What is the diffrence between tube & pipe?

A pipe is a vessel - a tube is structural.

A pipe is measured ID - a tube is measured OD.

How they are measured... Pipes are measured ID or inside diameter because they are vessels. Tubes are measured OD or outside diameter because they are structural.

Hope this helps.

Aaron

I don't buy the above answer at all.

Tubing is usually measured in NOMINAL ID UNLESS it's refrigeration tubing, then by actual OD. Example: The 1/2" copper tubing used for water is 5/8 OD. The type like K or L determines the wall thickness. Many people like to call this pipe, but it's really tubing.

Pipe is measured in NOMINAL OD. The schedule dtermines the wall thickness. This allows the same dies to be used for both say 2" schedule 40 and schedule 80 pipe.

See: Dimensions of Pipes and Tubes

Go to a hardware store and ask for a 3/4 copper sweat elbow and go into a refrigeration supply house and ask for a 7/8" elbow. You'll get the same thing.