JGC Technical Exam

General Engineering & EPC Concepts

1. Question: What is the primary difference between a PFD (Process Flow Diagram) and a P&ID (Piping and Instrumentation Diagram)?

  • Answer: A P&ID includes detailed information about piping, instrumentation, and control loops, whereas a PFD shows only the main process flow and major equipment.

  • Explanation: In EPC, P&IDs are used by all disciplines for detailed design, while PFDs are used by Process Engineers for mass and energy balance.

2. Question: Which valve type is best suited for "throttling" (regulating) flow?

  • Answer: Globe Valve.

  • Explanation: Unlike gate valves, globe valves are designed with a plug that can be adjusted to vary the flow rate precisely.

3. Question: What does the term "Lump Sum Turn Key" (LSTK) mean in a JGC contract?

  • Answer: The contractor agrees to complete the project for a fixed price and hand over a fully operational facility to the client.

  • Explanation: This shifts the risk of cost overruns to the contractor (JGC), making efficiency and accurate engineering critical.

4. Question: Convert 5 Bar to PSI (approximate).

  • Answer: 72.5 PSI.

  • Explanation: 1 Bar≈14.5 PSI1 \text{ Bar} \approx 14.5 \text{ PSI}. Quick unit conversion is a common "stress test" in technical exams.

5. Question: What is the purpose of a "Check Valve"?

  • Answer: To prevent backflow in a piping system.

  • Explanation: It is a unidirectional valve that allows fluid to flow in only one direction, protecting equipment like pumps from reverse flow.

Mechanical & Chemical Engineering

6. Question: What is NPSH, and why is it important for pumps?

  • Answer: Net Positive Suction Head; it is required to prevent cavitation.

  • Explanation: If the pressure at the pump suction drops below the vapor pressure of the liquid, bubbles form and collapse, damaging the impeller.

7. Question: In Thermodynamics, what defines an "Isentropic" process?

  • Answer: A process that is both adiabatic and reversible.

  • Explanation: In an isentropic process, the entropy of the system remains constant.

8. Question: Which heat exchanger type is most commonly used in oil refineries?

  • Answer: Shell and Tube Heat Exchanger.

  • Explanation: They are robust, can handle high pressures, and are easy to maintain in industrial settings.

9. Question: What happens to the viscosity of a liquid as temperature increases?

  • Answer: It decreases.

  • Explanation: Increased thermal energy reduces the cohesive forces between liquid molecules, allowing them to flow more easily.

10. Question: Define "Schedule Number" in piping.

  • Answer: It relates to the wall thickness of the pipe.

  • Explanation: As the schedule number increases (e.g., Sch 40 to Sch 80), the wall thickness increases to handle higher pressures.

Civil & Structural Engineering

11. Question: What is the difference between a "Fixed" support and a "Pinned" support?

  • Answer: A fixed support resists rotation (moment), while a pinned support does not.

  • Explanation: Fixed supports provide three reactions ($X, Y,$ and Moment), while pinned supports only provide two ($X, Y$).

12. Question: In reinforced concrete, what is the primary purpose of steel rebars?

  • Answer: To carry tensile loads.

  • Explanation: Concrete is strong in compression but very weak in tension; steel provides the necessary tensile strength.

13. Question: What is "Slump Test" used for in construction?

  • Answer: To measure the workability or consistency of fresh concrete.

  • Explanation: It ensures the concrete mix has the correct water-to-cement ratio before being poured into forms.

14. Question: Define "Young’s Modulus".

  • Answer: The ratio of tensile stress to tensile strain in the elastic region of a material.

  • Explanation: It measures the stiffness of a solid material.

Electrical Engineering

15. Question: What is the power factor, and why do plants want it close to 1.0?

  • Answer: The ratio of Real Power (kW) to Apparent Power (kVA); it indicates electrical efficiency.

  • Explanation: A low power factor means more "reactive power" is being drawn, which places a higher load on the utility grid and leads to penalties.

16. Question: What is the function of a Transformer?

  • Answer: To change the voltage level of an AC current.

  • Explanation: Stepping up voltage reduces current for long-distance transmission, while stepping down makes it safe for plant equipment.

17. Question: What does "IP65" rating signify for electrical enclosures?

  • Answer: It means the enclosure is dust-tight and protected against water jets.

  • Explanation: EPC projects in harsh environments require high IP (Ingress Protection) ratings to ensure equipment longevity.

General Logic & Materials

18. Question: If you are asked to design a pipe for a highly corrosive acid, which material is generally better: Carbon Steel or Stainless Steel?

  • Answer: Stainless Steel.

  • Explanation: Stainless steel contains chromium, which forms a passive layer of oxide that prevents corrosion, unlike carbon steel.

19. Question: In a project, if the "Critical Path" is delayed by 2 days, what happens to the project completion date?

  • Answer: The project completion date is delayed by 2 days.

  • Explanation: The critical path is the longest sequence of tasks; any delay here directly impacts the final deadline.

20. Question: Why is "Stress Relieving" (PWHT) performed after welding heavy-wall pipes?

  • Answer: To reduce residual stresses caused by the high heat of welding.

  • Explanation: Post-Weld Heat Treatment (PWHT) prevents brittle fracture and stress corrosion cracking in the joint.