Process and instrumentation diagram


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

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 International Society of Automation (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 Analysis and Critical Control Points ; HACCP common pronounced as HAZOP.

For processing facilities, it is a pictorial representation of

  • Key piping and instrument details
  • Control and shutdown schemes
  • Safety and regulatory requirements
  • 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

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.

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 Safety 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 Actuator, driver or unclassified final control element

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 listed letter for the measured variable.

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

Symbols of chemical apparatus and equipment

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

Symbols of chemical apparatus and equipment
Pipe
Thermally insulated pipe
Jacketed pipe
Cooled or heated pipe
Jacketed mixing vessel (autoclave)
Half pipe mixing vessel
Pressurized horizontal vessel
Pressurized vertical vessel
Pump
Vacuum pump or compressor
Bag
Gas bottle
Fan
Axial fan
Radial fan
Dryer
Packed column
Tray column
Furnace
Cooling tower
Heat exchanger
Heat exchanger
Cooler
Plate & frame heat exchanger
Double pipe heat exchanger
Fixed straight tubes heat exchanger
U shaped tubes heat exchanger
Spiral heat exchanger
Covered gas vent
Curved gas vent
(Air) filter
Funnel
Steam trap
Viewing glass
Pressure reducing valve
Flexible pipe
Valve
Control valve
Manual valve
Back draft damper
Needle valve
Butterfly valve
Diaphragm valve
Ball valve

See also

External links

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