Relief valves responsibility

Risk Reduction Factors Coutrol/ rator responses. Alarms, Control system response. Manual anti automatic ESD, Fire/gas detection system Sa/ety System Responses Relief valves. Depressurization system. Isolation systems, High reliability trips. Back-up systems... 

Sallel, D. W. and Somers, G. W., Flow Gapacity and Response of Safety Relief Valves to Saturated Water Flow, Plant/Operations Progress, 4 (4), 207-216, October 1985. 

A mismatch between operator procedures and the automatic control system of the reactor (see also Table 17) was the first active failure identified in this scenario. This precursor was still present mainly due to a shortage of people. Literally it was said that the pressure relief valve would open if the wrong value was inserted into the reactor s control system. The second precursor was the failure of the pressure relief valve (see also Table 17), which was not known to the responsible person who decided to ignore the difference between procedures and control system. The pressure relief valve failed, because resins stuck in the valve after it was used for the first time. Consequently the second time the valve was opened it was at a much higher pressure due to the build up of resins in the valve. If this second precursor had not been observed in time by damp on the pipes situated above the pressure relief valve or by the alarms in the control room a possible accident scenario existed. This was especially dangerous as the alarms in the control room are often ignored because of the high incidence of false alarms (see also Table 17), which was the third precursor present. 

The steam circuit is complete with automatic valves, safety relief valve, and steam traps. The supply of sterile steam is the responsibility of the customer. Steam injection is done through the CIP ports to ensure uniform steam distribution within the chamber. 

Figure 13.43. Pressure-flow response of a conventional spring-loaded relief valve.

The pressure-flow response of a pilot-operated relief valve is illustrated schematically in Figure 13.45. Leakage is eliminated and there is no blowdown. 

Rupture disks are often used upstream of relief valves to protect the relief valve from corrosion or to reduce losses due to relief valve leakage. Large rupture disks are also used in situations that require very fast response time or high relieving load (for example, reactor runaway and external fire cases). They are also used in situations in which pressure is intentionally reduced below the operating pressure for safety reasons. 

In 1984, one of the most notable process incidents occurred in Bhopal, India, at a plant owned by Union Carbide. On December 3, 1984, methyl isocyanate (MIC) was vented to the atmosphere from a vent gas scrubber after a run away reaction overwhelmed the scrubber. It is reported that more than 2500 people died and 20,000 people were injured as a result of exposure to MIC. The subsequent investigation showed that the run away reaction occurred in the MIC tanks after water was reportedly intentionally added to the tank. The safety systems, a pressure relief valve, a vent gas scrubber, and a flare were reportedly poorly maintained. The relief valve worked to vent the pressure, but the scrubber was overwhelmed, and the flare was down for maintenance. This incident highlighted several loss prevention areas that needed improvement. The first was mechanical integrity. No strong preventive maintenance effort appeared to be in place. The second was emergency preparedness and response. It appears that while the plant was built 1.5 miles away from the community, zoning problems allowed the community to expand to the plant limits. It does not appear that much effort was made to work with the community on commimication/notification or evacuation needs. ... 

A rigid insulated vessel is divided into two compartments one contains a fluid at Ti, Pi and the other is under vacuum. The compartments are coimected by a pipe fitted with a pressure relief valve the relief valve biusts. You, as the engineer responsible for the unit, examine the system two hoxus later. 

A mechanical safeguard is one that operates regardless of either instmment or human response. Two common examples of mechanical safeguards are check valves and pressure safety relief valves. They are described in Chapter 9—Asset Integrity. 

There are also important discipline interfaces in the case of control valves, motorized control devices (such as electrically actuated valves), and safety and relief valves. The interface is easily managed if appropriate procedures are available from the start as to which discipline will be responsible for what. 

LEADIR-PS 200 has a graceful and safe response to all anticipated transients. For example, an overcooling event (as could be caused by loss of feedwater control or spurious opening of steam relief valves in combination with control system failure) causes the core inlet temperature (normally 350°C) to fall as the freezing point of 327°C is approached the coolant viscosity increases, coolant flow decreases, and in the absence of any control system action, the negative temperature coefficients of the fuel and moderator reduce reactor power. Heat removal is maintained by natural convection. 

Phosgene-based synthesis of carbamate pesticides may pass through the intermediate methyl isocyanate, which was responsible for the catastrophe at the Union Carbide chemical plant in Bhopal, India, in 1984. A relief valve lifted on a storage tank containing methyl isocyanate, releasing a cloud of toxic gas onto residential areas surrounding the plant, ultimately causing the death of more than 15,000 people, and the injury of several hundred thousand more. ... 

Safety valves are considered to be a process system s last line of defense. They are designed to respond quickly to excess vapor or gas pressure. This type of valve is very similar in design to a relief valve. The three major differences between a relief valve and a safety valve are (1) liquid versus gas service, (2) pressure response time, and (3) size of exhaust port. Relief valves are designed to lift slowly, whereas safety valves tend to pop off. Because the exhaust port is much larger... 

A common example of two separate and independent devices concerns high pressure protection. A high-pressure switch (PSH) is the first level of response. It detects high pressure and initiates actions such as shutting off heat sources and stopping feed streams of the affected equipment. If these actions are insufficient to control the pressure, a second device, usually a pressure safety relief valve (PSRV), opens and quickly vents the vessel s contents to a safe location (usually a flare). 

On November 26, 1993, the USNRC issued Information Notice 93-89, "Potential Problems witii BWR Level Instrumentation Backfill Modifications," to alert licensees to potential problems that have been identified involving hardware modifications to the reactor vessel water level instrumentation system. This information involved the potential to pressurize the reference legs of the water level instrumentation if a backfill system is installed with the injection point on the instrumentation side of the manual isolation valve in the reference leg. If that valve is closed inadvertently during backfill system operation, the closure could result in a severe plant transient. At some plants, valve closure would cause all safety relief valves to open and potentially impact ECCS response. Licensees were advised to review the information for applicability to their facilities and consider actions, as appropriate, to avoid similar problems. 

Control system response Manual am automatic ESD Fire/gas detection system Safety system responses Relief valves... 

MSHA (Mine Safety and Health Administration), 851-852 NIOSH (National Institute for Occupational Safety), 852-853 nongovernmental organizations, 851. 862 Responsible Care program, 862 state and local government, 851 Rehearsal for ethical decisions, 814-815 Relief valves, 865... 

Process Design Responsibility for Relief Valve Design... 

Pressure relief device (PRD), such as pressure relief valve (PRV), rupture disk and rupture pm device, are used to protect equipment and lines from overpressure. It is process engineer s responsibility to show the requirement of a PRD at an equipment or line on the P ID drawings. It is also process engineer s responsibility to select the PRD type and its set pressure, and to do a contingency analysis to check out under what conditions the equipment or line will be over pressured, and what the relief rate will be. 

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