Pressure Relief Devices for Compressed Gas Cylinders

This section summarizes the information in CGA S-1.1, Pressure Relief Device Standards—Part 1—Cylinders for Compressed Gases, [4] Included are descriptions of pressure relief devices for use on cylinders having capacities of 1000 lb (453.6 kg) of water or less (see 49 CFR 173.34(d) for exceptions), TC/DOT-3AX, 3AAX, and 3T cylinders having capacities over 1000 lb, and TC/ DOT-4L insulated cylinders containing cryogenic liquids. 

The Compressed Gas Association has classified pressure relief devices according to type using the letter designation CG followed by a numeral. Each of these types is described in the following subsections. 

Type CG-1 (Pressure Relief Rupture Disk). A rupture disk (synonymous with the name burst disk within the industry) is a pressure-operated device which affords protection against development of excessive pressure in cylinders. This device is designed to sense ex- 

Rupture disk devices installed on compressed gas cylinders may be either an integral part of the cylinder valve assembly or may be installed on the cylinder as an independent attachment. The materials of construction selected must be compatible with the fluid in the cylinder as well as the cylinder valve materials with which the rupture disk device comes in contact in order to minimize corrosion. 

One of the most common types of rupture disk devices consists of (1) a gasket, (2) a rupture disk, and (3) a rupture disk holder. These components may be supplied as independent parts (see Fig. 7- l) or may be in the form of factory-assembled devices designed to be replaced as a unit (see Fig. 7-2). 

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CGA S-7, Method for Selecting Pressure Relief Devices for Compressed Gas Mixtures in Cylinders, describes the method for selecting pressure relief devices for compressed industrial gas mixtures, while CGA S-1.1 applies to pure gases and some medical gas mixtures [7]. 

Depending on the contents of a mixture, one or more pressure relief devices may be required on the container. Most pressure relief devices are an integral part of the valve. However, some devices are installed directly into the bottom or top of the container. For an in-depth discussion on pressure relief devices for mixtures, see CGA S-7, Method for Selecting Pressure Relief Devices for Compressed Gas Mixtures in Cylinders [13]. Also consult Chapter 8 of this handbook for a presentation on pressure relief de-... 

Pressure relief valves. Pressure relief devices used on cargo tanks and portable tanks are similar to the CG-7 devices described for compressed gas cylinders earlier in this chapter, but... 

CGA S-1.1, Pressure Relief Device Standards-Part 1-Cylinders for Compressed Gases, 8 ed.. Compressed Gas Association, Inc., 1725 Jefferson Davis Highway, Arlington, VA 22202. 

Each pressure relief device assembly must be examined to ensure it is free of visual indications of abuse, damage, extrusion of fusible metal and that it appears intact. Each device must be the appropriate type and pressure rating for the gas and cylinder as prescribed in DOT and TC regulations and CGA S-1.1, Pressure Relief Device Standards-Part 1-Cylinders for Compressed Gases [1, 2, 23]. 

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