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

A piping and instrumentation diagram (P&ID) is a drawing in the process industry. A P&ID shows all piping, including the “physical sequence of branches, reducers, valves, equipment, instrumentation and control interlocks.” A P&ID is used to operate the process system, since it shows the piping of the process flow along with the installed equipment and instrumentation.

P & IDs play a key role in maintaining and modifying the process they describe, because it is important to demonstrate the physical sequence of equipment and systems, including how these systems connect. In terms of processing facilities, a P&ID is a visual representation of key piping and instrument details, control and shutdown schemes, safety and regulatory requirements, and basic start-up and operational information.

A P&ID should include the following:

  • Instrumentation and designations
  • Mechanical equipment with names and numbers
  • All valves and their identifications
  • Process piping, sizes, and identification
  • Vents, drains, special fittings, sampling lines, reducers, increasers, and swaggers
  • Permanent start-up and flush lines
  • Flow directions
  • Interconnections references
  • Control inputs and outputs, interlocks
  • Interfaces for class changes
  • Computer control system
  • Identification of components and subsystems delivered by the process

A P&ID should NOT include the following:

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

A P&ID involves various symbols to represent all of the included parts, components, and information. Their symbology is defined on separate drawings referred to as “lead sheets” or “legend sheets.” Lead sheets should be customized to each company’s process plants, though in general, the P&IDs are based on a core set of standard symbols and notations. The most important part of the lead sheets is that they are organized logically so that it is possible to easily locate the symbols and tags. While it’s a good practice to have lead sheets for the major equipment in a factory, it may not be necessary because this major equipment already should be tagged and named with general specifications for identification purposes.

Letter and number combinations appear inside each graphical element and letter combinations are defined by the ISA standard. Numbers are user assigned and schemes vary. While some companies use sequential numbering, others tie the instrument number to the process line number, and still others adopt unique and sometimes unusual numbering systems. The first letter defines the measured or initiating variables such as Analysis (A), Flow (F), Temperature (T), etc. with succeeding letters defining readout, passive, or output functions such as Indicator (I), Recorder (R), Transmitter (T), etc.

Below are some piping and instrumentation diagram symbols with letters.


Because a P&ID contains such important information, it is critical to the workings of the process industry that the process plants apply tags or labels to keep track of all of the equipment, piping, valves, devices, and more. Those labels must match the symbology and should not fail, so that the plant’s operations run smoothly and efficiently. That’s why the unique identifiers involved in the P&ID, tagging, and labeling process are critical.

The P&ID and tags ensure that even collections of similar objects have unique tags so that identical valves, pumps, instruments, etc., can be uniquely identified
The P&ID and tags make it possible to assemble the process plant in a structured manner so that additions, deletions, changes, etc., are possible from a whole-unit scale down to a single valve on a pipe at any location.

The P&ID and tags contain scores of metadata that provides, or links to, more details including specifications, materials of construction, data sheets, etc.
Best Practices for Tagging Equipment When Considering P&ID.

Using a numeric-only system for tagging equipment is the best way for process industries to avoid the problems with labeling by abbreviated names. Structured tag systems are more intuitive for every team that deals with the equipment, including developers, operators, and maintenance. The equipment tag format should be a series of three numbers, beginning with an area number, followed by an equipment type code, and then ending with a unique sequence number.

Area numbers represent an area that may be determined by the physical, geographical, or logical grouping location by the plant site
Equipment types are fairly straightforward, but if equipment has multiple functions, users should determine how to select the most suitable equipment type code.

Sequence numbering is the consecutive numbering of similar equipment in any given area, and it’s important to being the sequence at 01 so that all equipment can have it’s own sequence number.

The Importance of Computer Aided Design (CAD) in India

Computer Aided Design in India, or CAD as it is better known, is a technology that is rather new in the world of construction and engineering, so you may not have heard of it. CAD is developing rapidly and changing the way people do things in the construction and engineering industry. CAD is, explained in a simple way, something that can be used in order to design products so that it would take a real and concrete appearance before it is even built. CAD exists in order to smoothen the working process between the engineer and the customer. The human mind is rather used to viewing and imagining things in a visual way. If you try to explain the way you want a building to be built in words, oftentimes there would be misunderstandings, and the working process would not develop smoothly. You may argue that you could just as easily use drawings in order to convey the appearance and design of a project, and that is true indeed. CAD itself is a form of drawing and designing. However, compared to the manual and traditional way of drawing, CAD is much more effective and efficient. By using CAD, you would be able to view details and calculations that you would not be able to otherwise if you use the manual way of designing. Also, the process could be finished a lot quicker, so it would be a time-saving as well as a cost-saving solution.

How Computer Aided Design (CAD) Helps You

There are several benefits that using a Computer Aided Design (CAD) service can provide for you:

  • Flexibility

CAD is more fluid and flexible than the traditional way of designing. You would be able to make changes easily because the design is stored in a digital way. If you tried to make changes to a traditional design drawing, then you would understand how difficult it could be at times to make changes—even small ones. You may have had to scrap the whole design at some point and make a whole new one. That would not be the case with CAD, and you can rest assured that your work would not be for naught.

  • 3D

The traditional way of drawing and designing would be limited to 2D, but with the arrival of CAD, engineering and construction has been cranked up another notch. 3D designs are now possible and in fact, rather easy and convenient to make. This would allow customers to be able to view the finished end product before the construction process has even started and make changes if necessary. The workers would also have a much easier time doing the construction because they have something real and concrete to base their work upon, and the end result would be all the more impressive.

  • Project Management

Communication is key when it comes to project management, and project management is really rather important. No matter how good the designer is or how savvy the leader of the project is, the fact is that a project cannot be accomplished with only few people. The whole team needs to understand the project completely if it were to be a success. This is one of the many benefits of CAD, as it would allow for easier communication and better project management.

  • Information

Because CAD stores the data digitally, it would only be too easy to spread the information to the whole team. No need for endless paperwork when all you need to do is sit in front of a computer to transfer the data.

CAD in India is important, and many major companies are changing the way they operate because of this. They are realizing how many benefits CAD could really give them, and it would not be a wise decision to ignore the development of technology.