Pipe Bends
There is always a doubt about the terms bends and
elbows on ships. They are frequently used as synonyms. The
difference between them is as follows:
o
Bend is a generic term for any offset
or change of direction in the piping. It is a vague term that also includes
elbows.
o
An elbow is an engineering term and
they are classified as 90 deg or 45 deg, short or long radius.
o
Elbows have industrial standards and
have limitations to size, bend radius and angle. The angles are usually 45 deg
or 90 degrees. All others offsets are classified as pipe bends.
o
Bends are generally made or
fabricated as per the need of the piping; however elbows are pre fabricated and
standard, and are available off the shelf.
o
Bends are never sharp corners but
elbows are. Pipe bending techniques have constraint as to how much material
thinning can be allowed to safely contain the pressure of the fluid to be
contained. As elbows are pre fabricated, cast or butt welded, they can be
sharp like right angles and return elbows which are 180 degrees.
o
Elbow is a standard fitting but bends
are custom fabricated.
o
In bends as the pipe is bent and
there is no welding involved, there is less pipe friction and flow is smoother.
In elbows, the welding can create some friction.
o
All elbows are bends but all bends
are not elbows.
o
Bend has a larger radius then elbows.
o
Generally the most basic difference
is the radius of curvature. Elbows generally have radius of curvature between
one to twice the diameter of the pipe. Bends have a radius of curvature
more than twice the diameter.
Short Radius
and Long Radius
Elbows are again classified as long radius or short
radius elbows. The difference between them is the length and curvature. A short
radius elbow will be giving the piping a sharper turn than a long radius elbow.
90 degree
short radius elbow
o
In a long radius elbow the radius of
curvature is 1.5 times the nominal diameter. In a standard elbow the radius of
curvature is 1.0 times the nominal diameter of the pipe.
o
Long radius elbows give less
frictional resistance to the fluid than the short elbows.
o
Long radius elbows create lesser
pressure drop than short radius elbows.
o
Short radius is less costly than long
radius elbows.
o
The short radius elbows are used
where there is scarcity of space.
In addition to this classification the elbows are
45 degrees, 90 degrees and 180 degrees also called as a return elbow.
180-Degree
Elbow
The 45 degrees elbow turns the fluid /piping at 45
degrees and so on.
45 deg short
radius elbow
Miter bends
Another type of bend is a Miter bend. A Miter bend is
a bend which is made by cutting pipe ends at an angle and joining the pipe
ends. A true miter bend is a 90 degree bend made by cutting two pipes at 45
degrees and joining them by welding. Similarly three pipes cut at 22.5
degrees will give a 90 degree miter bend.
Source: http://www.marineinsight.com/tech/pipeing/pipes-and-bends-an-essential-guide-for-second-engineers-part-2/
No comments:
Post a Comment