Shape
Pipes are always round in shape. Tubes can be square, rectangular or round.
Strength
Tube is stronger than pipe.
Rigidity
Although copper and brass tubes can be shaped relatively easily, tubes are are typically rigid. Pipes, on the other hand, are invariably rigid and cannot be shaped without special equipment.
Size
Pipe is typically available in larger sizes than tube.
Pipes accommodate larger applications with sizes that range from a half-inch to several feet. Tubes are generally used in applications that require smaller diameters. While 10-inch pipes are common, it’s rare that you will come across a 10-inch tube.
Applications
Only pipes are pressure rated and intended to be used for the transfer of fluids or gas. Tubes, on the other hand, are used in structural applications.
Tubes are often put to use in applications that require precise outside diameters, like with cooler tubes, heat exchanger tubes and boiler tubes.
Measurement
Pipes are only provided with an inside (nominal) diameter and a “schedule” (which means wall thickness). There’s an easy way to remember this: since pipe is used to transfer fluids or gas, the size of the opening through which the fluids or gas can pass through is probably more important to you than the outer dimensions of the pipe. Tube measurements, on the other hand, are provided as an outside diameter and set ranges of wall thickness.
The thickness of tubes increases in standard increments such as 1 mm or 2 mm. Pipe thickness depends on the schedule, so there is no fixed increment.
High Pressure Fluid
Pipes have a pressure rating and are schedule, which is why they are often used to carry fluids that must be contained.
Labor intensive
Joining pipes is more labor intensive as it requires welding, threading or flanges. Tubes can be joined quickly and easily with flaring, brazing or couplings, but for this reason, they don’t offer the same stability.