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How to Read Piping and Instrumentation Diagram

> P&ID How-Tos > How to Read Piping and Instrumentation Diagram
Posted by James Freeman | 04/22/2020
P&IDs, also known as Piping and Instrumentation Diagrams, or Process and Control Diagrams, are essential to many industrial operations. This page is a basic guide on how to read and understand Piping and Instrumentation Drawings (P&IDs).

In this article, we will explore the interpretation of Piping and Instrumentation Diagrams, or P&IDs. Being able to read P&IDs can benefit the process and management of a project a lot. Regardless of your experience or level of expertise, follow the instruction of this article, and you will find it rather easy to read a P&ID.


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What is Piping and Instrumentation Diagram?

Piping and instrumentation diagram, also called P&ID, is a diagram used to show a graphical display of a complete system. It includes all piping, instruments, valves and equipment that the system consist of. Through a P&ID, you can get the following information:

  • The mechanical and electrical details of a given system or process,
  • Piping information such as sizes and material specifications,
  • Continuation flags leading to the connecting P&ID’s,
  • Flow arrows, DCS alarm types
  • The connection types from the controllers to the field devices.

Process P&ID

How to Read Piping and Instrumentation Diagrams

Here are a few aspects that you should pay attention to while reading a piping and instrumentation diagram. It is important for you to know what P&ID symbols means in a P&ID, and also tell how each symbol is constructed using graphical elements and connecting lines. If you manage to do this, it wouldn't be difficult for you to read a piping and pnstrumentation diagram at all.

1. Identify and Understand Standard Equipment -Instruments

The first step to read a Piping and Instrumentation Diagram is to know how to read its symbols and shapes in the drawing. Edraw provides all kinds of symbols required in piping and instrumentation diagrams.

Equipment Instrument

According to ISA S5.1, there are mainly 4 four graphical elements: shared control/display, computer, function, and programmable logic controller. This shapes represent both the physical or the software devices. In either case , it implies all the shapes needed in a piping and instrumentation diagram. You will see these shapes anytime a system is shown on the P&ID.

Discrete instruments:

Discrete Instruments

Shared control/display

Shared control/display

Computer function

Computer function

Programmable logic controller

Discrete instruments are indicated by circular elements. Shared control/display elements are circles surrounded by a square. Computer functions are indicted by a hexagon and programmable logic controller (PLC) functions are shown as a triangle inside a square.

2. Learn to Use Graphical Elements and Connecting Lines

The connections between elements is a way for engineers to identify a particular pipe in a standardized way. And different color indicates different pipes to avoide confusion. Adding a single horizontal bar across any of the four graphical elements indicates the function resides in the primary location category. A double line indicates an auxiliary location, devices located behind a panel-board in some other inaccessible location are shown with a dashed horizontal line.

Piping and Connection Symbols

3. Know the Letter and Number Combinations of a P&ID

Letter and number combinations appear inside each graphical element and letter combinations are defined by the ISA standard. Numbers are user assigned. 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), Record (R), Transmit (T), and so forth.

factory P&ID Example

Piping and Instrumentation Diagram Example

Plant P&ID

Plant P&ID Example

Water Boiling Process P&ID

Water Boiling Process P&ID

Thermal System P&ID

Thermal System P&ID

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