P&ID and PFD drawings used various Symbols and legends.

If you want to learn how to read P&ID and PFD, you must know the legend used in these drawings. So please watch the video till the end. You can download this presentation for free. The link is available in the description.

PFD and P&ID are also known as PFS and PEFS. PFD is a Process Flow Diagram. P&ID is a Process or piping & Instrument Diagram. PFS means Process Flow Scheme, and PEFS means Process Engineering Flow Scheme.

Here, I have tried to cover symbols that are regularly used on the P&ID and PFD. There are other symbols; also, you can check the full list of the symbol by visiting this link. Before you start working on an actual plant or construction project, I advised you to check the project-specific symbol library, also known as P&ID lead sheets or P&ID legend drawing.

The level of information available on P&ID symbols and on P&ID may change from company to company, but more or less, they provide similar information.

P&ID and PFD Symbols

P&ID symbols are a graphical representation of physical equipment installed on the field.

There are few ISO and British standards available that provide symbols and best practices to draw PFD and P&ID, such as, ISA S5.1, BS 5070, and ISO 10628.

Pumps and Turbine P&ID Symbols

The symbols for various types of rotary equipment such as a centrifugal pump, vacuum pump, and also positive displacement pumps such as gear and screw types. The last two symbols are of vertical pump and turbine.

P&ID Quiz – Test yourself, Take This Quiz

Centrifugal Pump Symbols
Positive Displacement Pump P&ID Symbols

P&ID Symbols for Compressor

The symbols for the compressor, such as reciprocating, centrifugal, rotary, liquid ring, and turbine-driven, are shown below.

Centrifugal Compressor Symbols
Positive Displacement Compressor Symbols

Heat Exchanger P&ID symbol

These are the symbols for the heat exchanger. On the drawing, you can see both types of symbols are used the one on the right-hand side are more frequent than the one on the left-hand side.

Heat exchanger p&id symbol

Symbols for Static Equipment and Distillation column

Static equipment is straightforward. Vessel, drum, tanks, and furnace. Here you can see the symbols for dome roof tank, fixed roof tank, and internal floating roof tank. In case the tank is only a floating roof, then there will be no roof on this symbol.

Tank and Vessel Symbols for P&ID

Two types of towers are shown here, one with column internal and the other without internals. Different types of the internals are used in the column, and different symbols are used.

Here in the distillation tower, you can see the different types of internal, such as mist mat, pipe distributor, liquid spray distributor, vortex breaker, baffle plate, packing bed, and some other types of trays.

Distillation columns P&ID Symbols

Line Symbols for PFD and P&ID

The below image shows various lines and connections used on PFD and P&ID. Main process lines are shown as dark black lines, whereas minor lines are shown as thin black lines. You can also see the symbols for pneumatic, hydraulic, and capillary lines.

Electric signals are shown as a dotted line, and Electromagnetic signals are shown as a wave on a solid line.

Pipeline P&ID Symbols

P&ID Symbols for Piping Valves

This is the trickiest part of reading P&ID and PFD. Here you can see the various types of valve symbols. If you remember that I have mentioned that P&ID symbols change from company to company, valves symbols are the one that changes most of the time.

So, if you are moving from one company to another, don’t rely on your memory and refer to the lead sheets for symbols. Lead sheets are the one that contains all the project or plant-specific symbols.

Valve P&ID Symbols

Symbols for instruments

Now back to our symbols. Here you can see the various instrument bubble. In a process plant, more than 90 percent of instruments measured either pressure, temperature, flow, or level. You can see the small table on the side, which shows the first letter of the instrument. Now the function of these instruments is either to indicate, record, control or transmit the measured value.

P&ID Instrument Symbols for TI, TT, FT and FI

Here on this table, you can see the meaning of the first letter and subsequent letters. You can read all the letters and their meaning. Now, I will tell you the meaning of the horizontal line on the instrument bubble.

P&ID Instrument Symbols Explain
  1. A single horizontal line means the instrument is located on the main control panel and has access to the panel operator.
  2. No horizontal line means the instrument is installed in the field, near the process, and it is accessible to field operators.
  3. If there is a double horizontal line, the instrument is installed on some secondary satellite local panel in the field.
  4. The last type is the instrument bubble with a single dashed horizontal line. This symbol is used for instruments that are inaccessible in the field or hidden or password protected on the control system.

Check this link if you want to learn P&ID Symbology in extreme depth.

Click on the link to Download the P&ID Symbols List.

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Varun Patel - HardHat Engineer

About Author: Varun Patel is a Mechanical Engineer and an Oil & Gas Professional. He is a Certified Project Management Professional – PMP® from PMI® USA. With over nineteen years of experience, he has worked with Fortune 500 Oil & Gas Companies. Know more.