Mechanical PIPING Engineering Interview Questions and Answer
This is help Full for Piping QA/QC Engineer , Piping
Inspector ,Oil and Gas Piping Engineer and Sr Mechanical Piping Engineer
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01. 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.
02. What are functions of valves?
ANSWER :- Isolation, regulation, non-return and special purposes.
03. What are isolating valves?
ANSWER :- Gate, ball, plug, piston, diaphragm, butterfly, pinch.
04. What are regulation valves?
ANSWER :- Globe, needle, butterfly, diaphragm, piston. pinch.
05. What are non-return valves?
ANSWER :- check valve.
06. What are special valves?
ANSWER :- multi-port, flush bottom, float, foot, pressure relief, breather.
07. 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.
08. 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.
09. Which standard specifies trim numbers for valve?
ANSWER :- API 600.
10. What are wetted parts of valve?
ANSWER :- All parts that come in contact with surface fluid are called wetted parts.
11. What is wire drawing?
ANSWER :- 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 dosed tightly.
12. What is straight through valve?
ANSWER :- Valve in which the dosing operation of valve is achieved by 90 degrees turn of the dosing element.
13. What pressure tests are carried out on valves?
ANSWER :- Shell-hydrostatic, seat-hydrostatic, seat-pneumatic
14. What are available valve operators?
ANSWER :- 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).
15. What are ball valve body types?
ANSWER :- Single piece, double piece, three piece, the short pattern, long pattern, sandwich and flush bottom design.
16. What are two types of ball valve?
ANSWER :- Full port design and regular port design, according to type of seat, soft seat and metal seat.
17. Why ball valves are normally flanged?
ANSWER :- Because of soft seat PTFE which can damage during welding.
18. What are butterfly valve types?
ANSWER :- Double flange type, wafer lug type and wafer type.
19. What are types of check valve?
ANSWER :- Lift check valves and swing check valves.
20. What are non-slam check valves?
ANSWER :- Swing check valve, conventional check valve, wafer check valve, tilting disc check valve, piston check valve, stop check valve, ball check valve.
21. Where stop check valve is used?
ANSWER :- In stem generation by multiple boilers, where a valve is inserted between each boiler and the main steam header. It can be optionally dosed automatically or normally.
22. Where diaphragm valves are used?
ANSWER :- Used for low pressure corrosive services as shut off valves.
23. Where diaphragm valves are used?
ANSWER :- Used for low pressure corrosive services as shut off valves.
24. What is Barstock Valve?
ANSWER :- Any valve having a body machined from solid metal (barstock). Usually needle or globe type.
25. What is BIBB Valve?
ANSWER :- A small valve with turned down end, like a faucet.
26. What is Bleed Valve?
ANSWER :- Small valve provided for drawing off liquid.
27. What is BlowDown Valve?
ANSWER :- Refers to a plug type disc globe valve used for removing sludge and sedimentary matter from the bottom of boiler drums, vessels, driplegs etc.
28. What is Breather Valve?
ANSWER :- 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 1/2 to 3 ounces per square inch).
29. What is Drip Valve?
ANSWER :- A drain valve fitted to the bottom of a droplet to permit blowdown.
30.What is Flap Valve?
ANSWER :- A non return valve having a hinged disc or rubber or leather flap used for low pressure lines.
31.What is Hose Valve?
ANSWER :- 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.
32.What is Paper-Stock Valve?
ANSWER :- 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.
33.What is Root Valve?
ANSWER :- 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.
34. What is Slurry valve?
ANSWER :- A knife edge valve used to control flow of non-abrasive slurries.
35. What is Spiral sock valve?
ANSWER :- A valve used to control flow of powders by means of a twistable fabric tube or sock.
36. What is Throttling valve?
ANSWER :- Any valve used to closely regulate flow in the just-open position.
37. What is relief valve?
ANSWER :- 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.
38. What is safety valve?
ANSWER :- Rapid opening (popping action) full flow valve for air and other gases.
39. What is foot valve?
ANSWER :- Valve used to maintain a head of water on the suction side of sump pump. basically a lift check valve with integrated strainer.
40. What is float valve?
ANSWER :- 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 dose the valve and stop flow of water. Used in drip legs.
41. What are flush bottom valves?
ANSWER :- Special type of valves used to drain out the piping, reactors and vessels, attached on pad type nozzles.
42. What are types of flush bottom valves?
ANSWER :- Valves with discs opening into the tank and valves with disks into the valve.
43. What are types of flush bottom valves?
ANSWER :- Valves with discs opening into the tank and valves with disks into the valve.
44. What are the uses of three-way valve?
ANSWER :- Alternate connection of the two supply lines to a common delivery vise versa, isolating one safety valve, division of flow with isolation facility.
45. What are uses of four way valve?
ANSWER :- Reversal of pump suction and delivery, By pass of strainer or meter, reversal of flow through filter, heat exchanger or dryer.
46. What is metal seated lubricated plug valve?
ANSWER :- A plug valve with no plastic material, where grease is applied to contacting surfaces for easy operation.
47. What are three patterns of plug valve design?
ANSWER :- Regular pattern, short pattern and ventury pattern.
48. What is regular pattern plug valve?
ANSWER :- Rectangular port, area almost equal to pipe bore, smooth transition from round body to rectangular port, for minimum pressure loss.
49. What are short pattern plug valve?
ANSWER :- Valves with face to face dimension of gate valve, as a alternative to gate valve.
50. What are ventury pattern plug valve?
ANSWER :- Change of section through the body throat so graded to have ventury effect, minimum pressure loss.
50A. What are inverted plug design valve?
ANSWER :- Plug valve with taper portion up of plug. For 8" and higher size.
51. What is pressure balanced plug valve?
ANSWER :- With holes in port top and bottom connecting two chambers on top and bottom of plug, to reduce turning effort.
52. What are Teflon sleeved plug valve?
ANSWER :- PTFE sleeve between plug and body of valve, low turning effort, minimum friction, temperature limitation, anti static design possible.
53. What are permasil plug valve?
ANSWER :- 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.
54. What are eccentric plug valve?
ANSWER :- Off center plug, corrosive and abrasive service, on off action, moves into and away from seat eliminating abrasive wear.
55. What is pinch valve?
ANSWER :- 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.
56. What is needle valve?
ANSWER :- 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.
57. How to install a globe valve?
ANSWER :- 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.
58. What are globe valve port types?
ANSWER :- Full port: More than 85% of bore size, Reducer port: One size less than the connected pipe.
59. What are globe valve disk types?
ANSWER :- Flat faced type for positive shutoff, loose plug type for plug renewal or needle type for finer control.
60. What are characteristics of globe valve stem?
ANSWER :- Always rising design, with disk nut at the lower end and handwheel at upper end.
61. What is pinch valve?
ANSWER :- 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.
62. What is needle valve?
ANSWER :- 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.
63. How to install a globe valve?
ANSWER :- 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.
64. What are globe valve port types?
ANSWER :- Full port: More than 85% of bore size, Reducer port: One size less than the connected pipe.
65. What are globe valve disk types?
ANSWER :- Flat faced type for positive shutoff, loose plug type for plug renewal or needle type for finer control.
66. What are characteristics of globe valve stem?
ANSWER :- Always rising design, with disk nut at the lower end and handwheel at upper end.
67. What are types of globe valve?
ANSWER :- Angle globe valve, plug type disc globe valve, WYE-body globe valve, composite disc globe valve, double disc globe valve.
68. What is angle globe valve?
ANSWER :- Ends at 90 degree to save elbow, higher pressure drop.
69. Where plug type disc globe valve is used?
ANSWER :- For severe regulating service with gritty liquids such as boiler feedwater and for blow off service.
70. Where WYE body globe valve is used?
ANSWER :- In line ports with stem emerging at 45 degree, for erosive fluids due to smoother flow pattern.
71. What is double disc globe valve?
ANSWER :- Has two discs bearing on separate seats spaced apart, on a single shaft, for low torque, used for control valves.
72. What are port types for gate valves?
ANSWER :- Full port and reduced port. Default is reduced bore. Full port has to be specified in bom.
73. How to close a gate valve?
ANSWER :- Turn the hand wheel in clockwise direction.
74. What are port types for gate valves?
ANSWER :- Full port and reduced port. Default is reduced bore. Full port has to be specified in bona.
75. How to close a gate valve?
ANSWER :- Turn the hand-wheel in clockwise direction.
76. What is lantern ring?
ANSWER :- 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.
77. What are types of gate valves?
ANSWER :- 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.
78. What are the types of bonnets?
ANSWER :- Bolted bonnet, bellow sealed bonnet, screwed on bonnet, union bonnets, A U-bolt and damp type bonnet, breech-lock bonnet, pressure seal bonnet.
79 . What is preferred location for drain?
ANSWER :- Must be
located at the bottom section of drum.
80. 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.
81. What
are functions of valves?
ANSWER :- Isolation, regulation, non-return and special
purposes.
82. What
are isolating valves?
ANSWER :- Gate, ball, plug, piston, diaphragm,
butterfly, pinch.
83. What
are regulation valves?
ANSWER :- Globe, needle, butterfly, diaphragm, piston,
pinch.
84. What are
non-return valves?
ANSWER :- check valve,
85. What are
special valves?
ANSWER :- multi-port, flush bottom, float, foot,
pressure relief, breather.
86. 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.
87. 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.
88.Which standard
specifies trim numbers for valve?
ANSWER :- API 600.
89. What are wetted
parts of valve?
ANSWER :- All parts that come in contact with surface fluid are
called wetted parts.
90. What is wire
drawing?
ANSWER :- 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 dosed tightly.
91. What is straight through valve?
ANSWER :- Valve in which the closing operation of valve is achieved
by 90 degrees turn of the closing element.
92.What pressure
tests are carried out on valves?
ANSWER :- Shell-hydrostatic, seat-hydrostatic,
seat-pneumatic
93.What are
available valve operators?
ANSWER :- Hand-lever, hand-wheel, chain operator, gear
operator etc.
94. What is the full form of ASME?
ANSWER :- American Society for Mechanical Engineers.
95. Which Piping code is used for Power piping and which
code is used for Process Piping design?
ANSWER
:-
o Power Piping: ASME B 31.1
o Process Piping: ASME B 31.3
96. What are the main differences between ASME B 31.1 and ASME
B 31.3?
ANSWER :- The main differences are listed below:
o Material allowable stresses are different in both codes.
o Stress increases due to occasional loads are different in
each code.
o B 31.3 neglects torsion while calculating sustained
stresses, but B 31.1 includes it.
o Sustained stress calculation is specific in B 31.1 but
undefined for B 31.3.
o B 31.1 intensifies torsion but B31.3 does not intensify
it.
97. How to
calculate the basic allowable stress for a material?
ANSWER :- 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.
i00% of
average stress for a creep rate of o.oi% per woo hours.
67% of average
stress for rupture at the end of w0000 hours.
8o% of
minimum stress for ruptures at the end of w0000 hours.
For
austenitic stainless steel or nickel alloys the lower of yield strength and go%
of yield strength at temperature.
For structural
grade materials 0.92 times of the lowest value of point (a) to (f)
98. What is the
main difference between Constant and Variable Spring Hanger? When
to use these hangers?
ANSWER :-
o In Constant Spring hanger the load remains constant
throughout its travel range. But In variable spring hanger the load varies with
displacement.
o 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.
o Constant springs are used:
o When thermal displacement exceeds 5o mm
o When variability exceeds 25%
o 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
99. What are the types of compressors?
ANSWER :- Positive
Displacement, Centrifugal and Axial, rotary screw, rotary vane, rotary lobe,
dynamic, liquid ring compressors.
100. What are
types of compressor drives?
ANSWER :- Electric motor, gas turbine, steam turbine
and gas engine.
101. How
Centrifugal compressors work?
ANSWER :- 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.
102.What are types
of steam turbine and why are they popular?
ANSWER :- Condensing and non-condensing, Popular because can convert
large amounts of heat energy into
mechanical work very efficiently.
103. Where gas turbine drive is used?
ANSWER :- Desserts and offshore platforms where gas is available,
for gas transmission, gas lift, liquid pumping, gas re-injection and process compressors.
104. What are the auxiliary equipments of compressor?
ANSWER :- 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.
105. What are the
types of seal oil system?
ANSWER :- Gravity and pressurized.
106. What factors
to be considered while designing compressor housing?
ANSWER :- Operation, Maintenance, Climate conditions,
Safety, Economics.
107. What are the
compressor housing design points?
ANSWER :- Floor elevation, building width, building
elevation, hook centerline elevation.
108. What are the
types of compressor cases?
ANSWER :- Horizontal split case, Vertical split case.
109. How to
located temperature and pressure instruments?
ANSWER :- Temperature in liquid space, at down-corner side and
pressure in vapour space, in area except down-corner sector
110. What are
necessary parts of inlet line of compressor?
ANSWER :- 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.
110A. What points
to be considered for reciprocating compressor piping layout?
ANSWER :- High pulsation, simple line as low to grade
as possible for supporting, analog study, all branches dose to line support and on top, Isolate line support
from adjacent compressor or building foundations
