Rupture disc safety relief valves

All reactors should meet or exceed ASME Boiler and Pressure Vessel Codes with respect to appropriate materials of construction. The unit should also be sized properly and equipped with safety relief valves and/or rupture discs and contain appropriate piping and controls. 

A more conventional approach is to provide a safety relief valve or rupture disc to protect the vessel by venting material when pressure approaches certain limits, such as the maximum allowable working pressure. 

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. 

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. 

Operations supervisors should provide procedures to ensure proper isolation of flammable, toxic, or environmentally sensitive fluids in pipelines. Typically these procedures must be backed up with the proper overpressure device. If the trapped fluid is highly flammable, has a high toxicity, or is otherwise very noxious it is not a candidate for a standard rupture disc or safety relief valve, which is routed to the atmosphere. Those highly hazardous materials could be protected with standard rupture disc or safety valve if the discharge is routed to a surge tank, flare, scrubber, or other safe place. 

Relief devices safety relief valves. Safety relief valves should be mounted in the vertical position. The ASME Code requires that the space between a combination rupture disc mounted below an SRV must have a pressure gauge or other device to warn if the rupture disc is leaking. 

Larger capacity storage vessels are basically the same double-walled containers, but the evacuated space is generally filled with powdered or layered insulated material. For economic reasons, the containers are usually cylindrical with dished ends, approximating the shape of a sphere, which would be expensive to build. Containers must be constructed to withstand the weights and pressures that will be encountered and adequately vented to permit the escape of evaporated gas. Containers also should be equipped with rupture discs on both inner and outer vessels to release pressure if the safety relief valves should fail. 

Safety-relief valves Y 8 vaIves+8 rupture discs... 

Figure 12.19 A typical safety relief valve, SRV, and rupture disc combination for a chemical process vessel. The rupture disk protects against the metal-to-metal seats on the SRV from seeping. The pressure gage lets you know if the rupture disk has popped or is leaking. The space between the rupture disk and SRV is required to be monitored by the ASME Code.

There are numerous types of pressure relieving devices available, which include relief valves, safety valves, rupture or frangible disc and blow out hatches or panels. 

Another method is also employed to prevent loss of the contents of the reactor. A safety valve, placed after the rupture disc, is set to open about 50 psi below the bursting point of the frangible disc. Thus, a rupture of the diaphragm is.sure to be followed by the op ng of the relief valve which has been protected from the corrosive vapors of the autoclave. It is usually feasible to complete the run and then replace the disc and overhaul the safety valve. 

These composite relief devices introduce a hazard that must be catered for. A small leak, as through a pinhole in the disc, can raise the pressure between the disc and the valve to the normal operating level of the equipment being protected. The disc then will not rupture until the process pressure exceeds the pressure between the disc and the valve, not the atmospheric pressure, by an amount equal to the set point of the disc. This could result in catastrophic failure. Any gas that accumulates in the space between the two safety elements must be removed to prevent this. 

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.12. The bleed condenser, which is a vessel connected to the pressurizer and maintained at a lower pressure in normal operation, should be fitted with passive relief devices (e.g. rupture discs, rehef valves or safety valves operated by pilot valves) capable of transmitting steam, hquids and flashing liquids, since the condenser may be flooded in the event of large discharges of fluid from the RCS or the pressurizer. In the design of the bleed condenser, account should be taken of the range of pressures and temperatures of the RCS. 

To prevent leaks from relief vents, rupture disks can be used in combination with safety valves, possibly with a previous safety risk analysis . The pressure between the mpture disc and the safety valve is monitored to detect any leaks. If the safety valves are connected to an incinerator, rupture disks may not be necessary. 

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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