Piping and Instrumentation Diagram - P&ID

What is a Piping and Instrumentation Diagram - P&ID?

A Piping and Instrumentation Diagram - P&ID, is a schematic illustration of functional relationship of piping, instrumentation and system equipment components.

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 / size changes 
  • Flow directions 
  • Interconnections 
  • Control inputs and outputs, interlocks 

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

About the Author


{cb:Anton Dooley is a Piper with 30 years experience covering process plant engineering, design & training. He is the founder of pipingdesigners.com}

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