Basic P&ID symbols in the process industry documentation

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.

Figure 1.

 

General instrument or function symbols

 

Instrument Line symbols

 

Primary elements

 

Valves

 

Pumps

Centrifugal pumps

Positive displacement pumps

 

Compressors

Centrifugal compressors

PD Compressors

 

Heat Exchangers

 

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