Steel pipe elbow (sometimes also referred to as bends) is a key part of a pressure piping system used to change the fluid flow direction. It is used to connect two pipes with the same or different nominal diameters, and to make the pipe and thus the fluid direction turn to a certain direction of 45 degrees or 90 degrees. This change in fluid flow direction adds pressure losses to the system due to impact, friction, and re-acceleration.
Classification of Steel Pipe Elbows
Types of Elbows based on Direction Angle
According to the fluid flow direction of the pipes, elbows can be divided into different degrees, such as 45 degrees, 90 degrees, and 180 degrees, which are the most common elbows. Also, there are 60-degree and 120-degree elbows for some special pipelines. This degree is just a representation of the angle by which the fluid flow is going to change after flowing through the said elbow.
Types of Elbows based on Length and Radius
Elbows are split into two groups which define the distance over which the flowing fluid change direction; the centerline of one end to the opposite face. This is known as the “Center to Face” distance and is equivalent to the radius through which the elbow is bent.
If the radius is the same as pipe diameter (Center-to-Face dimension of 1.0 X diameter ), it is called Short Radius Elbow (SR elbow) used normally for low pressure and low-speed pipelines or in tight areas where clearance is the main issue. If the radius is larger than the pipe diameter (Center-to-Face dimension of 1.5 X diameter) then we call it a Long Radius Elbow (LR Elbow) used for high pressure and high flow rate pipelines.
Types of Elbows based on Connection with Pipe
As per the connection with pipe, elbows could be classified as Butt Welded elbows, Socket Welded elbows, and Threaded elbows.
Butt Welded Elbow
A buttweld elbow is a steel elbow formed by hot pressing or forging. Its connection form is to directly weld the elbow and steel pipe. Butt-welded elbows have beveled ends to allow for ease of welding. This bevel allows for full penetration weld in most cases. Butt-welded elbows are mainly used for elbows with higher pressure and temperature.
Socket Welded Elbow
Socket weld elbow is also welded to the pipe and fittings end. Unlike the butt weld elbow, the socket weld elbow has a trapezoidal area at the end. We can insert the pipe end into this area (the diameter of the SW elbow is matched with the outer diameter of the pipe), then do welding work to connect them together. Therefore, the actual diameter of the SW elbow end is greater than the elbow diameter.
The shape of the threaded elbow is similar to the SW elbow, except that the inner surface of the trapezoidal area has been machined into thread. It is easier to install and remove, good for pipeline repair and maintenance.