Short Answer:
Engineering drawings and process flow diagrams serve different purposes in engineering. Engineering drawings are detailed technical illustrations that show the shape, dimensions, materials, and assembly of mechanical parts or systems. They are used mainly for manufacturing and construction.
On the other hand, process flow diagrams (PFDs) show the steps and flow of processes in a system, such as in chemical, oil, or water treatment plants. PFDs focus on how materials move through equipment rather than physical part dimensions or shapes.
Detailed Explanation:
Difference between engineering drawings and process flow diagrams
In mechanical and industrial engineering, both engineering drawings and process flow diagrams are important tools. However, they are used in different situations, serve different audiences, and contain very different types of information.
Understanding the differences between the two helps engineers communicate more effectively, whether they are designing physical parts or analyzing industrial processes.
Engineering drawings
Engineering drawings (also called mechanical drawings or technical drawings) are precise visual representations of parts, assemblies, and structures. They are mainly used for:
- Manufacturing
- Construction
- Inspection and quality control
- Assembly and installation
These drawings follow strict standards like ISO, ANSI, or ASME, and include:
- Orthographic views (top, front, side)
- Section views (to show hidden features)
- Dimensions and tolerances
- Material specifications
- Surface finish symbols
- Welding symbols
- Title blocks and revision history
Each detail in an engineering drawing tells the manufacturer exactly how to make or assemble a component or machine.
Process flow diagrams (PFDs)
Process flow diagrams are simple graphical representations of a process or system. They are mostly used in chemical, manufacturing, and process industries, such as oil refineries, food processing, power plants, or water treatment.
PFDs show:
- Flow of materials or fluids
- Major equipment (pumps, compressors, tanks)
- Process steps (heating, mixing, separating)
- Connections between equipment
- Flow direction using arrows
- Basic operating data (temperature, pressure)
They do not show physical dimensions, shapes, or detailed mechanical features. Instead, PFDs help engineers and operators understand how a process works, where input materials go, and how the output is achieved.
Key differences
| Feature | Engineering Drawing | Process Flow Diagram (PFD) |
| Purpose | Show how to build or assemble | Show how a process works |
| Focus | Physical parts, dimensions, tolerances | Process steps, flow of materials |
| Used by | Mechanical engineers, fabricators | Chemical/process engineers, operators |
| Contains | Views, symbols, materials, tolerances | Equipment symbols, flow lines, data |
| Standards | ISO, ASME, ANSI (mechanical) | ISO 10628 or ISA S5.1 (process) |
Example use case
- A mechanical engineer creating a machine part will use an engineering drawing to specify size, material, and how it will be made.
- A process engineer designing a water purification system will use a process flow diagram to show how water flows through filters, pumps, and tanks.
Why both are important
In many industries, both drawings are used together:
- First, the PFD is created to show how the process should work.
- Then, engineering drawings are made for the actual parts and equipment needed to build the system.
This way, both the function (process) and the form (structure) are covered completely.
Conclusion:
Engineering drawings and process flow diagrams serve different but equally important roles in engineering. Engineering drawings focus on the physical details needed for manufacturing and construction, while process flow diagrams explain how materials or fluids move through a system. Understanding the difference between them helps ensure that both design and process work together smoothly in any project.