What is a P&ID?
Equipment, pipes, and tagged instruments for a process plant.
What the sheet is
A P&ID, or piping and instrumentation diagram, is an engineering drawing of a process plant. Equipment such as tanks, pumps, and heat exchangers appears as equipment symbols. Lines between them are pipes. Small circles, often called bubbles, are instruments, with tag codes such as FT for a flow transmitter or FIC for a flow indicating controller. Searches for p&id and for piping and instrumentation diagram mean this sheet.
ISA-5.1 is the common symbol and tag standard in many plants. This page does not reproduce that standard. Read the title block and the legend on the specific drawing in front of you. A P&ID is not a flowchart of office work, and it is not a scale map of the building. Physical distances live on a plot plan. The P&ID shows connectivity and control.
How to read one without pretending to design a plant
Start at a major piece of equipment and follow one line. Note the line number if it is printed. When you reach a bubble, read the tag: the first letters say what is measured or controlled, and the numbers identify which instrument. A change to a P&ID is a change to a plant document. It belongs to the people who own that document, with their revision process. Use this explanation to know what you are looking at in a meeting. Do not redraw a live P&ID from a blog.
For software, the matching introductory picture is an architecture diagram, not a P&ID. For a business procedure, use a process map.
Questions
- What is a piping and instrumentation diagram?
- A drawing of the equipment, piping, and control instruments in a process plant. Instruments are tagged. The drawing shows how the process is connected and controlled.
- What does a P&ID not show?
- It does not show exact pipe lengths, civil layout, or the steps a person takes in an office. Those belong on other drawings or in a procedure.
- Can I invent instrument tags for a school poster?
- For a class explanation, label a bubble as an example and say it is an example. For a real plant, use the site's legend and the governing standard, and change the sheet only through the plant's revision process.