A rupture disk, or bursting disc, is a safety device used in pressurised industrial processes, applications, and manufacturing systems. The disc itself is a sheet of metal that has been deliberately weakened so that it will burst – or rupture – at a specific pressure. This means that if the pressure in the system builds up and reaches dangerous levels, the disc bursts, relieving the excess pressure and preventing life-threatening injury as well as catastrophic damage to the equipment.
Definitions of a rupture disc are found in Section VIII of the Boiler and Pressure Vessel Code (BPVC) published by the American Society of Mechanical Engineers (ASME), and in the European ISO standard, ISO 4126-2:2018: Safety devices for protection against excessive pressure — Part 2: Bursting disc safety devices. These two documents highlight the key features of a rupture disc:
‘Non-reclosing’ means that once the disc has burst, there is no way to close the opening again. ‘Non-mechanical’ means that, unlike, pressure safety valves, the rupture disc has no moving parts.
Typically, the entire device consists of a disc and holder assembly, plus other components such as back pressure supports. The bursting disc itself is the pressure-containing and pressure-sensitive part of the safety device. It is designed to burst open at a predetermined differential pressure and specific temperature.
You can compare a rupture disc to the fuse in an electrical circuit: If there is a surge in current in the circuit, the fuse will blow and break the circuit. This prevents damage to the equipment connected to the circuit and protects anyone working nearby from electrocution. In addition, the fuse is relatively cheap and easy to replace.
Similarly, if there is a surge in pressure through the vessels and pipework in a manufacturing system, the rupture disc will blow and relieve the pressure. This likewise prevents damage to the equipment and protects anyone working nearby from injury. In addition, the disc is generally easier and cheaper to replace than the rest of the equipment.
Typical applications using rupture discs include chemical reactors, gas coolers, heat exchangers and bioreactors. Oil and gas refineries, powerships and switchgear in electrical sub-stations also operate at pressures of above 15 psig. They may therefore also require pressure safety devices.