Nowadays the design of industrial communications networks is based on heuristics which are well known by engineers experienced in this design process. Unexperienced engineers have difficulties to design networks because of their complexitiy. The approach of NetGen:X closes this gap by automating the design using the known heuristics. Additional requirements like the reliability of safety relevant process control functions require a function-oriented consideration of the network. Therefore we provide an approach to automatically evaluate the network using a network graph analysis. The analysis is based on the safety functions and their reliability requirements which are projected in the piping and instrumentation diagram (P&ID) of the computer aided engineering system (CAE system) for process plants. In this article we analyze P&IDs which are conform to the standard EN IEC 62424 and identify additional constraints that need to be considered to enable an automated extraction of the information for the network graph analysis. We show that a slightly extended computer aided engineering eXchange model (CAEX model) is capable to provide all the necessary information.