Why 24 inch pipe is not 24 inches
Nominal Pipe Size is a label, not a measurement. NPS 24 pipe has an outside diameter of 24.000 inches, and it keeps that outside diameter in every schedule made. What the schedule number changes is the wall: at schedule 160 the wall is 2.344 inches, so the bore comes out at 19.312 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.
Frequently asked questions
What is the wall thickness of 24 inch schedule 160 pipe?
2.344 inches (59.54 mm). The outside diameter is 24.000 inches (609.60 mm) whatever the schedule, so this wall leaves an inside diameter of 19.312 inches.
What is the inside diameter of 24 inch schedule 160 pipe?
19.312 inches (490.52 mm). Inside diameter is outside diameter minus twice the wall: 24.000 - 2 x 2.344 = 19.312 inches.
Is 24 inch pipe actually 24 inches?
No. NPS 24 is a trade size, not a measurement. The pipe measures 24.000 inches across the outside and 19.312 inches across the bore in this schedule. Only the outside diameter is fixed across schedules.
How much does 24 inch schedule 160 pipe weigh?
542.64 pounds per foot plain end (808.27 kg per metre), for carbon steel. Stainless of the same dimensions runs a little lighter, and the figure excludes coatings, linings and fittings.
Where these figures come from
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 - 2.344 in (b3610m-fbc), 2.343 in (b3610m-wikipedia); 59.54 mm (b3610m-ferrobend), 59.54 mm (b3610m-wermac), 59.51 mm (b3610m-wikipedia). The figure printed is 2.344 in (59.54 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.