Custom Pipe Bending – 1D to 5D Bends


Custom pipe bending is generally any type of pipe bends that do not conform to standard short or long radius bends in the standard bend degrees of 45deg, 90deg, and 180deg of rotation. In the pipe bending world, bend types are often called out and referred to by their respective bend radii.

With standard pipe bending this is done so by comparing the bend radius to the diameter of the pipe being bent. 1D, 2D, and 3D bends are often referred to as short radius and long radius bends; with the 1D, 2D and 3D specifications calling out the center line radius of the bend as the multiplier of the pipe’s respective diameter. 1D would be a centerline bend radius that is one times the diameter of the pipe. This means a 1D bend on a 6-inch pipe would be a 6-inch centerline radius. Short radius bends are specified to be 1D bends.

1.5D bends and up are considered long radius bends. A 2D bend on a 6-inch pipe would have a 12-inch centerline radius. This would be referred to as a long radius bend, which includes 2D up to and including 5D bends – or the center line radius that is 5 times the pipe’s respective diameter. These standard bend specifications in their standard degrees of rotation are all rolled in a single plane with simple level geometry.

Custom pipe bends are anything that is not the standard 1D to 5D centerline bend radius with standard bend degrees. To understand why let’s discuss the process used to make these bends – mandrel pipe bending or rotary draw bending. A complete set of dies is required for a rotary draw bending machine to achieve a successful bend in the standard 1D to 5D range. This includes a forward clamp, a bending die, a mandrel, a wiper die and a push assisting die. This set of tooling is dedicated to a specific pipe diameter and a specific centerline radius. Specifying these 1D to 5D bends as standard allows engineers to specify radii on a wide variety of pipe diameters while still being able to acquire the parts at a moderate cost in a reasonable amount of time.

Custom pipe bending can be specified at any radius and are much more complex because some parts require multiple bends within a single piece. This is often referred to as a spool. A spool is a length of prefabricated pipe with a certain specification regarding the number of bends and geometry of those bends within a single length of pipe and pipe flange affixed on either end, readying the pipe to be bolted into place when installed. Pipe spools can contain as many bends as the manufacturer/fabricator of the part will allow or can accommodate. Many times, these types custom pipe bending is called 3D bends as the plane of bending changes from bend to bend requiring positive and negative rotations of the pipe in between bends, allowing the spool to twist and turn and snake its way into the desired position often required by the spool’s specific application.

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