PSLP Revision 15 Event Tree Hazan PDF

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Plant Safety and Loss Prevention Term Test 2 Practice Name Admin No

Tutorial Class

Answer all questions. minutes 1.

40

The pressure of a reactor in Power Seraya is kept at a constant value by a pressure control system. If this pressure control system fails, the pressure inside the reactor will increase and an alarm will be activated. Upon activation of this alarm, the technician on duty will manually release the excessive pressure. If for any reason, the technician is unable to do so, an emergency pressure vent system will be activated to release the excessive pressure. Given that the pressure control system fails 0.5 times/year, estimate the number of uncontrolled high pressure situations that will occur each year by constructing an event tree. You may use the data provided in Table 1 below. System

Failure / Demand

High pressure alarm

0.05

Operator releases pressure manually

0.06

Emergency pressure vent

0.01 Table 1 (10 marks)

1

2.

The temperature of a distillation tower is controlled by a temperature control system consisting of a thermocouple, controller and control valve as shown in Figure 1 below. The thermocouple constantly sends temperature readings to the controller which will in turn regulate the opening of the control valve based on these readings.

Controlle r Thermocoup le

Steam Coils Steam out

Steam in Control Valve Figure 1

Equipment

Failure Rate,  (faults per year)

Controller

0.29

Control Valve

0.60

Thermocouple

0.52 Table 2

By using the information provided in Figure 1 and Table 2, calculate the reliabilities of the thermocouple, controller and control valve. Hence determine the overall failure rate of the temperature control system. Assume a 1 year operating period. Give your final answer corrected to 3 decimal places. (6 marks)

3.

Describe the FOUR typical steps in event tree. (4 marks)

-------------------- End of Paper -------------------Appendix

2

R(t) = e-t MTBF =

1 

P=1–R Parallel : P = P1  P2  …..  Pn Series R = R1  R2  …..  Rn

Answer 1.

3

• •

Total uncontrolled  2.9 10  4  2.5 10  4 5.4 10  4 per year

•

RTC  e 0.52  0.5945



R C e 0.29  0.7483

high

pressure

situations

2.

 

RCV  e 0.60  0.5488 Since components are in series, Roverall  0.5945 0.7483 0 .5488 0 .244

 

0.244 e o  1  o 1.410 faults / year

3. •   

Identify an initiating event of interest. Identify the safety functions designed to deal with the initiating event. Construct the event tree. Describe the resulting accident event sequences.

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