Studying a variety of P&IDs is the best way to learn how to read one of them. Although the symbols used in these diagrams are the same, the way they are used in piping and instrumentation diagrams differ. Below here is one more P&ID for you to study. This P&ID is adapted from a real plant instrument diagram to help learn the basics of how to read such diagrams:
Symbols Used in the P&ID
The first thing to do with any P&ID is to try to identify the various
instrument symbols used. This can usually be
gotten from the library of symbols located somewhere in the P&ID legend. To help in understanding the above P&ID, the various symbols used in the diagram and their meaning are indicated in the table below:
gotten from the library of symbols located somewhere in the P&ID legend. To help in understanding the above P&ID, the various symbols used in the diagram and their meaning are indicated in the table below:
Instrument Abbreviations Used in the P&ID
Another key part of the above piping and instrumentation diagram is the
instrument abbreviations used in tagging each of the instrument symbol
used. The table below illustrates all the instrument symbols used and
their various meanings:
| Instrument Abbreviation | Meaning of Abbreviation Used | Function |
|---|---|---|
| TI | Temperature Indicator |
It helps to measure and indicate the temperature ofthe process fluid entering the vessel |
| PI | Pressure Indicator | Measures and indicates the pressure inside the process vessel |
| LT | Level Transmitter | The transmitter continuously measures the level of liquid inside the process vessel and transmits its value to LIC |
| LI | Level Indicator | It helps to indicate level locally in the field such that plant operators can easily get an idea of the level of liquid in the vessel |
| LIC | Level Indicator and Controller | LIC receives the electronic value of level of process liquid in the vessel from LT and based on the set point in LIC helps to actuate the level control valve to remove liquid from the process vessel. |
| LAL | Level Alarm Low | The continuous level measured by LT is configured for a low level alarm such that when the level of liquid in the process vessel gets to that set point, a Level Alarm Low signal is indicated in the control room. |
| LAH | Level Alarm High | The continuous level measured by LT is configured for a high level alarm such that when the level of liquid in the process vessel gets to that set point, a Level Alarm High signal is indicated in the control room. |
To fully understand how the instrument abbreviations are formed please read:
