What is the difference between pipes and tubing? Many technicians commonly interchange the use of these terms; however, there is a technical difference between the two, and that is how they are sized.
Pipes are sized based on their nominal pipe size (NPS), which is the approximate, but not exact, inside diameter. The inside diameter will vary based on the pipe’s wall thickness, which is known as its schedule. The outside diameter is held constant. The schedule of a pipe can vary based on how it is ordered. For example, the inside diameter of a 2-inch schedule 40 pipe is 2.067 inches, whereas the inside diameter of a 2-inch schedule 80 pipe is 1.939 inches. The outside diameter for both is 2.375 inches, and their inside diameters are close to 2 inches.