Why 4 inch pipe is not 4 inches
Nominal Pipe Size is a label, not a measurement. NPS 4 pipe has an outside diameter of 4.500 inches, and it keeps that outside diameter in every schedule made. What the schedule number changes is the wall: at schedule 10 the wall is 0.120 inches, so the bore comes out at 4.260 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 4 inch schedule 10 pipe?
0.120 inches (3.05 mm). The outside diameter is 4.500 inches (114.30 mm) whatever the schedule, so this wall leaves an inside diameter of 4.260 inches.
What is the inside diameter of 4 inch schedule 10 pipe?
4.260 inches (108.20 mm). Inside diameter is outside diameter minus twice the wall: 4.500 - 2 x 0.120 = 4.260 inches.
Is 4 inch pipe actually 4 inches?
No. NPS 4 is a trade size, not a measurement. The pipe measures 4.500 inches across the outside and 4.260 inches across the bore in this schedule. Only the outside diameter is fixed across schedules.
How much does 4 inch schedule 10 pipe weigh?
5.62 pounds per foot plain end (8.37 kg per metre), for carbon steel. Stainless of the same dimensions runs a little lighter, and the figure excludes coatings, linings and fittings.