The primary difference between pipe and tubing is how the size is designated. Pipe is designated by a "Nominal Pipe Size" based upon the ID (inside diameter) of the most common wall thickness. Tubing is designated by the measured OD (outside diameter). For Example: A 3/4 inch iron pipe has an OD of 1.050 inches, while a 3/4 inch steel tube has an OD of 0.75 inches.
The Copper industry calls all cooper tubular products "Tubes" but they designate a "Type". Each type has specified OD and ID dimensions
The size of a tube is determined by it's OD and the thickness. The actual OD of a tube is just the same as it's nominal OD. A certain size of a tube will keep the same OD no mater what the thickness is. It is true for pipe except that the actual OD is larger than it's nominal OD.
For example, for a 1" schedule 5s pipe, the actual OD is 1.315", the thickness is 0.065" and the ID is 1.185". When it's thickness is schedule xxs (0.358"), then it's ID is reduced to 0.599" while keeping it's OD. Furthermore, the actual OD of a pipe is just the same as it's nominal OD when the size is the same as or larger than 14" per ASME/ANSI B36.10/19 . Consequently, both the size of tube and pipe is measured by it's OD and the thickness.
Actually tube is used when we need to transfer heat from its walls and we want this to be happen while in pipes we try to stop the heat transfer such as we use tubes in boilers because we make steam we need to transfer the heat while when we transport steam we use pipes because we wana save heat energy.
2: pipe can be thick according to formula d/t >10 while tube will must thin according to this formula.
The Real Difference:
Sorry to say; wrong! Pipe and tube is ever so simple. Pipes are used to transport something, and tubes to construct something; hence, tubes are defined by the od "outside diamater" and wt "wall thickness" (for construction stability), and pipes id inside diamater to allow a calculation for transportation viz., speed, volumes etc. (od = id + 2 * wt).