Pressure relief facilities

Selection of gapless surge arrester Classification of arresters Surge protection of motors Pressure relief facility Assessing the condition of an arrester... 

Testing, certification, and installation rules for reheving devices are extensive. Eveiy chemical engineer responsible for the design or operation of process units should become veiy familiar with these rules. The pressure-relief-device paragraphs are the only parts of Sec. TII, Division I, that are concerned with the installation and ongoing operation of the facility all other rules apply only to the design and manufacture of the vessel. 

Conventional Flare System - The majority of pressure relief valve discharges which must be routed to a closed system are manifolded into a conventional blowdown drum and flare system. The blowdown drum serves to separate liquid and vapor so that the vapor portion can be safely flared, and the separated liquid is pumped to appropriate disposal facilities. The blowdown drum may be of the condensible or noncondensible type, according to the characteristics of the streams entering the system. Selection criteria, as well as the design basis for each type of blowdown drum, are detailed later in this volume. The design of flares, including seal drums and other means of flashback protection, is described later. 

The most important safety devices in a production facility are the pressure relief valves, which ensure that pipes, valves, fittings, and pressure vessels can never be subjected to pressures higher than their design pressures. Relief valves must be designed to open rapidly and fully, and be adequately sized to handle the total flow of gas and liquids that could potentially cause an overpressure situation. They relieve the pressure by routing this stream to a safe location where it can be vented to atmosphere or burned. 

Two 4 1 cylindrical glass(QVF) vessels with stainless steel end plates, serve as reservoirs(Figure 1) for surfactant solution(B) and water(9). Facility is available to evacuate these vessels as required by means of a rotary vacuum pump with glass cold trap in line to minimise water vapour. Another pipeline permits supply of pure nitrogen, or other gas, at low pressure, to the vessels, to provide a blanket, as desired. Proper operation and safety from over pressure is ensured by a pressure relief valve(10 in Figure 1) and the pressure gauge(P in Figure 1). 

Facility is provided to bring the equipment up to the desired absolute pressure without subjecting the test unit to excessive pressure difference between its interior and exterior. This is accomplished by first filling the test cell with water by means of a hand operated hydraulic pump(17 in Figure 1) to a suitable value as indicated on the Bourdon dial gauges(P in Figure 1). The pressure thus developed is used also to control the appropriate back-pressure relief valve... 

Temperature relief valves for use on unvented hot-water systems are beyond the scope of this entry. Combined pressure and temperature relief valves became popular in the United Kingdom in the early 1990s, but these devices are merely pressure-relief valves with additional facility for actuation by a temperature-sensitive element. As the bore of a combined valve is not required to choke, the addition of a temperature-sensitive actuator... 

The PCPS consists of the protective shelter, support kit, and hermetically sealed filter canister. The shelter consists of a tent and fly. The tent floor and fly are made of a saranaex composite material. An attached aluminum structure helps to support the tent. When overpressure is applied, the shelter will provide protection from liquid and vapor chemical agent penetration and biological agent penetration. An airlock allows decontamination of entering personnel. The PCPS provides an uncontaminated, positive pressure shelter for use as a command and control facility or a rest and relief facility for 14 people at a time in a contaminated environment. 

It would appear that adding this element to the updated standard would greatly increase the number of covered facilities. But the work needed to be done at a typical facility would not be all that high. The main focus would be on the integrity of pressure relief systems. 

New process equipment installed within 7.6 meters from the grade/ground level will require pressure relief devices due to fire scenario. For revamp cases, it may be advantageous to place vessels on platforms at >7.6 meters if fire case relief load is most credible and bottlenecks the existing flare system. Fire circle or zone is defined as the maximum affected area during any equipment fire in the facility. API 521 (2014) defines its area as 230 to 460 m. Addition of process equipment inside an existing fire circle may increase the fire circle size. Hence, care shall be taken to review the fire circle size with each equipment addition. It will impact the peak relief load during the fire scenario. 

There are a number of other possible utihties which may be provided to a laboratory. Among these are natural gas, compressed air, distilled water, vacuum, steam, refrigerated brine, and other gases. In some instances, there are safety issues, such as limitations on the pressure available from a compressed air hne and the need to incorporate provisions for pressure relief, to ensure that personnel will not be injured by explosions due to excess pressure. Often the quahty of the air is more of a problem. The compressor supplying the system should be capable of supplying air which is clear of oil and moisture. Some facilities which have a large, pressurized liquid nitrogen tank at hand, use the vapors from the tank as a source of ultra clean compressed air to clean woik surfaces. 

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