Why 2 inch pipe is not 2 inches
Nominal Pipe Size is a label, not a measurement. NPS 2 pipe has an outside diameter of 2.375 inches, and it keeps that outside diameter in every schedule made. What the schedule number changes is the wall: at schedule 5s the wall is 0.065 inches, so the bore comes out at 2.245 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 2 inch schedule 5s pipe?
0.065 inches (1.65 mm). The outside diameter is 2.375 inches (60.32 mm) whatever the schedule, so this wall leaves an inside diameter of 2.245 inches.
What is the inside diameter of 2 inch schedule 5s pipe?
2.245 inches (57.02 mm). Inside diameter is outside diameter minus twice the wall: 2.375 - 2 x 0.065 = 2.245 inches.
Is 2 inch pipe actually 2 inches?
No. NPS 2 is a trade size, not a measurement. The pipe measures 2.375 inches across the outside and 2.245 inches across the bore in this schedule. Only the outside diameter is fixed across schedules.