P&ID Instrumentation

Process Control Schemes
Process flow and control diagrams generally do not show equipment controls, safety controls, and miscellaneous minor instruments. When incorporating process controls on the P&ID, the plant designer makes hardware and software choices that were unavailable to the process control designer. These choices can affect the function of the process controls and should be reviewed with the process control expert.

Equipment Control Schemes
If they are very simple, major equipment controls should be shown on the process P&ID. Otherwise, they should be shown in detail on a separate equipment P&ID and referenced on the process P&ID.

Equipment control schemes should be developed in coordination with equipment vendors, and Company and design agency equipment control specialists. The resulting P&IDs should be reviewed with an equipment control expert.

Review and approve equipment controls that are completely determined by the Vendor in packaged systems. With packaged systems, a Company instrumentation expert should be consulted before it is too late to make changes.

Minor Instrumentation
The P&ID designer is responsible for putting all minor instrumentation on the P&ID, including the following:
• Locally mounted pressure gages
• Remote temperature indicators
• Local temperature indicators
• Local level indication
• Remote flow indicators
• Alarm and shutdown systems
• Pressure sensors for automatic pump starters
• Toxic and combustible gas monitors
• Transmitter output indicators