What does API 6D mean?
API 6D is an international professional standard developed by the American Petroleum Institute (API) for pipeline valves (such as ball valves, gate valves, plug valves, etc.). The latest version is API 6D Edition 25 (released in 2022). Its core specifications include:
1. Design Pressure and Temperature: The standard covers pressure ratings from Class 150 to Class 2500 (PN20 to PN420), and a temperature range of -196℃ to 538℃ (adjusted according to material differences).
2. Material Requirements: Valve bodies must conform to standards such as ASTM A216 (WCB) and A352 (LCC), and sealing materials must pass high-temperature and high-pressure tests.
3. Testing Standards: Valves must pass a 100% body pressure test (1.5 times the rated pressure) and a seal pressure test (1.1 times the rated pressure), referring to Appendix A of API 598.
Criteria for Determining Hard Seals vs. Soft Seals and Selection Recommendations
API 6D does not mandate specific seal types, but the following clauses indirectly influence selection:
1. Hard Seal Valves
- Characteristics: Metal-to-metal seal (e.g., tungsten carbide/stainless steel), suitable for high-temperature (>250℃), high-pressure, or particulate-containing media.
- Standard Basis: API 6D Appendix F recommends for Class 600 and above or acidic environments containing H₂S.
- Typical Applications: Long-distance natural gas pipelines, refinery residue systems.
2. Soft Seal Valves
- Characteristics: Non-metallic seal (e.g., PTFE, rubber), good sealing performance but poor temperature resistance (typically <180℃).
- Standard Basis: API 6D Clause 7.4 requires soft seal materials to pass an anti-aging test (ASTM D2000).
- Typical Applications: Low-pressure urban gas pipelines, chemical media with weak corrosiveness.
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