Controlled safety pressure relief systems

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... 

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. 

The RPV is provided with a pressure relief system which consists of 12 safety (relief) valves connected evenly onto the four steam lines, with blowdown pipes leading down into the condensation pool. The safety (relief) valves are own medium operated valves, each being controlled by two pilot valves, one pressure activated and one electrically controlled this means that actuation can be initiated in a controlled way by pressure monitoring equipment, to avoid over pressurization or to achieve depressurization. In addition, control valves are provided downstream two of the safety valves, in order to enable proper pressure control of the reactor also in the event of isolation (loss of the turbine condenser function). 

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. 

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. 

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. 

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,... 

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. 

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. 

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