A P&ID can be a detailed flow diagram of a processing unit of a plant or factory.
This diagram will show a graphical representation of the devices interconnected in a process and it will also show the equipment that controls the process.

A Piping & Instrumentation Diagrams should provide following data

1. Equipment’s – tanks, vessels, pumps, compressors, columns etc. have to be indicated with type, reference tag numbers, basic design data etc.

2. Drains and Vents – are normally indicated using typical symbols along with their size and type (single valve, double valve etc.).

3. Lines – reference tag numbers, piping material class, line size, fluid service, insulation type and thickness etc.