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
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| P&IDs should | P&IDs should not |
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- 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
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- 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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