Dimensional standard
ASME B16.11
Forged Fittings, Socket-Welding and Threaded
ASME B16.11 covers forged socket weld and threaded fittings used mainly on small-bore piping, with pressure classes expressed as 2000, 3000, 6000 and 9000.
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What it covers
- Socket weld fittings in Class 3000, 6000 and 9000.
- Threaded fittings in Class 2000, 3000 and 6000.
- Elbows, tees, crosses, couplings, half couplings, caps, plugs, bushings and unions.
- Typically applied to small-bore lines up to around NPS 4.
Practical notes
Points to specify
- Socket weld fittings require a socket bore and shoulder; a small gap is normally left before welding to allow for expansion.
- Threaded fittings use NPT threads to ASME B1.20.1 unless another thread form is specified.
- Class designations describe strength ratings, not psi values, and depend on material.
Common questions about ASME B16.11
- When are socket weld fittings preferred over buttweld?
- On small-bore piping where a full buttweld is impractical, socket weld fittings give a quick, repeatable joint with simpler fit-up.
- What does Class 3000 mean?
- It is a strength class defined in the standard. The allowable working pressure depends on the material and temperature, not on the number itself.
More references
General guidance only. Work from the current published edition of the standard and your project specification; sizes, grades, classes and documentation are confirmed per enquiry.