Hi Rodrigo,
The input for the weld neck at the back of the flange is just used to check minimum clearance between the pipe and the bolt circle diameter as suggested per TEMA.
Did you enter the flange ID as shown in Figure 2-4 (7)? For the integral ring flange it should be the pipe ID.
If you still need help then send your file and your hand calculations to supportcoade.com.
_________________________
Best Regards,
Mandeep Singh
CADWorx & Analysis Solutions
Hexagon PPM