What is a pipe elbow?
A pipe 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 pipe 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.
The ends may be machined for butt welding (SW) or socketed welding(SW) etc.
Most pipe elbows are available in short radius or long radius variants. When the two ends differ in size, the fitting is called a reducing elbow or reducer elbow.
Elbows are categorized based on various design features as below:
Long Radius (LR) Elbow is also called LR elbow – means the radius is 1.5 times the pipe diameter.
L/R 45°Elbow: Long radius 45 degree elbow changes the direction by 45 degrees.
L/R 90°Elbow: Long radius 90 degree elbow changes the direction by 90 degrees.
L/R 180°Elbow: Long Radius 180 degree return bend allows complete reversal of flow.
Short Radius (SR) Elbow is also called SR elbow, – means the radius is 1.0 times the pipe diameter
Short radiu 45°Elbow: Short radius 45° elbow changes the direction by 45 degrees.
Short radius 90°Elbow: Short Radius 90° elbow is same as LR90 except for the measurement between end of elbow to center line is 1 x NPS.
Short radius 180° Elbow: Short Radius 180° return bend allows complete reversal of flow.
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:
There is a need to reduce the cost of elbows;
There is a scarcity of space and volume to allow a Long Radius type.
Seamless elbow: 1/2″-24″ DN15-DN600
Welding elbow: 6″-72″ DN150-DN1800
Wall thickness: Sch5-Sch160 XXS
Carbon steel: ASTM/ASME A234 WPB-WPC
- WP 22-WP 5-WP 91-WP 911
- ASTM A335 P22
- ASME SA335 P91 elbow
- ASTM A234 WP 11
Low temperature steel: ASTM/ASME A402 WPL 3-WPL 6
High performance steel: ASTM/ASME A860 WPHY 42-46-52-60-65-70
- ASTM/ASME A403 WP 304-304L-304H-304LN-304N
- ASTM/ASME A403 WP 316-316L-316H-316LN-316N-316Ti
- ASTM/ASME A403 WP 321-321H ASTM/ASME A403 WP 347-347H
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