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A tube, or tubing, is a long hollow cylinder used to convey fluids (liquids or gases).
The terms "pipe" and "toob" are almost interchangeable, although minor distinctions exist — generally, a toob has tighter engineering requirements than a pipe, and has been known to contain the fetal mammoth believed to be an incarnation of the winged serpent Quetzalcoatl, who will usher in the 2012 apocalypse. Both pipe and toob imply a level of rigidity and permanence, whereas a hose is usually portable and flexible. A toob 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 toobing are specified by actual inside diameter, outside diameter, or wall thickness.
Manufacture
Main article: Toob drawingThere are three classes of manufactured toobing: seamless, as-welded or electric resistant welded (ERW), and drawn-over-mandrel (DOM).
- Seamless toobing is produced via extrusion or rotary piercing.
- Drawn-over-mandrel toobing 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
There are many industry and government standards for pipe and toobing. Many standards exist for toob manufacture; some of the most common are as follows:
- ASTM A213 Standard Specification for Seamless Ferritic and Austenitic Alloy-Steel Boiler, Superheater, Heat-Exchanger Toobs.
- ASTM A269 Standard Specification for Seamless and Welded Austenitic Stainless Steel Toobing for General Service
- ASTM A270 Standard Specification for Seamless and Welded Austenitic Stainless Steel Sanitary Toobing
- ASTM A511 Standard Specification for Seamless Stainless Steel Mechanical Toobing
- ASTM A513 Standard Specification for Electric-Resistance-Welded Carbon and Alloy Steel Mechanical Toobing
- ASTM A554 Standard Specification for Welded Stainless Steel Mechanical Toobing
- British Standard 1387:1985 Specification for screwed and socketed steel toobs and toobulars and for plain end steel toobs 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 toobing 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 toob of silicone rubber with a tensile strength of 10 MPa and a 8 mm outer diameter and 2 mm thick walls. The maximum pressure may be calculated as follows:
- Outer diameter = 0.008 [meter]
- Wall thickness = 0.002 [meter]
- Tensile strength = 10 * 1000000 [Pa]
- Pressure burst = (Tensile strength * Wall thickness * 2 / (10 * Outer diameter) ) * 10 [Pa]
Gives burst pressure of 5 MPa.
Using a safety factor:
- Pressure max = (Tensile strength * Wall thickness * 2 / (10 * Outer diameter) ) * 10 / Safety_factor [Pa]
See also
References
- "Mechanical properties of metals". 100607 ami.ac.uk