Basic P&ID symbols in the process industry documentation

Posted 18 Jul 2017 by Nikolay
The P&ID symbols indicate various instruments, equipment or functions.
The P&ID symbols indicate various instruments, equipment or functions.

A standard set of symbols is used by the process engineers when designing the Piping and Instrumentation diagrams. The first thing to do when reading P&ID is do get to know the symbol's legend.

Like other specialized diagrams, P&IDs are built up of standard shapes and symbols. There is a huge variety of symbols, depending on industry and manufacturer. Most industries have standardized their symbol representation according to the ISA Standard S5.1 Instrumentation Symbol Specification and use them to design: P&IDs, Flow Diagrams, Logic Plans.

The shapes in the legend are representative of the functional relationship between piping, instrumentation, and system equipment units.

They can be broken to some main groups:
- general instrument or function symbols
- instrument line symbols
- primary elements
- valves
- pumps
- compressors
- vessels
- heat exchangers

On Figure 1 is show a basic example of representing the physical equipment on the in the P&ID.

P&ID Elements
Figure 1.


General instrument or function symbols

P&ID General instrument and function symbols


Instrument Line symbols

P&ID Line symbols


Primary elements

P&ID Primary elements



P&ID Valves



Centrifugal pumps

P&ID Pumps

Positive displacement pumps

P&ID Pumps



Centrifugal compressors

P&ID Compressors

PD Compressors

P&ID Compressors


Heat Exchangers

P&ID Heat exchangers



P&ID Filters


Related articles:

    Process Flow Diagrams, Piping and Instrumentation Diagrams - basic definitions

    Piping and Instrumentation Diagrams

    TAG Numbers in process industry used to identify field devices according to ISA-5.1




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