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Stress Analysis Interview Questions:- Part-3

18. Why do we provide drip leg in steam line?
To remove condensate when there is a rise of same in the pipe along the flow direction. If drip leg is not provided in steam line, the condensate which forms inside the pipe will result in water hammer effect causing damage to piping system.
19. What is the design standard followed for the calculation of allowable forces / moments in nozzles of centrifugal compressor & Steam turbines nozzle?
The strain sensitive equipment piping to be routed and supported to limit nozzle loading and moment in equipment within allowable limits furnished by respective vendors or in absence of vendor data API 560/610/615/621/661 & NEMA SM23. (referred by API 617) is used for compressor & steam turbine nozzle.
20. What is the mill tolerance to be considered for the thickness of pipe during stress analysis as per ASME B31?
(i) 1%
ii) 2.5%
(iii) 7.5%
iv) 12.5%
Static loads are those which are applied slowly enough so that the system has time to react and internally distribute the loads, thus remaining in equilibrium. In equilibrium, all forces and moments are resolved (i.e., the sum of the forces and moments are zero), and the pipe does not move. Dynamic loads are those which changes quickly with time. The piping system may not have time to internally distribute the loads, so forces and moments are not always resolved & resulting in unbalanced loads, and therefore pipe movement. Since the sum of forces and moments are not necessarily equal to zero, the internally induced loads can be different either higher or lower than the applied loads.

22. Give different types of dynamic loads with example?
A. Random – wind, earthquake.
B. Harmonic – equipment vibration, pulsation, acoustic vibration.
C. Impulse – fluid hammer, relief valve opening, slug flow.
23. What is dynamic analysis and why it is used?
Dynamic analysis is performed for all two phase lines in order to ensure that the line supported is safe from vibrations loads which may occur during normal operation as well as in start up or any upset condition. (diesel mixed with hydrogen in DHDT process).
24. What are WRC 107 / WRC 297?
Localised stresses at nozzle to shell is calculated by WRC 107 / 297 and these computed stress values shall be limited in accordance with ASME sec VIII for pressure vessels.
25. Why loop is provided in piping system?
26. What is the maximum expansion absorbed in loops in normal design?
10 Inches.
27. What is the allowable stress range for CS pipes?
2070 kg/cm2