API 598 Needle Valve Testing Procedure | Quality Standards – Perfect Engineers

What is API 598?

API 598 is the American Petroleum Institute’s standard for:

• Valve inspection and test methods
• Hydrostatic and pneumatic pressure testing
• Seat leakage classification and criteria

It applies to valves used in:

• Oil & gas
• Petrochemical
• Refining
• Power plants
• Process instrumentation systems

Needle valves, though small in size, must meet the same quality, safety, and leak-tightness standards as large process valves.

API 598 Testing for Needle Valves – What’s Included?

1. Hydrostatic Shell Test

• Purpose: Check body integrity under pressure
• Medium: Water (typically with corrosion inhibitor)
• Pressure: 1.5x rated working pressure
• Duration: At least 1 minute
• Acceptance: No visible leakage allowed

2. Hydrostatic Seat Test

• Purpose: Verify leak-tightness at valve seat
• Medium: Water
• Pressure: 1.1x rated pressure
• Acceptance: No leakage at either port (Class VI or bubble-tight for needle valves)

3. Air Seat Test (Optional / On Request)

• Medium: Dry air or nitrogen
• Pressure: ~80–100 psi
• Purpose: Confirm tight shutoff under low-pressure gas conditions
• Method: Visual check for bubble formation in water bath
• Common for instrumentation valves, gas applications, and high-purity systems

Each needle valve undergoes both seat and shell testing to validate safety and performance across its full pressure class (up to 10,000 PSI).