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&IDs should

P&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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