically require SIL 2 or above)

• Failure mode on air loss (Fail Closed / Fail Open)

• ESD systems should undergo actual measured action time testing, not just reference theoretical values.

VI. Reference Configuration by Process Unit

VII. Valve Selection Precautions

• Recommend reserving an 18%–25% margin for Cv value.

• Determine NACE compliance based on H₂S partial pressure.

• Low-temperature valves require impact test and low-temperature sealing test reports.

• ESD valves should undergo field action time testing.

• Actuator torque must be verified for large-diameter butterfly valves.

• Pay attention to stem low-emission leakage requirements.

• Fire rating should comply with API 607 or project specifications.

VIII. Frequently Asked Questions (FAQ)

Q1: How to select the regulating valve structure for a high differential pressure natural gas pressure regulating station?

A: When the differential pressure exceeds 8 MPa, a multi-stage pressure reduction structure can reduce flow velocity step by step, minimizing cavitation and noise. Field measurement data can serve as a reference for selection.

Q2: Why do LNG system valves require an extended bonnet design?

A: The extended bonnet structure isolates the stem and actuator from the low-temperature zone, preventing stem freezing and seal failure, meeting the temperature requirements of low-temperature conditions.

Q3: Is a bellows seal necessary for natural gas containing H₂S?

A: When the H₂S concentration is high, a bellows seal reduces the risk of medium external leakage. Materials must provide NACE MR0175 qualification certificates.

Q4: Should a ball valve or a butterfly valve be used for an emergency shutdown valve on a long-distance pipeline?

A: Trunnion-mounted ball valves are commonly used for pipelines DN600 and below. For DN600 and above, double-offset or triple-offset butterfly valves can be selected, depending on pipeline diameter, torque, and response time requirements.

Q5: How much Cv value margin should be reserved during valve selection?

A: Generally, an 18%–25% margin is recommended, while also considering summer peak and winter trough flow rate variations.

IX. Reference Standards

• API 6D

• API 598

• API 607

• NACE MR0175 / ISO 15156

• BS 6364

• ANSI/FCI 70-2

X. Closing Note (Disclaimer)

This content is compiled based on natural gas engineering project operational records and current standards. Process conditions and safety integrity levels vary by project. Final valve selection should be verified and confirmed based on specific parameters and third-party certification documents.