Yes, an OPIM license is not require or be charged for usage if creating an Stress Isometric using AutoPIPE Advance or Nuclear editions
HOWEVER, if OPIM software or cad models are accessed directly without using AutoPIPE, then YES the user will need a OPIM license and usage charges will be incurred.
Again, use AutoPIPE commands:
a. Save Stress Isometric (File > Isometric > Save Stress Isometric)
b. OpenPlant Isometrics Manager (File > Isometric > OpenPlant Isometrics Manager)
Note: an AutoPIPE Stress Isometric drawing can be viewed with Bentley View without any usage charge against OPIM Licensing.