Piping and Instrumentation Diagram (P&ID)

The Piping & Instrumentation Diagram, which may also be referred to as the Process & Instrumentation Diagram, gives a graphical representation of the process including hardware (Piping, Equipment) and software (Control systems); this information is used for the design construction and operation of the facility.

The PFD defines “The flow of the process” The PFD covers batching, quantities, output, and composition.

The P&ID also provides important information needed by the constructor and manufacturer to develop the other construction input documents (the isometric drawings, or orthographic physical layout drawings, etc.). The P&ID provides direct input to the field for the physical design and installation of field-run piping. For clarity, it is usual to use the same general layout of flow paths on the P&ID as used in the flow diagram.

The P&ID ties together the system description, the flow diagram, the electrical control schematic, and the control logic diagram. It accomplishes this by showing all of the piping, equipment, principal instruments, instrument loops, and control interlocks. The P&ID contains a minimum of text in the form of notes (the system description minimizes the need for text on the P&ID).

The typical plant operation’s environment uses the P&ID as the principal document to locate information about the facility, whether this is physical data about an object, or information, such as financial, regulatory compliance, safety, HAZOP information, etc.

The P&ID defines “The control of the flow of the process” where the PFD is the main circuit; the P&ID is the control circuit. Once thoroughly conversant with the PFD & Process description, the engineers from the relevant disciplines (piping, electrical & control systems) attend a number of HAZOP sessions to develop the P&ID.