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What are the differences between 1D, 1.5D and 2.5D elbows?

Aug. 08, 2025

A 1D elbow has a bend radius of 1D, which is equal to 1 times the diameter of the object (pipe) being bent.

A 1.5D elbow has a bend radius of 1.5D, which is equal to 1.5 times the diameter of the object (pipe) being bent.

A 2.5D elbow has a bend radius of 2.5D, which is equal to 2.5 times the diameter of the object (pipe) being bent.

A short-radius elbow has a curvature radius equal to 1 times the pipe diameter; also known as 1D, the curvature radius of the elbow is equal to 1 times the pipe diameter and is typically a 90° angle.

Differentiation of Short-Radius Elbows

Intuitively, short-radius elbows are much shorter than long-radius elbows, and their bend radius is very abrupt. Long-radius elbows are the most commonly used and are generally the default. Long-radius elbows are used in high-pressure or high-flow applications. For solids transport pipelines with stringent resistance requirements, larger-radius elbows are used. Applications of Short Radius Elbows

Short radius elbows are generally used in low-pressure fluids or where elbows are restricted. If there are no restrictions or if they are not specified in the contract, long radius elbows are preferred.

Calculation Formula

1. Elbow Height

1.5 times the elbow center height = diameter * 1.524. This is essentially diameter * multiple, rounding the decimal point to the nearest integer. For example, if the diameter of a 219 is 200, the center height is 200 * 1.524 = 304.8, so we choose 305. For example, if the diameter of a 114 is 100, the center height is 100 * 1.524 = 152.4, so we choose 152.

2. Stamp Height

Center height + elbow radius. For example, the stamp height of an elbow with a diameter of 219 is 1.5 times the elbow center height = 305 + 219/2 = 305 + 109.5 = 414.5. 3. Outer Arc Length

(Center Height + Radius) * 3.14 * 2 / 360 * Degrees, or (Stamp Height) * 3.14 * 2 / 360 * Degrees. From this, we can deduce that the outer arc length of a 90-degree elbow = Stamp Height * 3.14 / 2.

4. Inner Arc Length

(Center Height - Radius) * 3.14 * 2 / 360 * Degrees.

5. Elbow Cutting Length

(Elbow Center Height * 3.14 / 2 * Elbow Outer Diameter / Pipe Diameter + (Pipe Wall Thickness * 3) + Machining Allowance). For example, if you are cutting a 180 x 8" pipe and making a 273" elbow, using the above formula, you can calculate the cutting length = 381 * 1.57 * 273 / 180 + 24 = 931.22 mm + Machining Allowance. The Difference Between 1.5D and 2.5D Elbows

1.5D and 2.5D refer to the elbow's bend radius, with 1.5 and 2.5 referring to the coefficient of the elbow's bend radius. D refers to the nominal diameter of the elbow. For example, for a DN100 elbow, the bend radius of 1.5D = 150mm (1.5 x 100 mm); the bend radius of 2.5D = 250mm (2.5 x 100 mm). Therefore, the difference between a 1.5D and 2.5D elbow is similar to the difference between a circle drawn with 150mm and 250mm (a circle is divided into four parts, one of which is a 90° elbow). This method is suitable for calculating the curvature radius of elbows DN100 and above, providing a quick and convenient method.

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