Bends and Elbows are both very common pipe fittings products which are used to change the flowing direction in a piping systems. Some times they are interchangeable, but not same.
What is the difference between elbow and bend in piping?
“All bends are elbows but all elbows are not bends.”
In fact,the pipe is bent to form an elbow.
Elbows are pre-fabricated and are firm in design.
There are issues with bends since the tickness at the bend radius reduces as we bend the pipe.
Sharp bends are normally called Elbows. Bends typically have a minimum bending radius of 1.5 times pipe radius (R). If this bending radius is less than 1.5R, it is called Elbow. Reference to any international / industry standard need to be traced. 1.5, 3 & 4.5 R are the most common bending radii in industry. What is the difference between a Pipe Bend and an elbow?
A pipe bend means a piece of pipe which are bent to some angle to join two pipings. they can be nearly any bending radius and angles . Pipe bends are commonly produced on site to meet a specific need by hot induction bending or cold bending. A elbow means a specific pipe bend as per the standard ANSI/ASME B16.9 (or EN 10253, or other pipe fittings standards). Commonly the elbows have a bending radius of 1.5D or 1D (Here the D means nominal diameter of this bend) ,which are called “Long Radius elbow (LR elbow)” or “Short Radius elbow(SR elbow)” . and the angle of an elbow is 45 degree or 90 degree usually, some times there are also custom-designed elbows which are 30 degree,60 degree ,180 degree or other angles.
The pipe bends should be as per the standard of ANSI/ASME B16.49 which did not specific the bending radius and angle , the regular pipe bend radius are 2.5D, 3D ,5D ,7D or 8D , but it can be any other bending radius according to the design need, and bending angle can be in any degree, 5 ,10 ,15, 90 degree or any other. People said “All bends are elbows but all elbows are not bend”, it is not true . Actually “All elbows are pipe bends but not all bends are elbows” is more reasonable.
An "elbow" and a "bend" are two different animals - as the terms are generally employed in the process industry.
A BEND is the generic term for what is called in piping as an "offset" - a change in direction of the piping. A bend is usually meant to mean nothing more than that there is a "bend" - a change in direction of the piping (usually for some specific reason) - but it lacks specific, engineering definition as to direction and degree. Bends are usually custom-made (using a bending machine) on site and suited for a specific need.
An ELBOW, on the other hand, is a specific, standard, engineered bend pre-fabricated as a spool piece and designed to either be screwed, flanged, or welded to the piping it is associated with. An elbow can be 45o or 90o. There can also be custom-designed elbows, although most are catagorized as either "short radius" or long radius".
A bend can be an elbow; an elbow does not mean a bend. If you use the term elbow, it should also carry the qualifiers of type (45 or 90o) and radius (short or long) - besides the nominal size.
Additionally, if you are using tube and not pipe, there is a marked difference. As you can bend tube for pressure applications you will get less interuption and turbulence in your flow; this translates to less pressure drop than with fitted 90 or 45 elbows.
Long radius elbow is used to change the direction of flow gradually, 90 degrees.
Short radius elbow is used to change the direction of flow rapidly, 90 degrees.
45° elbow is used to change the flow only 45°.
Return bends are used to change the direction of flow 180°.
The physical difference between Long Radius and Short Radius Elbows is graphically illustrated in the attached Workbook that I have put together for this thread.
The following is the criteria I use when deciding which to use:
Long Radius Elbows are used when:
there is a need to keep the frictional fluid pressure loss down to a minimum;
there is ample space and volume to allow for a wider turn and generate less pressure drop;
the fluid being transported is abrasive or has solids in it.
Short Radius Elbows are used when: