Cap Dimensions
A domed end closure welded onto the end of a run. E is measured from the welding end to the outside of the crown, so it is the length the cap adds to the pipe.
- Standard
- ASME B16.9
- Dimension
- Length E
- Size range
- NPS 1/2 – NPS 24
- Sizes published
- 21
Dimensions are given in inches, with the millimetre equivalent beneath in grey.
| Size | Matching pipe OD | Length E |
|---|---|---|
| NPS 1/2 | 0.840 in | 1.0025.40 mm |
| NPS 3/4 | 1.050 in | 1.0025.40 mm |
| NPS 1 | 1.315 in | 1.5038.10 mm |
| NPS 1 1/4 | 1.660 in | 1.5038.10 mm |
| NPS 1 1/2 | 1.900 in | 1.5038.10 mm |
| NPS 2 | 2.375 in | 1.5038.10 mm |
| NPS 2 1/2 | 2.875 in | 1.5038.10 mm |
| NPS 3 | 3.500 in | 2.0050.80 mm |
| NPS 3 1/2 | 4.000 in | 2.5063.50 mm |
| NPS 4 | 4.500 in | 2.5063.50 mm |
| NPS 5 | 5.563 in | 3.0076.20 mm |
| NPS 6 | 6.625 in | 3.5088.90 mm |
| NPS 8 | 8.625 in | 4.00101.60 mm |
| NPS 10 | 10.750 in | 5.00127.00 mm |
| NPS 12 | 12.750 in | 6.00152.40 mm |
| NPS 14 | 14.000 in | 6.50165.10 mm |
| NPS 16 | 16.000 in | 7.00177.80 mm |
| NPS 18 | 18.000 in | 8.00203.20 mm |
| NPS 20 | 20.000 in | 9.00228.60 mm |
| NPS 22 | 22.000 in | 10.00254.00 mm |
| NPS 24 | 24.000 in | 10.50266.70 mm |
B16.9 dimensions are a function of NPS only and do not change with schedule or wall thickness.
Same size, any schedule. Because these dimensions depend on NPS alone, a spool drawing can be dimensioned before the schedule is fixed. The wall thickness still has to be ordered to match the pipe, or the weld prep will not line up.
Common questions
What is the length e of an NPS 8 buttweld cap?
4.00 in (101.6 mm). ASME B16.9 dimensions depend on NPS only, so this figure is the same in every schedule.
Does the buttweld cap dimension change with wall thickness?
No. ASME B16.9 sets fitting dimensions from NPS alone. A schedule 40 and a schedule 160 fitting of the same size have identical centre-to-end dimensions — only the wall thickness and the bore differ, so the fitting still matches its pipe at the weld.
What material are buttweld caps made from?
Carbon steel fittings are normally ASTM A234 WPB, matched to A106 Gr B pipe. Low-temperature service uses A420 WPL6, stainless uses A403 WP304/WP316, and chrome-moly uses A234 WP11, WP22 or WP91. See the material grade reference.