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

A Definition of 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. Piping and Instrumentation DiagramP & 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.
Items to Include In a P&ID
The following list outlines the items that typically are found in a P&ID:

  • 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

Codes, Tags, and Labels for P&IDs
As you can imagine, 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. Using Piping and Instrumentation Diagrams
Because a P&ID contains such important information, it is critical to the workings of the process industry that the process plant 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. In fact, there are three main reasons that the tagging should be done correctly:

  • 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 sown sequence number

Recommended Reading
For more information on P&ID, unique IDs, and durable labels, visit the following articles:

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