ASME B16.11 covers forged steel fittings with socket welding or threaded ends, from NPS 1/8 to NPS 4, in classes 2000, 3000, 6000 and 9000. The class is not a pressure in psi: it corresponds to a wall thickness and a matching pipe schedule, and it decides which fitting can be used on a given small bore line.
Class and the pipe schedule it matches
| Class | Approximate pipe schedule | Typical use |
|---|---|---|
| 2000 | SCH 80 / XS in the smaller sizes | Utility and low pressure small bore |
| 3000 | SCH 80 / XS | The default for small bore process lines |
| 6000 | SCH 160 | Higher pressure small bore |
| 9000 | XXS | Highest pressure, limited size range |
The class-to-schedule relationship is approximate and size dependent. The working pressure is read from the B16.11 pressure–temperature ratings for the material, not from the class number alone.
Products in the B16.11 line
| Product | Ends | Size range | Where it is used |
|---|---|---|---|
| 90° and 45° elbow | Socket weld or threaded | NPS 1/8–4 | Direction change on small bore lines |
| Tee and cross | Socket weld or threaded | NPS 1/8–4 | Branch take-off and cross connections |
| Full and half coupling | Socket weld or threaded | NPS 1/8–4 | Pipe joint, extension and instrument connection |
| Cap | Socket weld or threaded | NPS 1/8–4 | Line end closure |
| Union, plug, bushing, nipple | Threaded | NPS 1/8–4 | Removable joints and transitions |
Socket weld or threaded?
| Point | Socket weld | Threaded |
|---|---|---|
| Joint | Pipe sits in the socket and is fillet welded outside | Screwed NPT joint, no welding |
| Where it is preferred | Small bore lines where a full penetration weld is not practical | Where hot work is not allowed, or the joint has to be broken |
| Limit to know | Needs an expansion gap at the bottom of the socket, about 1.6 mm, to avoid cracking at the weld | Thread engagement and sealant decide the joint; not used for high pressure |
What to state on a B16.11 enquiry
Product, size, class (2000 / 3000 / 6000 / 9000), end type (socket weld or threaded), grade and quantity. For a socket weld item, state the pipe schedule; for a threaded item, state NPT and whether the thread is male or female.
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Related pages
Socket weld fittings · Threaded fittings · ASME B16.9 dimensions · MSS SP-97 olets
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