A tube, or tubing, is a long hollow cylinder used to convey fluids (liquids or gases).
The terms ‘pipe’ and ‘tube’ are almost interchangeable, although minor distinctions exist — generally, a tube has tighter engineering requirements than a pipe. Both pipe and tube imply a level of rigidity and permanence, whereas a hose is usually portable and flexible. A tube and pipe may be specified by standard pipe size designations, e.g., nominal pipe size, or by nominal outside or inside diameter and/or wall thickness. The actual dimensions of pipe are usually not the nominal dimensions: A 1-inch pipe will not actually measure 1 inch in either outside or inside diameter, whereas many types of tubing are specified by actual inside diameter, outside diameter, or wall thickness.
There are many industry and government standards for pipe and tubing. Many standards exist for tube manufacture; some of the most common are as follows:
ASTM A213 Standard Specification for Seamless Alloy-Steel Boiler, Superheater, Heat-Exchanger Tubing.
ASTM A269 Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for General Service
ASTM A270 Standard Specification for Seamless and Welded Austenitic Stainless Steel Sanitary Tubing
ASTM A511 Standard Specification for Seamless Stainless Steel Mechanical Tubing
ASTM A513 Standard Specification for Electric-Resistance-Welded Carbon and Alloy Steel Mechanical Tubing