Basics of P&ID (piping and instrumentation diagram)

What is P & ID?

A Process and Instrumentation Diagram (P & ID) shows the process flow and interconnection of process equipment which is used control a process. The P & ID includes every mechanical aspect of the plant except stream flows, pipe routing, pipe lengths, pipe fittings, supports, structure & foundations.

A P&ID provides information to begin planning for construction of plant. There are different Sets of symbols are used to depict mechanical equipment, piping, piping components, valves, drivers and instrumentation and controls. A P&ID diagram contains following information regarding the equipment: size, rating, throughput, and utility usage.

Purpose and Function of P&IDs

P&IDs serve as a crucial tool for both the maintenance and modification of the processes they represent graphically. During the design phase, these diagrams lay the groundwork for the development of system control schemes, such as Hazard and Operability Study (HAZOP).

In processing facilities, P&IDs offer a visual representation of:

1. Essential piping and instrument details

2. Control and shutdown schemes

3. Safety and regulatory requirements

4. Basic start-up and operational information

Who uses them and When to use P&IDs

P&IDs are utilized as a schematic representation of the functional relationship between piping, instrumentation, and system equipment components in the field of instrumentation, control, or automation.

Typically created by engineers designing a manufacturing process for a physical plant, these diagrams are essential for facilities that involve complex chemical or mechanical processes.

They are crucial for constructing and maintaining plant safety, serving as a reference for Process Safety Information (PSI) in Process Safety Management (PSM). In case of any issues, reviewing the P&ID is often the first step taken.

P&IDs are invaluable documents that are essential for streamlining existing processes, replacing equipment, or guiding the design and implementation of new facilities.

With the information they provide, changes can be planned safely and effectively using Management of Change (MOC). Field technicians, engineers, and operators use P&IDs to gain a better understanding of the process and how instrumentation is interconnected. These diagrams can also be beneficial for training workers and contractors.

Uses of P & ID:

P&IDs are essential in process engineering as they visually represent the piping and instrumentation systems within a process plant, showing how different components interact. However, they are quite helpful in a variety of ways, such as

• Used for planning & construction of plant
• Used to operate the process
• Used for maintenance & modification of the process
• Used by mechanical technicians & safety personnel
• Used for HAZOP study of plant
• The controlled document formally issued at various stages of the project

How to create a P&ID?

Different software is available to create or draw a P&ID diagram. Only a few steps to follow to create a p&id diagram, but one who does it should know well knowledge about the plant process.

• Create the full list of instruments and equipment required for the process. Check the symbols used for each equipment from the library.
• Arrange all equipment in the process order and do the connection.
• Then review the details with a trusted colleague.  Walk through the process several times and search for inefficiencies.
• Discuss with the collates

P&ID symbols and abbreviations:

Process lines:

Instrument Bubbles:

Process equipments:

Valve types:

VS — Gate Valve
VD — Globe, Needle or Angle Valve
VR — Plug Valve
VB — Ball or 3-way Plug Valve
VDR — Check Valve
VF —  Butterfly Valve
VM — Diaphragm Valve
VP — Piston Valve

Temperature:

These symbols are represented in the respective instrument bubbles:

TE = Temperature sensing element
Th = Thermometer Indicator
TRC = Recorder-controller
TR = Recorder

Pressure:

These symbols are represented in the respective instrument bubbles:

PC = Controller
PI = Indicator
PIC = Indicator-controller
PR = Recorder

Level:

LC = Controller
LG = Glass
LI = Indicator
LR = Recorder

  Flow:

FC = Controller
FE = Test orifice plate
FI = Indicator
FR = Recorder

How to read a P&ID?

Each instrument in the process and their connections are drawn in a P&ID diagram. Thus the process is simply described in the diagram. Specification of the instruments is written with the instrument symbol. The specification of the line is code in the line or above the line as shown in the below picture:

Area Code:

01 : Urea
02 : Reforming Section
03 : CO2 absorption Section
04 : Synthesis gas compression
05 : Ammonia Synthesis
06 : Steam Generation
07 : Power Generation
08 : CW circulation

Fluid Type:

KS  : Very High-Pressure Steam
HS : High-Pressure Steam
LS  : Low-Pressure Steam
P : Process Fluid
IA : Instrument Air
UA : Utility Air
UN : Utility Nitrogen

Material:

1 : Carbon Steel
3 : Austenitic Stainless Steel
4 : Reinforced Thermal Resin Pipe
5 : Si Killed Carbon Steel or CrMo steel
6 : Ferritic Alloy Steel
7 : Cast Steel
8 : Austenitic SS or Ferritic Alloy Steel
9 : Urea Grade SS

Material Rating:

1 : 150#
3 : 300#
5 : 600#
6 : 900#
7 : 1500#
8 : 2500#
9 : Special

Insulation Specification:

N : Not Painted /Insulated
PP : Personnel Protected
S : Internal Treated/External Painted
A : Internal Treated, External coated
B : External Coated
E : Electric traced
F : Cold Insulated
I : Hot Insulated
T : Steam traced
V : External painted
W : Jacketed

What’s the difference between a process flow diagram (PFD) and a piping & instrumentation diagram (P&ID)?

Instrumentation detail varies with the degree of design complexity. Simplified or conceptual designs are called process flow diagrams (PFDs). A PFD shows fewer details than a P&ID and is usually the first step in the design process–more of a bird’s eye view. More fully developed piping and instrumentation diagrams (P&IDs) are shown in a P&ID.

What are the limitations of P&ID?

Since P&IDs are visual depictions of processes, they come with certain limitations. They cannot be considered as exact replicas of the actual systems, as they may not be drawn to scale or with complete geometric accuracy.

Additionally, there is no universally accepted standard for P&IDs, leading to variations in appearance across different companies or even within the same organization, depending on internal guidelines, software platforms, and individual preferences. This underscores the significance of creating and scrutinizing documentation that delves into the detailed specifics of support materials.

What should a P&ID include?

A P&ID should include the following components according to the PIP (Process Industry Practice) standards:

1. Mechanical equipment with names and numbers

2. All valves and their identifications

3. Process piping, sizes and identification

4. Miscellaneous items such as vents, drains, special fittings, sampling lines, reducers, increasers, and swagers

5. Permanent start-up and flush lines

6. Flow directions

7. Interconnections reference

8. Control inputs and outputs, interlock

9. Seismic category

10. Interfaces for class changes

11. Quality level

12. Annunciation inputs

13. Computer control system input

14. Vendor and contractor interfaces

15. Identification of components and subsystems delivered by others

16. Intended physical sequence of the equipment

17. Equipment rating or capacity.

What should a P&ID not include?

A P&ID should not include certain elements to avoid clutter and maintain clarity. It is recommended to exclude the following:

• Instrument root valves
• Control relays
• Manual switches
• Primary instrument tubing and valves
• Pressure, temperature, and flow data
• Elbows, tees, and similar standard fittings –
• Extensive explanatory notes