Interview Questions

100 + PIPING INTERVIEW QUESTIONS

1. How to select a proper flange facing?

A. The selection of a proper flange facing is depended on certain factors like flange material. Gasket material, Bolt strength, operating pressure, and temperature, and also fluid properties contained.

2. What is a flange?

A. A flange is a mechanical connection with two pipes, basically, it connects two pipes. The flanges can be used to connect pipes to other components like a valve, choke, etc.

3. What are the properties of the conveyed fluid that must be considered for a piping?

A. Type of fluid, flow rate, pressure and temperature

4. What are the three major categories of piping?

A. Large bore piping – This type of piping has more than two inches in diameter.        

Small bore piping– this type of piping will have diameter less than or equal to two inches.

Tubing – This type of piping has a diameter of more than four inches but it has less wall thickness than the above-mentioned types

5. What is the importance of piping engineering?

A. Piping engineering can be explained as designing, constructing, and fabricating lines for conveying fluids. This piping should maintain pressure and temperature difference and it also must maintain flow rate.

6. Where do we use power piping?

A. This type of piping is mostly used in electric power generating stations, geothermal heating systems, and district heating and cooling systems

7. Where do we use process piping?

A. Process piping is mostly used in petroleum refineries, chemicals, pharmaceuticals, textile, paper, processing plants, etc.

8. Explain the design pressure in piping?

A. The design pressure is the pressure of each component in a piping system, this design pressure of a component in a piping system should not be less than the high pressure which could occur during the service.

9. Elaborate piping?

A. Piping can be described as an assembly of pipes, fittings, valves, instruments, and specialty components.

10. What are the major components in a piping system?

A. The major components in a piping systems are

  • Pipe
  • Fittings(Elbows, reducers, flange connections)
  • Flanges, gaskets, bolting
  • Valves
  • Pipe support

11. What is the importance of piping specification?

A. By the help of piping specification the proper material of a pipe and also the components in a piping system can be determined.

12. Why do we need elbows in a piping system?

A. Elbow would make an angle between the adjacent piping, there are elbows of 90 degrees and 45 degrees.

13. Explain pipe caps?

A. Pipe caps are specialized fittings which is used to close an open end.

14. What are weldolets ?

A. Weldolets are integral reinforcement fittings used for branch connection strength

15. What is a swage nipple?

A. This is a reducing fitting which is used to join piping of different sizes

16. Explain soluble dam?

A. A soluble dam is a water soluble material and it can be used to restrict the purging gas in a pipe.

17. What is the difference between a machine bolt and stud bolt?

A. One side of the machine bolt consists of the head while the other side has a nut, while in the case of a stud bolt it has nuts on both sides.

18. What are the basic functions of instruments?

A. The major function of instruments are to sense, transmit, indicate, read, and control.

19. What is SMAW and TIG welding?

A. SMAW- Shielded metal arc welding, TIG – Tungsten inter gas welding

20. What is the purpose of eccentric reducer and concentric reducer?

A. Eccentric reducers are used in pump suction to avoid cavitation and concentric reducers are used in pump discharge.

21. What would happen if we use concentric reducers in pump suction?

A. Air pockets will form if we use concentric reducers in pump suction and this would lead to cavitation and the pump will be damaged.

22. Explain pump cavitation?

A. A pump is not capable to handle vapor, it is designed to handle liquid. Vapor will be formed if the pump pressure falls below the liquid’s vapor pressure and this would cause cavitation

23. Explain NPSH?

A. NPSH is a net positive suction head, it is the pressure that is available in the pump suction after excluding the vapor pressure.

24. How to calculate the net positive suction head (NPSH)?

A. Static head + surface pressure head – the vapor pressure of the product – the friction loss in the piping, valves, and fittings.

25. What are the insulation material which is used for the piping system

A.Rigid – Calcium silicate, cellular glass     Fibrous – Rock & glass wool

26. What is the standard for petroleum pumps?

A. The standard for centrifugal pumps in petroleum industry is API 610

27. What is the need for positive displacement pumps and where is it used?

A. It is used to move the viscous liquids and also it would inject chemicals or addictive into a system.

28. What are the types of rotary pumps?

A. External gear, cam and piston, two lobe, single screw, two screw

29. Where should we use rotary pumps?

A.  It can be used for viscous fluids which is free of hard and abrasive fluids

30. Explain the code ANSI B31.1 and code ANSI b31.3?

A. The B31.1 is the code for power piping and B31.3 is for refinery or for chemical plants

31. Which of the following piping is more health hazardous Fuel oil piping, Process piping with caustic, process piping with HF acid, sulphuric-acid piping?

A. Process piping with HF acid

32. What could be the consequence if there is a steam piping with a low pocket but without any steam trap?

A. Condensate build-up would happen to a point that a slug will be pushed by the steam flow. This slug condensate could cause the water hammer and it could damage the piping.

33. Explain steam tracing?

A. It is a process to prevent the fluid passing through a process line from freezing by keeping the temperature high for free flow of fluid and thus maintaining pumpability.

34. What should be done before conducting flushing and hydro-test?

A. Certain components such as control valves, orifice plates, rotameters, safety valves, thermowells are dropped or replaced with temporary spools before the hydro test.

35. What is the need for a dampner in the piping of a reciprocating pump?

A. It is used to handle pulsation

36. Why do we use a full bore valve in connecting pipeline of launcher receiver?

A. It is used for pigging.

37.  Classification of flanges according to facing?

A. Flat face, raised face, tongue and groove, and ring type joint

38. What are the different types of gaskets?

A. Full face, spiral wound, octagonal ring, metal jacketed, and inside bolt circle

39. Where should we do a branch connection in a pipeline?

A. The branch connection should be on the top side of the pipe if the fluid is gas, air, or steam. The branch connection should be on the bottom side of the pipe if the fluid is liquid.

40. Where should a boiler feed water pump must be located?

A. It must be located close to the deaerator, because these pumps takes water from the deaerator.

41. What is the need for drip leg in a steam line?

A. It is used to remove the condensate if there is a rise in the pipe along the flow direction. So if there is no drip leg in a steam line then it could cause pipe damage due to a water hammer.

42. What is the need for high point vent and low point drain in a pipeline?

A. The high point vent will remove the air during the hydro test and the low point drain would drain the water after the hydro test.

43. Why do we use blind flange in a pipeline?

A. It is used if there is a change that should be done for piping in the future and also for cleaning and inspection.

44. Where should be a centrifugal pump must be located in a vacuum service?

A. It must be located directly below the tower

45. What are the requirements for suction line?

A. Reducer, strainer, block valve, pockets, proper straight length

46. What are the requirements for discharge piping?

A.  Pressure indicator, reducer, block valve, check valve

47. How can we locate feed nozzle?

A. It would be oriented in a specific area of tray by means of internal piping

48. What are the types of compressor drives?

A. Gas turbine, electric motor, steam turbine, and gas engine

49. What is galvanizing?

A. it is the process in which the surface of iron or steel will be covered by zinc

50. What is the need for a loop in a piping?

A. It is to control the expansion and contraction of a pipe due to the change in fluid temperature.

51. Explain full couplings?

A. A pipe segment can be connected to the other one with the help of this device

52. What is the need for strainers in a pipeline?

A. Strainers can remove solid particles from liquids, mostly strainers are placed in mainline so that all the process fluid will pass through them.

53. What are the types of strainers?

A. Basket strainers, Wye strainers, and Start-up strainers

54. What is the need for a steam trap in a pipeline?

A. A steam trap is used in a pipeline to separate the condensate and the steam

55. What are the types of steam trap?

A. Impulse, thermodynamic, mechanical, and thermostatic

56. What is the need for valve in a pipeline?

A. A valve can start, stop, or control the flow of liquid or gas in a pipeline

57. What is threaded joints?

A. This type is mostly used for many industries because many small size pipes can be joined by this method and it can be done without any material concern.

58. Why do we use tees and crosses in a pipeline?

A. It is used when more than two branches of piping is to be connected at the same time

59. What are the types of pressure relieving devices?

A. Relief valves, safety valves, safety relief valves, conventional and balance valve, and frangible disk

60. Explain the set pressure?

A. It is the inlet pressure at which the safety or relief valve is adjusted to open, this pressure is set without any back pressure on the discharge of the valve.

61. Explain overpressure?

A. If there is a pressure increase over the set pressure of the primary relieving device it is the overpressure

62. What is accumulation?

A. If there is an increase in pressure over the maximum allowable working pressure of the vessel during the discharge through the safety or relief valve, expressed as a percent of that pressure.

63. What is blow-down?

A. It is the reduction of the flowing pressure below the set point that is needed for a device to close. It can also be described as the difference between the set pressure and the resetting pressure of a safety valve

64. Explain back pressure?

A. It is the pressure that is created on the discharge side of the safety valve, this pressure could be created by the flowing fluids when it passes through the relief discharge piping.

65. How to select a pipe?

A. It must be selected according to the size, material, and thickness

66. How to do the vent connection in a pipeline that carries liquid?

A. In a pipeline that carries liquid, we need to vent out the air. In order to do this vent connection, a valve is fitted at the topmost point in a pipeline.

67. What is called a hot load or an operating load and what is a cold load?

A. It is the weight that the spring needs to support during the operation of the pipeline. The cold load is the weight that the spring needs to support while the pipeline is not operating

68. What are the types of pipe support?

A. Snubbers (hydraulic and mechanical), sway braces, Rigid or weight support, and Rigid restraints and anchors

69. What is a variable spring support?

A. These supports would provide varying supporting forces to the pipe when the pipe moves vertically because of the contraction or elongation.

70. What is the need for a constant spring support?

A. This type of supports is needed when the thermal movements are high, this type of spring supports is required to reduce the load created in the pipeline.

71. Where should we locate the pipe supports?

A. The pipe support must be located near to the loads such as valves, flanges, etc. So the bending force can be kept to a minimum.

72. How to do the piping stress analysis?

A. Make sure that the stress in the pipeline components is within the limits. Restrict the problems that are caused by mechanical vibrations such as fluid hammer and pulsation. We must also solve the problems related to the temperature.

73. How to select a flange for the pipeline?

A. It must be selected according to the type and facing, Pipe size must be considered, Pressure class of the flange must be considered, and it should also be selected according to the pipe schedule and material.

74.  What is routing?

A. The routing is the way in which the pipeline is developed into space, cold pipelines are used to connect static objects like tanks, vessels, etc. The hot pipelines are capable to handle the thermal expansion during cold to hot conditions.

75. What is a blind flange?

A. A blind flange is a flange that doesn’t have a bore and it is used to close the piping system or the vessel opening

76. Explain drip valve?

A. It is a type of drain valve which is fitted at the driplet bottom in order to do the blow-down

77. What is SIS?

A. It is the safety instruction sheet which would give the full design details regarding the pipeline

78. What are the contents of an isometric drawing?

A. An isometric drawing would have line conditions, construction material, Orientation, piping, and drawing details.

79. What is PIP?

A. It is the process industry practice, and it would include the details of the requirements for industry practice.

80. What is a blow-down valve?

A. It is a type of globe valve which can remove sludge from the boiler drums, vessels, driplegs etc.

81. What is a breather valve?

A. A breather valve is used in a storage tank so that it can release gas or vapor in case of internal pressure.

82. What is a static and dynamic load in a pipeline?

A. A static load is applied slowly so there would be time to distribute this load. The dynamic load will change quickly with time, so there won’t be any time to distribute this load and this would cause pipe movements.

83. What is a plain end?

A. Plain ends are cut square and reamed to remove burrs and this end is used for mechanical couplings and socket weld fittings

84. Where do we use beveled ends?

A. These are used for butt weld applications

85. Explain the straight tee and reducing tee?

A. The straight tee consist of three openings, two of them have the same axis and the third one will be perpendicular to this axis in order to connect a branch line. The reducing tee is similar to the straight tee and the only difference from the straight tee is that the branch line connection is smaller in size

86. What is the need for a gasket in a valve?

A. Gaskets can prevent the leakage around the closure mechanism and it can also prevent the leakage of fluid to the atmosphere

87. What are the factors that would affect the pipe span?

A.  Size, schedule, liquid or vapor, insulated or bare pipe

88. How to do the rack design?

A. First create a line routine diagram then calculate the bent spacing, then set the width of the rack, at last, decide elevations and levels

89. What are the types of temperature measurement instruments?

A. Thermowells, thermocouples, RTD, and Filled system bimetallic thermometer

90. What are the inferential methods of level measurement?

A. Hydrostatic head, buoyancy, conductance, radiation, float.

91. What is the need for restriction orifice plates in a pipeline?

A. It is required for the effective distribution of fluid in a piping network

92. What are the types of direct level measurement?

A. Dip sticks, gauge glasses, reflex or transparent

93. Name the pressure instruments which is used in chemical industries?

A. Manometer, bourdon tubes, bellows, and diaphragms

94. What are the types of flow measurement devices?

A. Rotameter, variable area flowmeter, magnetic flow meter, orifice plate, turbine flow meter, and positive displacement meter.

95. Where do we use butterfly control valves?

A. Butterfly valves are used for large size piping network and it can handle clean fluids

96. What are the factors that must be considered while routing a pipe underground?

A. Flange joints must be avoided in U/G piping and also avoid the U/G routing of the pipe that handles hazardous fluids. The minimum pipe size that is routed underground should not be less than one inch. The buried piping must be protected from corrosion and also freeze protection must be done for outdoor piping.

97. What is a PIG in a pipeline?

A. It is a device that moves inside a pipeline in order to do the cleaning. It would remove any debris which is left in the line and also it can maintain the line efficiency there are two types of PIG’s and they are cleaning pigs and sealing pigs.

98. Describe the process flow diagram?

A. It is a type of block diagram which shows the unit operation and unit processes. This diagram would show all the major equipment and main piping and its flow.

99. Where should be a drain be located?

A. It must be located at the bottom section of the drum

100. Where should be a temperature instrument be located?

A. It must be located in liquid space, mostly at the bottom portion of the drum

101. What is the need for a glandless piston valves?

A. These valves are maintenance free valves and they are used in the steam service

102. What is a stress intensity factor?

A. It is the ratio of the maximum stress intensity to normal stress

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