Views: 1 Author: Monica Publish Time: 2025-12-01 Origin: Site
As a professional manufacturer of butt-welded pipe fittings, we frequently receive inquiries about the precise dimensions and tolerances of steel pipe caps (also known as end caps or manifold caps). This article introduces ASME B16.9-2023, as well as the dimension tables and tolerances for carbon steel, stainless steel, duplex stainless steel, and nickel alloy pipe caps.
The ASME B16.9-2023 standard recognizes two types of factory-manufactured forged butt-welded pipe caps. Each type is clearly defined by its head geometry, dimensional requirements, and application.
Type A – Ellipsoidal (2:1 Elliptical) Pipe Cap
This is the most widely used butt-welding steel pipe cap under the ASME B16.9 standard.
Its concave portion features a 2:1 ellipsoidal geometry. When the cap's manufacturing specifications are the same as or higher than the connecting pipe, they are suitable for all pressure-temperature ratings of ASME B31.1, B31.3, B31.4, and B31.8 piping systems. These steel pipe caps account for over 99% of global inventory and project-use caps.
Type B – Hemispherical Pipe Cap
Hemispherical caps have a true hemispherical concave portion (the inner radius equals the inner diameter of the cap).
Because the wall thickness of a hemispherical head under internal pressure is approximately half that of a 2:1 ellipsoidal head, hemispherical heads are primarily used in ultra-high pressure applications (>2500), vessel nozzles, or applications with extremely high requirements for minimum weight and maximum volume. They are more expensive to form, require heavier initial blanks for the same pressure rating, and are rarely kept in stock.
Dimensions are not listed in ASME B16.9.
ASME B16.9 covers overall dimensions, tolerances, ratings, testing, and markings for factory-made wrought butt-welding fittings in sizes NPS 1/2 through NPS 48 (DN 15 through DN 1200). Steel pipe caps fall under this standard when they are designed for butt-welding to pipe ends.
Two main types of steel pipe caps are defined:
Type A: Ellipsoidal (2:1 elliptical head shape)—most common.
Type B: Hemispherical—used for very high pressure or special applications (rarely stocked).
Below we introduce the widely used Type A ellipsoidal pipe caps.
Nominal Pipe Size (NPS) | DN | Outside Diameter at Bevel | Length, E [Note (1)] | Limiting Wall Thickness for Length, E | Length, E [Note (2)] |
1/2 3/4 1 1 1/4 1 1/2 2 2 1/2 3 3 1/2 4 5 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 | 15 20 25 32 40 50 65 80 90 100 125 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000 1050 1100 1150 1200 | 21.3 26.7 33.4 42.2 48.3 60.3 73.0 88.9 101.6 114.3 141.3 168.3 219.1 273.0 323.8 355.6 406.4 457 508 559 610 660 711 762 813 864 914 965 1016 1067 1118 1168 1219 | 25 25 38 38 38 38 38 51 64 64 76 89 102 127 152 165 178 203 229 254 267 267 267 267 267 267 267 305 305 305 343 343 343 | 4.57 3.81 4.57 4.83 5.08 5.59 7.11 7.62 8.13 8.64 9.65 10.92 12.70 12.70 12.70 12.70 12.70 12.70 12.70 12.70 12.70 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . | 25 25 38 38 38 44 51 64 76 76 89 102 127 152 178 191 203 229 254 254 305 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
Note: For NPS 26 and larger diameter steel pipe end caps, dimensions are usually project-specific and follow MSS SP-75 or custom drawings.
Parameter | Tolerance |
Outside diameter at bevel (D) | NPS ≤24: ±1.6 mm NPS ≥26: ±3.2 mm |
Inside diameter at bevel | Not specified (shall allow free passage of pipe) |
Overall height (O) | ±3 mm (all sizes) |
Wall thickness at bevel end (T) | Not less than 87.5% of nominal pipe wall |
Out-of-roundness (Dmax – Dmin) | ≤1% × D (max 3 mm for NPS ≤18, 5 mm for larger) |
End-to-end alignment (squareness) | Bevel face perpendicular to axis within 0.5° |
Weight | ±10% of theoretical weight |
The following weight table is calculated according to ASME B16.9-2023, using theoretical formulas for standard dimensions and ellipsoidal caps.
Weight is in kilograms (kg), based on the density of carbon steel/stainless steel ≈ 7850 kg/m³.
Actual weight may deviate by ±10%, which is within the range specified in the standard.
NPS | DN | Schedule | Nominal Wall Thickness (mm) | Approx. Weight (kg) |
1/2 | 15 | Sch 40 | 3.73 | 0.1 |
Sch 80 | 4.78 | 0.2 | ||
Sch 160 | 7.47 | 0.3 | ||
3/4 | 20 | Sch 40 | 3.91 | 0.2 |
Sch 80 | 5.56 | 0.3 | ||
1 | 25 | Sch 40 | 4.55 | 0.4 |
Sch 80 | 6.35 | 0.5 | ||
Sch 160 | 9.09 | 0.8 | ||
1¼ | 32 | Sch 40 | 4.85 | 0.6 |
Sch 80 | 6.86 | 0.8 | ||
1½ | 40 | Sch 40 | 5.08 | 0.8 |
Sch 80 | 7.14 | 1.1 | ||
2 | 50 | Sch 40 | 5.54 | 1.2 |
Sch 80 | 8.74 | 1.8 | ||
Sch 160 | 11.07 | 2.3 | ||
2½ | 65 | Sch 40 | 7.01 | 2.2 |
Sch 80 | 9.53 | 2.8 | ||
3 | 80 | Sch 40 | 7.62 | 3.2 |
Sch 80 | 11.13 | 4.6 | ||
Sch 160 | 15.24 | 6.0 | ||
4 | 100 | Sch 40 | 8.56 | 5.5 |
Sch 80 | 13.49 | 8.5 | ||
Sch 160 | 18.26 | 11.2 | ||
5 | 125 | Sch 40 | 9.53 | 9.5 |
Sch 80 | 15.29 | 14.8 | ||
6 | 150 | Sch 40 | 10.97 | 14.5 |
Sch 80 | 18.26 | 23.5 | ||
Sch 160 | 28.58 | 35.0 | ||
8 | 200 | Sch 40 | 12.70 | 28 |
Sch 80 | 23.01 | 49 | ||
Sch 120 | 27.76 | 58 | ||
Sch 160 | 36.91 | 75 | ||
10 | 250 | Sch 40 | 15.09 | 52 |
Sch 80 | 28.04 | 94 | ||
Sch 120 | 35.71 | 117 | ||
12 | 300 | Sch 40 | 17.48 | 86 |
Sch 80 | 33.32 | 158 | ||
Sch 120 | 43.52 | 202 | ||
14 | 350 | Std | 12.70 | 95 |
XS | 19.05 | 140 | ||
16 | 400 | Std | 14.27 | 140 |
XS | 21.44 | 207 | ||
18 | 450 | Std | 15.88 | 197 |
XS | 23.80 | 290 | ||
20 | 500 | Std | 17.48 | 270 |
XS | 26.19 | 400 | ||
24 | 600 | Std | 20.62 | 450 |
XS | 30.96 | 670 |
Notes:
Weights above are theoretical and calculated using ASME B16.9 standard dimensions + the ellipsoidal volume formula.
For stainless steel (304/316/321), duplex (S31803/S32205), super duplex (S32750/S32760) and nickel alloys (Inconel 625, Monel 400, Hastelloy C276, Incoloy 825 etc.), actual weights are almost identical (±1-2%) because density variation is minimal compared to carbon steel.
For schedules not listed (XXS, Sch 100, Sch 140, etc.) or non-standard thicknesses, weights can be calculated proportionally or supplied upon request.
Larger than NPS 24: usually custom-made to MSS SP-75 or project-specific drawings.
For Butt Weld Cap
Standard: ASTM A234, MSS SP-75, ASTM A403.
Manufacturing Standard: ASME B16.9, DIN2615, JIS B2312.
Size Range: 1/2”, 1”, 2”, 3”, 4”, 6”, 8”, 10”, 12”, 16”, 20” to 48”. (DN15-DN1200).
Thickness: SCH 10, SCH 40, SCH 80.
Surface Coatings: Black Painted, Varnished, Epoxy Coated, Galvanized.
For Socket Weld Cap (and Threaded Cap)
Standard: ASTM A105, ASTM A182.
Manufacturing Standard: ASME B16.11.
Dimensions: 1/2" , 1" , 1/2" , 2" and up to 4".
Pressure Ratings: 2000#, 3000#, 6000#, 9000#.
Need exact weights for your specific material (e.g., ASTM A403 WP316L Sch 80S, UNS S32750 Sch 160, or Inconel 625 Sch 40)?
Send us your inquiry with material grade, schedule/thickness, and quantity—we will provide a Precise Quotation within 24 hours.
