ASME/ANSI STEEL ELBOW
Steel elbows are used to change the direction of the pipeline and implement specific layouts.
They can be classified based on the degree and the radius of the flow change:
45 / 90 / 180 DEG. ELBOW
As the name evocates, 45, 90 and 180 degrees elbows create, respectively, a 45, 90 or 180 turn of the pipeline.
SHORT / LONG RADIUS
For long radius elbows, the center to face distance is always 1.5 times the nominal pipe size (the center to face dimension is "B" in the image below, which represents a long radius elbow); for short radius elbows, the center to face distance is equal to the nominal pipe size ("A" in the image below, related to a short radius elbow). (so, for example: for a 4 inch LR elbow, the center to face distance is 4 x 25.4 x 1.5 = 152.4 mm, for a SR elbow the center to face distance is instead 4 x 25.4 x 1 = 101.6 mm). ASME B16.9 and ASME B16.28 defines the dimensions, tolerances, etc. for long and short radius butt welding elbows. A short radius exists only for the 90 and 180 deg. elbows (not for the 45 degrees), while long radius elbows are available for all degrees.
- construction type: seamless (up to 24 inches) / welded (generally above 24 inches) / mitered
Special types of elbows:
- 3D, 5D elbows (special radius elbows)
- Reducing elbows: Reducing elbows have two different diameters at the two ends. Reducing elbows are sometimes used instead of the more traditional combination between a standard elbow and a concentric reducer (which is a cheaper solution, but not always possible due to space constraints).
The quality of a steel elbow is strictly connected to the quality of the bending procedures and the strenght of the product in its most fragile part, which is at the beding point.