Understanding Process Flow Diagrams and P&IDs

If you need a visual representation of the steps to take in your engineering project, then it is advisable to use a Process Flow Diagram. A PFD is also known as a System Flow Diagram, is a chart that illustrates the relationship between all the main components of a system. A PFD is used commonly within the Engineering Industry within the Process and Chemical Engineering fields. A PFD can be used in the below instances:

  • To improve knowledge of how a process is done.
  • To study a process for improvement.
  • To document a process.
  • When planning a project.
  • To communicate to others how a process is done.
  • When better communication is needed between people involved with the same process.

It is important to not worry too much when creating the PFD, just to ensure that those involved understand the process. Remembering to classify and include all important participants in the process is also critical. Including them from the planning stages ensures all points of view are taken into consideration.

Process and Instrumentation Drawing (P&ID)

A process and instrumentation drawing is more multifaceted than a process flow diagram. Basically, P&IDs convey more information than PFDs do. They are also referred to as Piping and Instrumentation diagrams. Personnel such as, Instrumentation technicians, Mechanical and safety engineers implement P&IDs. It is a schematic diagram which is used for outlining a process control installation as well as start-up and operational information. Chemical apparatus such as pipes, pumps, fans, vents, valves, furnace, etc. have symbols which represent them in P&IDs, and they are the most accurate means of documenting processes.

Comparison between Process Flow diagrams (PFD) & Process and Instrumentation Drawing (P&ID)

The two diagrams are almost always confused with each other. P&IDs expand the information from PFDs by including the following;

  • Instrumentation and Controls
  • Direction of process flow
  • Connections and Component types
  • Sequence of processes
  • Connectivity and order of equipment for the process

PFDs mandatorily contain the following:

  • Major equipment symbols, names and identification numbers
  • Valves, primarily control valves that affect operation of the system
  • Layout of the interconnection between systems
  • The Primary recirculation and bypass lines.
  • Ratings of the system and the operational values which could be; minimum, average and maximum flow. Temperature and pressure ratings not neglected
  • Fluids constituents or composition.

In India, many Engineering and particularly manufacturing firms employ the use of PFDs and PIDs to fully conceptualize the span of manufacturing processes. They employ the use of Computer aided design/ Computer aided manufacturing (CAD/CAM) software to highlight the details of even the minutest process relationship.

In conclusion, regardless of the differences between the two, they are extremely vital tools to conceptualize processes and complex projects.