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Fault Tree Analysis Notes

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Published in: Civil | EVS
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Fault Tree Analysis Notes

Akhilesh K / Lucknow

4 years of teaching experience

Qualification: M.Sc (NIT Rourkela - 2019)

Teaches: All Subjects, English, Mathematics, Science, Chemistry, Physics, Algebra, IIT JEE Mains, AIPMT, NEET

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  1. Fault Tree Analysis (FTA) is a popular tool used by engineers to anticipate system failures and identify weak links present in the systems,
  2. Flat Tire on an Automobile (i) tire failure (ii) driving over debris on the road (such as nail)
  3. Tire Failure OR Flat Tire OR Road Debris Defect ive Tire Worn Tire
  4. * FTA is a "top-down" hazard-analysis tool that uses Boolean logic (gates) to describe combinations of individual faults that can create a hazardous event or an accident, * Each level of the tree lists the lower level events that are necessary to cause the event shown in the level above it.
  5. (i) Top Event (ii) Intermediate Events: can be defined in terms of basic event (iii) Basic Events: that can not be defined further
  6. Defective Tire The circles denote basic events rectangles denote intermediate and top event, Tire Failure
  7. OR - Gate A+B 0 0 A+B 0
  8. AND - Gate AB AB
  9. ??? - 6atz
  10. There are Many
  11. Boolean logic (gates) are useful to write the computer code for any fault-tree diagram of complex size
  12. Flat Tire Tire Failure Defect ive Tire Road Debris Worn Tire
  13. If the individual probabilities for all the basic events are known (not feasible in most abstract cases) the frequency of the top event to occur can be calculated FTA was originally developed to calculate quantitative probabilities, But it is more often used qualitatively
  14. Pressure Vessel Line-I Al Line-2 TANK
  15. The safety system consists of four valves, which are connected to the tank. The valves will open if the pressure in the tank exceeds a certain level (for example PO). The content in the tank will be released to the environment if both valves Al and A2 on Line-I or both valves A3 and A4 on Line-2 are open. What is the probability that the safety system fails to function when needed, i.e. the valves do not open when the pressure in the tank exceeds PO?
  16. The first step in FTA is to define the Top Event,
  17. The safety system fails to release the content in the tank when the pressure is more than PO
  18. The safety system of the pressure tank fails to work, when the following two events occur simultaneously: (i) Line-I fails to open (ii) Line-2 fails to open
  19. Note that the failure could not occur if either one of these two events does not occur. Therefore, these two intermediate events are connected with the top event through "AND" logical relationship,
  20. Construction of the fault tree continues by identifying the appropriate events at lower levels and their logical relationship to the higher-level events, This process is continued until basic failure events are identified,
  21. The safety system fai Is to release the content in the tank when the pressure is more than PO Line-I fails to open AND Line-2 fails to open Al fails to open fails to open fails to open fails to open
  22. Question was to calculate the probability of the top event to occur, For that, we should know the probability of each of the basic events to occur
  23. How will we know the probabilities of the basic events? direct experimentation historical experience Estimation
  24. Let us assume p (Al fails to open) = p (A2 fails to open) = p (A4 fails to open) = 0.001 open) = p (A3 fails to
  25. Advantages 1. It is structured and rigorous approach to identify failure modes in a system operation 2. Since it is a deductive method it can easily handle more complex system 3. The graphic aid in FTA is self explanatory and it is very useful for management for a quick review 4. Qualitative as well as quantitative reliability analysis can be performed using FTA 5. This method is suitable for computer programme
  26. Disadvantages 1. more involved and time consuming approach as compared to other similar methods 2. Every event in FTA is considered either in failed condition or in working condition. The partial failure states are difficult to handle in FTA

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