What Is ASME B16.11?
ASME B16.11 is the American National Standard for forged fittings, socket-welding and threaded, from NPS 1/8 through NPS 4. Threaded-end fittings are covered in Classes 2000, 3000, and 6000; socket-weld-end fittings in Classes 3000, 6000, and 9000.
Fitting Types Covered
- 90° / 45° Elbows — socket weld and threaded
- Tees — equal and reducing
- Couplings — full, half, and reducing
- Unions — socket and threaded
- Caps, Plugs & Bushings — socket and threaded
- Crosses — socket and threaded
Pressure Classes
| End Type | Pressure Classes |
|---|---|
| Threaded fittings | Class 2000 / 3000 / 6000 |
| Socket-weld fittings | Class 3000 / 6000 / 9000 |
Materials
A105 (carbon steel), A182 F304 / F316 / F321 (stainless), A350 LF2 (low temperature) — forged construction for high-pressure integrity.
Related Standards
FAQ
What sizes does ASME B16.11 cover?
NPS 1/8 through NPS 4. Socket-weld flanges per B16.5 also end at NPS 4 — above that use buttwelding connections.
What is the difference between Class 3000 and 6000 fittings?
Class designates pressure-temperature rating, not schedule. Higher class = thicker wall for higher service pressure.
Threaded or socket weld — which is better?
Socket weld gives a more leak-tight, higher-pressure joint than threaded; threaded suits lower pressure and easy disassembly. Choose by service and code requirements.
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