Pipe Fittings Interview Questions

Learn pipe fittings and flanges interview questions and answers, including flange types, pressure classes, and differences between reducers.

The Complete Guide to Pipe Flanges and Gaskets

Mastering the selection of pipe flanges and gaskets is essential for ensuring the safety and longevity of industrial piping systems. This guide provides clear answers to the most common technical questions regarding flange attachment types, pressure ratings, and surface finishes. Whether you are working with ASME B16.5 standards or selecting the right spiral wound gasket for high-temperature service, this professional overview will help you make informed engineering decisions.

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Section 1: Flange Classifications

Q1. How can flanges be classified based on Pipe Attachment?

Answer: Flanges are grouped by how they connect to the pipe:

  • Slip-on: Welded inside and outside, forged construction.
  • Socket Weld: Welded on one side only, used for small bore.
  • Screwed: Used where welding cannot be carried out.
  • Lap Joint: Used with stub ends.
  • Welding Neck: Butt welded to pipe, used for critical services.
  • Blind: To close ends.
  • Reducing: Connect larger to smaller sizes.
  • Integral: Cast with the component/equipment.

Q2. How can flanges be classified based on Pressure-Temperature ratings?

Answer: Ratings include: 150#, 300#, 400#, 600#, 900#, 1500#, and 2500# (Refer to Pressure-temperature rating charts in ASME B16.5).

Q3. How can flanges be classified based on facing?

Answer: There are five primary face types:

  • A. Flat Face (FF)
  • B. Raised Face (RF)
  • C. Tongue and Groove (T/G)
  • D. Male and Female (M/F)
  • E. Ring Type Joint (RTJ)

Q4. How can flanges be classified based on face finish?

Answer: They are classified into two main categories:

  • Smooth finish
  • Serrated finish

Q5. Where are smooth and serrated finish flanges used?

Answer: The choice depends on the gasket material:

  • Smooth finish: Use with metallic gaskets.
  • Serrated finish: Use with non-metallic gaskets.

Q6. What are the types of serrated finish provided on a flange face?

Answer: Serrations can be either Concentric or Spiral (Phonographic).

Q7. How is the serration on flanges specified?

Answer: By the Arithmetic Average Rough Height (AARH).

Q8. Where is concentric serration insisted for face finish?

Answer: It is required where the fluid has a very low density and can find a leakage path through the cavity of a spiral finish.

Section 2: Gasket Selection & Materials

Q9. How are Gaskets classified based on the type of construction?

Answer: Standard constructions include:

  • Full face
  • Spiral wound metallic
  • Ring type
  • Metal jacketed
  • Inside bolt circle

Q10. What is the most commonly used material for Gaskets?

Answer: Compressed Asbestos Fibre.

Q11. Which type of gasket is recommended for high temperature & high-pressure application?

Answer: Spiral Wound Metallic Gasket.

Q12. What are the criteria for selection of MOC of Spiral Wound metallic Gasket winding material?

Answer: Selection is based on Corrosive nature, operating temperature, and relative cost.

Q13. What are the most common materials used for spiral wound metallic gasket winding?

Answer: Austenitic SS 304/316/321 with asbestos filler.

Q14. Which material is used as filler for spiral wound gaskets in high temperature services?

Answer: Graphite filler.

Q15. What is a centering ring in connection to a spiral wound gasket?

Answer: It is a carbon steel external ring.

Q16. What will be the AARH finish on a flange face for using a spiral wound gasket?

Answer: The finish must be 125-250 AARH.

Q17. On which type of flanges are the use of spiral wound gaskets restricted?

Answer: ASME B16.5 does not recommend 150# spiral wound gaskets on flanges other than welding neck and lap joint.

Conclusion

Properly identifying flange types and matching them with the correct gasket materials is vital for the safety and efficiency of any industrial piping system. By following ASME B16.5 standards and considering factors like pressure, temperature, and fluid density, engineers can ensure long-lasting, leak-free connections.

Technical information provided by aienginear.com

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ASME B16.5
01 / 10

Flanges Classifications
& Types

A new process line will handle a highly toxic, high-pressure fluid. The specification mandates 100% radiographic inspection of all pipe joints. Which flange attachment must be used?

During installation of a complex piping spool piece, the field crew anticipates severe difficulty aligning bolt holes with the mating equipment nozzle. Which flange type facilitates easy alignment?

A piping modification must be done inside an active chemical storage facility where ‘hot work’ (welding or cutting) permits are strictly denied. Which flange attachment method is required here?

You are designing a ΒΎ-inch instrumentation impulse line. To prevent weld spatter from entering the narrow pipe, it must be welded on the outside only. Which flange fits this requirement?

A future expansion project requires a pipeline header to be installed now, but its final connection won’t be made for two years. How should the open end of this pressurized header be secured safely?

For a non-critical, low-pressure cooling water line, the project manager wants a cost-effective welded flange. The pipe can be welded on both the inside and the outside. Which type is most appropriate?

A vendor submits a quote for flanged valves rated for ‘Class 500#’ according to ASME B16.5. How should you respond as the reviewing engineer?

Your material take-off (MTO) lists several ‘stub ends’ that need to be procured. Which specific type of flange must be ordered to pair perfectly with these fittings?

To ensure a tight seal under extreme pressure, the design requires a flange face with a deep, specialized groove machined into it to accept a metallic seal. What is this facing type?

A technician replaces a gasket and notes one flange has a raised plateau while the mating flange has a matching depression for it to fit into. What type of configuration is this?

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