What Are ASME B16.9 Pipe Caps?
ASME B16.9 buttwelding caps close the end of a piping system, from NPS 1/2 through NPS 48. They are dished (torispherical) wrought fittings welded directly to the pipe, sized per Table 6.1-10.
Dimensions (Table 6.1-10)
Values in mm (inch). E2 = cap length (small/medium sizes, E3 applies to large sizes); lim = wall thickness at the top of the dish.
| NPS | Outside Diameter (mm / in) | lim — Top Wall (mm / in) | E2 — Length (mm / in) | E3 — Length (mm / in) |
|---|---|---|---|---|
| 1/2 | 21.3 (0.84) | 4.57 (0.18) | 25.0 (1.0) | 25.0 (1.0) |
| 3/4 | 26.7 (1.05) | 3.81 (0.15) | 25.0 (1.0) | 25.0 (1.0) |
| 1 | 33.4 (1.32) | 4.57 (0.18) | 38.0 (1.5) | 38.0 (1.5) |
| 1-1/4 | 42.2 (1.66) | 4.83 (0.19) | 38.0 (1.5) | 38.0 (1.5) |
| 1-1/2 | 48.3 (1.9) | 5.08 (0.2) | 38.0 (1.5) | 38.0 (1.5) |
| 2 | 60.3 (2.38) | 5.59 (0.22) | 38.0 (1.5) | 44.0 (1.75) |
| 2-1/2 | 73.0 (2.88) | 7.11 (0.28) | 38.0 (1.5) | 51.0 (2.0) |
| 3 | 88.9 (3.5) | 7.62 (0.3) | 51.0 (2.0) | 64.0 (2.5) |
| 3-1/2 | 101.6 (4.0) | 8.13 (0.32) | 64.0 (2.5) | 76.0 (3.0) |
| 4 | 114.3 (4.5) | 8.64 (0.34) | 64.0 (2.5) | 76.0 (3.0) |
| 5 | 141.3 (5.56) | 9.65 (0.38) | 76.0 (3.0) | 89.0 (3.5) |
| 6 | 168.3 (6.62) | 10.92 (0.43) | 89.0 (3.5) | 102.0 (4.0) |
| 8 | 219.1 (8.62) | 12.7 (0.5) | 102.0 (4.0) | 127.0 (5.0) |
| 10 | 273.0 (10.75) | 12.7 (0.5) | 127.0 (5.0) | 152.0 (6.0) |
| 12 | 323.8 (12.75) | 12.7 (0.5) | 152.0 (6.0) | 178.0 (7.0) |
| 14 | 355.6 (14.0) | 12.7 (0.5) | 165.0 (6.5) | 191.0 (7.5) |
| 16 | 406.4 (16.0) | 12.7 (0.5) | 178.0 (7.0) | 203.0 (8.0) |
| 18 | 457.0 (18.0) | 12.7 (0.5) | 203.0 (8.0) | 229.0 (9.0) |
| 20 | 508.0 (20.0) | 12.7 (0.5) | 229.0 (9.0) | 254.0 (10.0) |
| 22 | 559.0 (22.0) | 12.7 (0.5) | 254.0 (10.0) | 254.0 (10.0) |
| 24 | 610.0 (24.0) | 12.7 (0.5) | 267.0 (10.5) | 305.0 (12.0) |
| 26 | 660.0 (26.0) | 12.7 (0.5) | 267.0 (10.5) | — |
| 28 | 711.0 (28.0) | 12.7 (0.5) | 267.0 (10.5) | — |
| 30 | 762.0 (30.0) | 12.7 (0.5) | 267.0 (10.5) | — |
| 32 | 813.0 (32.0) | 12.7 (0.5) | 267.0 (10.5) | — |
| 34 | 864.0 (34.0) | 12.7 (0.5) | 267.0 (10.5) | — |
| 36 | 914.0 (36.0) | 12.7 (0.5) | 267.0 (10.5) | — |
| 38 | 965.0 (38.0) | 12.7 (0.5) | 305.0 (12.0) | — |
| 40 | 1016.0 (40.0) | 12.7 (0.5) | 305.0 (12.0) | — |
| 42 | 1067.0 (42.0) | 12.7 (0.5) | 305.0 (12.0) | — |
| 44 | 1118.0 (44.0) | 12.7 (0.5) | 343.0 (13.5) | — |
| 46 | 1168.0 (46.0) | 12.7 (0.5) | 343.0 (13.5) | — |
| 48 | 1219.0 (48.0) | 12.7 (0.5) | 343.0 (13.5) | — |
Materials & Schedules
Caps are supplied in A234 WPB carbon steel (-29°C to 425°C), A403 WP304 / WP316 stainless (up to 538°C), and A420 WPL6 low-temperature carbon steel, in schedules matching ASME B36.10 / B36.19 pipe.
Related Standards
- ASME B16.9 — Buttwelding Fittings (parent standard)
- ASME B16.9 Elbows
- ASME B16.9 Tees
- ASME B16.9 Reducers
- ASME B16.11 Caps (small forged size)
- ASTM A403 WP316 Stainless
- Our Fittings Range
FAQ
What is a pipe cap used for?
A cap permanently seals the end of a pipe run or vessel branch. Unlike a blind flange, it is butt-welded in place.
What sizes do B16.9 caps cover?
NPS 1/2 through NPS 48, per Table 6.1-10.
What is the difference between E2 and E3 in Table 6.1-10?
They are cap length dimensions for different size ranges — E2 applies to smaller sizes (NPS 1/2–24), E3 is defined for the larger sizes per the standard.
Can caps be used in high-temperature service?
Yes — A234 WPB to 425°C, stainless grades up to 538°C. For extreme conditions consult the material standard.
Do you supply caps in duplex or special alloys?
We regularly supply carbon and stainless grades; special alloys are available on request — send your material specification.
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.