A tube, or tubing, is a long hollow cylinder used for moving fluids (liquids or gases) or to protect electrical or optical cables and wires.
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.
Manufacture.
There are three classes of manufactured tubing: seamless, as-welded or electric resistant welded (ERW), and drawn-over-mandrel (DOM).
Standards.
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 material specifications generally cover a variety of grades or types that indicate a specific material composition. Some of the most commonly used are:
In installations using hydrogen, copper and stainless steel tubing must be factory pre-cleaned (ASTM B 280) and/or certified as instrument grade. This is due to hydrogen's particular propensities: to explode in the presence of oxygen, oxygenation sources, or contaminants; to leak due to its atomic size; and to cause embrittlement of metals, particularly under pressure.
Calculation of strength.
For a tube of silicone rubber with a tensile strength of 10 MPa and an 8 mm outside diameter and 2 mm thick walls. The maximum pressure may be calculated as follows:
Outside diameter = 
Wall thickness = 
Tensile strength = 10 * 1000000 [Pa]
Bursting pressure = (Tensile strength * Wall thickness * 2 / (10 * Outside diameter) ) * 10 [Pa]
Gives bursting pressure of 5 MPa.
Using a safety factor:
Pressure max = (Tensile strength * Wall thickness * 2 / (10 * Outer diameter) ) * 10 / Safety_factor [Pa]
33
Applications.
Tubes are essential components in heat exchange systems to assist with cooling down motors and other instruments. Industrial applications use pressure-resistant tubes to safely contain gases and liquids under pressure without leading to air leakage or malfunction. Moreover, devices powered by ultrasound often employ special types of thin-walled tubes that can generate vibration when exposed to an electric field. Finally, tube components provide efficient energy conservation in housing insulation materials such as silicon rubber foam insulation and polyethylene foam insulation.
See also.
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