Knowledge of Long Radius Elbows

The definition of the long radius elbow
The long radius elbow is the elbow which the radius of curvature of is 1.5 times the diameter of the pipe; if the radius of curvature is greater than 1.5 times, the long radius elbow will be called the bend. The short radius elbow means that the radius of curvature of the elbow equals the diameter of the pipe, or 1 time the diameter of the pipe in common words. D is used to represent the diameter of the elbow. The long radius is used most commonly, and it is also the default radius. When it is the place with the high pressure or the high flow rate, the long radius elbow is usually used. If the resistance requirements of the solid transmission pipeline are strict, the larger radius elbows will be used. 

The short radius elbow is generally used for the low pressure fluid or when there are some limits concerning the installation of the elbow. If there is no conditional limit or nothing marked in the contract particularly, the long radius elbow shall be preferred. Boxes, pallets, etc. will be used for the package. The long radius elbows are generally made of the stainless steel, the carbon steel and the alloy steel, and they are widely used in the sewage treatment, chemical, thermal, pharmaceutical, aerospace, power, paper and other industries.

The standard of the long radius elbow
The National Standard GB/T12459-2005
The National Standard GB/T13401-2005
The National Standard GB/T10752-1995
The Chemical standard HGJ514-87
The electric power standard DL/T695-1999 
The electric power standard D-GD87-0219

What is the radius of curvature?
Radius of curvature is the curvature of a curve. The curvature of a plane curve is defined as the rotation rate of the tangent angle of a point on the curve to the length of the arc. It is defined by differentiation and it shows the degree of the curve deviating from the line. The reciprocal of curvature is the radius of curvature. The radius of curvature is mainly used to describe the extent of curvature variation of a point on a curve.

Technical requirements for the long radius elbow
It is required that the radius of curvature should be controlled. For example, if the radius is 1.5D, then the radius of curvature must be within the required tolerance range. Because most of these pipe fittings are used for welding, in order to improve the quality of welding, the end will be turned into the groove and it will keep the certain angle and edge. This requirement is quite strict, and the thickness of the edge, the angle as well as the deviation range are all defined. There are more requirements on the physical dimension of long radius elbows than those on the pipe fittings. The surface quality and mechanical properties of the elbow are almost the same as the pipe's. To facilitate welding, the long radius elbow should be made of the same kind material of the pipe to be connected.