Exemption cylinders

Low pressure cylinders exempt from hydrostatic testing... 

The first category covers cylinders exempted from hydrostatic retesting requirements of DOT and TC by virtue of their exclusive use in non-corrosive gas service. Since they are not subject to internal corrosion they do not require internal shell inspection, and, therefore, can be requali-fied by an external visual inspection. However, if internal corrosion is suspected, cylinders of this type should be internally inspected and hydrostatically tested. 

The 0.1 kg exemption level provides assurance against the explosion of small, bare cylinders of UFg [15]. The 0.1 kg level is well below the toxic risk limit of 10 kg, based on Refs [16, 17]. 

Exemption cylinders. Many lightweight filament wound cylinders and high-strength steel cylinders are in use. Their specifications, uses and handling are as specified by DOT exemption. 

Small containers exempt from cylinder requirements... 

The second category is low pressure cylinders not exempted from hydrostatic retest requirements in the applicable regulations because interior corrosion potentially exists. See 49 CFR 173.34 [1]. Cylinders not exempt require a periodic hydrostatic retest, and an external and internal visual examination. Defect limits for the external examination are the same as for exempted cylinders. 

DOT and TC have authorized by exemptions the use of ultrasonic wall thickness measurement for the requalification of certain compressed gas cylinders. 

Retest pressure, retest period, and permanent expansion rejection criteria for DOT and TC specification cylinders are cited in 49 CFR, CAN/CSA B-339, and current exemptions [3]. 

DOT exemptions have also been authorized for stainless steel cylinders, as well as portable containers. 

Ethylene is authorized for shipment in cylinders under DOT and TC regulations. It is also shipped in bulk quantities under DOT exemption. 

By Rail In DOT/TC approved cylinders and seamless tank cars as a compressed gas, and in cylinders and tank cars as a cryogenic liquid. Insulated portable tanks for cryogenic liquid are permitted by exemption (forbidden on passenger-carrying rail cars). 

Liquid hydrogen is authorized for shipment in TC/DOT specification insulated welded cylinders, TC/DOT specification insulated cargo tanks, TC/DOT specification cryogenic liquid tank cars, and insulated portable tanks under exemption. 

MAPP Gas is shipped in steel cylinders conforming to DOT 4BW or in aluminum cylinders conforming to TC/DOT specification 4E. Service pressure must be at least 240 psig (1650 kPa). It is also shipped in 1 pound disposable containers under DOT exemptions. 

Most cylinders authorized for gaseous oxygen service must be requalified by hydrostatic retest every 5 or, under more restricted service requirements, 10 years. No periodic retest is required for cylinders of specifications 3C, 3E, 4C, and 7. Cylinders of specification 4L authorized for liquid oxygen service are also exempt from periodic retest requirements. See 49 CFR 173.34 [15]. 

Silane is shipped as a compressed gas in cylinders and, in the United States, also in tube trailers under DOT exemption. 

C-6.2 Guidelines for Visual Inspection and Re-qualification of Fiber Reinforced High Pressure Cylinders. Provides data and details including exemption numbers about fiber reinforced cylinders to help cylinder retesters examine and hydrostatically retest composite cylinders. Contains tables listing allowable defects and color photos of defects. Previous edition cited in 49 CFR (15 pages). 

Small Containers Exempt from Cylinder Requirements... 

In addition to external inspection, low pressure steel cylinders not exempted from hydrostatic retesting and high pressure cylinders must be inspected internally at least every time the cylinder is periodically retested. 

By Highway On trucks utilizing cylinders with a water capacity not to exceed 250 lb (113.4 kg) also in larger portable containers (by DOT exemption). 

By Rail In cylinders, and by DOT exemption in DOT 113A tank cars in low temperature liquid form. 

By Highway In cylinders on trucks and in tube trailers and by DOT exemption in insulated truck cargo tanks liquefied at low temperatures. 

By Rail Gaseous hydrogen is authorized to be shipped in TC/DOT specification cylinders and in TC/DOT Specification 107A seamless tank cars. Liquid hydrogen is authorized to be shipped in TC/DOT Specification 113 cryogenic liquid tank cars and in insulated portable tanks under exemption. 

By Rail In cylinders and multi-unit tank cars (TC/DOT-106A800X) and tank cars under exemption. 

By Highway In cylinders, tube trailers and cargo and portable tanks by exemption. 

By Rail In cylinders. As a liquid in tank cars designed for cryogenic gases, shipped under TC or DOT exemption. 

Authorized pressure relief devices for cylinders of nitrous oxide are of the Type CG-1 rupture disk. [9] Type CG-7 devices can be used up to 500 psig charging pressure for DOT-4L cylinders by DOT exemption. The Type CG-7 device is a pressure relief valve. [9]... 

Department of Transportation—A periodic retesting or reinsp on of 3E specified cylinders is not currently required by the Department of Transportation (DOT). This also applies to DOT-E vessels manufactured under DOT-3E compliwce (finee-floating piston vessels marked as such). Reference Okie of Federal R ulations, Title 49, 173, 34(e), page 389, for additional and fiuther information, ne manufacturer s DOT exemption papers should also be referenced. Other types of cylinders may require periodic requalification. 

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