Gas cylinder
For mechanical devices used to impart a force from a pressurized liquid or gas, see pneumatic cylinder.A
Gas cylinder or
tank is a
pressure vessel used to store
gases at high
pressure.
Applications for gas cylinders include:
*
pneumatic reservoirs in
transport and
industry* storage of
medical gases
* storage of
breathing gases in
diving cylinder* storage of gaseous
fuels for
internal combustion engines,
heating equipment and
cooking such as
LP gas,
butane and
propane* storage of gases used for
oxyacetylene welding.
The transportation of high pressure cylinders is regulated by many governments throughout the world. Various levels of testing are generally required by the governing authority for the country in which it is to be transported. In the United States this authority is the
United States Department of Transportation (DOT), for Canada this authority is
Transport Canada (TC). Cylinders may have additional requirements placed on design and or performance from independent testing agencies such as Underwriter's Laboratory (UL). Each manufacturer of high pressure cylinders is required to have independent quality agent that will inspect the product for quality and safety.
There are a variety of tests that may be performed on various cylinders. Some of the most common types of tests are
hydrostatic test, burst test,
tensile strength,
Charpy impact test and pressure cycling.
The during the manufacturing process vital information is usually stamped or permantally marked on the cylinder. This usually includes the type of cylinder, the working or service pressure, the serial number, date of manufacture, the manufacture's registered code and sometimes the test pressure. Other information may also be stamped depending on the regulation requirements.
High pressure cylinders that are used multiple timesare hydrostatically or ultrasonically tested and visually examined every few years. In the U.S., hydrostatic/ultrasonic testing is required either every five years or every ten years, depending on cylinder and its service.
The valves on industrial, medical and diving cylinders are usually of different size and type, as are the valves for different products, making it more difficult to mistakenly misuse a gas.
In the US, valve connections are sometimes referred to as 'CGA connections,' since the
Compressed Gas Association (CGA) publishes guidelines on what connections to use for what products. E.g., an argon cylinder in the US will have a CGA 580 connection on the valve.
*Note: if the nut on a CGA connection has a notch in it, it uses a
left-handed thread.
High purity gases will sometimes use CGA-DISS ('Diameter Index Safety System') connections.
In the EU,
DIN connections are more common than in the US.
Gas cylinders are often
color coded, but the codes are not standard across different jurisdictions, and sometimes are not regulated. Do not trust the color of a cylinder to identify the product it contains. Check the cylinder's label/decal for product identification.
Because the contents are under pressure and are sometimes hazardous, there are special safety regulations for handling bottled gases. These include chaining bottles to prevent falling and breaking, proper ventilation to prevent injury or death in case of leaks and signage to indicate the potential hazards. Installing and replacing gas cylinders should be done by trained personnel.
In a fire, the pressure in a gas cylinder rises in direct proportion to its temperature (see the
ideal gas law). If this pressure exceeds the mechanical limitations of the cylinder, it will fail and may explode. For safety, medical gas cylinders in the UK and other countries have a seal of
Wood's metal between the valve block and the cylinder body. This seal melts at a comparatively low temperature (70°C) and allows the contents of the cylinder to escape in a controlled fashion, lessening the risk of explosion.
More common are simple burst-disc safety devices. A small burst disc is installed in the back of the valve. A burst disc is a small metal gasket engineered to rupture at a pre-determined pressure. Some of these burst disc are backed with a low-melting-point metal, so that the valve must be exposed to excessive heat before the burst disc can rupture.
The
Compressed Gas Association sells a number of booklets and pamphlets on safe handling and use of bottled gases. (Members of the CGA can get the pamphlets for free.)
*
Bottled gas*
Compressed Gas Association
