Introduction to P&ID Reading
and Design
Process Engineering
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Process engineering is often a synonym of
chemical engineering.
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It focuses on design, operation and
maintenance of chemical and material
manufacturing processes.
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Process engineering also involves developing
new processes, project engineering and
Process troubleshooting.
Services in Process Engineering
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Process conceptual and feasibility study
Process project scope definition
Process design, evaluation and modification
PFD and P&ID development
Process modeling and simulation
Process equipment sizing and selection
Process safety analysis
Process troubleshooting
Applications of Process Engineering
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Chemical plants
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Biotech plants
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Crude oil refineries
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Fertilizer production
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Oil & gas processing
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Food processing
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Pharmaceutical manufacturers
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Pulp paper mills
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Mineral processing
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Water treatment plants
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Nuclear power plants
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......
Type of Flow Diagrams
in Process Engineering
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Mass Flow Diagram
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Block Flow Diagram (BFD)
Also known as Information Flow Diagram
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Process Flow Diagram (PFD)
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Piping and Instrumentation Diagram (P&ID) Also
known as Mechanical Flow Diagram (MFD).
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Utility Flow Diagram
This is a type of P&ID for common plant utilities
(steam, utility air, fuel oil, etc.)
An Example of Block Flow Diagram (BFD)
Diluent
Diluted
Bitumen
NHT
CDU
Kerosene
DHT
Diesel
Upgrader
Naphtha
LVGO
VDU
Sour Gas
HC
HVGO
SCO
Treating
FG (upgrader)
Naphtha
SDA
DAO
Pitch
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EB
SRU
Diesel
GO
Sulfur
Gasifier H 2S
GSFR
H2 (upgrader)
Syn Gas
Composed of only blocks (rectangles) and straight lines
Each block represents one or more unit operations
The lines represent the major process flow streams (material/
energy flows)
Process Flow Diagram (PFD)
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A PFD is a schematic representation of a process using
symbols to illustrate major operation units and major
process flow lines.
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A PFD also tabulates process design values for the
streams in different operating modes (minimum, normal
and maximum).
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A PFD is typically the first drawing developed for a
process, often in the pre-conceptual or conceptual
design phase.
What should be included in a PFD
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A PFD should include:
 Major equipment (symbols, names and identification #)
 Main process piping and flow direction
 Operating pressure and temperature
 Major bypass and recirculation lines
 Major control and instrumentation (optional)
A PFD should not include:
 Pipe line numbers
 Minor components and minor bypass lines
 Isolation and shutoff valves
 Maintenance vents and drains
 Relief and safety valves
 Code class information
A Sample of PFD
Piping & Instrumentation Diagram (P&ID)
– Scope
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It is a detailed symbolic representation of
process interconnection, including all equipment,
piping, and instrumentation.
All items are identified using a standard
numbering system.
It should be developed at the Basic Engineering
stage.
It is the basis for all Detail Engineering work in
plant design.
Piping & Instrumentation Diagram (P&ID)
– Synonyms
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Process and instrument diagram (P&ID) √
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Piping and Instrument diagram (P&ID) √
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Mechanical flow diagram (MFD)
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Engineering flow diagram (EFD)
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Piping and wiring diagram (P&WD)
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Pipe and identification diagram (P&ID)
Piping & Instrumentation Diagram (P&ID)
– Multidisciplinary
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Technical contents of P&IDs rely on multidisciplines:
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Process
Mechanical
Piping
Control and Instrumentation
Plant Operation
P&ID – Classification
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Process P&ID
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Utility Plant P&ID
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Show the distribution of utilities within a given process. Valving and
instrumentation on piping are shown for main headers up to and
including branch root valves.
Interconnecting (Rack) P&ID
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Define utility units such as cooling towers, air compressors, boilers,
unit drain collection systems, fire water systems, and water
treatment plants.
Utility Distribution P&ID
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Define on-plot process unit design, as well as off-plot tankage and
shipping systems
They are the connecting link between individual process, utility plant,
and utility distribution P&IDs. They are usually prepared for the
offsite pipe racks and link the various process and utility plants.
Vendor P&ID
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Prepared for systems that support major equipment packages.
Piping & Instrumentation Diagram (P&ID)
– Format
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There are no universal format to be used in
developing P&IDs.
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The P&ID formats vary with industry segments and
contractors.
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In reality, every industrial company that develops or
uses P&IDs has its unique formats/guidelines for
P&IDs.
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The P&ID preparation should follow the formats from
individual clients.
The P&ID formats are similar for different companies
in the same industry.
Two Key Elements in P&IDs
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Piping:
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Physical elements that interconnect equipment and process flow.
In different sizes, normally expressed as nominal sizes
In different materials. The most common material is carbon steel.
Other metals, such as various grades of stainless steel, and
plastic materials, such as PVC, Teflon, are also used.
With thermal insulation, if required.
Instrumentation
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Devices used to measure, control, and monitor the process
variables. These variables can be flowrate, temperature,
pressure, liquid level, viscosity, and others.
Control valves and relief valves are also an important part of the
instrumentation.
Relationship between PFD and P&ID
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For a process, a PFD is a simple representation, while a P&ID
is a definitive and comprehensive representation.
A PFD shows major equipment and major process lines, while
a P&ID shows all equipment and all process lines.
A PFD shows major operating conditions (flow, temperature
and pressure), while a P&ID shows piping, valves and
instruments that monitor and control the process.
P&IDs are more important in the design process, but PFDs
provide a basis for P&IDs development.
PFDs and P&IDs use the same symbols and formats.
What should be included in a P&ID?
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All equipment with names and identification numbers
Piping with flow direction and line numbers (pipe specifications
and line sizes are included in line numbers)
All valves
All instrumentation with controlling devices and signal inputs and
outputs
Interconnection references (from one P&ID to another P&ID)
Miscellaneous – vents, drains, special fittings, sample lines, and
reducers
Permanent start-up and flush lines
Interfaces for class changes
Vendor and contractor interfaces
Identification of components and subsystems delivered by others
Intended physical sequence of the equipment
What should not be included in a P&ID?
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Manual switches
Equipment rating or capacity
Pressure, temperature and flow data
Supplier package piping which is internal to the
package and has no operational interface
Elbows, tees and similar standard pipe fittings
Extensive explanatory notes
Physical details and dimensions
Piping connections and type (e.g. threaded, flanged,
etc.)
Basic Steps for P&ID Preparation
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Show all equipments with necessary piping to carry out
the process
Show all connecting process piping necessary to carry
out the process
Show all other piping required for auxiliaries
Show all required valves and major non-standard fittings
Show all required instruments and control loops
Mark size, fluid code, material code & identification
numbers of all pipe lines
Mark interlock numbers as per interlock description
Review P&ID considering all operational, startup
/shutdown, safety, maintenance & aesthetic aspects
Three Key Types of Symbols in P&IDs
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Equipment symbols:
Process operation units for mass transfer, heat
transfer, momentum transfer and chemical reaction
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Piping symbols:
Relevant to pipe, valves, and connections
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Instrumentation symbols:
Sensing, monitoring and controlling
The symbology follows the ISA standard ANSI/ISA5.1-1984 (R1992).
Equipment Symbols in P&IDs
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Pumps
Compressors
Fans & blowers
Mixers & agitators
Conveyors & feeders and other material handling
Separation equipment (liquid-liquid, liquid-gas, liquid-solid,
gas-solid, gas-gas)
Tanks & drums (storage)
Heat exchangers
Heating & cooling elements
Reactors
Turbines, generators and motors
Transportation equipment
Examples of Equipment Symbols
Piping Symbols in P&IDs
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Process flow lines (often combined with signal
lines for instrumentation)
Valves
P&ID connectors
Reducers/Increasers
Caps
Connections
In-line items
Fire and safety
Miscellaneous labels
Examples of Piping Symbols
Instrumentation Symbols in P&IDs
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General instrument or function symbols
Signals and lines
Sensors (four basic instrument groups)
 Temperature (T)
 Pressure (P)
 Flowrate (F)
 Level (L)
Self-actuated devices
 Pressure (regulators, relief/safety valves)
 Temperature, flow, and level (regulators)
Valve actuators
 Pneumatic & electric (solenoid, diaphragm, cylinder,
motor, etc.)
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With & without positioners
Miscellaneous labels
Signal/Line Symbols
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Some Sensor & Control Valve Symbols
Exercise: Identification of P&ID Symbols
General Instrument Symbols
Instrument Symbol
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Instrument Location
Solid line: Control room panel
No line: Field
Double solid: Remote panel
Dash line: Behind panel in control room
Double dash line: Behind remote panel
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A circle -- individual measurement
instruments such as transmitters,
sensors, and detectors for pressure,
temperature, flow, level
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A square with a circle inside -instruments that both display
measurement readings and perform
some control function (e.g. DCS
connection and control)
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A hexagon -- computer functions.
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A square with a diamond -- PLC
(Programmable Logic Control)
functions.
Instrument Identification – Tag Number
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Instrument symbols should contain
letters and numbers.
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The letters indicate the instrument
type, and the numbers identify the
control loop.
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PI
PI
PI
217
217
217
a
b
c
Usually 2 or 3 letters are used.
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Examples of Instrument #
The first letter identifies the
measured or initiating variable,
The second is a modifier,
The remaining letters identify the
function.
Normally a plant # should be
prefixed to the Tag#.
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e.g. 265-PI217 (265 is a plant #)
a.
b.
c.
Pressure indicator, Loop 217,
located in the field.
Pressure indicator, Loop 217, on
control panel, located in the
control room.
Pressure indicator, Loop 217,
signal to DCS.
Instrument Identification Letters
First Letter
Measured or Initiating
Variable
Modifier
Succeeding Letters
Readout or Passive
Function
Output Function
Modifier
User’s Choice
User’s Choice
A
Analysis
Alarm
B
Burner, Combustion
User’s Choice
C
User’s Choice
D
User’s Choice
E
Voltage
F
Flow Rate
G
User’s Choice
H
Hand
I
Current
J
Power
Scan
K
Time
Time Rate of Change
L
Level
M
User’s Choice
N
User’s Choice
User’s Choice
O
User’s Choice
Orifice
P
Pressure, Vacuum
Test Point
Q
Quantity
R
Radiation
S
Speed, Frequency
T
Temperature
U
Multivariable
V
Vibration, mechanical analysis
W
Weight, Force
X
Unclassified
x-axis
Y
Event, State or presence
y-axis
Relay, Compute, Convert
Z
Position, Dimension
z-axis
Driver, Actuator
Control
Differential
Sensory (Primary)
Ratio
Glass, Viewing Device
High
Indicate
Control Station
Light
Low
Momentary
Middle
User’s Choice
User’s Choice
Integrate, Totalize
Record
Safety
Switch
Transmit
Multifunction
Multifunction
Multifunction
Unclassified
Unclassified
Well
Unclassified
Some Combinations of Instrument Letters
PC
Pressure controller
TA
Temperature alarm
PI
Pressure indicator
TI
Temperature indicator
PT
Pressure transmitter
TR
Temperature recorder
PR
Pressure recorder
TY
Temperature I/P converter
PY
Pressure converter
TW
Temperature well
PIC
Pressure indicating controller
TIC
Temperature indicating controller
PRC
Pressure recording controller
TRC Temperature recording controller
PSV
Pressure safety valve/
Pressure relief valve
TCV
PCV
Pressure control valve
I/P: Current to Pneumatic.
Temperature control valve
Some Combinations of Instrument Letters
FA
Flow alarm
LA
Level alarm
FE
Flow element
LAH
Level alarm high
FI
Flow indicator
LAL
Level alarm low
FR
Flow recorder
LC
Level controller
FT
Flow transmitter
LG
Level glass
FY
Flow I/P converter
LI
Level indicator
FF
Flow ratio
LIC
Level indicating controller
FCV
Flow control valve
LRC Level recording controller
FRC
Flow recording controller
LCV
Level control valve
A Control Loop Example in P&ID
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FT123: field-mounted flow transmitter
FIC123: panel-mounted flow indicating
controller located in a shared
control/display device
TY123: temperature I/P converter
located in an inaccessible location
TT123: filed-mounted temperature
transmitter
TIC123: field-mounted temperature
indicating controller. Its output is
connected via an internal software or
data link to the setpoint (SP) of
FIC123.
YIC123: an event indicating controller.
All inputs and outputs are wired to a
PLC accessible to the operator. YIC
typically indicates a controlled on/off
valve.
Rules of Thumb in P&ID Design
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P&IDs are typically developed from PFDs, so that understanding
the designed process is a key basis for P&ID design.
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P&IDs do not have a drawing scale and usually present only the
functional relationship, not the relative physical locations of
components.
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P&IDs are done in a “single line” format that represents all piping
and ductwork as a single line regardless of size.
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P&IDs should be specific to one system only, i.e. no more than one
system should be shown on a single diagram.
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P&IDs should be configured such that major flow should generally
be from left to right and from top to bottom, if possible. Primary
flow paths should not suffer major changes in directions on P&IDs.
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P&IDs should start simple and then be enhanced in several
revisions to address the real process by various disciplines.
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Following the style from the existing P&IDs for the same client.
Line Designation (Line Number) in P&IDs
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Line # is required for piping in P&IDs
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Position of the line #: normally above piping lines
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Different formats of line # for different companies
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A line # contains the following basic information:
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Plant #
Commodity symbol
Line serial #
Piping/Line size
Piping/Line class (optional)
An example: 6N1-4”-CA2B
Plant 6, Nitrogen line 1, 4” pipe, piping class – CA2B
Styles for Flow Direction in P&IDs
1.
Flow arrow at each turning point
2.
3.
Flow arrow at the end of each line
Flow arrow at the middle of each line
Valve Status for Bypass Lines
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It’s better to mark the valve status on the bypass
lines including safety relief lines:
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NC – Normal Closed
NO – Normal Open
CSC – Car Seal Closed
CSO – Car Seal Open
LC – Lock Closed
LO – Lock Open
Relief valves need to indicate their set pressures
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e.g. SET @125 PSIG
Accompanying Deliverables from P&IDs
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Equipment List
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Line List (Line Designation Table - LDT)
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Valve List
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Instrument List
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Tie-In List
A Tie-in List shall be issued indicating the extent of the Vendor package battery limits
each time a P&ID issue is made starting with IFA. For plant modification, the tie-in
point is the point where from process or utility is connected in the existing systems.
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“Holds” List
A "Holds" list must be issued each time a P&ID issue is made starting with IFD. The
"Hold" indicates where the information used as input to the P&ID is preliminary and
the item is used with risk in the downstream design.
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Revision list
A Revision List defines the changes made in the design so that appropriate action
can be taken to accommodate those changes. A Revision List must accompany any
issue of P&IDs after IFH if the changes are too extensive to be distinguished in the
revision box and by clouding.
(IFA - Issued for Approval, IFD - Issued for Design, IFH - Issued for HAZOP)
“As-Built” P&IDs
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When there are modifications done in construction,
commissioning, qualification, or at any other time after the
facility has been validated and operating, the P&ID must be
modified to indicate the latest information.
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Frequently these modifications arise from construction,
post-construction, and C&Q walk-downs prior to the
system turn-over from IQ, OQ and PQ.
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All changes must be processed through the Quality
Management System (QMS).
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All changes on a P&ID must be bubbled, signed and dated.
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Often a new revision number should be assigned to a “AsBuilt” P&ID.
Software for Developing P&IDs
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AutoPLANT P&ID – AutoCAD-based (Bentley)
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PlantSpace P&ID – MicroStation-based (Bentley)
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SmartPlant P&ID – Able to convert AutoCAD or
MicroStation based P&ID to SmartPlant P&ID
(Intergraph)
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CADWorx P&ID – AutoCAD-based (CodeCAD Inc.)
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AutoCAD P&ID – AutoCAD-based (Autodesk)
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CADPIPE P&ID – AutoCAD-based (AEC Design Group)
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AutoFLOW – AutoCAD-based (PROCAD)
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HexaCAD P&ID – (Hexagon Software)
AutoCAD P&ID 2007
for Developing P&IDs
1.
Industry standard P&ID symbols
2.
Dynamic process and signal lines
3.
Dynamic components
4.
Report and list generation
5.
Import and export to MS Excel
6.
Tag generation and uniqueness
7.
Search and edit using a spreadsheet interface
8.
Easy symbol creation and substitution
9.
Review and approve data edits
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