Pipe Fittings · ASME B16.9 · B16.11
Cap — ASME B16.9
Cap — a fitting that closes the end of a pipe. Buttweld caps are dished ends welded to the pipe; forged caps are threaded or socket-weld. Used at dead ends and future connection points.
- ASME B16.9
- 22 grades
- EN 10204 3.1 / 3.2
Reviewed by the Kanak Steel & Engineering Co. technical team · Updated October 2026
Cap: What to Know Before Ordering
- Buttweld dished caps
- Threaded and socket-weld caps
- Wall to match the pipe
Cap Materials & Grades
| Grade | Material standard | Best for |
|---|---|---|
| Inconel 825 cap | ASTM B366 WPNICMC (buttweld) · ASTM B564 (forged) | Sulphuric and phosphoric acid service, chloride stress-corrosion cracking and sour gas |
| SS 904L cap | ASTM A403 WP904L (buttweld) · ASTM A182 F904L (forged) | Dilute sulphuric acid, phosphoric acid and chloride-bearing cooling water |
| SS 304 cap | ASTM A403 WP304 (buttweld) · ASTM A182 F304 (forged) | General corrosion resistance, food, water and architectural work |
| SS 304L cap | ASTM A403 WP304L (buttweld) · ASTM A182 F304L (forged) | Welded tanks, piping and vessels in general corrosive service |
| SS 310 / 310S cap | ASTM A403 WP310S (buttweld) · ASTM A182 F310 (forged) | Furnaces, burners and heat treatment at high temperature |
| SS 316 / 316L cap | ASTM A403 WP316L (buttweld) · ASTM A182 F316L (forged) | Chloride-bearing process fluids, marine air and pharmaceutical service |
| SS 321 cap | ASTM A403 WP321 (buttweld) · ASTM A182 F321 (forged) | High-temperature service between 425 and 815 °C |
| SS 347 cap | ASTM A403 WP347 (buttweld) · ASTM A182 F347 (forged) | Welded high-temperature piping in refineries and power plants |
| Duplex 2205 cap | ASTM A815 WPS31803 / WPS32205 (buttweld) · ASTM A182 F51 / F60 (forged) | Strength with chloride resistance at a stainless-steel budget |
| Super Duplex 2507 cap | ASTM A815 WPS32750 (buttweld) · ASTM A182 F53 (forged) | Seawater and high-chloride service where strength also matters |
| Inconel 600 cap | ASTM B366 WPNCI (buttweld) · ASTM B564 (forged) | High-temperature oxidation, caustic and nuclear service |
| Inconel 625 cap | ASTM B366 WPNCMC (buttweld) · ASTM B564 (forged) | Seawater, high strength and high temperature in one alloy |
| Inconel 718 cap | Machined from B637 on request (buttweld) · ASTM B637 (forged) | Very high strength at temperatures up to about 650 °C |
| Incoloy 800 / 800H / 800HT cap | ASTM B366 WPNIC (buttweld) · ASTM B564 (forged) | Furnaces, petrochemical heaters and high-temperature piping |
| Hastelloy C276 cap | ASTM B366 WPHC276 (buttweld) · ASTM B564 (forged) | The most aggressive mixed acids, wet chlorine and hypochlorite |
| Hastelloy C22 cap | ASTM B366 WPHC22 (buttweld) · ASTM B564 (forged) | Mixed oxidising and reducing acids, and weld overlays |
| Monel 400 cap | ASTM B366 WPNC (buttweld) · ASTM B564 (forged) | Seawater, hydrofluoric acid and marine service |
| Super Duplex S32760 cap | ASTM A815 WPS32760 (buttweld) · ASTM A182 F55 (forged) | Seawater firewater, injection and offshore piping |
| ASTM A106 Gr B cap | ASTM A234 WPB (buttweld) · ASTM A105 (forged) | High-temperature process and steam piping in refineries and power plants |
| ASTM A333 Gr 6 cap | ASTM A420 WPL6 (buttweld) · ASTM A350 LF2 (forged) | Cold-climate and refrigerated piping down to −45 °C |
| ASTM A335 P11 cap | ASTM A234 WP11 (buttweld) · ASTM A182 F11 (forged) | Steam and hot-oil piping up to about 550 °C |
| ASTM A335 P22 cap | ASTM A234 WP22 (buttweld) · ASTM A182 F22 (forged) | High-pressure steam and hydrogen service up to about 580 °C |
Other pipe fittings
ElbowA fitting that changes the direction of a pipe run.TeeA fitting with a 90° branch that splits or combines flow.ReducerA fitting that joins two pipes of different sizes.Stub endA short pipe length with a flared lap that works with a lap joint flange.CrossA four-way fitting with branches at 90°.BendA pipe bend with a larger radius than a standard elbow.LateralA fitting with a 45° branch.CouplingA short forged fitting that joins two pipes.UnionA three-piece forged fitting that joins pipes and can be taken apart.NippleA short length of pipe, threaded or plain, used to connect fittings.PlugA threaded fitting that closes a female connection.
Cap dimensions — ASME B16.9
Values in mm, the same for every material; the wall thickness matches the pipe schedule.
| NPS | OD | Cap length E |
|---|---|---|
| ½" | 21.3 | 25 |
| ¾" | 26.7 | 25 |
| 1" | 33.4 | 38 |
| 1½" | 48.3 | 38 |
| 2" | 60.3 | 38 |
| 3" | 88.9 | 51 |
| 4" | 114.3 | 64 |
| 6" | 168.3 | 89 |
| 8" | 219.1 | 102 |
| 10" | 273.1 | 127 |
| 12" | 323.9 | 152 |
| 16" | 406.4 | 178 |
| 20" | 508.0 | 229 |
| 24" | 610.0 | 267 |
Full chart: ASME B16.9 fitting dimensions.
Cap — questions buyers ask
Can a cap take full line pressure?
Yes — a buttweld cap of matching schedule is rated like the pipe it closes.
Which grades are caps available in?
Inconel 825, SS 904L, SS 304, SS 304L, SS 310 / 310S, SS 316 / 316L, SS 321, SS 347, Duplex 2205, Super Duplex 2507, Inconel 600, Inconel 625, Inconel 718, Incoloy 800 / 800H / 800HT, Hastelloy C276, Hastelloy C22, Monel 400, Super Duplex S32760, ASTM A106 Gr B, ASTM A333 Gr 6, ASTM A335 P11, ASTM A335 P22.
Which standard covers cap dimensions?
ASME B16.9 · B16.11. The material standard depends on the grade.
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