Tubing is most commonly described as a long hollow cylindrical or square pipe that is used to convey fluids, gases or other substances. Tubing and piping are very similar except for one distinctive difference where tubing is considered to have a tighter engineering requirement that a pipe. Hoses are flexible, whilst tubing and piping are generally rigid and constructed of metals and hard plastics.
Tube manufacturing generally starts with coils of steel which are slit to the correct width for the size of tube that is required. This strip of coil is called a skelp and by passing it through a series of rolls, it is cold-formed into a tubular shape. An electric resistance welder is used to join the edges together and as no filler is used in the welding process, the entire tube is consturcted of the parent material.
There are three different classifications or classes of manufactured tubing:-
- Seamless – produced by extrusion or rotary piercing
- Welded or Electric Resistant Welded (ERW)
- Drawn Over Mandrel (DOM) – formed from cold drawn electrical resistance welded tube which has been drawn through a die and also over a mandrel to produce weld integrity, dimensional accuracy and an exceptional surface finish.
There are also a wide range of standards to which the tubing is manufactured both from an industry perspective as well as from government standards. The various standards are important to consider when understanding what each is capable of as well as their material compositions.
Any installation that involves hydrogen for example will require the use of copper and stainless steel tubing that has been factory pre-cleaned (ASTM B 280) and is certified as instrument grade. Without such precautions, hydrogen could react with oxygen causing the metal to become brittle and unstable.