May. 23, 2020

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When we use the 45 degree elbow center formula and the 90 degree elbow center formula, we can't remember what the elbow center formula is. Today I'm going to talk about the 90 degree elbow center formula.

For standard degrees of pipe elbows such as 45° and 90°, elbow center to end dimensions are available in standard pipe charts. But many times, custom elbow angles are required at site which should be cut from standard 45° or 90° elbows.

**Elbow length in mm = Tan(Elbow Angle/2) X Elbow Radius in mm**

For 90° Long Radius elbows, center to end dimension given in dimension tables of ASME B16.9 is same as radius of elbow. This is because Tan(90/2) i.e. Tan 45 is 1.

Normally custom elbow angles from 45 degree to 90 are cut from 90 degree standard elbow. But for custom elbow angles smaller than 45 degree, elbow is normally cut from existing standard 45 degree elbow. Center to end dimension given in dimension tables for 45 degree elbow must be divided by Tan(22.5) to get elbow radius for standard 45 degree elbow. Then we can use above formula to get elbow angle for custom degrees.

Same procedure applies to 3D elbows.

Calculate elbow center to end dimension for 4 inch nominal pipe diameter elbow at 60 degree angle, cut from 90 degree LR elbow.

From ASME B16.9, center to elbow dimension for 4 in elbow is 152 mm.

Length = Tan (60/2) X 152

Length = 0.57735027 X 152

Length = 87.757 i.e. 88 mm Approx.

Calculate elbow center to end dimension for 2 inch nominal pipe diameter elbow at 30 degree angle, cut from 45 degree LR elbow.

From ASME B16.9, center to elbow dimension for 2 inch 45 degree elbow is 35 mm.

Radius of elbow = 35/Tan(22.5)

Radius of elbow = 35/0.4142 = 84.5 mm

Length = 0.26795 X 84.5

Length = 22.64 i.e. 23 mm Approx.

Elbows are split into two groups which define the distance over which they change direction; the center line 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.

The center to face distance for a "long" radius elbow, abbreviated LR always is "1½ x Nominal Pipe Size (NPS) (1½D)", while the center to face distance for a "short" radius elbow, abbreviated SR even is to nominal pipe size.

Here below, for example, you will find the

center to face distance of NPS 2 elbows

(the A distance on the image)

**1. 90°-LR : = 1½ x 2(NPS) x 25.4 A=76.2 mm****2. 180°-LR : = 2 times the 90° LR elbow A=152.4 mm****3. 90°-SR : = 2(NPS) x 25.4 A=50.8 mm****4. 180°-SR : = 2 times the 90° SR elbow A=101.6 mm**

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