300+ TOP PIPING Engineering Interview Questions and Answers pdf

PIPING Engineering Interview Questions :-

1 . What is preferred location for drain?
Must be located at the bottom section of drum.

2 . What are the steps in selection of valve?
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.

3. What are functions of valves?
Isolation, regulation, non-return and special purposes.

4. What are isolating valves?
Gate, ball, plug, piston, diaphragm, butterfly, pinch.

5. What are regulation valves?
Globe, needle, butterfly, diaphragm, piston, pinch.

6. What are non-return valves?
check valve,

7. What are special valves?
multi-port, flush bottom, float, foot, pressure relief, breather.

8. What materials are used for construction of valves?
Cast iron, bronze, gun metal, carbon steel, stainless steel, alloy carbon steel, polypropylene and other plastics, special alloys.

9. What is trim?
Trim is composed of stem, seat surfaces, back seat bushing and other small internal parts that normally contact the surface fluid.

10. Which standard specifies trim numbers for valve?
API 600.

11. What are wetted parts of valve?
All parts that come in contact with surface fluid are called wetted parts.

12. What is wire drawing?
This term is used to indicate the premature erosion of the valve seat caused by excessive velocity between seat and seat disc, when valve is not closed tightly.

13. What is straight through valve?
Valve in which the closing operation of valve is achieved by 90 degrees turn of the closing element.

14. What pressure tests are carried out on valves?
Shell-hydrostatic, seat-hydrostatic, seat-pneumatic

15. What are available valve operators?
Hand-lever, hand-wheel, chain operator, gear operator etc.

16. What is the full form of ASME?
American Society for Mechanical Engineers.

17. Which Piping code is used for Power piping and which code is used for Process Piping design?
ANS:

• Power Piping: ASME B 31.1
• Process Piping: ASME B 31.3

18. What are the main differences between ASME B 31.1 and ASME B 31.3?
The main differences are listed below:

• Material allowable stresses are different in both codes.
• Stress increases due to occasional loads are different in each code.
• B 31.3 neglects torsion while calculating sustained stresses, but B 31.1 includes it.
• Sustained stress calculation is specific in B 31.1 but undefined for B 31.3.
• B 31.1 intensifies torsion but B31.3 does not intensify it.

19. How to calculate the basic allowable stress for a material?
The basic allowable stress is defined in respective code. For example as per B 31.3 the basic allowable stress for a material is the minimum of the following:
1/3rd of tensile strength at design temperature.
2/3rd of yield strength at design temperature.
100% of average stress for a creep rate of 0.01% per 1000 hours.
67% of average stress for rupture at the end of 100000 hours.
80% of minimum stress for ruptures at the end of 100000 hours.
For austenitic stainless steel or nickel alloys the lower of yield strength and 90% of yield strength at temperature.
For structural grade materials 0.92 times of the lowest value of point (a) to (f)

20. What is the main difference between Constant and Variable Spring Hanger? When to use these hangers?
ANS:

• In Constant Spring hanger the load remains constant throughout its travel range. But In variable spring hanger the load varies with displacement.
• Spring hangers are used when thermal displacements are upwards and piping system is lifted off from the support position. Variable spring hanger is preferable as this is less costly.
• Constant springs are used:
• When thermal displacement exceeds 50 mm
• When variability exceeds 25%
• Sometimes when piping is connected to strain sensitive equipment like steam turbines, centrifugal compressors etc and it becomes very difficult to qualify nozzle loads by variable spring hangers, constant spring hangers can be used.

21. What do you mean by variability? What is the industry approved limit for variability?
Variability= (Hot Load-Cold load)/Hot load = (Spring Constant × displacement)/Hot load.
Limit for variability for variable spring hangers is 25%.

22. What are the major parameters you must address while making a Spring Data-sheet?
Major parameters are: Spring TAG, Cold load/Installed load, Vertical and horizontal movement, Piping design temperature, Piping Material, Insulation thickness, Hydro-test load, Line number etc.

23. How to calculate the height of a Variable Spring hanger?
Select the height from vendor catalog based on spring size and stiffness class.
For base mounted variable spring hanger the height is mentioned directly. It is the spring height.
For top mounted variable spring hanger’s ass spring height with turnbuckle length, clamp/lug length and rod length.

24. Can you select a proper spring hanger if you do not make it program defined in your software?
What is the procedure?
In your system first decide the location where you want to install the spring. Then remove all nearby supports which are not taking load in thermal operating case. Now run the program and the sustained load on that support node is your hot load. The thermal movement in that location is your thermal movement for your spring. Now assume variability for your spring. So calculate
Spring constant = (Hot load × variability)/displacement. Now with spring constant and hot load enter any vendor catalog to select spring inside the travel range.

25. What is the software available for performing piping stress analysis?
Caesar II, AutoPipe etc.

26. What are the types of compressors?
Positive Displacement, Centrifugal and Axial, rotary screw, rotary vane, rotary lobe, dynamic, liquid ring compressors.

27. What are types of compressor drives?
Electric motor, gas turbine, steam turbine and gas engine.

28. How Centrifugal compressors work?
High-speed impellers increase the kinetic energy of the gas, converting this energy into higher pressures in a divergent outlet passage called a diffuser. Large volume of gas at moderate pressure.

29. What are types of steam turbine and why are they popular?
Condensing and non-condensing, Popular because can convert large amounts of heat energy into mechanical work very efficiently.

30. Where gas turbine drive is used?
Desserts and offshore platforms where gas is available, for gas transmission, gas lift, liquid pumping, gas re-injection and process compressors.

31. What are the auxiliary equipments of compressor?
Lube oil consoles, Seal oil consoles, Surface condensers, Condensate pump, Air blowers, Inlet air filters, waste heat system, compressor suction drum, knock out pot, Pulsation dampner, volume bottles, Inter and after coolers.

32. What are the types of seal oil system?
Gravity and pressurized.

33. What factors to be considered while designing compressor housing?
Operation, Maintenance, Climate conditions, Safety, Economics.

34. What are the compressor housing design points?
Floor elevation, building width, building elevation, hook centerline elevation.

35. What are the types of compressor cases?
Horizontal split case, Vertical split case.

36. How to located temperature and pressure instruments?
Temperature in liquid space, at down-comer side and pressure in vapour space, in area except down-comer sector.

37. What are necessary parts of inlet line of compressor?
Block Valve, Strainer, Break out flanges in both inlet and outlet to remove casing covers, Straightening vane in inlet line if not enough straight piece in inlet line available, PSV in interstage line and in discharge line before block valve.

38. What points to be considered for reciprocating compressor piping layout?
High pulsation, simple line as low to grade as possible for supporting, analog study, all branches close to line support and on top, Isolate line support from adjacent compressor or building foundations

39. What are the types of compressor shelters?
On ground with no shelter, Open sided structure with a roof,
Curtain wall structure (Temperate climates), Open elevated installation, Elevated multi-compressor structure.

40. What are drum internals?
Demister pads, Baffles, Vortex breakers, Distribution piping.

41. What are drum elevation requirements?
NPSH, minimum clearance, common platforming, maintenance, operator access.

42. What are drum supports?
Skirt for large drums, legs, lugs, saddles for horizontal drums.

43. What are necessary nozzles for non-pressure vessel?
Inlet, outlet, vent, manhole, drain, overflow, agitator, temperature element, level instrument, and steam-out connection.

44. What are necessary nozzles for pressure vessel?
Inlet, outlet, manhole, drain, pressure relief, agitator, level gauge, pressure gauge, temperature element, vent and for steam-out.

45. What is preferred location for level instrument nozzles?
Away from the turbulence at the liquid outlet nozzle, although the vessel is provided with a vortex breaker, instrument should be set in the quiet zone of the vessel for example on the opposite side of the weir or baffle or near the vapor outlet end.

46. What is preferred location for process nozzles on drum?
Minimum from the tangent line.

47. What is preferred location for steam out nozzle on drum?
At the end opposite to the maintenance access.

48. What is preferred location for vent?
AT the top section of drum at the end opposite the steam out connection.

49. What is preferred location for pressure instrument nozzle on drum?
Must be anywhere in the vapor space, preferable at the top section of drum

50. What is preferred location for temperature instrument?
Must be in liquid space, preferably on the bottom section of drum.

51. What are various temporary closures for lines?
Line blind valve, line blind, spectacle plate, double block and bleed, blind flanges replacing a removable spool.

52. Why horizontal displacement is specified in data-sheet? What will you do if the angle due to displacement is more than 4 degree?
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.

53. Which spring will you select for your system: Spring with low stiffness or higher stiffness and why?
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.

54. What do you mean by Stress? What are the types of Stresses that are generated in a Piping?
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:

• Axial Stresses
• Tangential or Hoop stress
• Longitudinal Stress
• Radial Stress
• Expansion Stress
• Stress due to occasional events like Seismic and Wind effects.

55. What factors to consider for site selection?
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.

56. Why Stress Analysis is required?
Ensure reliability and safety of working by

• Limiting Stresses (sustained, expansion, hydro-test, occasional) within code allowable.
• Limiting nozzle load and moments connected to equipment (Pump/Vessel/Heat Exchanger etc) within allowable values.
• Reducing damaging effects of dynamic loads.
• Avoiding leakage at joints.
• Limiting sagging and displacements within allowable limits.
• Avoiding high loads on supporting structures.

57. What is the difference between Stress and Pressure?
Stress is generated because of internal resistance force. Pressure is generated because of external force.
Pressure can be a cause to generate stress.

58. Where jacked screwed flange is used?
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.

59. What is double block and bleed?
Two valves with bleed ring in between with a bleed valve connected to the hole of bleed ring.

60. Where blind flange is used?
It is used with view to future expansion of the piping system, or for cleaning, inspection etc.

61. What are crude oil ranges?
Crude oil BP Range: 100F-1400F, lightest material: below 100F, Heavier materials- upto 800F, Residue above 800F.

62. What is batch shell process?
feed, heat, condense, heat more, condense, low quality.

63. What are types of towers?
Stripper, Vacuum tower, trayed, packed towers.

64. What is chimney tray?
It’s a solid plate with central chimney section, used at draw-off sections of the tower.

65. What factors to consider while setting tower elevation?
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.

66. How to located tower maintenance access nozzles?
At bottom, top and intermediate sections of tower, must not be at the down-comer section of tower and in front of internal piping.

67. How to located feed nozzle?
Must be oriented in specific area of tray by means of internal piping.

68. What are the steps in selection of valve?
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.

69. What are functions of valves?
Isolation, regulation, non-return and special purposes.

70. What are isolating valves?
Gate, ball, plug, piston, diaphragm, butterfly, pinch.

71. What are regulation valves?
Globe, needle, butterfly, diaphragm, piston, pinch.

72. What are non-return valves?
check valve.

73. What are special valves?
multi-port, flush bottom, float, foot, pressure relief, breather.

74. What materials are used for construction of valves?
Cast iron, bronze, gun metal, carbon steel, stainless steel, alloy carbon steel, polypropylene and other plastics, special alloys.

75. What is trim?
Trim is composed of stem, seat surfaces, back seat bushing and other small internal parts that normally contact the surface fluid.

76. Which standard specifies trim numbers for valve?
API 600.

77. What are wetted parts of valve?
All parts that come in contact with surface fluid are called wetted parts.

78. What is wire drawing?
This term is used to indicate the premature erosion of the valve seat caused by excessive velocity between seat and seat disc, when valve is not closed tightly.

79. What is straight through valve?
Valve in which the closing operation of valve is achieved by 90 degrees turn of the closing element.

80. What pressure tests are carried out on valves?
Shell-hydrostatic, seat-hydrostatic, seat-pneumatic

81. What are available valve operators?
Handlever, handwheel, chain operator, gear operator, powered operator likes electric motor, solenoid, pneumatic and hydraulic operators, Quick acting operators for non-rotary valves (handle lift).

82. What are ball valve body types?
Single piece, double piece, three piece, the short pattern, long pattern, sandwich and flush bottom design.

83. What are two types of ball valve?
Full port design and regular port design, according to type of seat, soft seat and metal seat.

84. Why ball valves are normally flanged?
Because of soft seat PTFE which can damage during welding.

85. What are butterfly valve types?
Double flange type, wafer lug type and wafer type.

86. What are types of check valve?
Lift check valves and swing check valves.

87. What are non-slam check valves?
Swing check valve, conventional check valve, wafer check valve, tilting disc check valve, piston check valve, stop check valve, ball check valve.

88. Where stop check valve is used?
In stem generation by multiple boilers, where a valve is inserted between each boiler and the main steam header. It can be optionally closed automatically or normally.

89. Where diaphragm valves are used?
Used for low pressure corrosive services as shut off valves.

90. What is Barstock Valve?
Any valve having a body machined from solid metal (barstock).
Usually needle or globe type.

91. What is BIBB Valve?
A small valve with turned down end, like a faucet.

92. What is Bleed Valve?
Small valve provided for drawing off liquid.

93. What is BlowDown Valve?
Refers to a plug type disc globe valve used for removing sludge and sedimentary matter from the bottom of boiler drums, vessels, driplegs etc.

94. What is Breather Valve?
A special self acting valve installed on storage tanks etc. to release vapour or gas on slight increase of internal pressure (in the region of ½ to 3 ounces per square inch).

95. What is Drip Valve?
A drain valve fitted to the bottom of a droplet to permit blowdown.

96. What is Flap Valve?
A non return valve having a hinged disc or rubber or leather flap used for low pressure lines.

97. What is Hose Valve?
A gate or globe valve having one of its ends externally threaded to one of the hose thread standards in use in the USA. These valves are used for vehicular and firewater connections.

98. What is Paper-Stock Valve?
A single disc single seat gate valve (Slide gate) with knife edged or notched disc used to regulate flow of paper slurry or other fibrous slurry.

99. What is Root Valve?
A valve used to isolate a pressure element or instrument from a line or vessel, or a valve placed at the beginning of a branch form the header.

100. What is Slurry valve?
A knife edge valve used to control flow of non-abrasive slurries.

101. What is Spiral sock valve?
A valve used to control flow of powders by means of a twistable fabric tube or sock.

102. What is Throttling valve?
Any valve used to closely regulate flow in the just-open position.

103. What is Vacuum breaker?
A special self-acting valve or any valve suitable for vacuum service, operated manually or automatically, installed to admit gas (usually atmospheric air) into a vacuum or low-pressure space. Such valves are installed on high points of piping or vessels to permit draining and sometimes to prevent siphoning.

104. What is Quick acting valve?
Any on/off valve rapidly operable, either by manual lever, spring or by piston, solenoid or lever with heat-fusible link releasing a weight which in falling operates the valve. Quick acting valves are desirable in lines conveying flammable liquids. Unsuitable for water or for liquid service in general without a cushioning device to protect piping from shock.

105. What is diverting valve?
This valve switch flow from one main line to two different outlets. WYE type and pneumatic control type with no moving part.

106. What is sampling valve?
Usually of needle or globe pattern, placed in branch line for the purpose of drawing all samples of process material through the branch.

107. What are blow off valve?
It is a variety of globe valve confirming with boiler code requirements and specially designed for boiler blow-off service. WYE pattern and angle type, used to remove air and other gases from boilers etc.

108. What is relief valve?
Valve to relieve excess pressure in liquids in situations where full flow discharge is not required, when release of small volume of liquid would rapidly lower pressure.

109. What is safety valve?
Rapid opening (popping action) full flow valve for air and other gases.

110. What is foot valve?
Valve used to maintain a head of water on the suction side of sump pump, basically a lift check valve with integrated strainer.

111. What is float valve?
Used to control liquid level in tanks, operated by float, which rises with liquid level and opens the valve to control water level. It can also remove air from system, in which case, air flows out of system in valve open condition, but when water reaches valve, float inside valve raises to close the valve and stop flow of water. Used in drip legs.

112. What are flush bottom valves?
Special type of valves used to drain out the piping, reactors and vessels, attached on pad type nozzles.

113. What are types of flush bottom valves?
Valves with discs opening into the tank and valves with disks into the valve.

114. What are the uses of three-way valve?
Alternate connection of the two supply lines to a common delivery vise versa, isolating one safety valve, division of flow with isolation facility.

115. What are uses of four way valve?
Reversal of pump suction and delivery, By pass of strainer or meter, reversal of flow through filter, heat exchanger or dryer.

116. What is metal seated lubricated plug valve?
A plug valve with no plastic material, where grease is applied to contacting surfaces for easy operation.

117. What are three patterns of plug valve design?
Regular pattern, short pattern and ventury pattern.

118. What is regular pattern plug valve?
Rectangular port, area almost equal to pipe bore, smooth transition from round body to rectangular port, for minimum pressure loss.

119. What are short pattern plug valve?
Valves with face to face dimension of gate valve, as a alternative to gate valve.

120. What are ventury pattern plug valve?
Change of section through the body throat so graded to have ventury effect, minimum pressure loss.

121. What are inverted plug design valve?
Plug valve with taper portion up of plug. For 8” and higher size.

122. What is pressure balanced plug valve?
With holes in port top and bottom connecting two chambers on top and bottom of plug, to reduce turning effort.

123. What are Teflon sleeved plug valve?
PTFE sleeve between plug and body of valve, low turning effort, minimum friction, temperature limitation, anti static design possible.

124. What are permasil plug valve?
Plug valves with Teflon seat instead of sleeves, for on-off applications, can handle clean viscous and corrosive liquids, Graphite seat for high temperature applications. Drip tight shut off not possible.

125. What are eccentric plug valve?
Off center plug, corrosive and abrasive service, on off action, moves into and away from seat eliminating abrasive wear.

126. What is dimensional standard for plug valve?
API 599.

127. What is pinch valve?
Similar to diaphragm valve, with sleeves of rubber or PTFE, which get squeezed to control or stop the flow, Cast iron body, for very low service pressures like isolation of hose connections, manufacture standard.

128. What is needle valve?
Full pyramid disc, same design as globe valve, smaller sizes, sw or threaded, flow control, disc can be integral with stem, inside screw, borged or barstock body and bonnet, manufacturers standard.

129. How to install a globe valve?
Globe valve should be installed such that the flow is from the underside of the disk, Usually flow direction is marked on the globe valve.

130. What are globe valve port types?
Full port: More than 85% of bore size, Reducer port: One size less than the connected pipe.

131. What are globe valve disk types?
Flat faced type for positive shutoff, loose plug type for plug renewal or needle type for finer control.

132. What are characteristics of globe valve stem?
Always rising design, with disk nut at the lower end and handwheel at upper end.

133. What are types of globe valve?
Angle globe valve, plug type disc globe valve, WYE-body globe valve, composite disc globe valve, double disc globe valve.

134. What is angle globe valve?
Ends at 90 degree to save elbow, higher pressure drop.

135. Where plug type disc globe valve is used?
For severe regulating service with gritty liquids such as boiler feedwater and for blow off service.

136. Where WYE body globe valve is used?
In line ports with stem emerging at 45 degree, for erosive fluids due to smoother flow pattern.

137. What is double disc globe valve?
Has two discs bearing on separate seats spaced apart, on a single shaft, for low torque, used for control valves.

138. What are port types for gate valves?
Full port and reduced port. Default is reduced bore. Full port has to be specified in bom.

139. How to close a gate valve?
Turn the hand-wheel in clockwise direction.

140. What is lantern ring?
It’s a collection point to drain off any hazardous seepage or as a point where lubricant can be injected; it is in the middle of packing rings.

141. What are types of gate valves?
Solid plane wedge, solid flexible wedge, split wedge, double disc parallels seats, double disc wedge, single disc single seat gate or slide, single disc parallel seats, plug gate valve.

142. What are the types of bonnets?
Bolted bonnet, bellow sealed bonnet, screwed on bonnet, union bonnets, A U-bolt and clamp type bonnet, breech-lock bonnet, pressure seal bonnet.

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