WT_LEN is a line stock parameter from which the piping solid derives the density value for mass property calculations. Creo Parametric sets the density value for a piping solid using the following equation:

where

^ is power

OD is outline diameter (from line stock)

WT is wall thickness (from line stock)

When you regenerate the piping solid in Assembly mode, the solid checks the current line stock for the segment and looks at the OD and WT_LEN values to verify that the current density is correct.

However, if you regenerate the piping solid in Part mode, the density value remains frozen because the line stock parameters are not available.