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Segment Bends

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Sample method to bend 3-1/2″ rigid conduit around a storage tank with a diameter of 160 feet.

Segment bending is a method of bending conduit by making several small bends to produce one larger bend.  The method on this page illustrates a technique for bending a 3-1/2″ rigid conduit around a tank with a 160′ diameter.

The steps for calculating a large radius segment bend are:

  1. Determine the radius of the desired bend. 

The following procedure illustrates the procedure to bend a length of 3-1/2″ rigid conduit around a storage tank with an 80′ radius, or a 160′ diameter.

First, find the circumference of the tank.

Diameter in inches, with 2 strut, 1 on each side, plus 1 conduit diameter, or 1/2 for each side, = 160 x 12 + 1-5/8 x 2 + 2 x 2 = 1925.625″

Circumference = Pi x Diameter = 3.14159265 x 1925.625 = 6,049.53″.  This is the total length of conduit needed to complete the bending angle of 360 degrees to go all the way around the tank.  A 10′ length of 3-1/2″ rigid conduit without the coupling is 9′ 10-1/4″ = 118-1/4″.  The number of conduit required to go all the way around the tank, or 360 degrees, is 6,049.53 / 118.25 = 51.16.

Divide the total angle to go around the tank, 360 by the number of conduits required, 51.16, to get the angle required to bend each length of conduit. 360 / 51.16 =  7.04 degrees for  each length of conduit.

  1. Determine the number of segments desired or required for the completed bend.

    If a length of conduit is going to be bent to such a small angle, it is practical to only make 2 or 3 bends on each length of conduit.  

  2. Determine the Developed Length of the bend.

    Developed length (DL) is the length of conduit that is actually bent. The formula to calculate the developed length of a bend is:  Developed length (DL) is equal to the centerline radius (R) of the bend times the angle (A) of the bend times 0.01745.  DL = R x A x 0.01745

    The radius of the tank plus the strut and conduit is 962.8125″  The developed length for a 7.04 degree bend with a 962.8125″ radius is 7.04 x 962.8125 x 0.01745 = 118.28″.

    DL = 7.04 x 962.8125 x 0.01745 = 118.28″.  You can see that this is one length of 3-1/2 rigid conduit.

If you want to make the bend with 1 bend, you can make on 7 degree bend in the center of the conduit.    More realistically, partly for purposes of strapping the conduit, and NEC requirements for distance from any junction boxes to straps, I would make 2 bends of about 3.5 degrees at about 30″ and 90″ on the length of conduit, at approximately the 1/3 and 2/3 distances on the conduit.

You could select a larger number of bends, but I think it would be more difficult to bend to a smaller angle, although the bends will look smoother.

 

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