Piping & Instrumentation Diagrams (P&ID) Handbook - ISA P&ID Symbols - Reading and Identification

Oct 29, 2026

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P&ID (Piping and Instrumentation Diagram) is a schematic engineering document used in process plants to show process flow, installed equipment, instrumentation interconnections, and design details. It supports layout and piping design checks, material take-off for bills of materials, and maintenance or modification by documenting equipment sequence and connectivity. The handbook explains how ISA S5.1 instrument symbols represent discrete instruments, shared control/display, computer functions, and programmable logic controllers, including primary, auxiliary, and field location indicators.

LanguageEnglish

CategoryTechnology

FormatPDF

Pages39

Reading Time1 h 38 min

AccessFree to download

P&ID Handbook Overview

Role of P&IDs in process plant design

What information P&IDs include

P&IDs in maintenance and modification

ISA P&ID Symbols

ISA standard S5.1 instrument symbol categories

Instrument location categories (primary, auxiliary, field)

Symbol shapes for discrete, shared, computer, and PLC functions

Location bars and dashed-line conventions

Instrument Identification Codes

Letter-number combinations and assigned functions

Measured variables and readout/output functions

Letter breakdown for instrumentation diagrams

Reading Example

Interpreting P&ID Drawing 1 (FT 501 and FIC 501)

P&ID stands for Piping and Instrumentation Diagram or Drawing. Alternatively, it could also be called Process and Instrumentation Diagram or simply P&I diagram or drawing. P&IDs are also known as Engineering Flow Diagrams or Mechanical Flow Diagrams .P&IDs are often used in the process industry to show the process flow and other installed equipment and instruments. They show the interconnection of process equipment and the instrumentation used to control the process. The Piping & Instrumentation Diagrams (P&ID) Handbook Piping and Instrumentation Diagrams play a crucial role in the design and engineering of process plants and piping systems. P&IDs are schematic diagrams that contain engineering and design details of the process plants. It is a pictorial 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 is a working document that is used by every discipline involved in the design, engineering and construction of process plants. It is used as a Process Plant Layout and Piping Design reference for checking engineering and design documents and drawings associated with a project. Control System Documentation: Applying Symbols and Identification: 1. P&IDs are also used in material take-off, in generating a “Bill of Materials” for procurement and construction. P&IDs typically contain the following information: 2. All the equipment and their specifications, usually presented in the form of a table 3. All piping and line specifications 4. All piping system components such as fittings, flanges and valves with their specifications 5. All instrumentation and control components 6. Flow directions 7. Information on process variables such as pressure and temperature. 8. Material Specifications 9. Specialty Items such as strainers. 10. Control Input and Output, Interlocks and Alarm System 11. Interconnections References 12. Computer Control System input 13. Identification of Components and Subsystems Delivered To and By Others P&IDs play very important roles in plant maintenance and modification in that they demonstrate the physical sequence of equipment and system as well as how they all connect. During the Design stage they provide the basis for the development of system control schemes, allowing for further safety and operational investigations like HAZOP (Hazards and Operability Study) . The Piping & Instrumentation Diagrams (P&ID) Handbook ISA P&ID Symbols: In the process industry, a standard set of symbols are used to prepare piping and instrumentation diagrams (P&IDs) . Most of the P&ID drawings you may come across have instrument symbols based on ISA standard S5.1 (ISA stands for Instrumentation Systems and Automation Society) . Let us start by understanding the ISA standard symbols for developing P&ID drawings ISA S5.1 defines four general symbols for identifying instruments on a Piping and instrumentation diagram (P&ID) . They are: (a) Discrete instruments (b) Shared control/display (c) Computer function (d) Programmable logic controllers These distinct symbols used in P&IDs are grouped into three location categories namely: (a) Primary location usually a central control room (b) Auxiliary location possibly a local panel in the field or process plant (c) Field mounted The Piping & Instrumentation Diagrams (P&ID) Handbook On P&ID drawings, individual instruments are indicated by circular symbols or circle. Shared control/display elements are circles surrounded by a square. Computer functions are indicated by a hexagon and programmable logic controller function are shown as a diamond inside a square 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, and no line places the device or instrument in the fi

FAQs

What does a P&ID show in a process plant?

A P&ID shows the process flow, interconnection of process equipment, and the instrumentation used to control the process. It also includes control and shutdown schemes, safety and regulatory requirements, and basic start-up/operational information.

Why are P&IDs important during design and engineering?

P&IDs are working documents used across design, engineering, and construction. During the design stage, they support developing system control schemes and further safety and operational investigations such as HAZOP.

What do ISA S5.1 instrument symbols represent?

ISA S5.1 defines four general symbols for identifying instruments: discrete instruments, shared control/display, computer function, and programmable logic controllers. These are further interpreted using location categories and graphical conventions like single/double bars or dashed lines.

Oct 29, 2026

Upload by Mia