The Piping Eng Interview

You will tend to get many different answers to most of these questions. Some questions will have what seems to be an absolute right answer. Others will not. These other answers will be based on the type and level of training and experience of each responder. Each answer will appear to be wrong to some readers and right to others.

Example:
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 steam piping with a low point 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: This is a very controversial point. You will get all kinds of answers to this. My answer is “never put the eccentric reducer in the bottom flat position.”

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 to 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 specialty piping (SP) items do you know? Why it is called a piping special? Why do we not 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 Unit Header Block Valves situation 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 hoses and 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 cooled 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. An air fin cooler (2 air coolers with each having 2 inlet nozzles) needs a typical piping arrangement. How many types of piping arrangement are possible?
Answer: There are a number of ways to pipe a Fin-Fan cooler depending on what the P&ID call for?

#3.
Hydrofluoric acid is extremely corrosive and a contact poison. It should be handled with extreme care, beyond that accorded to other mineral acids, in part because of its low dissociation constant, which allows HF to penetrate tissue more quickly. Symptoms of exposure to hydrofluoric acid may not be immediately evident. HF interferes with nerve function and burns may not initially be painful. Accidental exposures can go unnoticed, delaying treatment and increasing the extent and seriousness of the injury.[5] HF is known to etch bone, and since it penetrates the skin it can weaken bones without destroying the skin.[6] More seriously, it can absorb into blood through skin and react with blood calcium, causing cardiac arrest.

In the body, hydrofluoric acid reacts with the ubiquitous biologically important ions Ca2+ and Mg2+. In some cases, exposures can lead to hypocalcemia. Thus, hydrofluoric acid exposure is often treated with calcium gluconate, a source of Ca2+ that sequesters the fluoride ions. HF chemical burns can be treated with a water wash and 2.5% calcium gluconate gel[7][8][9] or special rinsing solutions.[10][11] However, because it is absorbed, medical treatment is necessary — rinsing off is not enough. In some cases, amputation may be required.

#6
The use of Bolts and Gaskets that are not compatible with the SS Spec could result in stress corrosion.

#10
The primary purpose of a “Double Block & Bleed” is Safety. This should be easy to understand. If the service connected to the vessel is low pressure steam and the vessel has a higher operating pressure and some unauthorized person opens both valves there could be contamination of the steam system, damage to the steam piping and injury or death to the operator.

The next better “Safety” set-up would be Double Block Valve with a Spec Blind between the valves. The need to break the flanges to spin the spec blind maybe would make the person to think twice.