P & I Diagram :Introduction
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, 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
This figure depict a very small and simplified P&ID:
A P&ID should not include:
- Instrument root valves
- control relays
- manual switches
- equipment rating or capacity
- primary instrument tubing and valves
- pressure temperature and flow data
- elbow, tees and similar standard fittings
- extensive explanatory notes
