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Process Piping Interview Questions

Piping Interview Questions

These are the important thing in piping
1) What is the minimum distance to be maintained between two welds in a pipe?
The thumb rule is that the minimum distance between adjacent butt weld is 1 D . if not, it is never closer than  1 – 1/2 “ . this is supposedly to prevent the overlap of HAZs. minimum spacing of circumferential weld between centerlines shall not be less than 4 times the pipe wall thickness or 25 mm whichever is greater.
2) What are weldolet and socket? And where they are used?
Welolet  and sockolet are basically self – reinforced fitting. Weldolet is used for butt weld branch connection where standard tee is not available due to size restriction and the piping is of critical/high pressure service. sockolet is used for socket welding branch connection , which require reinforcing pad
3)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.
4)What is the basis of using of short  radius & long radius elbow ?
Long radius are used for  small pressure drop whereas short radius elbow are used high pressure drops. For catalyst flow vary long radius are used
5)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.
6)How the pipe fittings are classified based on end connections?
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

7)How the pipe fittings are classified based on end connection ?
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
8)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
9)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 ).
10)From which size onwards NB of pipe is equal to OD of pipe ?
From the size 14 “ and onwards NB = OD of pipe
11)What should be the radius of long radius elbow ?
1.5 D ( where  ‘ D’  is the diameter of the pipe )
12)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 are 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 line only .
Screwed – The screwed-on flanges are used on pipe lines where welling cannot be carried out
Lap joint – The lap joint flanges are used with stub ends. The stub ends are welded with pipe & 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 service 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 size without using a reducer, In case of reducing flanges, the thickness of flange be that of the higher diameter.
Integral – Integral flanges are those, which are cast along with the piping component or equipment

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  1. I like its very basic questions but there asking too much deep, can add on what kind of external corrosion and internal corrosion in in-service piping

  2. I like this page. please share critical piping design consideration with Q & Ans along merits and demerits so as we relate ourselves easily and its very easy to understand…

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