The Pipe Bending Elongation Rule node (the PipeBendingElongationPerSpec sheet in the Piping.xls workbook) defines the amount of "stretch" that occurs to the pipe length during the piping bending process. By using this rule, the software can report the correct cut length on the billofmaterials for the isometric drawing.
Cut length = Calculated centerline length  Pipe elongation
where:
calculated centerline length = L1 + L2  2.0 × R × Tan (a / 2.0) + R × a
You can define the "stretch" length by doing one of the following:

Specifying the amount of pipe elongation per unit of bend angle for each applicable nominal piping diameter and bend radius.

Specifying the pipe elongation values at a specific bend angle for each applicable nominal piping diameter and bend radius.

Specifying the pipe elongation values using a combination of the two methods. If both methods are defined for a nominal piping diameter and bend radius, the pipe elongation value at a specific bend angle takes precedence and is used.
This sheet contains all the default values that the software is to use in the piping specification. You can define exceptions for a particular piping materials class in the Pipe Bending Elongation Per Spec under the Piping Material Class node.
Bend Angle (Required)
Specify the bend angle for which the pipe bending elongation applies.
Nominal Piping Diameter (Required)
Specify the pipe diameter for which the flared pipe information applies.
Nominal Piping Diameter Units (Required)
Specify the unit of measurement, in or mm for example, for the value in the Nominal Piping Diameter column.
Pipe Bend Radius (Required)
Specify the pipe bend radius. Be sure to include the units of measurement when defining this value.
Pipe Elongation (Required)
Specify the elongation value of the plain piping due to the bending process as an absolute value for a specific bend angle.
Pipe Elongation Unit Bend Angle (Required)
Specify the elongation of the plain piping due to the bending process per unit of bend angle. This value is the factor in the following equation: Elongation = Factor * Bend Angle.