What is the difference between API 6D and API 594?
API Standard 594 covers the design, materials, face-to-face dimensions, pressure-temperature ratings, and inspection, testing, and examination requirements for two types of check valves.
API SPEC 6D adopts ISO 14313: 1999, Oil and gas industry-Pipeline transport systems-Pipeline valves. This international standard specifies and provides recommendations for the design, manufacture, testing, and documentation of ball valves, check valves, gate valves, and plug valves used in pipeline systems.
Standard Positioning & Scope
| Aspect | API 6D | API 594 |
|---|---|---|
| Applicable Objects | Pipeline valves (ball/gate/check valves, etc.) | Check valves only (swing/lift types) |
| Core Content | Design, manufacturing, and testing requirements | Specialized performance & testing for check valves |
Differences
API 6D:
Covers various valve types (including check valves in Chapter 10)
Requires bidirectional sealing tests (low/high-pressure verification).
API 594:Exclusive check valve tests:
Backflow leakage test
Water hammer resistance test
Cracking pressure test
Stricter endurance test: ≥100,000 open/close cycles.
Applications
API 6D: Main valve selection for oil/gas pipelines (e.g., ball/gate valves).
API 594: Critical check valve applications (e.g., pump outlet backflow prevention, chemical process protection).
API 6D Valve and API 594 Valve in stock
