A P&ID Should Include and Should not Include

This figure depict a very small and simplified P&ID:

P&ID shows all of piping including the physical sequence of branches, reducers, valves, equipment, instrumentation and control interlocks. The P&ID are used to operate the process system.
A P&ID should include:

• Instrumentation and designations
• Mechanical equipment with names and numbers
• All valves and their identifications
• Process piping, sizes and identification
• Miscellaneous – vents, drains, special fittings, sampling lines, reducers, increasers and swagers
• Permanent start-up and flush lines
• Flow directions
• Interconnections references
• Control inputs and outputs, interlocks
• Interfaces for class changes
• Seismic category
• Quality level
• Annunciation inputs
• Computer control system input
• Vendor and contractor interfaces
• Identification of components and subsystems delivered by others
• Intended physical sequence of the equipment

A P&ID should not include:

• Instrument root valves
• Control relays
• Manual switches
• Equipment rating or capacity
• Primary instrument tubing and valves
• Pressure temperature and flow data
• Elbow, tees and similar standard fittings
• Extensive explanatory notes