ASME B36.10M (welded and seamless wrought steel pipe) · DN 500
Outside diameter 20.000" (508.00 mm), wall 1.281" (32.54 mm), inside diameter 17.438" (442.92 mm), 256.34 lb per foot.
| Trade size | NPS 20 · DN 500 |
|---|---|
| Schedule | Schedule 100 |
| Standard | ASME B36.10M (welded and seamless wrought steel pipe) |
| Outside diameter | 20.000" · 508.00 mm |
| Wall thickness | 1.281" · 32.54 mm |
| Inside diameter | 17.438" · 442.92 mm |
| Weight, plain end | 256.34 lb/ft · 381.55 kg/m |
Cross-check: the standard plain-end weight formula W = 10.6802 x t x (OD - t) gives 256.10 lb/ft here, 0.1% from the published 256.34 lb/ft. The published figure is the one printed above.
NPS 20 schedule 100 pipe measures 20.000 in (508.00 mm) across the outside with a 1.281 in wall, so the bore is 17.438 in (442.92 mm). That bore gives a flow area of 238.8 in² and holds 12.41 US gallons per foot (154.1 litres per metre). The outside diameter is 15.6 times the wall, and the steel itself has a cross-section of 75.33 in² and weighs 256.34 lb per foot plain end. One trade size up, NPS 22 in the same schedule carries 1.22 times the flow area.
Schedule 80 is the next lighter wall at NPS 20: 1.031 in, 0.250 in thinner, which opens the bore to 17.938 in and adds 5.8% to the flow area, for 18% less weight per foot.
Schedule 120 is the next heavier wall at NPS 20: 1.500 in, 0.219 in thicker, which narrows the bore to 17.000 in and cuts 5.0% from the flow area, for 16% more weight per foot.
Next trade size up in this schedule: NPS 22 schedule 100, bore 19.250 in.
| Flow area | 238.8 in² |
|---|---|
| Capacity | 12.41 US gal/ft · 154.1 L/m |
| Metal area | 75.33 in² |
| Moment of inertia | 3315 in⁴ |
| Section modulus | 331.5 in³ |
| Radius of gyration | 6.634 in |
| Outside surface | 5.236 ft² per foot |
Plain geometry of a hollow circle with OD = 20.000 in and ID = 17.438 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 100 the wall is 1.281 inches, so the bore comes out at 17.438 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 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 |
1.281 inches (32.54 mm). The outside diameter is 20.000 inches (508.00 mm) whatever the schedule, so this wall leaves an inside diameter of 17.438 inches.
17.438 inches (442.92 mm). Inside diameter is outside diameter minus twice the wall: 20.000 - 2 x 1.281 = 17.438 inches.
No. NPS 20 is a trade size, not a measurement. The pipe measures 20.000 inches across the outside and 17.438 inches across the bore in this schedule. Only the outside diameter is fixed across schedules.
256.34 pounds per foot plain end (381.55 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:
Sources disagree here. Published tables split on the last digit here - 1.281 in (b3610m-fbc), 1.28 in (b3610m-wikipedia); 32.54 mm (b3610m-ferrobend), 32.54 mm (b3610m-wermac), 32.51 mm (b3610m-wikipedia). The figure printed is 1.281 in (32.54 mm), carried by the majority of the sources. The two readings describe the same wall: they differ by less than a thousandth of an inch, far inside the mill tolerance of minus 12.5 percent on wall thickness.
Last-digit inch walls across the whole table: 0.594, 0.688, 0.719, 0.844, 0.938, 1.094, 1.219, 1.438, 1.969, 2.344 in (b3610m-fbc) against 0.593, 0.687, 0.718, 0.843, 0.937, 1.093, 1.218, 1.437, 1.968, 2.343 in (b3610m-wikipedia). Two families of inch figures are in circulation, one a thousandth of an inch below the other, and they come from rounding the millimetre wall the standard tabulates rather than from any difference in the pipe. The higher family is what the majority of the sources read here carry and is what this site prints; the affected rows say so individually. Nothing turns on the choice: the wall tolerance is minus 12.5 percent, which at a half-inch wall is sixty times the gap.
NPS 14 extra strong (XS): 0.469 in (b3610m-fbc) against 0.500 in (b3610m-etb) against 0.500 in (b3610m-wikipedia). 0.500 in is printed here. Two of the three inch sources give it, both millimetre sources give 12.70 mm which is 0.500 in, and extra strong is a 0.500 in wall at every size from NPS 12 up. The 0.469 in reading looks like a misplaced row in that one chart, but it is recorded rather than deleted.
Nearby sizes