What are the differences between pipe, tube, and sanitary tube?

It is fairly common for people to use pipe, tube, and sanitary tube interchangeably. They are similar terms but have different meanings.

What is "pipe"?

Pipe is the workhorse of any set up that doesn't require sanitary standards. It is made based on nominal diameter, that the diameter is approximately that size. For example, 2" pipe has neither an outer nor an inner diameter of 2". Another factor is the schedule of piping, which is the wall thickness with the diameter factored in. A schedule 40 pipe may have similar thicknesses under 8", but can vary greatly above that. Standard combinations of pipe are covered by ASME B36.10 for carbon or alloy steels and ASME B36.19 for stainless steels.

What is "tube"?

Tube refers to round, square, rectangular or oval hollow sections that can be used for pressure equipment, mechanical applications, or general fabrication. Tube measurements need both true dimensions and wall thickness. These specs are more accurate than pipe and a greater level of quality control is implemented during fabrication. 

What is "sanitary tube"?

Sanitary tube refers specifically to the material used in fluid handling installations in industries such as petrochemicals, food & beverage, and pharmaceutical facilities. The cross-section is always round. Different degrees of polish are available depending on the final application. For breweries, wineries, and distilleries, all process lines should be run in sanitary tubing.