What Are ASME B16.11 Socket-Weld Fittings?
ASME B16.11 covers forged, socket-welding end fittings from NPS 1/8 through NPS 4, in pressure classes Class 3000, Class 6000 and Class 9000. The pipe slips into a machined socket and is fillet-welded at the end — a compact, leak-tight connection for high-pressure small-bore piping (instrument, hydraulic, chemical and utility lines).
Fitting Types Covered
- 90° / 45° elbows — dimensions per ASME B16.11 Table 4 (socket-welding elbows, tees and crosses)
- Tees & crosses — equal and reducing outlets, Table 4
- Full couplings, half-couplings & reducing couplings — Table 5
- Unions (socket) — Table 5
- Caps, plugs & bushings — end-to-end caps Table 5; plugs and bushings Table 6
Pressure Classes
| End Type | Pressure Classes | Size Range |
|---|---|---|
| Socket-weld fittings | Class 3000 / 6000 / 9000 | NPS 1/8 – 4 |
Available combinations by class and NPS are listed in ASME B16.11 Table 7. Class-to-schedule correlation is given in Table 8.
Materials
Forged construction: A105 carbon steel (-29°C to 425°C), A182 F304 / F316 / F321 stainless steel (up to 538°C), A350 LF2 low-temperature forged carbon steel. Chemistry and mechanical properties per the applicable ASTM forging standard.
Related Standards
- ASME B16.11 — Forged Fittings (parent standard)
- ASME B16.11 Threaded Fittings — Classes 2000/3000/6000
- ASME B16.9 — Buttwelding Fittings (NPS 1/2–48)
- ASME B16.5 — Socket-Weld Flanges (NPS 1/8–4)
- Our Fittings Range
FAQ
What sizes do socket-weld fittings cover?
NPS 1/8 through NPS 4. Above NPS 4, buttwelding fittings per ASME B16.9 are used instead.
What is the difference between Class 3000, 6000 and 9000?
These are pressure-temperature ratings, not schedules. Higher class = thicker forging wall for higher service pressure. Available size-by-class combinations are in B16.11 Table 7.
How is a socket-weld fitting assembled?
The pipe is inserted into the machined socket (with a small gap per the code), then fillet-welded around the rim. The joint is stronger and more leak-tight than threaded.
Can socket-weld fittings be used for high pressure?
Yes — Class 6000 and Class 9000 are standard for high-pressure instrumentation, hydraulic and chemical injection lines.
Which materials are available?
A105 carbon steel, F304/F316/F321 stainless, and LF2 low-temperature forged steel — all forged per their respective ASTM specifications.
Which dimension tables should I consult?
Elbows, tees and crosses: Table 4. Couplings, half-couplings, unions and caps: Table 5. Plugs and bushings: Table 6.
Need This Standard for Your Project?
We manufacture and export flanges, fittings and gaskets to ASME standards. Send your standard, size, material, and quantity — we reply within 24 hours.