By: Ryan Malone
Piping and Instrumentation Diagrams—abbreviated P&IDs—are the schematics used in the field of instrumentation and control.
Field techs, engineers, and operators use P&ID symbols to better understand the process and how the instrumentation is interconnected.
Most industries have standardized the symbols according to the ISA standard S5.1 Instrumentation Symbol Specification. Some organization may also refer to P&IDs as “Process & Instrumentation Diagrams” or “Process Flow Diagram-PFD” (simplified version of the P&ID).
Using pictorial diagrams like this one may be informative; however, they are not practical or CAD friendly especially in a multi-loop process.
Rather than rendered images, the P&ID will use symbols and circles to represent each instrument and how they are interconnected in the process.
In this article, we’ll look specifically at some of the most commonly used P&ID symbols for various instruments and vessels on a P&ID.
Tag numbers are the letters and numbers that engineers place within or near the instrument to identify the type and function of the device.
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.
Engineers use these symbols to identify how the instruments in the process connect to each other and what type of signal is being used (electrical, pneumatic, data, etc.).
The control valve symbols on a P&ID differ depending on the type of valve specified for the application. Here are the most common P&ID symbols for control valves:
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