Piping Engineer Interview Questions

PIPING INTERVIEW QUESTIONNAIRE

COMPRESSORS

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

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

3. How Centrifugal compressors work ?
Ans : Highspeed 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.

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

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

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

7. What are the types of seal oil system?
Ans : Gravity and pressurized.

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

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

10. What are the types of compressor cases?
Ans : Horizontal split case, Vertical split case.

11. What are compressor suction line requirements ?
Ans : Minimum 3D straight pipe between elbow and inlet nozzle,
increases based on inlet piping layout. 4D


12. What are necessary parts of inlet line of compressor?
Ans : 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.

13. What points to be considered for reciprocating compressor piping
layout?
Ans : 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

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

DRUMS

15. What are drum internals?
Ans : Demister pads, Baffles, Vortex breakers, Distribution piping.

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

17. What are drum supports?
Ans : Skirt for large drums, legs, lugs, saddles for horizontal drums.

18. What are necessary nozzles for non-pressure vessel?
Ans : Inlet, outlet, vent, manhole, drain, overflow, agitator, temperature
element, level instrument, and steamout connection.

19. What are necessary nozzles for pressure vessel?
Ans : Inlet, outlet, manhole, drain, pressure relief, agitator, level guage,
pressure gauge, temperature element, vent and for steamout.

20. What is preferred location for level instrument nozzles?
Ans : 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.

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


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

23. What is preferred location for vent ?
Ans : AT the top section of drum at the end opposite the steam out
connecton.

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

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

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

PIPING INTERVIEW QUESTIONNAIRE

valves

1. What are the steps in selection of valve?
Ans : 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.
2. What are functions of valves?
Ans : Isolation, regulation, non-return and special purposes.
3. What are isolating valves?
Ans : Gate, ball, plug, piston, diaphragm, butterfly, pinch.
4. What are regulation valves?
Ans : Globe, needle, butterfly, diaphragm, piston, pinch.
5. What are non-return valves?
Ans : check valve,
6. What are special valves?
Ans : multi-port, flush bottom, float, foot, pressure relief, breather.
7. What materials are used for construction of valves?
Ans : Cast iron, bronze, gun metal, carbon steel, stainless steel, alloy
carbon steel, polypropylene and other plastics, special alloys.
8. What is trim?
Ans : Trim is composed of stem, seat surfaces, back seat bushing and
other small internal parts that normally contact the surface fluid.
9. Which standard specifies trim numbers for valve ?
Ans : API 600.
10. What are wetted parts of valve?
Ans : All parts that come in contact with surface fluid are called wetted
parts.
11. What is wire drawing?
Ans : 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.
12. What is straight through valve?
Ans : Valve in which the closing operation of valve is achieved by
90degrees turn of the closing element.
13. What pressure tests are carried out on valves?
Ans : Shell-hydrostatic, seat-hydrostatic, seat-pneumatic
14. What are available valve operators?
Ans : 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 two types of ball valve?
Ans : Full port design and regular port design, according to type of seat,
soft seat and metal seat.
16. What are ball valve body types?
Ans : Single piece, double piece, three piece, the short pattern, long
pattern, sandwitch and flush bottom design.
17. Why ball valves are normally flanged?
Ans : Because of soft seat PTFE which can damage during welding.
18. What are butterfly valve types?
Ans : Double flange type, wafer lug type and wafer type.
19. What are types of check valve?
Ans : Lift check valves and swing check valves.
20. What are non-slam check valves?
Ans : 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 ?
Ans : 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.
22. Where diaphragm valves are used ?
Ans : Used for low pressure corrosive services as shut off valves.
23. What is Barstock Valve?
Ans: Any valve having a body machined from solid metal (barstock).
Usually needle or globe type.
24. What is BIBB Valve?
Ans: A small valve with turned down end, like a faucet.
25. What is Bleed Valve?
Ans: Small valve provided for drawing off liquid.

26. What is BlowDown Valve?
Ans Refers to a plug type disc globe valve used for removing sludge and
sedimentary matter from the bottom of boiler drums, vessels, driplegs
etc.
27. What is Breather Valve?
Ans: A special self acting valve installed on storage tanks etc. to release
vapor or gas on slight increase of internal pressure ( in the region of ½ to
3 ounces per square inch).
28. What is Drip Valve?
Ans: A drain valve fitted to the bottom of a driplet to permit blowdown.
29. What is Flap Valve?
Ans: A non return valve having a hinged disc or rubber or leather flap
used for low pressure lines.
30. What is Hose Valve?
Ans: 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.
31. What is Paper-Stock Valve?
Ans: 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.
32. What is Root Valve?
Ans: 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.
33. What is Slurry valve?
Ans: A knife edge valve used to control flow of non-abrasive slurries.
34. What is Spiral sock valve?
Ans: A valve used to control flow of powders by means of a twistable
fabric tube or sock.
35. What is Throttling valve?
Ans: Any valve used to closely regulate flow in the just-open position.
36. What is Vacuum breaker?
Ans: A special self-acting valve or nay 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.
37. What is Quick acting valve ?
Ans: 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.
38. What is diverting valve ?
Ans : This valve switch flow from one main line to two different outlets.
WYE type and pneumatic control type with no moving part.
39. What is sampling valve?
Ans : Usually of needle or globe pattern, placed in branch line for the
purpose of drawing all samples of process material thru the branch.
40. What are blow off valve?
Ans : It is a variety of globe valve confirming with boiler code
requirements and specially designed for boiler blowoff service. WYE
pattern and angle type, used to remove air and other gases from boilers
etc.
41. What is relief valve?
Ans : 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.
42. What is safety valve?
Ans : Rapid opening(popping action) full flow valve for air and other
gases.
43. What is foot valve?
Ans : Valve used to maintain a head of water on the suction side of sump
pump, basically a lift check valve with integrated strainer.
44. What is float valve?
Ans : 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.
45. What are flush bottom valves?
Ans : Special type of valves used to drain out the piping, reactors and
vessels, attached on pad type nozzles.
46. What are types of flush bottom valves?
Ans : Valves with discs opening into the tank and valves with disks into
the valve.
47. What are the uses of three-way valve?
Ans : Alternate connection of the two supply lines to a common delivery
vise versa, isolating one safety valve, division of flow with isolation
facility.
48. What are uses of four way valve?
Ans : Reversal of pump suction and delivery, By pass of strainer or
meter, reversal of flow through filter, heat exchanger or dryer.
49. What is metal seated lubricated plug valve?
Ans : A plug valve with no plastic material, where grease is applied to
contacting surfaces for easy operation.
50. What are three patterns of plug valve design?
Ans : Regular pattern, short pattern and ventury pattern.

51. What is regular pattern plug valve?
Ans : Rectangular port, area almost equal to pipe bore, smooth transition
from round body to rectangular port, for minimum pressure loss.
52. What are short pattern plug valve?
Ans : Valves with face to face dimension of gate valve, as a alternative to
gate valve.
53. What are ventury pattern plug valve?
Ans : Change of section through the body throat so graded to have
ventury effect, minimum pressure loss.
54. What are inverted plug design valve?
Ans : Plug valve with taper portion up of plug. For 8” and higher size.
55. What is pressure balanced plug valve?
Ans : With holes in port top and bottom connecting two chambers on top
and bottom of plug, to reduce turning effort.
56. What are Teflon sleeved plug valve?
Ans : PTFE sleeve between plug and body of valve, low turning effort,
minimum friction, temperature limitation, anti static design possible.
57. What are permasil plug valve?
Ans : Plug valves with Teflon seat instead of sleeves, for on off
applications, can handle clean viscous and corrosive liqiuids, Graphite seat
for high temperature applications. Drip tight shut off not possible.
58. What are eccentric plug valve?
Ans : Off center plug, corrosive and abrasive service, on off action,
moves into and away from seat eliminating abrasive wear.
59. What is dimensional standard for plug valve?
Ans : API 599.
60. What is pinch valve?
Ans : Similar to diaphragm valve, with sleeves of rubber or PTFE, which
get sqeezed to control or stop the flow, Cast iron body, for very low
service pressures like isolation of hose connections, manufacture
standard.
61. What is needle valve?
Ans :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.
62. How to install a globe valve ?
Ans : 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.
63. What are globe valve port types?
Ans : Full port: More than 85% of bore size, Reducer port: One size less
than the connected pipe.
64. What are globe valve disk types?
Ans :Flat faced type for positive shutoff, loose plug type for plug renewal
or needle type for finer control.
65. What are characteristics of globe valve stem?
Ans : Always rising design, with disk nut at the lower end and handwheel
at upper end.
66. What are types of globe valve?
Ans : Angle globe valve, plug type disc globe valve, wye-body globe
valve, composite disc globe valve, double disc globe valve.
67. What is angle globe valve?
Ans : Ends at 90 degree to save elbow, higher pressure drop.
68. Where plug type disc globe valve is used?
Ans : For severe regulating service with gritty liquids such as boiler
feedwater and for blow off service.
69. Where WYE body globe valve is used ?
Ans : In line ports with stem emerging at 45 degree, for erosive fluids
due to smoother flow pattern.
70. What is double disc globe valve ?
Ans : Has two discs bearing on separate seats spaced apart, on a single
shaft, for low torque, used for control valves.
71. What are port types for gate valves?
Ans : Full port and reduced port. Default is reduced bore. Full port has to
be specified in bom.
72. How to close a gate valve ?
Ans :Turn the handwheel in clockwise direction.
73. What is lantern ring?
Ans : It’s a collection point to drain off any hazardous seepages or as a
point where lubricant can be injected, it is in the middle of packing rings.
74. What are types of gate valves?
Ans : Solid plane wedge, solid flexible wedge, split wedge, double disc
paralles seats, double disc wedge, single disc single seat gate or slide,
single disc parallel seats, plug gate valve.
75. What are the types of bonnets?
Ans : Bolted bonnet, bellow sealed bonnet, screwed on bonnet, union
bonnets, A U-bolt and clamp type bonnet, breechlock bonnet, pressure
seal bonnet.