P&ID : Piping and Instrumentation Diagram

Piping and Instrumentation Diagrams or simply P&IDs are the schematics used in the field of instrumentation and process control. The P&ID is used by technicians, engineers, and operators to immediately identify an instrument and understand the process and how the instruments are inter connected.

The P&ID will use symbols and circles to represent each instrument and how they are inter-connected in the process.



“Tag  numbers” composed of letters and numbers are placed within or near the instrument to identify the type and function of the device. The first letter is used to designate the measured variable. The succeeding letter(s) are used to designate the function of the component, or to modify the meaning of the first letter. The topmost instrument shown in the animation above for example: tagged TRC is a temperature Recording Controller. The numbers that follows corresponds to the  inventory number of the instruments.

P&ID Identification

For the complete list of Identification and reference designation
Click Here.

The presence or absence of a line determines the location of the physical device. For example no line means the instrument is installed in the field near the process.

  • No Line The instrument is mounted in the field near the process, (close to the operator)
  • Solid Line The instrument is mounted in the control room (accessible to the operator)
  • Hidden Lines or Dotted lines means that the instrument is mounted out of sight (not accessible to the operator)

Some instruments are part of a Distributed Control System (DCS) where a specific controller or indicator can be selected from many others but shown in one location. Type and location of the instruments are also illustrated  in the summary below.

location of instruments

Below are symbols  used to identify how the instruments in the process connect to each other. And what type of signal is being used. (electrical, pneumatic, data, etc)

piping and connections

Valve symbols are also emphasized depending on its functions and used. Click Here to see more of its symbols. 

valve symbols

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