Piping and Instrumentation Diagram

on . Posted in Design Engineering

In the design process, a piping and instrumentation diagram, abbreviated as P&ID, is created following the Block Flow Diagram and Process Flow Diagram.  The P&ID contains all the piping, valves and instrumentation in a process.  The P&ID also shows relationships between control mechanisms such as control valves and level control switches or valve position related to the temperature of a process.  Essentially, the P&ID is a roadmap on how the process will function.

P&IDs contain a great amount of detail.  The instrumentation tags, line numbers, primary and secondary lines, control mechanisms etc. should all be included on on the P&ID.


P&ID's Should Include

P&IDs shouldP&IDs should not
  • The information found on a Process Flow Diagram with the exceptions of what is shown on the right.
  • Instrumentation, designations, types, ranges where applicable, etc
  • All valves, sizes and their identifications
  • Flanges including break out spools for maintenance, spectacle blinds, blind flanges, as appropriate, to define how the process works. 
  • All process piping, sizes and identification including all bypass and recirculation lines.
  • Miscellaneous lines and items including vents, drains, special fittings, sampling lines, reducers, and swages
  • Permanent start-up and flush lines
  • Interconnecting references to other systems
  • Control inputs and outputs, interlocks
  • Interfaces for class changes clearly marked
  • Annunciation inputs and outputs
  • Computer control system input
  • Vendor and contractor interfaces (eg skid limits)
  • Identification of components and subsystems delivered by others
  • Intended physical sequence of the equipment
  • Major equipment symbols, names and identification numbers
  • Flow directions
  • System ratings and operational values as minimum, normal and maximum flow, temperature and pressure
  • Composition of Fluids
  • Show geographical elements of the piping unless the process requires a specific piping orientation as an example, meter runs
  • Instrument root valves
  • control relays
  • manual switches with the exception of HOA or JOA type switches.
  • primary instrument tubing and valves
  • extensive explanatory notes


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