MCQ Piping Interview Questions - Part 03

Question No. 51
What are various temporary closures for lines?
Answer: Line blind valve, line blind, spectacle plate, double block and bleed, blind flanges replacing a removable spool.

Question No. 52
Why horizontal displacement is specified in data-sheet? What will you do if the angle due to displacement is more than 4 degree?
Answer: For bottom mounted springs it is mentioned to avoid large spring bending by frictional force and displacement. So that additional measures can be taken to lower frictional force by providing PTFE/graphite slide plate.
For top mounted spring hangers horizontal displacement is mentioned to check angularity of 4 degree to reduce transmission of horizontal force to piping systems as spring hangers are designed to take the vertical load only.
If angle becomes more than 4 degree due to large horizontal movement then install the spring hanger in a offset position so that after movement the angle becomes less than 4 degree.

Question No. 53
Which spring will you select for your system: Spring with low stiffness or higher stiffness and why?
Answer: Springs with lower stiffness provides less load variation for same travel. So this spring is a better choice than a spring hanger with higher stiffness.

Question No. 54
What do you mean by Stress? What are the types of Stresses that are generated in a Piping?
Answer: Whenever a force is applied to any object it applies a reaction force against the deformation by that force. That reaction force per unit area is the measure for the generated stress.
There has to be an external force to create stress. In a piping system there are various reasons for the generation of stress like Piping Weight, Internal and External pressure, Change in temperature, Seismic and Wind forces, PSV reaction force etc.
The stresses generated in a piping system are as follows:
  1. Axial Stresses
  2. Tangential or Hoop stress
  3. Longitudinal Stress
  4. Radial Stress
  5. Expansion Stress
  6. Stress due to occasional events like Seismic and Wind effects.

Question No. 55
What factors to consider for site selection?
Answer: District classification, Transportation facilities, Manpower availability, industrial infrastructure, community infrastructure, availability of raw water, effluent disposal, availability of power, availability of industrial gas, site size and nature, ecology and pollution.

Question No. 56
Why Stress Analysis is required?
Answer: Ensure reliability and safety of working by
  1. Limiting Stresses (sustained, expansion, hydro-test, occasional) within code allowable.
  2. Limiting nozzle load and moments connected to equipment (Pump/Vessel/Heat Exchanger etc) within allowable values.
  3. Reducing damaging effects of dynamic loads.
  4. Avoiding leakage at joints.
  5. Limiting sagging and displacements within allowable limits.
  6. Avoiding high loads on supporting structures.

Question No. 57
What is the difference between Stress and Pressure?
Answer: Stress is generated because of internal resistance force. Pressure is generated because of external force.
Pressure can be a cause to generate stress.

Question No. 58
Where jacked screwed flange is used?
Answer: For spectacle discs, one flange is jacked screw flange. This flange has two jacked screws 180 degree apart which are used to create sufficient space between flange for easy removal and placement of line blind or spectacle blind.

Question No. 59
What is double block and bleed?
Answer: Two valves with bleed ring in between with a bleed valve connected to the hole of bleed ring.

Question No. 60
Where blind flange is used?
Answer: It is used with view to future expansion of the piping system, or for cleaning, inspection etc.

Question No. 61
What are crude oil ranges?
Answer: Crude oil BP Range: 100F-1400F, lightest material: below 100F, Heavier materials- upto 800F, Residue above 800F.

Question No. 62
What is batch shell process?
Answer: feed, heat, condense, heat more, condense, low quality.

Question No. 63
What are types of towers?
Answer: Stripper, Vacuum tower, trayed, packed towers.

Question No. 64
What is chimney tray?
Answer: It’s a solid plate with central chimney section, used at draw-off sections of the tower.

Question No. 65
What factors to consider while setting tower elevation?
Answer: NPSH, Operator access, Maintenance access, Minimum clearance, re-boiler type , common area, type of support, Tower dimensions, type of head, bottom outlet size, foundation details, minimum clearances.

Question No. 66
How to located tower maintenance access nozzles?
Answer: At bottom, top and intermediate sections of tower, must not be at the down-comer section of tower and in front of internal piping.

Question No. 67
How to located feed nozzle?
Answer: Must be oriented in specific area of tray by means of internal piping.

Question No. 68
What are the steps in selection of valve?
Answer: What to handle, liquid, gas or powder, fluid nature, function, construction material, disc type, stem type, how to operate, bonnet type, body ends, delivery time, cost, warranty.

Question No. 69
What are functions of valves?
Answer: Isolation, regulation, non-return and special purposes.

Question No. 70
What are isolating valves?
Answer: Gate, ball, plug, piston, diaphragm, butterfly, pinch.

Question No. 71
What are regulation valves?
Answer: Globe, needle, butterfly, diaphragm, piston, pinch.

Question No. 72
What are non-return valves?
Answer: check valve.

Question No. 73
What are special valves?
Answer: multi-port, flush bottom, float, foot, pressure relief, breather.

Question No. 74
What materials are used for construction of valves?
Answer: Cast iron, bronze, gun metal, carbon steel, stainless steel, alloy carbon steel, polypropylene and other plastics, special alloys.

Question No. 75
What is trim?
Answer: Trim is composed of stem, seat surfaces, back seat bushing and other small internal parts that normally contact the surface fluid.
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