How to Read Piping and Instrumentation Diagram
Part 1: What is Piping and Instrumentation Diagram?
Piping and instrumentation diagram, also called P&ID, is a diagram used to show a graphical display of a complete system. It includes all piping, instruments, valves and equipment that the system consist of. Through a P&ID, you can get the following information:
- The mechanical and electrical details of a given system or process,
- Piping information such as sizes and material specifications,
- Continuation flags leading to the connecting P&ID’s,
- Flow arrows, DCS alarm types
- The connection types from the controllers to the field devices.
Part 2: How to Read Piping and Instrumentation Diagrams
Here are a few aspects that you should pay attention to while reading a piping and instrumentation diagram. You need to know what P&ID symbols mean in a P&ID and tell how each symbol is constructed using graphical elements and connecting lines. If you manage to do this, it wouldn't be difficult for you to read a piping and instrumentation diagram at all.
1. Identify and Understand Standard Equipment -Instruments
The first step to read a Piping and Instrumentation Diagram is to know how to read its symbols and shapes in the drawing. Edraw provides all kinds of symbols required in piping and instrumentation diagrams.
According to ISA S5.1, there are mainly 4 four graphical elements: shared control/display, computer, function, and programmable logic controller. This shapes represent both the physical or the software devices. In either case , it implies all the shapes needed in a piping and instrumentation diagram. You will see these shapes anytime a system is shown on the P&ID.
Discrete instruments:
Shared control/display
Computer function
Programmable logic controller
Discrete instruments are indicated by circular elements. Shared control/display elements are circles surrounded by a square. Computer functions are indicted by a hexagon and programmable logic controller (PLC) functions are shown as a triangle inside a square.
2. Learn to Use Graphical Elements and Connecting Lines
The connections between elements is a way for engineers to identify a particular pipe in a standardized way. And different color indicates different pipes to avoide confusion. Adding a single horizontal bar across any of the four graphical elements indicates the function resides in the primary location category. A double line indicates an auxiliary location, devices located behind a panel-board in some other inaccessible location are shown with a dashed horizontal line.
3. Know the Letter and Number Combinations of a P&ID
Letter and number combinations appear inside each graphical element and letter combinations are defined by the ISA standard. Numbers are user assigned. 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), Record (R), Transmit (T), and so forth.
Part 3: Piping and Instrumentation Diagram Examples
Plant P&ID
Water Boiling Process P&ID
Thermal System P&ID
