piping engineering interview questions with answers part 2

piping engineering interview questions with answers part 2

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11. What are the different types of pipe fittings and their functions?

Answer:
Pipe fittings connect pipes and change the flow direction or size. Common types include:

• Elbows (90°, 45°) – Change direction.

• Tees (Equal, Reducing) – Split or combine flow.

• Reducers (Concentric, Eccentric) – Change pipe size.

• Couplings & Unions – Connect two pipes.

• Flanges (Slip-on, Weld Neck, Blind) – Enable easy assembly/disassembly.

• Valves (Gate, Ball, Check, Butterfly) – Control flow.

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12. What is NPS and DN in piping?

Answer:

• NPS (Nominal Pipe Size) is a North American standard that defines pipe diameter (in inches).

• DN (Diameter Nominal) is the international metric equivalent, measured in millimeters.

• Example: NPS 2" = DN 50

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13. What are the common welding techniques used in piping?

Answer:

• SMAW (Shielded Metal Arc Welding) – Manual stick welding, widely used.

• GTAW (TIG - Gas Tungsten Arc Welding) – Precise, used for stainless steel and thin materials.

• GMAW (MIG - Gas Metal Arc Welding) – Faster, used in fabrication shops.

• FCAW (Flux-Cored Arc Welding) – Similar to MIG but with flux-cored wire.

• SAW (Submerged Arc Welding) – Used for large-diameter pipes.

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14. How do you prevent water hammer in piping systems?

Answer:
Water hammer is a pressure surge caused by sudden flow stoppage. It can be prevented by:

• Installing air chambers or surge arrestors.

• Using slow-closing valves to reduce sudden stoppage.

• Installing pressure relief valves.

• Supporting pipes properly to reduce vibrations.

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15. What is a pigging system in pipelines?

Answer:
A pigging system uses a device called a pig to clean, inspect, or remove debris from pipelines. It is commonly used in oil & gas and chemical industries.

• Types: Cleaning pigs, Inspection pigs, Gel pigs.

• Benefits: Reduces blockages, detects corrosion, and improves efficiency.

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16. What is a check valve, and where is it used?

Answer:
A check valve allows fluid flow in one direction only, preventing backflow. It is used in:

• Pump discharge lines to prevent reverse flow.

• Steam and condensate systems.

• Compressed air and gas pipelines.

Common types: Swing check, Lift check, Ball check, and Dual-plate check valves.

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17. What are the different types of pipe coatings?

Answer:
Pipe coatings prevent corrosion and extend pipe life. Common types include:

• External Coatings:

  • Fusion Bonded Epoxy (FBE) – Corrosion resistance.

  • Coal Tar Enamel – Used in buried pipelines.

  • Polyethylene (PE) Coating – Water-resistant.

• Internal Coatings:

  • Epoxy lining – Prevents scale buildup.

  • Cement mortar lining – Used for water pipes.

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18. What is the difference between hot tapping and cold tapping?

Answer:

• Hot tapping is connecting to a live (pressurized) pipeline without shutdown. Used in oil & gas.

• Cold tapping is performed on depressurized pipelines.

Hot tapping advantages:

• Avoids shutdown and production loss.

• Prevents system drainage.

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19. What is the purpose of a steam trap in a piping system?

Answer:
A steam trap removes condensed water (condensate) while preventing steam loss. It improves system efficiency in steam lines.

Types of steam traps:

• Mechanical (Float & Thermostatic)

• Thermodynamic

• Thermostatic (Bimetallic, Bellows type)

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20. How do you calculate pipe support spacing?

Answer:
Support spacing depends on:

• Pipe size and material.

• Operating temperature and weight.

• Fluid type (gas, liquid, steam).

Example Formula:

$$L = C \times \sqrt{\frac{D}{W}}$$

Where:

• $L$ = support spacing

• $C$ = constant based on pipe material

• $D$ = outer diameter

• $W$ = weight per unit length

For carbon steel pipes, approximate spacing:

• NPS 1" → 1.5m

• NPS 6" → 3.5m

• NPS 12" → 5.0m

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