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A rupture disk, also known as a pressure safety disc, burst disc, bursting disc, or burst diaphragm, is a non-reclosing pressure relief safety device that, in most uses, protects a pressure vessel, equipment or system from overpressurization or potentially damaging vacuum conditions.
A rupture disk is a type of sacrificial part because it has a one-time-use membrane that fails at a predetermined differential pressure, either positive or vacuum. The membrane is usually made out of metal, but nearly any material (or different materials in layers) can be used to suit a particular application. Rupture disks provide instant response (within milliseconds or microseconds in very small sizes) to an increase or decrease in system pressure, but once the disk has ruptured it will not reseal. Major advantages of the application of rupture disks compared to using pressure relief valves include leak-tightness, cost, response time, size constraints, and ease of maintenance.
Rupture disks are commonly used in petrochemical, aerospace, aviation, defense, medical, railroad, nuclear, chemical, pharmaceutical, food processing and oil field applications. They can be used as single protection devices or as a secondary relief device for a conventional safety valve; if the pressure increases and the safety valve fails to operate or can't relieve enough pressure fast enough, the rupture disk will burst. Rupture disks are very often used in combination with safety relief valves, isolating the valves from the process, thereby saving on valve maintenance and creating a leak-tight pressure relief solution. It is sometimes possible and preferable for highest reliability, though at higher initial cost, to avoid the use of emergency pressure relief devices by developing an intrinsically safe mechanical design that provides containment in all cases.
Although commonly manufactured in disk form, the devices also are manufactured as rectangular panels (rupture panels, vent panels or explosion panels) and used to protect buildings, enclosed conveyor systems or any very large space from overpressurization typically due to an explosion. Rupture disk sizes range from 0.125 in (3 mm) to over 4 ft (1.2 m), depending upon the industry application. Rupture disks and vent panels are constructed from carbon steel, stainless steel, hastelloy, graphite, and other materials, as required by the specific use environment.
Rupture disks are widely accepted throughout industry and specified in most global pressure equipment design codes (ASME, PED, etc.). Rupture disks can be used to specifically protect installations against unacceptably high pressures or can be designed to act as one-time valves or triggering devices to initiate with high reliability and speed a sequence of actions required.
Two disk technologies
There are two rupture disk technologies used in all rupture disks: forward-acting (tension loaded) and reverse buckling (compression). In the traditional forward-acting design, the loads are applied to the concave side of the rupture disk, stretching the dome until the tensile forces exceed the ultimate tensile stress of the material and the disk bursts. Flat rupture disk do not have a dome but, when pressure is applied, are still subject to tension loaded forces and are thus also forward-acting disks. The thickness of the raw material employed and the diameter of the disk determines the burst pressure. In later iterations on forward-acting disk designs, precision-cut or laser scores in the material during manufacturing were used to precisely weaken the material allowing for more variables to control of the burst pressure. This approach to rupture disks, while effective, does have limitations. Forward-acting disks are prone to metal fatigue caused by pressure cycling and operating conditions that can spike past recommended limits for the disk, causing the disk to burst at lower than its marked burst pressure. Low burst pressures also pose a problem for this disk technology. As the burst pressure lowers, the material thickness decreases. This can lead to extremely thin disks (similar to tin foil) that are highly prone to damage and have a higher chance of forming pinhole leaks due to corrosion. These disks are still successfully used today and are preferred in some situations.
Reverse buckling rupture disks are the inversion of the forward-acting disk. The dome is inverted and the pressure is now loaded on the convex side of the disk. Once the reversal threshold is met, the dome will collapse and snap through to create a dome in the opposite direction. While that is happening, the disk is opened by knife blades or points of metal located along the score line on the downstream side of the disk. By loading the reverse buckling disk in compression, it is able to resist pressure cycling or pulsating conditions. The material thickness of a reverse buckling disk is significantly higher than that of a forward-acting disk of the same size and burst pressure. The result is greater longevity, accuracy and reliability over time. Correct installation of reverse buckling disks is essential. If installed upside down, the device will act as a forward acting disk and, due to the greater material thickness, will burst at much higher than the marked burst pressure.
Blowout panels, also called blow-off panels, areas with intentionally weakened structure, are used in enclosures, buildings or vehicles where a sudden overpressure may occur. By failing in a predictable manner, they channel the overpressure or pressure wave in the direction where it causes controlled, directed minimal harm, instead of causing a catastrophic failure of the structure. Blow-off panels are used in ammunition compartments of some tanks to protect the crew in case of ammunition explosion, turning a catastrophic kill into a lesser firepower kill. An alternative example is a deliberately weakened wall in a room used to store compressed gas cylinders; in the event of a fire or other accident, the tremendous energy stored in the (possibly flammable) compressed gas is directed into a "safe" direction, rather than potentially collapsing the structure in a similar manner to a thermobaric weapon.
In military ammunition storage, blowout panels are included in the design of the bunkers which house explosives. Such bunkers are designed, typically, with concrete walls on four sides, and a roof made of a lighter material covered with earth. In some cases this lighter material is wood, though metal sheeting is also employed. The design is such that if an explosion or fire in the ammunition bunker (also called a locker) were to occur, the force of the blast would be directed vertically, and away from other structures and personnel.
Applications in biology
Some models of gene gun also use a rupture disc, but not as a safety device. Instead, their function is part of the normal operation of the device, allowing for precise pressure-based control of particle application to a sample. In these devices, the rupture disc is designed to fail within an optimal range of gas pressure that has been empirically associated with successful particle integration into tissue or cell culture. Different disc strengths can be available for some gene gun models.
|Wikimedia Commons has media related to Rupture discs.|
- Rupture disc sizing calculator to calculate discharge area requirement of a simple system.