Plant Documentation Series: Process Flow Diagrams (PFDs)


Week One: Process Flow Diagrams (& Heat and Material Balance)



What are they?


In contrast to highly detailed Piping and Instrumentation Diagrams (P&IDs), the process flow diagram (PFD) illustrates the interconnectivity of plant assets in a simplified way. PFDs summarize the “big picture” of a detailed unit within a plant.


While there is no strict rule on what is included in a PFD, they will typically include process piping, equipment, and instrumentation critical to the process. Due to their high-level nature, they generally do not include more detailed equipment such as valves, flanges, secondary flows, etc. Adding further detail is balanced with the broader goal of personnel easily and quickly comprehending the overall process flow in just a few pages.

A PFD of a Nitric Acid Process - though PFDs are used across many different industries (image: Towler and Sinnott, 2013)
A PFD of a Nitric Acid Process - though PFDs are used across many different industries (image: Towler and Sinnott, 2013)

In addition to the process flow diagram, it is common to find a corresponding Heat and Material Balance (HMB) in a table. The HMB includes information such as design flow, temperature, pressure, and composition.



Not only are PFDs great tools, but they are required within a plant’s process safety management (PSM) program for covered processes.



How are PFDs used?


PFDs are typically created in the initial construction project. They act as a guiding document for adding details into the project, including P&IDs and piping one-line diagrams (“isometrics”).


Because of PFDs summarizing nature, it is a primary tool used for reference, knowledge, and communication.


You may also find PFDs used as...

  • A learning tool to train new personnel or provide refreshers to existing employees

  • A brainstorming tool to narrow your focus when troubleshooting

  • A communication tool to present big ideas to site management

  • A modeling support tool to set a baseline for running process model scenarios


How PFD Digitization can support a better field experience:


  • Since PFDs are a great starting point for many users, a digitized PFD could be used to accurately navigate to specific P&IDs

  • A digitized PFD could be used to quickly view equipment information without having to navigate to other systems

  • When building a process model, the digital PFD’s flow chart and equipment information can help establish a baseline simulation.

  • Instead of dashboards and charts, integrating process historian & analytics into digital PFDs can enable more engaging process monitoring


Have ideas or see something missing? Let us know what you think!



This blog is part of Cerebre’s Plant Documentation Series.


As the industrial world races into digital, plant documentation is an important tool for everyday decisions. Specifically, there are many different kinds of industrial drawings used to support process, safety, mechanical, and even management decisions.


We see tremendous opportunity in how the digitization of these documents can support a variety of digital and field objectives and want to share that with you!