Overpressure protection piping

Vessels should be provided with overpressure protection as required. Vents and relief valve vent piping should be so arranged Uiat Uie vented vapors will not constitute a liazard. Relief valves must be kept free from corrosion or fouling and should be operable at all Umes. 

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. 

These creative individuals had set up a scheme to purge through the top of the air dryer and out of a partially opened ball valve on the lower piping. They, no doubt, failed to realize that the dryers were not individually equipped with safety relief valves. The overpressure protection was on the compressors. A new operator to the area did not open the exit valve sufficiently during the cool-down step. 

This 12-ft. (3.7 m) diameter and 24-ft. (7.3 m) high tank was equipped with a fill line from the process, a 4-inch (10 cm) overflow line, a 3-inch (7.5 cm) vent line and a 6-inch (15 cm) vacuum relief device. Overpressure protection was intended to be supplied by the vent system piping or the overflow line. The designers did not include a high-maintenance pressure-relief device, because the 3-inch (7.5 cm) valve-free vent line was the overpressure device relieving into the scrubber. Neither the vent line nor the overflow line were equipped with block valves. The 4-inch (10 cm) overflow line was routed to a chemical collection/treatment sewer. 

Figure 7-5 Expansion bottles protecting piping from overpressure.

We all need to understand thermal expansion of liquids. I have often heard that heating a completely liquid-full container, such as piping, a vessel, or a heat exchanger, will result in tremendous pressures. I always try to ensure that the situation not arise by encouraging procedures to avoid the situation or providing overpressure protection, but until now I had not taken the time to calculate the ultimate pressures that could develop. 

A sodium leak detection system provides early warning of any sodium-to-air leaks from the IHTS piping. In the event of an SG tube leak, the sodium-water reaction pressure relief subsystem (SWRPRS) provides overpressure protection of the IHTS and IHXs. The SWRPRS consists of a safety-grade rupture disk, a sodium dump tank, a cyclone/separator tank, a vent stack, and a hydrogen igniter. To separate the reactants, the SWRPRS also initiates the water-side isolation of the SGS and pressure relief. 

During a startup of the Biblis A plant on December 17, 1987, the first check valves in the pipe from the reactor coolant system to the residual heat removal (RHR) system had to close for overpressure protection. The position indication and a plant computer alarm annunciated a non-closed position of the first check valve in one train of the RHR system. This was overlooked by the operator. Therefore plant startup was continued with the check valve in the open position. The leakage through the first check valve caused the actuation of a relief valve, releasing primary coolant to the chemical and volume control system. 

Overpressure protection device for service line Customer s meter (piping beyond the outlet of the customer s meter set assembly covered by ANSI Z223.1)... 

The reactor vessel is invariably jacketed. In the absence of especial requirements, the jacket is designed to the same specifications as the vessel. The jacket is covered with chloride-free fiberglass insulation which is fully enclosed in a protective shroud as shown in Eig. 18. The jacket is provided with overpressure protection through a relief valve located on the jacket or its associated piping. 

The ADS consists of several valves through which the reactor can be rapidly depressurized. It also provides overpressure protection to the reactor and outlet piping. The valve banks are located in the containment building steam tunnel, with the discharge flow suppressed into the containment pool. 

BLEVEs (Boiling Liquid Expanding Vapor Explosions) A pressurized tank of VCM or associated piping exposed to an external fire may fail due to metallurgical weakening. Such failure may result in a catastrophic tank failure, a fireball and the potential for rocketing fragments. Relief valve overpressure protection will not prevent a BLEVE. 

Install flame arresters on atmospheric vents to prevent fire on the outside of the tank from propagating back into the vapor space inside the tank. Provide fire resistant insulation for critical vessels, piping, outlet valves on tanks, valve actuators, instruments lines, and key electrical facilities. Provide remote controlled, automatic, and fire-actuated valves to stop loss of tank contents during an emergency provide fire protection to these valves. Valves should be close-coupled to the tank, and must be resistant to corrosion or other deleterious effects of spilled fluids. Vessels should be provided with overpressure relief protection. 

Drums and towers, 6 m and less in diameter, constructed of pipe, pipe fittings or equivalent, do not require PR valves for protection against fire, on the basis that piping is not provided with protection against overpressure from this contingency. PR valves are required on such vessels, however, if overpressure can result from contingencies other than fire. 

LOCA, is presented in Table 3.4.5-1. In preparing the event tree, reference to the reactor s design determines the effect of the failure of the various systems. Following the pipe break, the system should scram (Figure 3.4.5-2, node 1). If scram is successful, the line following the node goes up. Successful initial steam condensation (node 2 up) protects the containment from initial overpressure. Continuing success in these events traverses the upper line of the event tree to state 1 core cooled. Any failures cause a traversal of other paths in the evL-nl tree. 

A throttling device can also be placed in the suction piping to protect against overpressure or to limit the horsepower demand to the maximum available from the driver. 

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