A piping and instrumentation diagram/drawing (P&ID) is a diagram in the process industry which shows the piping of the process flow together with the installed equipment and instrumentation.


Contents and Function

An example of a P&ID.

A piping and instrumentation diagram/drawing (P&ID) is defined by the Institute of Instrumentation and Control as follows:

  1. A diagram which shows the interconnection of process equipment and the instrumentation used to control the process. In the process industry, a standard set of symbols is used to prepare drawings of processes. The instrument symbols used in these drawings are generally based on Instrumentation, Systems, and Automation Society (ISA) Standard S5. 1.
  2. The primary schematic drawing used for laying out a process control installation.

P&IDs play a significant role in the maintenance and modification of the process that it describes. It is critical to demonstrate the physical sequence of equipment and systems, as well as how these systems connect. During the design stage, the diagram also provides the basis for the development of system control schemes, allowing for further safety and operational investigations, such as the hazard and operability study (HAZOP).

For processing facilities, it is a pictorial representation of

  • Key piping and instrument details
  • Control and shutdown schemes
  • Safety and regulatory requirements and
  • Basic start up and operational information

List of P&ID items

  • Instrumentation and designations
  • Mechanical equipment with names and numbers
  • All valves and their identifications
  • Process piping, sizes and identification
  • Miscellanea - vents, drains, special fittings, sampling lines, reducers, increasers and swagers
  • Permanent start-up and flush lines
  • Flow directions
  • Interconnections references
  • Control inputs and outputs, interlocks
  • Interfaces for class changes
  • Computer control system input
  • Identification of components and subsystems delivered by others

Identification and Reference Designation

The P&ID is used for the identification of measurements within the process. Identification letters for measurements are based on Standard S5. 1 and ISO 14617-6:

First-Letter Measurement
D Density
E Electricity
F Flow
H Hand
J Power
K Time, Time Schedule
L Level
M Moisture
P Pressure
Q Quality
R Radiation
S Speed, Frequency
T Temperature
V Viscosity
W Weight

For reference designation of any equipment in industrial systems the standard IEC 61346 (Industrial systems, installations and equipment and industrial products — Structuring principles and reference designations) can be applied. For the function Measurement the reference designator B is used, followed by the above listet letter for the measured variable.

For reference designation of any equipment in power station the KKS Power Plant Classification System can be applied.

Symbols of chemical apparatus and instrumentation

Below are listed some symbols of chemical apparatus and instrumentation normally used in a P&ID, according to DIN 30600 and ISO 14617.

Symbols of chemical apparatus and instrumentation
Insulated pipe.svg
Thermally insulated pipe
Jacketed pipe.svg
Jacketed pipe
Cooled or heated pipe.svg
Cooled or heated pipe
Jacketed mixing vessel (autoclave)
Half pipe reactor.svg
Half pipe mixing vessel
Pressurized vessel horizontal.svg
Pressurized horizontal vessel
Pressurized vessel vertical.svg
Pressurized vertical vessel
Vacuum Pump or Compressor.svg
Vacuum pump or compressor
Gas bottle.svg
Gas bottle
Axial fan.svg
Axial fan
Radial fan.svg
Radial fan
Fluid contacting column.svg
Packing column
Tray column.svg
Tray column
Cooling tower.svg
Cooling tower
Heat exchanger no cross.svg
Heat exchanger
Heat exchanger with cross.svg
Heat exchanger
Plate heat exchanger.svg
Plate & frame heat exchanger
Double pipe heat exchanger.svg
Double pipe heat exchanger
Fixed straight tubes heat exchanger.svg
Fixed straight tubes heat exchanger
U shaped tubes heat exchanger.svg
U shaped tubes heat exchanger
Spiral heat exchanger symbol.svg
Spiral heat exchanger
Covered gas vent.svg
Covered gas vent
Curved gas vent.svg
Curved gas vent
Dust trap.svg
Dust trap
Steam trap.svg
Steam trap
Viewing glass.svg
Viewing glass
Pressure reducing valve.svg
Pressure reducing valve
Flexible pipe.svg
Flexible pipe
Control valve.svg
Control valve
Manual valve.svg
Manual valve
Back draft damper.svg
Back draft damper
Needle valve.svg
Needle valve
Butterfly valve.svg
Butterfly valve
Diaphragm valve.svg
Diaphragm valve
Ball valve.svg
Ball valve