What are the calculation methods for the geometric dimensions of the elbow

The elbow is a commonly used pipe fitting in installation, which is used for connecting at the bends of pipes and to change the direction of the pipes. 

Other names: 90° elbow, right-angle bend, Ai Er bend, stamped elbow, pressed elbow, mechanism elbow, welded elbow, etc. 

Purpose: Connect two pipes with the same or different nominal diameters, enabling the pipeline to make 90°, 45°, 180° and various degrees of turns. 

A bend with a bending radius no greater than 1.5 times the pipe diameter is classified as a "bend pipe", while a bend with a bending radius greater than 1.5 times the pipe diameter is considered a "bent pipe". 

Technical requirements for producing elbows: 

The curvature radius must be controlled. For example, if the radius length is 1.5D, then the curvature radius must be within the required tolerance range. Since most of these pipe fittings are used for welding, in order to improve the welding quality, the ends are ground into bevels, leaving a certain angle and a certain edge. This requirement is also quite strict. The thickness of the edge, the angle and the deviation range all have regulations. There are many more items in this requirement compared to the pipe fittings. The surface quality and mechanical properties of the elbow are basically the same as those of the pipe. For the convenience of welding, the steel material of the elbow must be the same as that of the connected pipe. 

Geometric dimension calculation method:

1. 1.5 times elbow (also known as conventional long-radius elbow, 1.5D elbow): Center height A = nominal diameter D * 1.524. This is actually the multiple of the nominal diameter D. The decimal part of the result is rounded off to the nearest integer.

Example 1: The nominal diameter D of Φ219 is 200, so the center height is 200 * 1.524 = 304.8, which is rounded to 305.

Example 2: If the nominal diameter of Φ114 is 100, the center height is 100 * 1.524 = 152.4, which is rounded to 152.

(This algorithm is applicable to the calculation of the curvature radius of elbows with a diameter of DN100 and above, and is convenient and quick.) 

2. Height above center = Center height A + Radius of the elbow

Example 1: For a 219 mm diameter elbow, the height above center = 305 + 219/2 = 305 + 109.5 = 414.5

Example 2: For a 114 mm diameter elbow, the height above center = 152 + 114/2 = 209 

3. The length of the outer arc = (center height + radius) * 3.14 * 2 / 360 * degree, that is, (center height * 3.14 * 2 / 360 * degree). Thus, the length of the outer arc of a 90-degree elbow = center height * 3.14 / 2.

Example 1: For a 219mm elbow, the length of the outer arc = 414.5 * 3.14 / 2 = 650.8

Example 2: For a 114mm elbow, the length of the outer arc = 209 * 3.14 / 2 = 328.1 

4. Inner arc length = (Center height - Radius) * 3.14 * 2 / 360 * Degree = (Center height - Radius) * 3.14 / 2

Example 1: For a 219mm diameter elbow, the inner arc length = (305 - 219/2) * 3.14 / 2 = 306.9

Example 2: For a 114mm diameter elbow, the inner arc length = (152 - 114/2) * 3.14 / 2 = 149.1 

5. The cutting length of the elbow = The center height of the elbow * 3.14/2 * Outer diameter of the elbow / Diameter of the pipe + (Pipe wall thickness * 3) + Processing allowance

Example 1: For a 219 mm diameter elbow, the cutting length = 305 * 3.14/2 * 219 / Diameter of the pipe + Pipe wall thickness * 3 + Processing allowance

Example 2: For a 114 mm diameter elbow, the cutting length = 152 * 3.14/2 * 114 / Diameter of the pipe + Pipe wall thickness * 3 + Processing allowance