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Close Radius Pipe Bending

A pipe bend is classified according to the centerline radius (CLR) of the bend as a ratio to the nominal pipe diameter. 4 N.P.S. pipe that is bent on a 6 CLR is classified as a 1D bend or 1 times the nominal pipe diameter. When 4 N.P.S. pipe is bent on a 12 CLR, the bend is classified as a 3D bend or 3 times the nominal pipe diameter.

Close Radius Pipe Bending involves the process of providing a machine formed pipe bend made at ambient temperatures to a centerline radius of 1 times the nominal pipe size. The major reason for choosing 1D is that it is interchangeable with long radius butt weld elbows. This allows for the substitution of a pipe bend for a Long Radius 90 and 45 Butt Weld Elbow Fitting. (The centerline radius of a Long Radius 90 or 45 Elbow that is manufactured to ASME/ANSI B16.9 is also 1 times the nominal pipe size. A 4 Long Radius 90 Elbow is 6 center-to-face.)

The replacement of bends for elbows will provide piping with higher integrity, faster fabrication, and lower cost. Lower costs are achieved by:

  1. Not having to procure the elbow fitting.
  2. Eliminating the welds associated with the elbow fitting.
  3. No Non-Destructive Testing of the welds (i.e. radiography)

In addition, engineering drawings or isometric drawings do not need to be changed to permit bending. When modifying an existing pre-formed system, a standard weld fitting can be used or vice versa.

Further information regarding 1D and 3D bending is available in specification ES-7 .