Control valve failure

When a fire occurs, it is assumed that all fluid flow to and from the fire risk area has been stopped. Therefore, flow loads such as control valve failure or incoming feed streams are not additive to the fire load. Credit is not generally given to flow out through normal channels, since they could also be blocked during the fire emergency. 

Failure of Individual Control Valve - The following individual control valve failures should be included in the analysis of control systems for determination of pressure rehef requirements ... 

When analyzing such individual control valve failures, one should consider the action of other control valves in the system. In the first two cases above, credit may be taken, where applicable for the reduction in pressure of a high-pressure source due to net inventory depletion during the period that the downstream equipment pressure is rising to relieving pressure. However, the pressure relieving facilities must be sized to handle the calculated peak flow conditions. 

This is clearly a double jeopardy failure two unrelated events occurring at exactly the same time. One has nothing to do with the other. Therefore, you need to calculate the relief capacity for one scenario at a time. For the loss of power to a pump scenario, the relief load would be based on the amount of vapour generated at the normal rate of steam. For the steam control valve failure scenario, the relief capacity would be based on the amount of vapour generated by the heat provided by a wide-open steam valve even accounting for the amount of vapour condensed in this failure, the condenser would still be in operation. So the SRV should be sized for the worst condition. 

The safety system consists of the alarm because of a high filling level and the corresponding instruction to open the motor valve M in the bypass of the methanol outlet by pushing a button. However, the alarm is only useful in case of control valve failure. 

Mode of operation Although the SIF operates as part of normal operation 4 times per day, the SIF is not operating in continuous mode. The SIF dangerous failure is not the initiating cause of the hazardous event. The operating mode is determined by the process demand from a hazards standpoint. The hazardous event caused by misoperation of the control valve failure is estimated at 1/10 years. The SIF operates in demand mode with regard to the hazard. 

The types of problems a fired heater or furnace system typically encounters include flame impingement on tubes, coke buildup inside the tubes, hot spots inside the furnace, fuel composition changes, burner flameout, control-valve failure, and feed-pump failure. 

During normal operations, checklists and samples are collected as advanced instrumentation monitors the process. The types of problems a fired heater or furnace system typically encounter include flame impingement on tubes, coke buildup inside the tubes, hot spots inside the furnace, fuel composition changes, burner flameout, control valve failure, and feed-pump failure. Other problems may include incorrect temperature indicator readings, failure of oxygen analyzers, oxygen leaks on the furnace, and the unexpected shutdown of downstream equipment. A fired heater system is designed to run almost continuously, 24 hours a day, 7 days a week. The operational team is in place to ensure that the equipment and systems operate safely, effectively, and produce a quality product that meets or exceeds customer expectations. 

Although there are limited common control valve failure modes, the dominant problems are usually related to leakage, speed of operation, or complete valve failure. Table 9-1 lists the more common causes of these failures. 

Blocked outlet 2) inadvertent valve open 3) control valve failure (full open or close) 4) loss cooling stream 5) instrument aii failure 6) power failure 7) abnomiaJ heat input 8) equipment failure 9) heat exchanger tube ruphue ID) thermal expansion 11) fire 12) chemical reaction 13) steam out, 14) operator error, etc. 

Check valve failure Blocked discharge Control valve failure Thermal expansion of liquid Heat exchanger tube rupture Reflux failure and overhead system Loss of reboiler heat Venting of storage tank Failure of individual motor Accidental closure of valve... 

Control valve failure is an important scenario in contingency calculation. The following general guidelines are normally used to estimate control valve failure contingency. 

The suction scrubber of a gas compressor operates at 4000 kPaG. The liquid collected in the scrubber is discharged to a separator tank, which is open to the atmosphere, through a level-control valve installed on the liquid outlet line. In a particular situation of control valve failure (control valve goes fully... 

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