Modular process plants require a new interaction of process engineering and automation engineering. During the engineering of Process Equipment Assemblies (PEA) the automation functions are encapsulated in services which represent process operations. In this work an approach is presented, where System Control Diagrams (SCD) are utilized to create a transition from process operations to automation functions to services all on the basis of the Piping and Instrumentation Diagram (P&ID). Using this method, a comprehensible graphical and machine-readable link between both sides is created. In combination with existing tools, it is shown that part of the automation could already be prepared during the design of the P&ID. The proposed concept is evaluated using a water deionization PEA.