Gas cylinders store gases under high pressures. Gas cylinders can store both flammable gases, such as acetylene, and inert gases such as helium.

Many countries have different color coding systems that are used to classify different gases and types of cylinders. These identification markings are used to indicate important data about the capabilities, ownership, and inspection history of the cylinder. More information can be seen in the image below.

1. Cylinder specification

2. Cylinder serial number

3. Date of manufacture

4. Neck ring identification

5. Retest markings

6. Bar code label

7. Cylinder manufacturer's inspection marking

8. Cylinder tare (empty) weight

It is important to note that there are differences in the terms used to describe gas cylinders from country to country. In the United States, for example, gas cylinders are sometimes called bottled gas. In addition, different types of gas cylinders (e.g., industrial, medical, or home use) will have different release valves.  

Type of Gas

The three main types of compressed gases that are stored in gas cylinders include:

Liquefied gases are gases which can become liquids at normal temperature when they are inside cylinders under pressure. They exist inside the cylinder in a liquid-vapor balance or equilibrium. Common examples are anhydrous ammonia, chlorine, propane, and carbon dioxide.

Non-liquefied gases are also known as compressed, pressurized, or permanent gases. These gases do not become liquid when they are compressed at normal temperatures, even at high pressures. Common examples are oxygen, nitrogen, helium, and argon.

Dissolved gases are very unstable. The most common example is acetylene, which can explode even at atmospheric pressure. Acetylene cylinders are fully packed with an inert, porous filler that is saturated with acetone to prevent explosions. As acetylene is added to the cylinder, the gas dissolves in the acetone making the acetylene solution stable.

State of Gas

Gases contained in a compressed gas cylinder can be toxic, flammable, oxidizing, corrosive, and/or inert. Special care should be taken when dealing with compressed gas cylinders, such as an argon gas cylinder, to prevent falling and breaking and to ensure proper ventilation. Typically, a gas cylinder rack or gas cylinder cabinet is used to safely and conveniently store gas cylinders.

Material of Construction

Gas cylinders can be made from aluminum, steel, alloys, and composite materials. Mechanical strength, corrosion resistance, and impact resistance are critical factors in determining which material is used. Carbon fiber composite cylinders can be very light due to the high tensile strength of carbon fiber, but are more difficult to manufacture.

A commonly used type of gas cylinders is a propane tank. Propane is a gas used in homes, farms, businesses, and industry. Propane is typically used for heating and must be stored in specially designed propane tanks. Some gases that are very unstable in their confined form, such as acetylene, require specially made gas cylinders (e.g., an acetylene gas cylinder) to reduce the hazards from shock and heat. 

Gas Cylinder Valves

Gas cylinders have a valve to control the release of the gases.  A cap, collar, or neck ring commonly protects the valve assembly from damage when the gas is not in use.  A pressure regulator assembly is utilized when dispensing gas from a cylinder to control the flow of gas at the desired pressure.

Applications

Gas cylinders are used in a wide variety of industries, including food processing, water treatment, and laboratory. They are most commonly found in the manufacturing and medical industries. In manufacturing, gas cylinders are used for storing fuel for heating systems, vehicles, and torches as well as storing the source of energy for power tools or assembly line machinery.  

Medical gas cylinders provide supplemental oxygen, nitrous oxide (anesthetic functions), nitrogen (surgical tools), and carbon dioxide (to inflate tissue).

Regulations and Standards

The International Organization for Standardization (ISO) technical committee developing standards for specifying the standardization of gas cylinders and their fittings is ISO/TC 58. Specific standards include BS EN ISO 102286 for gas cylinder terminology and BS EN ISO 11114-4 for cylinders transporting gas.

Compressed gases are subject to a requirement by the United States Department of Transportation (US DOT) in Title 49 Section 173 of the United States Code of Federal Regulations (49 CFR 173) mandating the use of hazardous materials placards during shipment.

The Occupational Safety & Health Administration (OSHA) maintains standards for gas cylinders. Learn more about OSHA standards here.

Resources

Compressed Gas Cylinders: Cylinders

Cyl-Tec

Image Credits:

Cyl-Tec | MIT EHS | Airgas | Airgas