Sulfur hexafluoride cylinders

Sulfur hexafluoride is packaged as a Hquefted gas in DOT 3AA 2015 steel cylinders containing 52 kg. Larger quantities are available in tube trailers containing ca 11,000 kg. 

The fluorine thereby obtained is directly processed further (to uranium hexafluoride, sulfur hexafluoride) or liquefied (b.p. -188°C) and filled into pressure cylinders. Pressure cylinders with mixtures of fluorine and nitrogen, with 10 or 20% by volume of fluorine, are widely marketed (utilized, for example, for the surface fluorination of vehicle fuel tanks). The worldwide fluorine capacity is estimated to be ca. 7.5 10 t/a, of which 60% is in the USA, 25% in Europe and 15% in Japan. Ca. 75% of the fluorine manufactured is utilized in the manufacture of uranium hexafluoride, 22.5% in the manufacture of sulfur hexafluoride and 2.5% in the manufacture of tetrafluoromethane. In 1986 ca. 100 t of fluorine was utilized in the manufacture of fluorographite (high conductivity) for use in batteries. 

Sulfur hexafluoride is sold in cylinders containing 100 lb of the material at about 3 per lb (1959 price). It is used as the electrical insulator in coaxial cables, high voltage X-ray transformers, and high voltage generators (35, 211). Its availability is a stimulus to research dealing with the substance. Many studies use the substance because it is inert or because it is made up of nearly spherical molecules. There is also much theoretical interest in its structure and in the nature of the chemical bond involved. Many studies are related to its usefulness as an electrical insulator. 

Sulfur hexafluoride is authorized for shipment in cylinders under DOT/TC regulations [4, 5]. 

The maximum filling density permitted for sulfur hexafluoride in cylinders is 120 percent (percent water capacity by weight). 

Cylinders that meet the following TC/DOT specifications are authorized for sulfur hexafluoride service 3A1000, 3AA1000,... 

Cylinders authorized for sulfur hexafluoride service must be requalified every 5 years with the exception that no retest is required for specification 3E cylinders. Furthermore, specification 3A and 3AA cylinders may be requalified every 10 years instead of every 5 years if they meet the requirements of 49 CFR 173.34 and CAN/CSA B339 [4, 7]. 

Pressure relief devices authorized for use on sulfur hexafluoride cylinders are the Type CG-1 rupture disk, CG-5 combination rupture disk/fusible plug, and CG-7 pressure relief valve. [6] When cylinders are over 65 inches (1651 mm) long exclusive of the neck and a Type CG-5 device is used, one is required at each end of the cylinder. [6]... 

The standard connection in the United States and Canada for sulfur hexafluoride cylinders is Connection CGA 590. [7]... 

Albert and Shultz (2(X)2) used the stable and inert trace gas sulfur hexafluoride (SFe) to study both diffusive and advective transport in Arctic snow at Summit, Greenland. Chemical diffusivity in wind-packed surface snow was determined by measuring the rate of disappearance of SFe from the headspace of a steel cylinder inserted into the snow pack. Wind pack is high-density snow and consists of small rounded crystals, generated by strong and cold winds (Domind et al., 2008). The effective diffusivity was 0.06 cm s . The reduction of the molecular diffusivity by the presence of the snow pack was well described by Equation 18.12 and the empirically derived exponent n was close to the theoretically expected value of 1.5. 

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