Industrial Valves

Valves are critical components in oil and gas pipelines, controlling flow, pressure, and direction of fluids (oil, gas, water, and chemicals). The selection depends on pressure, temperature, fluid type, and operational requirements.

 1. Main Types of Valves in Oil & Gas  

A. Gate Valve  

- Function: On/Off isolation (not for throttling).  

- Design: A sliding gate (wedge or knife) moves up/down to block flow.  

- Applications:  

  - High-pressure pipelines (ASME Class 600+).  

  - Crude oil, natural gas transmission.  

- Advantages:  

  - Low pressure drop when fully open.  

  - Bi-directional sealing.  

- Disadvantages:  

  - Slow operation, not for frequent use.  

  - Prone to erosion if partially open.  

B. Ball Valve  

- Function: Quick shut-off or flow control (quarter-turn operation).  

- Design: A rotating ball with a bore (full/ported) aligns with the flow path.  

- Types:  

  - Floating Ball Valve – For low/medium pressure.  

  - Trunnion-Mounted Ball Valve – For high-pressure (API 6D).  

- Applications:  

  - Pipeline isolation, pigging stations.  

  - LNG, sour gas (corrosion-resistant materials).  

- Advantages:  

  - Fast operation, tight sealing.  

  - Low maintenance.  

- Disadvantages:  

  - Cavitation risk in high-pressure drops.  

C. Globe Valve  

- Function: Throttling and flow regulation.  

- Design: A plug (disc) moves perpendicular to flow, adjusting the opening.  

- Applications:  

  - Pressure control, metering stations.  

  - Cooling water, fuel gas systems.  

- Advantages:  

  - Precise flow control.  

  - Good shut-off capability.  

- Disadvantages:  

  - High pressure drop.  

  - Heavier than gate/ball valves.  

D. Check Valve (Non-Return Valve - NRV)  

- Function: Prevents backflow.  

- Types:  

  - Swing Check Valve – Hinged disc swings open with flow.  

  - Lift Check Valve – Disc lifts vertically (better for high pressure).  

  - Dual Plate Check Valve – Compact, fast-closing (API 6D).  

- Applications:  

  - Pump discharge, compressor stations.  

  - Subsea pipelines.  

- Advantages:  

  - No manual operation needed.  

  - Protects equipment from reverse flow.  

- Disadvantages:  

  - Water hammer risk if closing too slowly.  

E. Butterfly Valve  

- Function: On/Off or throttling in large pipelines.  

- Design: A rotating disc controls flow (lightweight, compact).  

- Types:  

  - Wafer Type – Clamped between flanges.  

  - Lug Type – Bolted for dead-end service.  

- Applications:  

  - Low-pressure gas, water pipelines.  

  - Fire protection systems.  

- Advantages:  

  - Low cost, easy installation.  

  - Quick operation.  

- Disadvantages:  

  - Not for high-pressure/temperature.  

  - Limited sealing compared to ball valves.  

F. Plug Valve  

- Function: On/Off or diverting flow.  

- Design: A cylindrical or conical plug rotates to open/close.  

- Applications:  

  - Slurry, corrosive fluids.  

  - Wellhead control.  

- Advantages:  

  - Minimal leakage, multi-port options.  

- Disadvantages:  

  - High torque required for large sizes.  

G. Pressure Relief Valve (PRV) / Safety Valve  

- Function: Protects pipelines from overpressure.  

- Types:  

  - Spring-loaded PRV – Adjustable set pressure.  

  - Pilot-operated PRV – For high-capacity systems.  

- Applications:  

  - Storage tanks, boilers.  

  - Compressor stations.  

 2. International Standards for Valve Manufacturing  

Valves in oil & gas must meet strict standards for safety and performance:  

A. API (American Petroleum Institute)  

- API 6D – Pipeline valves (gate, ball, check valves).  

- API 600 – Bolted bonnet steel gate valves.  

- API 598 – Valve inspection & testing.  

- API 6A – Wellhead & Christmas tree valves.  

B. ASME (American Society of Mechanical Engineers)  

- ASME B16.34 – Pressure ratings for steel valves.  

- ASME B16.10 – Face-to-face dimensions.  

C. ISO (International Organization for Standardization)  

- ISO 14313 – Equivalent to API 6D (pipeline valves).  

- ISO 10434 – Bolted bonnet steel gate valves.  

D. MSS (Manufacturers Standardization Society)  

- MSS SP-44 – Steel pipeline flanges.  

- MSS SP-61 – Hydrostatic testing.  

E. NACE (Corrosion Resistance)  

- NACE MR0175/MR0103 – Valves for sour (H₂S) service.  

F. EN (European Norms)  

- EN 593 – Butterfly valves.  

- EN 12516 – Pressure shell design.  

 3. Material Selection for Valves  

| Material       | Application                     | Limitations              |  

| Carbon Steel   | General service (WCB, LCB)      | Not for corrosive fluids    |  

| Stainless Steel| Corrosive, high-temp (CF8M, 316)  | Expensive                 |  

| Duplex Steel   | Offshore, sour gas (UNS S31803)   | High cost               |  

| Alloy 20      | Acidic environments (Carpenter 20)| Limited availability        |  

| Titanium      | Seawater, chlorides               | Very high cost           |  

 Conclusion  

- Gate & Ball Valves dominate high-pressure pipelines.  

- Check Valves prevent backflow in pump/compressor systems.  

- Globe Valves are used for precise flow control.  

- API 6D & ASME B16.34 are key standards for oil & gas valves.  

 Main Tests for Industrial Valve Quality Control  

To ensure reliability, safety, and compliance with international standards, industrial valves undergo rigorous quality control testing. Below are the key test items performed during valve manufacturing and inspection.  

1. Standard Valve Tests (API 598, ISO 5208, ASME B16.34)  

 A. Shell Test (Pressure Test)  

- Purpose: Checks valve body and bonnet for leaks or structural defects.  

- Procedure:  

  - Pressurize the valve body with water (or air/gas) at 1.5x the rated pressure (e.g., 2250 psi for a 1500# valve).  

  - Hold for a specified duration (typically ≥30 seconds).  

- Acceptance Criteria: No visible leakage or pressure drop.  

 B. Seat Test (Sealing Test)  

- Purpose: Ensures tight sealing of the disc/ball against the seat.  

- Procedure:  

  - For low-pressure valves (Class 150-600): Air or nitrogen at 60-100 psi.  

  - For high-pressure valves (Class 900+): Hydrostatic test at 1.1x rated pressure.  

- Types:  

  - Double Block & Bleed (DBB) Test: Checks both upstream and downstream seats.  

  - Single Seat Test: For one-directional valves (e.g., check valves).  

- Acceptance Criteria: Max allowable leakage per API 598/ISO 5208 (e.g., 0 bubbles/min for soft-seated valves).  

 C. Backseat Test (Stem Seal Test)  

- Purpose: Verifies stem sealing when the valve is fully open.  

- Procedure:  

  - Open the valve fully, pressurize the bonnet at 1.1x rated pressure.  

- Acceptance Criteria: No leakage past the stem packing.  

 D. High-Pressure Gas Test (Optional for Critical Service)  

- Purpose: Ensures safety in gas pipelines (e.g., natural gas, hydrogen).  

- Procedure:  

  - Test with helium or nitrogen at 1.1x working pressure.  

  - Detected via mass spectrometer or soap bubble test.  

- Acceptance Criteria: Leak rate < 100 ppm (API 6D).  

2. Functional & Performance Tests  

 A. Operation Torque Test  

- Purpose: Ensures smooth operation without excessive force.  

- Procedure:  

  - Measure torque required to open/close using a torque wrench.  

- Acceptance Criteria: Within manufacturer’s specified limits.  

 B. Cryogenic Test (For LNG Valves, -196°C)  

- Purpose: Validates performance in extreme cold.  

- Procedure:  

  - Cool valve with liquid nitrogen, then perform seat & shell tests.  

- Standards: BS 6364, ISO 28921.  

 C. Fire Test (API 607/API 6FA)  

- Purpose: Ensures valve integrity during fire exposure.  

- Procedure:  

  - Expose valve to 1,400°F (760°C) flame for 30 mins, then perform seat test.  

- Acceptance Criteria: No leakage (soft seats may melt but metal seats must seal).  

 D. Fugitive Emissions Test (ISO 15848, API 624, TA-Luft)  

- Purpose: Checks for VOC (Volatile Organic Compound) leakage from stem seals.  

- Procedure:  

  - Helium or methane detection at stem & body joints.  

- Acceptance Criteria:  

  - ISO 15848 Class AH/BH (≤50 ppm).  

  - API 624 (≤100 ppm).  

3. Material & Non-Destructive Testing (NDT)  

 A. Dye Penetrant Test (PT)  

- Purpose: Detects surface cracks in cast or welded valves.  

- Procedure:  

  - Apply fluorescent dye, inspect under UV light.  

- Standards: ASTM E165, ASME Sec V.  

 B. Magnetic Particle Test (MT)  

- Purpose: Finds subsurface defects in ferromagnetic materials.  

- Procedure:  

  - Magnetize part, apply iron particles.  

- Standards: ASTM E709, ASME Sec V.  

 C. Ultrasonic Test (UT)  

- Purpose: Detects internal flaws (porosity, inclusions).  

- Procedure:  

  - High-frequency sound waves measure material thickness.  

- Standards: ASME Sec V, ASTM E317.  

 D. Radiographic Test (RT)  

- Purpose: X-ray inspection for welds & castings.  

- Procedure:  

  - Uses X-ray or gamma-ray imaging.  

- Standards: ASME Sec VIII, ASTM E94.  

 E. Hardness Test (Brinell/Rockwell)  

- Purpose: Ensures material meets strength requirements.  

- Procedure:  

  - Indentation test on valve body, stem, and seats.  

- Standards: ASTM E10, ASTM E18.  

4. Final Inspection & Documentation  

- Dimensional Check: Verifies flange face, bore size, and end connections.  

- Marking & Tagging: Compliance with API 6D, ASME B16.34.  

- Certification: Mill Test Report (MTR), NACE MR0175 (if applicable).  

Conclusion  

Industrial valves undergo shell, seat, backseat, and functional tests to ensure leak-proof operation. Critical applications (LNG, sour gas) require cryogenic, fire, and fugitive emissions testing. NDT methods (PT, MT, UT, RT) validate material integrity.  

Key Standards:  

- API 598 (Valve Testing)  

- ISO 5208 (Industrial Valve Leakage)  

- API 6D (Pipeline Valves)  

- ASME B16.34 (Pressure Testing)