Almostly both pipes and tube components are interchangeably used. While they both are hollow, their main function is to form a system to ferry across various gaseous or liquid media, there are several distinct differences that separate the two.
Pipe - The structure of the pipe is circular, which means that the members have a circular cross section and a hollow center. These components are used to distribute media in piping systems, including particles, powders, gases and fluids, and even vapors. Pipes will be specified by NPS or DN, which is the nominal pipe size. In North American systems, NPS is a standard set of pipe sizes that can be used in applications involving high or low pressure and temperature requirements. Pipe nominal terms refer to non-specific terms in a pipe, which can also help determine the diameter of a hollow in a dimensionless number. In short, although the NPS value does not match the true diameter of the pipe, it can give a rough estimate of the pipe's capacity. One of the most important features of pipes is their size. These sizes include inner or inner diameter, outer or outer diameter, and wall thickness or WT. Wall thickness is also known as piping specification. The size of the pipe will affect the liquid capacity of the pipe. This can be determined by calculating the od minus 2 WT or wall thickness (or schedule). Since the specified wall thickness refers to a schedule, most stainless steel tubes have values such as SCH.std., SCH.XS., SCH.XXS or SCH.40. Separate pipes with different NPS can be made under the same plan, however, different wall thicknesses (in inches or millimeters) are possible.
Tube - Although tubes are always round in shape, they can come in a variety of shapes, including round, rectangle, square or oval. Similar to pipes, these components come in sizes such as od and WT, which makes them easier to order. The hollow section of the tube assembly is estimated from the od or OD, combined with the wall thickness or WT. The only difference here is that for tubes these dimensions are expressed in inches or millimeters. The size of a pipe usually indicates the exact size of its hollow section.