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Piping Design Engineer Interview Questions:- Part-3


1. What is the ASME code followed for design of piping systems in Process piping (Refineries & Chemical Industries)?
A) B31.1 B) B31.3 C) B31.5 D) B31.9
Ans: (B)
2. What do you mean by following items?
A) ISLB-400 B) ISMB-600 C) ISHB-350 D) ISMC-300 E) ISJB-150 F) ISLB-200 G) ISMB-450 H) ISWB-400 I) ISJC-200 J) ISLC-350 K) ISMC-250
A)Indian STD light weight beam, Web size – 400
B)Indian STD medium weight beam, Web size – 600
C)Indian STD ‘H’ beam, Web size – 350
D)Indian STD medium weight channel, Web size –300
E)Indian STD junior beam, Web size – 150
F)Indian STD lightweight beam, Web size – 200
G)Indian STD medium weight beam, Web size – 450
H)Indian STD wide flange beam, Web size – 400
I)Indian STD junior channel, Web size – 200
J)Indian STD lightweight channel, Web size – 350
K)Indian STD medium weight channel, Web size – 250
3. What is this item?
A) ISA-100X100X12 B) ISA-80X50X10 C) ISLT-100X100
A) Equal angle size 100×12 THK,B) Unequal angle size 80x50x10 THK,C) Indian STD lightweight tee bar size 100×100
4. What is the difference between stub in and stub on branches? Which one is preferred?
For branching of one size lesser of run pipe, Stub On is preferred. For other branching less than one size of run pipe stub in is preferred. The Design is based on ANSI B 31.3
5. What is the difference between Pipe and Tube?
Pipe is identified by NB and thickness is defined by Schedule whereas Tube is identified by OD.
6. From which size on wards NB of pipe is equal to OD of Pipe?
From the size 14” and on wards NB = OD of pipe.
7. Write down the outside diameter of following pipe?
A) 3 inch B) 6 inch C) 10 inch D) 14 inch
A)3 inch = 88.9mm ,B)6 inch = 168.28mm,C)10 inch = 273.06mm,D)14 inch = 355 mm (OD= SizeX25.4)
8. What is the difference between machine bolt and stud bolt?
Machine bolt has a head on one side and nut on other side but stud bolt have nuts on both sides.
9. What is soluble dam?
Soluble dam is a water-soluble material used for restricting the purging gas within the pipe.
10. While welding of pipe trunion to pipe/reinforcement pad you have to put a hole or leave some portion of welding why?
For venting of hot gas which may get generated due to welding.
11. What do you mean by following type of welding?
1. SMAW 2. TIG
12. What should be the radius of long radius elbow?
1.5D (Where “D” is the diameter of the pipe)
13. Normally where do we use the following?
A) Eccentric reducers (ER) B) Concentric reducers (CR)
A)ER = Pump suction to avoid Cavitations, to maintain elevation (BOP) in rack,B)CR = Pump discharge, vertical pipeline etc.
14. Concentric reducer is used in pump suction. (Yes / No). Explain.
No. Air pockets may form if concentric reducer is used at pump suction, which results in Cavitations, and cause damage to Pump. To avoid this problem, Eccentric Reducer with Flat Side Up (FSU) is used in Pump Suction.
15. What do you mean by Cavitation in Pump?
A pump is designed to handle liquid, not vapour. Vapour forms if the pressure in the pump falls below the liquid’s vapour pressure. The vapour pressure occurs right at the impeller inlet where a sharp pressure drop occurs. The impeller rapidly builds up the pressure which collapses vapour bubbles causing cavitation and damage. This is avoided by maintaining sufficient NPSH.
(Cavitation implies cavities or holes in the fluid we are pumping. These holes can also be described as bubbles, so cavitation is really about the formation of bubbles and their collapse. Bubbles form whenever liquid boils. It can be avoided by providing sufficient NPSH.)

16. What do you mean by NPSH? How do you calculate it?
NPSH = Net Positive Suction Head. NPSH is the pressure available at the pump suction after vapour pressure is subtracted. It is calculated as: Static head + surface pressure head – the vapor pressure of your product – the friction losses in the piping, valves and fittings. It thus reflects the amount of head loss that the pump can sustain internally before vapor pressure is reached.
17. What is the ASTM code for the following?
A) CS pipe B) CS fittings C) CS flanges D) AS pipe P5/P11 E) Cast CS Valves
A) CS pipe = A106 Gr.B, B)CS fittings = A234 Gr.WPB/WPBW, C)CS flanges = A105, D)AS pipe = A335 Gr P5/P11, E)Cast CS Valves = A216 Gr. WCB
18. What is the thumb rule to calculate spanner size for given bolt?
1.5 x diameter of Bolt
19. What is the thumb rule to calculate Current required for Welding?
Current (Amp) = [Diameter of Electrode (mm) X 40] + 20
20. What is steam tracing? How do we decide the location of SSM & CRM?
Steam Tracing is a process which is used to prevent the fluid passing through a process line from freezing by keeping the temperature high enough for free flow of fluid and thus maintaining palpability. SSM and CRM are generally located 38M max for open system and 24 M max for closed system when we use LP Steam up to 3.5-kg/sq cm. as a heating media.
21. Which piping items will you drop down before conducting Flushing and Hydro test?
Items like Control Valve, Orifice plates, Rotameters, safety valves; Thermo wells are dropped or replaced with temporary spools before hydro test.
22. Why do we provide a Dampener in the Piping of Reciprocating Pump?
To take care of Pulsation.
23. Why do we provide Full Bore Valve in connecting pipeline of Launcher/Receiver?
For Pigging.
24. Which parameters will u check during checking Piping Isometrics?
Bill of Material, Pipe Routing w.r.t. GAD, Supporting arrangement, details of insulation, hydro test pressure, painting specs and provision of Vent and Drains at appropriate locations.
25. What is the ANSI/ASME dimensional standard for steel flanges & fittings?
A) B16.3 B) B16.5 C) B16.9 D) B16.10
Ans: (B)
26. How can flanges be classified based on facing?
A. Flat Face B. Raised Face C. Tongue and groove D. Ring type joint
27. What do you mean by AARH (Flange Finish)?
Arithmetic Average Roughness Height.
28. Which are the different types of Gaskets?
Full Face, Spiral Wound, Octagonal Ring Type, Metal Jacketed and Inside Bolt Circle.
29. What should be the relative hardness between the RTJ gasket and flange groove?
For a RTJ flange, the joint ring should have a 30-40 Vickers hardness less than that of the mating face of flange. (Brinnel hardness for RTJ groove shall be 20-50 BHN more than the corresponding gasket hardness)
30. From which side of pipe will you take a branch connection?
When Fluid is Gas, Air or Steam and Cryogenic Service – Topside. When Fluid is Liquid – Bottom Side.

31. Why don’t we take a branch for Cryogenic Service from bottom side though the fluid is in liquid state
There is the chance of Ice formation during normal operation and since ice flows from the bottom of the pipe it will block the branch pipe connection.
32. Why do we provide Drip Leg in Steam Line?
To remove Condensate when there is a rise in the pipe along the flow direction. If we do not provide the drip leg in steam line, the condensate which forms inside the pipe will result in Water Hammer effect causing damage to piping system.
33. Which standard and codes will you refer while designing the piping?
Following are the codes and standards –
ASME SEC I: Rules for construction of Power Boilers.
ASME SEC VIII: Rules for construction of Pressure Vessels.
ASME B 31.1: Power Piping
ASME B 31.3: Process Piping
ASME B 31.4: Pipeline Transportation system for liquid hydrocarbon & other liquids.
API RP 520: Sizing selection and installation of Pressure Relieving Devices in refineries
API Std 610: Centrifugal Pumps for Petroleum, Heavy Duty Chemical and Gas Industry Services.
ANSI/NEMA SM 23: Steam Turbines for Mechanical Drive Services.
API Std 617: Centrifugal Compressor for Petroleum, Chemical and Gas Industry Service.
EJMA: Expansion Joints Manufacturer’s Association.
OISD – 118: Layout for Oil and Gas Installations.
IBR: Indian Boiler Regulations.
NACE MR – 0175: Sulfide Stress Cracking Resistant Metallic Materials for Oilfield Equipment.
NACE MR – 0284: Evaluation of Pipeline and Pressure Vessel Steel for Resistance to Hydrogen Induced Cracking.
NACE TM – 0177: Laboratory Testing of Metals for Resistance to Sulfide Stress Cracking in H2S Environment.
34. How do you support any small size HDPE/PVC (Plastic) pipe?
It should be supported continuously by using channel or Angle so that line should not sag or fall from the sleeper/rack due to uneven expansion because of Hot Temp.
35. Why do we provide High Point Vent (HPV) and Low Point Drain (LPD) in piping?
HPV – for removing Air during Hydro-test.
LPD – for draining water after conducting Hydro-test.
36. What do you mean by IBR and which lines comes under IBR purview?
IBR = Indian Boiler Regulation Act.
Steam lines with conditions listed bellow comes under IBR purview –
Lines for which design pressure is 3.5 kg/sq cm and above.
Line size above 10” having design pressure 1.0 kg/sq cm and above.
Boiler feed water lines to steam generator, condensate lines to steam generator and flash drum.
37. What are Weldolet and Sockolet? And where they are used?
Weldolet and Sockolet are basically self reinforced fittings. Weldolet is used for Butt weld branch connection where standard tee is not available due to size restrictions and the piping is of critical / high pressure service. Sockolet is used for socket welding branch connection, which require reinforcing pad.
38. What is the MOC for Super heated high pressure Steam Lines?
A 335 Gr P I / P II, Composition: 0.5 Mo (P1) / 1.25 % Cr-.5% Mo (P11)
39. What is the normal upstream and downstream straight length of orifice flow meter?
Upstream – 15D Downstream – 5D
40. What are the essential data required for the preparation of equipment layout?
1) PFD and P&ID 2. Project Design data 3. Equipment Sizes & Buildings
41. What are the various statutory requirements to be considered during layout?
State Industrial Development Corporation (SIDC)
Central / State Environmental Pollution Control Boards (PCBS)
Factory Inspectorate
State Electricity Boards
Chief Controller of Explosives (CCOE)
Static & Pressure Vessel Rules (SMPV)
Tariff Advisory Committee
Aviation Laws
Chief Inspector of Boilers (CIB)
Oil Industry Directorate (OISD)
Food and Drug Administration (FDA)
Ministry of Environment and Forest (MoEF)
42. What do you mean by Insulated Joint?
Insulating Joints are a prefabricated, non-separable union used to isolate specific sections of Pipelines to prevent corrosion caused by stray electrical currents or interference from other pipelines and power transmission cables.
43. What do you mean by Composite Flange?
The flange that is made up of more than one MOC is called a Composite flange.
A. Lap Joint Flanges. Insert Flanges are a specialty in the arena of pipe size flanges and consist of two parts – the insert and the flange ring. The flange ring is the outer part of the insert flange assembly, containing the boltholes. The two-piece construction of the insert flange also offers the economy of matching the insert material to the process pipe (usually some corrosion resistant alloy) while the outer flange ring may be manufactured from steel. When the environment requires the flange ring to be made of some alloy the rotating feature is still maintained.
B. RF flanges with Raised of one MOC and rest of the flange with different MOC
C. RF blind flange with an overlay of 90/10 Cuni for Seawater service.
44. What is mean by ‘PWHT’? Why it is required?
POST WELD HEAT TREATMENT” This is done to remove residual stress left in the joint, which may cause brittle fracture.
45. Describe different types of destructive and non-destructive tests?
DESTRUCTIVE TEST: Bend test, Tensile test, Impact test, and Hardness test.
NON-DESTRUCTIVE TEST: DPT, MPT, Radiography and ultrasonic test
46. What are Insulating Gasket Kits?
Insulation gasket kits are designed to combat the effects of corrosion often found in flanged pipe systems. Galvanic corrosion between dissimilar metal flanges (flow of currents), flange insulation associated with cathodic protection of underground piping are also the places where Insulating gasket kits are used. It consists of
Gasket Neoprene faced Phenolic /Glass Reinforced Epoxy (G10)
Insulation sleeve Reinforced Phenolic/Nylon/Polyethylene/(G10)
Insulation washer Reinforced Phenolic/Nylon/Polyethylene/(G10)
Plated Washer Electro plated steel washer
47. What do you mean by Jacketed Piping?
Piping which is recognized as providing the most uniform application of heat to the process, as well as maintaining the most uniform processing temperatures where steam tracing is not capable of maintaining the temperature of fluid constant. Usually used for molten sulphur, Polymers service.
48. What is the minimum distance to be maintained between two welds in a pipe?
The rule of thumb is that the minimum distance between adjacent butt welds is 1D. If not, it is never closer than 1-1/2″. This is supposedly to prevent the overlap of HAZ s. Minimum spacing of circumferential welds between center lines shall not be less than 4 times the pipe wall thickness or 25 mm whichever is greater.
49. What are the different hardness tests carried out?
Brinell Hardness Test
Rockwell Hardness test
Vicker Hardness Test
50. What is the relation between Brinell Hardness No and Rockwell Hardness No?
22 HRC (Rockwell Hardness) = 238 BHN (Brinell Hardness No) Harder

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