Basic Knowledge about Piping and Instrumentation Diagram
Piping and instrumentation diagram plays a crucial role in the design and engineering of process plants and piping systems, by showing the interaction of process used to control the process. P&ID is a schematic illustration of functional relationship of piping, instrumentation and system equipment components
What is the Difference Between PFD and P&ID?
Instrumentation detail varies with the degree of design complexity. For example, simplified or conceptual designs, often called process flow diagrams (PFDs), provide less detail than fully developed piping and instrumentation diagrams (P&IDs). Since a PFD shows less details than a P&ID, it is used only to understand how the process works.
Knowledge About P&ID Symbols
To better understand the process and instrumentation diagram, you need to decipher the symbols used in the piping and instrumentation diagram.
Letter and number combinations appear inside each graphical element and letter combinations are defined by the ISA standard. Numbers are user assigned and schemes vary. while some companies use sequential numbering, others tie the instrument number to the process line number, and still others adopt unique and sometimes unusual numbering systems. The first letter defines the measured or initiating variables such as Analysis (A), Flow (F), Temperature (T), etc. with succeeding letters defining readout, passive, or output functions such as Indicator (I), Recorder (R), Transmitter (T), etc.
Below are some piping and instrumentation diagram symbols with letters.
What Should a P&ID Include and NOT Include?
P&ID is a very common term used in the world of process industries. A process engineer in a manufacturing plant need to create new and/or modify the already existing P&ID to the as-is plant modifications. All the Chemical Engineering and related Engineering students have also learned about it or at least heard. A P&ID is a detailed graphical representation of a process including the hardware and software (e.g., piping, equipment, instrumentation) necessary to design, construct and operate the facility. As defined in the PIC001: Piping and Instrumentation Diagram Documentation Criteria by Process Industry Practice (PIP) - a consortium of process industry owners and engineering construction contractors who serve the industry.
A P&ID Should Include:
- Instrumentation and designations;
- Mechanical equipment with names and numbers;
- All valves and their identifications;
- Process piping, sizes and identification;
- Miscellaneous - vents, drains, special fittings, sampling lines, reducers, increasers and swagers;
- Permanent start-up and flush lines;
- Flow directions;
- Interconnections references;
- Control inputs and outputs, interlocks;
- Seismic category;
- Interfaces for class changes;
- Quality level;
- Annunciation inputs;
- Computer control system input;
- Vendor and contractor interfaces;
- Identification of components and subsystems delivered by others;
- Intended physical sequence of the equipment;
- Equipment rating or capacity.
A P&ID Should NOT Include:
- Instrument root valves;
- Control relays;
- Manual switches;
- Primary instrument tubing and valves;
- Pressure temperature and flow data;
- Elbow, tees and similar standard fittings;
- Extensive explanatory notes.