P&ID drawings are the backbone of process engineering documentation. If you work in oil and gas, utilities, chemical processing, pharmaceuticals, or any industry involving pipework and instrumentation, you will encounter P&IDs constantly. This guide explains what they are, what they contain, how to read them, and how to manage their production.

What is a P&ID drawing?

A P&ID, or Piping and Instrumentation Diagram, is a detailed technical diagram showing the pipework, equipment, instrumentation, and control systems within a process facility. It shows every pipe, valve, instrument, and control loop in the system in a schematic format that is not to scale and does not represent the physical layout of the plant.

P&IDs are used throughout the life of a process facility — from early design development through detailed engineering, construction, commissioning, operations, and maintenance. They are living documents that must be kept up to date throughout the life of the plant.

What does P&ID stand for?

P&ID stands for Piping and Instrumentation Diagram. You will also see it written as P and ID, piping and instrumentation diagram, or process and instrumentation diagram. All refer to the same document type.

What information does a P&ID drawing contain?

A P&ID contains all pipework including pipe sizes, specifications, and line numbers. All major equipment such as vessels, heat exchangers, pumps, and compressors with their equipment numbers. All valves including isolation valves, control valves, and safety relief valves with tag numbers. All instrumentation including pressure gauges, temperature sensors, flow meters, and level gauges. All control loops showing how instruments and control valves work together. Safety systems including relief valves, rupture discs, and interlock logic. Utility connections and tie-in points.

P&ID symbols — the ISA 5.1 standard

P&ID symbols are standardised under ISA 5.1 (Instrumentation Symbols and Identification) published by the International Society of Automation. This standard defines the symbols used for instruments, control valves, and lines. Equipment symbols are typically company or project specific and defined in the project symbol library.

Outsource CAD works to ISA 5.1 as standard and can work to client-specific symbol libraries.

P&ID vs PFD — what is the difference?

A Process Flow Diagram (PFD) provides a high-level overview of a process showing the main equipment and primary flow paths. It is used for process design and understanding. A P&ID is more detailed, showing all pipework, all instruments, all valves, and all control systems. P&IDs are used for engineering, construction, and operations. Both documents are produced for most process engineering projects.

What standards do P&ID drawings follow?

P&ID drawings are produced to ISA 5.1 and BS EN ISO 10628. In addition, most operators have their own company standards and symbol libraries that supplement these international standards.

Who needs P&ID drawings?

P&IDs are used by oil and gas operators and EPC contractors, utilities and water treatment companies, chemical and petrochemical manufacturers, pharmaceutical and food processing facilities, and any organisation operating process equipment involving pipework and instrumentation.

How to outsource P&ID drawing production

Outsource CAD specialises in P&ID drawing production and has completed over 500 P&ID drawings for UK and international clients. We work in AutoCAD and AutoCAD Plant 3D and can work to any operator-specific standard. Contact us for a free quote.