What is P&ID? (Piping and Instrumentation Diagram)?

What is P&ID? (Piping and Instrumentation Diagram)?

Synergy Codes

21 min
What is P&ID? (Piping and Instrumentation Diagram)?

P&ID (Piping and Instrumentation Diagram or Drawing) is a technical drawing used in process engineering. It represents all details of the chemical process at processing plants, such as oil refineries, food processing plants, cement plants, pharmaceutical manufacturing facilities, or other plants where raw material is chemically or mechanically turned into ingredients or finished products.

Everyone involved in the design, construction, management, operations, or maintenance of a process plant, will have to work with a P&ID (Piping and Instrumentation Diagram) at some point. Therefore, everyone should either know how to read these drawings or have a good graphic interface or simulation software to access them, as they are basically a representation of how the processing facility works.

How To Create a P&ID

Back in the day, designers, constructors, engineers, managers, and staff of process facilities had to work with multiple hand-drawn P&IDs. Those Piping and Instrumentation Diagrams drawings would all need to be updated whenever the parameters of the process changed – be it at the design and construction stage, or during plant operation, or when some equipment was modernized. Even after CAD software was introduced, managing an archive of all these drawings took hours of very meticulous work and strict procedures.

Today, the way we use and manage P&IDs is much more intelligent and faster. Not only are there dedicated Piping and Instrumentation Diagrams software and database systems out there, but with an experienced developer team, you can create a custom, collaborative tool that guides you through design and budgeting, safety regulations, and provides a live simulation of the whole facility.

What is included in P&ID Diagrams

Piping and Instrumentation Diagrams contains all the details about physical components involved in material processing, i.e.:

  • Process equipment with specifications (e.g. turbines, fans, vessels, pumps, etc.);
  • Piping and line specifications, as well as process piping system components (e.g. fittings, flanges, valves, actuators, insulation, etc.);
  • Instrumentation and control system components (e.g. indicators, gauges, alarms, interlocks, control input and output);

The function of P&IDs is also to specify parameters of those components as well as parameters of the processed material flowing along the pipelines and the operating procedures of the facility:

  • Flow directions and process variables such as temperature, pressure or flow rate;
  • Material specifications;
  • Computer Control System input.

How to read P&ID drawings

Piping and Instrumentation Diagrams – unlike floor plans or maps – are not scaled drawings. They don’t visually represent the proximity of given components, their shape, or their physical coordinates in the facility. Their main purpose is to show the parameters and elements of the processing system, not its proportions or topography.

Symbols drawn in P&IDs are represented by codes and graphic symbols. These may vary from company to company, so P&IDs (Piping and Instrumentation Diagram) come with Lead Sheets (or Legend Sheets) attached, where notation rules and symbols are explained. Usually, they follow industry standards, such as ANSI/ISA-5.1-2009 (Instrumentation Symbols and Identification).

Because going back and forth between the process drawing and the Lead Sheet is quite cumbersome, a more convenient approach might be displaying the processing facility in a digital model instead, where all the relevant information is easily accessible.

P&ID Codes And Symbols

Decoding P&ID Tagging Systems

Every engineering team establishes their own instrument and equipment tagging convention and explains it on the Lead Sheet. The instrument tags are written in callout bubbles next to the device or inline with the piping or electrical line.

There are some common tagging conventions. For example:

Instrument Symbol Tag Indetification
  1. “P” – First Letter stands for “Pressure”
  2. “D” – Second letter is a modifier for the first and stands for “Differential”
  3. “I” – Third letter stands for “Indicating”
  4. “T” – Fourth letter stands for “Transmitter”
  5. 1703 is the loop number (the Electrical Engineering eggheads need loop numbers too)

You can find a fuller identification and reference designation list on Wikipedia or in the ISA-5.1 standard guide.

P&ID symbols

Here are some of the P&ID (Piping and Instrumentation Diagram) instrument symbols you are most likely to encounter in the processing industry:

1. Instruments – devices used for measurement and control of fluids and material streams. They measure, display, and control parameters such as flow, temperature, pressure, etc.

Instruments are identified on the P&ID diagram through their tagging code (according to a tagging convention included in the Lead Sheet), while the graphic symbol of the instrument represents how it can be accessed and operated, rather than what the device’s function is (for example, a pressure gauge can be represented by the same graphic symbol as level transmitter – they will be identified through their tags).

Instrumentation and control symbols


Image: Instrumentation that contains a transmitter, a controller, and a control valve:
Source: ANSI/ISA-5.1-2009 – Instrumentation Symbols and Identification

2. Piping: lines connecting different parts of the process, where the media flows through. These are pipes, tubes, and hoses. Process lines on the drawing will also have a tag with parameters such as line number, piping size, class, insulation, etc.

3. Communication/Signal Lines – Lines representing process control systems, with different signal types to communicate information between components, instruments, and the control system computers.

Various types of signals

4. Most Common Process Equipment

There are dozens of different equipment types that are used in process engineering, and each one of them can be drawn differently on Piping and Instrumentation Diagrams according to a given company’s guidelines. Below, you can see some of the examples of the most common ones.

Valves – the essential elements that regulate, direct, or control the flow of a fluid in the pipeline, by opening, closing, or partially obstructing the passageways.

Most common valve types
Other valve types

Vessels – containers where fluids are stored or processed through chemical reactions, mechanical manipulation, heating, cooling, stirring, and other methods.


Pumps – devices that move fluids (liquids or gases), or sometimes slurries, along the pipeline.

Other Equipment – there are dozens of other types of process equipment that would make their own book to be listed. Some typical examples are fans, turbines, motors, conveyors, compressors, drains, and many others.

On top of that – every company can add their proprietary equipment and this is why engineers use their own P&ID graphic libraries in the design software they use.

Examples of process equipment:

More P&ID (Piping and Instrumentation Diagram) Examples

The best way to start learning how to draw a P&ID is to study diagrams made by other engineers. The examples below can be a good reference for how these documents are laid out and annotated:

1) Via Benvalle.comdirect link

2) Robert Cook via AIChE.orgdirect link

3) Via Automation Forum – P&ID diagram for Air supply system

4) Typical compressor P&ID via EnggCyclopediadirect link

How is P&ID used in process engineering?

Piping and Instrumentation Diagram is a more detailed elaboration of a Process Flow Diagram (PFD). PFD is the main drawing created by process engineers to show the relationships between a chemical process’ major equipment (pumps, vessels, turbines, heaters, etc.) and the flow and properties of chemical fluids used in the process (temperature, pressure, fluid density, flow rate, etc.) The process Flow Diagram doesn’t show minor components (e.g. pressure-flow instruments) nor details about piping systems in the facility.

P&IDs (Piping and Instrumentation Diagram) are used in design, development, operations, management and maintenance of chemical processing plants. They are used extensively by all engineering disciplines, like process, piping, mechanical, civil, electrical and instrumentation.

process flow diagram for electric circuit
An example of a process flow diagram made for the electric circuit simulations

Process Design And Development

P&IDs are usually developed by process engineers based on the PFD to add details required for the facility design and construction project.

P&IDs are used in front-end engineering design (FEED) as well as engineering, procurement, and construction (EPC), where they serve as a basis to generate a “Bill of Materials.”

P&ID is the roadmap of any process plant engineering project. It is used to plan its staffing, timeline, and budget. Other engineers, project managers, and construction workers use it as a basis for their work, so small changes made to P&IDs (Piping and Instrumentation Diagram) during the construction stage might force other engineers or contractors to redo their work, causing delays and additional costs.

Piping engineers use P&IDs for material procurement and for designing pipe routing in the plant, electrical engineers use it to plan electrical circuits and architects – to design the facility building. Multiple, connected P&IDs are created for different parts of the process flow of a processing facility

Operations, Safety And Maintenance

P&IDs are used for operation, control, and shut-down procedures of a processing plant. They specify regulatory and plant safety requirements; they are used to developing facility operation guidelines (such as start-up and shut-down, monitoring procedures) and standards. Piping and Instrumentation Diagram is also a guide for operational data.

They are used in the training of facility operating staff, field engineers, and maintenance professionals. P&ID is the fundamental document for HAZOP, Model review, and Process Safety Management.

Over the plant’s lifetime, P&IDs are usually updated as the facility gets expanded, modernized, or modified to meet recommendations of Process Safety Management audits.

How A Custom-built P&ID Software Makes A Difference In Process Design And Management

Although there is a set of standards for P&ID (Piping and Instrumentation Diagram) drawings, every company that needs to make them has different needs, graphic styles, and workflows. This is where collaborating with software developers on a customized solution can end up saving costs further down the line.

Personalized P&ID (Piping and Instrumentation Diagram) interfaces for managers and non-engineers

Designing a process flow requires very specialized engineering experience, but since not everyone working for a processing company is a process engineer, they should have a customized yet simple-to-read interface that displays the information they need to know in order to accomplish the tasks. The interactive palette with custom objects is the feature that enriches the diagram drafting platform we developed for the customer.

For example, production managers’ work – be it procurement, facility management, safety and health regulations, etc. – will be much easier if they can get a dashboard that displays components that need to be purchased or will soon need replacement due to expiring warranty or abnormalities registered by sensors. Here, the visual libraries, such as GoJS come with help. The library enables simple drag&drop functionality that enables quick and easy operating on nodes, as well as positioning components at any place on the canvas. Instead of working with multiple drawings, applications, and plugins, our client uses a single platform that integrates into one interface their supplier libraries, equipment monitoring, and a financial system to help manage their budget. Not only can financial managers extract reports easily, but process designers will also know whether they’re staying within budget limits as they add and modify elements of the drawing.

Process Flow diagram in product configurator
Process flow diagram to illustrate the product configuration

Faster and mistake-proof P&ID design process

Customized process design platforms can make the job easier, more reliable, and streamlined for engineers.

With a custom symbol library accessible to all stakeholders of the process plant, the P&ID elements stay consistent and updated across different projects and subunits of the company. One of the most valuable application features, for increased readability and efficiency of design, is being able to add custom nodes and links and nesting complex subsystems within a wider context. You can benefit from various functionalities that GoJS visual library enables you to use.  A whole process loop can be displayed as a simple element in the process overview, and the internal details can be expanded into a separate drawing with one click. Selected parts of any P&ID can be hidden or shown as needed.

A custom-built solution that we developed with a client from the oil&gas industry, also integrates best design practices and safety rules to validate the P&ID in real-time, as it is being developed by the engineer. The design tool highlights the parts that need to be remade and display HAZOP warnings with safety recommendations.

And lastly, the platform enables real-time collaboration and P&ID (Piping and Instrumentation Diagram) review process to assure that no mistake or opportunity for improvement goes unnoticed by the engineering team. While working with IoT sensors connected to the system, the user can gather and observe the actual condition of the whole set-up. The visual representation enables ad hoc reactions and delivering the most suitable solutions to the occurring issues.

Live Process Flow Simulation

For a client in the oil & gas industry, we developed an application that simulates events in the processing system, based on the Process Flow Diagram. The SCADA diagram below is a simple simulation of the flow along the pipes.

GoJS flow diagram
Flow diagram for simulation made with GoJS

This simulation can reflect the exact changes that occur in the process flow when a selected part of the P&ID is manipulated. Depending on the user’s needs, various alerts can be set up to notify of possible threats as certain elements are modified.

Using a diagram editor with a simulation feature creates a digital twin of the processing facility, which allows people involved in its operations to explore different scenarios, such as modernization plans or H&S (Health and Safety) scenarios.

While preparing and conducting simulations in P&ID, there are plenty of modern technical approaches merging visualization and engineering. JS visual libraries, such as GoJS, can be helpful as they work well for creating interactive diagrams used in simulations. In simple words, GoJS can be beneficial for simulations as it allows for reusable templates. The user benefits from previously created templates to superimpose data on them and observe changes in the simulation model. The GoJS makes the diagrams acting like a state machine that records, saves, and recreates the required state for further analysis. From the visual point of view, the GoJS enables choosing various data representations for one data model to change templating data. With virtualization functionality, the user can process bog data sets or map grid infrastructures.

Read more on how we created live simulation features for a client in the gas & oil sector.


P&IDs are as old as the process industry. While the rules and guidelines of the domain have been more or less consistent over the past decades, the digital transformation has revolutionized the way engineering is done, and switching to a custom-built P&ID P&ID (Piping and Instrumentation Diagram) platform can make a significant difference by boosting productivity, reducing the number of applications used and lowering the risk of costly and dangerous mistakes.

Creating custom P&ID (Piping and Instrumentation Diagram) software with a dedicated development team can give you more than just a diagram design tool. You can build one platform for all your design, management, and security needs, with real-time monitoring and design simulation of the processing facility.

P&IDs are no longer just technical drawings and the digital solutions built to create and manage them reflect that.

GoJS library for diagrams and charts