- For structural tubing, see hollow structural section.
Tubing is a pipe or hollow cylinder for the conveyance of fluids (liquids or gases). The terms 'pipe' and 'tubing' are almost interchangeable, although minor distinctions exist (generally, "tubing" implies tighter engineering requirements than "pipe"). Both "pipe" and "tube" imply a level of rigidity and permanence, whereas a "hose" is usually portable and flexible. Tubing 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 (i.e., a "1-inch" pipe will not actually measure 1" in either outside or inside diameter) — whereas many types of tubing are specified by actual I.D., O.D., and/or wall thickness. There are many industry and government standards for pipe and tubing.
Manufacture
There are three classes of manufactured tubing: seamless, as-welded, and drawn-over-mandrel (DOM).
- Seamless tubing is produced via extrusion.
- Drawn-over-mandrel tubing is made from cold-drawn electrical-resistance-welded tube that is drawn through a die and over a mandrel to create such characteristics as dependable weld integrity, dimensional accuracy, and an excellent surface finish.
Standards
Many standards exist for tube manufacture. Some of the most common ones are as follows:
- ASTM A213 seamless stainless steel pressure tubing
- ASTM A269 welded stainless steel pressure tubing
- ASTM A270 seamless and welded stainless steel sanitary tubing
- ASTM A511 seamless stainless steel mechanical tubing
- ASTM A513 welded carbon steel mechanical tubing
- ASTM A554 welded stainless steel mechanical tubing
- British Standard 1387:1985 Specification for screwed and socketed steel tubes and tubulars and for plain end steel tubes suitable for welding or for screwing to BS 21 pipe threads
ASTM material specifications generally cover a variety of grades or types that indicate a specific material composition. Some of the most commonly used are:
- TP 304
- TP 316
- MT 304
- MT 403
- MT 506
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 and/or oxygenation sources/contaminants), to leak due to its size molecular/atomic size, and to cause embrittlement of metals, particularly under pressure. Tubing quality and source must be documented [1].
