【2025: Understand at a Glance】Understand the differences between PFD and P&ID diagrams in one picture
Thread Content
This post was last edited by zhoudingshengs on 2025-5-5 10:27. The attached image shows: Understanding the differences between PFD and P&ID diagrams at a glance.
Process Flow Diagram: Also known as PFD, it contains key information about the entire plant, operating conditions (temperature, pressure, flow rates, etc.), material balance (the properties, flow rates, and operating conditions of various material streams are all indicated in the material balance tables), heat balance (heat loads, etc.), design calculations (the dimensions of equipment, heat transfer areas, pump flow rates, etc.), as well as the main control points and control strategies.
Process piping and instrumentation diagram (commonly known as “process flow diagram with control points”): that is, piping & instrument diagram, abbreviated as PID.
PID is developed on the basis of PFD, through the joint efforts of disciplines such as process engineering, piping installation, and automatic control. It is necessary to draw all the equipment, instruments, pipes along with their specifications and insulation thickness, as these serve as the main basis for creating pipe layout diagrams.
The PID diagram has its initial version developed during the process package stage; as the design progresses, it is continuously refined and improved, and it is released in stages and across various versions. The publication of various versions of the PID reflects the progress of engineering design, providing relevant design information at each stage for specialties such as process engineering, automatic control, equipment, electrical systems, telecommunications, piping, piping machinery, piping materials, equipment layout, and water supply and drainage.
PID is one of the main elements and outcomes in the preliminary design and detailed design; it represents the comprehensive result of the process design, equipment design, layout design of equipment and pipelines, and control instrument design.
PFD is a macroscopic perspective of process engineering, suitable for the early stages of design and process understanding.
A P&ID is a key document for project construction, operation, and maintenance, with more detailed information.
The two complement each other: the PFD is designed first, followed by the P&ID, which then serves to further refine the design and be used in actual project implementation.
In engineering projects, the PFD is used for overall process evaluation and design, while the P&ID serves as a guide for construction, commissioning, and operation; both are essential.
Key features of a PFD • Focuses on the main process flows without delving into details • Shows only the primary process equipment (such as reactors, heat exchangers, towers, pumps, compressors, etc.) • Displays the main material flow paths, including: • The flow direction of the main fluids • The names and numbers of the materials • Key parameters such as flow rate, pressure, temperature, etc. • May include mass/energy balance information • May include the main control loops (but does not show detailed control instruments)