ASME B36.10M (welded and seamless wrought steel pipe) · DN 500
Outside diameter 20.000" (508.00 mm), wall 0.375" (9.53 mm), inside diameter 19.250" (488.94 mm), 78.67 lb per foot.
| Trade size | NPS 20 · DN 500 |
|---|---|
| Schedule | Standard wall (STD) · same wall as 20, 40S |
| Standard | ASME B36.10M (welded and seamless wrought steel pipe) |
| Outside diameter | 20.000" · 508.00 mm |
| Wall thickness | 0.375" · 9.53 mm |
| Inside diameter | 19.250" · 488.94 mm |
| Weight, plain end | 78.67 lb/ft · 117.15 kg/m |
Cross-check: the standard plain-end weight formula W = 10.6802 x t x (OD - t) gives 78.60 lb/ft here, 0.1% from the published 78.67 lb/ft. The published figure is the one printed above.
NPS 20 standard wall (std) pipe measures 20.000 in (508.00 mm) across the outside with a 0.375 in wall, so the bore is 19.250 in (488.94 mm). That bore gives a flow area of 291.0 in² and holds 15.12 US gallons per foot (187.8 litres per metre). The outside diameter is 53.3 times the wall, and the steel itself has a cross-section of 23.12 in² and weighs 78.67 lb per foot plain end. One trade size up, NPS 22 in the same schedule carries 1.22 times the flow area.
Schedule 10 is the next lighter wall at NPS 20: 0.250 in, 0.125 in thinner, which opens the bore to 19.500 in and adds 2.6% to the flow area, for 33% less weight per foot.
Extra strong (XS) is the next heavier wall at NPS 20: 0.500 in, 0.125 in thicker, which narrows the bore to 19.000 in and cuts 2.6% from the flow area, for 32% more weight per foot.
Next trade size up in this schedule: NPS 22 standard wall (std), bore 21.250 in.
| Flow area | 291.0 in² |
|---|---|
| Capacity | 15.12 US gal/ft · 187.8 L/m |
| Metal area | 23.12 in² |
| Moment of inertia | 1113 in⁴ |
| Section modulus | 111.3 in³ |
| Radius of gyration | 6.940 in |
| Outside surface | 5.236 ft² per foot |
Plain geometry of a hollow circle with OD = 20.000 in and ID = 19.250 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 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 standard wall (std) the wall is 0.375 inches, so the bore comes out at 19.250 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 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 80 | 1.031 | 17.938 | 209.06 |
| 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 |
| Extra strong (XS) · 30, 80S | 0.500 | 19.000 | 104.23 |
| Schedule 10S | 0.218 | 19.564 | not published |
0.375 inches (9.53 mm). The outside diameter is 20.000 inches (508.00 mm) whatever the schedule, so this wall leaves an inside diameter of 19.250 inches.
19.250 inches (488.94 mm). Inside diameter is outside diameter minus twice the wall: 20.000 - 2 x 0.375 = 19.250 inches.
No. NPS 20 is a trade size, not a measurement. The pipe measures 20.000 inches across the outside and 19.250 inches across the bore in this schedule. Only the outside diameter is fixed across schedules.
78.67 pounds per foot plain end (117.15 kg per metre), for carbon steel. The figure excludes coatings, linings and fittings.
Yes, at NPS 20. 20 and 40S are the same 0.375 inch wall here. That coincidence is per size and does not hold everywhere: standard wall and schedule 40 part company above NPS 10, and extra strong and schedule 80 part company above NPS 8.
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