To bend tube and pipe, almost all bending machines require more material than the usable arc in the finished bend. These bending tangents, or the straight piece of the tube on each end of the bent arc (see Figure 1), are required by the bending machine to apply leverage to the material during bending.
These required tangents vary but range from two to four times the tube and pipe’s OD on each end. Let these required bending tangents work for you and not against you.
If the bent part will be attached to more straight material in service, design the bend so that these bending tangents remain on the bend and are not removed by the bender. This reduces labor at the bender and the amount of straight material needed at the next fabrication step.
This also reduces the cost to attach the bend, in terms of labor and welding, to the rest of the fabrication because this extended end of the bending tangent is inherently less distorted by the bending pressures and will mate with tube and pipe of the original size with little or no roundup or rework.
Another reason to consider tangents when designing bends regards the standard tube and pipe lengths commonly available. Before designing bends, determine the common lengths available that will work for your project, then design with these lengths in mind to avoid higher than necessary material costs.
To get the maximum bent arc from the available lengths, subtract the required bending tangents from the available length to determine the maximum economical bent arc per piece. Otherwise, additional material must be welded to the material to be bent to allow for these required bending tangents. This additional material cost will be minimal compared to the welding stub cost. Experience has shown that the wise use of bending tangents generally can save from 10 percent to 50 percent on your next bending job.