Rupture disc relief systems

An alternate approach to the above is to provide parallel relief valve-rupture disc systems. The valve will have a setting slightly above the normal operating pressure with the rupture disc at about a 10% higher setting. The relief valve should control minor pressure excursions, can vent material and then reseat to minimize process losses. The rupture disc would provide the ultimate safety protection. 

An important problem with rupture discs is the flexing of the metal as process pressures change. Flexing could lead to premature failure at pressures below the set pressure. For this reason some rupture disc systems are designed to operate at pressures well below the set pressure. In addition, vacuum service may cause rupture disc failure if the relief system is not specifically designed for this service. 

The resistance to flow method (K[ ), which has been employed by industry for years, has now been adopted by the ASME Code for rupture disc. Sizing is performed on a relief system basis and not by capacity of individual components. The key elements of tills metliod are ... 

The rupture disc is treated as another component in the relief system that provides some resistance to flow. 

Many accidents, particularly on batch plants, have been due to runaway reactions, that is, reactions that get out of control. The reaction becomes so rapid that the cooling system cannot prevent a rapid rise in temperature, and/or the relief valve or rupture disc cannot prevent a rapid rise in pressure, and the reactor ruptures. Examples are described in the chapter on human error (Sections 3.2.1 e and 3.2.8), although the incidents were really due to poor design, which left traps into which someone ultimately fell. 

Correlations are needed to predict whether two-phase flow will occur after vapor venting is initiated by rupture disc failure or relief valve opening. Research is needed in this area, but for the present we recommend the following correlations to predict batch swell. For systems with low viscosity (less than 500 cp) an equation based on bubble column hold-up is used to obtain a swell ratio ... 

Equations 9-2 and 9-3 apply to rupture discs discharging directly to the atmosphere. For rupture discs discharging into a relief system (which might include knockout drums, scrubbers, or flares), the rupture disc is considered a flow restriction, and the flow through the entire pipe system must be considered. The calculation is performed identically to regular pipe flow (see chapter 4). The calculation to determine the rupture disc area is iterative for this case. Isaacs5 recommended assuming that the rupture disc is equivalent to 50 pipe diameters in the calculation. 

If appreciable backpressures exist from downstream relief systems, a procedure similar to the procedure used for liquid reliefs through rupture discs is required. The procedure is iterative. 

The reactor system in a pilot plant contains stock tanks that are 24 in in diameter and 36 in high. A relief system must be designed to protect the vessel in the event of fire exposure. The vessel contains a flammable polymer material. What rupture disc diameter is required to relieve the vessel properly Assume a discharge pressure of 10 psig. The molecular weight of the liquid is 162.2, its boiling point is 673°R, the heat of vaporization is 92.4 Btu/lb, and the heat capacity ratio of the vapor is 1.30. 

Provided that the appropriate regulations allow this, a single rupture disc can be used on its own for system protection. Rupture discs can be used for both primary relief and as an additional secondary rdief in combination with another pressure rdief device... 

Economic considerations If the system is a corrosive environment, a rupture disc with the more exotic and corrosion-resistant material can be selected upstream and downstream of the SRV. It acts as the barrier between the corrosive system and the relief valve. 

Some method of pressure relief is required on all pressure vessels and for other process equipment where increasing pressure might rupture the vessel. Much of the piping used in modern chemical operations also requires overpressure protection. Safety relief valves or rupture discs are employed for pressure relief. In many cases, either a rupture disc or a safety relief valve can be used. Safety relief valves are usually used for process protection and rupture discs are used for vessel protection. The safety relief valve or rupture disc must be designed to operate at a known pressure and prevent the pressure within the system from increasing. Therefore, it is important to consider the flowrate the valve can handle. 

Tests conducted with the propellant build-up configuration in the ignition end of the conveyor resulted in more erratic and aggressive burning reactions than observed in Stage one tests. Approximately 60 pounds of MISP was used for each test. For these tests, aluminum rupture discs 0.0008-inch thick were used on each pressure relief vent. One IR detector activating the sprinkler system was located in No. 1 (see Figure 4) position. 

Other ways to reduce the risk is the use of spark-free materials in the construction, explosion suppression systems or the use of explosion venting by rupture discs or pressure relief panels [5]. 

Mechanical Relief Devices. The water seals discussed above in Section 9.1.10.1 are effective only at very low differential pressures. After the compression of chlorine, and particularly in liquefaction and storage systems, more conventional relief devices, rupture discs and pressure relief valves, are used. With some fluids, there is a simple choice to be made between discs and valves. While the former are less likely to permit bypassing of small quantities of fluid, they are destroyed when they open. A release will continue even after the pressure on the system drops below the set point of the disc. Relief valves have the opposite characteristics. 

Corrosive fluids are less likely candidates for the use of pressure relief valves. Whether by corrosion of the valve itself or of surrounding pipework, they often create a problem with deposits on the valve element or its seat. These deposits can prevent proper sealing and allow the slow escape of fluid. To combine the advantages of rupture discs and relief valves, the two devices can be installed in series, with the disc before the valve. Even if the valve is not precisely seated, there is no release from the system until the disc bursts. The same overpressure then also opens the valve. Once the piessme has dissipated and dropped below its set point, the valve reseats and prevents further release. 

Figure 11.25 also shows pressure relief on the column. The normal design pressure for vessels containing liquid chlorine is 15-20 atmospheres. The suction chiller, however, is connected directly to the compressor suction, where the pressure rating is much lower. The relief system on the suction chiller must also protect the compressor. Standard construction is a reverse-buckling Monel rupture disc in combination with a safety valve having Monel internals and a PTFE O-ring seal. 

Pressure relief system—safety system that includes relief valves, safety valves, rupture discs, piping, drums, vent stacks, pressure indicators, pressure alarms, pressure control loops, and flare systems. 

Pressure relief equipment includes relief valves, safety valves, rupture discs, piping, drums, vent stacks, pressure indicators, pressure alarms, pressure control loops, and flare systems. Pressure relief devices can be placed on pumps, compressors, tanks, piping, reactors, distillation columns, refrigeration systems, and many other kinds of equipment. Materials that cannot be released to the atmosphere are recycled back to the system, or sent to a scrubber or flare system. The discharge from pressure relief equipment is collected in a closed piping system and sent to a flare stack. Harmless gases are discharged at a safe distance from plant operations areas. 

Diversion of flow safely All the above systems discussed are part of electronic system requiring power. As a next layer of protection there are mechanical devices (requiring no power to meet power failure situations) to divert the flow safely. Safety and relief valves are used to in case to depressurize when SIS fails to take care (e.g., say due to control power failure). Pressure relief valve diverts the fluid for safe passage. These relief valves are spring force to close so that when pressure is below setting it is closed. Many cases rupture discs are used but in that case system needs to be closed to attain the disc. To a certain extent quartz bulb in sprinkler system does the same function. 

A large leak exposes the secondary sodium drcuit to the operating steam pressure. It is essential to protect the intermediate heat exchangers, which are part of the reactor primary containment boundary, from damage by this pressure. This is normally done by a pressure relief system incorporating rupture discs set to burst at a pressure weU below that which the rest of the circuit can tolerate. 

Between the steam generator and dump vessel, there are two pressure relief lines with rupture discs. A second pressure relief system connects the gas space in the dump vessel to the environmental atmosphere above the steam generator building. 

Ruptiue disc A pressure-relief component moimted in the relieving device and designed to rupture at a predetermined pressure so that fluid will be discharged and the probability of rupture of the vessel or system containing the fluid reduced. 

A bursting or rupture disk is a pressure relief device that protects a vessel or system from excess pressures. They have been commonly used in aerospace, aviation, defense, nuclear, and oilfield applications often as a backup device for a conventional safety valve. In this instance, if the pressure increases and the fitted safety valve fails to operate, the rupture disk will burst as required. The discs are usually made from thin metal foil, and gold has been used in some instances because of its ductility and resistance to corrosion. Gold discs fitted to liquid ammonia tanks, for example, have shown good durability in this application compared to other metals. The use of gold in this application was reviewed in the 1970s when this industrial application for gold was more common [10]. 

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