In this article, experts from Mirach Metallurgy Co.,Limited share difference between aluminum tube and aluminum pipe.  Before purchase aluminum tube products, you should keep the following idea in mind.

A brief discussion of the difference between pipe and tube:
Pipe is generally more rigid than tube, and is usually produced in heavier wall thicknesses.
Pipe is specified by a nominal dimension which bears little or no resemblance to the actual dimensions of the pipe. 1″ Schedule 40 pipe, for instance, has an actual OD of 1.32″, a wall of 0.133″, and an inner diameter of 1.049″. Tube dimensions are actual dimensions.
Pipe fittings are sized to meet pipe sizes, but not tube sizes. A 1″ schedule 40 nipple will fit correctly on a 1″ schedule 40 pipe, but not on a 1″ OD tube.