Post/Pipe Diameter

[DAdams]

This is a technicality but we really need some clarification. And I'm only asking because one of our volunteers, a pipe salesman, brought me up to speed on types of pipe.
The rules state that the tower is made from 1 1/2" diameter pipe. The problem is that the rules don't specify if this is Outside Diameter or Inside Diameter. To be exact, PIPE is always measured by ID, making the OD bigger by a quarter inch. On the other hand, TUBING is measured by OD, making the true outside measurement 1 1/2". But the rules say 1 1/2" PIPE, which is a bit contradictory.
Are we looking at 1 1/2" outside or inside diameter?
Thanks for your help.
DAdams
Team 1828