Overpressure fusible plug

A further hazard exists when compressed air jets are used to clean machine components in workplaces flying particles have caused injury and blindness. Cylinders may fail if overpressurized or weakened by the application of heat. Liquefied gases, e.g. butane or propane, respond more rapidly to heat than the permanent gases such as nitrogen or oxygen. Cylinders are normally protected by pressure relief valves, fusible plugs or bursting discs. 

Each chlorine ton cylinder has three fusible plugs on each end of the tank to protect it from over-temperature. These plugs are designed to melt between 158° and 165° F (70° to 74° C). They are designed to protect the tank from overpressure if the cylinder is accidentally... 

The protection philosophy seems to be to protect the cylinder from overpressure by protecting it from over-temperature that would vaporize the liquid chlorine. Each of the fusible plugs is in a 3/4-inch threaded plug. If the fuse melts, the resulting hole is about 11/32 inch in diameter. 

While moderate heating of an SO2 cylinder is not likely to cause a problem of overpressure, the user should bear in mind that the cylinders are protected by fusible plugs. 

Fusible Plugs A fusible plug is a plug made of a metal that will melt at a selected temperature and relieve pressure in a container. Fusible plug applications include boilers, compressed gas cylinders, and other pressure vessels. They allow overpressure to vent when a container becomes heated from fire or other sources. A plug may consist entirely of the alloy... 

Limitations Since the fusible plug is a thermally operated device, it is designed to function only when the fusible metal melts out. Hence, it does not protect against overpressure from improper charging practices. 

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