A pipe bend is classified according to the centerline radius (CLR) of the bend as a ratio to the nominal pipe diameter. 4² N.P.S. pipe that is bent on a 6² CLR is classified as a 1½D bend or 1½ times the nominal pipe diameter. When 4² N.P.S. pipe is bent on a 12² 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 1½ times the nominal pipe size. The major reason for choosing 1½D 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 1½ times the nominal pipe size. A 4² Long Radius 90° Elbow is 6² 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.