ASME B16.9 sets the dimensions of factory-made butt welding fittings from NPS 1/2 to NPS 48: elbows, tees, reducers, caps and stub ends. The wall thickness is not in B16.9 — it comes from the pipe schedule the fitting has to match. The table below gives the two dimensions that decide most layouts: the centre-to-end of a 90° long radius elbow, and the centre-to-end of an equal tee.
ASME B16.9 — centre-to-end dimensions (mm)
| NPS | Pipe OD (mm) | 90° LR elbow A (mm) | Equal tee C = M (mm) |
|---|---|---|---|
| 1/2 | 21.3 | 38 | 25 |
| 3/4 | 26.7 | 38 | 29 |
| 1 | 33.4 | 38 | 38 |
| 1-1/4 | 42.2 | 48 | 48 |
| 1-1/2 | 48.3 | 57 | 57 |
| 2 | 60.3 | 76 | 64 |
| 2-1/2 | 73.0 | 95 | 76 |
| 3 | 88.9 | 114 | 86 |
| 4 | 114.3 | 152 | 105 |
| 5 | 141.3 | 190 | 124 |
| 6 | 168.3 | 229 | 143 |
| 8 | 219.1 | 305 | 178 |
| 10 | 273.0 | 381 | 216 |
| 12 | 323.8 | 457 | 254 |
| 14 | 355.6 | 533 | 279 |
| 16 | 406.4 | 610 | 305 |
| 18 | 457.0 | 686 | 343 |
| 20 | 508.0 | 762 | 381 |
| 24 | 610.0 | 914 | 432 |
A = centre-to-end of a long radius 90° elbow. C = centre-to-end of the run, M = centre-to-end of the branch; for an equal tee C = M. Data to ASME B16.9 — confirm against the project specification before fabrication.
What B16.9 fixes, and what it does not
| Item | Fixed by B16.9 | Comes from the order |
|---|---|---|
| Centre-to-end (A, C, M) | Yes, by size | — |
| Outside diameter at the ends | Yes, matches the pipe OD | — |
| Wall thickness | No | The pipe schedule, for example SCH 40 or SCH 80 |
| Grade and impact testing | No | ASTM A234 WPB, WPL6, WP11, WP22, or A403 for stainless |
| End preparation | Bevelled to ASME B16.25 | Root face and bevel where the welding procedure asks for a variant |
Elbow radius: LR or SR
A long radius elbow has a centreline radius of 1.5 times the nominal size and is the default; a short radius elbow is 1.0 times and is used where space is tight, at the cost of a higher pressure loss. The two are not interchangeable on a line that has to be radiographed or flow-checked, so the radius and the angle belong on the enquiry.
Reducers and caps
A concentric or eccentric reducer follows the tee centre-to-end of its larger size: a 6 x 4 in reducer is 143 mm long, the same C as a 6 in tee. A cap is specified by its length E, which is also fixed by B16.9. State whether the reducer is concentric or eccentric, and give both the large and the small end.
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Related pages
Butt weld fittings · Butt weld elbow · Butt weld tee · Butt weld reducer · ASME B16.11
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