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Piping and instrumentation diagram

A piping and instrumentation diagram/drawing (P&ID) is a diagram in the process industry which shows the piping and vessels in the process flow, together with the instrumentation and control devices.

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

They usually contain the following information:

P&IDs are originally drawn up at the design stage from a combination of process flow sheet data, the mechanical process equipment design, and the instrumentation engineering design. 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 a Hazard and operability study (HAZOP). To do this, it is critical to demonstrate the physical sequence of equipment and systems, as well as how these systems connect.

P&IDs also play a significant role in the maintenance and modification of the process after initial build. Modifications are red-penned onto the diagrams and are vital records of the current plant design.

They are also vital in enabling development of;

P&IDs form the basis for the live mimic diagrams displayed on graphical user interfaces of large industrial control systems such as SCADA and distributed control systems.

Based on STANDARD ANSI/ISA S5.1 and ISO 14617-6, the P&ID is used for the identification of measurements within the process. The identifications consist of up to 5 letters. The first identification letter is for the measured value, the second is a modifier, 3rd indicates passive/readout function, 4th - active/output function, and the 5th is the function modifier. This is followed by loop number, which is unique to that loop. For instance FIC045 means it is the Flow Indicating Controller in control loop 045. This is also known as the "tag" identifier of the field device, which is normally given to the location and function of the instrument. The same loop may have FT045 - which is the flow transmitter in the same loop.

Letter Column 1 (Measured value) Column 2 (Modifier) Column 3 (Readout/passive function) Column 4 (Output/active function) Column 5 (Function modifier)
A Analysis Alarm
B Burner, combustion User choice User choice User choice
C User's choice (usually conductivity) Control Close
D User's choice (usually density) Difference Deviation
E Voltage Sensor
F Flow rate Ratio
G User's choice (usually gaging/gauging) Gas Glass/gauge/viewing
H Hand High
I Current Indicate
J Power Scan
K Time, time schedule Time rate of change Control station
L Level Light Low
M User's choice Middle / intermediate
N User's choice (usually torque) User choice User choice User choice
O User's choice Orifice Open
P Pressure Point/test connection
Q Quantity Totalize/integrate Totalize/integrate
R Radiation Record Run
S Speed, frequency Switch Stop
T Temperature Transmit
U Multivariable Multifunction Multifunction
V Vibration, mechanical analysis Valve or damper
W Weight, force Well or probe
X User's choice (usually on-off valve as XV) X-axis Accessory devices, unclassified Unclassified Unclassified
Y Event, state, presence Y-axis Auxiliary devices
Z Position, dimension Z-axis or Safety Actuator, driver or unclassified final control element
Symbols of chemical apparatus and equipment
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, ,MK,,,

Radial fan.svg
Radial fan
Fluid contacting column.svg
Packed 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
(Air) filter
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

  • Instrumentation and with unique tag identifiers
  • 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
  • Identification of components and subsystems delivered by others
  • Control and shutdown schemes
  • Safety and regulatory requirements
  • Start-up sequences
  • Operational understanding.
  • - A list of P&ID symbols in SVG format


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