Monday, June 11, 2012

Typical Questions For Piping Engineer’s Knowledge Testing (With Answers)


Note: Each answer will appear to be wrong to some readers and right to others. Some questions will have what seems to be an absolute right answer. Others will not. So if you have got any good answer for below questions, leave us a comment. Find more details see at the end of article.

1. Can you explain in detail three or more major differences between code ANSI B31.1 and code ANSI B31.3?

Answer: There is only one major difference between the two, B31.1 is for Power Piping and B31.3 is for Refinery/Chemical Plant Piping.

2. There is a power plant inside a Process refinery. Where exactly the ANSI B31.1 & ANSI B31.3 scope break occurs?

Answer: Based on my experience there were two cases. Case #1, B31.1 stopped at the Power Plant Unit block valves. Thus all piping inside the Power Plant was B31.1. Case #2, B31.1 stopped at the equipment (Boiler) isolation block valves and then all other piping was B31.3. This is normally the choice of the owner/operator/client.

3. Which of the following piping system is more health hazardous. A) Fuel oil piping b) Process piping with Caustic c) process piping with HF acid d) Sulphuric acid piping.

Answer: c) process piping with HF acid

4. There is a steam piping with low pocket but without steam trap. What will be worst consequence of this layout?

Answer: There will be a build up of condensate to the point that a slug will be pushed by the steam flow. This slug of condensate will cause “water hammer” and could rip the piping apart.

5. In what circumstance, the reducer of a pump suction piping will be in bottom flat position. Explain why the reducer should be so.

Answer: When reducers are placed in pipe Rack they are generally bottom side flat to maintain BOP to facilitate supporting. (Answer Credit: Samir Kumar)

6. A P&ID shows a spec break (at Flange) between carbon steel & stainless steel specification. What additional arrangements you have to make for that dissimilar material flange joint?

Answer: Use the Gasket and bolts from the SS spec.

7. A stainless steel piping specification mentions Galvanized carbons steel bolts. What is your first reaction ti this and how do you rectify it?

Answer: If that is what the Spec call for then that is what I am supposed to use. But, I would ask the Piping Material Engineer (PME) why he/she specified galvanized bolts.

8. How many types of piping specialty items do you know? Why it is called a piping special? Why not we include them in standard piping specification.

Answer: I could possibly count 50 or more depending on the PME and how the piping material specs were developed. They are called them SP items because they are NOT written into the normal Piping Material (Line Class) Specifications. They are not included because they are normally of limited use, purchased from a limited product line vendor and are often after thoughts.

9. Draw a typical steam trap station layout and explain why the existence of a by-pass line around the trap is not a good idea, when the condensate is returning to a condensate header?

Answer: (No drawing) It is not advisable to have a bypass around a steam trap because the block valve could be left open and defeat the purpose of the trap.

10. Explain what is a “Double block & Bleed” valve? Why we need a bleed valve? When do we use this?

Answer: The primary purpose of a “Double Block & Bleed” is Safety. However it is not fail safe. The next better “Safety” set-up would be Double Block Valve with a Spec Blind between the valves. The higher level of safety would be double block valves with a removable spool for absolute isolation.

11. In a typical tie-in where should the spectacle blind be inserted? a) after block valve and towards existing plant b) before block valve and towards new plant. Explain why.

Answer: The Spec Blind shall be placed on the Unit side of the Unit Block valves. This placement allows for the closing of the Unit isolation block valve, the unit side is depressured and drained. Then the spec blind can be installed for isolation of the unit.

12. “Stress intensification factor (SIF)” Where do we use this? Explain this term. How many types of these SIF’s exist?

Answer: Stress Intensification Factor (SIF) is a multiplier on nominal stress for typically bend and intersection components so that the effect of geometry and welding can be considered in a beam analysis. Stress Intensification Factors form the basis of most stress analysis of piping systems. As for the quantity, ask a Stress Engineer.

13. When all design parameters are same, whose thermal expansion is higher among the following? A) Carbon steel b) Stainless steel c) Duplex steel d) Cast Iron e) Galvanized Carbon steel.

Answer: b) Stainless steel

14. In a hose station the hose couplings used for water, air & steam should be different type. Do you agree? Explain your view.

Answer: I agree. If they are all the same then the hoses can be connected to the wrong services and could result in the injury of an operator (i.e.: thinking the hose is connected to water when it is connected to steam).

15. What is your view on the usage of Metallic expansion joints? When they become necessary and when they could be avoided?

Answer: I do everything I can as a piping designer to avoid the use of all types of expansion joints. Expansion joints are always the weakest point in any system where they are used.

16. A water cooler heat exchanger, located on a 20 m high structural platform. Water header is located u/g. What precaution do you take, in case of Pressure loss in cooling water header?

Answer: I do not understand this question it does not appear to be a piping issue. I would assume that the cooling water system has a (loss of) pressure sensor and the plant shut-down alarms and sequence would be activated.

17. In what order do you arrange the pipes in the Pipe rack and why? How much % of area should be reserved for Future expansion? Specify a range.

Answer: The largest hottest lines on the outside edge of the pipe rack working in with cooler lines in towards the middle of the rack. This allows the longer loop legs as you lay the loops back over the other lines to the other side of the rack and back. The lower temperature loops would be “nested” inside the larger, hotter loops. 

“Future rack space” is normally at the direction of the Client. It may be anything from 0% to as much as 25%.

18. When a utility line (like condensate or water etc) is connected permanently to a process piping what precaution we have to take to avoid cross contamination?

Answer: Option #1, double block valve with a drop-out spool.
Option #2, Double block valve with a spec blind.
Option #3, double block valves with a bleed valve.

19. A air fin cooler (2 air coolers with each having 2 inlet nozzles) needs a Typical piping arrangement. How many types of piping arrangement is possible.

Answer: There are a number of ways to pipe a Fin-Fan cooler depending on what the P&ID call for?

Thanks to (for the answers)

Mahathir Che Ap Piping Designer

Still some answers are not so much satisfactory with total explanation, so if any of you does not agree with any of the above answers, give me feedback by leaving comments on this article or mail me the answers at When i would receive the answers from any source, i would publish it here & would update the article accordingly.

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  1. I like it,the answers are almost satisfactory and i hope this type of articles will be posted continuously.It helps me a lot and i am very thank full to you.
    Keep it up 

  2. Thank you Varun for your appreciation. If you can also some material which you would like to share with all, please do send us that to . That would be really helpful and you would be given full credit for that. Thanks

  3. For Question number: 6 - the answer is wrong.
    The right answer is "Insulating gasket kit".
    Reason:  It is used in order to avoid stray currents generated due to contact of dissimilar metals which would result in galvanic corrosion on the flanges. this may lead to the failure of the piping system.

  4. Thanks for correcting us Piping Engineer :) I'll make the proper modifications in post as required now.

  5. Thank you very much Mr.Ankit. Do you have SP3D softwere.

  6. Answer to qustion 5- Normally Flat side bottom reducer used for slurry pump suction line so as to avoid the accumulation of solids inside the suction lines.

  7. answer to question no 16
    please to be put loop for liquid holdup at discharge side if pressure drop in header then sufficient amt of liquid hold are there in cooler.

  8. answer to question no 16
    please to be put loop for liquid holdup at discharge side if pressure drop in header then sufficient amt of liquid hold are there in cooler.

  9. answer to question no 16
    please to be put loop for liquid holdup at discharge side if pressure drop in header then sufficient amt of liquid hold are there in cooler.

  10. Does anyone know how to calculate SIF for Y pipe? I mean by using FEM software like ANSYS or Abaqus.

  11. The answer to no. 6 is not wrong and is the usual practice in the process piping industry globally-the bolts and gaskets of the higher grade material, i.e. stainless steel material, should be used. Why? Though galvanic corrosion could set in because of dissimilar metals, the use of insulating kits may not be feasible at all times especially when higher temperatures are concerned. Insulating kits are made of composite materials (phenol or fiberglass) and have limited usage at higher temperatures normally encountered in process plants.

  12. Answer to no.19: The answer is quite honest. One basic fact regarding aircooler piping design is to know how it is constructed, how it is supported and knowing the allowable loads per API 661. Most aircoolers are constructed (there are other ways that may need verification with equipment engineer) very much like how a cassette tape slides into a slot. The whole aircooler box (containing the finned tubes) are installed on huge C-shape slots permitting the aircooler to slide a few inches lengthwise, sideways and even upward (usually 1/4" or 6 mm) with thermal expansion caused by attached piping. For the most part, a "waterfall" piping arrangement or what I call a "piano" arrangement wherein pipes flow down from a header to the nozzles, is the most ideal for airfin coolers. The routing has to be reasonably arranged with a few elbows and pipe length for pipe flexibility to ensure nozzle loads on airfin coolers (which are commonly low) are not exceeded. Some companies would require that aircoolers be at least twice or three times the allowable loads per API 661.

  13. Answer to no.7: The combination of zinc and carbon on the galvanized carbon steel bolts are not good for use on stainless steel piping and would result in iron particle contamination and/or zinc attack on the stainless steel items. The bolts should be replaced with stainless steel bolts to prevent dissimilar metal contamination.


  15. Very interesting questions. More Piping quiz are available at

  16. Ans For que. No. 5: Actually at the pump inlet reducers are flat site down to avoid the cavitation at the pump inlet which would damage impellers and gives abnormal sound and leads to damage of pump casing too.



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