PFD vs P&ID: What is the Difference?

Two of the most common engineering diagrams are the Process Flow Diagram (PFD) and the Piping and Instrumentation Diagram (P&ID). Both are essential in process engineering, but they serve very different purposes. Understanding the difference helps you choose the right diagram for the right situation.

What is a PFD?

A Process Flow Diagram shows the overall flow of a process at a high level. It focuses on the major steps and equipment, and shows how material moves through the system from input to output.

A PFD typically shows:

• Major unit operations (crushing, milling, flotation, thickening)
• Primary flow lines between units
• Key process streams and their labels
• Mass balance data (flow rates, compositions, temperatures)
• Major equipment with names and tags

PFDs are used in the early stages of project design, in feasibility studies, and for communicating the process to non-technical stakeholders. They are also used in operating plants to give operators a clear overview of the circuit.

What is a P&ID?

A Piping and Instrumentation Diagram is a much more detailed document. It shows every pipe, valve, instrument, control loop and piece of equipment in a process system.

A P&ID typically shows:

• All pipes, including sizes and specifications
• All valves (manual, control, safety)
• All instruments (flow meters, pressure gauges, level sensors)
• Control loops and signal lines
• Equipment with full mechanical details
• Safety systems and interlocks

P&IDs are used during detailed engineering, construction and commissioning. They are essential for plant maintenance and are the primary reference document for operators and instrument technicians.

Key Differences at a Glance

Aspect	PFD	P&ID
Purpose	Show overall process flow	Show detailed piping and instrumentation
Level of detail	High-level, simplified	Detailed, comprehensive
Audience	Engineers, managers, stakeholders	Engineers, technicians, operators
Shows valves?	Major valves only	All valves
Shows instruments?	Key instruments only	All instruments and control loops
Used when?	Conceptual and basic design	Detailed design, construction, operations
Complexity	Simple, easy to read	Complex, requires expertise to read

Which One Do You Need?

The answer depends on your purpose:

• Use a PFD when you want to communicate the process concept, prepare a feasibility study, train new operators, or present to management and stakeholders.
• Use a P&ID when you need to detail the engineering for construction, procurement or maintenance.

In a typical project, the PFD is created first and then developed into a P&ID as the design progresses. The PFD remains the primary reference for understanding what the plant does, while the P&ID is the reference for how it is built and operated in detail.

Creating PFDs with PfdLabs

PfdLabs is designed specifically for creating professional Process Flow Diagrams. With 35 isometric 3D industrial symbols covering comminution, classification, separation, hydromet and transport equipment, you can build clear and accurate PFDs quickly — without any design experience.