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60+ Frequently Asking Piping Engineering Interview Question


Question 1 :-What Are The Major Parameters You Must Address While Making A Spring Data sheet?
Answer : 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.


Question 2 :-How To Calculate The Height Of A Variable Spring Hanger?
Answer : 
  • 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.
Question 3 :-Can You Select A Proper Spring Hanger If You Do Not Make It Program Defined In Your Software? What Is The Procedure?
Answer : 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.


Question 4 :-What Do You Mean By Variability? What Is The Industry Approved Limit For Variability?
Answer : 
Variability= (Hot Load-Cold load)/Hot load = (Spring Constant × displacement)/Hot load.
Limit for variability for variable spring hangers is 25%.

Question 5 :- What Is The Main Difference Between Constant And Variable Spring Hanger? When To Use These Hangers?
Answer : 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.
Question 6 :-What Is Preferred Location For Drain?
Answer : Must be located at the bottom section of drum.


Question 7 :-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 8 :-What Are Functions Of Valves?
Answer : Isolation, regulation, non-return and special purposes.


Question 9 :-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 10 :-What Are Isolating Valves?
Answer :  Gate, ball, plug, piston, diaphragm, butterfly, pinch.


Question 11 :-What Are Special Valves?
Answer :  Multi-port, flush bottom, float, foot, pressure relief, breather.


Question 12 :-What Are Regulating Valves?
Answer :  Globe, needle, butterfly, diaphragm, piston, punch.


Question 13 :-What Are Non-return Valves?
Answer :  Check valve.


Question 14 :-What Are Wetted Parts Of Valve?
Answer :  All parts that come in contact with surface fluid are called wetted parts.

Question 15 :-What Is Straight Through Valve?
Answer : Valve in which the closing operation of valve is achieved by 90 degrees turn of the closing element.


Question 16 :- What Are Available Valve Operators?
Answer :  Hand-lever, hand-wheel, chain operator, gear operator etc.

Question 17 :-What Pressure Tests Are Carried Out On Valves?
Answer : Shell-hydrostatic, seat-hydrostatic, seat-pneumatic.


Question 18 :-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.


Question 19 :-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 closed tightly.

Question 20 :-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.


Question 21 :-What are ball valve body types?
Answer : Single piece, double piece, three piece, the short pattern, long pattern, sandwitch and flush bottom design.

Question 22 :-Why ball valves are normally flanged?
Answer : Because of soft seat PTFE which can damage during welding.

Question 23 :-What are butterfly valve types?
Answer : Double flange type, wafer lug type and wafer type.


Question 24 :-What are types of check valve?
Answer : Lift check valves and swing check valves.

Question 25 :-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.


Question 26 :- What Is The Full Form Of Asme?
Answer :  American Society for Mechanical Engineers.

Question 27 :- What Is The Full Form Of NPSH?
Answer :  NPSH: Net Positive Suction Head.


Question 28 :- Which Piping Code Is Used For Power Piping And Which Code Is Used For Process Piping Design?
Answer : 
  • Power Piping: ASME B 31.1
  • Process Piping: ASME B 31.3

Question 29 :- What Are The Main Differences Between Asme B 31.1 And Asme B 31.3?
Answer :  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.
Question 30 :- 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.
  • 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).
Question 31 :- What Is The Software Available For Performing Piping Stress Analysis?
Answer :  Caesar II, Auto Pipe etc.


Question 32 :- What are the types of compressors?
Answer : Positive Displacement, Centrifugal and Axial, rotary screw, rotary vane, rotary lobe, dynamic, liquid ring compressors.


Question 33 :- How Centrifugal compressors work ?
Answer :  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.


Question 34 :- 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.


Question 35 :- What are types of compressor drives?
Answer :  Electric motor, gas turbine, steam turbine and gas engine.


Question 36 :- 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.

Question 37 :- What factors to be considered while designing compressor housing?
Answer : Operation, Maintenance, Climate conditions, Safety, Economics.


Question 38 :- What are compressor suction line requirements ?
Answer :  Minimum 3D straight pipe between elbow and inlet nozzle, increases based on inlet piping layout. 4D


Question 39 :- What are the types of seal oil system?
Answer :  Gravity and pressurized.


Question 40 :- What are the compressor housing design points?
Answer :  Floor elevation, building width, building elevation, hook centerline elevation.


Question 41 :-  What is velocity head?
Answer :  The head loss caused by the consumed power to accelerate stationary fluid to suction line velocity during pump startup. It’s about 1 ft.


Question 42 :- How is suction line supported?
Answer : Commonly supported under the elbow adjacent to the pump nozzle.


Question 43 :- Normally where do we use: i) Eccentric reducer, ii) Concentric reducer?
Answer : 
  • i) Eccentric reducer: Pump suction to avoid cavitation, to maintain (BOP) in rack
  • ii) Concentric reducer: Pump discharge, vertical pipeline etc.,


Question 44 :- What are suction line requirements?
Answer :  To flat reducer, strainer, block valve, no pockets, as short as possible with consideration to stress, min straight length of 3D.


Question 45 :- What is special requirement for discharge line of positive displacement pump?
Answer : Relief valve whose discharge is connected in suction line between the isolating valve and the pump.


Question 46 :- Concentric reducer is used in pump suction. YES/NO? Explain.?
Answer : NO. Air pocket may form if concentric reducer is used at pump suction, which results in cavitation and causes damage to pump. To avoid this eccentric with Flat Side Up (FSU) is used in pump suction.


Question 47 :- How should the suction line reducer be placed ?
Answer : It should be placed top flat.

Question 48 :- What is Cavitation?
Answer : Cavitation is a rapid collapse of vapour pressure that can produce noise, result in loss of head and capacity and create a severe erosion of the impeller and casing surface in the adjacent inlet areas.The vapour pressure occurs right at the impeller inlet where a share pressure drop occurs.


Question 49 :- While welding of pipe trunion to pipe/reinforcement pad you have to put a hole or leave some portion of welding. why?
Answer : For venting of hot gas which may get generate due to welding.


Question 50 :- What is the Full Form of SMAW & TIG ?
Answer : 
  • SMAW: Shielded Metal Arc Welding
  • TIG: Tungsten Inter Gas welding.

Question 51 :- Where are positive displacement pumps used?
Answer : Used to move viscous liquids, injects chemicals or additives into a system, or pump quantities too small for centrifugal pumps.


Question 52 :- What is accepted distance between pumps?
Answer : 1200 MM / 4 feet.


Question 53 :- How can flanges be classified based on facing?
Answer : 
  • Flat face
  • Raised face
  • Tongue and Groove
  • Ring type joint.


Question 54 :- What are different types of Gaskets?
Answer : Full face, spiral wound, Octagonal ring type, Metal jacket and inside bolt circle.


Question 55 :-  Where Double pipe or Fin Tube Exchangers used?
Answer : Used when the liquid has a greater resistance to heat flow than another or when the surface area is small.

Question 56 :- Why do we provide Drip leg in steam line?
Answer : To remove condensate when there is a rise in the pipe along the flow direction. If we do not provide the drip leg in streamline, the condensate forms inside the pipe will result in water hammer effect causing damage to the piping system.

Question 57 :- What is mean by ‘PWHT’? Why is it needed?
Answer : ‘Post Weld Heat Treatment’ This is done to remove residual stress left in the joint which may cause a brittle fracture.


Question 58 :- What should be clearance between flanges of exchangers?
Answer : 1000 MM.


Question 59 :- What are the types of tube arrangments?
Answer : U-tube, Fixed tube, kettle arrangement.


Question 60 :- What are drum internals?
Answer :  Demister pads, Baffles, Vortex breakers, Distribution piping.

Question 61 :- What is preferred location for level instrument nozzles?
Answer :  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.


Question 62 :- What is preferred location for process nozzles on drum?
Answer :  Minimum from the tangent line.


Question 63 :- What are drum supports?
Answer :  Skirt for large drums, legs, lugs, saddles for horizontal drums.


Question 64 :- What is preferred location for steam out nozzle on drum?
Answer :  At the end opposite to the maintenance access.


Question 65 :- What are necessary nozzles for non-pressure vessel?
Answer :  Inlet, outlet, vent, manhole, drain, overflow, agitator, temperature element, level instrument, and steamout connection.


Question 66 :- What are necessary nozzles for pressure vessel?
Answer :  Inlet, outlet, manhole, drain, pressure relief, agitator, level guage, pressure gauge, temperature element, vent and for steamout.

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