Flanges are projecting or internal components
used to support mechanical parts. Most often, they're rims, and that
they are put in place to strengthen the mechanical part or provide a way of attaching that part to another part or
surface. A simple pipe flange
would be a slip-on or threaded flange that fits
around one end of a pipe and
provides a way to bolt that pipe
to a wall or fixture. Such a flange would be a circular component with a central
means of holding the pipe and bolt holes placed evenly in the outer rim.
As already described, the most used flange
types ASME b16.5 are: Welding Neck, Slip On, Socket Weld,
Lap Joint, Threaded and Blind flange. Below you'll find a short description and definition of every type,
completed with a detailed image.
Most common flange types
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. The long tapered hub provides a very important reinforcement to be used in many
applications involving high pressure,
sub-zero and / or elevated temperatures. The graceful transition from projection thickness to pipe or fitting wall thickness affected by the taper is extremely helpful, under
conditions of repeated bending,
caused by line expansion or other variable forces. These flanges are bored to match the
inside diameter of the sex
pipe or fitting therefore there will be no restriction of
product flow. This prevents turbulence at the joint and reduces erosion. They also give excellent
stress distribution through the tapered hub and are simply radio
graphed for flaw detection.
This flange type will be welded to a pipe or
fitting with a single full penetration, V weld (Butt-weld).
1.
Weld Neck flange 2. Butt-Weld
3. Pipe or Fitting
3. Pipe or Fitting
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. The X measure on the image, are
approximately:
Wall thickness of pipe + 3 mm. This space is necessary, to do not damage the flange face, during the welding process.
Wall thickness of pipe + 3 mm. This space is necessary, to do not damage the flange face, during the welding process.
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.
1.
Slip On flange 2. Filled weld outside
3. Filled weld inside 4. Pipe
3. Filled weld inside 4. Pipe
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 one 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.
The
disadvantage of this flange is right the gap, that must be made. By corrosive
products, and mainly in stainless steel pipe systems, the crack between pipe
and flange can give corrosion problems.
1.
Socket Weld flange 2. Filled Weld 3. Pipe
X = Expansion gap
X = Expansion gap
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".
These
flanges are nearly identical to a Slip On flange with the exception of a
radius at the intersection of the flange face and the bore to accommodate the
flanged portion of the Stub End.
Their
pressure-holding ability is little, if any, better than that of Slip On
flanges and the fatigue life for the assembly is only one tenth that of WeldingNeck flanges. They may be used at all pressures and are available in a full
size range. Lap Joint flanges have certain special advantages:
- Freedom
to swivel around the pipe facilitates the lining up of opposing flange
bolt holes.
- Lack
of contact with the fluid in the pipe often permits the use of inexpensive
carbon steel flanges with corrosion resistant pipe.
- In
systems which erode or corrode quickly, the flanges may be salvaged for
re-use.
1.
Lap Joint flange 2. Stub End
3. Butt Weld 4. Pipe or Fitting
3. Butt Weld 4. Pipe or Fitting
Threaded
Flanges are used for special circumstances with their main advantage being that
they can be attached to the pipe without welding. Sometimes a seal weld is also
used in conjunction with the threaded connection. Although still available in
most sizes and pressure ratings, screwed fittings today are used almost exclusively
in smaller pipe sizes.
A
threaded flange or fitting is not suitable for a pipe system with thin wall
thickness, because cutting thread on a pipe is not possible. Thus, thicker wall
thickness must be chosen...what is thicker?
1.
Threaded flange 2. Thread 3. Pipe or Fitting
Blind
Flanges are manufactured without a bore and used to blank off the ends of
piping, Valves and pressure vessel openings. From the standpoint of internal
pressure and bolt loading, blind flanges, particularly in the larger sizes, are
the most highly stressed flange types. However, most of these stresses are
bending types near the center, and since there is no standard inside diameter,
these flanges are suitable for higher pressure temperature applications.
Details of Blind flange
1.
Blind flange 2. Stud Bolt 3. Gasket 4. Other flange
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