ASME B36.10M (welded and seamless wrought steel pipe) · DN 450
Outside diameter 18.000" (457.20 mm), wall 0.312" (7.92 mm), inside diameter 17.376" (441.36 mm), 58.94 lb per foot.
| Trade size | NPS 18 · DN 450 |
|---|---|
| Schedule | Schedule 20 |
| Standard | ASME B36.10M (welded and seamless wrought steel pipe) |
| Outside diameter | 18.000" · 457.20 mm · designated 457 mm in the metric column |
| Wall thickness | 0.312" · 7.92 mm |
| Inside diameter | 17.376" · 441.36 mm |
| Weight, plain end | 58.94 lb/ft · 87.71 kg/m |
Cross-check: the standard plain-end weight formula W = 10.6802 x t x (OD - t) gives 58.94 lb/ft here, 0.0% from the published 58.94 lb/ft. The published figure is the one printed above.
NPS 18 schedule 20 pipe measures 18.000 in (457.20 mm) across the outside with a 0.312 in wall, so the bore is 17.376 in (441.36 mm). That bore gives a flow area of 237.1 in² and holds 12.32 US gallons per foot (153.0 litres per metre). The outside diameter is 57.7 times the wall, and the steel itself has a cross-section of 17.34 in² and weighs 58.94 lb per foot plain end. One trade size up, NPS 20 in the same schedule carries 1.23 times the flow area.
Schedule 10 is the next lighter wall at NPS 18: 0.250 in, 0.062 in thinner, which opens the bore to 17.500 in and adds 1.4% to the flow area, for 20% less weight per foot.
Standard wall (STD) is the next heavier wall at NPS 18: 0.375 in, 0.063 in thicker, which narrows the bore to 17.250 in and cuts 1.4% from the flow area, for 20% more weight per foot.
Next trade size up in this schedule: NPS 20 schedule 20, bore 19.250 in.
| Flow area | 237.1 in² |
|---|---|
| Capacity | 12.32 US gal/ft · 153.0 L/m |
| Metal area | 17.34 in² |
| Moment of inertia | 678.2 in⁴ |
| Section modulus | 75.36 in³ |
| Radius of gyration | 6.255 in |
| Outside surface | 4.712 ft² per foot |
Plain geometry of a hollow circle with OD = 18.000 in and ID = 17.376 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 18 pipe has an outside diameter of 18.000 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 0.312 inches, so the bore comes out at 17.376 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 18.000 inches throughout - only the wall and the bore move.
| Schedule | Wall (in) | ID (in) | Weight (lb/ft) |
|---|---|---|---|
| Schedule 5 · 5S | 0.165 | 17.670 | 31.46 |
| Schedule 10 | 0.250 | 17.500 | 47.44 |
| Schedule 30 | 0.438 | 17.124 | 82.23 |
| Schedule 40 | 0.562 | 16.876 | 104.67 |
| Schedule 60 | 0.750 | 16.500 | 138.30 |
| Schedule 80 | 0.938 | 16.124 | 171.08 |
| Schedule 100 | 1.156 | 15.688 | 208.15 |
| Schedule 120 | 1.375 | 15.250 | 244.37 |
| Schedule 140 | 1.562 | 14.876 | 274.48 |
| Schedule 160 | 1.781 | 14.438 | 308.79 |
| Standard wall (STD) · 40S | 0.375 | 17.250 | 70.65 |
| Extra strong (XS) · 80S | 0.500 | 17.000 | 93.54 |
| Schedule 10S | 0.188 | 17.624 | not published |
0.312 inches (7.92 mm). The outside diameter is 18.000 inches (457.20 mm) whatever the schedule, so this wall leaves an inside diameter of 17.376 inches.
17.376 inches (441.36 mm). Inside diameter is outside diameter minus twice the wall: 18.000 - 2 x 0.312 = 17.376 inches.
No. NPS 18 is a trade size, not a measurement. The pipe measures 18.000 inches across the outside and 17.376 inches across the bore in this schedule. Only the outside diameter is fixed across schedules.
58.94 pounds per foot plain end (87.71 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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