process flow diagram (PFD) is a diagram commonly used in chemical and process engineering to indicate the general flow of plant processes and equipment. The PFD displays the relationship between major equipment of a plant facility and does not show minor details such as piping details and designations. Another commonly used term for a PFD is a flowsheet.

Another definition can be that it is a very detailed map of every step in a process, including hidden factory steps.

Typically, PFDs of a single unit process will include the following:

Generally they do not include:

  • Pipe classes or piping line numbers
  • Instrumentation details
  • Minor bypass lines
  • Instrumentation
  • Controllers like Level Control or Flow Control
  • Isolation and shutoff valves
  • Maintenance vents and drains
  • Relief and safety valves
  • Flanges

Process flow diagrams of multiple process units within a large industrial plant will usually contain less detail and may be called block flow diagrams or schematic flow diagrams.

Some visual examples:

process flow diagram example
Flow diagram of a typical oil refinery
process flow diagram example
Flow diagram of a typical amine treating process used in industrial plants