Argon Compression

Argon belongs to the family of inert, rare gases of the atmosphere. It is plentiful compared to the other rare atmospheric gases; 1 million ft3 (28 300 m3) of dry air contains 9340 ft3 (264 m3) of argon. Argon is colorless, odorless, tasteless, and nontoxic. It is extremely inert and forms no known chemical compounds. It is slightly soluble in water. 

GRADES AVAILABLE:

Table 1 from CGA G-11.1, Commodity Specification for Argon, presents the component maxima in parts per million, ppm (v/v), unless otherwise shown, for the grades of argon, which are also sometimes denoted as quality verification levels (QVLs) [1].  Gaseous argon is referred to as Type I and liquid argon as Type II. A blank indicates no maximum limiting characteristic. The absence of a value in a listed grade does not mean to imply that the limiting characteristic is or is not present, but merely indicates that the test is not required for compliance with the specification. 

USES: 

Argon is extensively used in filling incandescent and fluorescent lamps, and electronic tubes; as an inert gas shield for arc welding and cutting; as a blanket in the production of titanium, zirconium, and other reactive metals; to flush molten metals to eliminate porosity in castings; and to provide a protective shield for growing silicon and germanium crystals. 

TABLE 1. DIRECTORY OF LIMITING CHARACTERISTICS
(UNITS IN PPM (V/V) UNLESS OTHERWISE STATED)
QUALITY VERIFICATION LEVELS

Source: CGA G-11.1-1992.

Notes: 

1. Value noted is combined carbon dioxide and carbon monoxide. 
2. To be determined between supplier and customer. 

II/Properties, Manufacture, Uses, and Special Requirements for Safe Handling

TABLE 2. TYPICAL USES*

*Uses defined in this table are not all-inclusive.

PHYSIOLOGICAL EFFECTS: 

Argon is nontoxic and largely inert. It can act as a simple asphyxiant by diluting the concentration of oxygen in air below levels necessary to support life. Inhalation of it in excessive concentrations can result in dizziness, nausea, vomiting, loss of consciousness, which prevents self-rescue. At low-oxygen concentrations, unconsciousness and death may occur in seconds without warning. 

Gaseous argon must be handled with all the precautions necessary for safety as with any nonflammable, nontoxic compressed gas. All precautions necessary for the safe handling of any gas liquefied at very low temperatures must be observed with liquid argon. Extensive tissue damage or burns can result from exposure to liquid argon or cold argon vapors. 

MATERIALS OF CONSTRUCTION: 

Gaseous argon is noncorrosive and inert, and consequently may be contained in systems constructed of any common metals and designed to safely withstand the pressures involved. At the temperature of liquid argon, ordinary carbon steels and most alloy steels lose their ductility and are considered unsafe for liquid argon service. Satisfactory materials for use with liquid argon include austenitic stainless steel (for example, types 304 and 316), copper, Monel, brass, aluminum, and other nickel-chromium alloys. 

SAFE STORAGE, HANDLING, AND USE:

Gaseous argon is commonly stored in high pressure cylinders, tubes, or tube trailers. Liquid argon is commonly stored at the consumer site in cryogenic liquid containers and specially designed vacuum-insulated cryogenic storage tanks. All of the precautions necessary for the handling of any nonflammable gas or cryogenic liquid must be taken. For additional details, see Chapter 2 and the compressed gas manufacturers MSDS. Liquid and gaseous systems should be designed and installed only under the direction of personnel thoroughly familiar with liquid and gaseous argon equipment and in compliance with state, provincial, and local requirements. 

DISPOSAL: 

Position discharge valve away from personnel and vent argon gas slowly to a well-ventilated outdoor location remote from personnel work areas and building air intakes. Return cylinders to the supplier with residual pressure, the cylinder valve tightly closed, and the valve caps in place. Allow liquid argon to evaporate in well-ventilated outdoor locations, which are remote from work areas and building air intakes. 

HANDLING LEAKS AND EMERGENCIES: 

Ventilate adjacent enclosed areas to prevent the formation of oxygen-deficient atmospheres caused by the release of gaseous argon or by the evaporation of liquid argon. Personnel, including rescue workers, should not enter areas where the oxygen concentration is below 19 percent, unless provided with an SCBA or airline respirator. Avoid contact of the skin with liquid argon or its cold boil-off gas. Flush liquid argon spills with water to accelerate evaporation. 

First Aid

In case of frostbite from exposure to liquid argon, the frostbitten part should be placed in warm water, 100oF to 105oF (37.8oC to 40.6oC). If warm water is not available, or it is impractical to use, wrap the affected part gently in blankets. Let circulation re-establish itself naturally. Encourage the victim to exercise the affected part while it is being warmed. Consult a physician [4].

METHODS OF SHIPMENT: 

Under the appropriate DOT and TC regulations, argon is authorized for shipment as follows [2, 3]: 

• By Rail: In DOT/TC approved cylinders, portable tanks, and tank cars as a compressed gas; and in cylinders and cargo tanks as a cryogenic liquid. 
• By Highway: In DOT/TC approved cylinders, portable tanks, and cargo tanks as a compressed gas; and in cylinders and cargo tanks as a cryogenic liquid.
• By Water: In the United States, in DOT approved cylinders, portable tanks, and cargo tanks on cargo vessels and passenger vessels within Stowage category “A” limitations for compressed gas and category “B” for cryogenic liquid. 

In Canada, cylinders, portable tanks, and cargo tanks must be stowed according to the requirements of the IMDG code [5]. 

• By Air: In the United States and Canada, in cylinders as a compressed gas with a maximum net weight per cylinder of 165 lb (75kg) aboard a passenger aircraft, and up to 330 lb (150kg) aboard a cargo aircraft. As a cryogenic liquid in cylinders with a maximum net weight per cylinder of up to 110 lb (50kg) aboard a passenger aircraft, and up to 1102 lb (500kg) aboard a cargo aircraft. 

CONTAINERS: 

Argon gas is authorized for shipment in cylinders, tube tank cars, and tube trailers. Liquid argon is shipped as a cryogenic fluid in vacuum insulated cylinders, insulated portable tanks, insulated tank trucks, and tank cars. 

Filling Limits

For gaseous argon, the maximum filling limits authorized are as follows: Cylinders and tube trailers may be filled to the authorized service pressure marked on the cylinder or tube assemblies at 70oF (21.1oC). Cylinders of specifications 3A, 3AA, 3AX, 3AAX, and 3T that meet special requirements may be filled up to 10 percent in excess of their marked service pressures. See 49 CFR 173.302 ( c) [2]. Tube tank cars (uninsulated cars of the TC/DOT 107A Type) are authorized to be filled to not more than seven-tenths of the marked test pressure at 130oF (54.44oC). For liquid argon, the maximum filling limits authorized are: specification TC/DOT 4L cylinders are authorized for the transportation of liquid argon when carried in the vertical position. The filling density must be in accordance with Table 3. 

Cylinders

Cylinders that comply with TC/DOT specifications 3A and 3AA are the types usually used to ship gaseous argon, but it is authorized for shipment in any cylinders approved for nonliquefied compressed gas. These include cylinders meeting specifications 3A, 3AA, 3AX, 3AAX, 3B, 3E, 3T, 3AL, 39, 4B, 4BA, and 4BW; in addition, continued use of cylinders complying with specifications 3C, 3D, 4, 4A, 4C, 3, 25, 26, 33, and 38 is authorized, but new construction is not authorized. Liquid argon is authorized for shipment in cylinders that meet TC/DOT specification 4L. For liquid argon at pressures under 25.3 psig (174 kPa), the container specification is not regulated by DOT. However, in Canada, compressed gases and refrigerated liquids are regulated regardless of pressure. All cylinders authorized for gaseous argon service must be requalified by hydrostatic retest every 5 or 10 years under present regulations with the following exceptions: TC/DOT 4 cylinders require retest every 10 years, and cylinders of types 3C, 3E, and 4C require no periodic retest. Also, cylinders of the 4L type authorized for liquid argon service require no periodic retest for requalification. 

Tank Cars 

Gaseous argon is authorized for rail shipment in tank cars that comply with TC/DOT specifications 107A. DOT/TC regulations require that the pressure to which the containers are charged must not exceed seven-tenths of the marked test pressure at 130oF (54.4oC). Liquid argon is also shipped in vacuum-insulated tank cars (AAR204W) at pressures less than 25.3 psig (174 kPa). 

TABLE 3. FILLING DENSITY OF ARGON IN TC/DOT 4L LIQUID CYLINDERS.

Tube Trailers

Gaseous argon is shipped in tube trailers with capacities ranging to more than 40 000 ft3 (1130m3). These trailers are built to comply with DOT cylinder specifications 3A, 3AA, 3AX, 3AAX, or 3T.

Tank Trailers (Cargo Tanks)

Liquid argon is shipped in bulk at pressures below 25.3 psig (174 kPa) in special insulated tank trailers with capacities in excess of 400, 000 ft3 (11,300m3).

Small Portable Containers

Liquid argon is shipped and stored in small portable containers (dewar flasks), which hold quantities ranging from 1 gal to 25 gal (4 L to 95 L) or more. These containers are encased in shells and are heavily insulated; they maintain the liquid at atmospheric pressure. 

Cylinder Valve Outlet Connections

Refer to the introduction of Part II for information on valve outlet connections. A full listing of valve connection assignments for compressed gases in cylinders can be found in Chapter 9, Table 9-1. 

Pressure Relief Devices

Refer to the Introduction to Part II for information on pressure relief devices. A full alphabetical list of gases and device assignments can be found in Chapter 8, Table 8-2.

METHODS OF MANUFACTURE: 

Argon is manufactured in air separation plants by means of fractional distillation after the liquefaction of air. 

Reference the table below for common industries and applications using Argon