Pipe OD

No.

Go to a pipe supplier web site and look at the dimensions.

No....for example if you are talking about 6 inch NPS (nominal pipe size). OD will remain same for all thickness (schedule), however ID will be changing depending on thickness. See this link for handy chart. http://www.engineershandbook.com/Tables/pipe.htm

NO, The outside diameter of the pipe is a fixed parmater for each pipe size. By changing the pipe schedule, the pipe thickness will change and the pipe inside diamter.

For pipe sizes larger than 12", the pipe outside diamter is the pipe size. For example a pipe of 20" NPS has an outside diamter equals 20".

I have seen some confusion between"pipe" and "tubing".As i understood it,pipe size is the measurement of "ID",and tubing size is the "OD".

No! Wrong. That is not the primary difference.

The big difference is in a number of different facts about each.

The way each is made: Pipe- some is made with a straight seam weld, some is made with a spiral welded seam and some is made seamless. Tubing- All is made seamless.

Available sizes: Pipe- available in 1/4" to 180" and larger. Tubing- 1/8" to 4"

Manner of supply: Pipe- Single Random lengths (18' to 22'), Double Random Lengths (38' to 42') and Coil (for Pipeline projects). Tubing- 10' or 20' or coil.

Method of joining: Pipe- Socket Weld, Screwed or Butt Weld fittings. Tubing- Special Tubing fittings with a Ferrel or soldered or braised slip fittings.