Pipeline Bend
05.16
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:
1. Bend
is a generic term for any offset or change of direction in the piping. It is a
vague term that also includes elbows.
2. An
elbow is an engineering term and they are classified as 90 deg or 45 deg, short
or long radius.
3. 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.
4. 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.
5. 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.
6. Elbow
is a standard fitting but bends are custom fabricated.
7. 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.
8. All
elbows are bends but all bends are not elbows.
9. Bend
has a larger radius then elbows.
10. 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 betweenthem 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
1. 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.
2. Long
radius elbows give less frictional resistance to the fluid than the short
elbows.
3. Long
radius elbows create lesser pressure drop than short radius elbows.
4. Short
radius is less costly than long radius elbows.
5. 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.
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.
Sumber:
http://www.marineinsight.com/tech/pipeing/pipes-and-bends-an-essential-guide-for-second-engineers-part-2/
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