Basic Details if Piping Flanges

BASIC DETAILS OF FLANGES

INDEX:- 

Description 

Classification and Types 

Advantages

Disadvantages

Description:- 

• A flange is a method of connecting pipes, valves,pumps and other equipment to form a piping system. 

• It also provides easy access for cleaning, inspection or modification. 

• Flanges are usually welded or screwed.

•  Flanged joints are made by bolting together two flanges with a gasket between them to provide a seal.

• Flanges are used when the joint needs dismantling.

•  These are used mainly equipments, valves and specialties. 

• In certain pipe lines where maintenance is a regular feature, breakout flanges are provided at definite intervals on pipe lines.

•  A flanged joint is composed of three separate and independent although interrelated components; the flanges, the gaskets and the bolting; which are assembled by yet another influence, the fitter. 

 

Flanges can be classified based on pipe attachments:

 1. Slip-on
 2. Socket Weld
 3. Screwed/ Threaded 
 4. Lap Joint
 5. Welding Neck
 6. Blind
 7. Reducing
 8. Integral

Based on Flange Facing:-

 1. Flat Face (FF)

 2. Raised Face (RF)

 3. Tongue and groove (T/G)

 4. Male and Female(M/F)

 5. Ring Type Joint (RTJ)

1. Slip-on Flange:- 

• The calculated strength from a Slip On flange under internal pressure is of the order of two-thirds that of welding neck flanges, and their life under fatigue is about one-third that of the latter.
• The connection with the pipe is done with 2 fillet welds, as well at the outside as also at the inside of the flange.
•  A disadvantage of the flange is, that principle always firstly a pipe must be welded and then just a fitting. 
• A combination of flange and elbow or flange and tee is not possible, because named fittings have not a straight end, that complete slid in the Slip On flange.

 2. Socket Weld Flange :- 

• Socket Weld flanges were initially developed for use on small-size high pressure piping. Their static strength is equal to Slip On flanges, but their fatigue strength 50% greater than double-welded Slip On flanges.
• The connection with the pipe is done with 1 fillet weld, at the outside of the flange. But before welding, a space must be created between flange or fitting and pipe.
• The purpose for the bottoming clearance in a socket weld is usually to reduce the residual stress at the root of the weld that could occur during solidification of the weld metal.
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3. Screwed Flange :- 

• The screwed-on flanges are used on pipe lines where welding cannot be carried out. Socket welding and threaded flanges are not recommended for service above250°C and below -45°C. 

  

  Screwed Flange
  
  

  
  

4. Lap Joint  Flange :- 

• Lap Joint Flanges have all the same common dimensions as any other flange named on this page however it does not have a raised face, they used in conjunction with a "Lap Joint Stub End".

• The Lap Joint flanges are used with stub ends when piping is of a costly material. The stub ends will be butt-welded to the piping and the flanges are kept loose over the same. The inside radius of these flanges is chamfered to clear the stub end radius.

5. Weld Neck Flange :- 

• Welding Neck Flanges are easy to recognize at the long tapered hub, that goes gradually over to the wall thickness from a pipe or fitting.

• These flanges are bored to match the inside diameter of the mating pipe or fitting so there will be no restriction of product flow. This prevents turbulence at the joint and reduces erosion.

•  This flange type will be welded to a pipe or fitting with a single full penetration, V weld (Butt weld).
• The long tapered hub provides an important reinforcement for use in several applications involving high pressure, sub-zero and / or elevated temperatures.
  
  
  

6. Blind Flange :- 

• The Blind flanges are used to close the ends, which need to be reopened later.

• Blind Flanges are manufactured without a bore and used to blank off the ends of piping, valves and pressure vessel openings. 
  
  
  

7. Reducing Flange:- 

• The Reducing flanges are used to connect between larger and smaller sizes without using a reducer.

8. Integral Flange:-

• Integral flanges are those, which are cast along with the piping component or equipment. Thickness of integrally cast flanges and welded on flanges differ in certain sizes. 

Based on Facing:

Flat Face (FF):- 

• The flat face flange has a gasket surface in the same plane as the bolting circle face. 
• Applications using flat face flanges are frequently those in which the mating flange or flanged fitting is made from a casting.
• Flat face flanges are never to be bolted to a raised face flange.

Raised Face (RF):- 

• The raised face flange face is the most common type used in process plant applications, and is easily to identify. It is referred to as a raised face because the gasket surfaces are raised above the bolting circle face.
•  This face type allows the use of a wide combination of gasket designs, including flat ring sheet types and metallic composites such as spiral wound and double jacketed types.
•  The purpose of a RF flange is to concentrate more pressure on a smaller gasket area and thereby increase the pressure containment capability of the joint.

 Common in point for  Flange facing:-

• Raised face is used in higher ratings.

• There are two types of finishes done on to the facings. They are the smooth finish and serrated finish.
• The smooth finish flanges are specified when metallic gaskets are used.
• The serrated finish flanges are specified when non-metallic gaskets are used.

Advantages:- 

• A new line can contain multiple pipe spools and can be manufactured in a workshop.

• This pipe spools can be assembled in the plan without the need to be welded.

•  NDO (X-ray, Hydro test etc.) in the plant is not necessary, because this has been done in the workshop.

• Blasting and painting in the plant is not necessary, because even this has been done in a workshop.

• As with many things, everything has its pros and cons.

Disadvantages:- 

• Each flange connection can leak (some people claim that a flange connection is never 100 percent leak proof).

•  Flanged pipe systems need much more space (just think of a pipe rack).

•  Insulation of flanged pipe systems is more expensive (special flange caps).

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