Gas cylinder
[2] In South Africa, a gas storage cylinder implies a refillable transportable container with a water capacity volume of up to 150 litres.
[citation needed] The United Kingdom and other parts of Europe more commonly refer to "bottled gas" when discussing any usage, whether industrial, medical, or liquefied petroleum.
[citation needed] The term cylinder in this context is sometimes confused with tank, the latter being an open-top or vented container that stores liquids under gravity, though the term scuba tank is commonly used to refer to a compressed gas cylinder used for breathing gas supply to an underwater breathing apparatus.
Steel is generally the most resistant to rough handling and most economical, and is often lighter than aluminium for the same working pressure, capacity, and form factor due to its higher specific strength.
Steel cylinders are typically withdrawn from service after 70 years, or may continue to be used indefinitely providing they pass periodic inspection and testing.
Due to the very high tensile strength of carbon fiber reinforced polymer, these vessels can be very light, but are more expensive to manufacture.
[citation needed] Fibre composite cylinders were originally specified for a limited life span of 15, 20 or 30 years, but this has been extended when they proved to be suitable for longer service.
[citation needed] The Type 1 pressure vessel is a seamless cylinder normally made of cold-extruded aluminum or forged steel.
[17] Steel cylinders are often used because they are harder and more resistant to external surface impact and abrasion damage, and can tolerate higher temperatures without affecting material properties.
They also may have a lower mass than aluminium cylinders with the same gas capacity, due to considerably higher specific strength.
The dished profile allows them to stand upright on a horizontal surface, and is the standard shape for industrial cylinders.
The cylinders used for emergency gas supply on diving bells are often this shape, and commonly have a water capacity of about 50 litres ("J").
Domed end industrial cylinders may be fitted with a press-fitted foot ring to allow upright standing.
For example, the US standard DOT 3AA requires the use of open-hearth, basic oxygen, or electric steel of uniform quality.
[20] Steel cylinders may be manufactured from steel plate discs stamped from annealed plate or coil, which are lubricated and cold drawn to a cylindrical cup form, by a hydraulic press, this is annealed and drawn again in two or three stages, until the final diameter and wall thickness is reached.
The cylinders are machined to provide the neck thread and o-ring seat (if applicable), then chemically cleaned or shot-blasted inside and out to remove mill-scale.
[4] An alternative production method is backward extrusion of a heated steel billet, similar to the cold extrusion process for aluminium cylinders, followed by hot drawing and bottom forming to reduce wall thickness, and trimming of the top edge in preparation for shoulder and neck formation by hot spinning.
[3] Type 2 is hoop wrapped with fibre reinforced resin over the cylindrical part of the cylinder, where circumferential load is highest.
The fibres share the circumferential load with the metal core, and achieve a significant weight saving due to efficient stress distribution and high specific strength and stiffness of the composite.
Hoop winding is at an angle to the length axis of close to 90°, so the fibres carry negligible axial load.
Winding angles are optimised to carry all the loads (axial and circumferential) from the pressurised gas in the cylinder.
The outside of the neck of the insert is not covered by the fibre wrapping, and may have axial ridges to engage with a wrench or clamp for torsional support when fitting or removing the cylinder valve.
The ends are usually domed by cold pressing from a circular blank, and may be drawn in two or more stages to get the final shape, which is generally semi-elliptical in section.
Cylinders may have additional requirements placed on design and or performance from independent testing agencies such as Underwriters Laboratories (UL).
Within the UK the "competent authority" — the Department for Transport (DfT) — implements the regulations and appointment of authorised cylinder testers is conducted by United Kingdom Accreditation Service (UKAS), who make recommendations to the Vehicle Certification Agency (VCA) for approval of individual bodies.
[3] In Australia, Europe and North America, tapered neck threads are generally preferred for inert, flammable, corrosive and toxic gases, but when aluminium cylinders are used for oxygen service to United States Department of Transportation (DOT) or Transport Canada (TC) specifications in North America, the cylinders must have parallel thread.
Repeated secure installations are possible with different combinations of valve and cylinder provided they have compatible thread and correct O-ring seals.
During storage, transportation, and handling when the gas is not in use, a cap may be screwed over the protruding valve to protect it from damage or breaking off in case the cylinder were to fall over.
For example, a hydrogen cylinder valve outlet does not fit an oxygen regulator and supply line, which could result in catastrophe.
[citation needed] The Compressed Gas Association publishes a number of booklets and pamphlets on safe handling and use of bottled gases.
