Final answer:
The P&ID for an area should be changed when a change is made in the process equipment, such as adding new machinery or altering existing ones.
Step-by-step explanation:
The P&ID, which stands for Piping and Instrumentation Diagram, for an area must be changed every time that a change is made in the process equipment. These diagrams are essential for understanding the mechanical and chemical processes in a facility, and any alteration to the process equipment can impact how the system operates. For example, adding a new reactor or modifying a distillation column would necessitate an update to the P&ID to accurately reflect these changes. Regular updates on a schedule and changes in supervision typically do not require changes to P&IDs. However, if the cost of equipment goes up but doesn't result in a change in the physical equipment or process, then P&ID would not need to be updated for this reason alone.