Controlled safety pressure relief

EN 4126 Part 5 = Controlled Safety Pressure Relief Systems (CSPRS)... 

Power actuated/assisted safety valves (CSPRS - controlled safety pressure relief system) A spring-operated safety valve actuated or assisted by an externally powered control device which can be hydraulic, pneumatic or electric (Figure 3.15). 

The controlled safety pressure relief system (CSPRS) (Figure 5.31) is a special type of actuated SRV that has mainly been used in Europe and in power applications, primarily in the German power industry, for the last 40 years. So far, it has not been used extensively in other parts of the world, but it has become more important since it has its own EN/ISO 4126 Part 5 code in the new European regulation. 

CEN - European Committee for Standardization Brussels wvwv.cenorm.be EN/ISO 4126- Safety Devices for Protection Against Excessive Pressure Part 1 - Safety Valves Part 2 - Bursting Disc Safety Devices Part 3 - Safety Valves and Bursting Disc Safety Devices in Combination Part 4 - Pilot Operated Safety Valves Part 5 - Controlled Safety Pressure Relief Systems Part 6 - Application, Selection and Installation of Bursting Disc Safety Devices Part 7 - Common Data... 

Safety Devices Pressure relief devices, flame arresters, and methods for handhng effluent from controlled releases provide control of accidental undesirable events. Special equipment should be considered for highly toxic chemical service. The following matters are considered ... 

Another required safety feature on water heaters is a temperature and pressure relief valve. This is mounted near or on top of the tank. The temperature and pressure valves are designed to vent water if the temperature or pressure in the tank becomes too high. If there is no relief valve and the controls fail to limit water temperature, there is a danger of a powerful explosion from superheated, pressurized water flashing to steam as the water heater bursts. 

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. 

As with the case of mass, there are several approaches to metrics for this aspect. One can simply sum numbers and/or mass of chemicals possessing hazards in different areas for example, process safety, occupational exposure, or environmental hazard. Typically, most companies will use a banding approach for materials that allows a quick identification of the hazard category, and usually marries hazard with a suggested control approach for example, layers of protection, pressure relief valves, and so on. One is then able to rapidly identify issues and potential opportunities for elimination, substitution, or control. 

The term engineered safety covers the provision in the design of control systems, alarms, trips, pressure-relief devices, automatic shut-down systems, duplication of key equipment services and fire-fighting equipment, sprinkler systems and blast walls, to contain any fire or explosion. 

In the MBR, the applicator of plate steel was an important safety feature in the possible event of vessel rupture or explosion. Temperature and pressure measurements, stirring, infinitely variable control of microwave power input, the cold-finger, as well as a pressure relief valve, have all contributed significantly to the safety and reliability of the system. 

Please note that, some of the identified precursors (re-occurring deviations) are manifestly affected safety barriers. That is to say the precursor itself is a safety barrier and malfunctions repeatedly e.g. the pressure relief valve defect (number 4 in Table 16). Moreover, the precursor may be a process control measure (often tripping of a pressure relief (safety) valve). The presence of these kinds of precursors illustrates what is stated in Chapter 3, that if actors in the operational process don t perceive a deviation as possessing direct safety related consequences, they permit these deviations to exist in the operational process. 

Valves are used for shut-off (isolation), control and safety or relief operations. For the pressure level of 300 bar and above stem valves are typically applied up to around 200 bar, ball-valves are well regarded also. 

Nuclear Boiler Assembly. This assembly consists of the equipment and instrumentation necessary to produce, contain, and control the steam required by the turbine-generator. The principal components of the nuclear boiler are (1) reactor vessel and internals—reactor pressure vessel, jet pumps for reactor water circulation, steam separators and dryers, and core support structure (2) reactor water recirculation system—pumps, valves, and piping used in providing and controlling core flow (3) main steam lines—main steam safety and relief valves, piping, and pipe supports from reactor pressure vessel up to and including the isolation valves outside of the primary containment barrier (4) control rod drive system—control rods, control rod drive mechanisms and hydraulic system for insertion and withdrawal of the control rods and (5) nuclear fuel and in-core instrumentation,... 

After loss of control of the synthesis reaction, the technical limit will be reached (MTSR > MTT) and the decomposition reaction could theoretically be triggered (MTSR > TD24). In this situation, the safety of the process depends on the heat release rate of both the synthesis reaction and decomposition reaction at the MTT. The evaporative cooling or the emergency pressure relief may serve as a safety barrier. This scenario is similar to class 3, with one important difference if the technical measures fail, the secondary reaction will be triggered. 

Although many pressure relief devices are called SRVs, not every SRV has the same characteristics or operational precision. Only the choice of the correct pressure safety device for the right application will assure the safety of the system and allow the user to maximize process output and minimize downtime for maintenance purposes. Making the correct choice also means avoiding interference between the process instrumentation set points in the control loop and the pressure relief device limits selected. These SRV operational limits can vary greatly even when all are complying with the codes. 

It is common on chemical plant to install safety devices such as trips and relief valves which protect the plant in the event of a malfunction of control systems or human error. Unfortunately, these devices can (and do) fail occasionally. The problem is that the failures cannot be seen until they are tested or until they are called upon to act (a plant may operate perfectly normally even though, say, a pressure relief valve is faulty, because under normal conditions the valve is never activated). It is thus necessary to test safety devices periodically to ensure they are functioning. 

Ancillary equipment, designed for at least 2.5 MPa (25 bar) meters and flow controls for pressurized ammonia feed and effluent streams centrifugal pumps for discharging into liquid ammonia supply piping and for liquid ammonia loading equipment for safe pressure relief for ammonia vapor and inerts (see Fig. 118 and [1268]). Design of pressure storage tanks and the related safety aspects are discussed in [1270]. 

Provide safety and alarm devices, such as fire-alarm systems, combustible-vapor detectors, flame arresters, pressure-relief venting of equipment, flame-failure controls for oil- and gas-fired equipment. 

Chemical reactors and pressure vessels must be protected against an intolerable pressure rise by the installation of safety devices. If measuring and control devices are not sufficient to control a runaway reaction, then the only remaining protective measure is, as discussed in the previous section, to provide a pressure relief system, such as a bursting disk or safety valve. 

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