Tube and Tube Fittings

Tube, like pipe, is a hollow structure designed to provide an enclosed pathway for fluids to flow. In
the case of tubing, it is usually manufactured from rolled or extruded metal (although plastic is a
common tube material for many industrial applications). This section discusses some of the more
common methods for joining tubes together (and joining tube ends to equipment such as pressure
instruments).
One of the fundamental differences between tube and pipe is that tube is never threaded at the
end to form a connection. Instead, a device called a tube fitting must be used to couple a section of
tube to another tube, or to a section of pipe, or to a piece of equipment (such as an instrument).
Unlike pipes which are thick-walled by nature, tubes are thin-walled structures. The wall thickness
of a typical tube is simply too thin to support threads.
Tubes are generally favored over pipe for small-diameter applications. The ability for skilled
workers to readily cut and bend tube with simple hand tools makes it the preferred choice for
connecting instruments to process piping. When used as the connecting units between an instrument
and a process pipe or vessel, the tube is commonly referred to as an impulse tube or impulse line