"The values for the flanges (service limits) have been entered by using the standard import in the PCC software. However with the calculations I still get an overrun or error. The P and Pmax should be equal at the different temperatures. I get this mistake for all size. Is this due to rounding or what am I doing wrong?"

Refer to below image:



The PCC software gives the correct validation messages. The above happens if you select flanges from one standard and the design conditions from another standard. The flange standards have been changed during the years. Make sure you select consistently the flange standard for the design conditions and the flanges in the pipe classes.

For example selection of the design conditions in the Pipe Class Edit dialog:



the default materials:



and the actual selected flanges for the pipe class:



Now the verification of the flange rating (according ASME B16.5 edition 2009) is consistent with the selected flanges.