P&ID - Piping and Instrumentation Diagram

Schematic illustration of a functional relationship between piping, instrumentation and system components. A P&ID shows all piping including physical sequences of branches, reducers, valves, equipment, instrumentation and control interlocks.

P&ID - Piping and Instrumentation Diagram

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

Key Elements to Include:

  • Instrumentation and designations
  • Mechanical equipment with names and numbers
  • All valves and their identifications
  • Process piping, sizes and identification
  • Miscellaneous components (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

Should NOT Include:

  • Equipment rating or capacities
  • Instrument root valves
  • Control relays
  • Manual switches and indicating lights
  • Primary instrument tubing and valves
  • Pressure temperature and flow data
  • Elbows and similar standard fittings
  • Extensive explanatory notes
Component TypeDescriptionIdentification RequiredPurpose in P&ID
PipingProcess flow lines with sizesYes - with size designationDefine fluid paths and line sizing
ValvesControl, isolation, relief, check valvesYes - unique identificationControl and regulate flow
EquipmentPumps, compressors, reactors, heat exchangersYes - name and numberPrimary process equipment
InstrumentationSensors, transmitters, indicators, controllersYes - per ISA standardsMonitor and control parameters
FittingsReducers, increasers, swagers, teesOnly special fittingsConnect piping components
InterlocksControl logic and interconnectionsYes - with referenceSafety and operational logic
Vents & DrainsAtmospheric or process connectionsYes - identifiedSystem maintenance and safety