The "Enter Pipe" option is only a convenience option to use when the stack is fabricated from pipe material, rather than rolled from plate.  For Example, if the stack was fabricated from 36 inch (914 mm) Dia Standard Wall pipe, you could enter it as shown in the attached video.

It is no different than entering it the conventional way, it only has a database of pipe diameters and thicknesses for each schedule of pipe for convenience for the user.