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American Valve Test Standards (API/ASME/MSS): A Deep, Engineer-Friendly Guide

In North America, valve requirements are defined by multiple complementary standards that cover design, ratings, leakage acceptance, fire-safety, emissions, and waterworks performance.

  • ASME B16.34 — Design, materials, wall thickness, P–T ratings, marking, baseline tests.
  • API 598 — General inspection and testing for isolation valves.
  • API 6D / ISO 14313 — Pipeline valve integrity (DBB/DIB, cavity relief, gas seat tests, torque).
  • MSS SP-61 — Common pressure-testing practice for steel valves.
  • FCI/ANSI 70-2 — Control valve leakage Classes II–VI.
  • API 607 / API 6FA — Fire tests; ISO 10497 global equivalent.
  • API 641 / 622 / 624 — Low-emission standards.
  • AWWA Series — Waterworks standards (C509, C515, C504, C507).

Valve Test Standards

ASME B16.34 — THE CONSTRUCTION & RATING SPINE

ASME B16.34 covers metallic valves and defines pressure–temperature ratings, material groups, minimum wall thickness, marking, and baseline pressure tests.

Practical use:

  • Select material per chemistry and temperature.
  • Confirm P–T rating for worst-case condition.
  • Use ASME B16.5/B16.47 for flanges.

Spec line: “Valves shall conform to ASME B16.34 for design, materials, wall thickness, and P–T ratings.”

API 598 — THE EVERYDAY INSPECTION & TEST STANDARD

Defines hydrostatic shell and seat tests, low-pressure gas tests, backseat tests, and operational checks.

Acceptance:

  • Soft seats: zero visible leakage.
  • Metal seats: limited visible leakage allowed.
  • Check valves: specific criteria apply.

Engineer’s tip: shell test hydro, seat test per API 598, add low-pressure air test for soft seats.

API 6D — PIPELINE VALVES

Includes DBB/DIB verification, cavity relief, high-pressure gas seat tests, torque checks, and documentation requirements. Stricter than API 598.

Spec line: “Pipeline valves shall meet API 6D, verify DIB as specified, cavity relief, gas seat tests, torque.”

MSS SP-61 — STEEL VALVES TESTING

Standard pressure-testing practice for steel valves. Commonly used where API 598 is not mandated and often paired with ASME B16.34.

FCI/ANSI 70-2 — CONTROL VALVE SHUTOFF

Defines Classes II–VI for control valve seat leakage. Class IV is typical default; Class V/VI used for demanding services.

Spec line: “Control valve shutoff shall meet FCI 70-2 Class IV unless otherwise specified.”

FIRE-SAFE TESTING

Fire test standards include API 607, API 6FA, and ISO 10497. Valves are exposed to fire while pressurized to measure primary and secondary leakage.

Spec line: “Valves in hydrocarbon service shall be fire-tested per API 607 or API 6FA/ISO 10497.”

LOW EMISSIONS STANDARDS

Low-emission requirements include API 641 for quarter-turn valves, API 622 for packing, and API 624 for rising-stem valves.

Spec line: “Valves in VOC service shall meet API 641 or API 624 with API 622 packing.”

WATERWORKS — AWWA

AWWA standards apply to potable water valves and differ from API/ASME in pressure classes, coatings, torque expectations, and service conditions.

FACTORY ACCEPTANCE TESTS (FATs)

  • Hydrostatic shell test ~1.5× rating.
  • Directional hydro seat test.
  • Low-pressure air seat test (soft seats).
  • Backseat test (if provided).
  • Operational/torque checks.
  • Special tests: fire-safe, FE, cryogenic, vacuum, DBB/DIB.

ACCEPTANCE & DOCUMENTATION

  • Soft seats: zero leakage.
  • Metal seats: limited leakage per API/ISO.
  • MTCs, calibrations, test records, markings, fire-safe/FE certificates.

API VS EN/ISO DIFFERENCES

API focuses on procedural testing and visual acceptance, while EN/ISO uses numeric leakage classes. Projects often blend the two.

Example: “Shell per API 598; Seat per ISO 5208, Rate A.”

EXAMPLE SPECIFICATION LANGUAGE

  • Isolation valves: ASME B16.34 design, API 598 tests, ISO 5208 leakage rates.
  • Pipeline valves: API 6D, DBB/DIB, cavity relief, gas seat tests.
  • Control valves: IEC 60534-4, FCI 70-2 Class IV.
  • Fire-safe: API 607/6FA/ISO 10497.
  • Low emissions: API 641/624/622.
  • Waterworks: AWWA + NSF coatings.

COMMON PITFALLS

  • Over-specifying Class VI for control valves.
  • Skipping gas seat tests for gas service.
  • Confusing DBB vs DIB terminology.
  • Not specifying soft-seat air test.
  • Mixing AWWA with API without caution.

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.