ASME B36.10M (welded and seamless wrought steel pipe) · DN 300
Outside diameter 12.750" (323.85 mm), wall 0.250" (6.35 mm), inside diameter 12.250" (311.15 mm), 33.41 lb per foot.
| Trade size | NPS 12 · DN 300 |
|---|---|
| Schedule | Schedule 20 |
| Standard | ASME B36.10M (welded and seamless wrought steel pipe) |
| Outside diameter | 12.750" · 323.85 mm · designated 323.8 mm in the metric column |
| Wall thickness | 0.250" · 6.35 mm |
| Inside diameter | 12.250" · 311.15 mm |
| Weight, plain end | 33.41 lb/ft · 49.71 kg/m |
Cross-check: the standard plain-end weight formula W = 10.6802 x t x (OD - t) gives 33.38 lb/ft here, 0.1% from the published 33.41 lb/ft. The published figure is the one printed above.
NPS 12 schedule 20 pipe measures 12.750 in (323.85 mm) across the outside with a 0.250 in wall, so the bore is 12.250 in (311.15 mm). That bore gives a flow area of 117.9 in² and holds 6.123 US gallons per foot (76.04 litres per metre). The outside diameter is 51.0 times the wall, and the steel itself has a cross-section of 9.817 in² and weighs 33.41 lb per foot plain end. One trade size up, NPS 14 in the same schedule carries 1.19 times the flow area.
Schedule 10 is the next lighter wall at NPS 12: 0.180 in, 0.070 in thinner, which opens the bore to 12.390 in and adds 2.3% to the flow area, for 28% less weight per foot.
Schedule 30 is the next heavier wall at NPS 12: 0.330 in, 0.080 in thicker, which narrows the bore to 12.090 in and cuts 2.6% from the flow area, for 31% more weight per foot.
Next trade size up in this schedule: NPS 14 schedule 20, bore 13.376 in.
| Flow area | 117.9 in² |
|---|---|
| Capacity | 6.123 US gal/ft · 76.04 L/m |
| Metal area | 9.817 in² |
| Moment of inertia | 191.8 in⁴ |
| Section modulus | 30.09 in³ |
| Radius of gyration | 4.420 in |
| Outside surface | 3.338 ft² per foot |
Plain geometry of a hollow circle with OD = 12.750 in and ID = 12.250 in: flow area π/4·ID², metal area π/4·(OD² − ID²), moment of inertia π/64·(OD⁴ − ID⁴), section modulus I ÷ (OD/2), radius of gyration √(I ÷ metal area), capacity flow area × 12 ÷ 231 (231 in³ to the US gallon). Nominal dimensions, so mill tolerance and corrosion allowance are not included.
Nominal Pipe Size is a label, not a measurement. NPS 12 pipe has an outside diameter of 12.750 inches, and it keeps that outside diameter in every schedule made. What the schedule number changes is the wall: at schedule 20 the wall is 0.250 inches, so the bore comes out at 12.250 inches.
That is the practical consequence. Fittings, flanges, supports and threading dies are sized to the outside diameter, so they fit any schedule of the same trade size. Flow, pressure drop and anything that has to pass through the pipe depend on the inside diameter, which changes with every schedule. Order by trade size and schedule; work your hydraulics from the bore.
Same outside diameter of 12.750 inches throughout - only the wall and the bore move.
| Schedule | Wall (in) | ID (in) | Weight (lb/ft) |
|---|---|---|---|
| Schedule 5 · 5S | 0.156 | 12.438 | 21.00 |
| Schedule 10 · 10S | 0.180 | 12.390 | 24.19 |
| Schedule 30 | 0.330 | 12.090 | 43.81 |
| Schedule 40 | 0.406 | 11.938 | 53.57 |
| Schedule 60 | 0.562 | 11.626 | 73.22 |
| Schedule 80 | 0.688 | 11.374 | 88.71 |
| Schedule 100 | 0.844 | 11.062 | 107.42 |
| Schedule 140 | 1.125 | 10.500 | 139.81 |
| Schedule 160 | 1.312 | 10.126 | 160.42 |
| Standard wall (STD) · 40S | 0.375 | 12.000 | 49.61 |
| Extra strong (XS) · 80S | 0.500 | 11.750 | 65.48 |
| Double extra strong (XXS) · 120 | 1.000 | 10.750 | 125.61 |
0.250 inches (6.35 mm). The outside diameter is 12.750 inches (323.85 mm) whatever the schedule, so this wall leaves an inside diameter of 12.250 inches.
12.250 inches (311.15 mm). Inside diameter is outside diameter minus twice the wall: 12.750 - 2 x 0.250 = 12.250 inches.
No. NPS 12 is a trade size, not a measurement. The pipe measures 12.750 inches across the outside and 12.250 inches across the bore in this schedule. Only the outside diameter is fixed across schedules.
33.41 pounds per foot plain end (49.71 kg per metre), for carbon steel. The figure excludes coatings, linings and fittings.
This table runs from NPS 1/8 to NPS 24 and stops there. ASME B36.10M itself continues to NPS 80; those larger sizes are not carried here, so a size above NPS 24 is missing rather than undefined.
Dimensions are as defined by ASME B36.10M (welded and seamless wrought steel pipe). This site is an independent reference and is not affiliated with, endorsed by or approved by any standards body.
Every value on this page was cross-checked against 5 independent published sources:
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