ASME B36.10M (welded and seamless wrought steel pipe) · DN 500
Outside diameter 20.000" (508.00 mm), wall 1.031" (26.19 mm), inside diameter 17.938" (455.62 mm), 209.06 lb per foot.
| Trade size | NPS 20 · DN 500 |
|---|---|
| Schedule | Schedule 80 |
| Standard | ASME B36.10M (welded and seamless wrought steel pipe) |
| Outside diameter | 20.000" · 508.00 mm |
| Wall thickness | 1.031" · 26.19 mm |
| Inside diameter | 17.938" · 455.62 mm |
| Weight, plain end | 209.06 lb/ft · 311.19 kg/m |
Cross-check: the standard plain-end weight formula W = 10.6802 x t x (OD - t) gives 208.87 lb/ft here, 0.1% from the published 209.06 lb/ft. The published figure is the one printed above.
NPS 20 schedule 80 pipe measures 20.000 in (508.00 mm) across the outside with a 1.031 in wall, so the bore is 17.938 in (455.62 mm). That bore gives a flow area of 252.7 in² and holds 13.13 US gallons per foot (163.0 litres per metre). The outside diameter is 19.4 times the wall, and the steel itself has a cross-section of 61.44 in² and weighs 209.06 lb per foot plain end. One trade size up, NPS 22 in the same schedule carries 1.21 times the flow area.
Schedule 60 is the next lighter wall at NPS 20: 0.812 in, 0.219 in thinner, which opens the bore to 18.376 in and adds 4.9% to the flow area, for 20% less weight per foot.
Schedule 100 is the next heavier wall at NPS 20: 1.281 in, 0.250 in thicker, which narrows the bore to 17.438 in and cuts 5.5% from the flow area, for 23% more weight per foot.
Next trade size up in this schedule: NPS 22 schedule 80, bore 19.750 in.
| Flow area | 252.7 in² |
|---|---|
| Capacity | 13.13 US gal/ft · 163.0 L/m |
| Metal area | 61.44 in² |
| Moment of inertia | 2772 in⁴ |
| Section modulus | 277.2 in³ |
| Radius of gyration | 6.716 in |
| Outside surface | 5.236 ft² per foot |
Plain geometry of a hollow circle with OD = 20.000 in and ID = 17.938 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 20 pipe has an outside diameter of 20.000 inches, and it keeps that outside diameter in every schedule made. What the schedule number changes is the wall: at schedule 80 the wall is 1.031 inches, so the bore comes out at 17.938 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 20.000 inches throughout - only the wall and the bore move.
| Schedule | Wall (in) | ID (in) | Weight (lb/ft) |
|---|---|---|---|
| Schedule 5 · 5S | 0.188 | 19.624 | 39.82 |
| Schedule 10 | 0.250 | 19.500 | 52.70 |
| Schedule 40 | 0.594 | 18.812 | 123.23 |
| Schedule 60 | 0.812 | 18.376 | 166.56 |
| Schedule 100 | 1.281 | 17.438 | 256.34 |
| Schedule 120 | 1.500 | 17.000 | 296.65 |
| Schedule 140 | 1.750 | 16.500 | 341.41 |
| Schedule 160 | 1.969 | 16.062 | 379.53 |
| Standard wall (STD) · 20, 40S | 0.375 | 19.250 | 78.67 |
| Extra strong (XS) · 30, 80S | 0.500 | 19.000 | 104.23 |
| Schedule 10S | 0.218 | 19.564 | not published |
1.031 inches (26.19 mm). The outside diameter is 20.000 inches (508.00 mm) whatever the schedule, so this wall leaves an inside diameter of 17.938 inches.
17.938 inches (455.62 mm). Inside diameter is outside diameter minus twice the wall: 20.000 - 2 x 1.031 = 17.938 inches.
No. NPS 20 is a trade size, not a measurement. The pipe measures 20.000 inches across the outside and 17.938 inches across the bore in this schedule. Only the outside diameter is fixed across schedules.
209.06 pounds per foot plain end (311.19 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 4 independent published sources:
Nearby sizes