PDHonline Course E522 (3 PDH)
Anatomy of P&ID (Process &
Instrument Diagram)
Instructor: Clifford T Johnson, P.E., CSE
2020
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Anatomy of P&ID (process& Instrument Diagram)
Clifford T Johnson, PE, Control Systems Engineer .
COURSE CONTENT
1. Introduction
The acronym “P&ID” is widely understood within the process industries as the name for the
principal document used to define a process-- the equipment, the piping and all the Instrument
& Control (I&C) system components. The comprehensive dictionary of instrumentation and
control (1988 edition) states “abbreviation for piping and instrumentation drawing, which is the
primary schematic drawing used for laying out a process control installation”. The P&ID show
the interconnection of process equipment and the instrumentation used to control processes.
The fact that the P&ID is the principal, defining document is proven by its widespread use
across most processes and industries. Once you become familiar with the language of the
symbols and the presentation, you will come to appreciate its efficiency and simplicity in
documenting salient information in an easily understandable way.
The fact that confusion exists is understandable because, oddly, there is no universal standard
that specifies the information that should be included on the P&ID or how it should be shown.
Even more strangely, the meaning of the letters P&ID are not even universally agreed upon.
You may know what “P” stands for or what the “D” means or even what a P&ID contains but
the person in the facility down the road probably doesn’t agree in every way. For instance the
“P” in P&ID may stand for piping or process. The “I” may refer to instrumentation or
instrument. The “D” may mean Drawing or Diagram. P&IDs may even be called flow
diagrams, which are not to be confused with the process flow diagram (PFD) discussed later in
this course.
Since the P&IDs are the definitive resource used by operations and maintenance staff to
understand the process, they are likely to be the document that organizes the plants equipment
identification system and they are the key to work done by most design entities. Consequently,
it is necessary to first ensure that all required information is shown and that it is presented in
the best way possible. The owner gets to define “required” and once that is established,
everyone involved must be sure the expectation is met every time.
From the P&ID comes the instrument list or index, which documents the specification,
acquisition and installation of all the instruments. The P&ID gives the motor list and the
horsepower. From the P&ID, the piping line list, sizes, service and purpose. The P&IDs even
documents critical information regarding tanks, vessels and other equipment. All of this
information is used to lay out equipment on the location plan drawings and to start specification
and purchasing efforts.
A PE’s stamp is required and some states. This means that an engineer licensed by the state
where the design will be implemented is in charge of the design and will review or approve the
drawings as if you. The engineer who stamp appears on the drawing is responsible for the
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content and accuracy. This can be challenging requirement to fulfill when designs are
developed remotely from the physical construction site, as is often the case.
All members of the project team in charge of design have access to the P&ID in most cases the
mechanical department is in charge of actually developing the drawing in a Computer Aided
System; however the electrical, instrument and process departments all have access to the
drawing as necessary. As mentioned above, the drawings are so important that key milestones
are often built into the project schedule based on the different issues of the P&IDs. Large
projects may have many P&IDs as they normally assign one for each area or process. Typically
P&ID and drawing issues may include: issue for scope definition, issue for client approval,
issue for bid, Issue for detailed design, and issue for construction. The first construction issue is
typically “0”, and as the project continues construction issues will be revised as number 1,2,3,4,
etc.
Before we start looking more closely at a P&ID we will define a few terms.
Acronyms for some of the common type control systems are:
o ACS = Analyzer Control System.
o DMS = Burner Management System.
o CCS = Computer Control System.
o CEMS = Continuous Emissions Monitoring Systems.
o DCS = Distributed Control System.
o HMI = Human Machine Interface.
o MMS = Machine Monitoring System.
o PCCS = Personal Computer Control System.
o PLC = Programmable Logic Controller.
o SCADA = Supervisory Control And Data Acquisition
o SIS
= Safety Instrumented System.
o VMS = Vibration Monitoring System.
Instrument:
o Devices for measuring the value of an observable attribute; the device may
merely indicate the observed value, or it may also record or control the value
Process Control: The regulation or manipulation of variables influencing the conduct of
a process in such a way as to obtain a product of desired quality and quantity in an
efficient manner. Before even thinking about developing a P&ID the person must be
familiar with process control; the sensing of the parameters or services to be controlled,
the comparing those to the set points set of the controllers and then correcting a the
process by manipulating the final control elements such as valves and pumps. This
course does not go into the depths of the actual control of the process, it is assumed that
the person taking this course understands these parameters and wants to learn how they
are depicted in a P&ID. This course attempts to help that person understand the graphic
symbols and identification tags that are used in the P&ID to show the instruments and
mechanical devices used in the control system.
All first – level control – process or discrete – consist of three parts:
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Sensing
Comparing
Correcting
2. Standard for I&C Diagrams and Drawings
ISA (International Society of Automation) Standard ANSI/ISA-5.1-2009 Instrumentation
Symbols and Identification; ISBN: 978-1-936007-29-5 is used in the development of the P&ID
and may be purchased from ISA.org. The standard was first published in 1949 as non
mandatory rather than as a mandatory consensus document. Versions of the standard have been
used for more than 50 years. Most of the identification letter and symbol meanings or
definitions that were contained in the original version have taken on proprietary nature and
have become accepted industry practice and assumed to be mandatory.
ISA-5.1 uses the term Basic Process Control System is the control system needed for normal
plant or process operation and High Level Control System as a SIS (Safety Instrument System).
The SIS systems purpose is to take the process to a safe state when predetermined conditions
are met.
All types of process control include three functions: sensing, comparing and correcting.
Instrumentation, or “measurement and control” devices are used to accomplish each of these
functions or even all of these functions simultaneously, along with indicating and presenting
information to the operator.
3. Major Documents developed by the I&C Department
The following document types are developed sequentially as a project progresses and as the
relevant information becomes available. They will be covered in future courses.
1. The Process Flow Diagram (Not developed by the Instrument Department)
The Process Flow Diagram (PFD) is the starting point for designing any process plant. It is the
macroscopic, schematic view of the major features of a process or facility; it is the "talking
document" for managers, planners and the process design team. The I&C design group has little
involvement in developing the PFD, due to its macroscopic nature. The Mechanical and
Process departments create the PFD and share it with all departments involved in the project.
The PFDs are used to develop a project scope and is the basis for the all important P&ID
Supply
Tank
Receiver
Tank
Fig 1- PFD
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2. Piping and Instrumentation Drawing
The Piping and Instrumentation Drawing (P&ID) is the overall design document for a process
plant. It defines - using symbols and word descriptions - the equipment, piping, and I&C
system. It is also the key to other documents. For example instrument tag numbers are shown
on a P&ID. This tag number is the key to finding additional information about this device on
many other documents. The same is true for line and equipment numbers.
From the P&ID comes the instrument list or index, which documents the specification,
acquisition and installation of all the instruments. The P&ID gives the motor list and the
horsepower. From the P&ID, the piping line list, sizes, service and purpose. The P&IDs even
documents critical information regarding tanks, vessels and other equipment. All of this
information is used to lay out equipment on the location plan drawings and to start specification
and purchasing efforts.
LT
102
I/P
H
LICA
102
LY
102
A.S.
N.C.
LSH
102
3/4 in PVC sched 40
A.S.
LV
102
LIK
102a
HS
121
S
FC
DE
3/4 in PVC
sched 40
LIK
EN 102b
LCV
102
Receiver
Supply
T1
T2
SC
121
FI
103
3/4 in PVC
sched 40
1 in PVC sched 40
P1
Fig 2- P&ID 202 developed from PFD
The P&ID shows two control loops: Level control for Receiver tank and Speed control for the
water pump. A single self contained rotameter for measuring the water flow to the receiver tank
(T2) has a loop number FI-103, but does not require a Loop Sheet to be developed. LIK-102a
& b are Level Indicating Stations, “a” controls air pressure to the bubbler tube that is measuring
the level in the receiver tank. The LT-102 is measuring the back pressure inches of water
created by the tank level and then transmitting it via a 4-20mA signal to the LICA-102
controller. The controller also received an on-off signal from the LSH-102 that opens on high
level. The controller LICA-102 controls LCV-102, Level Control Valve, and LV-102 Solenoid
Valve that would dump the air control pressure to the LCV on high level. NOTE: an interlock
symbol could be shown next to LCV. HS-121 is a hand on-off switch that operates the VSD to
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the pump motor. The following index describes the instrument devices only, there are separate
listis developed by other departments for mechanical items like pumps, tanks and piping.
3. Instrument Index (list or database)
The Instrument Index is a searchable database all instrument I&C components and functions.
Instrument Indexes are organized using the alphanumeric tag numbers of the I&C devices, but
also able to be sorted by any field. They reference the documents such as P&ID, Location
drawing, Specification Sheets, etc. Fig 3 is an example of the bare minimum fields required. A
future course will define it in detail.
Fig 3- Instrument Index
A usable index would contain separate the ISA tag field to Instrument (FI) and Loop (103)
Type would be expanded to Type, Modifier and Alarm. A viable instrument index may contain
as many as 80 fields, however, there are several computer applications available that automate
the development providing specification sheets, control panel terminations, wire numbering,
cable numbering and conduit runs. If your project is larger than 100 loops I recommend trying
AVEVA Instrumentation’s four integrated program modules that support the entire
Instrumentation and Control system lifecycle from engineering and design, through installation,
maintenance and modification.
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4. Specification Forms
The Specification Forms or instrument data sheets define each tagged instrument and control
system device--with sufficient detail so a supplier can quote and eventually furnish the device.
Fig 4 – Specification sheet
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5. Logic Diagrams
Logic Diagrams are the drawings used to design and define the on-off or sequential part of a
continuous process plant.
Fig 5 – Logic & Electrical Elementary
6. Loop Diagrams
A Loop Diagram is a schematic representation of a single control loop (sensing element,
control component, and final element). It depicts the process connections and the components'
interconnection to the power sources and transmission systems (pneumatic, electronic, or
digital). It also shows graphically the various areas that device are located to support the efforts
of construction and maintenance.
Field
Junction Box
Main Control Room
115
VAC
LSH
123
EV123C BLK
NO
LSH123C BLK
com
H
LSH123C WHT
NC
N
EV123C BLK
EV123C WHT
123
F5
Blk-L1
To level Xmitter
(not shown
LIC
123
Wht-L2
N
Grn-Gnd
G
EV
123
Local Control Area
S
FC
LCV123C
DE
Receiver
Tank
EV123C
LIK
123b
EN
LCV
123
IY
123
A.S.
FI
123
P2
From Supply
Tank
P1
Fig 6 – Loop Diagram
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7. Installation Details
Installation Details are used to show how the instrumentation and control system components
are connected and interconnected to the process. They provide the methods the plant uses to
support the devices and the specific requirements for properly connecting to the process.
Installation Details are discussed in.
Fig 7 (8.2) Installation Detail
8. Location Plans
Location Plans are orthographic views of the plant, drawn to scale, that show the locations of
instruments and control system components. They often show other control system hardware
including marshaling panels, termination racks, local control panels, junction boxes, instrument
racks, and perhaps power panels and motor control centers. For a typical Location Plan, see
Figure).
Fig 8 – Location Plans
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4. Minor Drawings that may be created by the I&C department
SAMA (Scientific Apparatus Makers Association) diagram
Drawing Index
Cable Conduit Schedule
Control Panel Layout
Control Panel Terminals & Components
Configuration Logic for programmable devices
Motor Controls Elementary (Electrical Schematics)
For examples of actual drawings by Cliff Johnson for a typical set of these drawings Click Here
5. Symbols and identification
The ISA -5.1 sets the standard for the symbols, identification and tagging for development of
the P&ID. Unfortunately, the ISA standard is copy righted and I cannot directly show it in this
course. If you search on the Internet for the standard you can find some illegal copies that are
outdated. I have, however, put together an Identification listing because of my need to use them
in my position as Control Systems Engineer. If, however, you are a member of the ISA you can
log on to ISA.org and view the ISA standards. The symbols and tagging information that I have
developed is not as all encompassing as is the ISA standard, but should help you to understand
the actual standard better.
Standard definitions or meanings for letters used in identification and for symbols used in
graphic depiction of I&C devices and functions will be stated in this course or linked to web
sites for the information. Consistency is the one criterion that should govern that selection and
application of identification and graphic schemes. All sets of P&ID must include a Legend
sheet depicting every symbol and identification used in the set of diagrams because many
organizations customize the standards to suit their purpose. Also, the standards include letters
that are intended for the users own purpose.
Fig 5-1 Legend Sheet
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The symbols and designations are used as conceptualizing aids, as design tools, as teaching
devices, and as a concise and specific means of communications in all types and kinds of
technical engineering, procurement, construction, and maintenance documents, and not just
piping and instrument diagrams.
Fig 5-2 Letters A-P for tag creation
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Tagging format Q-Z
Fig 5-3 Letters Q-Z for tag creation
Creating the first part and letter of an instrument tag is not too difficult because it basically uses
the first letter of the measurement or sensor that is to be described. The “P” is used for pressure,
the “T” is used for temperature, the letter “F” is used for flow, the letter “L” is used for level
and these measurements are the majority of the services that are used in instrument and control.
The second letter can modify the measurement or sensor as shown in the tadding format listing,
or it can identify the type if device. The minimum of two letters must be used to identify the
measurement (or service) and the type of instrument. A maximum of five letters as in “PDIAH”
Pressure Differential Indicating Alarm High. Fig 6a list many of the more common tags
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showing the instrument measurement, function and device type along with part two of the tag,
the loop number.
Some of the letters used, like “Y” for Relay, Compute, or Convert don’t make sense and just
have to be taken with a grain of salt. A device that “converts” is a commonly known as a
Transducer, but we cannot use the letter “T” because it identifies a Transmitter. So a pressure
to current device that measure 0-100 PSIG and converts to 4-20mA should be identified as a
“Transmitter” (PT), but if is measuring a standard instrument signal and converting it to
another standard signal such as measuring 3-15 PSIG and converting it to 4-20mA it would be
a transducer and the tag would be “PY”. In plan English, if a device is measuring a process
pressure and “Transmitting” it to a controller or recorder it would be a Transmitter, however, if
the device is converting a standard communication signal to a another device, it would be a
“transducer”. Unfortunately, many manufacturers of measuring devices that are truly
transmitters misidentify them as transducers. This particular error plays havoc with P and IDs
sense a transmitter that should be identified as a “T” is then identified with a “Y”. The simplest
way to make this identification would be if that the device has its source in a pump, tank or
pipe it would be a transmitter, on the other hand, if the source is another instrument device it
would be a transducer.
ISA 5.1 added a significant modifier to the first letter that being the letter “Z” as a modifier
meaning safety or safety instrument system. I have revised my tagging format to include as the
first letter actually two letters. Thusly a Pressure Safety Differential Indicating Alarm High
would require a identifier that is six letters “PZDIAH” and may not all fit in the instrument
bubble and that would be OK
PZDIAH
123
Fig 5-4 shows how addition letters are depicted.
Since the primary bubble cannot state everything that is required to identify the instrument
additional information about it can be inserted at the upper right to the bubble as is required for
the “AIT” tag must have because it can only state that it is an analytical device. It should be
AIT
123
pH
shown as:
Fig 5-5 states that the transmitter is measuring pH acidity. The
additional information shown in Fig 5-7 is inside a box, ether method is acceptable, I
personally do not use the box an normally show like Fig 5-5 unless the client has a standard
that takes president. Fig 5-7 below shows a Flow Transducer FY-101 as an I/P
Curent/Pneumatic.
Additional symbols are used to show other functions such as the diamond that indicates when a
6
FC
device is interlocked by another:
Fig 5-6 Valve is shown interlocked by
instrument listed as number 6 on the right side of the diagram or drawing. See Fig 5-8 for an
interlock listing.
In addition to the letter part of the tag there is a second part made up of numerals. The numbers
would indicate the loop in which the device is operating. A Loop Diagram a schematic
representation of the complete hydraulic, electric, magnetic or pneumatic circuit. This loop
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number would be later used in loop sheets that detail the complete installation of the devices in
that loop which include such items as wiring and wire numbers, terminals etc. Loop numbers
are simply sequential and a majority of cases, although normally only numbers, if there are
more than one letter identification of the device such as in our sample P&ID where we have a
couple devices that are the same a lowercase character starting with “a” may be added to the
loop number to identify the different devices. In the sample loop 123 we can make it 123a and
123b, see Loop Sheet on page 8. The anatomy of a loop sheet will be covered in future courses.
The quiz that you must take to receive your PDH credits will include questions on how you
make up a tag. The same loop number is assigned to all devices that are in a loop that consist as
a minimum of the following devices:
Fig 5-7 Instrument loop
A listing of interlocks would be stated on the right side of a drawing to what the interlocks were
for as show here:
INTERLOCKS
1-High level on Oil Storage Tk
2-High Level on Separation Tk
3-High Level on Mix Tank
4- High Level on Batch Tank
5- High Level on Batch Tank
6- High Level on Mix Tank
7- High Level on Water Tank
Fig 5-6 interlock list
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6. I&C Devices and Functions Symbols
Fig 6-1 Graphic depiction of a device and location
A circle means that the device is mounted out in the process area. A line added to the center of
the circle means the device is located in a primary location normally accessible to the operator.
If a second line is added parallel to the first, the device is located in an auxiliary location
normally accessible to the operator. A dashed line through the center of the circle shows that
the device is normally inaccessible to the operator such as inside a panel. If an external square
is added to the circle the symbols represent devices or functions that are part of a shared display
computer console, perhaps a DCS. If we substitute a hexagon for the circle or the squared circle
the symbols represent a computer function. A diamond within the square is used to define
functions within an alternate displayed shared control system, perhaps a PLC or safety
instrument system (SIS). Symbols #4 & 5 are rarely used, but, any symbol that is used should
be depicted and described on the Legend sheet.
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Fig 6-2 Common field installed instruments
Fig 6a shows the symbols for field installed instruments, however, I would personally change
some of the tags and “SV” should be “EV” because “S” is Speed. I would use “CV” for “XV”.
This only shows that nothing is set in stone, and does show why Legend sheets are a must
In addition to the primary symbol showing the main instrument devices there are other symbols
shown in figure 6-3 that are placed along side the primary symbol that indicate interlocks and
modify the primary symbol like “AT” for analysis Transmitter to state that it is for “pH”. An
actuated valve would usually be FV, PV, TV, or FV, however, automated ball valves used for
diverting and directional like 3 way used in batch processing would use XV.
The “U” Multivariable can be used when nothing else fits, but, make sure it is identified on the
Legend sheet.
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7. Line Symbols used on instrument drawings & diagrams
Fig 7 - Lines used on instrument Diagrams
Fig 7 depicts the primary lines used to connect various devices on I&C drawings, however ISA
5.1 does show several others that are seldom employed. The above EM and Sonic symbol is
show being a guided wave; if you remove the line it would be un-guided to depict“wireless”
devices. If you use a dotted line for the software connection it could be depicting a connection
between “smart” devices. If you replace the circle (○) with a diamond (◊) you would be
showing the connection between “bus” devices. You may modify the symbols as necessary,
but, be sure to show them on the Legend drawing.
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8. Flow Element Symbols
Fig 8-1 Flow Element (sensor) Symbols
The flow element symbols may represent both the element and transmitter, but many times it is
not the case. Since the element may be purchased from a different supplier than the transmitter
or gauge (indicator). See below for the depiction of separate items.
FT
107
dp
FE
107
Fig 8-2 Flow Element and transmitter
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9. Valve Symbols, Types and Actuators
Fig 9 Valve types on left, actuators on right
Pick the types of valve, then choose the actuator and you have the most common control
Valves (CV) used in systems
10.Pressure Regulators
Fig 10 – Various styles of pressure regulating valves
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11.Vessels and tanks
Fig 11-1 – various vessels & tanks
Fig 11-2 Pump, mixer. Compressor, Fan and vessel Symbols
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12. P&ID Examples
Oil
Instrument Air
Oil
Oil
To sump
To Separation from Mix
STM
9902
HV-1
FS
1701
FS
5701
LT
3102
HV-3
LT
3101
LT
3105a
FT
1904
4
PT
3202
LT
6101
cor
PSH
6601
cond
LT
6102
P7
Batch
Tank
T4200
PSH
4601
AT
3801
HV-11
FT
2903
LSL
3303
LSL
3301
View
window
PT
3201
PSL
6301
FT
4902
LT
5102
6
FV
6
water
LSH
5702
TT
5501
FT
5902
FDM
9901
FT
5901
Air Purge
Load Cells
PT
5201
FT
3902
View
window
PSH
5601
VB
9902a
FY
3902
LSL
5301
LT
5103
PY
5201
LT
4103
HV-9
LT
5101
Mix
Tank
T5100
LSL
4301
P2
TSL
2401
water
VB
9902b
To sump
FT
4903
TT
4501
PT
4201
PSH
3601
HV-12
LT
LY
3103 3103
HV-AS
Mixer
LY
5101
TT
5502
P5
LY
6101
LT
5104
HV10
P3
7
FT
3901
pH
AT
1803
Oil
cor
LT
2102
FY
FT
3903 3903
water
Symbols
LY
1102
Water
T1100
LSH
2302
Oil Storage
Tank
T2100
TT
2501
PSH
2601
P6
LT
2104
FT
1902
FT
1901
AT
1802
TT
1501
LT
1105
cor
INTERLOCKS
LSL
1301
LT
1104a
AY
1802
LT
1106
mag
Wireless Instrument
UltraSonic meter
Annubar (dp type)
Turbine Meter
Vortex Meter
Orifice Meter (dp type)
Magnetic Meter
Coriolis Meter
HV-6
FY
FT
1903 1102
LSY
2301
LT
2103
FT
1905
cond
pH
LSL
2301
HV-13
LT
1102
LSH
1302
LT
2101
FT
1906
HV-7
LT
1104b
LT
1101
PT
2201
FV
7
AT
1803a
AT
1803b
LY
2102
FY
2901
STM
9903
cond
Oil
VB
9901b
FV
4
LSH
4302
FT
4901
TT
3501
Separation
Tank
T3100
PSL
9601
FY
3
mag
Over Flow
Tank
SUMP
T6100
HV14
FT
2901
FY
FT
2902 2902
LT
4102
cor
PSH PY
3602 3602
Oil
1
LT
4101
TT
5503
To sump
P4
FV
1
5
cor
LSH
6302
FV
3
To Separation from Water
LSH
3302
LY
6302
PT
6201
2
TSH
3401
LT
6103
FT
6901
3
STM
9901
FV
5
LY
3101
FS
3701
HV-2
FV
2
PT
9201
HV-8
AT
1801
PSY
1601
PT
1201
PSH
1601
FT
1909
1-High level on Oil Storage Tk
2-High Level on Separation Tk
3-High Level on Mix Tank
4- High Level on Batch Tank
5- High Level on Batch Tank
6- High Level on Mix Tank
7- High Level on Water Tank
mag
HV-5
FT
1908
FT
1907
cor
cor
HV-4
VB
9901a
P1
STM
9904
LT
1103
AIR PURGE
Interactive Plant Environment
Process & Instrument
6/1/2016
Diagram (P&ID)
C T Johnson, PE
Fig 12-1 Interactive Plant Environment for Emerson Process
The above example is not typical of a P&ID; I developed for a training facility for individual
instruments. It consists entirely of field instruments that are tagged to identify their service
(measurement) and type. I showed a legend of special symbols on the drawing because the
clients requested that only one sheet be used and it would print on a 11X17 sheet . The following
drawing was provided me to develop the P&ID.
Fig 12-2 Emerson Training Plant
©2 16 Clifford T Johnson, PE, CSE
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AS
LV
102
I/P
HIK
102A
P-13
Close Open
FV
108
O-C
HS
108B
P-11
M
LY
102
FT
104
FI
104
P-30
P-22
LAH
103
P-12
LIC
102
P-11
P-29
Close Open
LAL
LI
114
HS
109B
FV
109
FI
105
FT
105
FI
113
P-24
LT
102
P-10
M
P-18
Cor
LT
114
P-25
P-14
F
I-9
Close Open
FV
110
HS
110B
LSH
103
FI
106
FT
106
M
P-9
Mag
P-16
HS
111B
FV
111
P-15
F
I-8
Close Open
FT
107
dp
FI
107
FE
107
M
P-6
P-18
P-7
1 in
P-19
1 inch
P-5
Sply
Tnk
Sply
Tnk
E-3
1 1/2 inch
P-4
E-2
P-4
P-1
P-31
Σ
FY
101
1 inch
1
FIC
101
SZ
101
P-26
P-28
HOA
2
1 inch
SZ
112
P-2
E-1
1 1/2 inch
HOA
FIC
112
E-4
Fig 12-3 Flow Lab at Central Piedmont Community College
I designed Flow Lab as a tool for the Instrument coursing I taught at the local community
college. Instruments were donated by Emerson Process and Endress + Hauser. The control
system was an Emerson Delta-V DCS
It is a good example of symbols: FY-101 is a summing function in the DCS, the diamond
indicating an interlock; SZ-101 is a local operator accessible Hand-Off-Auto portion of the
final control device.
There are a total of fourteen instruments loops. Loop numbers are usually sequential as they are
in this P&ID, however, they can be used to show different areas or process systems by using
the first of three numbers to indicate areas (assuming there are no more than 99 loops in an
area), if there are more than 99 loops in and area a four digit loop number can be used.
It was also used with a Honeywell single loop controller as show in P&ID 202 Anatomy next.
©2 16 Clifford T Johnson, PE, CSE
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13. P&ID 202Anatomy
LT
102
I/P
H
LICA
102
LY
102
N.C.
LSH
102
3/4 in PVC sched 40
A.S.
LV
102
LIK
102a
HS
121
S
FC
DE
3/4 in PVC
sched 40
LCV
102
Receiver
Supply
T1
T2
SC
121
FI
103
3/4 in PVC
sched 40
1 in PVC sched 40
P1
Fig 13-1 - P&ID-I-202 Flow Lab at CPCC
Fig-13-2 Instrument Index for P&ID I-202
©2 16 Clifford T Johnson, PE, CSE
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LIK
EN 102b
A.S.
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14. SAMA Logic used in place of P&ID for Boiler Control
To become somewhat familiar with how a SAMA diagram replaces a P&ID for Boiler control
Click Here for a Siemens overview. SAMA was a forerunner of the P&ID and developed by
Bailey Controls. There are still many power plants they use the diagram because it does break
the control systems components down further that the P&ID, but it also used much more
drawing space to show a similar system. The following is the symbol for a controller
The PT-48 is the
same as the P&ID
The I/O address
would be a BUBBLE.
However, the
controller is made up
of several symbols that
include the Signal
Processing PID, the
transfer switch and
indicator, that would
all be one BUBBLE in
a P&ID
The I/O address
would be a BUBBLE
The I/P would be a
BUBBLE and
the Valve would be a
BUBBLE
Fig 15 Symbol for control loop in SAMA Logic
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15. Summary
You should now be able to make sense of a P&ID for use in maintenance or construction, but
you will need to study more examples to actually develop one. There are some good examples
Click Here
Microsoft Visio may be a good choice for learning the symbols because it has a fair symbols
library, but Visio is somewhat difficult to use.
Libre Open Office is a good (and free) drawing application which I did use when I was
teaching; however, it has no symbols, but is easier to use.
A newer drawing application EDRAW is good, but its support is none existing as I tried their
email support and they failed. It has a trial package to download and I did install it, but it does
not import Vision very well. It does have a very good library of symbols which makes it
worthwhile to try.
TurboCAD is my choice for CAD because it allows me to open AutoCAD and other files that
my clients use and it is not expensive. I does have symbol libraries, but not for I&C.
Related Links
For additional technical information related to this subject, please visit the following websites:
http://ctjohnson.com/Programs.html
http://www.instrumentationtoolbox.com/2011/01/piping-and-instrumentation-diagrams-p4.html#axzz4E7Xzqt1z
https://en.wikipedia.org/wiki/Piping_and_instrumentation_diagram
https://www.google.com/search?q=P%26ID&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwjB
6trHk-fNAhUH9h4KHYzKCxYQsAQIOQ&biw=1212&bih=786
http://www.engineeringtoolbox.com/p-id-piping-instrumentation-diagram-d_466.html
https://www.lucidchart.com/pages/p-id-symbols-legend
http://www.autodesk.com/products/autocad-p-id/overview
https://www.edrawsoft.com/knowing-pid.php
https://www.edrawsoft.com/pid-legend.php
https://www.edrawsoft.com/pfd-examples.php
http://www.aiche.org/chenected/2010/09/interpreting-piping-and-instrumentation-diagrams
Once you finish studying the above course content, you need to take a quiz to
obtain the PDH credits.
DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the
part of PDHonline.org or any other person/organization named herein. The materials are for general information
only. They are not a substitute for competent professional advice. Application of this information to a specific project
should be reviewed by a registered professional engineer. Anyone making use of the information set forth herein
does so at their own risk and assumes any and all resulting liability arising there from.
©2 16 Clifford T Johnson, PE, CSE
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