Process Legend or Symbols
The process legend are like alpha bates of the Process Engineers language.
They provides the information needed to interpret and read the P&ID ( The book). Process legends are found at the front of the PFD and P&ID. The legend includes information about piping, instrument and equipment.
Some symbols are common among plants; others differ from plant to plant. Some standardization of process symbols and diagrams is taking place. The symbols used in the tutorial reflect a wide variety of Oil and Gas Domain.
Process Flow Diagrams
New Engineers and technicians are required to study a simple flow diagram of their assigned Design Project or the operating system. Process flow diagrams typically include the major equipment and piping path the process takes through the unit. As Engineer learn more about symbols and diagrams, they graduate to the much more complex P&IDs
Please click below link to read a brief but effective guideline for understanding the same.
PFD & P&ID Tutorial