API 598 Butterfly Valves
What API 598 requires for butterfly valves — applicability, key and testing requirements, the alternative standards, and compliant supply with full certification.
What does API 598 require for butterfly valves?
API 598 (Valve Inspection and Testing, American Petroleum Institute (API)) sets the design, material and testing requirements for butterfly valves in its scope. API 598 is the universal valve testing and inspection standard, defining acceptable leakage rates (leak classes) for hydrostatic shell tests, seat leakage tests, and backseat tests. It is referenced by virtually every valve purchasing specification globally and defines the distinction between Class A (zero leakage - metal seat) and Class D (maximum soft seat leakage) tests.
Applicable Pressure Classes
Key Requirements
- Shell test: 1.5× rated pressure, water or air, duration per table
- Low-pressure seat test (air): 80–100 kPa (12–15 psig), duration per table
- High-pressure seat test (water): 1.1× rated pressure, duration per table
- Backseat test (for OS&Y gate/globe valves with backseat): 1.1× rated pressure
- Leak Class A: zero leakage (bubble-tight) - metal seats, safety valves
- Leak Class D: soft-seat maximum - up to 0.18 mL/min/NPS for NPS ≤2" in liquid
Testing Requirements
- Shell test: 1.5× rated CWP, minimum duration per table
- High-pressure seat: 1.1× rated CWP, liquid, duration per table
- Low-pressure seat: 80–100 kPa, gas (air/N₂), duration per table
- Backseat test where specified
Alternative Standards for Butterfly Valves
Other standards that also govern butterfly valves — useful for spec cross-acceptance.
Related Standards
Connected Engineering
Need API 598 butterfly valves?
We supply API 598-compliant butterfly valves with full certification — share your size, class and service for a 24-hour quote.