Pressure-relieving devices Rupture disks

Burst Pressure the inlet static pressure at which a rupture disk pressure-relieving device functions or opens to release internal pressure. 

Figure 7-7B. Pressure level relationships for rupture disk devices. Reprinted by permission, Sizing, Selection and Installation of Pressure Relieving Devices in Refineries, Part 1 "Sizing and Selection," API RP-520, 5th Ed., July 1990, American Petroleum Institute.

Set pressure is the pressure at which the device begins to relieve, e.g., lift pressure of a spring-actuated relief valve, bursting pressure of a rupture disk, or breaking pressure of a breaking pin device. 

Pressure-relief-device requirements are defined in Subsec. A. Set point and maximum pressure during rehef are defined according to the service, the cause of overpressure, and the number of relief devices. Safety, safety relief, relief valves, rupture disk, breaking pin, and rules on tolerances for the relieving point are given. 

Relief valves are preferred for use on clean materials, because automatic closure prevents excessive discharge once excessive pressure is relieved. Rupture disks are less susceptible to plugging or other malfunctions but may allow complete emptying of the vessel, thus creating a safety or environmental hazard. Where fluctuating pressures or very corrosive conditions exist, or where polymerizable materials could prevent proper operation of a relief valve, some designers install two safety devices in series, ie, either two rupture disks or an upstream rupture disk followed by a relief valve. With either arrangement, it is imperative that the space between the two relief devices be monitored so that perforation or failure of the relief device closest to the vessel may be detected (86). 

In other words, all the above had to happen to cause the explosion. If the relief had operated properly, it would not have prevented reaction runaway but it could have prevented the explosion. In addition to using rupture disks as relieving devices, one can also use pressure relief valves, In many cases sufflcieni care is not taken to obtain data for the reaction at hand and to use it to properly size the relief device. This data can be obtained using a batch reactor called the ARSST. 

Mechanical equipment that performs an action to relieve pressure when the normal operating range of temperature or pressure has been exceeded. Physical relief devices include pressure relief valves, thermal relief valves, rupture disks, rupture pins, and high temperature fusible plugs. 

Just before the exit end of the barrel and usually located at the six o clock position (toward the floor) is a hole in the barrel fitted with a device called a rupture disk (Fig. 2.9). This device is an important safety component. If excessive pressure builds up at the head, a weld in the rupture disk will fail, allowing molten polymer to escape through the device onto the floor to relieve the pressure. Since normal operating pressures can approach or exceed 5,000 psi and most barrels are designed for approximately 10,000 psi, rupture disks are usually rated for 7,000 to 9,000 psi. A properly designed screw/barrel system is long-lasting and safely provides the die with excellent melt quality. 

Type CG-8, This is a combination device consisting of a rupture disk device followed by and in series with a pressure relief valve. The piping connecting the rupture disk and pressure relief valve is equipped with a sensing device to indicate pressure. The system is designed and constructed so the required relieving capacity is achieved and the operation of the relief valve is not impeded. 

Should the rupture disk rupture, the relief valve instantly pops fully open, and after tank pressure is relieved and returns to a safe working pressure, the relief valve will reseat and function as a conventional spring-loaded relief valve until it is convenient to replace the rupture disk portion of the device. 

Extruders are equipped with rupture disks and pressure gauges to eliminate the possibility of blowing the die off the end or the extruder and to monitor the pressure in and before the die. Make sure the pressure gauges are functioning properly. If the extruder does not have a rupture disk (device at the end of the extruder barrel to relieve high pressure), it should be added. Alternatively, the extruder should have a pressure gauge with a feed back loop that automatically shuts the extruder down in the event a certain preset pressure is reached. Most extruders are equipped with both a rupture disk and high-pressure... 

Pressure relief device (PRD) is a safety device to protect equipment or piping from damage due to overpressure or vacuum, but in this chapter, we wiU discuss FRD to provcfit overpressure only. Commonly used pressure relief devices are spring-loaded and pilot-operated pressure relief valve (PRV), rupture disk, or pin-actuated pressure relief device. For equipment, it is installed cither directly on the equipment or at its inlet/outlet piping. When the equipment or piping pressure reaches the pressure relief de vice set pressure, it will open to relieve fluid inside the equipment or piping to avoid overpressure. The relief fluid can be vapor, liquid, or two phase mixture. The relieved fluid is either sent to floic system to be disposed or relieved to atmosphere. 

Among the relief devices mentioned above, spring-ioaded and pilot-operated pressure relief valve (PRV) are the ones used most fiequently, PRV is a reclosing pressure relief device, since after it is opened and relieved, it will be reclosed, when equipment or piping pressure is dropped below PRV set pressure. Once it is dosed, h will continue to protect the equipment or piping from overpressure- Rupture disk or pin-actuated relief device is the non-reclosing pressure relief device, since it cannot be reused after it is ruptured or actuated - its rupture disk or pin needs to be replaced. 

Used to indicate the inlet pressure and temperature of a pressure relief device at a specific overpressure. The relieving pressure is equal to the valve set pressure (or rupture disk burst pressure) plus the overpressure. The temperature of the flowing fluid at relieving conditions may be higher or lower than the operating temperature. 

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