Table of Content:
What is a P&ID (Piping and Instrumentation Diagram)?
A P&ID is a graphic representation of a process system that includes the piping, vessels, control valves, instrumentation, equipment, and other process components and equipment in the system found in proces enviromts such as oil & gas, chemical plants, cement factories & paper mills. The symbols contained in P&IDs represent the equipment in the process such as actuators, sensors, and controllers. Process equipment such as valves, instruments, and pipelines areidentified by codes and symbols.
It is also known as a Process Engineering Flow Scheme (PEFS).
P&IDs serve as the primary schematic drawing used for laying out a process control system’s installation. They are used throughout the entire lifecycle of a plant, from pre-EPC to operation.
P&IDs are more detailed and complex than Process Flow Diagrams (PFDs). "A single PFD can have multiple P&IDs" (Hardhatengineer). P&IDs show how a process works, building upon the general flow of plant processes depicted in PFDs.
Types of Drawings:
Process Flow Diagram (PFDs) -What a process does?
Piping & INstrumentation Diagram(P&ID)- How it Works?
Layout Diagram - How it looks?
Mechancial Drawing - How to build?
Construction Drawing - How to build ?
Importance and Applications of P&IDs:
1. Design and Layout
P&IDs are crucial for designing and laying out process systems, particularly for the piping and instrumentation disciplines. They help engineers visualize the flow paths, control loops, and interconnections of various components in a plant.
2. Component Specification
These diagrams help engineers specify the necessary pumps, valves, instruments, pipelines, and control systems required for a process. This ensures that the right components are selected for efficiency and safety.
3. Control System Development
P&IDs form the foundation for designing control system schemes. Engineers use them to develop:
Process automation strategies
Instrumentation loops
Control logic for plant operations
4. Safety and Operational Analysis
P&IDs play a vital role in safety assessments such as:
HAZOP (Hazard and Operability Study) – Identifying potential hazards and operability issues.
SIL (Safety Integrity Level) Assessment – Ensuring the reliability of safety instrumented systems.
By demonstrating the physical sequence of equipment and their interconnections, P&IDs help engineers conduct safety reviews and risk assessments to prevent potential failures.
5. Installation and Construction
During the construction phase, P&IDs serve as a blueprint for installing piping and equipment. They guide construction teams in assembling process systems accurately and efficiently, ensuring compliance with design specifications.
6. Training of Operators and Engineers
P&IDs are widely used for training purposes. They provide a clear and structured view of plant operations, helping operators and engineers understand process flows, control mechanisms, and safety systems.
7. Maintenance and Modification
P&IDs are essential records for maintenance, troubleshooting, and modifications. Any changes in the plant design are noted directly on these diagrams.
"Modifications are red-penned onto the diagrams and are vital records of the current plant design." – (Piping Mantra)
Engineers and maintenance teams rely on updated P&IDs to:
Troubleshoot issues efficiently.
Ensure system modifications align with plant design.
Maintain accurate documentation for future upgrades.
8. Cost Estimation and Project Planning
P&IDs are used to estimate project costs by determining the required materials, equipment, and labor. They help in capital cost estimation, ensuring budget accuracy for process industries.
9. EPC Contract Specification
Engineering, Procurement, and Construction (EPC) contracts rely on P&IDs for defining project scope, technical requirements, and deliverables. They serve as contractual documents that ensure all parties align with the project's design and execution plan.
Components of a P&ID: Information Contained in a PIPING AND INSTRUMENTATION DIAGRAM
P&ID's represent the fundamental elements of a piping system, such as pipes, valves (gate, globe, check, etc.), pumps, and instruments (pressure gauges, flow meters, etc.).
The instrument symbols used in these drawings are generally based on International Society of Automation STANDARD (ANSI/ISA S5.1, ISO 14617-6 and ISO 10628.)
These symbols are also labeled with words, letters, and numbers to further identify and specify the components that they are representing.
1. Equipment and Piping
A P&ID provides a detailed representation of all equipment and associated piping, including:
Main equipment such as pumps, compressors, heat exchangers, and reactors.
Installed spares for backup and redundancy.
Piping systems, including drain and vent lines.
Insulation and jacketing requirements for pipelines handling high-temperature or cryogenic fluids.
2. Instrumentation
Instrumentation plays a critical role in monitoring and controlling process parameters. A P&ID shows:
Control loops that regulate temperature, pressure, flow, and level.
Sensors and transmitters providing real-time process data.
Actuators and control valves that adjust process conditions.
3. Utilities
P&IDs also detail the utilities required for plant operation, such as:
Cooling water for heat exchangers.
Steam for heating applications.
Compressed air for pneumatic controls.
Inert gases like nitrogen for purging.
4. Piping Components
Each pipe in a P&ID is labeled with critical specifications, including:
Size and class for proper flow and pressure handling.
Tag number for identification and tracking.
Insulation and heat tracing details for temperature-sensitive lines.
5. Design, Construction, and Operation Information
A P&ID also provides guidelines for plant design, construction, and operation, such as:
Line slope for gravity-driven flows.
Minimum/maximum distances between equipment and instruments.
Minimum straight lengths required after control valves or flow meters for accurate readings.
6. Line Numbers
Each pipeline is uniquely identified by a line number that contains:
Pipe size and fluid service (e.g., water, gas, chemicals).
Unit or facility number for plant section identification.
Serial number for tracking.
Pipe service class (e.g., process, utility, drain).
Flange rating and piping material to ensure compatibility with pressure and temperature conditions.
Insulation type and thickness for thermal protection.
Example of Pipe Line No
10” – Represents the size of the line in inches, the line size is 10 inches.
PL – Represents the service fluid.
12007 – The first two digits (12) of 12007 represent a unit area or facility number. And the last three digits (007) of 12007 represent the serial number or line number.
B12B – Represents pipe classification or service class of piping.
We can further divide the class of piping service B12B as shown below
B – Represents the rating of the flange.
12 - Represents the material used for piping
B - It is a suffix to qualify the piping material.
IA – Represents the type of insulation.
50 - Represents thickness of the insulation
7. Valves
A P&ID clearly indicates different valve types and their specifications, including:
Gate, globe, ball, butterfly, and check valves.
Actuation type (manual, pneumatic, hydraulic, or electric).
Fail-safe positions, such as:
NO (Normally Open)
NC (Normally Closed)
FO (Fail Open)
FC (Fail Closed)
8. Nozzles
All nozzles on equipment are displayed on a P&ID in their approximate locations with tag numbers. These are essential for:
Connecting pipelines to equipment.
Ensuring proper flow and process efficiency.
Facilitating maintenance and modifications.
Key Elements and Symbols in P&IDs
Lines in P&IDs
Lines in a P&ID indicate different types of process connections, signal paths, and control systems.
Thick continuous lines represent process pipes.
Lines crossing without a break indicate connected pipes.
Lines crossing with a break or "hump" signify that the pipes are not connected.
Bold lines are used for main process lines.
Different line styles represent various signal types:
Solid lines for mechanical or process connections.
Dashed lines for pneumatic signals.
Dotted lines for electric signals.
Dash-dot lines for data or control signals.
Flow Direction
Flow direction is a crucial element of a P&ID, ensuring that all engineers and operators understand the process flow within the system.
Flow direction is indicated by arrowheads along the pipes.
These arrows help visualize how fluids, gases, or signals move through the system.
Line Breaks and Changes
Line breaks in a P&ID indicate changes in line number, specification, material, tracing, or insulation.
Triangle symbol → Represents a line break, indicating a line number change. The new and old line numbers are specified.
Triangle symbol absent → Indicates a property change such as insulation, tracing, or material variation.
Revision Clouds and Process Flow Tags
Revision clouds or triangles indicate changes made to the drawing. These help in tracking modifications over different versions of a P&ID.
Process flow tags identify where a pipe originates and where it leads to on other P&ID drawings. This is essential in large-scale projects with multiple interconnected diagrams.
Termination Points and Hazard Level Ratings
Termination points mark where new work connects to existing plant systems. These are important when integrating new equipment or piping into an operational facility.
Hazard level ratings are included to indicate the danger associated with the fluid in the pipe. These ratings help in safety assessments and operational planning.
Instrumentation Symbols and Representation
Instrumentation plays a vital role in process control and monitoring. Instruments are represented using "bubbles" (circles, squares, or hexagons) with different line styles to indicate mounting locations.
No line in bubble → Field-mounted instrument.
Single solid line → Control panel-mounted instrument.
Double solid line → Sub-panel mounted instrument.
Dashed line → Instrument is inaccessible, such as on the back side of a control panel.
Square symbols → Represent shared displays or control interfaces.
Hexagon symbols → Represent computer systems and digital controllers.
Instrument Tag Numbers and Functions
Each instrument in a P&ID is assigned a unique alphanumeric tag that defines its purpose and function.
Tag Format:
[Process Variable] [Function] [Loop Number]Example: FIC-101
F → Flow
I → Indicator
C → Controller
101 → Loop Number
Common Process Variables:
F → Flow
P → Pressure
T → Temperature
L → Level
Common Instrument Functions:
I → Indicator
C → Controller
T → Transmitter
R → Recorder
V → Valve
These tags help engineers quickly identify an instrument’s purpose, location, and function within the process.
Valve Symbols and Actuators
Valves are essential for controlling the flow of process fluids. Each valve type has a specific symbol to indicate its functionality.
Gate valves – Represented by a simple line across a pipe.
Globe valves – Shown with a filled-in black circle.
Ball valves – Depicted with a filled circle and two lines.
Check valves – Shown with a tilted line indicating one-way flow.
Butterfly valves – Represented by a simple cross inside the pipe.
Valve Actuator Symbols:
Manual valves – Represented without additional symbols.
Pneumatic actuators – Indicated with a spring or diaphragm symbol.
Electric actuators – Represented with a small motor symbol.
Hydraulic actuators – Shown with a cylinder symbol.
Understanding these symbols is essential for reading, designing, and troubleshooting process systems in industrial facilities.
How to Read a P&ID
Reading a Piping and Instrumentation Diagram (P&ID) involves understanding the flow of process lines, interpreting the symbols and their interconnections, and identifying key information like line numbers and equipment tags.
The process flow is represented by the lines on the diagram, with the direction indicated by arrows. Tracing the lines allows you to follow the path of the process stream through various equipment and components. [Source: https://www.lucidchart.com/pages/tutorial/p-and-id]
Symbols on a P&ID represent different types of equipment, instrumentation, and components. Common symbols include pumps, valves, vessels, instruments, and heat exchangers. Each symbol has a specific meaning and provides information about the function and type of the component. [Source: https://www.realpars.com/blog/p-id]
Line numbers and equipment tags are crucial for identifying and referencing specific elements on the P&ID. Line numbers are assigned to each process line, while equipment tags uniquely identify individual pieces of equipment or instrumentation. These labels are essential for cross-referencing with other documentation and communicating about specific components.
Use Cases and Benefits of P&IDs
P&IDs serve several critical purposes across the lifecycle of a process plant or facility:
Process Design and Engineering: P&IDs are essential during the design phase, enabling engineers to visualize and optimize the process flow, equipment layout, and instrumentation requirements. They facilitate communication and collaboration among multidisciplinary teams.
Construction and Installation Guidance: Contractors and installation teams rely on P&IDs as a roadmap for proper equipment placement, piping routes, and instrument connections. This ensures accurate and efficient construction while minimizing errors and rework.
Operation and Maintenance Reference: Plant operators and maintenance personnel use P&IDs as a vital reference for understanding process flows, equipment functions, and instrumentation readings. This aids in troubleshooting, process optimization, and preventive maintenance activities.
Safety and Regulatory Compliance: P&IDs document critical safety systems, such as relief valves, emergency shutdown systems, and hazardous material handling. They help demonstrate compliance with industry standards and regulatory requirements, ensuring safe and responsible operations. Source: https://www.plannedparenthood.org/learn/birth-control/birth-control-pill/what-are-the-benefits-of-the-birth-control-pill
By providing a comprehensive visual representation of the entire process, P&IDs enable effective communication, coordination, and decision-making among various stakeholders throughout the plant's lifecycle.
P&ID Development and Maintenance
1. Phases of P&ID Development
The development of a P&ID follows a structured approach and involves multiple engineering disciplines.
Phase 1: Conceptual Design
P&IDs are created based on Process Flow Diagrams (PFDs).
Key process details, including fluid type, flow direction, and instrumentation, are determined.
Equipment layouts and preliminary pipe routing are considered.
Phase 2: Detailed Engineering
Piping, instrumentation, and mechanical equipment details are added.
Control loops, alarms, safety interlocks, and emergency shutdown (ESD) systems are defined.
Pipe specifications, valve types, and instrumentation tags are assigned.
Phase 3: Review and Validation
The P&ID is reviewed by process, piping, instrumentation, and safety engineers.
Hazard and Operability Study (HAZOP) analysis ensures compliance with safety standards.
Final modifications are incorporated before issuing the Approved for Design (AFD) version.
Phase 4: Construction and Commissioning
The P&ID serves as the primary reference during piping installation.
Any field modifications are marked as redline changes.
A final As-Built P&ID is issued after commissioning.
2. Pipe Sizing in P&ID Development
Proper pipe sizing is essential for flow efficiency and pressure control. It is done in parallel with P&ID creation using factors such as:
Flow rate and velocity limits to prevent erosion, vibration, or excessive pressure drop.
Pipe material and pressure class based on temperature and fluid type.
Industry standards such as ASME B31.3 for process piping.
Incorrect pipe sizing can lead to flow restrictions, excessive pressure drops, or cavitation, impacting process efficiency and equipment longevity.
3. Line Numbering: Ensuring Systematic Identification
Every pipe in a P&ID is assigned a unique alphanumeric identifier, known as a line number. This helps in tracking, maintenance, and troubleshooting.
Typical Line Number Format:
Example: 6"-W-1001-A1
6” → Pipe size
W → Service code (e.g., W = Water, S = Steam, G = Gas)
1001 → Unique serial number
A1 → Area code or revision number
Line numbering must be consistent across all engineering documents, including piping isometrics and process data sheets.
4. Modification Control: Maintaining Accuracy
P&IDs must be regularly updated to reflect changes in process modifications, equipment replacements, and safety upgrades.
Key Aspects of P&ID Modification Control:
Redlining: Temporary field changes are marked in red ink before final updates.
Revision Control: Every modification must have a revision number, date, and approver's initials.
Approval Workflow: Changes should be reviewed by process engineers, piping designers, and safety teams before final approval.
Uncontrolled changes can lead to inaccurate documentation, causing safety risks and operational inefficiencies.
5. Security of P&IDs: Protecting Critical Information
P&IDs contain valuable intellectual property and engineering know-how. Unauthorized access or leaks can lead to serious safety, operational, and competitive risks.
Security Measures for P&IDs:
Access Control: Limit access to authorized personnel only.
Digital Security: Store P&IDs in secure servers or cloud-based platforms with encryption.
Version Control: Implement strict change management protocols.
Backup Systems: Maintain regular backups to prevent data loss.
Unauthorized modifications or data breaches can result in safety hazards, regulatory violations, and financial losses.
P&ID Examples and Templates
P&IDs are widely used across various industries, including chemical, oil and gas, pharmaceutical, food and beverage, and more. Examples of P&IDs in these industries can illustrate their versatility and adaptability to different processes and systems.
In the chemical industry, P&IDs are essential for designing and operating complex plants and processes involving multiple unit operations, such as reactors, distillation columns, and heat exchangers. Source
Pre-built P&ID templates are available from various software vendors and online repositories, offering a starting point for creating industry-specific diagrams. These templates typically include common equipment symbols, line styles, and annotation conventions tailored to different sectors.
While templates provide a solid foundation, customization is often necessary to accurately represent unique process requirements, equipment configurations, or company standards. Most P&ID software tools allow for symbol library customization, enabling users to create or modify symbols to match their specific needs.
Limitations of P&IDs
P&IDs are essential tools for process design, operation, and maintenance, but they have certain limitations. They do not provide detailed process conditions, physical layouts, or precise piping information, and they must be used alongside other engineering documents for a complete understanding of the process.
Information NOT Included in a P&ID
Despite their extensive details on piping and instrumentation, P&IDs do not provide the following information:
1. Process Conditions and Physical Data
P&IDs do not include critical process parameters such as:
Temperature and pressure values.
Flow rates and velocities.
Chemical compositions and reaction details.
These details are typically found in Process Flow Diagrams (PFDs) or Process Data Sheets.
2. Operating Conditions
While P&IDs show the interconnections of equipment and instruments, they do not specify:
Normal operating ranges.
Start-up and shutdown procedures.
Process safety limits.
Engineers refer to operating manuals and process control strategies for this information.
3. Streamflow Details
P&IDs do not provide the complete mass and energy balance of a process. Information on:
Material flow rates.
Heat transfer calculations.
Phase changes (e.g., liquid to gas).
is documented in PFDs or Heat & Mass Balance Diagrams.
4. Equipment Locations (Precise)
A P&ID is a schematic representation and does not show the actual physical layout of equipment within the plant.
Equipment positions and spacing are determined in General Arrangement (GA) drawings and 3D models.
5. Pipe Routing, Length, and Fittings
P&IDs do not specify:
The exact path of pipelines.
Pipe lengths and elevations.
Elbows, tees, reducers, or other fittings.
For this information, engineers use piping isometrics, layout drawings, and stress analysis reports.
6. Support and Structural Details
P&IDs do not include:
Pipe supports, hangers, and brackets.
Structural steel information.
Equipment foundations or civil works.
These aspects are covered in structural and civil engineering drawings.
Limitations of P&IDs
While P&IDs are essential for process control and system understanding, they have some inherent limitations:
1. P&IDs Do Not Represent the Entire Process
P&IDs focus primarily on piping and instrumentation and do not include:
Chemical reactions and thermodynamics.
Material balances.
Safety interlocks in full detail.
These details are found in process descriptions, safety analysis reports, and PFDs.
2. P&IDs Are Not to Scale
Symbols on a P&ID are not dimensionally accurate.
Relative sizes of equipment and piping are not represented.
The actual plant layout may differ significantly from what is depicted.
For spatial accuracy, engineers refer to plant layout drawings and 3D models.
3. P&IDs Do Not Represent Physical Locations
The positioning of equipment, valves, and instruments on a P&ID does not indicate their actual physical proximity.
Equipment that appears close on a P&ID may be far apart in reality.
For real-world placements, engineers rely on plot plans, site maps, and piping layout drawings.
4. P&IDs Require Supporting Documents
While P&IDs provide an overview of the process, they are not standalone documents. Additional documents are necessary for a complete design, including:
Equipment datasheets – Technical specifications of machinery.
Instrument specifications – Details of sensors and control devices.
Piping isometrics – Exact dimensions and routing of pipes.
By recognizing what P&IDs do and do not include, engineers can use them effectively while referring to the appropriate supporting documents for detailed design and implementation.
Key Features of P&ID Software
P&ID software typically includes a comprehensive symbol library with drag-and-drop tools for easily creating and arranging P&ID components like pipes, valves, pumps, and instrumentation. As described in Understanding OpenAI's "Temperature" and "Top_p" Parameters in Language Models, "Top_p" or nucleus sampling is a setting that decides how many possible words to consider when generating text. A high "top_p" value means the model looks at more potential word choices.
Revision control and collaboration features allow multiple users to work on the same P&ID simultaneously, tracking changes and maintaining version history. Integration with other engineering tools like 3D modeling software, instrumentation databases, and plant design applications enables seamless data exchange and project coordination.
Putting the 'Pipe' in P&ID
Piping design and specifications play a crucial role in the creation and interpretation of P&IDs. P&IDs are primarily focused on representing the piping system, along with its associated instrumentation and equipment. Proper piping design is essential for the safe and efficient operation of any industrial process.
In a P&ID, the piping components are depicted using various symbols and notations. These include representations for pipes, fittings, flanges, valves, and other piping accessories. The piping layout, sizing, material specifications, and flow directions are all conveyed through the P&ID drawing. Additionally, piping support structures, insulation requirements, and other design details may be included, depending on the level of detail required.
The integration of piping and instrumentation is a critical aspect of P&IDs. Instruments such as flow meters, pressure gauges, and temperature sensors are strategically placed along the piping network to monitor and control the process. The P&ID clearly shows the connections between the piping system and the associated instrumentation, allowing for proper monitoring, control, and safety measures to be implemented.
Accurate representation of piping and its integration with instrumentation is essential for effective communication between various stakeholders, including engineers, designers, operators, and maintenance personnel. A well-designed P&ID serves as a comprehensive reference for piping and instrumentation, facilitating efficient installation, operation, and maintenance of the process system. [Source: Detailed P&ID Guide for Industrial Processes]
Industry Standards and Best Practices
Creating P&IDs requires adherence to established industry standards to ensure clarity, consistency, and effective communication among engineers, technicians, and operators.
International Society of Automation (ISA) Standards:
ISA-5.1: Defines instrumentation symbols and notations.
ISA-5.2: Covers binary logic diagrams for process control.
ANSI/ASME Y32.3 Standard:
Provides graphic symbols for fluid power systems, including hydraulic and pneumatic components.
Importance of Standardization:
Ensures uniformity and clarity across industries.
Facilitates collaboration between teams and organizations.
Improves interpretability and efficiency in design, operation, and maintenance.
Following these standards helps create accurate, readable, and universally understood P&IDs, making process documentation more effective and reliable.
Top Software for P&ID Development
1. AutoCAD P&ID
Best for: Engineering firms, large-scale industrial projects
Key Features:
Industry-standard P&ID symbols and libraries.
Intelligent database-driven diagrams for easy modifications.
Integration with AutoCAD Plant 3D for 3D modeling and project management.
Why Use It?
AutoCAD P&ID is widely used in oil & gas, power plants, and manufacturing industries due to its extensive customization and integration capabilities.
2. MicroStation
✅ Best for: Infrastructure and plant design professionals✅ Key Features:
Supports 2D and 3D design workflows.
High compatibility with other CAD software.
Advanced tools for complex process system designs.
🔹 Why Use It?MicroStation is known for its powerful visualization capabilities and is often used in industries requiring large-scale infrastructure planning.
3. SmartPlant P&ID (Intergraph)
✅ Best for: Large-scale EPC (Engineering, Procurement, and Construction) projects✅ Key Features:
Rule-based intelligent P&ID design.
Integration with SmartPlant Enterprise for complete project lifecycle management.
Automated validation and consistency checks.
🔹 Why Use It?SmartPlant P&ID is ideal for projects requiring high accuracy, regulatory compliance, and seamless data integration.
4. CAESAR II
✅ Best for: Piping stress analysis and engineering✅ Key Features:
Finite Element Analysis (FEA) for piping systems.
Load case evaluations for thermal, seismic, and weight stress conditions.
Integration with P&ID and 3D piping models.
🔹 Why Use It?Although CAESAR II is not a direct P&ID software, it is widely used in piping system design where stress analysis is required.
5. Visio P&ID
✅ Best for: Small to mid-scale process design projects✅ Key Features:
User-friendly drag-and-drop interface.
Pre-built P&ID templates and symbols.
Seamless integration with Microsoft Office for reporting.
🔹 Why Use It?Visio P&ID is an excellent choice for quick, simple P&ID creation without the complexity of full-fledged CAD software.
6. Lucidchart PID
✅ Best for: Cloud-based, collaborative P&ID design✅ Key Features:
Web-based P&ID design tool for remote teams.
Easy sharing and real-time collaboration.
Predefined templates for fast diagram creation.
🔹 Why Use It?Lucidchart is a great option for teams working remotely or requiring quick P&ID sketches without CAD expertise.
7. SolidPlant P&ID
✅ Best for: Process and plant engineers✅ Key Features:
3D P&ID integration with plant models.
Intuitive user interface for quick diagram creation.
Compatible with SolidWorks and other CAD software.
🔹 Why Use It?SolidPlant P&ID is ideal for mechanical engineers who need seamless integration with 3D models.
8. ProCAD P&ID
✅ Best for: Piping professionals in small and mid-sized industries✅ Key Features:
Simple and cost-effective P&ID drafting tool.
Includes industry-standard symbols.
Integration with ProCAD’s full suite of piping design tools.
🔹 Why Use It?ProCAD P&ID is an excellent choice for budget-conscious teams needing a dedicated P&ID tool.