Piping QC – Inspectors Questions and Answers [Pipe Fittings]

Piping QC – Inspectors Questions and Answers

1. How can flanges be classified based on pipe attachment?

Flanges can be classified based on pipe attachment as:-

Slip – on:- The Slip-on type flanges a re attached by welding inside as well as outside. These flanges are of forged construction.

Socket Weld:- The Socket Weld flanges are welded on one side only. These are used for small bore lines only.

Screwed:- The Screwed-on flanges are used on pipe lines where welding cannot be carried out.

Lap Joint:- The Lap Joint flanges are used with stub ends. The stub ends are welded with pipes & flanges are kept loose over the same.

Welding Neck:- The Welding Neck flanges are attached by butt welding to the pipe. These are used mainly for critical services where the weld joints need radiographic inspection.

Blind:- The Blind flanges are used to close the ends which need to be reopened.

Reducing:- The Reducing flanges are used to connect between larger and smaller sizes without using a reducer. In case of reducing flanges, the thickness of flange should be that of the higher diameter.

Integral:- Integral flanges are those, which ar e cast along with the piping component or equipment.

2. How can flanges be classified based on Pressure – temperature ratings?

Flanges are classified based on pressure temperature ratings as:-

A. 150 #

B. 300 #

C. 400 #

D. 600 #

E. 900 #

F. 1500 #

G. 2500 #

Pressure temperature rating carts in the standard ASME16.5 specify the non-shock working gauge pressure to which the flange can be subjected to at a particular temperature.

3. How can flanges be classified based on facing?

Flanges are classified based on facing as:-

A. Flat face. (FF)

B. Raised face. (R/F)

C. Tongue and groove. (T/G)

D. Male and female. (M/F)

E. Ring type joint. (RTJ)

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

Flanges are classified based on face finish as:-

A. Smooth finish.

B. Serrated finish.

5. Where the smooth finish flange & serrated finish flange finds its use?

The smooth finish flange is provided when metallic gasket is provided and serrated finish flange is provided when non-metallic gasket is provided.

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

A. Concentric or

B. Spiral (phonographic)

7. How the serration on flanges is specified?

The serration on flanges is specified by the number, which is the Arithmetic Average Rough Height (AARH).

8. Where the concentric serration is insisted for face finish?

Concentric serration are insisted for face finish where the fluid being carried has very low density and can find leakage path through cavity.

9. How the gaskets are classified based on the type of construction?

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Based on the type of construction, gaskets are classified as: –

A. Full face.

B. Spiral wound metallic.

C. Ring type.

D. Metal jacketed.

E. Inside bolt circle.

10. What is the most commonly used material for gasket?

Compressed Asbestos Fibre.

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

Spiral Wound Metallic Gasket.

12. What are the criteria for selection of MOC of spiral wound metallic gasket winding material?

The selection of material of construction for gasket winding depends upon:-

A. The corrosive nature and concentration of fluid being carried.

B. The operating temperature of the fluid.

C. The relative cost of alternate winding material.

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

The most commonly used material for spiral wound metallic gasket winding is:-

A. Austenitic stainless steel 304 with asbestos filler.

B. Austenitic stainless steel 316 with asbestos filler.

C. Austenitic stainless steel 321 with asbestos filler.

14. Which material is used as filler material for spiral wound gasket in case of high temperature services?

For very high temperature services, graphite filler is used.

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

Spiral wound gaskets are provided with carbon steel external ring called centering ring.

16. On which type of flanges the use of spiral wound gasket are restricted?

ASME B16.5 does not recommend the use of 150 # rating spiral wound gasket on flanges other than welding neck and lapped joint type.

17. Up to what temperature limits the low strength carbon steel bolts should not be used for flanged joints?

Flanged joints using low strength carbon steel shall not be used above 200# C or below – 28# C.

18. How the pipe fittings are classified based on end connections?

Pipe fittings are classified based on end connection as: –

A. Socket weld fittings.

B. Screwed end fittings.

C. Beveled end or butt weld fittings.

D. Spigot socket fittings.

E. Buttress end fittings.

19. Up to what temperature the carbon steel materials shall be used?

Carbon steel materials shall be used for temperature up to 425C.

20. Which material is used for temperature above 426# C?

Alloy steel materials shall be used for temperature above 426C.

21. Which type of material is used for corrosive fluid?

Stainless steel materials shall be used for corrosive fluid.

22. Which type of piping materials are used for drinking water, instrument air etc?

Galvanized steel materials shall be used for drinking water, instrument air and NI lines (LP).

23. What is the difference between pipe and tube?

Pipe is identified by NB and thickness is defined by Schedule whereas Tube is identified by OD & its thickness as BWG (Brimingham Wire Gauge or 1/100 inch).

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24. From which size onwards NB of pipe is equal to OD of pipe?

From the size 14” and onwards NB = OD of pipe.

25. What should be the radius of long radius elbow?

1.5D (Where “D” is the diameter of the pipe.)

26. What should be the radius of short radius elbow?

1D(Where “D” is the diameter of the pipe.)

27. What is the basis of using of short radius & long radius elbow?

Long radius elbow are used for small pressure drop whereas short radius elbow are used for high pressure drops. For catalyst flows vary long radius elbows are used.

28. Normally where do we use the following?

A. Eccentric reducers.

B. Concentric reducers.


A. Eccentric reducers = pump suction to avoid Cavitation, To maintain elevation (BOP) in rack.

B. Concentric reducers = pump discharge, vertical pipeline etc.

29. Concentric reducer is used in pump suction. (Yes / No). Explain.

No. Air pockets may form if concentric reducer is used at pump suction, which results in cavitation and cause damage to pump. To avoid this problem, eccentric reducer with flat side up (FSU) is used in pump suction.

30. Where the ERW spiral & longitudinal pipes are used?

Use depends upon the availability of pipes. Nothing functional difference.

31. What is the main use of ASTM A53 & A106 Gr.B pipes?

ASTM A53 pipes are mainly used for utility services whereas A106 Gr. B pipes are used for high pressure & high temperature services.

32. From which side of pipe will you take a branch connection?

When fluid is gas, air or steam and cryogenic service – topside.

When fluid is liquid – bottom side.

33. Why don’t we take a branch for cryogenic service from bottom side though the fluid is in liquid state?

There is the chance of ice formation during normal operation and since ice flows from the bottom of the pipe it will block the branch pipe connection.

33. Why do we provide High Point Vent (HPV) and Low Point Drain (LPD) in piping?

HPV – For removing air during hydro-test.

LPD – For draining water after conducting hydro-test.

34. What do you mean by jacketed piping?

Piping which is recognized as providing the most uniform application of heat to the process, as well as maintaining the most uniform processing temperatures where steam tracing is not capable of maintaining the temperature of fluid constant. Usually used for molten sulphur, polymers service.

35. What is the minimum distance to be maintained between two welds in a pipe?

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Answer:- The thumb rule is that the minimum distance between adjacent butt welds is 1D. If not, it is never closer than 1-1/2″. This is supposedly to prevent the overlap of HAZs. Minimum spacing of circumferential welds between centerlines shall not be less than 4 times the pipe wall thickness or 25 mm whichever is greater.

36. What do you mean by IBR and which lines comes under IBR purview?

IBR: Indian Boiler Regulation Act.

Steam lines with conditions listed bellow comes under IBR purview :–

1) Lines for which design pressure is 3.5 kg/sq.cm and above.

2) Line size above 10” having design pressure 1.0 kg/sq.cm and above.

3) Boiler feed water lines to steam generator, condensate lines to steam generator and flash drum.

37. What are weldolet and sockolet? And where they are used?

Weldolet and sockolet are basically self-reinforced fittings. Weldolet is used for butt weld branch connection where standard tee is not available due to size restrictions and the piping is of critical / high-pressure service. Sockolet is used for socket welding branch connection, which require reinforcing pad.

38. What is the MOC for superheated high pressure steam lines?

A 335 Gr. P I / P 11, composition: Cr. – ½ Mo (P1) / 1¼ Cr. – ½ Mo (P11)

39. What is the normal upstream and downstream straight length of orifice flow meter?

Upstream – 15D Downstream – 5D

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

125-250 AARH finish.

Where the ERW & seamless pipes are used?

Above 18” ERW pipes are used. Below 18” seamless pipes are used. Seamless pipes can sustain higher temperature & pressure.


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