Interview Question and Answer – Set 3

Interview Question and Answer – Set 3 (Piping Engineering)

This article is the third part of our piping interview series. It contains important non-MCQ interview questions with detailed answers and explanations. These questions are frequently asked in piping design, construction, inspection, and maintenance interviews for industries such as oil & gas, power, chemical, and refineries.

1. What ASME code is used for process piping in refineries and chemical plants?

Answer: ASME B31.3 – Process Piping.

Explanation: ASME B31.3 covers the design, materials, fabrication, inspection, testing, and safety requirements of piping systems in chemical plants, refineries, pharmaceutical facilities, and related industries. It is one of the most widely used piping codes worldwide.

2. Which major American organizations provide piping standards?

Answer: American Petroleum Institute (API), American Society for Testing and Materials (ASTM), American Society of Mechanical Engineers (ASME), American Iron and Steel Institute (AISI), American Welding Society (AWS), American Water Works Association (AWWA).

Explanation: These organizations develop technical standards governing materials, design, fabrication, welding, testing, and inspection of piping systems.

3. Explain the main ASME B31 piping codes.

Answer:

• ASME B31.1 – Power Piping
• ASME B31.2 – Fuel Gas Piping
• ASME B31.3 – Process Piping
• ASME B31.4 – Liquid Pipeline Transportation
• ASME B31.5 – Refrigeration Piping
• ASME B31.8 – Gas Transmission and Distribution
• ASME B31.9 – Building Services Piping
• ASME B31.11 – Slurry Transportation Piping

Explanation: Each code addresses different service conditions and industries.

4. What are the main sections of the ASME Boiler and Pressure Vessel Code?

Answer:

• Section I – Power Boilers
• Section II – Materials
• Section III – Nuclear Power Plant Components
• Section IV – Heating Boilers
• Section V – Nondestructive Examination
• Section VI – Care and Operation of Heating Boilers
• Section VII – Care of Power Boilers
• Section VIII – Pressure Vessels
• Section IX – Welding and Brazing Qualifications

Explanation: These sections together govern construction, materials, testing, and certification of pressure equipment.

5. Which standards are used for selecting flanges and fittings?

Answer:

• ASME B16.5 – Pipe flanges and flanged fittings
• ASME B16.47 – Large diameter flanges
• ASME B16.9 – Butt-welding fittings
• ASME B16.11 – Socket-welded and threaded fittings

6. What is the difference between NPS and DN?

Answer: NPS is the nominal pipe size in inches. DN is the metric nominal diameter in millimeters. Both are nominal systems and do not directly represent actual dimensions.

7. Explain pipe schedule.

Answer: Pipe schedule indicates wall thickness. A higher schedule number means thicker pipe wall, higher pressure capacity, and smaller inside diameter.

8. What is corrosion allowance?

Answer: Corrosion allowance is extra thickness added to the pipe wall to compensate for material loss due to corrosion over the service life of the plant.

9. Why is hydrostatic testing performed?

Answer: Hydrostatic testing verifies the strength and leak tightness of the piping system before commissioning.

10. What is PWHT?

Answer: Post Weld Heat Treatment is applied after welding to relieve residual stresses, improve ductility, and reduce hardness in the heat-affected zone.

11. What is the purpose of pipe supports?

Answer: Pipe supports carry weight, control thermal movement, reduce vibration, and protect equipment.

12. What is an anchor in piping?

Answer: An anchor is a rigid support that restrains all six degrees of freedom of a pipe.

13. What is the difference between guide and line stop?

Answer: A guide allows axial movement but restricts lateral movement. A line stop restricts movement in one direction.

14. What is a flexible joint?

Answer: A flexible joint absorbs vibration and accommodates thermal expansion.

15. What is pipe stress analysis?

Answer: It is the evaluation of stresses and displacements in piping due to loads such as pressure, weight, temperature, wind, and seismic forces.

16. Why are expansion loops used?

Answer: To absorb thermal expansion and reduce stresses in long piping systems.

17. What is the purpose of insulation?

Answer: Insulation reduces heat loss, protects personnel, and prevents condensation.

18. What is a spool drawing?

Answer: A spool drawing is a detailed fabrication drawing showing dimensions, welds, and materials of prefabricated piping sections.

19. What is line numbering in piping?

Answer: Line numbering uniquely identifies each piping line with service, size, class, and sequence information.

20. Why is documentation important in piping projects?

Answer: Proper documentation ensures traceability, quality control, regulatory compliance, and safe operation of the plant.

Conclusion

This interview question and answer set covers core knowledge required for piping engineers. Mastering these topics strengthens understanding of design codes, materials, construction practices, and operational safety in industrial piping systems.