Liquid Argon

Most of what appears below was taken from the Air Products’ website with its permission.

Information Specific to Liquid Argon

General

Liquid argon is tasteless, colorless, odorless, non-corrosive, nonflammable, and extremely cold. Belonging to the family of rare inert gases, argon is the most plentiful of the rare gases, making up approximately 1% of the earth’s atmosphere. It is monatomic and extremely inert, forming no known chemical compounds. Special materials of construction are not required to prevent corrosion. However, materials of construction must be selected to withstand the low temperature of liquid argon.

Vessels and piping should be designed to American Society of Mechanical Engineers (ASME) specifications or the Department of Transportation (DOT) codes for the pressures and temperatures involved. Although used more commonly in the gaseous state, argon is commonly stored and transported as a liquid, affording a more cost effective way of providing product supply. When argon is converted to liquid form it becomes a cryogenic liquid. Cryogenic liquids are liquefied gases that have a normal boiling point below -238°F (-150°C). Liquid argon has a boiling point of -302.6°F (-185.9°C).

The temperature difference between the product and the surrounding environment, even in winter, is substantial. Keeping this surrounding heat from the product requires special equipment to store and handle cryogenic liquids. A typical system consists of the following components: a cryogenic storage tank, one or more vaporizers, a pressure control system, and all of the piping required for fill, vaporization, and supply. The cryogenic tank is constructed like a vacuum bottle. It is designed to keep heat away from the liquid that is contained in the inner vessel. Vaporizers convert the liquid argon to its gaseous state. A pressure control manifold controls the pressure at which the gas is fed to the process.

Health Effects

Being odorless, colorless, tasteless, and nonirritating, argon has no warning properties. Humans possess no senses that can detect the presence of argon. Argon is nontoxic and largely inert. It can act as a simple asphyxiant by displacing the oxygen in air to levels below that required to support life. Inhalation of argon in excessive amounts can cause dizziness, nausea, vomiting, loss of consciousness, and death. Death may result from errors in judgment, confusion, or loss of consciousness that prevents self-rescue. At low oxygen concentrations, unconsciousness and death may occur in seconds and without warning. Personnel, including rescue workers, should not enter areas where the oxygen concentration is below 19.5%, unless provided with a self-contained breathing apparatus or air-line respirator. Extensive tissue damage or burns can result from exposure to liquid argon or cold argon vapors.

Physical Properties

  • Molecular Weight: 39.95
  • Boiling Point @ 1 atm: -302.6°F (-185.9°C, 87oK)
  • Freezing Point @ 1 atm: -308.8°F (-189.4°C, 85oK )
  • Critical Temperature: -188.4°F (-122.4°C)
  • Critical Pressure: 705.8 psia (48.0 atm)
  • Density, Liquid @ BP, 1 atm: 87.40 lb/scf
  • Density, Gas @ 68°F (20°C), 1 atm: 0.1034 lb/scf
  • Specific Gravity, Gas (air=1) @ 68°F (20°C), 1 atm: 1.38
  • Specific Gravity, Liquid (water=1) @ 68°F (20°C), 1 atm: 1.40
  • Specific Volume @ 68°F (20°C), 1 atm: 9.67 scf/lb
  • Latent Heat of Vaporization: 2804 BTU/lb mole
  • Expansion Ratio, Liquid to Gas, BP to 68°F (20°C): 1 to 840

Containers

Liquid argon is stored, shipped, and handled in several types of containers, depending upon the quantity required by the user. The types of containers in use are the Dewar, cryogenic liquid cylinder, and cryogenic storage tank. Storage quantities vary from a few liters to many thousands of gallons. Since heat leak is always present, vaporization takes place continuously. Rates of vaporization vary depending on the design of the container and the volume of stored product. Containers are designed and manufactured according to the applicable codes and specifications for the temperatures and pressures involved.

Liquid product is typically removed through insulated withdrawal lines to minimize the loss of liquid product to gas. Insulated flexible or rigid lines are used to withdraw product from storage tanks. Connections on the lines and tanks vary by manufacturer. NOTE: Liquid cylinders designed to dispense gaseous argon have valves equipped with standard Compressed Gas Association (CGA) outlets. Suitable pressure regulating equipment may be attached. Valves provided for the withdrawal of liquid product are also equipped with standard CGA outlets, but are different than the connections used for gaseous discs to protect the cylinders from pressure build-up. These containers operate at pressures up to 350 psig and have capacities between 80 and 450 liters of liquid. Product may be withdrawn as a gas by passing liquid through an internal vaporizer or as a liquid under its own vapor pressure.

Cryogenic Liquid Cylinders

The image below shows a typical cryogenic liquid cylinder. Cryogenic liquid cylinders are insulated, vacuum-jacketed pressure vessels. They come equipped with safety relief valves and rupture disks.

Cryo_LN2

Handling and Storage

Store and use this product with adequate ventilation. Do not store in a confined space. Cryogenic containers are equipped with pressure relief devices to control internal pressure. Under normal conditions, these containers will periodically vent product. Do not plug, remove, or tamper with any pressure relief device. Never allow any unprotected part of the body to come in contact with uninsulated pipes or equipment that contains cryogenic product. The extremely cold metal will cause the flesh to stick fast and tear when one attempts to withdraw from it.

Use a suitable hand truck for container movement. Containers should be handled and stored in an upright position. Do not drop, tip, or roll containers on their sides. Do not remove or interchange connections. Contact the vendor if you experience any difficulty operating the container valve or with the container connections. Discontinue use. Use the proper connection. DO NOT USE ADAPTERS! Use piping and equipment designed to withstand the pressures to be encountered. On gas withdrawal systems, use a check valve or other protective apparatus in any line or piping from the container to prevent reverse flow.

To prevent cryogenic liquids or cold gas from being trapped in piping between valves, the piping should be equipped with pressure relief devices. Only transfer lines designed for use with cryogenic liquids should be used. Some elastomers and metals such as carbon steel may become brittle at low temperatures and will easily fracture. These materials must be avoided in cryogenic service. It is recommended that all vents be piped to the exterior of the building.

Personal Protective Equipment (PPE)

One must be thoroughly familiar with the properties and safety considerations before handling a cryogenic liquid and its associated equipment. The eyes are the most sensitive body part to the extreme cold of the liquid and vapors of cryogenic liquids. The recommended personal protective equipment for handling cryogens includes a full face shield over safety glasses, loose-fitting thermal insulated or leather gloves, long sleeve shirts, and trousers without cuffs. In addition, safety shoes are recommended for people involved in the handling of containers. Depending on the application, special clothing suitable for that application may be advisable.

A special note on insulated gloves: Gloves should be loose-fitting so they are able to be quickly removed if cryogenic liquid is spilled on them. Insulated gloves are not made to permit the hands to be put into a cryogenic liquid. They will only provide short-term protection from accidental contact with the liquid. In emergency situations, self-contained breathing apparatus (SCBA) may be required.